Preparation Of Oligosaccharides From Cyperus Esculeutus Meal And Its Effect On Quality Characteristics Of Fermented Milk

As a kind of tuber crop of the Cyperaceae family,Cyperus esculeutus（CE）is planted all over the world,and the planting area in our country is also increasing year by year in recent years.Its tubers are rich in dietary fiber and minerals,such as potassium,phosphorus,calcium,magnesium,zinc,copper,vitamin C and E,as well as a variety of essential fatty acids,and its extract can effectively treat and prevent a variety of diseases.The main fatty acid in the components of CE oil is monounsaturated fatty acid,with a content of more than 60%,which makes its quality equal to that of hazelnut oil and olive oil.In recent years,with the widespread application of CE in the oil pressing industry,the residual CE meal contains rich nutrients,and its secondary utilization has attracted extensive attention.At present,the by-products of CE are mainly as animal feed or discarded,resulting in resource waste and environmental pollution,which has become an urgent problem for the food industry to solve.Based on previous studies,CE meal is rich in carbohydrates.The purpose of this study is to comprehensively develop and utilize CE meal resources on the basis of green development,increase their added value,and provide new research ideas for the secondary development of CE by-products and resource reuse in the food industry.The research contents mainly include the optimization of ultrasonic-assisted extraction and purification of water-soluble sugar from CE meal（CES）,enzymatic transformation to prepare CE meal oligosaccharides（CEO）and its structure characterization and probiotic activity analysis,effect of CEO on the quality of fermented milk during storage.1.Optimization of water-soluble sugar extraction from CE meal by ultrasonic-assisted hot water extractionWith the extraction rate as the index,the optimized process conditions were confirmed to ultrasonic time of 16 min,extraction temperature of 75℃and extraction time of 3 h.Under the optimized conditions,the extraction rate was（52.61±0.51）%.The purification process innovatively uses isoelectric point precipitation combined with membrane separation technology to deproteinize the CES.The results indicated that the protein clearance rate reached 51.35%and the sugar retention rate reached64.91%.2.Preparation,structural characterization and probiotic activity analysis of oligosaccharides from CE mealFructosyltransferase was used to convert the CES to produce CEO.The structure of CEO and CES was characterized by UV and IR spectroscopy,the IR spectrum results showed that there was a fructosan-related absorption peak at 930.2 cm^-1.It was speculated that there was fructosan in CEO.High performance liquid chromatography（HPLC）was used to detect the sugar components.When the addition ratio of enzyme was 1‰,the CEO was mainly composed of GF₂and GF₃,which were 27.53%and2.72%,respectively.In this case,the content of fructo-oligosaccharides can reach up to 30.25%.Scanning electron microscopy（SEM）analysis showed that the CEO showed irregular geometry and compact three-dimensional structure.In the probiotic experiment,the growth curve,24-hour viable bacterial count,and acid-producing ability of three lactic acid bacteria（Lactobacillus paracasei JLU_S66,Bifidobacterium BB-12,and Lactobacillus plantarum P5）with different concentrations of CEO as a carbon source were studied using glucose medium as a control.The results showed that 4%CEO had the best effect on the proliferation of Lactobacillus paracasei JLUs66 and Lactobacillus plantarum P5,and 8%CEO had the best effect on the proliferation of bifidobacterium BB-12,indicating that CEO had good probiotic activity and could promote the growth of probiotics,the proliferation effect was stronger than glucose culture medium.3.Effects of CE meal oligosaccharides on the quality of fermented milk during storageIn order to further explore the impact of CEO on the quality of fermented milk during storage.First of all,the p H and rheological properties of fermented milk during cold storage were used as evaluation indicators to screen the mixed starter.The effect of adding 5%,6%,7%and 8%CEO in fermented milk on the quality characteristic of fermented milk during storage was studied,with 6%white granulated sugar as control.The changes in viable bacterial count,p H,water holding capacity,whey release rate,color,texture characteristics,rheological properties,and sensory scores of fermented milk during storage were compared.The results showed that adding a certain proportion of CEO in fermented milk could reduce the p H and the rate of whey release to varying degrees,improve the number of viable bacteria,water holding capacity and sensory evaluation score during cold storage,and improve the appearance,texture and rheological properties of fermented milk.The quality of fermented milk with 7%CEO was the best by comprehensive comparison of various indicators.In conclusion,the CES was recovered and converted into prebiotics,which were applied in fermented milk.Reintroducing waste materials into production provides a new research idea and experimental basis for optimizing the use of resources.