Food gels: gelling process and new applications

Food gels are viscoelastic substances and several gelled products are manufactured throughout the world. The gelling agents in foods are usually polysaccharides and proteins. In food gels, the polymer molecules are not cross-linked by covalent bonds with the exception of disulphide bonds in some protein gels. Instead, the molecules are held together by a combination of weak inter-molecular forces like hydrogen bonds, electrostatic forces, Van der Waals forces, and hydrophobic interactions. Polysaccharides including hydrocolloids are strongly hydrated in aqueous medium but they tend to have less ordered structures. The mechanism of gelation depends on the nature of the gelling agent(s) and on the conditions of gel formation like the temperature, the presence of ions, the pH, and the concentration of gelling agents, etc. Characterization of gels can be performed in several ways of which rheological measurements are frequently practiced. Multi-component or mixed gel system is an important area of interest in which two or more gelling components are simultaneously used to achieve certain specific structural and functional characteristics. We here discuss about the different gels and gelling agents, the characterization of gels, and the mechanism of gelation with an emphasis on mixed or multi-component gels that would have significant commercial applications.     

Gelling agents

The characteristic physical properties of food gels result from the ability of certain proteins and polysaccharides to form continuous three-dimensional molecular networks. Development of new products based on gels, and improvements to existing ones, require a basic understanding of the intermolecular forces by which network cross-linkages are formed and stabilized. In this review new methods for studying food gels are described. The mechanisms by which molecular networks are formed by the gelling agents most frequently used by the food industry are discussed, with emphasis on the role of the solvent (water) and added solutes such as salts and sugars. More complex mixed gelling systems are discussed in some detail because of their practical importance and recent significant developments in this area.     

The key role alginates play in health

The role of alginates, widely utilised gelling agents in pharmaceutical and food applications, in human health has broadened recently with the recognition that they have a number of potentially beneficial physiological effects in the gastrointestinal tract. These include an effect on intestinal absorption and colonic health. Importantly, alginates have also been shown to moderate human appetite and energy intake. It has been proposed that, following ingestion, ionic gelation of alginate in stomach acid can modulate feeding behaviour through slowed gastric clearance, stimulation of gastric stretch receptors and attenuated nutrient uptake. It should be recognised however that these alginate formulations utilise gastric acid as the ‘trigger mechanism’ for gelation which can be unreliable because a number of factors may reduce gastric acidity. To address this concern, we have developed an alginate:calcium carbonate powder mix that when reconstituted with water and ingested, does not rely on stomach acid to ‘trigger’ ionic gelation. The formulation development process and a series of randomised, controlled trials to assess whether the novel alginate beverage could modulate feeding behaviour are discussed. The findings suggest a role for appropriately designed alginate formulations in the management of overweight and obesity.     

Tamarind seed: properties, processing and utilization

Tamarind seed is an underutilized byproduct of the tamarind pulp industry. Only a small portion of the seed, in the form of tamarind kernel powder (TKP), is used as a sizing material in the textile, paper, and jute industries. Though many applications of this seed are possible, there have been hardly any other uses for it including using it as an additive in food formulations. The excellent gelling cum adhesive characteristics of the decorticated seed powder can lead to several applications in food and pharmaceutical industries which are evident by the number of research papers as well as patent applications. This article thus focuses on the possibilities of using the seed in several food and non-food industries with particular reference to physical and engineering properties, hydration behavior, rheological properties, functional and nutritional characteristics, and the processing of the tamarind seed for wider applications.     

“Green labelled” pectins with gelling and emulsifying properties can be extracted by enzymatic way from unexploited sources

Functional properties of “green labelled” pectins extracted with enzymes from chicory root, citrus peel and cauliflower by-products were assessed. Chicory and citrus pectins were selected to study their gelling properties, while cauliflower pectin was chosen to investigate its emulsifying ability. High methoxy chicory and citrus pectins were shown to gel in the presence of sucrose at acidic pH, whereas their corresponding low methoxy pectins were able to gel in the presence of calcium. Additionally, HM cauliflower pectin exhibited emulsifying ability. Atomic Force Microscopy was used to better understand the gelling mechanism of pectins and particularly the first steps of gel setting. The present work demonstrates that “green labelled” enzyme-extracted pectins can be successfully used as gelling or emulsifying agents. The present study allows enhancing the value of “green” extraction of pectins, since such extraction leads to products with good functional properties that can directly be used for food and non-food purposes.     

Aspects of milk-protein-stabilised emulsions

Milk proteins are widely used as ingredients in prepared foods, in which they perform a wide range of key functions, including emulsification, thickening, gelling and foaming. An important functionality of milk proteins in food colloids is their ability to facilitate the formation and stabilisation of oil droplets in emulsions. The ability of milk proteins to adsorb at the oil–water interface and to stabilise emulsions has been exploited by the food industry in the manufacture of nutritional products, specialised medical foods, dietary formulations, cream liqueurs and dairy desserts. This article provides an overview of the properties and functionalities of food emulsions formed with milk proteins, focusing on the structure and composition of adsorbed protein layers, competition between proteins and the physical and chemical stability of emulsion droplets. Of particular importance is the understanding of the behaviour of milk-protein-based emulsions under the conditions relevant to digestion in the human gastrointestinal tract. Recent relevant research in this area is reviewed and discussed.     

Innovative Uses of Milk Protein Concentrates in Product Development

Milk protein concentrates (MPCs) are complete dairy proteins (containing both caseins and whey proteins) that are available in protein concentrations ranging from 42% to 85%. As the protein content of MPCs increases, the lactose levels decrease. MPCs are produced by ultrafiltration or by blending different dairy ingredients. Although ultrafiltration is the preferred method for producing MPCs, they also can be produced by precipitating the proteins out of milk or by dry‐blending the milk proteins with other milk components. MPCs are used for their nutritional and functional properties. For example, MPC is high in protein content and averages approximately 365 kcal/100 g. Higher‐protein MPCs provide protein enhancement and a clean dairy flavor without adding significant amounts of lactose to food and beverage formulations. MPCs also contribute valuable minerals, such as calcium, magnesium, and phosphorus, to formulations, which may reduce the need for additional sources of these minerals. MPCs are multifunctional ingredients and provide benefits, such as water binding, gelling, foaming, emulsification, and heat stability. This article will review the development of MPCs and milk protein isolates including their composition, production, development, functional benefits, and ongoing research. The nutritional and functional attributes of MPCs are discussed in some detail in relation to their application as ingredients in major food categories.     

Gel extracted from Khruea‐ma‐noi (Cyclea barbata Miers) leaves: chemical composition and gelation properties

Gel extracted from Khruea‐ma‐noi leaves, which are widely consumed by villagers in Northeast Thailand, has a unique characteristic that could be used for food and nutritional applications, such as in therapeutic diets and in the food industry. Since little is known scientifically about this plant, this study identified the plant's scientific name and determined the chemical composition of the Khruea‐ma‐noi polymer and its gelling mechanism. Results reveal that Khruea‐ma‐noi is classified as Cyclea barbata Miers. Its main polymer is polygalacturonic acid of average molecular weight 741 kDa with 66.3% methylated. Dried powders of extract and purified gels contained 415 and 724 g kg^?1 of soluble dietary fiber and 7.1 and 13.9 g kg^?1 of divalent cations, respectively. Factors affecting gelling ability and characteristics include phenolic compounds, oxidizing and reducing agents, pH, divalent cations and temperature. Most gels formed were thermoreversible except at pH 7. Copyright © 2005 Society of Chemical Industry     

A clouding agent based on modified soy protein

Several food proteins, together with some naturally occurring water-soluble gums (viscosity builders) and lecithin, are evaluated as clouding agents for formulated orange drinks. The use of these three types of natural products represents a significant advantage over the present formulations in which synthetic emulsifiers and weighting agents are used.
The effects of concentration of each of the above ingredients, pH, temperature and mode of preparation are explored and related to cloud stability, droplet size distribution and the opacity of the emulsion both in concentrated and diluted formulations. A mechanism for protein adsorption onto the droplets is suggested.     

Structural and physical properties of dietary fibres,and consequences of processing on human physiology

Dietary fibre encompasses very diverse macromolecules exhibiting a large variety of physico-chemical properties. They might be naturally present in the food (in cell walls of vegetables and fruits, for instance) or introduced in the food to improve their nutritional properties (e.g. bran in bread products) or their physical characteristics (e.g. gelling agents or improved resistance to storage). The properties that are nutritionally relevant are mainly the particle size and bulk volume, the surface area characteristics, the hydration and rheological properties, and the adsorption or entrapment of minerals and organic molecules. Amongst these properties, the viscosity and ion exchange capacity are the main contributors to metabolic effects (glucose and lipid metabolisms) whereas fermentation pattern, bulking effect and particle size are strongly involved in effects on colonic function. Technological treatments can modify the physico-chemical properties of the fibre. This can be further exploited to optimise both their techno-functional and physiological properties.     

植物蜡及液态植物油构建油凝胶的物性研究

以米糠蜡、棕榈蜡、蜂蜡3种食品级植物蜡为凝胶剂,葵花籽油、油茶籽油、亚麻籽油、棉籽油为基料油,构建了植物油基油凝胶,系统分析了油凝胶的外观形态、持油能力、微观结构、硬度、晶型及熔化结晶行为。结果发现,棕榈蜡基油凝胶涂抹性能优良,蜂蜡基油凝胶在三者中具有最高的持油能力。微观分析表明,米糠蜡形成的油凝胶晶体结构较为清晰,呈细长的针状;蜂蜡形成的油凝胶晶体结构最为细小,呈细小的针状;棕榈蜡形成的油凝胶,针型细密,并呈絮状结晶。晶体密度及样品硬度均随凝胶剂质量分数增加而增加。油凝胶的晶型与凝胶剂质量分数、基料油的种类无太大关系,主要取决于凝胶剂的种类。熔化结晶行为表明,凝胶剂种类相同时,随着其质量分数的增加,油凝胶的结晶/熔化峰值温度均升高。     

Applications of soy protein hydrolysates in the emerging functional foods: a review

Several applications of protein hydrolysates have been documented including gelation, solubility and emulsifying properties. However, very rare reviews have solely explored the potentials of soy protein hydrolysates (SPHs). Varying and abundant pieces of information on the physicochemical properties of soy proteins, such as foaming, solubility, emulsifying, gelling, fat- and water-holding capacities, suggest their hydrolysates to be equally or more important. In this regard, this review highlights the different methods that have been used to prepare SPHs, coupled with the most promising applications and potentials of SPHs. Nonetheless, further investigations are necessary to validate the potentialities of SPHs as food agents for the emerging functional foods.     

Development of formulations for reduced‐sugar and sugar‐free agar‐based fruit jellies

Because of the increasing consumer awareness of health‐related issues, there is a rising demand for noncariogenic, reduced‐energy confectionery products. This study was carried out to develop formulations for reduced‐sugar and sugar‐free, agar‐based jelly products. This was obtained by substituting sucrose and glucose syrup through a combination of sugar replacers, fibre, gelling agents and sweeteners. The application of a combination of polydextrose, oligofructose, sucralose and erythritol resulted in a sensory sweetness profile that was comparable to that of a sugar‐containing standard product. Concerning texture and sensory properties, reduced‐sugar and sugar‐free jellies processed using the respective formulations were comparable to the sugar‐containing standard products. Consumer evaluation using the Just‐about‐right technique exhibited satisfactory acceptance of the sugar‐free jellies.     

果胶的分类、功能及其在食品工业中应用的研究进展

果胶是一类结构复杂的天然多糖,是高等植物细胞壁的重要组成部分.根据其单糖组成及分子结构的差异,可分为同型半乳糖醛酸聚糖、I型鼠李半乳糖醛酸聚糖、II型鼠李半乳糖醛酸聚糖、木糖半乳糖醛酸聚糖等类型.果胶结构复杂,生物活性多样,如免疫调节作用、抗肿瘤、抗氧化、降血糖、改善胃肠道功能等.一些特定来源的果胶可作为天然的多功能型...     

Application of high‐pressure homogenization on gums

High‐pressure homogenization (HPH) is an emerging process during which a fluid product is pumped by pressure intensifiers, forcing it to flow through a narrow gap, usually measured in the order of micrometers. Gums are polysaccharides from vegetal, animal or microbial origin and are widely employed in food and chemical industries as thickeners, stabilizers, gelling agents and emulsifiers. The choice of a specific gum depends on its application and purpose because each form of gum has particular values with respect to viscosity, intrinsic viscosity, stability, and emulsifying and gelling properties, with these parameters being determined by its structure. HPH is able to alter those properties positively by inducing changes in the original polymer, allowing for new applications and improvements with respect to the technical properties of gums. This review highlights the most important advances when this process is applied to change polysaccharides from distinct sources and molecular structures, as well as the future challenges that remain. © 2017 Society of Chemical Industry     

多糖的增稠、胶凝及乳化特性研究进展

多糖是可再生的天然大分子物质,具有显著的增稠、胶凝、乳化等特性,在食品工业中常作为添加剂应用。然而,多糖种类繁杂、结构差异大、流变特性多样,长期以来国内有关多糖流变学特性的报道相对有限。本文从多糖水溶性高分子的本质特征出发,综述了食品多糖增稠、胶凝、乳化特性及其凝胶化影响因素的基本原理,同时介绍了非凝胶多糖和表面活性多糖分子聚集的原理,旨在为多糖在食品工业中的进一步应用提供理论指导。     

结冷胶凝胶特性及在食品工业中的应用

目的:介绍新型微生物多糖--结冷胶的凝胶特性及其在食品工业中的应用现状和前景.方法:查阅今年来国内外的相关文献报道,并进行分析、整理和归纳.结果:结冷胶组织相容性和复配性能良好,具有良好的透明性,凝胶性能卓越,具有独特的胶凝和融化温度,可形成多种凝胶质构,在极低的用量下形成的预(弱)凝胶可以发挥良好的悬浮、稳定作用.结论:结冷胶作为一种新型凝胶剂,其优异的性能将在食品工业中得到广泛应用.     

Vanillin biotechnology: the perspectives and future

The biotechnological production of fragrances is a recent trend that has expanded rapidly in the last two decades. Vanillin is the second most popular flavoring agent after saffron and is extensively used in various applications, e.g., as a food additive in food and beverages and as a masking agent in various pharmaceutical formulations. It is also considered a valuable product for other applications, such as metal plating and the production of other flavoring agents, herbicides, ripening agents, antifoaming agents, and personal and home-use products (such as in deodorants, air fresheners, and floor-polishing agents). In general, three types of vanillin, namely natural, biotechnological, and chemical/synthetic, are available on the market. However, only natural and nature-identical (biotechnologically produced from ferulic acid only) vanillins are considered as food-grade additives by most food-safety control authorities worldwide. In the present review, we summarize recent trends in fermentation technology for vanillin production and discuss the importance of the choice of raw materials for the economically viable production of vanillin. We also describe the key enzymes used in the biotechnological production of vanillin as well as their underlying genes. Research to advance our understanding of the molecular regulation of different pathways involved in vanillin production from ferulic acid is still ongoing. The enhanced knowledge is expected to offer new opportunities for the application of metabolic engineering to optimize the production of nature-identical vanillin. © 2018 Society of Chemical Industry     

葛粉保健果冻生产工艺研究

以葛粉为主要原料,卡拉胶、魔芋胶、黄原胶为胶凝剂,研究葛粉保健果冻的生产工艺。采用单纯形格子混料设计,确定复合胶凝剂的最佳配比,采用单因素及正交试验,确定葛粉保健果冻的最佳配方。结果表明：复合胶凝剂的最佳比例为魔芋胶50.1%、卡拉胶23.7%、黄原胶26.2%;以葛粉:水=1:15 调制葛粉液,添加复合胶0.5g/100mL、蔗糖7.0g/100mL、柠檬酸0.3g/100mL,所制果冻产品凝胶强度大,质地均匀,口感适宜。     

Carrageenans and their use in meat products

Carrageenans are sulfated linear polysaccharides of D‐galactose and 3,6‐anhydro‐D‐galactose extracted from red seaweeds. They have been used by the food industry for their gelling, thickening, and stabilizing properties, and more recently by the meat industry for reduced fat products. Meat is a complex system of muscle tissue, connective tissue, fat, and water; during processing, numerous interactions occur among all these components. These interactions are responsible for the functional properties of the meat system. In meat products, carrageenans contribute to gel formation and water retention. Their addition is of special interest in low‐fat meat products because fat reduction often leads to unacceptable, tough textures. When carrageenans are incorporated in these formulations, they improve the textural characteristics of the product by decreasing toughness and increasing juiciness. Although carrageenan interactions with milk proteins have been studied extensively, the mechanism by which carrageenans interact with meat proteins and the other meat components is not fully understood.