Monitoring The Fermentation Process Of Homemade Apo Pickle Based On Colorimetric Sensors

In recent years,as the concept of healthy living gradually deepens,more and more young people living in urban areas are making homemade fermented foods,especially fermented vegetables.As a representative of traditional fermented vegetable food in the Jiangnan region,the Apo pickle is popular for its effectiveness in relieving summer heat and enhancing appetite.It has become a major pickled vegetable in many families.Traditional Apo pickles are mainly based on natural fermentation at home,which is still not industrially produced and has no standardized pickling process.There are many factors affecting the quality of its finished products.When pickled at home,its fermentation endpoint is difficult to judge,and its quality is difficult to control.This thesis identifies the characteristics of the traditional fermented Apo pickle,determines the main pickling process parameters for the traditional fermentation of the Apo pickle,screens fermentation strains for standardized fermentation,and prepares a simple label for nondestructive testing of the Apo pickle,provides fermentation tools,techniques,and testing methods for modern homemade Apo pickle.The specific study contents and results are as follows:(1)The biochemical properties of traditional Apo pickles were examined at the ripening stage,and the effect of pickling time and salinity on fermentation was studied.The results showed that the total acid during the ripening period was about 7.00 g/Kg when the nitrite content was 3.58 mg/Kg,which was lower than the national safety standard 20 mg/Kg;the nonvolatile organic acids were mainly lactic acid and acetic acid,and the volatile substances were mainly acids,esters,and alcohols;The dominant genus in the late fermentation stage was Lactobacillus,of which the main strains were Lactobacillus sakei and Lactobacillus zymae;the optimal conditions for pickling were determined as 8% salt addition and pickling two days,which possessed faster fermentation speed and fermentation quality.(2)The specific process of traditional fermentation of Apo pickle was analyzed.The colorimetric sensor array(CSA)was constructed and optimized according to the fermentation characteristics of pickles.Finally,the CSA was applied to detect the traditional fermentation process of Apo pickles.The results show that fermentation does not mature until 49 days at15°C when the p H drops to 4.0,and the total acid exceeds 7.00 g/Kg;the organic acids were mainly lactic acid and acetic acid,and the lactic acid gradually increased with the fermentation time,and the volatile substances were mostly esters at the beginning of fermentation,and mainly acids and aldehydes at the end of fermentation;The CSA data were classified using principal components analysis(PCA)and linear discriminant analysis(LDA),and the LDA had better classification results compared to PCA.The backtracking validation of the CSA before and after optimization was 94.79% and 100%,and the cross-validation was 78.13% and 90.63%,respectively,indicating that indicator sensitization can improve the colorimetric sensor resolution.The optimized CSA results were fitted to the physicochemical index results using the partial least squares regression(PLSR),with correlation coefficients of 0.85 and 0.71 for p H and total acid,respectively.(3)LP-165 is Lactobacillus plantarum,which has good salt tolerance,fast acid production,and strong growth ability.It was screened from seven lactic acid bacteria as the fermentation strain.It compared the fermentation process of inoculated and non-inoculated Apo pickles at25℃.The results showed that the total acid of inoculated Apo pickle exceeds 7.00 g/Kg on the fifth day,and the fermentation was mature,LP-165 significantly improving the fermentation speed.In contrast,it took 30 days to ferment and mature for the same fermentation temperature without inoculated fermentation and was prone to quality problems such as spoilage.The inoculated fermentation increased the organic acid content of Apo pickle,especially lactic acid and acetic acid,but in the volatile species,were less than natural fermentation,mainly acids;the backtracking verification and cross-validation of the LDA results of CSA for the inoculated fermented Apo pickle were 100% and 92.71%,respectively,and the correlation coefficients with p H and total acid were 0.70 and 0.75,respectively.(4)CSA was applied to the interior of the vessels of Apo pickle inoculated fermentation.The fermentation process was monitored in real-time,and both PCA and LDA had correct classification results,with 100% and 92.85% backtracking and cross-validation for LDA,respectively.The natural dye Butterfly bean flower(Clitoria ternatea,CT)anthocyanin and the chemical dye Methyl red sodium salt-Bromocresol green(MB)were also used as indicators mixed with gelatin and starch to make colorimetric membranes,CTSG and MBSG,respectively,in order to determine the fermentation status visually by the color change of the film.The physical properties of the colorimetric films and their practical applications showed that both CTSG and MBSG could successfully indicate the fermentation endpoints of Apo pickle,and the anthocyanins were not only safe and non-toxic but also improved the performance of the films compared with chemical dyes.