Physicochemical and microbiological changes during two-stage fermentation production of umqombothi

Abstract

Umqombothi is a traditional South African fermented beverage. The brewing process limits its consumption to a day or two after production due to the constant production of carbon dioxide. In this study the physicochemical and microbial changes in Umqombothi produced at two-stage fermentation temperatures [U1 (30-30 °C), U2 (30-25 °C), U3 (25–30 °C)] were studied over 52 h. Samples were collected before first fermentation (BFF), after first fermentation (AFF), before second fermentation (BSF), after second fermentation (ASF) and after final product (FP). For all three fermentation temperatures, there was a significant increase (p < 0.05) in microbial counts and a significant drop in pH following fermentation stages (AFF and ASF), with a considerable decrease in total soluble solids (TSS) after ASF. The total viable count (TVC), lactic acid bacteria (LAB), yeast, and mould were not detected in the BSF samples for all three fermentation temperatures. The LAB count was significantly (p < 0.05) different at 5.18, 5.36 and 5.25 log CFU/mL for U1, U2 and U3, respectively. The pH was 3.96, 4.12 and 4.34 for U1, U2 and U3, respectively, and was significantly (p < 0.05) different. Total soluble solids significantly (p < 0.05) increased at the BSF at all temperatures. There was no significant (p > 0.05) difference in specific gravity and ethanol content of Umqombothi at all fermentation temperatures. At all fermentation temperatures, Umqombothi was characterised by redness and yellowness, with that collected from U1 being the lightest in colour (L* = 71.24). Colour difference (ΔE) in the between of 4–8 was perceivable but acceptable as they had a ΔE value of 3.58, 2.07 and 2.02 for U1–U2, U1–U3 and U2–U3 respectively. Umqombothi produced at 30 °C for first and second fermentation (U1) was the most preferred by the consumer panellist and consequently, the best fermentation temperature to produce Umqombothi.