Physicochemical properties of the water extracted polysaccharides from the sugary kefir grains

• Main Authors: Yu-Jhen Wang, 王淯湞
• Other Authors: Lih-Shiuh Lai
• Format: Others
• Language: zh-TW
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/48778506670666489584

碩士 === 國立中興大學 === 食品暨應用生物科技學系所 === 103 === Kefir is a fermented drink, including milky kefir and sugary kefir. For the production of sugary kefir, a muscovado sugar solution (80 g L⁻¹) is fermented by a consortium of microorganisms which were originated from the sugary kefir grains. Sugary kefir grains contain a water soluble polysaccharide known as sugary kefir polysaccharide. Since researches on the properties of sugary kefir polysaccharide are quite limited, the objectives of this study is to investigate the physicochemical properties of sugary kefir polysaccharide extracted by different ethanol concentration. The sugary kefir polysaccharide A is precipitated by 71% ethanol concentration, and the abbreviation of sugary kefir polysaccharide A is KA. The other sugary kefir polysaccharide B is precipitated by 79% ethanol concentration, namely KB. In addition, the effect of sugary kefir polysaccharide addition on the pasting behavior and rheological properties of corn, wheat and tapioca starch were characterised. According to the results of yield (5.44-5.87% db), total carbohydrate content (95.79-99.29% db), ash content (1.06-1.08% db), molecular weight (1.47×10⁶-1.48×10⁶ Da), there is no significant difference between KA and KB. The monosaccharide composition of KA and KB are composed of mainly glucose and trace amount of mannose, without the presence of uronic acid. In consistence with the total carbohydrate content, KA and KB are neutral polysaccharide with high purity. ¹H, ¹³C and 2D NMR analysis revealed that the structure of sugary kefir polysaccharide is α-D-Glc (1→6)α-D-Glc. Rheological behavior of 6-10% sugary kefir polysaccharide belongs to shear-thinning fluid. When mixed different concentration (0.5-5%) of sugary kefir polysaccharide with 10% starch (corn, wheat and tapioca), the pasting behavior of starch was modified significantly. Specifically, the peak viscosity of starch paste was decreased, accompanied with an increase in pasting temperature as sugary kefir polysaccharide concentration increased. Dynamic viscoelastic results also revealed that the sugary kefir polysaccharide/starch blends belonged to weak gels, and the modulus of sugary kefir polysaccharide/starch blends decreased as sugary kefir polysaccharide concentration increased. Such results implied that the presence of sugary kefir polysaccharide would retard or interrupt the swelling of starch granules, leading to pronounced modification of the pasting behavior of starch. The information of sugary kefir polysaccharide will be useful, if the opportunity ever arises to use them commercially.