Antibacterial activity of different formulations of cheese and whey produced with kefir grains

Resumo

The development of different products that confer health benefits on the population is a challenge for those
who work with food. The aim of this study was to elaborate two formulations of kefir cheese (C1 and C2) and whey (W1, W2),
and to evaluate their in situ antibacterial activity against microorganisms of interest in food. Pasteurized milk, powdered milk
and kefir grains were used in preparing the products and their percentage composition was determined. C1, C2, W1 and W2
were contaminated with five different logarithmic fractions (A = 8log to E = 4log CFU/ml) of Staphylococcus aureus (ATCC
25923) and Escherichia coli (ATCC 11229), with antibacterial activity assessed over 0, 24, 48 and 72 hours of exposure. The
results demonstrated the antibacterial activity of kefir cheese and whey, especially after 24 hours. Escherichia coli was the
most sensitive of the bacteria, with maximum antibacterial activity seen in the cheese at population densities D and E, and in
the whey at densities B, C, D and E after 48 and 72 h, showing that the in situ antibacterial activity of foods produced with
kefir grains tends to be lower when compared with studies in vitro. The greater the nutrient content of the food, the lower
the antibacterial activity seen, probably due to the protective action that the nutrients confer on the microorganisms against
bacteriocins and the metabolites from fermentation.