| As characteristic products of Guizhou Province,Rosa roxburghii tratt and coix seed not only have the characteristics of rich nutrition and wide planting area,but also complement each other in nutritional function,but the deep processing is less.And because of the bitter taste of Rosa roxburghii tratt,its consumption is limited to a certain extent.Edible fungi are rich in a variety of enzymes,and the fermentation of edible fungi may overcome the bitter taste of Rosa roxburghii tratt.Due to the low content of protein and starch in Rosa roxburghii tratt,coix seed can be supplemented.Therefore,before fermenting Rosa roxburghii tratt by edible fungi,it is best to saccharify coix seed and compound with Rosa roxburghii tratt juice,which can give full play to the fermentation effect of edible fungi.Because the new functional yogurt with good flavor is very popular among consumers,the fermented Rosa roxburghii tratt and coix seed fermented by edible fungi can be mixed with milk(milk powder)and inoculated with lactic acid bacteria for co-fermentation.it is possible to obtain a new type of Rosa roxburghii tratt and coix seed yogurt with high quality and good flavor.Therefore,in this paper,edible fungus Trametes versicolor was used to ferment the compound liquid of Rosa roxburghii tratt and coix seed,and the fermentation liquid was further mixed with milk powder to be inoculated with lactic acid bacteria for the development of yogurt products.the purpose of this paper is to obtain the sensory and good quality Rosa roxburghii tratt and coix seed yogurt with edible fungus flavor,aiming at deep processing of Rosa roxburghii tratt and coix seed,and developing a new flavor yogurt with high value and good flavor.To meet the people’s increasing demand for high-quality yogurt.The main research contents and results are as follows:(1)A combination of L.plantarum subsp.plantarum LB12,B.animalis subsp.lactis BLH1 and commercial S.thermophilus Q-1 were selected to ferment yogurt.The optimal fermentation process for Rosa roxburghii tratt and coix seed yogurt was determined by single-factor,Plackett Burman(PB)and response surface optimization design tests using sensory,polysaccharide,vitamin C,and viable bacterial count as indicators:17%skim milk powder,4%sucrose content,36%Rosa roxburghii tratt and coix seed liquid,39°C fermentation temperature,2%inoculum,strain ratio(LB12:BLH1:Q-1)is 2:1:1,fermentation time is 9.5 h.Under these conditions,the sensory score of Rosa roxburghii tratt and coix seed yogurt was 82.108,the polysaccharide content was 3.740 mg/m L,and the vitamin C content was 1.525 mg/g.(2)The changes in physical and chemical properties,nutritional indexes,and flavor quality of yogurt during fermentation were studied under the optimized parameters.The results showed that the p H of yogurt fermented by Trametes versicolor was decreased faster,and the contents ofγ-aminobutyric acid(GABA),polysaccharides,and free amino acids were higher.Trametes versicolor fermentation effectively improved the nutrients in Rosa roxburghii tratt and coix seed yogurt.The total concentration of flavor compounds in CY yogurt before and after fermentation decreased from 599.09μg/kg to 442.64μg/kg,and that in YCY yogurt decreased from373.59μg/kg increased to 1322.57μg/kg.Adding Trametes versicolor fermentation increased the content of acids,alcohols,and esters in Rosa roxburghii tratt and coix seed yogurt and improved yogurt flavor quality.The content of vitamin C,GABA,and the total number of living bacteria in YCY were 13.89,2.58,and 1.02 times higher than those in ordinary yogurt.YCY maintained a high level of microorganisms and showed the advantages of high nutritional composition and sensory score.(3)The changes in nutrients,antioxidation in vitro,microorganisms,and organic acids in yogurt during storage were studied.During storage,fermentation of Rosa roxburghii tratt and coix seed by Trametes versicolor improved the content of polysaccharides,soluble protein,and antioxidation in yogurt.Still,it decreased the content of vitamin C in yogurt.During the 21-day storage period,the number of LB12and Q-1 in CY and YCY had no significant downward trend,while the number of live bacteria in BLH1 decreased by 1.83 log CFU/m L and 2.14 log CFU/m L,respectively.But the viable bacteria counts of LB12 and Q-1 in all samples were above 10~6 CFU/m L during the whole storage period,which was higher than the recommended minimum concentration that could maintain the host’s potential health benefits.Adding Trametes versicolor fermentation decreased tartaric acid,malic acid,and acetic acid in the yogurt.It increased the contents of citric acid and lactic acid,which helped improve the yogurt’s taste coordination.(4)The quality changes of Rosa roxburghii tratt and coix seed yogurt stored at 5℃,15℃and 25℃were studied.The p H,viable bacteria count,and sensory score of Rosa roxburghii tratt and coix seed yogurt decreased gradually with storage time,while the titration acidity increased gradually.At 5℃,on the 24th day of storage,the p H value of yogurt decreased to 4.0,the number of probiotic living bacteria reached 4.11×10~8CFU/m L,and the sensory score was 73,which still maintained a high number of living bacteria and sensory score.According to the Pearson correlation coefficient between each index and the senses,the sensory and p H were determined to reflect the quality changes of yogurt in the storage environment.The first-order kinetics was used to fit the regression equation,and the prediction model based on p H and senses was obtained.Under the sensory prediction model,the predicted shelf life of Rosa roxburghii tratt and coix seed yogurt at 5℃,15℃,and 25℃was 18 days,5 days,and 2 days,respectively,and the actual values were 21 days,6 days and 2 days respectively.The relative error between the predicted and actual values is 10.32%<20%,which has high model accuracy. |
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