GB2179043A - Foamed products - Google Patents

Abstract

Aqueous foams are provided comprising at least one acidic foamable protein, preferably whey protein isolate or bovine serum albumin, and a cationic polysaccharide, preferably chitosan or partially hydrolysed chitosan. Enhanced tolerance to the presence of lipid is demonstrated, particularly in the presence of a water-soluble sugar such as sucrose. The foams can be used to produce foamed culinary products such as meringues and cake mixes and they can be used for non culinary purposes such as aerated lubricants and fire extinguishing compositions.

Description

SPECIFICATION Foamed products The present invention relates to foamed products, preferably for use as foodstuffs.

Protein foams may be obtained by whipping an aqueous solution of a protein. The whipping process comprises agitating the solution in the presence of air so that a foam consisting of air cells surrounded by the solution is formed. The function of the protein in these foams is to form a cohesive film or skin around the air cells to prevent the foam collapsing when whipping is stopped. The solution may contain other constituents such as sugar. Such foams are used for a variety of culinary purposes, such as the making of meringues in which the protein foam containing sugar is baked to produce a mass of air cells enclosed by solid walls of protein and sugar. The protein solution is commonly obtained from white of egg but many other sources of protein may be used.

The foam-forming capacity of a protein solution, as measured by the increase in volume of the solution on whipping, and also the stability on standing of the foam depends in part on the identity of the protein used. For example a solution of egg albumen gives a reasonable degree of expansion on whipping and the foam formed may be stored for a considerable time before collapsing.

The expansion on whipping and stability of the foam are affected by other constituents dissolved or dispersed in the protein solution. For example the presence of sucrose may increase both expansion on whipping and foam stability but the presence of even small quantities of lipids such as vegetable oils and fats generally suppresses foam formation either partially or completely. It has therefore been difficult to provide a satisfactory protein foam containing oils or fats and when making a protein foam it has been essential to avoid contamination of the solution by lipids, including contamination by yolk of egg.

The proteins used in culinary applications are normally acidic proteins, that is they have isoelectric points less than 7. The acidic proteins include egg albumen, bovine serum albumin, bovine plasma, whey protein isolates and hydrolysed soya isolates, and are obtainable from a wide range of sources including milk, eggs, blood plasma, legumes, meat and microorganisms.

It is known from UK-A-21 34117 and from J. Sci. Food Agric. 1984, 35, 701-711 that protein - protein interactions are important in the foaming of heterogeneous protein systems. It has now been found that certain polysaccharides can also advantageously interact with the proteins of food products to yield improved foams.

Although edible polysaccharides, such as starches and dextrins, are known as whipping agent stabilizers in food products, their action in foams is dependent on their viscosity enhancing properties and not on physical interaction with proteins in the composition.

It has now been found that a polysaccharide having cationic properties is capable of interacting with the acidic proteins for example in food compositions to yield a relatively stable foamed product. Cationic polysaccharides occur naturally and one well-known edible example, which can be extracted from fungi, is chitosan.

Chitosan is a strongly cationic polysaccharide which can also be prepared by the alkali-catalysed deacetylation of chitin, a ubiquitous material found, for example, in crab shells, and prawn and insect cuticle. It is composed of repeating glucosamine subunits linked by fl-1 -4 glycosidic likages into a linear polymer analogus to cellulose. It has one primary amino group per subunit. Chitosan has a variable molecular weight distribution depending on the severity of the processing conditions, but typically lies in the range 100,000 to 1 million.

Chitosan is soluble in several aqueous organic acids, for example acetic or citric. Its main use in food processing is as a protein precipitant, for example as a wine fining or in the recovery of protein from effluent streams. This it does by combining with the negatively charged acidic proteins to form insoluble complexes at concentrations of from 1 Omg/1 to 200mg/1.

Chitosan is presently not used as a functional food ingredient, although its lipid-binding properties have been described in US-A-4223023.

We have found that, surprisingly and in contradiction to the known teaching about chitosan, chitosan is able to interact with proteins without precipitation to yield an enhanced foaming system, and furthermore that chitosan's tendency to cause protein precipitation can be suppressed by the addition of at least one sugar, particularly sucrose.

Cationic polysaccharides may also be prepared by the chemical modification of non-cationic polysaccharides; for example, positively-charged arginine residues may be attached to polygalacturonic acid using a carbodiimide as an activating agent.

Although most acidic proteins form a stable foam with cationic polysaccharides, there is one class of protein that appears not to be able to foam. These are those proteins such as sodium caseinate and gelatin which have a random elongate structure, rather than an ordered compact structure such as that of the so-called "globular" proteins. The term "foamable protein" is used herein to refer to the proteins that foam and to exclude the defined class of proteins which do not.

In accordance with the present invention there are further provided both edible and non-culinary products formed from an aqueous foam comprising at least one acidic protein and a cationic polysaccharide.

It will be appreciated that there are many different "chitosans" depending on the nature of the source of the basic chitin and on the processing conditions used. In particular, the deacetylated chitin can be subjected to various degrees of hydrolysis to lower the average molecular weight thereof. Improved foaming has been found with hydrolysis products having a degree of hydrolysis of up to about 10%; that is with about 10% of the glycosidic bonds broken.

Furthermore, chemical modification of the deacetylated chitin is possible to enhance or suppress certain physical and chemical properties of the molecule. For example, chitosan's charge density can be increased by chemical modification of some of its hydroxyl groups.

Such hydrolysed and modified molecules are to be considered in this description to be within the meaning of the term "chitosan" if their foaming behaviour emulates deacetylated chitin.

The preferred concentration of the particular polysaccharide used is dependent on its identity and on the particular protein used, but is generally from 0.075 to 0.5w/v%, but could be higher. Similarly the weight ratio of protein to polysaccharide in the foam is variable, but is generally from 20:1 to 3:1, preferably from 10:1 to 6:1, with a total protein concentration of less than 1 0w/v%, preferably about 6w/v%.

Enhanced foaming has been found to occur within a pH range of from 5.0 to 7.5, preferably from 5.3 to 6, with a sucrose concentration of at least 1 0w/v%, preferably from 20w/v% to 30w/v%.

Surprisingly, it has been found that the foam enhancing ability of the polysaccharide is not destroyed by the presence of a lipid, but that up to 30w/v% of, for example, corn oil can be tolerated, provided that the concentration of polysaccharide (and therefore of protein) and of sucrose is not too low. Too much lipid will, of course, result in over-stressing and consequent break-down of the foam system.

In addition to sucrose, other water-soluble sugars, including glucose syrup, have been found to enhance foaming and to improve foam stability.

A wide variety of food products can be thus obtained both directly from and by heating the foam of this invention.

The present invention will now be described by way of example with reference to the following experimental results: In the following Examples, solutions in water containing the dissolved constituents given in the Tables were whipped at ambient temperature for 5 minutes in a food mixer (I < enwood Chef Model A 901 ) operated at 200 revolutions per minute. The initial volume of the solution before whipping and the volume of the foam produced immediately after whipping were measured. The foam was then allowed to stand undisturbed for 30 minutes at ambient temperature and the volume of liquid which had drained from the foam was measured, and the foam volume re-measured.

The % foam expansion (FE), % foam volume stability (FVS), and % foam liquid stability (FLS) were calculated as follows: (Initial volume of foam including FE = liquid - Initial liquid volume) x 100 Initial liquid volume FVS = (Final foam volume) x 100 Initial foam volume including liquid (Initial liquid volume-volume of FLS = liquid drained) x 100 Initial liquid volume For the solutions tested in Comparative Examples A and B and in Examples 1 to 23, the general method of preparation was as follows: Chitosan (No.C3646, obtained from Sigma Chemical Co.) was dissolved at a level of 0.5% in 0.5% acetic acid.

The chitosan dissolved after about 1.5 hours. Protein solutions were prepared independently, and then mixed, except when 0.4% chitosan was required. Then the protein was dissolved directly in the chitosan solution. The pH value was adjusted using either 5M or 1 M sodium hydroxide and hydrochloric acid.

In each case 250 ml of solution were tested and where "oil" was added the oil used was corn oil, unless otherwise specified.

In general in the tabulated results of the Examples, the protein, polysaccharide and sucrose concentrations are expressed as percentages of the total volume of the solution tested on a weight per volume basis. For the oil, the concentrations given are on a percentage volume per volume basis and are the amounts of oil added to the solution to be tested. The Comments are the Inventor's subjective observations on the appearance of the solution immediately after mixing and on any foam produced thereby.

Comparative Examples A and B For comparative purposes, two test solutions were prepared using bovine serum albumin (BSA) and a whey protein isolate (WPI) without any chitosan being present. The results appear in Table 1, Example A being for BSA and example B being for WPI.

TABLE 1 Ex protein chitosan sucrose oil pH FE FVS FLS Comments A 1.0 0.0 0.0 10 6.0 50 0 0 Practically no foam B 1.0 0.0 10 0 6.0 180 65 5 poor Since BSA is on its own quite easily foamed, some oil was added in Comparative Example A to demonstrate more clearly the effect of chitosan. Oil addition was not necessary for WPI.

Examples 1 to 5 The importance of pH was examined using BSA as the protein source, and the results appear in Table 2 TABLE 2 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 1 1.0 0.1 0.0 10 4.0 30 0 0 practically no foam 2 1.0 0.1 0.0 10 5.0 130 35 10 flowy 3 1.0 0.1 0.0 10 6.0 380 85 30 stiff foam 4 1.0 0.1 0.0 10 6.5 200 70 10 flowy 5 1.0 0.1 0.0 10 7.0 100 40 10 poor Although some foam expansion was obtained both at pH 4.0 and at pH 7.0, it is clear that for optimum foaming there is a preferred pH, which in the case of BSA, in the absence of sucrose, is about 6.0.

Examples 6 to 8 The effect of varying amounts of sucrose on the foaming behaviour of chitosan/protein solutions is shown in Table 3.

TABLE 3 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 6 1.0 0.1 10 10 6.0 530 95 70 very stiff 7 1.0 0.1 20 10 6.0 700 100 80 very stiff 8 1.0 0.1 50 10 6.0 540 100 100 extremely stiff It will be noted that the general trend is for superior foams to be produced with increasing levels of sucrose.

However, with large amounts of sucrose the foam expansion tends to be reduced, presumably because of the increasing weight per unit volume of the foam. About 20% sucrose appears to yield optimum foaming behaviour.

Examples 9 to 12 The tolerance of the BSA/chitosan foaming system to the presence of lipid is demonstrated in Table 4 (also see Example 7).

TABLE 4 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 9 1.0 0.1 20 20 6.0 540 100 95 very stiff 10 1.0 0.1 20 30 6.0 340 90 50 fairly stiff 11 1.0 0.1 50 30 6.0 45 45 20 very poor 12 4.0 0.4 50 30 6.0 430 100 100 very thick stiff By using sucrose at what appears to be an optimum concentration, quite high concentrations of lipid can be tolerated.

Examples 13 to 16 Using BSA as the protein source, the optimum ratio is protein to chitosan was sought, and the results are shown in Table 5.

TABLE 5 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 13 1.0 0.05 20 10 6.0 130 65 20 poor 14 1.0 0.1 20 10 6.0 700 100 80 very stiff 15 1.0 0.2 20 10 6.0 660 100 90 very stiff 16 1.0 0.33 20 10 6.0 200 70 10 poor These results suggest that about a 10:1 protein/chitosan ratio is usually suitable.

Examples 17to 19 The WPI/chitosan system's tolerance of lipid was tested, but was found - for the particular samples tested - to be markedly less than for BSA as Table 6 shows.

TABLE 6 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 17 1.0 0.1 10 0 6.0 780 100 90 very stiff 18 1.0 0.1 10 1.0 6.0 480 85 40 stiff 19 4.0 0.4 10 10 6.0 40 0 0 very poor precipitated a lot An attempt to make the WPI/chitosan system tolerant of the presence of 10% corn oil by increasing the concentration of chitosan - and consequently of WPI in order to maintain the optimum protein/chitosan ratio lead to break-down of the foaming system due to precipitation of the protein out of solution by the chitosan. It is postulated that an increase in the sucrose concentration could assist foam stability despite the presence of corn oil at the 10% level.

Examples 20 and 21 The effect of altering the pH of the solution for WPI is markedly demonstrated in Table 7. (It should be noted that these results were obtained at sub-optimum chitosan/protein ratios).

TABLE 7 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 20 4.0 0.1 10 10 6.0 40 0 0 very poor precipitated a lot 21 4.0 0.1 10 10 5.3 220 80 20 moderate. Milky solution The optimum pH for WPI appears to be slightly lower than for BSA. These results suggest that for each type of protein used - and possibly each protein extraction method used - there is an optimum pH for foaming with chitosan.

Examples 22 and 23 Taken together with the results of Examples 20 and 21, the results set out in Table 8 show how the selection of pH is also important in the avoidance of precipitation, despite quite high levels of chitosan.

TABLE 8 Ex protein chitosan sucrose oil pH FE FVS FLS Comments 22 4.0 0.2 10 10 5.3 280 90 60 moderate. Milky solution 23 4.0 0.4 10 10 5.3 780 100 100 extremely stiff In the following Examples 24 to 107 two types of chitosan were used; a native chitosan (chitosan N) and a slightly hydrolysed derivative (chitosan SH), both supplied by Protan Laboratories, Inc. Redmond, Washington, U.S.A. A comparison of their properties is set out in Table 9. the sample of native chitosan was used for the preparation of samples of varying degrees of hydrolysis. Chitosan SH was used in most of Examples 24 to 107 in preferance to the chitosan N because its viscosity was low enough to facilitate mixing, and its solubility characteristics were better. It also showed a markedly decreased tendency to precipitate acidic proteins out of solution.The molecular weight could not be measured accurately because chitosan is heterodisperse; that is, it contains a wide range of molecular weights. However, the material can be defined accurately in terms of its viscosity (see Table 9) or degree of hydrolysis (percentage of glycosidic bonds cleaved).

TABLE 9 Property Native chitosan Slightly hydrolysed chitosan (chitosan N) (chitosan SH) Viscosity (1% in 1% acetic acid) 585 cps 25 cps %ash 1.0 0.61 %deacetylation 8.47 88.3 %moisture 12.0 13 In Examples 24 to 107 the following variable were studied: Examples a) Total concentration of protein + chitosan 24-27 b) Effect of homogenisation prior to aeration 28-29 c) Ratio of chitosan to protein 30-35 d) pH 36-45 e) Sugar concentration 46-55 f) Type of acidic protein 56 g) Salt (sodium chloride) concentration 57-64 h) Type of fat/oil 65-78 i) Temperature 79-82 j) Effects of sugars and related compounds 83-92 k) Effect of degree of hydrolysis of chitosan. 93-107 The results are tabulated in Tables 10 to 20/21, respectively.

Examples 24 to 27 The influence of total concentration of protein and chitosan SH was assessed using a whey protein isolate (WPI) A WPI/chitosan ratio of 10:1 by weight was maintained and the WPI concentration varied from 2-8% by weight to establish the optimum. Sucrose and corn oil concentrations were fixed at 10% by weight and the pH at 6.0. The results appear in Table 10.

TABLE 10 Ex. %Protein (WPI) %Chitosan SH FE% FVS% FLS% Comments 24 2.0 0.2 140 60 10 poor 25 4.0 0.4 500 95 75 moderately stiff 26 6.0 0.6 550 100 90 stiff 27 8.0 0.8 - - - formed dense aggregate which could not be whipped The results suggest that 6% by weight is the optimum protein concentration in the case of WPI.

With BSA and chitosan N (see Example 6) a comparable foam was obtained at a protein concentration of only 1% by weight. Therefore, although WPI is effective, it is not as good as BSA.

Examples 28 and 29 An experiment was carried out to establish whether emulsification of the oil with the protein solution prior to the addition of chitosan and adjustment of pH improved foaming properties. The solution used contained by weight whey protein isolate (6%), chitosan SH (0.6%) sucrose (10%) and corn oil (10%) at pH 6.0. In general the results were more consistent after emulsification and the solutions were less turbid. Foam expansion was increased (as shown in Table 11) and the foam texture was better. This method was therefore used for all subsequent whipping tests as the preferred method.

TABLE 11 Ex. Treatment FE% FVS% FLS% Comments 28 none 550 100 90 stiff 29 emulsified 590 100 90 stiff Examples 30 to 35 The protein concentration was fixed at 6% by weight and the concentration of chitosan SH varied. The results in Table 12 show that a ratio of 0.7 to 6 gave the best results. The mixture needed no pH adjustment which is advantageous for technical reasons. Foaming was poor at ratios below 1 to 10.

TABLE 12 Ex. %Chitosan SH FE% FVS% FLS% Comments 30 0.1 140 65 15 poor 31 0.2 100 60 20 poor 32 0.4 100 60 20 poor 33 0.6 550 100 90 fairly stiff 34 0.7 560 100 95 very stiff 35 0.8 560 100 95 very stiff This optimum ratio compares closely with the ratio found for a different system using chitosan N and BSA as described in Examples 13 to 16.

In the subsequent Examples the phrase "optimum system" is used to refer to a solution containing the following in weight percent: WPI 6%, chitosan SH 0.7%, sucrose 10%, and corn oil 10%.

Examples 36 to 45 The influence of pH was tested using the "optimum system". Controls without chitosan (labelled "-") were tested. The results in Table 13 show that pH 6 gave the best results. This is consistent with theory since the two species will only be oppositely charged and therefore able to interact above pH 5.3 (the isoelectric point of WPI). At pH 6.5, the interactions may be too strong, resulting in the formation of insoluble precipitates.

TABLE 13 Ex. pH Chitosan SH FE% FVS% FLS% Comments 36 4.5 + 75 50 10 poor 37 4.5 - 120 55 0 poor 38 5.0 + 100 60 20 poor 39 5.0 - 170 65 10 poor 40 5.5 + 280 100 95 fairly stiff 41 5.5 - 195 70 10 poor 42 6.0 + 560 100 95 very stiff 43 6.0 - 160 60 5 poor 44 6.5 + 90 60 25 poor 45 6.5 - 155 60 0 poor The effect of pH with more-extensively hydrolysed chitosan is considered in subsequent Examples. The results of Table 13 are similar to those obtained with chitosan N and WPI (see Examples 20 and 21) and BSA (see Examples 1-5).

Examples 46 to 55 The "optimum system" was used to assess the effect of different levels of sucrose. Table 14 shows that all foam parameters improved with sucrose concentration, and completely stable foams were obtained at 20% sucrose and above. Sucrose had no effect in the absence of chitosan. The level of sucrose used in subsequent Examples was 30% by weight.

TABLE 14 Ex. Sucrose Chitosan SH FE% FVS% FLS% Comments concentration (%w/v) 46 10 + 560 100 95 very stiff 47 10 - 160 60 5 poor 48 20 + 565 100 100 very stiff 49 20 - 130 55 0 poor 50 30 + 650 100 100 very stiff 51 30 - 115 55 0 poor 52 40 + 640 100 100 very stiff 53 40 - 125 55 0 poor 54 60 + 615 100 100 very stiff 55 60 - 110 55 0 poor Similar results were obtained with chitosan N and BSA as shown in Examples 6-8.

Example 56 Bovine serum albumin and whey protein isolate are typical examples of soluble globular acidic proteins which work effectively in combination with chitosan under suitable conditions. A hydrolysed wheat protein ("Hyfoama") also gave good results as shown in Table 15.

TABLE 15 Ex. FE% FVS% FLS% Comments 56 570 90 30 moderately stiff However, sodium caseinate and gelatin gave poor results. These are examples of protein molecules having a random elongate structure and they seem to be unable to interact in the controlled manner necessary.

Examples 57 to 64 The effect of sodium chloride concentration was tested with the "optimum system". Sodium chloride solution was added after mixing of other ingredients.

Table 16 shows that foaming is impaired only slightly by the salt concentrations likely to be found in foods.

The foam became softer in texture as the salt concentration was increased.

TABLE 16 Ex. Molarity of Chitosan SH FE% FVS% FLS% Comments sodium chloride 57 0 + 650 100 100 very stiff 58 0 - 115 55 0 poor 59 0.05 + 430 100 100 very stiff 60 0.05 - 120 55 0 poor 61 0.20 + 520 100 100 stiff 62 0.20 - 230 55 0 poor 63 0.40 + 540 100 100 fairly stiff 64 0.40 - 120 55 0 poor Examples 65 to 78 Many different types of fats are used in foods and a representative range was tested, using the "optimum system", except that 20% by weight fat was used unless indicated otherwise. As Table 17 shows good results were obtained with all fats apart from lecithin, which is known to be particularly detrimental to foaming.

TABLE 17 Ex. Type of fat/oil Chitosan FE% FVS% FLS% Comments 65 corn oil + 570 100 100 very stiff 66 corn oil - 130 55 0 poor 67 coconut oil + 870 100 100 stiff 68 coconut oil - 80 45 0 poor 69 butter oil + 910 100 75 fairly stiff 70 butter oil - 130 50 0 poor 71 cocoa butter + 630 100 100 fairly stiff 72 cocoa butter - 95 45 0 poor 73 lard + 300 85 35 poor 74 lard - 90 45 0 poor 75 lecithin (0.1%) + 170 70 20 poor 76 lecithin (0.1%) - 200 65 0 poor 77 lard (10%) + 970 90 100 very stiff 78 lard (10%) - 90 45 0 poor Examples 79 to 82 In food processing, mixes are often aerated at chill temperatures.The effect of foaming at these temperatures was assessed for the chitosan SH/WPI system. The results in Table 18 show that reducing the temperature had little effect on foaming of the "optimum system" with 20% by weight fat.

TABLE 18 Ex. Fat/temperature FE% FVS% FLS% Comments 79 Corn oil 7"C 570 100 100 stiff 80 Corn oil 25"C 570 100 100 very stiff 81 Coconut oil 7 C 830 100 100 very stiff 82 Coconut oil 25"C 870 100 100 stiff Examples 83 to 92 Various sugars and polysaccharides are used in foods to sweeten them or to affect their texture. A representative range of "sugars" was tested with the "optimum system" of chitosan SH and WPI, with 10% corn oil and with the "sugar" under test at 30% by weight (except where indicated). Table 19 shows that good foams were obtained with sucrose, sorbitol, glucose syrup (42 Dextrose Equivalent) and polydextrose, but that methyl cellulose prevented foaming.

TABLE 19 Ex. Saccharide Chitosan FE% FVS% FLS% Comments 83 Sucrose + 720 100 100 fairly stiff 84 Sucrose - 115 55 0 poor 85 Sorbitol + 900 100 100 stiff 86 Sorbitol - 100 50 0 poor 87 Glucose syrup (42 DE) + 770 100 100 stiff 88 Glucose syrup (42 DE) - 100 50 0 poor 89 Polydextrose + 930 100 100 very stiff 90 Polydextrose - 100 50 0 poor 91 Methyl cellulose (0.1%) + 270 60 0 poor 92 Methyl cellulose (0.1%) - 100 50 0 poor Examples 93 to 107 Chitosan N was hydrolysed to varying degree of hydrolysis ("DH") values by the addition of sodium nitrite. It is known that sodium nitrite deaminates chitosan and causes breakage of the glycosidic bond at the point of deamination.The number of glycosidic bonds broken is reported to be equivalent to the number of moles of sodium nitrite added. Chitosan samples were prepared having 5, 10, 15 and 20% of the glycosidic bonds cleaved, with correspondingly lower molecular weight distributions. The following composition was used to test the foam-enhancing properties of chitosan at various pH values: WPI = 6%; chitosan=0.7%; sucrose=30%; corn oil = 1 0%. Table 20 shows that chitosan with a DH of 5% showed a wider pH range of foaming compared to unhydrolysed chitosan or chitosan hydrolysed to a DH of 10%. Good foams were obtained at pH 7; 1 pH unit higher than unhydrolysed. Thus moderate hydrolysis improves the overall foam-enhancing properties. Hydrolysis beyond 10% yielded samples of poor foam enhancing power.

TABLE 20 a) Foam expansion (FE%) Degree ofhydrolysis pH Ex. of chitosan/% 4.5 5.0 5.5 6.0 6.5 7.0 7.5 93 0 80 100 280 550 90 - 80 94 5 - - 190 720 780 830 250 95 10 - - 230 470 700 520 230 96 15 - - - 350 - - - 97 20 - - - 480 - - - b) Foam liquid stability (FLS%) 98 0 10 20 95 95 25 - 40 99 5 - - 20 100 100 100 20 100 10 - - 20 90 100 90 20 101 15 - - - 65 - - 102 20 - - - 75 - - Table 21 shows that with BSA (2%), chitosan hydrolysed to DH values of 5 and 10% was still effective at the 0.2% level at pH 6.0. However DH 15% and DH 20% chitosan was not very effective. The composition used was chitosan N with BSA 2%, corn oil 10%, and sucrose 10% at a pH of 6.0.

TABLE 21 Ex. Degree of hydrolysis FE% FVS% FLS% Comments of chitosan/% 103 0 770 100 90 stiff 104 5 770 95 75 fairly stiff 105 10 550 95 50 runny 106 15 300 80 15 poor 107 20 175 10 70 poor The solutions described above may be foamed in order to produce foamed culinary products of kinds which are already known, such as meringues, cake mixes and batters. They may also be used in aerated food products which contain lipids, such as low calorie dietary foods, which have not hitherto been made by a foaming process. Foams made from the protein solutions may also be used for non-culinary purposes, for example as aerated lubicants and fire-extinguishing compositions.

Claims (24)

1. An aqueous foam comprising at least one acidic foamable (as defined) protein and a cationic polysaccharide.

2. A foam as claimed in claim 1 wherein the concentration of the polysaccharide in the foam is from 0.075 to 0.3w/v%.

3. A foam as claimed in claim 2 wherein the concentration of the polysaccharide in the foam is about 0.1 w/v%.

4. A foam as claimed in any one of the preceding claims wherein the weight ratio of protein to polysaccharide in the foam is from 20:1 to 3:1.

5. A foam as claimed in claim 4 wherein the weight ratio of protein to polysaccharide in the foam is from 10:1 to 6:1.

6. A foam as claimed in any one of the preceding claims wherein the protein concentration in the foam is less than 10w/v%.

7. A foam as claimed in claim 6 wherein the protein concentration in the foam is about 6w/v%.

8. A foam as claimed in any one of the preceding claims wherein the protein is edible.

9. A foam as claimed in claim 8 wherein the protein is a whey protein isolate.

10. A foam as claimed in any one of the preceding claims wherein the pH of the foam is from 5.0 to 7.5.

11. A foam as claimed in claim 10 wherein the pH of the foam is from 5.3 to 6.

12. A foam as claimed in any one of the preceding claims wherein the polysaccharide is partially hydrolysed.

13. A foam as claimed in claim 12 wherein the hydrolysed polysaccharide has a degree of hydrolysing of from 5% to 10%.

14. A foam as claimed in any one of the preceding claims in which the polysaccharide is edible.

15. A foam as claimed in claim 14 wherein the polysaccharide is chitosan.

16. A foam as claimed in any one of claims 1 to 14 wherein the polysaccharide is a cationic derivative of a non-cationic polysaccharide.

17. A foam as claimed in any one of the preceding claims further comprising a water soluble sugar in an amount of at least 10w/v%.

18. A foam as claimed in claim 17 comprising a soluble sugar in an amount of from 20 to 30w/v%.

19. A foam as claimed in claim 17 or claim 18 in which the sugar is sucrose.

20. A foam as claimed in any one of the preceding claims wherein up to 30w/v% of a lipid is additionally present.

21. A foam as claimed in claim 20 wherein the lipid is corn oil.

22. An edible product consisting of or comprising a foam as claimed in any one of the preceding claims.

23. An edible product obtained by heating a foam as claimed in any one of claims 1 to 21.

24. A non-culinary product consisting of or comprising a foam as claimed in any one of the preceding claims.