Study On The Mixed Milk Base Flavor Of Cream And Whey Prepared By Biochemical Methods

Due to its high flavor value,cream has been widely used in the preparation of natural milk flavor or milk base flavor by enzymatic method.Because of its high nutritional value and good functional,whey has been widely used in beverage production or infant formula,whereas little used in the natural flavors.Milk base flavors were prepared by different methods.For example,fermented by Lactobacillus paracasei and Lactobacillus helveticus in 60 hours,fermented and cooperated with enzymolysis by protease,lipase,both protease and lipase in 60 hours,fermented in 60 days,fermented and cooperated with enzymolysis by protease in 60 days,fermented in 30 days after adding soy peptides to deal with cream and whey were researched in this study.There were different kinds of flavor and taste in milk base flavors.Differences and changes of their fermentation characteristics and volatile flavor components in the process of fermentation or the process of fermentation cooperated with enzymolysis were discussed,which provided theoretical and practical basis for the use of fermentation engineering technology and enzyme engineering technology in the promotion of dairy flavor.The main results were as follows:(1)The fermentation process of cream was optimized,the results showed that homogenous treatment was beneficial to the growth of lactic acid bacteria and the production of titratable acidity in the cream.The pressure was 20 MPa and the temperature of milk base flavors was 75? in homogeneous treatment.The ingredients of milk base flavors were optimized by analyzing their viable cell number of lactic acid bacteria,titratable acidity and pH value,volatile flavor components,shape,taste and odour,found that the best milk base flavor(T5)was comprised of 14% fat and 4.6% protein.(2)The mixed milk base flavors were fermented and cooperated with enzymolysis by 0.1% protease,0.1% lipase,both 0.1% protease and 0.1% lipase in 60 hours.The effect of protease or lipase was researched by analyzing their viable cell number of lactic acid bacteria,titratable acidity and pH value.The addition of protease could reduce pH value,promoted the proliferation of lactic acid bacteria and the increase of acid.The promoting effect was positively correlated with the amount of addition in the milk base flavors.The addition of lipase significantly improved titration acidity,but inhibited the proliferation of lactic acid bacteria and output of propionic acid.The protease was interfered with the hydrolysis of lipase.(3)The volatile flavor components were analyzed by headspace solid-phase micro-extraction and gas chromatography-mass spectrometry,the results showed protease obviously promoted the increase of ketones;lipase significantly promoted the content of carboxylic acids while inhibited the increase of ketones,and the species of carboxylic acids and ketones were increased.The outstanding effect of lipase on the volatile flavor compounds was that the addition of lipase caused esters.Protease and lipase added in combination had the better results with lipase added in single,which could increased yield of esters,and combined with the advantages of the two enzymes to moderate large amounts of fatty acids from irritating sour,thus making flavor richer and more gentle.Principal component analysis and sensory evaluation were used.Protease and lipase added in combination had the biggest influence on flavor and changed it significantly while lipase came second.Protease had least influence on the change of volatile flavor components and mainly improved quality of flavor.(4)The two kinds of mixed milk base flavors containing 21% and 28% fat were prepared and fermented in 60 days.The same indicators were determinated.Increasing the fat content in the mixed milk base flavor had no effect on the growth and decay of lactic acid bacteria during the early period of growth and decay,but in the late period of decay,the activity of lactic acid bacteria picked up.Increasing the fat content in the mixed high-fat milk base flavor was bad for the increase of the carboxylic acids,but was advantageous to the increase of the ketones and esters after a long time fermentation.(5)The mixed milk base flavors containing 21% fat were fermented and cooperated with enzymolysis by 0.1% protease in 60 days The same indicators were determinated.The addition of protease could promote the decay of lactic acid bacteria,but it was unfavorable to decline of pH value in the late fermentation.The addition of protease was beneficial to the generation of volatile free fatty acids and 2,3-diketones,but bad for the production of esters and other ketones,and the effect on lactones was not obvious.(6)The mixed milk base flavors containing 21% fat were fermented by adding 0.6% and 1.2% soybean peptide respectively in 30 days The same indicators were determinated,the results showed that pH value was descend,titratable acidity was rose,viable cell number of lactic acid bacteria was rose in the short time.The degree of acceleration was positively correlated with adding quantity.However,fermented a long time,it was disadvantageous for the death of lactic acid bacteria,the decrease of pH and the increase of titratable acidity.The degree of inhibition was negatively correlated with the addition amount.The addition of soy peptides was negative for the production of volatile flavor compounds during the long fermentation.