Study On Thickening Properties Of Barley Flour In Yoghurt And Its Mechanism

Yogurt,a kind of health food,is favored by consumers.As the improvement of living standard,people have higher requirements for nutritional function and safety of yogurt.Conforming to the trend of clean food labels,natural substances were developed to replace yoghurt additives,and it has become the development direction of yogurt products.Barley is a kind of nutritious food,and its composition such as starch,beta-glucan can improve texture of food.Barley powder used in yogurt,not only can improve nutritional functions and food security of yogurt,rich product category,but also extend the application scope of barley,providing new ideas for the further development and utilization of barley resources.In this paper,barley and yogurt were selected as the research object,analyzed the effect of barley powder and thickener on yogurt,and discussed the thickening mechanism of barley powder in yogurt.The main study contents and results are as follows:1.The effect of processing way on the quality of the barley powder was researched.Yangsi number 3,Russia nutuns and Jisi number 1 as barley raw material,material composition and particle properties of barley were compared,the effect of processing methods on composition,powder characteristics,freeze-thaw stability and stability undering acid system of barley flour were researched by grinding and baking method,high pressure steaming method,and electromagnetic fried making method.Results showed that Jisi number 1 contains the highest content of starch and beta glucan among the three kinds of barley raw material,65.32g/100 g and 3.54g/100 g respectively,with moderate grain hardness,epigranular grain,meaning the best application characteristics.Among Three kinds of processing methods,barley flour obtained by electromagnetic fried making method was the best,with starch gelatinization degree of 57.6%,uniform color,moisture content of 3.64 g/100 g,flour yield as high as 78.7%,higher the freeze-thaw stability of barley flour with better flavor,lower hydrolysis rate under the weak acid environment.2.The effect of barley powder on the sensory quality of yogurt was researched.Results showed that quantity and particle size of barley flour and fermentation time had a significant influence on sensory quality of yogurt.When barley flour quantity of 2%,particle size to 30 microns,fermentation time of 10 hours,inoculation quantity of 3%,yogurt has the best sensory quality,and other indexes of yoghurt were in accordance with requirements in GB19302.Compared with the commercial yoghurt,solids content is higher,particularly living bacterium number as high as 2.14×108CFU/mL in barley flavor of yogurt with increased flavor substances.3.The effect of barley powder on the quality of yogurt during fermentation,storage and transport was researched.Growth curve of lactic acid bacteria and pH in fermentation,acidity,water holding capacity,viscosity and total number of lactic acid bacteria during the storage,whey exhalation rate and the freeze-thaw stability in transportation were determined.Results showed that 1.5% ~ 3% barley flour promoted production of acid,fast growth period of lactic acid bacteria extended 0.2h,increased number of living bacterium;After 24 hours,viscosity and WHC of yogurt increased 43.52% and 3.71% with the increasing barley flour quantity,respectively.The number of lactic acid bacteria in yogurt added with1.5% barley flour as high as 2.72×109CFU/mL;viscosity and WHC remain relatively stable,and the number of living bacterium maintained a higher level in shelf life,of which number lactic acid bacteria in yogurt added with1.5% barley flour still as high as 1.98×109CFU/m L at16 th day during storage.Compared to whey protein,barley flour increased the freeze-thaw stability of yogurt,reduced the whey separation,of which whey exhalation rate of yoghurt with 2% barley flour was 19.71%,while exhalation rate of yoghurt with 2%whey protein was 34.62%.4.The mechanism under the thickening effect of barley flour on yogurt was researched based on correlation analyze between viscosity and total solid content,pH,microstructure and extracellular polysaccharide.Results demonstrated that the addition barley flour increased total solid content of ferment system,holding capacity for free water increased,compared with 2% whey protein group,increasing 13.01%.Secondly,barley flour promoted production of acid,lowered fermentation pH value,2% whey protein group was 4.1,2% barley powder group was 3.8.SEM indicated linking between protein molecules to form stable network structure,network gap was filled by barley flour,lessened network free-end.The accumulation effect between barley flour with casein was stronger,and increased with the decreasing of particle size of barley flour,density and rigidity of network increased,compared with 2% whey protein group,the light transmittance of 2% barley powder group dropped 4.13%,stability of system was improved.In addition,barley flour stimulated producing more hydrophilic extracellular polysaccharide,2% whey protein group(47.63 mg/L),2% barley powder group(113.46 mg/L),reduced charged molecules in the system,decreased the repulsion between components,formed more complex and stable network structure,and increased viscosity of yogurt.