Effect of KCl replacement of NaCl on fermentation kinetics, organic acids and sensory quality of sauerkraut from Northeast China

High-throughput characterization of the effect of sodium chloride and potassium chloride on 31 lactic acid bacteria and their co-cultures

Salt (NaCl) is associated with a risk of hypertension and the development of coronary heart disease, so its consumption should be limited. However, salt plays a key role in the quality and safety of food by controlling undesirable microorganisms. Since studies have focused primarily on the effect of salts on the overall counts of the lactic acid bacteria (LAB) group, we have not yet understood how salt stress individually affects the strains and the interactions between them. In this study, we characterized the effect of sodium chloride (NaCl) and potassium chloride (KCl) on the growth and acidification of 31 LAB strains. In addition, we evaluated the effect of salts on a total of 93 random pairwise strain combinations. Strains and co-cultures were tested at 3% NaCl, 5% NaCl, and 3% KCl on solid medium using an automated approach and image analysis. The results showed that the growth of LAB was significantly reduced by up to 68% at 5% NaCl (p < 0.0001). For the co-cultures, a reduction of up to 57% was observed at 5% NaCl (p < 0.0001). However, acidification was less affected by salt stress, whether for monocultures or co-cultures. Furthermore, KCl had a lesser impact on both growth and acidification compared to NaCl. Indeed, some strains showed a significant increase in growth at 3% KCl, such as Lactococcus lactis subsp. lactis 74310 (23%, p = 0.01). More importantly, co-cultures appeared to be more resilient and had more varied responses to salt stress than the monocultures, as several cases of suppression of the significant effect of salts on acidification and growth were detected. Our results highlight that while salts can modulate microbial interactions, these latter can also attenuate the effect of salts on LAB.

Soluble sugar and organic acid composition and flavor evaluation of Chinese cherry fruits

Chinese cherry is an economically important fruit crop native to China. Flavor quality is greatly influenced by compositions of soluble sugars and organic acids. To better understand the flavor quality of Chinese cherry, we determined sugar and acid components in thirty-eight landrace and cultivar collections, and two wild resources using the HPLC method. Glucose and fructose were the main components, accounting for 85.91% of soluble sugars. Malic acid was the predominant organic acid, with an average proportion of 65.73% of total acids. Correlation and PCA analysis revealed seven key indicators for evaluating fruit flavor. Compared with wild Chinese cherry, the cultivated collections exhibited higher levels of soluble sugars, especially fructose, and lower levels of organic acid, particularly malic acid in fruits. Finally, we have established grading criteria for seven flavor indicators in Chinese cherry. Our study provides valuable references for identifying flavor compounds and improving flavor quality of Chinese cherry.

Exploring potential correlations between bacterial communities, organic acids, and volatile metabolites of traditional fermented sauerkraut collected from different regions of Heilongjiang Province in Northeast China

In this study, the bacterial communities and flavor metabolites of 27 traditional naturally fermented sauerkraut samples collected from nine regions of Heilongjiang Province in Northeast China were investigated. The dominant genera were Lactobacillus, Pseudomonas, Alcaligenes, Arcobacter, Pseudarcobacter, Lactococcus, Comamonas, Pediococcus, Prevotella, and Insolitispirillum. A total of 148 volatile compounds were detected in seven categories; esters and acids were the most abundant volatiles. Additionally, the highest content (15.96 mg/g) of lactic acid was detected in YC1. Acetic acid, oleic acid, palmitic acid, elaidic acid, and dehydroacetic acid were the key differential volatile compounds, which may be related to the bacterial communities. Spearman's correlation analysis revealed that Lactococcus and Lactobacillus were significantly positively correlated with flavor metabolites, suggesting that they may play a more significant role in flavor formation. The results of this study can help in the development of better quality of fermented vegetables.

Detection of the Inoculated Fermentation Process of Apo Pickle Based on a Colorimetric Sensor Array Method

Apo pickle is a traditional Chinese fermented vegetable. However, the traditional fermentation process of Apo pickle is slow, easy to ruin, and cannot be judged with regard to time. To improve fermentation, LP-165 (L. Plantarum), which has a high salt tolerance, acidification, and growth capacity, was chosen as the starter culture. Meanwhile, a colorimetric sensor array (CSA) sensitive to pickle volatile compounds was developed to differentiate Apo pickles at varying degrees of fermentation. The color components were extracted from each dye in the color change profiles and were analyzed using principal component analysis (PCA) and linear discriminant analysis (LDA). The fermentation process of the Apo pickle was classified into four phases by LDA. The accuracy of backward substitution verification was 99% and the accuracy of cross validation was 92.7%. Furthermore, the partial least squares regression (PLSR) showed that data from the CSA were correlated with pH total acid, lactic acid, and volatile acids of the Apo pickle. These results illustrate that the CSA reacts quickly to inoculated Apo pickle and could be used to detect fermentation.