The effect of storage temperature on the physicochemical characteristics, volatile compounds and microbial community of a traditionally fermented dairy product

Traditional fermentation is a widespread household practice among women and small-scale processors in rural communities globally. However, limited refrigeration poses a challenge for proper storage, often resulting in products being kept at ambient conditions before consumption. We examined the effect of temperature on the quality characteristics and microbial community composition of two variants of mabisi, a spontaneously fermented dairy product from Zambia. Samples were analyzed for their volatile organic compounds and physicochemical properties, including pH and total titratable acidity (TTA) over a storage period of 24 days at refrigeration temperatures (chilled, ≈4.5 °C) and 16 days at ambient temperatures (un-chilled, 22.7 °C). The microbial counts and community composition were determined using culture-based and non-culture-based techniques. Bacterial communities were identified and classified through sequencing the V3–V4 region of the 16S rRNA gene, while the yeast communities were identified using internal transcribed spacer (ITS) sequencing. Minimal variations in pH and TTA were found at the onset of storage. As post-acidification became more prominent towards the end of the un-chilled storage, a clear distinction was noticed between the chilled and un-chilled regarding their volatile organic compounds. The bacterial communities for the two variants were stable at ambient and refrigeration temperatures, but the yeast communities varied markedly towards the end of the un-chilled storage with a drop in the total microbial counts. Overall, limited post-acidification during chilled storage indicated the ability of low temperatures to enhance shelf life.