Gelatin alternatives for the food industry

Transcription

1 Progr Colloid Polym Sci (1999) 114 : 127±131 Ó Springer-Verlag 1999 N.A. Morrison G. Sworn R.C. Clark Y.L. Chen T. Talashek Gelatin alternatives for the food industry N.A. Morrison (&) á R.C. Clark Y.L. Chen á T. Talashek Monsanto Company 8355 Aero Drive San Diego, CA , USA G. Sworn Monsanto Plc, Water eld, Tadworth Surrey KT20 5HQ, UK Abstract The issue of gelatin replacement has been around for many years for the vegetarian, halal and kosher markets, but has recently gained increased interest especially within Europe with the emergence of the bovine spongiform encephalopathy virus. The total gelatin market in western Europe alone is 60,000 tonnes per annum, of which 80% is in foods. The textural and rheological properties of gelatin when utilised in various food applications is discussed. Various gelatin alternatives are proposed, and the mechanism to alter the functional properties of mixed or single polysaccharide systems is discussed. One possible gelatin alternative for the food industry is gellan gum. Recent studies have shown that both the levels of glycerate and acetate substituents in gellan gum can be controlled independently. A range of gellan gums with varying structural and functional properties are studied. Changes in the glycerate parameters have a profound e ect on the structural and rheological characteristics of gellan gum gels. These new gellan gum products have unique properties and will lead to a range of functionality in food systems with one versatile hydrocolloid ingredient. Key words Gellan á Gelatin Introduction Gelatin is a product obtained by partial hydrolysis of collagen derived from the skin, white connective tissue and bones of animals. Industrial preparation of gelatin can occur by one of two routes: an acid pretreatment, which produces type A gelatin, and an alkali pretreatment, which produces type B gelatin [1]. Gelatin is a high-molecular-weight polymer, which derives most of its functionality from the collagen triple helix that is the basis of the polypeptide gel network. The molecule has a well-de ned order±disorder conformation transition, that results in low hot viscosities, and the unique reversible set-melt characteristics of the gel. Also the exibility of this network gives the elastic properties associated with gelatin gels. The issue of gelatin alternatives has been around for many years, but has recently gained increased interest especially within Europe with the emergence of the bovine spongiform encephalopathy virus that has infected cattle. This resulted in the bannins of gelatin and beef sales from the United Kingdom to other European Union countries, from 1996 until recently, and has heightened consumer knowledge of the source of gelatin, forcing certain producers to incorporate gelatin alternatives when formulating existing or new processed foods. Additionally the low melt-set characteristics of gelatinbased gels can also be a disadvantage when the formulated product is not refrigerated, especially in hotter climates. The polysaccharide-based gelatin alternatives generally have less exible molecular backbones, leading to higher hot viscosities than gelatin. Many gelatin alternatives proposed for the food industry are polysaccharides, which gel based on cationinduced junction zones, and which do not have the well-

2 128 de ned melt-set characteristics of gelatin, such as many gellan, alginate or carrageenan based gels. There are notable exceptions, such as xanthan/locust bean gum gels, which are thermoreversible, but which have relatively high hot viscosities, even compared to polysaccharide gelling systems [2]. The approach to developing gelatin alternatives for the food industry should be application/process speci c. It is unlikely that a universal ingredient, or a system of polysaccharide gums, will replace gelatin in every food application. Examples of proposed gelatin alternatives are shown in Table 1. One possible gelatin alternative for the food industry is gellan gum. Gellan gum is the extracellular polysaccharide produced by the organism Sphingomonas elodea during aerobic fermentation [3]. The biopolymer is produced with two acyl substituents present on the 3-linked glucose, namely, L-glyceryl, positioned at O(2), and an acetyl substituent at O(6). Gellan gum is currently commercially available in both the high-acyl (HA) and the low-acyl form (LA). When hot solutions of gellan gum are cooled in the presence of gelpromoting cations, gels ranging in texture from brittle to elastic are formed, through principally cation-mediated helix±helix aggregation [4]. A wide range of gel textures can be produced through manipulation of blends of HA and LA gellan gum. It has been shown that the textural properties of gellan gum are dependent on its acyl content [5, 6]. Partially deacylated products studied include low acetate (cold KOH treatment) and intermediate acyl products (hot KOH treatment). In these studies acetyl substituents were removed in preference to glyceryl residues. New studies have shown the ability to form acetate-rich gellan gum by chemical treatment. These new products may also be achieved through new strain development [7]. A comparison is made between these new intermediate acyl products and simple blends of HA and LA gellan gum products. Materials and methods A range of gellan gum products have been produced by base treatment of HA gellan gum. Samples were prepared from either native broth or reconstituted HA gellan gum [8]. The analysis of gellan gum for acyl substituent levels has previously been described [9]. Samples were cast for texture pro le analysis in cylindrical moulds of 14-mm height and 29-mm internal diameter. Gels were removed from the moulds after overnight storage at 5 C, and were compressed at 0.85 mm s )1 to either 30 or 15% of their original height (70±85%) strain, depending on the soluble solids loading. The modulus, a measure of the gel's initial rmness, and the brittleness, a measure of the strain at rupture, were recorded. The setting and melting behaviour of the samples were measured using a CarriMed controlled stress rheometer. Tests were performed using a 6-cm parallel plate, 0.5±1-mm gap, and a cooling/heating rate of 2 C/min. The strain was controlled at 1%, and the frequency at 10 rad s )1. Results and discussion It has been demonstrated that control of the acyl content by alkali treatment during the gum recovery process can lead to a diversity of textures [5]. To date, however, this control has not been realised on a commercial scale, and gellan gum remains available in two forms, namely LA and HA. A wide range of gel textures can be produced through manipulation of blends of HA and LA gellan gum as shown in Fig. 1. However, it has been demonstrated using di erential scanning calorimetry and rheological measurements that mixtures of the HA and LA forms exhibit two separate Table 1 Functional properties of gelatin in selected food applications with possible alternatives Food application Desired gelatin properties Current alternatives Technical constraints of alternative Desert gels RTE High-solids confectionery Foamed confectionery ± marshmallows Low-fat spreads Stirred yogurt Desserts ± Mousses Sour cream Clarity, elastic texture, melt in mouth Elastic texture, clarity, low hot viscosity, low set temperature Whipping/aeration agent, foam stabiliser, elastic texture Elastic gel texture, fatlike melt mouthfeel, emulsion stabilisation Creamy mouthfeel, gelled network prevents separation or syneresis Whipping agent, creamy consistency, low set temperature Smooth texture, creamy mouthfeel Algin, gellan and carrageenan systems Gellan gum blends, carrageenan systems, thinned-starch systems Gellan/starch/emulsi er blends, modi ed starch/emulsi ers Sodium alginate/gellan/inulin/ simplesse/maltodextrin/ gum blends Gellan/modi ed starch/ xanthan/lbg/pectin/modi ed starch Alginate/starch blends Gellan gum with modi ed starch Hot viscosity, higher set temperature Set temperature and hot viscosity, texture-elasticity gels Textural constraints ± low elasticity and/or high set temperature Cost competitive, but good application for alternatives High viscosity and high set temperature in culture/production process Current production process, stored prior to aeration chilling High set temperature during processing

3 129 Fig. 1 Modulus (j) and brittleness (n) of mixed high acyl (HA) and low acyl (LA) gellan gum water jellies (1% total gum in 2 mm calcium) conformational transitions at temperatures coincident with the individual components [6, 10]. No evidence for the formation of double helices involving both HA and LA molecules was found. The setting temperatures of a deacylated gellan gum product and a HA product, and also a blend of the two components, which shows two distinct setting temperatures, are shown in Fig. 2. This means that the problems associated with the high gelation temperature (about 70 C) of the HA gellan gum are still present in blended systems. The high gelation temperature of HA gellan gum can be advantageous in some applications, such as fruit llings, where it can prevent otation of the fruit. In other applications, such as ready-to-eat jellies and high-solids systems, it can be a problem with regard to pregelation prior to depositing. Previous studies on the partial deacylation of HA gellan gum broth had reported that treatment with various levels of KOH (cold) had preferentially removed acetate residues, which led to nonbrittle textures, whereas treatment with variable levels of KOH (hot) removed both acetate and glycerate residues at a similar rate [5]. Morris et al. [6] have also reported that it is the glycerate residues that principally stabilise helical formation, leading to high setting temperatures of the HA product, and further helix±helix aggregation is hindered by acetyl substituents which lie on the periphery of the helix, resulting in soft elastic gels. New studies have shown that if the HA broth is treated with various levels of di erent bases, glycerate residues are removed preferentially to acetate residues [8]. Varying the type of base alters the rate of deacylation of glycerate versus acetate residues. This is clearly seen in Fig. 3, which shows that glycerate residues are liberated at a faster rate than acetate. By varying the level of this base, it is now possible to produce a wide range of rheological and textural properties of the intermediate acyl products. Unlike in the previous studies, it is now possible to produce elastic gel textures which have considerably lowered set and remelt properties. Again, if deacylation is continued, the distinct thermoreversible behaviour of the intermediate acyl products diminishes. This is shown for a range of partially deacylated gellan products for set-melt behaviour in Fig. 4. Residual glycerate and acetate substituents per repeat unit are denoted by f g and f a, respectively. The wide range of textures that can be achieved for these four products is also shown in Fig. 5. The lowering of the setting temperature of samples b and c, compared to the control sample, is apparent, whilst desirable properties such as elasticity and brittleness are maintained. These new gellan gum products have unique properties, and will lead to a range of functionality in food systems with one versatile hydrocolloid ingredient. Actual examples are shown in Fig. 6 for intermediate acyl products in two common food applications of Fig. 2 Cooling pro les of deacylated gellan gum (r), HA gellan gum (h) and a 1:1 blend of each (n). 0.5% total gum in 90 mm sodium (cooled at 2 C/min, 1% strain, 10 rad s )1 ) Fig. 3 E ect of base treatment on the liberation of acetate (n) and glycerate (h) from HA gellan gum

4 130 Fig. 4 Cooling (h) and heating (j) pro les of gellan gum samples (0.5% w/w in 2 mm calcium) with acyl content of a f g = 0.58, f a = 0.41, b f g = 0.32, f a = 0.35, c f g = 0.23, f a = 0.33 and d f g = 0.07, f a = 0.23 formulations and for stability in hot climates. In the high-solids example, the partially deacylated product is much closer to the gelatin texture than simple blends of HA and LA gellan gum components in terms of properties such as brittleness, elasticity and cohesiveness. Again if a rmer, harder gel is required for particular geographical preferences, a higher ratio of the LA component may be added to the formulation. Conclusions Fig. 5 Texture of gellan gum gels prepared from the samples in Fig. 4 (0.5% w/w in 2 mm calcium) gelatin, i.e., water jellies and high-solids systems. It can be seen in the water-based dessert gel formulation (15% solids) that a partially deacylated form of HA gellan can closely match the gelatin texture. This product will also be distinct from gelatin, in that it will have a higher meltset temperature, which is advantageous for rapid-set The examples provided illustrate the wide range of textures, from hard and brittle to soft and elastic, that can be achieved in many food applications with one versatile gelling agent. These textural properties are also strengthened by other parameters such as excellent clarity and avour release from gellan gum gels. It is hoped to commercialise these proprietary products in the near future by tailoring the gellan molecular structure to the speci c needs of various food application segments. Fig. 6 Comparison of the texture of partially deacylated gellan gum samples with commercial gelatin formulations in a water-based dessert gels (15% solids) and b a high-solids system (72% soluble solids)

5 131 References 1. Poppe J (1997) In: Imeson AP (ed) Thickening and gelling agents for food, 2nd edn. Blackie, London, p Williams PA, Phillips GO (1995) In: Stephen AM (ed) Food polysaccharides and their applications. Dekker, New York, p Kang KS, Veeder GT (1982) US Patent 4,326, Gibson W, Sanderson GR (1997) In: Imeson AP (ed) Thickening and gelling agents for food, 2nd edn. Blackie, London, p Baird JK, Talashek TA, Chang H (1992) In: Philips GO, Williams PA, Wedlock DJ (eds) Gums and stabilisers for the food industry 6. IRL, Oxford, p Morris ER, Gothard MGE, Hember MWN, Manning CE, Robinson G (1996) Carbohydr Polym 30: Jay AJ, Colquhoun IJ, Ridout MJ, Brownsey GJ, Morris VJ, Fialho AM, Leitao JH, SA-Correia I (1998) Carbohydr Polym 35: Sworn G, Chen Y-L, Talashek T, Morrison NA, Clark RC (1998) Eur Pat Appl G 9. Cheetham NWH, Punrickvong A (1985) Carbohydr Polym 5: Kasapis S, Giannouli P, Hember MWN, Evageliou V, Poulard C, Tort- Bourgeois B, Sworn G (1999) Carbohydr Polym (1999) 38: 145