Preparation And Application Of Low-molecular-weight β-1,3-glucan

Low molecular weight β-glucan has unique physiological and biochemical activities,such as moisturizing,sunscreen,anti-oxidation,antibacterial,promoting dissolution,and so on.At present,it has a broader application prospect in the fields of coal mining,food processing,pharmaceutical sustained release,cosmetic composition,and agricultural additives.In recent years,the research on the versatility of low molecular weight β-glucan is increasing at home and abroad.However,there are some problems,such as high cost,environmental pollution,and low conversion rate in the preparation of low molecular weight β-oligosaccharides.Glycerol is an attractive feedstock for biofuels since it accumulates as a byproduct during biodiesel operations.Hence,we consider converting glycerol into high value-added products under the mild conditions using microorganisms,which not only reduces the cost,but also provides a guarantee for the long-term development of the technology and the protection of the environment.Against this background,in this study,glycerol was used as the carbon source to domesticate the Agrobacterium sp.ATCC 31749 and produce low-molecular-weight β-glucan（LBG）.Its structure and composition was identified and analyzed.At the same time,the application of the product was studied.The main contents and results are as follows:（1）A good strain Agrobacterium sp.WS-8E3T,which used glycerol as carbon source to produce low molecular weightβ-1,3-glucan,was obtained.After further domestication,the tolerance of Agrobacterium sp.WS-8E3T to glycerol reached 150 g·L^-1.The addition of surfactant promoted cell membrane permeability and changed cell membrane morphology,and the yield of LBG increased by 58.15% compared with that without surfactant.（2）Extraction,separation,purification,physicochemical property analysis and structure identification of LBG.The pure LBG from different batches was separated and purified by ethanol fractionation precipitation,protein removal by Sevage and SPE solid phase extraction.The polysaccharides were characterized by relative molecular weight analysis,ultraviolet spectrum,infrared spectrum,nuclear magnetic resonance,monosaccharide composition and so on.It was proved that the extracellular polysaccharides obtained by Agrobacterium sp.WS-8E3T fermentation with glycerol as carbon source was β-1,3-glucan.The purity of LBG is（87.4±3.69）%,which meets the requirements of subsequent fermentation experiments;the molecular weight of the glucan is 3.218×10³ Da.（3）The digestion of LBG was simulated in vitro.The results showed that the total sugar,reducing sugar and molecular weight of LBG samples did not change after being digested by saliva and gastrointestinal juice,indicating that LBG could pass through the digestive system smoothly and reach the large intestine“safely”.In the in vitro fermentation system,LBG was used as carbon source to ferment healthy human fecal flora,and the effects of LBG on the structure and metabolism of intestinal flora was studied.The results showed that LBG could promote the growth and metabolism of short-chain fatty acids.（4）The application of LBG in the field of cosmetics.The results show that LBG samples have certain properties of moisturizing,moisture absorption,oxidation resistance and sun protection.LBG is mixed into the mixture containing xanthan gum,sodium alginate,white oil,salt ion and so on,and the different products have sun protection and moisturizing effect.It shows the potential of LBG in the field of cosmetics.（5）LBG solution was coated to explore the freshness of food.It was found that the water loss rate of LBG film was relatively low.To explore the effect of LBG on glucose transport rate,it is found that the existence of LBG can effectively alleviate the running rate of glucose in water,which shows that LBG also has potential application value in medical field.