1. Introduction
Sausages are favored all over the world for their high nutritional value and delicious taste [
1], and have important economic significance for the meat-packing industry. The main ingredients of sausages are pork lean meat, pork fat, isolated soy protein, and starch. In general, sausages are high in fat, exceeding 20%. However, the world health organization (WHO) recommends reducing fat intake [
2], since excessive fat intake could lead to coronary heart disease, cardiovascular disease, hypertension, and other diseases [
3,
4,
5]. Due to the popularity of sausages by consumers, it is necessary to develop low-fat sausages to reduce health problems.
Some meat technicians used plant additives (soy protein isolate and cellulose nanofiber complex gels) as fat substitutes to produce low-fat meat products [
6], but consumers often shun these plant additives which were obtained through chemical or transgenic pathways. Nowadays, natural and healthy food has become a research hotspot. Zhu et al. [
7] improved the fatty acid composition and sensory quality of sausages by using Jerusalem artichoke powder and olive oil to replace fat. Yinyu et al. [
8] added regenerated cellulose fiber to the fat-reduced emulsified sausage, which could effectively reduce the fat content without affecting the quality and sensory characteristics. In addition, Utama et al. [
9] found that the pre-emulsified perilla-canola oil could improve the hardness and maintain the acceptable appearance, flavor, and overall impression of the sausage. Najjar et al. [
10] added emulsified rapeseed oil and protein-based fat substitute to the beef filling, which could increase the hardness of the beef filling and reduce cooking loss.
In addition, camellia oil gel [
11], chicory root powder [
12], transesterified palm kernel oil [
13], hydroxypropyl methylcellulose oil gel [
14], hazelnuts [
15], rye bran fiber and collagen [
16], plant powder and konjac gel [
17], and Chitosan and gold flax seed powder [
18] were also used as fat substitutes in meat products.
Tremella is rich in protein and trace elements, so it could improve the detoxification ability of liver, protect the liver, and could be able to enhance the body’s anti-tumor immunity [
19]. Tremella extracts possess capacities of anti-fatigue and anti-hypoxia [
20]. Tremella is crystal clear, juicy and sticky, and resembles pig fat in appearance, showing good properties as a fat substitute. Therefore, tremella could be a good strategy to be obtained in the development of low-fat sausage. The objective of this research was to manufacture sausages added with tremella and investigate the effects of tremella as a fat substitute for low-fat sausages by measuring proximate component, color, water activity, pH, cooking loss, water holding capacity, textural profile analysis, free amino acids, and sensory evaluations.
2. Materials and Methods
2.1. Materials
Fresh pork was purchased from Jilin Huazheng Agriculture and Animal Husbandry Development Co., Ltd. (Changchun, Jilin, China). Tremella (basswood tremella, protein: 14%; fat: 3%, carbohydrate: 16%) was obtained from Heilongjiang Lvzhiyuan Agricultural and Sideline Products Co., Ltd. (Suihua, Heilongjiang, China). All of the additives were supplied by Sichuan Jinshan Pharmaceutical Co., Ltd. (Meishan, Sichuan, China) and all the chemical reagents were supplied by Beijing Beihua Co., Ltd. (Beijing, China).
2.2. Sausage Formulation and Processing
Dried tremella (100 g) was soaked in warm water at 40 °C for 30 min and cut into slices with a width of 0.5 cm. The lean meat and fat were ground through a 15 mm plate (TJ12, Panyu Liye Food Machinery Factory, Guangzhou, Guangdong, China). The formulations are presented in
Table 1. In the groups of improved sausages, a partial replacement of pork fat by tremella was performed as followed: TR25 (75% pork fat and 25% tremella); TR50 (50% pork fat and 50% tremella); TR75 (25% pork fat and 75% tremella) and TR100 (0% pork fat and 100% tremella). Each sausage formulation was replicated three times. According to the formulations, the above materials were homogenized for 140 s in a blender (Busch, Marburg, Germany). After the homogeneity, the raw material was put into the casing by sausage stuffer (Shandong Yaobang Equipment Co., Ltd., Linyi, Shandong, China). The sausages were baked at 68 °C for 30 min, braised at 80 °C for 50 min, and fumigated at 50 °C for 150 min by electric heating flue gas furnace (Jiaxing Case stainless steel machinery manufacturing Co., Ltd., Jiaxing, Zhejiang, China). The cooked sausages were cooled in ice-water bath, then put in polythene bags using a vacuum packing machine (Shanghai Yiguang Machinery Co., Ltd., Shanghai, China), and stored at 4 ± 1 °C until analyzing for physicochemical and textural properties.
2.3. Proximate Composition
Compositional properties of five groups of sausages were performed according to AOAC [
21]. The moisture content was determined by drying at 105 °C for 12 h to calculate the weight loss. The fat content was determined by soxhlet method and solvent extraction method following the AOAC Official Method 930.09. Protein content was measured by Kjeldahl method with a Kjeldahl nitrogen analyzer (KDY-9820, Beijing, China). The samples were burned at 550 °C to determine the ash content. Samples were removed from each treatment and the analysis was carried out at 25 °C in triplicate, and the average was then taken.
2.4. Water Activity and pH
The water activity of samples was measured with a water activity meter (Jiangsu Ronghua Instrument Manufacturing Co., Ltd., Jintan, Jiangsu, China). The chopped sausages (10 g) were put into a water activity meter and the data was recorded after 20 min. All determinations were performed at 25 °C in triplicate.
The pH values of sausages were determined by pH meter (Guangzhou Jiayi Precision Instrument Co., Ltd., Guangzhou, Guangdong, China). The samples were obtained in a homogenate (Changzhou Magnetat Instrument Co., Ltd., Guangzhou, Guangdong, China) with 10 g of sausage and 90 mL of distilled water. All determinations were performed at 25 °C in triplicate.
2.5. Color
The color of sausages was measured using a colorimeter (CX2064,
L* = 94.52,
a* = −0.86,
b* = 0.68) according to Wang et al. [
22]. The
L* (lightness),
a* (redness), and
b* (yellowness) values were measured using standard illuminant D65 light source. And the observation angle was 10°. The aperture of the meter was 14 mm. Four measurements (0° 90° 180° 270°) were taken from each sample surface. The test was repeated three times, and the average was taken. The total color difference (ΔE) and whiteness were calculated as follows [
23]:
where Δa =
a* −
a* sample, Δb =
b* −
b* sample, ΔL =
L* −
L* sample.
2.6. Cooking Loss and Water Holding Capacity (WHC)
Cooking loss was determined with the method of Wang et al. [
22]. Each raw sausage was cooked at 80 °C for 50 min. The cooking loss of sausage was obtained by measuring their weight before and after cooking as followed:
where m
1 was the weight of raw sausage and m
2 was the weight of cooked sausage.
The WHC of sausage was obtained with modified methods of Shin et al. [
24] and Wang et al. [
23]. Approximately 10 g of sausage samples were weighed and placed in a centrifuge tube to centrifuge (H1650R/1850R, Xiangyi Saide Instrument Co., Ltd., Changsha, Hunan, China) for 30 min at 12,000×
g at 4 °C, and then weighed. The WHC was calculated as followed:
where W
1 was the weight of the sausage before centrifugation and W
2 was the weight of the sausage after centrifugation.
2.7. Textural Profile Analysis (TPA)
The texture of cooked sausage was determined using a texture analyzer (TMS-Pro, FTC, Beijing, China). The conditions of texture analysis were as followed: TPA (1000 N), pause time 20 s, force induction 1000 N, probe retraction 30 mm, shape variable 50 s, detection speed 60 mm/min, minimum force 0.8 N. The samples were sliced into pieces of diameter 1.5 cm diameter and 1 cm thickness. All determinations were performed at 25 °C in triplicate.
2.8. Free Amino Acids
Amino acid contents were measured using ninhydrin reagent and separated by cation-exchange chromatography, using an L-8900 automatic amino acid analyzer (Hitachi High-Technologies Corporation, Tokyo, Japan) and a #2622PF column (60 × 4.6 mm) following the method of Jo et al. [
25]. The sample (1 g) was hydrolyzed with 10 mL of HCl (6 mol/L) at 110 ± 1 °C for 22 h, cooled to 25 °C, and then filtered. The solvent was removed at 50 °C by rotary evaporator (Zhengzhou Kaixiang instrument equipment Co., Ltd., Zhengzhou, Henan, China). The sodium citrate buffer solution was added to the dried sample, and the mixture was shaken evenly, filtered through 0.22 μm membrane and transferred to the injection bottle as sample determination solution. Samples were measured under the following conditions: AccQ-Tag Ultra C18 column, detection wavelength 260 nm, column temperature 49 °C, sample temperature 20 °C, and flow rate 0.7 mL/min.
2.9. Sensory Evaluation
The cooked sausages were evaluated in terms of appearance, texture, flavor, aroma, and overall acceptability. The sensory panel consisted of 30 staffs and graduate students from the Department of Food Science and Engineering at Jilin Agriculture University. Sausages were sliced into pieces of 9 mm thickness and identified with a three-digit random code. In addition, the sensory panel were provided with water and salt-free biscuits to clean their taste buds. Five samples presented at a time. The appearance, texture, flavor, aroma, and overall acceptability were evaluated using a 9-point Hedonic scale (1 = dislike very much, 9 = like very much).
2.10. Statistical Analysis
All determinations were designed three times and the values were showed as means ± standard deviations. An analysis of variance was performed on the results measured using SPSS software. The Duncan’s multiple range tests were used to determine the differences among mean values (p < 0.05).
4. Conclusions
This study showed that the substitution of pork fat with tremella in the sausage formulation could be a strategy with great promise to improve nutritional quality of the sausage. The fat content of sausage with tremella was decreased by 14.57% to 88.97%. The content of protein and ash of sausage were increased by 4.66% to 14.78% and 4.17% to 14.42%, respectively. Furthermore, the use of tremella improved the lightness, redness, water holding capacity, and textural profile analysis of the sausage. Moreover, some free amino acid increased, including lysine increased by 16.06% to 47.45%, isoleucine increased by 2.5% to 46.25%, proline increased by 4.17% to 42.86%, and tyrosine increased by 14.58% to 54.17%. From a sensory point of view, the best formulation for replacement proportion of tremella was 75%, which not only enhanced the aroma and flavor of the sausage, but also gave it a unique aroma. Based on these results, we are confident that tremella could be a promising ingredient for enhancing sausage flavor and overall quality.