Part II-Volatile Profiles of Kiwi Kefir-like Beverages Influenced by the Amount of Inoculum, Shaking Rate, and Successive Kefir Grain Passages.

This study analyzes the aromatic profiles of kiwi-based fermented beverages, inoculated with varying proportions of milk kefir grains and incubated under different shaking rates. The experiments were designed using response surface methodology and three consecutive batch cultures were performed under each experimental condition. At the end of each fermentation, the grains were separated from the beverage and reused as the inoculum for fermenting fresh kiwi juice in the subsequent batch. Based on the results, together with the previously determined microbiological and chemical characteristics, two beverages were identified as having broader aromatic profiles, lower contents of sugars, ethanol, and acids, and high counts of lactic acid bacteria (LAB) and yeasts (>106 CFU/mL). These beverages were produced under relatively low agitation rates (38 and 86 rpm) and high inoculum proportions (4.33% and 4.68% w/v) during the second and third batch cultures, respectively. Over 28 days of refrigerated storage, the pH values of both beverages remained relatively stable, and the LAB counts consistently exceeded 106 CFU/mL. Yeast counts, along with the production of ethanol, glycerol, lactic acid, and acetic acid, increased slightly over time. In contrast, the concentrations of citric acid, quinic acid, total sugars, and acetic acid bacteria declined by day 28.