Effect of container smoking and incubation temperature on the microbiological and some biochemical qualities of fermenting Ergo, a traditional ethiopian sour milk

Abstract

Raw milk was allowed to sour naturally at ambient temperature (25 °C) in smoked or unsmoked containers. Milk in smoked containers had a lower rate of pH drop and the fermented product had good flavour for a longer time after coagulation. The total count of non-lactic acid bacteria in milk in unsmoked containers reached a high count (> 108 cfu mL−1) within 12 h, whereas milk in smoked containers required more than 24 h to reach this level. Similarly, the growth of coliforms and lactic acid bacteria was slow in milk in smoked containers, thus assuring good and slow development of flavour components, safety of finished product and better keeping qualities. Lacto-bacilli dominated the flora of the fermented product in unsmoked containers, while lactococci were equally dominant in fermented milk in smoked containers. As the temperature of incubation increased (20 to 42 °C), the rate of pH drop also increased and the time of coagulation became shorter. At lower temperatures, the rate of acid formation was lower but the titratable acidity in the final products was higher. Milk incubated at lower temperatures had a better Ergo taste. The rate of growth of the various groups of bacteria increased with an increase in incubation temperature. At lower incubation temperatures, lactococci dominated the lactic flora, while lactobacilli dominated at higher incubation temperatures. Smoking of containers may help to produce a safer and tastier Ergo with better keeping qualities. In addition, lower incubation temperatures (around 20 °C) may favour the proliferation of lactic acid bacteria and thus guarantee a desirable fermentation.