Aflatoxin M1 absorption by non-viable cells of lactic acid bacteria and Saccharomyces cerevisiae strains in Frescal cheese

Abstract

The purpose of this study was to evaluate the ability of heat-killed cells (121 °C, 10 min) from two strains of lactic acid bacteria (LAB) (Lactobacillus rhamnosus and Lactococcus lactis) and one strain of yeast (Saccharomyces cerevisiae), alone or in combination, to reduce the levels of aflatoxin M1 (AFM1) in Frescal cheese during 30 days of storage. The experimental design was totally randomized, in a 2 × 2 × 2 factorial arrangement, corresponding to two levels of LAB (0 and L. rhamnosus at 1010 cells/kg + L. lactis at 1010 cells/kg), two levels of S. cerevisiae in milk (0 and 1010 yeast cells/kg) and two AFM1 levels (0 and 0.5 µg/kg) added to the cheese curd, totaling 8 treatments with three replicates per treatment. AFM1 levels in Frescal cheese were evaluated by using a high-performance liquid chromatography. Cheese fat and protein contents were not affected (P > 0.05) by any of the treatments, and only pH decreased (P < 0.05) in all treatments from days 2 to 30 of storage (usual shelf life of this type of cheese). AFM1 levels detected in contaminated cheeses decreased on day 2 of storage, varying from 0.09 µg/kg (cheese with addition of bacterial cells) to 0.29 µg/kg (no addition of LAB or yeast cells), this may have occurred due to loss of AFM1 in the Frescal cheese whey. The concentrations of detected AFM1 decreased (P < 0.05) in all treatments from days 2 to 10 of storage, and the maximum percentage reduction of the detectable levels (100%) was achieved after 10 and 20 days of storage in cheeses containing LAB and yeast cells, or prepared with yeast cells alone, respectively. The addition of heat-killed LAB (cells of L. rhamnosus and L. lactis) and Saccharomyces cerevisiae alone or in combination, has a potential ability for adsorbing the AFM1 in Frescal cheese during 30 days of storage.