Enzymatic Degradation Of Lactose And Its Application In Yogurt Ice Cream Products

People in all regions of the world have varying degrees of lactase deficiency.People with lactose intolerance cannot make good use of dairy products such as ice cream.At present,low-lactose and lactose-free ice cream are almost blank in the domestic market.Dairy products that are popular with both adults and children,for most people with lactose intolerance,producing low-lactose and lactose-free ice cream is one of the effective solutions.In this paper,lactase and fermenter are used,and combined modern biological enzymolysis technology and fermentation technology to prepare lactose-free yogurt ice cream.The main research results are as follows:（1）The lactose-free yogurt was prepared by a process in which the enzymatic hydrolysis and the fermentation simultaneously.The fermentation temperature was 42°C,the added amount of bacteria was 0.06 g/kg,amount of sugar was 6%,and the amount of enzyme was 2500 U/g.After 2 hours of enzymolysis,the residual amount of lactose in yogurt is≤0.5%（0.5 g/100g）,which meets the requirements of lactose-free products.Moreover,the apparent viscosity of the finished yogurt produced under this condition is highest when the shear rate is 0.01-1/s^-1.There is no significant difference in acidity compared with ordinary yogurt,and the water holding capacity after fermentation finished compared with ordinary yogurt was 124%,132.74%after 7 days of storage’s.The suspension stability was 45%higher on the first day,and 47%higher after 7 days of storage,which shows that lactose-free yogurt has better storage stability.PCA analysis results showed that there is a significant difference between the two flavors and odors,and it is easy to distinguish under the identification index≥98,but the lactose-free yogurt obtained under the same conditions of adding enzymes has no significant difference in odor between the groups（identification index 27）,only the taste.The difference is clear（identification index 94）.The umami taste of lactose-free yogurt has improved significantly,the salty taste has decreased,and the sour,sweet,and bitter tastes are weaker than ordinary yogurt.（2）Different heat treatment conditions can affect the macro characteristics and microstructure of lactose-free yogurt.The apparent viscosity value of lactose-free yogurt with a shear rate of 0.01-1/s^-1（85℃×10min）is slightly higher than that of ordinary yogurt.There is no significant difference in color index and acidity,and the overall sensory score is the highest.PCA analysis showed that there was no significant difference in odor（recognition index 42）.There is a significant difference in color and taste with the recognition index≥95,which is easy to distinguish.3275（light yellowish gray）is the main color number about overall color number,and it was the largest that the main color number of ordinary yogurt（83.15%）treated by heat（85℃×10min）.The main color number of lactose-free yogurt treated at the same temperature is 78.07%.The lactose-free yogurt group with different heat treatments has significantly improved in sourness and saltiness,and the bitterness and savory taste have decreased.Among them,the acidity,sweetness,and umami taste of the 95℃×5min heat treatment group are most prominent,which was the most coordinated of the five flavors.With the increase of heat treatment temperature,the water holding capacity of yoghurt increased,and the growth rate slows down slightly above85℃.The suspension stability was better in the 85℃×10min and 95℃×5min,and the poorer suspension stability was in the 65℃×30min and 75℃×15min.The increase in temperature leads to greater and denser cross-linking of the yoghurt gel network structure and smaller pores,which is conducive to the locking of moisture.Scanning electron microscopy also confirm the same results.Comprehensively,the optimal heat treatment conditions for lactose-free yogurt at 85℃×10min were further optimized.（3）The lactose-free yoghurt ice cream production process and optimal basic formula are established:lactose-free yoghurt 60%,sugar 13%,lactose-free milk 18.91%,coconut oil5%,butter 1%,eggs 1.5%,single Glycerin 0.2%,tamarind gum 0.1%,CMC 0.1%,sodium alginate 0.05%,xanthan gum 0.05%,and linseed gum 0.1%.The physical and chemical characteristics,texture characteristics and changes of lactic acid bacteria content during storage of normal yogurt ice cream and lactose-free yogurt ice cream were compared.Based on this formula,2%,4%,and 6%glucose were used to replace the amount of sugar.The total number of live lactic acid bacteria was 5.31×10⁸cfu/ml,8.25×10⁸cfu/ml,and9.48×10⁸cfu/ml,11.21×10⁸cfu/ml on the first day of the storage period.Although the total number of viable bacteria showed a downward trend during the 60-day storage period,the total number of viable bacteria in ice cream with a higher glucose addition ratio was still higher.The preliminary of the hypothesis verified that glucose has the ability to protect lactic acid bacteria in lactose-free yogurt ice cream and extend the shelf life of the product.