Construction Flavor Finger Porint Of Yoghurt With High Quality

The yogurt is one kind of fermented dairy products fermented by Lactobacillus bulgaricus and Streptococcus thermophilus, which uses fresh milk as the main raw material and also contains a lot of viable lactic acid bacteria. The volatile components in the yogurt mainly comes from three ways:①raw milk;②processing, such as the changes caused by heating and homogenizing;③metabolites of microorganism in milk. The methods of extracting volatile flavor compounds of yogurt consist of static headspace extraction, dynamic headspace extraction, solid phase extraction, supercritical fluid extraction, simultaneous distillation extraction, purge-coldtrap capture technology and solid phase micro-extraction. SPME is a pre-processing technology of sample in1990s in the world. Compared with the traditional flavor substances extraction methods, SPME is a simple and effective adsorption-elution technique, the extraction is simple, rapid, economic security, solvent-free, good selectivity and high sensitivity, which can be directly associated with gas chromatography-mass spectrometry (GC-MS), high performance liquid chromatography (HPLC), capillary electrophoresis (CE). The combination of the sampling, extraction, concentration, injection can greatly accelerate the speed of analysis so that it can be used for volatile components detection in cream and dairy products.This topic using the headspace solid phase micro-extraction method to deal with raw milk and yogurt, and extracts were separated and identified by GC-MS. The extraction fibre, extraction time, extraction temperature were optimized, and the better operating conditions were determined. The characteristics of volatile flavor compounds in yogurt of the different fermentation stages were detected and classified, and the MS data was automatically retrieve by the NIST2005standard library, and the detection results were contrasted according to the standard atlas. The relative content of each component was calculated by the area normalization method. The data was analyzed by statistical software SAS8.2. The natural logarithm of orthogonal results of stir options, adsorption time, adsorption temperature and content of sodium chloride added was taken, and the significant analysis of variance of test groups was carried out with Duncan test. The volatile components which played a major role in various stages of yogurt were analyzed, and the flavor substances which played a major role in each stage were determined. The several main stages of fermentation process were determined by using factor analysis.In this study the ultimately method of detection the volatile components in the yogurt was as follows, after3g sodium chloride was added, the sample was stirred for30min at45℃. The detection condition is as follows, samples were retained for4min at40℃, and subsequencely heated to140℃while the heating rate was5℃/min, then retained for10min. Again the samples were heated to210℃while the heating rate was5℃/min, then retained for12min. The Inlet temperature was240℃. The FID detector temperature was260℃. The flow rate of carrier gas was lml/min. At last19kinds of flavor components were determined, and the trend of change over time of characteristic components such as dual-acetyl, acetic acid and palmitic acid were derived. And5vectors were used to demonstrate the yogurt fermentation process and flavor characteristics during different stages of fermentation by principal component analysis. In this study, fatty acid content of raw milk and yogurt were detected, and the trend of the different fatty acids at different fermentation stages was determined.Based on the above experimental results, the conclusion of this subject was drawn as that by principal component analysis, the volatile components of yogurt during various fermentation stages changed apparently over time, and some components only were detected at the end of fermentation and in the final product, such as1-hydroxy-2-acetone,3-penten-2-ol, etc.. Based on the above analysis, it is likely that this kind of flavor compounds with larger molecular weight and complex structure is not dominant in the competitive adsorption of SPME, although which were produced in the early fermentation process, but the content was not enough to be detected. During the fermentation process, the test data showed that after four hours the content of material detected reached to the stable period, and there was no significant change during the later fermentation process. The characteristic flavor of yogurt obtained was similar to the research of others, which consisted of diacetyl, acetic acid, methyl formate and palmitic acid. During principal component analysis, these several types of ingredients got a moderate score of each component, in line with small changes of these substances during fermentation process. Moreover, these several types of substances produced at the beginning, the concentrations were lower, and gradually increased with time, but was not linear. It’s possible that the real circumstances at the sampling points were truly as this, but it could not be ruled out that the characteristics of SPME led to the material determined were less competitive at the sampling point. This possibility exited in this process, but the rationality of other points can not be denied, such as diacetyl. After the data of sampling at3.5hours was removed, all the other data of the early four hours increased gradually over time. Throughout the fermentation process the composition of volatile substances showed a jumping distribution, but the increasing trend was unchanged. In further study, reducing the sampling point interval can solve the problem.