| In this research,5 different kinds of chili peppers common to Zunyi were used as raw materials,and various quality indexes were comparatively analyzed before and after natural fermentation,and the volatile components of chili peppers before and after fermentation were determined by HS-SPME-GC-MS,while a variety suitable for fermentation of chili sauce was selected;And to screen the combinations of odorous and lactic acid bacteria species that are suitable for fermenting chili sauce,optimize its fermentation process,and analyze systematically the changes of major components of chili sauce during fermentation,thereby playing an important role in improving the quality of fermented chili and the development of Zunyi pepper industry.The following are the study’s primary conclusions:(1)Analysis of the changes of various quality indexes of 5 different varieties of peppers common in Zunyi before and after fermentation The findings demonstrated that chilli fermentation was significantly influenced by variety.The main organic acids were oxalic acid and citric acid;the main flavouring amino acids were sweet amino acids;the flavouring substances were mainly esters,terpenoids and aldehydes.The colour,amino acid nitrogen and carotenoid content of the fermented chilli sauce were significantly different(P<0.05),with the highest brightness in P4.F4 showed the least reduction in viscosity and the fermented sample(P4)had a high viscosity,with malic acid being the main organic acid;the fresh tasting amino acids had a more significant flavour than the sweet tasting amino acids,with the highest content of both in P4,reaching 1 336.21±32.97 mg/kg and 1 033.75±29.66 mg/kg.The main flavour substances of the fermented chilli sauce were mainly alcohols,ketones and a few aldehydes;P4 was richer in volatile components,showing more floral and fruit aromas,and the sensory evaluation showed the same results.To sum up,F4(Niujiao pepper)was selected as the raw material for the fermented chilli sauce and the subsequent fermentation experiments were carried out.(2)Using the pepper selected in Chapter 1 as raw material,four common yeast strains including Candida tropicalis,Pichia kudriavzevii,Metschnikowia pulcherrimaand Hanseniaspora uvarum were investigated for tolerance characteristics and the fermentation characteristics(total ester content,basic physicochemical index,organic acid)of the four yeast strains were determined together with the fermentation characteristics of Lactobacillus plantarum XZ3,which was selected from the natural fermented chilli products.Then the combination of strains suitable for fermented chili sauce was screened by sensory evaluation and total ester content.The fermentation process of chili sauce was optimized by combining single-factor and response surface tests at last.The results showed that all four strains of yeast could grow at pH 8 and salt concentration of 8%,which met the requirements of fermentation.The fermentation experiments with single and mixed bacteria revealed that the content of organic acids in the different samples varied depending on the strain they were inoculated with.Acetic acid and citric acid were only higher in the samples fermented by Lactobacillus plantarum;The total ester contents were higher in samples fermented with Metschnikowia pulcherrima,Candida tropicalis and Lactobacillus plantarum,and the sample fermented by Lactobacillus plantarum had the lower total ester content.The sensory evaluation of the four mixed fermentation combinations did not differ much,and combined with the weighting and de-quantitative treatment,Candida tropicalis in combination with Lactobacillus plantarum species performed the best,so this combination was selected as the fermentation strain of chili sauce.The optimum fermentation conditions were obtained by response surface optimisation with a 1:1 ratio of Lactobacillus plantarum XZ3 to Candida tropicalis,2%mixed bacteria addition,3%salt addition and 4 d fermentation time.(3)The optimized fermentation conditions were used to ferment the chili sauce,and the changes of basic physicochemical indexes,flavor components and antioxidant capacity were analyzed during the fermentation process.The results showed that the total acid and amino acid nitrogen content increased continuously during the fermentation process,reaching 1.67%and 0.21%at 60 h.The reducing sugar content showed a sharp decrease and then remained stable gradually;the nitrite content showed a trend of increasing and then decreasing,and its content decreased sharply at 24 h,which indicated that Lactobacillus plantarum XZ3 and C.tropicalis produced nitrite reductase content at a faster rate.The natural capsaicinoids showed fluctuating changes,dihydrocapsaicinoids showed a decreasing trend,but the content of capsaicinoids after fermentation decreased to a certain extent compared with unfermented pepper(0 h);the total organic acids increased and then decreased at 72 h(33.95±2.63 g/kg),and their species increased after fermentation with lactic acid,malic acid and citric acid being the main carbon sources of fermentation;the total phenols in general showed a trend of rising and then falling,reaching a maximum of 7.29 mg GA/g DW,with the growth rate of total phenols at 25%;total flavonoids showed a rising trend,with the content elevated by 13%before and after fermentation;a total of 10 major polyphenolic substances were detected,with rutin as the main polyphenolic substance.There was no significant change in the ABTS~+scavenging ability and reducing ability of the chilli sauce before and after fermentation,but the scavenging ability of DPPH radicals and hydroxyl radicals increased;the composition and content of flavour substances during fermentation changed significantly,gradually shifting from alcohols and aldehydes to esters,alcohols and ketones,with esters,alcohols and ketones becoming the characteristic flavour substances of fermented chilli sauce.Compared to the flavour substances of high-salt fermented chilli sauce,the flavour substances of chilli sauce,especially the types of esters,alcohols and ketones,were significantly increased by the addition of aroma-producing yeast and Lactobacillus plantarum fermentation,giving the chilli sauce a rich fruity and floral flavour.The fermented chilli sauce can also be clearly distinguished from fresh chillies in the PCA diagram of the electronic nose.In conclusion,it is recommended to use C.tropicalis and Lactobacillus plantarum XZ3 mixed bacteria fermentation of Niujiao pepper,the best process of compounding is the ratio of Lactobacillus plantarum XZ3 to C.tropicalis 1:1,the amount of mixed bacteria added 2%,salt added 3%,fermentation time of 4 d.The pepper sauce obtained by this process is bright,flavorful,sour and spicy.The content of total phenols and total flavonoids in chili sauce has been significantly increased,and the content of esters,alcohols,and ketones has increased significantly,giving chili sauce rich floral and fruity aromas. |
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