Effect Of Lactobacillus Plantarum P-8 And Yoghurt Starters On The Flavor Of Fermented Milk

The Lactobacillus(L.)plantarum P-8 is a probiotic strain that has strong tolerance to cholinite,good antibacterial activity,and high resistance against artificial gastric intestinal juice,making it a good candidate for use in the development of functional fermented milk.This work analyzed the fermentation characteristics and volatile flavor compounds of fermented milk produced by L.plantarum P-8 in combination of the common yogurt starter bacteria,L.bulgaricus IMAU 20401 and S.thermophilus IMAU40133(in a fixed proportion of 1:1000)during and post fermentation.The L.plantarum P-8 was added in different ratios in comparison to the common starter bacteria(in the ratio of 1:1,1:5,1:10,1:50,1:100 and 1:1000).The results are as follows:1.A total of 106 volatile compounds were identified across the fermented milks by the method of SPME-GC-MS.Results from the principal component analysis and the key flavor compounds profile showed that the application of L.plantarum P-8 at 1:100ratio produced the optimal product flavor.2.Many fermentation characteristics of the fermented milk produced by L.plantarum P-8 and mixed starter(1:100 proportion)significantly changed over the fermentation and storage period(P<0.05).The pH value was always above 4,and the highest value of titratable acidity did not exceed 100°T,which meet the consumers'requirements for the flavor of fermented milk.The number of live bacteria in the fermented milk was always above 10~8 CFU/mL,indicating good activity of the mixed starter.The viscosity was close to the highest value,while opposite trend was observed in the dehydration,suggesting good retention ability.These results together suggest that the application of L.plantarum P-8 used in a ratio of 1:100 produced yogurt of highly desirable fermentative properties.It meets the quality requirements of conventional yogurt.3.fermented milk produced by L.plantarum P-8 and mixed starter(1:100proportion).The main volatile flavor compounds at the stage of fermentation included valeraldehyde,hexanal,diacetyl,acetoin etc.The main volatile flavor compounds at the stage of storage included 2-heptanone,1-hexanol etc.These Rich flavor substances could endow fermented milk with good quality.4.Low similarity was observed between fermented milks produced with different proportion of starter bacteria,as reflected by the chromatograms.The similarity of the chromatogram of fermented milk produced by the 1:100 ratio varied within the range of0.64 to 0.96 during fermentation and storage.Thus the application of L.plantarum P-8at 1:100 ratio could produce rich flavor compounds,and could maintain a relatively stable state.It could endow fermented milk with good quality.