Study On The Preparation And Quality Of Oat Fermented Milk

Oat has good nutritional value and health benefits,with the highest protein and fat content in cereals.Oat is rich in soluble dietary fiber and a variety of phenolic substances.Oat milk,as one kind of oat products,is rich in small molecule sugars.Fermenting oat milk can increase the health effects with lactic acid bacteria and enrich plant-based fermented milk products.The reported articles usually combined oat milk with dairy milk for fermentation,but there are few reports on the preparation and quality of oat fermented milk only.In this paper,the fermentation properties of oat milk were investigated,and the effects of different fermentation starters and process conditions on the quality of oat fermented milk were discussed.The research here can provide theoretical basis and process reference for the development of oat fermented milk.The main research contents are as follows:Firstly,the composition of oat milk,soy milk and reconstituted milk and the quality of the corresponding fermented milk with lactic acid bacteria were compared.The result showed that oat milk was rich in glucose,which can provide sufficient carbon source for the growth of lactic acid bacteria.The content of free amino acids in oat milk and soy milk was about 2.2 ～ 2.4times that of reconstituted milk.With p H 4.5 as the ending of fermentation,the reconstituted fermented milk had the highest titratable acidity due to its good buffering capacity and high number of viable lactic acid bacteria.Oat milk had the fastest fermentation speed,and it only took 5 h to reach the end of fermentation.But the titratable acidity of oat fermented milk was only 35.11 °T due to its low buffering capacity.Soy fermented milk had the highest hardness(75.75±1.79 g)and water holding capacity(85.80±1.56%).The microstructure showed that soy fermented milk had denser gel structure.However,oat fermented milk had the lowest hardness(9.99±0.17 g)and water holding capacity(61.83±1.43%),and the gel structure was loose.The main volatile flavor components in fermented milk were ketones,and more aldehydes were detected in oat and soy fermented milk.Principal component analysis showed that the flavor of oat fermented milk was more similar to that of reconstituted fermented milk compared with soy fermented milk.Oat fermented milk had a high content of polyphenol(178.67±4.14 μg GAE/g)and β-glucan(2.67±0.17 mg/m L).Secondly,the effects of fermentation starters on the quality of oat fermented milk were investigated and their metabolites were comparably analyzed.Different starters directly affected the fermentation rate of oat milk and the number of lactic acid bacteria.The hardness of oat fermented milk prepared by different starters was low and the texture was weak.After fermentation with starter B or C,the antioxidant capacity of oat milk increased.After fermentation,the contribution of flavor substances such as green grass flavor in oat milk significantly decreased,with ketones(2,3-butanedione,1-octen-3-one,etc.)being the main flavor contributors.The oat fermented milk prepared by starter B had more characteristic flavor substances of yogurt with better flavor.Metabolic pathway enrichment revealed that during the fermentation process of oats,lipid-related metabolisms were the most vigorous.The metabolites of oat milk fermented by different starters showed big differences.Among the four types of direct vast set starters,oat fermented milk with starter B accumulated more dipeptides and small peptide substances,while that with starter C had more bioactive substances.Based on the comprehensive fermentation characteristics,flavor,and metabolite nutrition,starter B was more suitable for the preparation of oat fermented milk.Finally,the effects of heat treatment on oat fermented milk and oat protein acid-induced gel were investigated.The results showed that heating treatment on oat milk could significantly improve the texture of oat fermented milk.When the heating temperature increased from 95℃to 115℃,the titratable acidity of oat fermented milk increased from 38.79 °T to 43.97 °T,the hardness of oat fermented milk increased from 7.87 g to 94.07 g,and the water holding capacity increased from 75.93% to 90.09%.With the increase of heating temperature,the results of gel kinetic curve showed a significant increase point for the storage modulus.The microstructure images of fermented oat milk showed a denser gel network structure.On this basis,the reasons for improving the texture of oat fermented milk by heating were explored with oat protein as the research object.The results showed that heating treatment expanded the structure of oat protein,increased the random curling structure,enhanced surface hydrophobicity,and increased the content of free sulfhydryl groups on the oat protein surface.In the process of acid-induced oat protein gel,the interaction between oat protein molecules was enhanced,the gel network structure was more compact,and the gel hardness and water holding capacity were significantly enhanced.It is precisely due to the influence of heating on oat protein that heating treatment can significantly enhance the texture of oat fermented milk.