The Searches On The Relationships Between Favour And Enzymes And Sensory Attributes In Fermented Milk

Yogurt is one of the most concerned dairy products, which is welcomed by more and morepeople, because of its special flavor, creamy texture and healthy function to human body. There aremany flavor compounds in yogurts, but not every kind of which is crucial for yogurt flavor, only afew of them proved to have deterministic effect. Therefore we always select several main flavorcompounds in the researches. Carbonyl compounds are considered to be key to yogurt sensory dueto their relatively high concentration. Among which acetaldehyde and diacetyl are most concerned.And there are many influence factors affect yogurt sensory, in which microbial metabolism aremost important. There are enzymes produced in the process of microbial metabolism, which have agreat influence on flavor compounds. But for now few researches are focused on the relationshipbetween aroma and enzyme which are produced In the process of lactic acid bacteria metabolism.The sensory evaluation of yogurts is affected by flavor compounds. To better understand howflavor compounds affect yogurt sensory and how to reduce the deviation among individual, westudy the relationship between flavor compounds and sensory evaluation, and it is a field of studyat present.During the storage process, we determined acidity, diacetyl, acetaldehyde, β-galactosidaseand lactate dehydrogenase of yogurts fermented by5strains of thermophilic streptococcus,meanwhile we analyzed their correlation. Then we would find key enzymes for diacetyl andacetaldehyde generating, in order to provide a basis for the development of lactic acid bacteriawhich can produce high level of flavor compounds. Through the study of principal componentanalysis for sensory evaluation indicators and volatile flavor compounds, we can find therelationship between sensory and volatile flavor compounds, and then providing reference forfurther research.We analyzed acidity, diacetyl and acetaldehyde of yogurts fermented by different strainsduring storage, and found acidity and diacetyl increased. But acetaldehyde was not increasedbecause it is not accumulated as final product. Meanwhile we compared the ability to produce acidand aroma by different strains, and found KLDS3.1105having the strongest vitality for improving30.82°T acid during storage, however KLDS3.1101had weakest vitality for improving9.59°T acidduring storage. In the aspect of diacetyl production, KLDS3.1103possessed the strongest vitalityfor12.93μg/ml diacetyl increment, but the strain for the weakest vitality was KLDS3.1101which only produced0.81μg/ml diacetyl. In the aspect of acetaldehyde production, KLDS3.1105andKLDS3.0601produced more acetaldehyde, to the contrary, KLDS3.1101and KLDS3.1104produced little acetaldehyde. In storage time, β-galactosidase activity falled by degrees, and thestrain of highest activity was KLDS3.1105, the strains of lower activity were KLDS3.1101andKLDS3.1104.In the research of correlation among acidity, diacetyl, acetaldehyde and enzyme activity, inaddition to KLDS3.1101, there was significantly positive correlation between diacetyl and acidityin fermented yogurts by other strains. However correlation between acetaldehyde and acidity ordiacetyl was not obvious. The correlation between β-galactosidase activity and activity or diacetylwas better negative. But the correlation between β-galactosidase activity and acetaldehyde was notconsistent. For lactate dehydrogenase enzyme activity, Except the correlation between lactatedehydrogenase activity and diacetyl of KLDS3.1103and KLDS3.1105was significant, thecorrelation of other strains is not obvious. Therefore we can regulate and control acid and diacetylproduction by β-galactosidase in the process of storage time.Comparing with flavor of yogurts fermented by single and mixed strains, we found that mixedstrains could produce more diacetyl and acetaldehyde than single strain, and had better flavorcoordination and intensity, meanwhile the sensory evaluation were better. In addition, relevantindicators of combined strains KLDS3.1103+KLDS1.1028, KLDS3.1105+KLDS1.1028andKLDS3.0601+KLDS1.1028were better than combination of other strains. So we chose those threemixed strains for further research of principal component analysis.In the study of principal component analysis for sensory evaluation indicators and volatileflavor compounds of fermented yogurts, it had stronger taste of acid and astringency and longerpersistent aftertaste of fermented yogurts with combined strains KLDS3.1103+KLDS1.1028,which were increased in storage time. The combined strains KLDS3.1105+KLDS1.1028fermentedyogurts which possessed typical yogurt odor and had better milky odor, butter taste and creamyaftertaste, especially on sixth day storage, the sensory quality was the best. On the contrary,combined strains KLDS3.0601+KLDS1.1028fermented yogurts with poor milky odor, but on sixthday storage, butter taste and creamy aftertaste were the best. We made principal componentanalysis for volatile flavor compounds of9samples of yogurts, and found12kinds of volatileflavor compounds detected, only4kinds of which were appeared in9samples of yogurts. In thestudy of principal component analysis for4kinds of volatile flavor compounds, we found the4kinds of volatile flavor compounds were higher produced by combined strainsKLDS3.1103+KLDS1.1028than other combined strains. On10days, combined strainsKLDS3.1105+KLDS1.1028fermented yogurt which had lower n-Decanoic acid and higherHexanoic acid, Octanoic Acid and Butylated Hydroxytoluene. Combined strainsKLDS3.1105+KLDS1.1028fermented yogurt which had higher content of four kinds of volatileflavor compounds on6days than on10days. We found there is no significant correlation between sensory evaluation indicators andvolatile flavor compounds in this experiment.