CN110174330A - A kind of accurate evaluation method of acidified milk cream sense - Google Patents

Abstract

The invention provides an analytical sensory evaluation method for the creaminess of fermented milk. The invention combines sensory evaluation and instrument analysis technology to explore the flavor factors and texture factors that affect the perception of creaminess, and discusses the use of instruments to measure the creaminess of fermented milk products. The possibility of using a rheometer to measure emulsions and acid gels with different fat contents after simulated oral mastication found that using this method can distinguish the lubricity between samples, and at a shear rate of 20/min, each The coefficient of friction of the samples is negatively correlated with the fat content, that is, at the shear rate, the higher the fat content of the sample, the smaller the coefficient of friction and the better the lubricity. The coefficient of friction μ20/min measured using the instrument can predict the perceived smoothness in the human oral cavity. The invention provides a new idea for the development of dairy products with enhanced creaminess, and is of great significance for improving the nutritional quality and added value of dairy products in my country.

Description

An accurate evaluation method for the creaminess of fermented milk

technical field

The invention belongs to the technical field of food testing, and in particular relates to an accurate evaluation method for the creaminess of fermented milk.

Background technique

Fermented dairy products are dairy products made from fresh milk fermented with a starter to produce lactic acid. It has the characteristics of promoting lactose absorption, improving intestinal function, and mellow flavor. With the continuous expansion of the fermented milk market, the needs of consumers have also become diversified. According to the results of consumer preference surveys, the "creaminess" in fermented milk is the most popular feature among consumers.

Creaminess is a comprehensive sensory attribute often used to describe the characteristics of full-fat dairy products, and many consumers associate creaminess with pleasant and enjoyable characteristics. The perception of creaminess depends not only on the nature of the food (texture, fat and flavor), but also on the eating habits of the consumer. When tasting dairy products and evaluating the creaminess, each person will give different weights to the various attributes that affect the creaminess due to their own dietary experience or personal preferences. Although to consumers, creaminess seems to be very recognizable, consumers can even combine life experience and visual observation to evaluate creaminess without oral treatment at all. But for sensory science, it is very difficult to give a comprehensive and generally accepted definition, and it is still a big problem in the academic circle to determine and control the factors that affect the creaminess in fermented dairy products.

Contents of the invention

The present invention combines sensory evaluation and instrument analysis technology to explore the flavor factors and texture factors that affect the perception of creaminess, and explores the possibility of using instruments to measure the creaminess of fermented milk products. The purpose of the invention is to provide a creamy texture of fermented milk It is of great significance to improve the nutritional quality and added value of dairy products in my country by accurately evaluating methods and providing new ideas for the development of dairy products with enhanced creaminess.

The purpose of the present invention is achieved through the following technical solutions:

A method for accurately evaluating the creaminess of fermented milk, comprising the following steps:

(1) Texture characteristic detection

A. In vitro simulated oral chewing conditions: Add artificial saliva to the fermented milk to be tested and stir it with a glass rod at a speed of 200rpm for 15s in a water bath at 37°C to simulate the oral chewing process to obtain the sample fermented milk;

B. Use a rheometer to measure the lubricity of the sample fermented milk, set the shear rate to 20/min, and measure the coefficient of friction;

(2) Detection of flavor substances

The HS-SPME method was used to extract the flavor substances in the fermented milk to be tested. The conditions of the HS-SPME method were 50° C., 20 min equilibration and 20 min extraction.

Further, the accurate evaluation method also includes the following steps:

(3) Sensory evaluation

Based on the visual, olfactory, gustatory and oral tactile factors that affect the perception of creaminess, an analytical sensory evaluation for the creaminess of fermented milk was established, and the main factors included were mouth smoothness, mouth thickness, sweetness and milk fat taste.

Further, the ratio of the artificial saliva to the fermented milk to be tested in the step (1) A. is 1:4.

Further, the rheometer in the step (1)B. is a pressure-controlled rheometer.

Further, among the flavor substances in the step (2), the substances that contribute to the yogurt flavor include 4-octanone, 2-nonanone, 4-hydroxy-3-hexanone, 2-hydroxy-3-pentanone , butyric, valeric, heptanoic and caprylic acids.

Further, among the flavor substances in the step (2), substances that contribute to frankincense flavor include 2,3-butanedione, 4-penten-1-ol and 4-hydroxy-3-hexanone.

Further, among the flavor substances in the step (2), the substances that contribute to the sour milk flavor and fat flavor include 2,3-butanedione.

Further, the definition of each sensory property in the sensory evaluation described in the step (3) and the reference of different sensory elements thereof are:

The beneficial effect of the present invention compared with prior art is:

1. The present invention uses a rheometer to measure emulsions and acid gels with different fat contents after simulating oral chewing and finds that this method can be used to distinguish the lubricity between samples, and when the shear rate is 20/min, each The coefficient of friction of the samples is negatively correlated with the fat content, that is, at the shear rate, the higher the fat content of the sample, the smaller the coefficient of friction and the better the lubricity. The friction coefficient μ20/min measured by the instrument can predict the perceived smoothness in the human oral cavity;

2. The present invention found through research that 4-octanone, 2-nonanone, 4-hydroxy-3-hexanone, 2-hydroxy-3-pentanone, butyric acid, pentanoic acid, heptanoic acid, octanoic acid in fermented milk Flavor substances such as 2,3-butanedione, 4-penten-1-ol and 4-hydroxy-3-hexanone are related to the perception of milk flavor. Both food matrix and oral processing will affect the release and perception of flavor substances. The flavor perception of 2,3-butanedione mainly depends on the retronasal sense of smell, while the perception of yogurt and milk fat flavor mainly depends on the prenasal sense of smell;

3. According to the research of the present invention, the perception of oral smoothness, oral thickness, sweetness and milk fat taste has a positive effect on the perception of creaminess. The stronger the perceived intensity of these sensory characteristics, the stronger the creaminess felt by the human body; The perception of sour taste will negatively affect the perception of creaminess; compared with the perception of flavor, the perception of texture may be a more important factor affecting the perception of creaminess;

4. The present invention constructs an accurate evaluation method for the creaminess of fermented milk. Combined with sensory evaluation and instrument analysis technology, it can analyze the creaminess of fermented milk more accurately, clarify the factors affecting the perception of creaminess, and provide a basis for the development of enhanced creaminess Dairy products provide the rationale.

Description of drawings

Fig. 1 is the particle size distribution schematic diagram of different fat content standard emulsions;

Fig. 2 is the schematic diagram of the fluorescence microscope scanning result of the fat distribution in the emulsion of different fat contents;

Fig. 3 is the rheological characteristic curve of emulsion with different fat contents;

Fig. 4 is the friction mechanical characteristic curve of emulsion with different fat contents;

Fig. 5 is the rheological characteristic curve of protein acid gel system with different fat contents;

Fig. 6 is the tribological characteristic curve of protein acid gel system with different fat content;

Fig. 7 is the rheological characteristic curve of fermented milk sample;

Fig. 8 is the friction mechanical characteristic curve of fermented milk sample;

Fig. 9 is a schematic diagram of principal component analysis results of flavor substances of 6 fermented milk samples; wherein, the numbers in the figure represent different flavor substances. 1: Carbamic acid, 2: Cyclobutanol, 3: 2-hexylamine, 4: 2,3-butanedione, 5: 4-octanone, 6: 4-penten-1-ol, 7: Isopropyl Alcohol, 8: 3,3-dimethyl-2-butanone, 9: isopentenol, 10: 3-pentanol, 11: 2-nonanone, 12: 4-hydroxy-3-hexanone, 13 : 2-hydroxy-3-pentanone, 14: n-hexanol, 15: acetic acid, 16: benzaldehyde, 17: 2-undecanone, 18: acetone, 19: butyric acid, 20: 2-bromo-1- Chloro-propane, 21: valeric acid, 22: hexanoic acid, 23: butylated hydroxytoluene, 24: heptanoic acid, 25: octanoic acid;

Fig. 10 is a schematic diagram of principal component analysis results of descriptive sensory evaluation;

Figure 11 is a schematic diagram of the principal component analysis results of the flavor perception data in the descriptive sensory evaluation results and the flavor substance data measured by the instrument; wherein, the flavor substances represented by the numbers in the figure are the same as those in Figure 9;

Fig. 12 is the result of principal component analysis of oral tactile perception data in the descriptive sensory evaluation results and fermented milk physical property data measured by instruments.

Detailed ways

Example 1——Analysis of texture characteristics related to "creaminess" of fermented dairy products

Emulsions with different concentrations were prepared by using skim milk complex solution with 0% fat content and cream with 35% fat content. The target emulsion concentrations are 0%, 1.5%, 3%, 4.5%, 6%, 7.5%, 9%, and 10.5%, and the specific formulations are shown in Table 1. Put a certain amount of skimmed milk and cream into a 10mL centrifuge tube and mix, then use a vortex shaker to shake at a speed of 3000rpm/min for 2min, and then store at 4°C for use.

1.2% gluconolactone (GDL) was added to 10 mL of the prepared emulsion, stirred evenly and left to stand overnight at 4° C. to form acidified gel systems with different fat contents.

Artificial saliva: mix 2.2g of porcine gastric mucin, 0.381g of sodium chloride, 0.231g of calcium chloride, 0.738g of potassium phosphate, 1.114g of potassium chloride and 0.2g of sodium azide in 800mL of deionized water, using a small amount of sodium hydroxide Adjust the pH to 7 and make up to 1L. Store at 4°C for later use. In vitro simulated oral chewing conditions: artificial saliva was added to fermented milk and stirred with a glass rod at a speed of 200 rpm for 15 seconds in a water bath at 37°C to simulate the oral chewing process. The ratio of artificial saliva to fermented milk was 1:4.

Table 1 Emulsion formulations with different fat contents

The particle size and distribution state of fat in the emulsion will affect the perception of oral lubricity. In the experiment of this example, standard emulsions with fat contents of 0%, 1.5%, 3%, 4.5%, 6%, 7.5%, 9%, and 10.5% were prepared in order to obtain different tribological properties. The particle size distribution of the emulsion is shown in Figure 1. It can be seen that except for the 0% group, the fat particle sizes of the other groups are in the range of 1 μm-10 μm, indicating that the fat globule size of the emulsion prepared by this method is relatively uniform, and the particle size distribution of the 0% group is obvious The smaller size is because the emulsion does not contain fat globules with larger particle sizes, and the measured data is the size of casein micelles. It can be seen from Figure 2 that there is no large accumulation of fat in the prepared emulsion, indicating that the fat distribution of the prepared emulsion is uniform.

When the emulsion first enters the human oral cavity, the rheological properties of the emulsion mainly affect the sensory perception of creaminess. The viscosity of prepared emulsions with different fat contents varies with the shear rate as shown in Figure 3. It can be seen that when the shear rate is low (0.1/s—1/s), the viscosity of the group with higher fat content is also larger, but with the increase of shear rate, the viscosity of each group is decreasing. It can be seen from Table 2 that when the shear rate reaches 50/s, that is, when the human body masticates, there is no significant difference in the viscosity of the emulsions in each group.

Table 2 Viscosities of standard emulsions with different fat contents

Note: The viscosity of the emulsion when the shear rate is 50/s is represented by η _50/s ; different letters in the same column indicate that there are significant differences between groups (P<0.05)

As chewing progresses, the tribological properties of the emulsion become the main factor affecting the perception of cream. The friction mechanics characteristic curve of the emulsion is shown in Fig. 4, the abscissa is the shear rate, and the ordinate is the friction coefficient related to the characteristics of the lubricating medium and the lubrication model. As can be seen from the figure, the curves of all samples have a tendency to rise first and then decline. The reasons for this trend are as follows: when the test did not start, the state of contact between the stainless steel ball and the elastic plate (boundary lubrication model); With the increase of the shear rate, the milk fat and casein in the emulsion continuously enter the contact gap between the ball and the plate (mixed model), and during this process, the casein enters and adsorbs at the interface between the ball and the plate, which may lead to an increase in the friction coefficient; As the shear rate increases further, the fat globules in the emulsion break and the interface between the ball and the plate is completely separated due to the filling of the emulsion (hydrodynamic model). During the shearing process, it breaks and gathers to form a film, gradually increasing the lubricity of the system. At different shear rates, the group with higher fat content has a smaller coefficient of friction. The 10.5% fat group had the lowest coefficient of friction at all equivalent shear rates. Sensory experiments have shown that the higher the fat content of dairy products, the better the lubricity of the mouthfeel. This also shows that using this method can predict the lubricity of emulsion mouthfeel to a certain extent.

In emulsions with large fat globules, fat may float and accumulate during the gel formation process, thereby affecting the quality of the standard system. The value of d _3.2 can characterize the average size of particles in the system to a certain extent. Add GDL acidified gel to the prepared standard emulsion to form acidified gel systems with different fat contents. The fat particle size in the gel system is shown in Table 3. Except for the 0% group, there is no significant difference among other groups (P>0.05) and there was no significant difference (P>0.05) with the fat globule size of the emulsion, which indicated that the fat globules did not aggregate during the curd process.

Table 3 Fat globule size of standard acidified gel system with different fat contents

Note: Fat globule size is represented by d _3.2 ±sd; different letters ^ag in the same column represent significant differences between groups (P<0.05)

The rheological properties of the gel system can to some extent represent the perceived creaminess when it enters the mouth. The viscosity of the gel system changes with the shear rate as shown in Figure 5. At low shear rates, the higher the fat content of the gel system, the greater the viscosity. However, the viscosity of the gel system is significantly higher than that of the emulsion system during the whole shear process. This is because casein micelles exist in stable emulsions, and the hydrophilic C-terminal peptide chains of κ-casein protrude from the surface of micelles to form hairy layers, which can form steric and electrostatic repulsions to prevent further aggregation of sub-micelles. And maintain the stability of casein micelles. When the gel is acidified, the electrostatic repulsion of the hair layer is disrupted, causing casein micelles to aggregate and form a gel. The aggregation of casein will lead to an increase in the storage modulus of the system, thereby increasing the viscosity of the system. As shown in Table 4, when the shear rate reaches 50/s, that is, when the human mouth chews, there is no significant difference in the viscosity of the gel system in each group.

Table 4 Viscosities of standard acidified gel systems with different fat contents

Note: The viscosity of the emulsion at a shear rate of 50/s is represented by η50/s; different letters a-g in the same column indicate significant differences between groups (P<0.05)

The tribological properties of the gel system can to some extent represent its perceived creaminess in the later stages of oral processing. The friction mechanics characteristic curve of the acid gel is shown in Fig. 6. It can be seen that except the friction mechanics characteristic curve of the 0% group is a unimodal curve, the friction mechanics characteristic curves of the other groups are bimodal curves. The reason for the curve of such a trend in the 0% group is as follows: (1) at the beginning of the test, the elastic plate and the stainless steel ball are in contact (boundary model), and the shear rate is not enough to destroy the gel structure of the protein when it is less than 0.4/min. And at this time, the medium (gel) around the stainless steel ball may cause resistance to the rotation of the stainless steel ball, so the friction coefficient has a rising stage at the beginning. (2) As the shear rate increases (0.4/min-20/min), the medium begins to enter the gap between the ball and the plate (hybrid model), and the protein gel particles will enter the gap during this process, which may make the friction coefficient increase; but at the same time, the liquid medium is constantly entering the gap, reducing the contact area between the plate and the ball to reduce friction. Because of the opposite effects of the two, the friction coefficient curve at this stage shows a slow downward trend, which also shows that at this stage, compared with the adsorbed protein gel particles, the separation of the ball and plate caused by the fluid involved in the gap influence dominates. (3) As the shear rate further increases (>20/min), the plate and the ball are completely separated by the medium (broken gel) in the gap (hydrodynamic model), and the friction characteristics at this time depend on the Medium (broken gel) properties. At this shear rate, the weak gel of the protein will be further broken, reducing the internal friction of the broken gel, and at the same time, the gel system is further sheared and thinned, thereby reducing the friction of the entire system and improving the lubricating performance.

However, when there is fat in the gel system, the process of simulating oral chewing in vitro will lead to the rupture of the gel system, which will cause part of the fat in the system to escape, which will affect the tribological properties of the entire system. The initial friction coefficient of the 0% group was higher than that of other groups. It can be inferred that some fat escaped from the other groups after simulated chewing in the oral cavity, which made the friction coefficient at the beginning of the measurement (shear rate <0.4/min) lower. In the stage of shear rate 0.1/min-0.4/min, the friction coefficient curves of the 0% group and other groups have the same trend. When the shear rate is in the stage of 0.4/min-20/min, the friction coefficient of the experimental group with fat The curve shows a different trend from the 0% group. At this stage of shear rate, the medium begins to enter the gap between the plate and the ball (mixed model), and the friction coefficient at this stage is affected by three factors: (1) fat will enter the gap and decrease during this process Friction force; (2) The entry of the medium in the gap will cause the cricket to separate, thereby reducing the friction force; (3) The protein gel particles entering the gap may cause the friction force to increase, thereby increasing the friction coefficient.

It can be seen from Figure 6 that, except for the 0% group, the higher the fat content of the other groups, the faster the friction coefficient curve drops at the shear rate of 0.4/min-3/min, and the higher the fat content, A lower coefficient of friction means that at this stage the influence of fat entering the gap is dominant. As the shear rate increased (20/min-40/min), the gaps between the crickets were gradually separated by the medium, and more and larger protein gel particles entered into the gaps, resulting in an increase in the coefficient of friction. When the shear rate continues to increase (shear rate>40/min), the ball plate has been completely separated by the lubricating medium (hydrodynamic model), the change of the friction coefficient mainly depends on the lubricating medium itself, and the gel particles in the medium are Destruction and shear thinning, resulting in a drop in the coefficient of friction of the fat-containing group as rapidly as the 0% group. However, different from the 0% group, due to the presence of fat in the lubricating medium, the friction coefficients of each group at this stage are smaller than the 0% group.

It can be seen from Table 5 that when the shear rate is 20/min, there is an obvious correlation between the fat content and the friction coefficient, that is, the higher the fat content in the acid gel system, the greater the friction coefficient and the worse the lubricating properties. Sensory experiments have shown that the higher the fat content of dairy products, the better the lubricity of the mouthfeel. Therefore, follow-up studies used the coefficient of friction at this shear rate to predict the lubricity properties of fermented dairy products.

Table 5 Friction coefficients of standard acidified gel systems with different fat contents

Note: when the shear rate is 20/min, the coefficient of friction is represented by μ _20/min ; different letters in the same column indicate that there are significant differences between groups (P<0.05)

The variation trend of the viscosity of the fermented milk samples with the shear rate is shown in Figure 7. It can be seen that at the beginning of the shearing, there are large differences in the viscosity among the groups, among which No. 4 is the highest and No. 2 is the lowest. As the shear rate increases, the viscosities of all samples show a decreasing trend, which is consistent with the viscosity change trend of the standard gel system mentioned above. When the shear rate reaches 50/s (close to the shear rate when chewing in the human mouth), the viscosity of each group is shown in Table 6. It can be found that there is a significant difference in the viscosity of each group. No. 1, No. 3 and No. 6 Compared with other groups, it has the largest viscosity, and the viscosity of No. 2 and No. 5 is the smallest. It can be seen from Table 6 that there is no significant difference in the particle size of the fat globules of the samples in each group, indicating that the difference in viscosity is not caused by the different particle sizes of the fat globules. The reason for this difference may be due to the different strains used in the fermentation of each sample. The exopolysaccharide produced during fermentation was different, which led to the difference in viscosity among the groups.

The friction mechanical characteristic curve of the fermented milk sample is shown in Fig. 8. It can be seen that the curves of each group of samples are bimodal curves, which is consistent with the friction mechanical characteristic curve of the above-mentioned gel system. It can be seen that at low shear rates, there are partial differences in the friction coefficients of the groups. From the above results, it can be seen that the coefficient of friction at a shear rate of 20/min can be used to predict the lubricity of the gel system. The friction coefficients of fermented milk samples at a shear rate of 20/min are shown in Table 6. It can be seen that except for the friction coefficient of sample No. 1 which is significantly higher (P<0.05) than other groups, the friction coefficients of other groups do not exist Significant differences. When the shear rate was less than 100/min, there was a large difference in the friction coefficient of each group, but when the shear rate exceeded 100/min, the friction mechanical characteristic curves of each group tended to coincide. It shows that under the condition of high shear rate, the lubricating properties of each group of fermented milk tend to be consistent.

Table 6 Fat globule size, viscosity and friction coefficient of standard acidified gel system with different fat contents

Note: the particle size of fat globules is represented by d _3.2 ± sd, the viscosity of the emulsion is represented by η _50/ s when the shear rate is 50/s; the friction coefficient is represented by μ _1/ min when the shear rate is 1/min ; Different letters in the same column indicate significant differences between groups (P<0.05)

In this example, emulsion systems and gel systems with different fat contents were first established, and the possibility of using a rheometer to measure the lubricating properties of fermented milk was verified, and this method was applied to measure the physical properties of six fermented milk samples , the specific results are as follows:

(1) Emulsions and acidified gels with different fat contents and uniform fat globules were successfully prepared.

(2) The viscosities of emulsions and acidified gels with different fat contents were not significantly different at a shear rate close to that of human mouth chewing, but the viscosity of acidified gels was significantly higher than that of emulsions.

(3) By using a rheometer to measure emulsions and acid gels with different fat contents after simulated oral chewing, it was found that this method can be used to distinguish the lubricity between samples, and when the shear rate is 20/min, each The coefficient of friction of the samples is negatively correlated with the fat content, that is, at the shear rate, the higher the fat content of the sample, the smaller the coefficient of friction and the better the lubricity. From the above results, it can be confirmed that this method can be used to measure the lubricating properties of fermented dairy products, and the friction coefficient when the shear rate is 20/min is the most evaluation index.

(4) The physical properties of the six fermented milk products showed that the viscosity of the samples was significantly different under the shear rate close to oral mastication, and the viscosities of No. 1, No. 3 and No. 6 were significantly higher than those of other groups; In the measurement of friction mechanical properties, it was found that the friction coefficient of No. 1 was significantly higher than that of other groups at a shear rate of 20/min after simulated oral chewing, which may be compared with its observation by laser confocal microscope. related to the loose gel structure.

Example 2——Analysis of key flavor substances of fermented dairy products "creaminess"

In this example, headspace solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS) was used to measure the composition of flavor substances in fermented milk samples.

HS-SPME experimental method: Take 15g of commercially available fermented milk in a 60mL headspace bottle, add 15g of sodium chloride and a magnetic stirring rotor, and then seal the headspace bottle with a rubber gasket and bottle cap. Then place the headspace bottle in a magnetically stirred water bath at a certain temperature and fix it with a test tube rack to start the balance. When a certain equilibrium time is reached, insert the extractor into the headspace bottle and push out the pillow 3cm to start the extraction. After the extraction, retract the extraction head, pull out the needle from the headspace bottle and start the GC-MS measurement.

The injection mode of GC-MS is manual injection. GC conditions: the inlet temperature is 230°C, the carrier gas is helium, the flow rate is 1ml/min, splitless injection. The desorption time is 1.5min. Heating program: start at 40°C, keep for 3 minutes, rise to 120°C at 3°C/min, hold for 2 minutes, then rise to 230°C at 15°C/min.

Mass spectrometry conditions: the ionization mode is EI; the ion source temperature is 230°C, the quadrupole temperature is 150°C; the scanning range is 35-400amu.

Chromatographic analysis method: Integrator selects ChemStation, adaptability selects United States Pharmacopoeia (USP) peak filter and adjusts to absolute area>300000.

Compound Qualitative: Compare and confirm the mass-to-compound ratio of the measured compound with the data in the NIST14 database, and the positive and negative matching degrees are required to be greater than 700.

Temperature, equilibration, and extraction time during HS-SPME all have a significant impact on extraction results. The study found that when the heating temperature of HS-SPME pretreatment was 40°C, the number of extraction peaks would increase with the increase of extraction and equilibration time, and the total number of peaks in the three groups whose extraction time was 5 min was relatively small. When the extraction time reached 20min, the total amount of flavor substances extracted was the most. This result shows that even though the volatile flavor compounds in the headspace bottle have reached equilibrium, a longer extraction time is still required to fully extract the flavor compounds under the extraction condition of 40°C. When the treatment temperature was 50℃ and 60℃, the extraction effect was similar at these two temperatures. In order to prevent the change of volatile flavor compounds caused by heating, the optimal treatment temperature was selected as 50℃. When the equilibrium time reaches 10 minutes, continuing to increase the equilibrium time will not significantly improve the extraction effect; the extraction time will not significantly increase the extraction effect after the extraction time exceeds 10 minutes.

In this example, the influence of HS-SPME pretreatment conditions on the total peak area of the extraction was analyzed, and it was found that at a specific temperature and a certain equilibrium time, the longer the extraction time, the larger the peak area; in the 40°C group, In the case of equilibrium at 0 min, the extraction time was doubled from 5 min to 10 min, and the total extraction peak area also doubled, indicating that the adsorption space in the extraction head was not fully utilized in the case of extraction for 5 min; In the 60°C group, under the condition of equilibrating for 20 minutes, the total peak area did not increase significantly when the extraction time was doubled, so it can be judged that the adsorption space of the extraction head is close to saturation under this condition. Except for the 20min equilibration and 20min extraction group, the extraction peak areas of the other groups increased with the increase of temperature, which was because high temperature accelerated the adsorption of substances. There is no significant difference between 50°C and 60°C in the 20min equilibration and 20min extraction group, indicating that at 50°C, the adsorption space of the extraction head has been fully utilized under the equilibrium and extraction conditions. In addition to the adsorption space utilization of the extraction head, the competitive adsorption in the HS-SPME process is also an important factor affecting the results. Although at 60°C, the total peak area of the equilibrium 20min extraction for 10min or 20min adsorption is larger, but the species of wind species extracted at this temperature is less than that at 50°C, which may be because at higher temperatures, the competition The adsorption phenomenon is relatively serious, and the flavor substances with poor volatility cannot be successfully adsorbed on the extraction head. In addition, in the HS-SPME process, high temperature and high species concentration will intensify the competitive adsorption.

Based on the above experimental results, the optimal HS-SPME experimental conditions finally determined are 50°C, equilibration for 20 minutes, and extraction for 20 minutes. The determined optimal HS-SPME experimental conditions were used to determine the flavor components of six fermented milk products, as shown in Table 7. The measurement results showed that there were 14 kinds of flavor substances in No. 1 sample (2 kinds of alcohols, 5 kinds of ketones, and 5 kinds of acids); there were 12 kinds of flavor substances in No. 2 sample (3 kinds of alcohols, 6 kinds of ketones, 3 kinds); No. 3 sample has 20 kinds of flavor substances (5 kinds of alcohols, 6 kinds of ketones, 7 kinds of acids); No. 4 sample has 16 kinds of flavor substances (4 kinds of alcohols, 4 kinds of ketones, 7 kinds of acids 4 kinds); No. 5 sample has 16 kinds of flavor substances (3 kinds of alcohols, 6 kinds of ketones, 6 kinds of acids); No. 6 sample has 17 kinds of flavor substances (5 kinds of alcohols, 4 kinds of ketones, 6 kinds of acids 4 species). There are certain differences in the composition of flavor substances in each sample: sample No. 3 has the most types of flavor substances, and the most abundant types of ketones and acid compounds; sample No. 2 has the least types of flavor substances but rich in ketone compounds.

Table 7 Composition of flavor substances in six kinds of fermented milk

Note: Different letters ^af in the same column indicate significant differences between groups (P<0.05)

In this example, the peak area of 2,3-butanedione of No. 3 is significantly higher than that of other samples, which may cause the perception of creaminess of No. 3 sample to be higher than that of other groups. Among the six samples in this experiment, No. 5 sample had the highest butyric acid content, which may lead to the weaker perception of creaminess of No. 5 sample.

In order to explore the similarity of the composition of flavor substances in each sample, the results of principal component analysis can be intuitively reflected. The principal component analysis results of flavor substances of the six samples are shown in Figure 9. The cumulative variance contribution rate of the two principal components is 66.86%, among which the contribution rate of principal component 1 (PC1) is 50.02%, and that of principal component 2 (PC2) is 16.84%.

Combining Table 7 and Figure 9, it can be seen that the distribution of No. 1, No. 4 and No. 6 sample points is relatively concentrated, which shows that the composition of flavor substances in these three samples is similar; the type of flavor substances in No. 2 sample is the least, and its flavor substances The peak area of none of them was significantly larger than that of the other groups of samples, so there were no characteristic flavor substances around it in the principal component analysis diagram; The substances are characteristic flavor substances, and the content of these substances in No. 3 sample is also very high; No. 5 sample contains more kinds of acids and ketone flavor substances, and 2-nonanone, 4-hydroxy-3-hexanone Ketone, 2-undecanone and butyric acid are the characteristic flavor substances.

In this example, the composition of the flavor substances of the fermented milk sample before and after simulated oral chewing was measured, and the results are shown in Table 8 and Table 9. The results show that the types of flavor substances and peak area data measured in each fermented milk sample before and after oral cavity simulation are less than the total types of flavor substances measured in the above experiment, and the flavor substances measured before and after oral cavity processing are only acids, ketones and Alcohols, and only one kind of isopropanol was detected in the alcohol compounds, and the acid and ketone compounds also decreased to varying degrees, which shows that the food matrix of fermented milk does affect the release of flavor substances, and the volatile flavor in fermented milk Substances do not all contribute to flavor perception.

Volatile flavor components of fermented milk under table 8 oral cavity conditions

Note: Different letters ^af in the same column indicate significant differences between groups (P<0.05)

Table 9 Composition of headspace flavor components of fermented milk after simulated oral chewing

Note: Different letters ^af in the same column indicate significant differences between groups (P<0.05)

In summary, this embodiment:

(1) The optimal HS-SPME conditions were determined to be 50°C, 20min equilibration and 20min extraction. Under this condition, the most kinds of volatile flavor compounds can be extracted and the total peak area is the largest.

(2) The composition of flavor components of 6 fermented milk samples was determined. Among them, No. 3 sample has the most types of flavor substances, with 20 kinds; No. 2 sample has the least types of flavor substances, only 12 kinds; No. 5 sample has more types and contents of acid flavor substances; No. 3 sample has frankincense flavor Contributing 2,3-butanedione content was significantly higher than the other groups.

(3) Through the analysis of the principal component results, it is known that the composition of flavor substances of samples No. 1, No. 4 and No. 6 is similar; 2,3-butanedione, isopropanol, n-hexanol, acetic acid and other substances are characteristic flavor substances; Sample No. 5 has 2-nonanone, 4-hydroxy-3-hexanone, 2-undecanone and butyric acid as its characteristic flavor substances.

(4) By comparing the headspace flavor components of fermented milk samples before and after simulated oral processing, it was found that not all flavor compounds in fermented milk can be perceived by the human body through the food matrix; oral processing is conducive to the release of flavor compounds , and the effect of ketone compounds is the most significant.

Example 3 - Sensory evaluation of "creaminess" of fermented dairy products

In this embodiment, we choose to use the evaluation scale ranging from 0-10, and for the above sensory properties, select different standard products to represent their different intensities. The definition of specific sensory properties and the corresponding standard products and their representative strengths are shown in Table 10 shown.

Table 10 The definition of each sensory characteristic in the descriptive sensory evaluation and the reference of different sensory levels

Firstly, 13 sensory evaluators aged between 20 and 25 years old with no impairment of vision, smell, taste and taste were recruited to set up a descriptive sensory evaluation group. The experiment was carried out in a professional sensory evaluation room. Each sensory evaluator had an independent evaluation room. The evaluation room was equipped with incandescent lamps and water pools to unify the light conditions during the experiment and facilitate the experiment. The sensory evaluation test starts at two o'clock in the afternoon, and the test temperature is room temperature 25°C.

The fermented milk samples were stored in a 4°C freezer. Before the experiment started, each evaluation room was equipped with an ice box. During the sensory evaluation, the fermented milk samples were placed on the ice box to ensure the low temperature before the entrance of each sample. Also equipped with the standards mentioned in Table 20.

The experiment consists of three parts: sniffing, seeing, and tasting. The scoring in this experiment is all horizontal scoring, that is, scoring a certain indicator of all samples first.

First, please ask the sensory evaluator to smell the standard products with different strengths of a certain characteristic, and then score the characteristic of all samples horizontally. After one sample, put the lid back on until the sniffing part of the experiment is completed. After that, the visual perception part of the experiment was carried out. First observe the standard, then remove the cover and place the sample under incandescent light to observe and score this characteristic horizontally.

Next, the evaluation experiment of the olfactory part behind the nose is carried out. First, the sensory evaluators are asked to smell the standard products of different strengths of a certain characteristic, and then put the fermented milk sample into the mouth, pinch the nose during chewing, and feel the smell in the nasal cavity Intensity and score horizontally. Rinse your mouth with water for 15 seconds after tasting each sample before evaluating the next sample.

Then there is the taste part of the experiment. First, the sensory evaluators are asked to taste the standard samples of different strengths of a certain characteristic, and then put the fermented milk sample in the mouth, and feel the strength of a certain characteristic during the chewing process and score it horizontally. Rinse your mouth with water for 15 seconds after tasting each sample before evaluating the next sample.

The last part is the experiment of creaminess perception. First, the sensory evaluators are asked to taste the standard products with different strengths of a certain characteristic, and then put the fermented milk sample into the mouth, and feel the intensity of the creaminess during chewing and score it. Rinse your mouth with water for 15 seconds after tasting each sample before evaluating the next sample.

The descriptive sensory evaluation results are shown in Table 11. It can be seen from the table that No. 1 and No. 6 have the strongest perception of creaminess, No. 2 and No. 4 have the middle perception of creaminess, and No. 3 and No. 5 have the weakest perception of creaminess.

In terms of prenasal olfactory perception, No. 1 and No. 6 have the highest intensity of diacetyl flavor and milk fat flavor perception, which may be one of the reasons for their stronger creamy perception; No. 5 has the highest yogurt flavor perception , which is also consistent with the result of No. 5 sample having the highest acid type and content in Example 2, and the stronger perception of sourness may lead to a decrease in the perception of creaminess; No. 2 sample has no most prominent pre-nasal flavor perception, which may be due to The flavor substance content of the sample species is the least (the results are shown in Example 2). In terms of retronasal olfactory perception, sample No. 3 has the strongest postnasal diacetyl perception, which is consistent with the result obtained in Example 2 that No. 3 has the highest diacetyl content. In this example, the perception of diacetyl taste before the nose of sample No. 3 is not the strongest, but the perception of diacetyl taste behind the nose is the strongest, indicating that more diacetyl will be released from the food matrix and passed by the human body under oral processing conditions However, for sample No. 5 with higher content of acid compounds, the lactic acid taste perceived before the nose is higher than that perceived by the retronasal sense of smell, which may be due to the Possibly a more important process.

In terms of visual perception, many studies have mentioned that vision can affect people's judgment of food attributes. Consumers think that viscous dairy products have a creamy feel. There is no significant difference in color and visual smoothness of the 6 groups of samples (P>0.05 ), but samples No. 3 and No. 5 had the lowest visual viscosity, which may be one of the reasons for the weaker perception of creaminess in these two samples. In this study, samples No. 1 and No. 6 had the strongest perception of sweetness, which may enhance their perception of creaminess; samples No. 5, No. 4 and No. 6 had stronger perception of sourness, which may reduce their perception of creaminess. Although the sour perception of sample No. 5 is higher and similar to that of sample No. 6, the perception of sweetness and creaminess of No. 5 is significantly smaller than that of No. 6 (P<0.05), which indicates that the enhancement of sweetness perception may be significantly improved Creamy perception.

In terms of oral tactile contribution, in this example, there was no significant difference in the intensity of oral viscosity among all samples (P>0.05); the oral smoothness and viscous thickness of sample No. 1 were higher than those of other groups, which may be due to its creamy feeling An important reason for the strong perception.

Table 11 Descriptive sensory evaluation results

Note: Different letters in the same row indicate significant differences between groups (P<0.05)

In order to study which sensory perception may be related to the creamy perception and to compare the differences in sensory perception between samples, this example carried out principal component analysis on the results of the descriptive sensory evaluation, and the results are shown in Figure 10. The first two principal components The cumulative variance contribution rate is 67.90%, among which the variance contribution rate of the first principal component is 40.60%. Most oral perception characteristics are concentrated near the X-axis (such as oral viscosity, oral thickness and oral smoothness, etc.), so it can be The x-axis is believed to explain the mouthfeel properties of the fermented milk samples. The variance contribution rate of the second principal component is 27.30%, and more odor and taste perception characteristics are concentrated near the Y axis (such as pre-nasal diacetyl, pre-nasal and post-nasal buttery, sour, etc.), so it can be considered that Y axis explains the flavor profile of fermented milk, with the positive half axis representing non-acid perception and the negative half axis representing sour perception.

It can be seen from the figure that the perceptual attributes that are more correlated with the overall creaminess perception include oral smoothness, oral thickness, sweetness and milk fat. There are also many studies pointing out that flavor perception is also very important for creaminess perception. Diacetyl, acetoin and ketone compounds have a great contribution to creamy flavor perception, but in this example, the pre-nasal and post-nasal diacetyl flavors seem to is not an important factor affecting the perception of creaminess, which may be due to the fact that texture factors contribute more to creaminess than flavor factors when exploring the influencing factors of creaminess perception and evaluating flavor factors and texture factors together, that is to say, Compared with flavor perception, texture perception may be a more important factor affecting creaminess perception.

There are differences in the perception of features for each sample. The points of samples No. 1 and No. 6 are relatively close to the X-axis, indicating that the oral perception characteristics of these two samples are relatively prominent. It can also be seen from the above sensory evaluation results that the two samples have relatively high oral viscosity and smoothness, but there are still some differences in the reasons for their strong creamy perception: sample No. 1 has a greater contribution to the smell and taste, such as The taste of diacetyl, milk fat and sweetness of No. 1 sample are strong; while the mouthfeel and visual perception of No. 6 sample are important factors affecting its creamy perception. In addition, sample No. 6 is in the second quadrant and sample No. 1 is in the first quadrant, indicating that although the perceived intensity of creaminess of the two is similar, the perceived intensity of sourness of sample No. 6 is stronger.

The distribution of sample points of No. 3 and No. 5 is concentrated near the Y axis, indicating that these two samples are mainly characterized by the perception of taste and smell. The main perceptual characteristics of No. 3 sample are odor perceptions such as post-nasal diacetyl, pre-nasal and post-nasal buttery smells, which are consistent with the high content of 2.3-butanedione and acetone in No. 3 obtained in the previous experimental results. Existing studies have found that based on the food matrix can affect the release of flavor substances, oral processing may accelerate the release of flavor substances in certain food matrices and enhance human perception. In this experiment, although the content of 2,3-butanedione in No. High, but prenasal diacetyl perception does not seem to be its characteristic property, which may be related to the food matrix affecting the release of flavor substances, the food matrix of fermented milk may affect the release of 2.3-butanedione, diacetyl flavor under the conditions of oral processing Might be easier to perceive. Sample No. 5 is mainly characterized by the perception of sour smell and taste, which is consistent with the high content of acid compounds in Sample No. 5 measured in Chapter 3, and the sample point of Sample No. 5 is more inclined to the perception of sour milk taste before the nose points, indicating that in the sensory perception of sample No. 5, a higher intensity of yoghurt flavor can be perceived through the prenasal sense of smell.

For samples No. 2 and No. 4, they have neither outstanding sensory evaluation characteristics nor outstanding instrumental analysis characteristic data. The sour taste perception of No. 2 sample is slightly stronger than that of No. 4. The sour taste and flavor perception of No. 4 and the non-acid taste and flavor perception of No. 4 are relatively low, and the oral sensory characteristics are also at a medium or low level.

In order to explore the flavor perception contribution of flavor compounds in fermented milk, this example conducted principal component analysis on the flavor perception data in the descriptive sensory evaluation and the flavor composition data measured by the instrument, and the results are shown in Figure 11. The cumulative variance contribution rate of the two principal components is 64.20%, the variance contribution rate of the first principal component is 40.78%, and the variance contribution rate of the second principal component is 23.42%.

It can be seen from the figure that there are more ketones and acid flavor compounds, such as 4-octanone, 2-nonanone, 4-hydroxy-3-hexanone, 2-hydroxy-3-pentanone, butyric acid, Compounds such as valeric acid, heptanoic acid, and caprylic acid have a greater relationship with the perception of lactic acid taste before the nose, but there are almost no flavor compounds related to the perception of lactic acid taste after the nose. The main pathway of acid compounds. The point distributions of buttery, diacetyl and milk fat flavors are relatively concentrated, which shows that they are similar to a certain extent, and the compounds related to these flavor perceptions are carbamic acid, 2,3-butanedione, 4- Penten-1-ol and 4-hydroxy-3-hexanone. It has been reported that ketone compounds such as 2,3-butanedione and 4-hydroxy-3-hexanone are related to the perception of milk flavor in dairy products, and appropriate concentrations of ketone compounds can enhance the milk flavor of dairy products. The experiment in this example The results are consistent with literature reports.

In this example, the perception of post-nasal milk fat and pre-nasal diacetyl taste has little correlation with these flavor points, which shows that the way to perceive these two flavors in fermented milk samples is different, and the milk fat flavor is mainly The perception of diacetyl is mainly through the nasal sense of smell, which is consistent with the previous experimental results.

Some flavor substances such as 2-hexylamine, 3,3-dimethyl-2-butanone, benzaldehyde and 2-bromo-1-chloro-propane seem to have nothing to do with the several odor sensory properties involved in the experiment. Probably because their concentration in fermented milk is too low to be perceived by humans.

In order to explore whether the physical properties of fermented milk measured by the instrument can represent its oral perception characteristics, this example carried out principal component analysis on the oral tactile perception data in the descriptive sensory evaluation results and the physical properties of fermented milk measured by the instrument, and the results are shown in Figure 12 Show. The cumulative variance contribution rate of the two principal components is 73.39%, the variance contribution rate of the first principal component is 49.44%, and the variance contribution rate of the second principal component is 23.95%. The points of oral smoothness are located in the second quadrant, while the points of the friction mechanical properties measured by the instrument are all in the fourth quadrant, indicating that there is an obvious anti-correlation between the two, that is, the higher the oral smoothness, the higher the friction coefficient measured by the instrument. The greater the μ20/min, it also means that the instrumental measurement method of tribological properties established in Example 1 can successfully predict the tribological sensory properties (lubricity) of fermented dairy products in the mouth.

The apparent viscosity η50/s measured by the instrument is similar to the contribution of the oral viscosity in the sensory properties on the first principal component (similar to the abscissa), but the contribution to the second principal component is opposite, which shows that the instrumental determination There is only a certain degree of correlation between the apparent viscosity and the viscosity perceived by the oral cavity, and the apparent viscosity measured by the instrument cannot fully represent the perceived viscosity in the oral cavity. In fact, the apparent viscosity measured by our instrument is defined as the shear viscosity in physics, that is, a certain liquid is filled between a pair of parallel plates with an area A and a distance dr, and a thrust is applied to the upper plate. F, the force required to make it produce a speed change is the shear viscosity. Due to the effect of viscosity, when the object moves in the fluid, it is subject to frictional resistance and pressure difference resistance, resulting in loss of mechanical energy, which is why its points in the figure are relatively close to the point distribution of the friction coefficient.

To sum up, in this example, an analytical sensory evaluation system for the perception of fermented milk cream was first established, and a sensory evaluation team was established to conduct analytical sensory evaluation on 6 yoghurt samples. After that, principal component analysis was performed on the sensory evaluation data and the instrumental analysis data in the previous two chapters, and the main factors affecting the perception of creaminess were found, and it was discussed whether the results of instrumental measurement can predict human sensory experience. The specific results are as follows:

(1) The results of descriptive sensory evaluation showed that No. 1 and No. 6 had the strongest creamy perception, No. 2 and No. 4 had a medium creamy perception, and No. 3 and No. 5 had the weakest creamy perception.

(2) Through the principal component analysis of the descriptive sensory evaluation results, it was found that the perceptual attributes that are more related to the overall creamy perception include oral smoothness, oral thickness, sweetness and milk fat. The stronger the perceived intensity, the stronger the creaminess felt by the human body.

(3) Principal component analysis was carried out by combining the sensory evaluation data and the flavor substance data measured by the instrument. It was found that 4-octanone, 2-nonanone, 4-hydroxy-3-hexanone, 2-hydroxy-3-pentanone, Flavor substances such as butyric acid, valeric acid, heptanoic acid and octanoic acid are related to the perception of yogurt flavor; substances such as 2,3-butanedione, 4-penten-1-ol and 4-hydroxy-3-hexanone are related to the perception related. The flavor perception of 2,3-butanedione mainly depends on the retronasal sense of smell, while the perception of yogurt and milk fat flavor mainly depends on the prenasal sense of smell.

(4) By combining the sensory evaluation data and the physical property data measured by the instrument for principal component analysis, it was found that the friction coefficient μ20/min measured by the instrument can predict the perceived smoothness in the human oral cavity, but the apparent viscosity measured by the instrument cannot. Fully representative of the viscosity perceived in the human oral cavity.

The above is only a preferred embodiment of the present invention, it should be pointed out that, for those of ordinary skill in the art, without departing from the principle of the present invention, some improvements and modifications can also be made, and these improvements and modifications can also be made. It should be regarded as the protection scope of the present invention.

Claims (8)

1. an accurate evaluation method of fermented milk cream feeling, it is characterized in that, described method comprises the following steps: (1) Texture characteristic detection A. In vitro simulated oral chewing conditions: Add artificial saliva to the fermented milk to be tested and stir it with a glass rod at a speed of 200rpm for 15s in a water bath at 37°C to simulate the oral chewing process to obtain the sample fermented milk; B. Use a rheometer to measure the lubricity of the sample fermented milk, set the shear rate to 20/min, and measure the coefficient of friction; (2) Detection of flavor substances The HS-SPME method was used to extract the flavor substances in the fermented milk to be tested. The conditions of the HS-SPME method were 50° C., 20 min equilibration and 20 min extraction. 2. The accurate evaluation method according to claim 1, characterized in that the method further comprises the following steps: (3) Sensory evaluation Based on the visual, olfactory, gustatory and oral tactile factors that affect the perception of creaminess, an analytical sensory evaluation for the creaminess of fermented milk was established, and the main factors included were mouth smoothness, mouth thickness, sweetness and milk fat taste. 3. The accurate evaluation method according to claim 1, wherein the ratio of artificial saliva to fermented milk to be tested is 1:4 in the step (1) A. 4. The accurate evaluation method according to claim 1, characterized in that, the rheometer described in step (1) B. is a pressure-controlled rheometer. 5. The accurate evaluation method according to claim 1, characterized in that, in the flavor substances described in the step (2), the substances that contribute to the sour milk taste include 4-octanone, 2-nonanone, 4-hydroxyl -3-hexanone, 2-hydroxy-3-pentanone, butanoic acid, valeric acid, heptanoic acid and octanoic acid. 6. The accurate evaluation method according to claim 1, characterized in that, the substances that contribute to frankincense in the flavor substances described in the step (2) include 2,3-butanedione, 4-pentene-1 -alcohol and 4-hydroxy-3-hexanone. 7. The accurate evaluation method according to claim 1, characterized in that, among the flavor substances in the step (2), the substances that contribute to the sour milk flavor and fat flavor include 2,3-butanedione. 8. The accurate evaluation method according to claim 2, characterized in that, the definition of each sensory characteristic in the sensory evaluation of the step (3) and the references of different sensory characteristics thereof are: .