Study On Preparation Technology And Physicochemical Properties Of Brown Yogurt

Brown yogurt which has developed in recent years,is a kind of fermented milk evolved from roast yogurt.Compared with traditional fermented milk,it features flavor and color.Without using the pigment,improving preparation technology and adding ingredients can produce a more comfortable warm color and make the flavor unique.Its color and flavor are formed by the Maillard reaction.Because it is an emerging product,brown yogurt lacks corresponding national standards.What`s more,each manufacture will use various processes and parameters in production and it`s not clear what the harmful substances are and how much that formed in the Maillard reaction.At the same time,how to control the process conditions and manage the generation of harmful substances also needs to be elaborated.Based on the above reasons,this project studied the influence of brown yogurt production process parameters on product quality and safety,and hoped to have a useful guiding role for brown yogurt production and the development of national standards.The following conclusions are drawn.1.The single-factor experiments were used to compare the formation of 5-hydroxymethyl furfural with the Maillard reaction product under different conditions.It was found that: with the increase of heating time,heating temperature and the increase of glucose,5-hydroxyl the formation of methylfurfural was gradually increased.2.The response surface optimization experiment was used to optimize the brown yoghurt preparation process.The results showed that the factors affecting the sensory evaluation were heat treatment time > heat treatment temperature > glucose addition,the optimal process parameters were glucose addition was 6.51%,heat treatment temperature was 97.3℃,and heat treatment time was 4.1 h.Under this condition,the formation amount of 5-hydroxymethylfurfural was 1.71mg/L,which was within the threshold limit values.3.By measuring the sensory evaluation of yogurt,texture characteristics,effective lysine content,in vitro simulated protein digestibility and 5-hydroxymethyl furfural content,the sensory,nutritional and safety characteristics of the yogurt(ordinary yogurt and brown yogurt)and the brown yogurt prepared under the optimum conditions were compared and analyzed.The results showed that the brown yogurt prepared by Maillard reaction was more easily accepted and had higher sensory scores,while the synthetic texture was lower than the common yogurt.but it was higher than that of the market Brown yogurt;the protein content and the effective lysine content(0.697mg/mL)were lower than those of the ordinary yogurt(0.732mg/mL),but higher than the market Brown yogurt(0.589mg/mL);the protein digestibility(97.65%)is similar to that of the market yogurt,with only a slight difference.In general slightly lower than the ordinary yogurt(97.69%),and higher than the commercial Brown yogurt(97.58%);for the 5-hydroxymethyl furfural content,the brown yogurt(1.714mg/L)was far higher than the ordinary yogurt(0.468mg/L),and slightly lower than the commercially available Brown yogurt(1.800mg/L).4.By measuring the texture properties,pH,acidity,living bacteria number and water holding property of brown yogurt during storage,the storage stability of brown yogurt prepared under the optimal process conditions was analyzed.The results showed that the hardness of brown yogurt decreased first and then increased with storage time,and the firmness of the yogurt for 7 days was much greater than that of storage for 1 day;the cohesion of the yogurt was irregular with the prolongation of storage time,in which the internal cohesion of the storage 1 day was the least,0.427,and the maximum accumulation of 21 days was 0.931;stickiness followed storage time.The elongation decreased first and then increased,but the viscosity of the samples stored for 14 days was lower than that of the storage for 7 days,and the stickiness of the storage was irregular with the prolongation of storage time,in which the viscosity of the storage 5 days was the lowest,5.758,and the viscosity of the storage 21 days was the largest,which was 22.597.During the storage period,the pH and acidity of brown yogurt decreased with increasing storage time.During the storage of brown yogurt,the number of Lactobacillus bulgaricus and Streptococcus thermophilus decreased with the prolongation of storage time,resulting in the same change trend in the total number of living bacteria.The water holding capacity of brown yogurt decreased first and then increased during storage.In this study,glucose was added to the raw milk and then heated for a certain amount of time(4.1 h)at a high temperature(97.3℃),a kind of brown yoghurt was acquired with the color and flavor that consumers could accept.Compared with market yogurt,the formation amount of 5-hydroxymethylfurfural was increased,but it still within the threshold limit values;both the protein digestibility and the effective lysine content decreased,however,the flavor improved significantly,and no significant effect on other indicators.