| Zha-Chili is a kind of local cuisine in ethnic minorities ChongQing, SiChuan, GuiZhou or Han nationality and ethnic minorities mixed ethnic area, which is made from the mixture of crushed fresh chili, starch raw material and salt by the method of natural lactic acid fermentation, there are a few industrialized production, but research in fermentation of Zha-chili is still rare, especially in the formation of flavor and the influence factors. This paper regards Zha-Chili made by natural lactic acid fermentation as the research object, adopts the common ingredients in southwestern China and add corn flour, taro and japonica rice powder to crushed fresh chili as raw material, response surface method were used to optimize the SPME (solid phase micro-extraction) extracting conditions, and made a comparative study on the formation of taste and aroma quality of Zha-chili with different starch raw materials, compared the similarities and differences of flavor component between SDE and SPME extraction technology. The main conclusions are as follows:1. Effect of different starch raw materials on the formation of taste quality during Zha-Chili processing(1) The changes of umami and sour taste components during processingWith the extension of fermentation time, the content of free amino acid, total acid and total organic acid were on the rise, especially the total organic acid in 90 days of fermentation rised to 1.83-4.26 times than that before fermentation. After fermentation, the content of lactic acid, acetic acid, malic acid and tartaric acid increased, the content of oxalic acid and citric acid decreased, lactic acid content was the highest and could reach 42.47%-78.48% of total organic acid content, which could plays a dominant position in acid-forming efeect. Furthermore, under the interaction of several kinds of organic acid, the unique acid tastes in Zha-Chili were constituted. These changes make Zha-Chili more full-bodied in umami and sour taste after fermentation.Due to the difference of starch ingredients, umami and sour taste quality of Zha-Chili were different. At late fermentation stage, free amino acid content from high to low were japonica rice> taro-com> corn; Total acid content of corn Zha-Chili was significantly lower than the other two samples; Among three kinds of starch-sources Zha-Chili, corn samples was relatively lower at lactic acid content and the increase than the two others after fermentation, but had higher malic acid content and the content of acetic acid, tartaric acid and oxalic acid were significantly lower than them, and might be related to the differences in available carbon source and the utilization rate of microbe to carbon source substrate vary from substrate to substrate.(2) The changes of sweet and salty taste components during processingWith the extension of fermentation time, salt content of Zha-Chili was ascended, the moisture content, total soluble sugar and reducing sugar contents appeared downward trends. At late fermentation stage, there have no big difference on salt content among three kinds of Zha-Chili, the moisture content of taro-corn Zha-Chili was obviously higher than that of the other two samples, both Total soluble sugar and reducing sugar contents from high to low were corn> japonica rice> taro-corn.(3) The changes of piquancy taste components during processingWith the extension of fermentation time, capsaicin and dihydro capsaicin content of Zha-Chili were in a downward trend, This is probably because capsaicin and dihydro capsaicin in Zha-Chili have been transformed to low pungency degree capsaicin analogues. These changes alleviate fresh chili’s irritant piquancy, and gave Zha-Chili more suitable piquancy taste. At late fermentation stage, the capsaicin content of japonica rice Zha-Chili was slightly lower than the other two kinds of Zha-Chili, corn Zha-Chili’s dihydro capsaicin content was significantly higher than the two others, showed that corn Zha-Chili have stonger piquancy taste than the two others.2. Effect of different starch raw materials on the formation of aroma quality during Zha-Chili processing(1) Optimization of SPME extractiong for aroma components from Zha-Chili by response surface methodologyAccording to the results of singal factor experiment, we fixed the NaCl concentration of 0.1 g/mL, desorption time of 3 min, and choose factors that have significant influence on extraction efficiency:extraction time, extraction temperature, extraction quality, and then did a 3-factor 5-level central composite design experiment, the results showed that the influence of extraction temperature and extraction quality on total peak area were extremely significant (P < 0.01), influence of extraction time and interaction between factors on total peak area were not significant; the model analysis showed that the best extraction conditions were: extraction temperature of 53.32 ℃, extraction time of 71.0 min and extraction quality of 2.36 g.(2) The results of aroma compounds in Zha-Chili extracted by SDE and SPMEBased on the aroma compounds determination of 0 days,45 days, 90 days Zha-Chili with different starch raw materials by SDE and SPME method, the category of volatile substances inZha-Chili have increased in various degrees during processing. Taro-corn and corn Zha-Chili reached the maximum variety at fermentation of 45 days, which were 174, 181 respectively, while, japonica rice Zha-Chili reached the maximum variety of 162 at 90 days. With comprehensive analysis of the main components in three kinds Zha-Chili at each fermentation stage, only palmitic acid, ethyllinoleate, ethyl palmitate and linalool were found at the whole fermentation stage; and substances have in common after fermentation was alpha-terpineol only. These five substances may be the common material of Zha-Chili. At the same time, due to the different on starch raw materials, the main volatile substances were different from the variety of Zha-chili, each kind of Zha-Chili have its characteristics.With more volatile substances been produced and the change of each material’s relative contents, made Zha-Chili had softer flavor and better taste after fermentation. In both extraction approaches(SDE, SPME), the quantity of ester had increased obviously during processing; By SPME extraction, there were some common changes of volatile substances among these three kinds Zha-Chili, which were the relative contents and variety of esters had increased greatly after fermentation, and the relative contents of alcohols also increased in different degree but have a lower increase level than esters, relative content of alkenes, ketones, aldehydes, pyrazine have decreased in different degrees.Compared with SDE method, more low boiling point and smaller compounds had extracted with SPME, and more high boiling point substance such as long-chain fatty acids and long-chain fatty acid esters had got with SDE, only by combing these two extraction methods, can comprehensive evaluation of Zha-Chili’s volatile flavor component be obtained, and the results would be more comprehensive and reliable; Throughout the entire process of All three kinds of Zha-Chili, the substances detected have in common between SDE and SPME extraction method were ethyl palmitate, ethyl linoleate, linalool and stearic alkyl aldehyde, both taro-corn and corn Zha-Chili had 12 kinds of substances in common between SDE and SPME, and 9 kinds of substances were the same, besides, the kinds of substances had in common in japonica rice Zha-Chili were 4, this indicated that for both taro-corn and corn Zha-Chili have corn in them, that is to say there are some similarities in starch sources, there exist a certain degree of similarity in flavor substances between them.After three kinds of starch source Zha-Chili been extracted by SDE, we found that except that the main materials after fermentation for japonica rice Zha-Chili were esters and alcohols, the main materials in other samples that found before and after ferment were all acids and esters; After SPME extracting, the main materials been detected befor ferment were alcohols and aldehydes, while, after fermentation were esters and alcohols.(3) The sensory quality of Zha-Chili and the evaluation of aroma substances by principal component analysis Through the sensory evaluation, we found that taro-corn and corn Zha-Chili had best quality during 45 to 60 days fermentation, while japonica rice Zha-Chili was during 45 to 90 days, and corn Zha-Chili owned better sensory quality obviously than the other two kinds of Zha-Chili, and taro-corn Zha-Chili’s sensory quality was slightly better than that of japonica rice Zha-Chili; Based on the evaluation of aroma substances in Zha-Chili made by different starch sources by principal component analysis, it show that taro-corn and corn Zha-Chili owned better aroma quality than japonica rice Zha-Chili; considering the change of volatile compound’s relative contents and category during processing and principal component scores after fermentation, the suitable fermentation time for corn and taro-corn Zha-Chili were from 45 to 60 days, while, japonica rice Zha-Chili was suitable to fermented 90 days. |
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