Study On Effects Of Freezing On Biological Activity Of Bacteria In Probiotic Ice Cream

Probiotics ice cream were made by two strains of probiotics(Lactobacillus casei and Lactobacillus rhamnosus) commonly used in domestic and foreign ice cream and a strain isolated from Kumiss of Inner Mongolia traditional dairy products .This study mainly examined effects of freezing on biological activity of bacteria in probiotic ice cream in frozen storage.Firstly the strain isolated from Kumiss was identified by conventional physiology and biochemical and 16S rDNA Molecular identification methods .The identified strain was Lactobacillus plantarum. Then probiotics ice cream products were made by Lactobacillus casei, Lactobacillus rhamnosus and Lactobacillus plantarum and storaged 80d under -20℃and -40℃storage conditions.The characteristics of the strain in probiotic ice cream,including total viable count,acid resistance,producing aicd,bile tolerance, cholesterol-reducing and hydrolyzed protein ability were determined every 10 d in storage during storage period. The test result showed that under -20℃and -40℃storage conditions during 80d storage period with the passage of time, every biological indicator of the strain has significantly reduced except producing acid ability, then changed to be steady to a certain time and total viable count was 107cfu/ml.Producing acid,bile tolerance ability of the same strain, under -20 and -40℃freezing conditions in probiotic ice cream,was no significant difference between the index change. However, cholesterol redu- cing and hydrolyzed protein ability of the same strain under the same conditions was significant difference between the index change.Animal testing were carried out by probiotic ice cream with relative stable index and storaged 60 d. Mice were randomly divided into four groups:normal saline group as control,Lactobacillus casei ice cream group, Lactobacillus plantarum ice cream group,Lactobacillus rhamnosus ice cream group .They were administered for 10 days. During the 10 days,the numbers of bacterias in the intestine were counted selective medium.The numbers of bacterias on the intestinal in mice that were administered with Lactobacillus casei ice cream, Lactobacillus plantarum ice cream and Lactobacillus rhamnosus ice cream showed extremely significant dfference to those in normal saline as control.Compared with control group,there is also significant difference(p<0.01) on the numbers of the enterobacter in the intestinal. Studies have confirmed that the number of probiotics can be increased and the intestinal microflora in mice can be regulated by probiotic ice cream.