U.S. Department of Agriculture, Agricultural Research Service, Food Science and Market Quality and Handling Research Unit, Southeast Area, 322 Schaub Hall, Box 7624, North Carolina State University, Raleigh, North Carolina 27695-7624, USA.
J Food Prot. 2022 Sep 1;85(9):1273-1281. doi: 10.4315/JFP-22-068.
The pH changes that occur during the fermentation of vegetables by lactic acid bacteria depend on the production of weak acids and on the buffering of the fermentation medium. Undefined buffering components of fermentation media make estimates of pH from acid production difficult. The objective of this research was to develop buffer models for a model cucumber fermentation brine system linking pH changes to acid concentrations. A novel titration method was used to measure buffer capacity in cucumber juice medium made from three grades of pickling cucumbers based on diameter. Fermentation of juice made from cucumbers of different sizes resulted in differences in fermentation biochemistry. The results of modeling indicated that the pH of the medium after 24 and 48 h of fermentation by heterolactic Leuconostoc mesenteroides and homolactic Lactiplantibacillus pentosus could be predicted from acid concentrations based on the measured buffer capacity of the corresponding unfermented medium. The differences for all observed and predicted pH values of the fermentation samples, based on measured acid concentrations, had a root mean square error of 0.064 pH units. The buffer models included a quantitative measure of the effect on pH of the malolactic reaction caused by the lactic acid bacteria. These models may have application for assessing the influence of a variety of lactic acid bacteria buffering reactions on pH and fermentation ecology by linking pH to fermentation acid concentrations.
在乳酸菌发酵蔬菜的过程中，pH 值的变化取决于弱酸的产生和发酵介质的缓冲作用。发酵介质中未定义的缓冲成分使得根据产酸量估计 pH 值变得困难。本研究的目的是为黄瓜发酵盐水模型系统开发缓冲模型，将 pH 值变化与酸浓度联系起来。采用一种新的滴定方法来测量基于直径的三种腌制黄瓜的黄瓜汁培养基的缓冲能力。不同大小的黄瓜汁发酵导致发酵生物化学的差异。模型化的结果表明，在异乳酸乳球菌和同型乳酸植物乳杆菌发酵 24 和 48 小时后，基于相应未发酵培养基的测量缓冲能力，可以根据酸浓度预测培养基的 pH 值。基于测量的酸浓度，所有观察到的和预测的发酵样品的 pH 值之间的差异的均方根误差为 0.064 pH 单位。缓冲模型包括对由乳酸菌引起的苹果酸-乳酸反应对 pH 值影响的定量衡量。这些模型可用于通过将 pH 值与发酵酸浓度联系起来，评估各种乳酸菌缓冲反应对 pH 值和发酵生态学的影响。
