Effect of Different Factors on Biosynthesis of Exopolysaccharide from Antarctic Yeast

Production, characterization and antioxidant activity of exopolysaccharide from Sporidiobolus pararoseus PFY-Z1

At present, the study on exopolysaccharid is mainly focused on lactic acid bacteria, and the research on exopolysaccharide produced by yeast, especially Sporidiobolus pararoseus, is relatively few. Therefore, the aim of this study was to explore the characterization and antioxidant activities of a novel neutral exopolysaccharide SPZ, which was isolated and purified from S. pararoseus PFY-Z1. The results showed that SPZ was mainly composed of mannose, followed by glucose, with a molecular weight was 24.98 kDa, had O-glycosidic bonds, no crystalline, and no triple helix structure. Based on fourier transform-infrared, high-performance liquid chromatography and nuclear magnetic resonance analyses, SPZ was identified to be a exopolysaccharide with some side chains, presence of α-, β-pyranose ring and nine sugar residues. Furthermore, the morphology features of SPZ have performed a relatively rough and uneven surface, covered with small pores and fissures. Moreover, SPZ had higher antioxidant activities and the maximum scavenging abilities of ⋅OH, NO₂^- and reducing power were 28.05 ± 0.73%, 92.76 ± 1.86% and 0.345 ± 0.024, respectively. Hence, SPZ could be used as a potential antioxidant application in the food and pharmaceutical industries.

Yeast exopolysaccharides and their physiological functions

Mounting evidence indicated the capability of various microorganisms in biosynthesis of exopolysaccharides (EPSs). A wide range of evidence extensively investigated the ability of bacterial species for EPS synthesis and their favorable effects, so little is known regarding yeast species. Many factors like composition of growth media and fermentation conditions are related to the structural and physical properties of EPSs. The EPS protects the producer yeast strain against extreme environment. Researchers proposed that yeast EPSs have priority over bacterial EPSs because of high yields of EPS biosynthesis and easy separation methods from growth media. Besides, they have drawn increasing attention due to their interesting biological activities, food, pharmaceutical, and cosmetics applications. Although a limited number of studies exist, this review aims to highlight the EPS structure and various applications of known yeast species in detail.

Sugar reduction in bakery products: Current strategies and sourdough technology as a potential novel approach

The world is facing a big problem of non-communicable diseases, such as obesity, cardiovascular disease and diabetes. An excessive sugar consumption is considered as a main factor, which triggers these diseases. The two main sources of sugar in processed products on the market are sugar-sweetened beverages and sweet bakery products. Sugar reduction is challenging, especially in baked goods, since it interacts significantly with all ingredients. These interactions cause an increase in gelatinization temperature, a delay in gluten network development, an increase or decrease in yeast activity depending on the sugar concentration, as well as an enhancement of emulsification. Reflecting the molecular interactions on the product quality characteristics of different types of baked goods, sugar also contributes to browning reactions and extension of microbial shelf life. During cake preparation, sugar supports the batter aeration which results in the typical soft cake crumb. Furthermore, it contributes to the spreading process of biscuits during baking and enhances surface cracking due to recrystallization. Sugar reduction requires the development of different strategies; Two well-known strategies are the replacement of added sugar by the combination of bulking agents and high-intensive sweeteners, or by sweet bulking ingredients, such as polyols. The in-situ production of polyols to enhance sweetness, and exopolysaccharides to improve texture, in a sourdough system shows high potential as sugar replacement. Lactobacillus sanfranciscensis, Leuconostoc mesenteroides and Leuconostoc citreum are high mannitol producing lactic acid bacteria (LAB) strains with yields of 70-98% and Leuconostoc oenos was found to produce erythritol. Furthermore, the yeast strain Candida milleri isolated from sourdough produces xylitol in the presence of xylose. Exopolysaccharides produced by LAB and/or yeasts are known to improve the texture and structure of bakery products and, thus, have high potential as natural functional ingredients to compensate quality loss in sweet bakery goods.