Utilization of various starter cultures in the production of Amasi, a Zimbabwean naturally fermented raw milk product

Abstract

Fermented milk was prepared from unpasteurised milk using natural fermentation (R), back-slopping (B) and by addition of two different starter cultures (C1 and DL). The numbers of Escherichia coli, coliforms, lactic acid bacteria (LAB) and the changes in pH, carbohydrates, organic acids and volatile compounds were recorded during 48-h fermentation. After 48-h fermentation, the highest numbers of E. coli were found in R and B fermentations and the lowest in the DL fermentation. The DL culture reduced the pH faster than the other starter cultures. The DL and C1 had higher levels of LAB in the beginning of the fermentation than the other two. Galactose and lactic acid increased fastest in the DL and C1 fermentation, and R was slowest. The highest levels of succinate, ethanol and malty compounds were found in the R and B fermentations. Lower levels of LAB in the first part of the fermentations, but higher number of E. coli could explain the increased levels of succinate, ethanol and malty compounds.