An overview of classifications, properties of food polysaccharides and their links to applications in improving food textures
Introduction
The complexity of food systems arises from several aspects such as intricacy of components, interactions between the structurally different components, as well as their aggregation states (Aguilera, 2018; Mezzenga, Schurtenberger, Burbidge, & Michel, 2005). From the viewpoint of food textures, imparting food products with enhanced textural attributes requires a deep understanding on the components that can interact with each other and how these interactions occur (Dar & Light, 2014). It is understood by the fact that food textures are not only a key sensory feature well appreciated by consumers but also an important indicator for evaluating the quality of food products (Guimarães et al., 2020). In the past few decades, the study of food texture has received increasing attention and become an active area in food science. The major purpose for developing the study of food textures is to either improve the textural properties of food products or to design the foods with unique textures so as to meet the requirement of some special groups, e.g. the consumers who have difficulty consuming normal foods (Funami, Ishihara, Nakauma, Kohyama, & Nishinari, 2012; Nishinari, Turcanu, Nakauma, & Fang, 2019).
Due to non-toxicity, extensive accessibility and renewability, as well as health-promoting effects, polysaccharides have been increasingly used in the food industry as texture modifiers (Bernaerts, Gheysen, Foubert, Hendrickx, & Van Loey, 2019; Funami et al., 2012). In addition, some oligosaccharides have also been reported to exert an effect on food textures (Guimarães et al., 2020). However, the main functionality of oligosaccharides is to promote food nutrition as prebiotics ingredients and they do not belong to the category of polysaccharides. Hence, we will not discuss them in the present review. Although polysaccharides can be extracted and isolated from a variety of natural sources, only a portion of them can be called food polysaccharides. In a narrow sense, the term “food polysaccharides” is specially referred as the polysaccharides that are approved for usage as food additives. Food polysaccharides usually show remarkable rheological properties, such as thickening, stabilizing, gelling and emulsifying properties. Even if used at a very low concentration, many of them can have a significant impact on the textural properties of food products. In the past few decades, the texturizing roles of food polysaccharides have been well realized (Bernaerts et al., 2019; Guimarães et al., 2020). As an example, some polysaccharides have been successfully employed to improve the shelf-life of food products via influencing water crystallization, preventing creaming or settling, improving the freeze-thaw behavior and preventing syneresis or the retro-gradation of starch products. This means that food polysaccharides are promising materials for producing convenience foods, including dairy products, frozen products, confections, soft drinks, fruit juices, bread and pastry.
So far, a few review articles have summarized the applications of polysaccharides in the food industry, and highlighted their links to food texture optimization (He, Zhang, & Fang, 2019), including design of emulsion gels (Farjami & Madadlou, 2019), fabrication of functional biopolymer colloids (Wijaya, Patel, Setiowati, & Van der Meeren, 2017) and reformulation of meat products (Kaur & Sharma, 2019), etc., but we consider it necessary to give an overview by combining these approaches and focus on a critical discussion of the links between the properties of food polysaccharides and their applications in improving food textures.
As the basic skeletal components in numerous living species, polysaccharides may be the most abundant natural biopolymers on earth. A vast majority of food polysaccharides are plant-derived, including terrestrial plants and seaweeds (Bernaerts et al., 2019). In addition, some polysaccharides are of animal origins, typically chitin and chitosan. Other animal polysaccharides include glycogen, heparin, chondroitin sulfate, hyaluronic acid, keratin sulfate, acid mucopolysaccharide and glycosami noglycan, but they are rarely used in the food industry due to high cost and low accessibility.
Moreover, some micro-organisms have been found to secrete polysaccharides as secondary metabolites, usually called microbial polysaccharides (Phillips & Williams, 2009). Typical examples include xanthan, gellan, curdlan, pullulan, dextran and bacterial cellulose. Compared with plant- or animal-derived polysaccharides, microbial polysaccharides have a shorter production cycle, and the final products are more quality-controlled. Therefore, they have attracted increasing attention in the domains of food science and other fields.
Structurally, polysaccharides can be of linear or branched architecture, charged or neutral, depending on their origins, chemical structures and environmental factors. In some case, polysaccharides simultaneously contain hydrophobic and hydrophilic groups in the same molecule chains, which are empirically termed as amphiphilic polysaccharides (Phillips & Williams, 2009). In addition, because naturally occurring polysaccharides often contain numerous –OH (hydroxyl) and/or –COOH (carboxyl) groups in their molecular chains, allowing extra functional groups to be covalently introduced by chemical modification methods (e.g. sulfation, methylation, carboxymethylation, acetylation, selenylation and etherification) (Garcia-Valdez, Champagne, & Cunningham, 2018; Wang, Xie, Shen, Nie, & Xie, 2018; Xu et al., 2019). Despite the complexity, we still attempt to propose a diagram to classify various types of polysaccharides (see Fig. 1). It should be noted that, however, many polysaccharides may simultaneously possess several structural characteristics. A typical example is pectin: it is both plant-derived, negatively charged and of branched-architecture (Chan, Choo, Young, & Loh, 2017).
Section snippets
Hydration
Commercially accessible polysaccharides are mostly transported, sold and stored as dry powder form. Prior to any application, it is required to disperse the polysaccharide powder into water. By doing this, polysaccharide can immediately interact with water, causing agglomeration of the powder and subsequently its wetting, dispersion and dissolution (Einhorn-Stoll, 2018; Einhorn-Stoll, Benthin, Zimathies, Görke, & Drusch, 2015). For most polysaccharides, dissolution can be described as a
Links between the properties of polysaccharides to food textures
The term “food textures” has been defined by the International Standards Organization (ISO) as “All the rheological and structure (geometrical and surface) attributes of a food product perceptible by means of mechanical, tactile and appropriate visual and auditory receptors” (Dar & Light, 2014). In a broad sense, food textures define the eating experience and affect the preference of consumer to food products. In recent years, the science and technology of designing and optimizing food textures
Conclusions and outlook
Depending on the intrinsic structures and extrinsic environmental factors, polysaccharides often exhibit versatile rheological properties, which further affect their applications in food products. At present, the rheological properties of polysaccharides have been extensively reported, but a full understanding of the structure-property relationship is still in need. For example, although there is a general agreement that the emulsifying capacity of polysaccharides is predominantly determined by
Declaration of competing interest
The authors declare no conflict of interests in this work. Black-and-white for any figures in print is required.
Acknowledgements
The authors are grateful for the financial support by China Agriculture Research System (CARS-28).
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