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.

Keywords: Aflatoxin; Binding; Cheese; Decontamination; Lactic acid bacteria; Yeast.