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Evaluation of the efficiency of lactic acid bacteria and Saccharomyces cerevisiae in reducing the availability of aflatoxin M1 in Minas Frescal cheese

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Bruna Leonel Gonçalves
Total Authors: 1
Document type: Doctoral Thesis
Press: Pirassununga.
Institution: Universidade de São Paulo (USP). Faculdade de Zootecnica e Engenharia de Alimentos (FZE/BT)
Defense date:
Examining board members:
Carlos Humberto Corassin; Adriano Gomes da Cruz; Cintia Bernardo Gonçalves; Carlos Augusto Fernandes de Oliveira; Anderson de Souza Sant'Ana; Vildes Maria Scussel
Advisor: Carlos Humberto Corassin; Eliana Setsuko Kamimura

The present study aimed to: a) evaluate the occurrence of AFM1 in seven different dairy products, with official inspection, that produced Minas Frescal cheese with or without the addition of milk yeast and b) evaluate the efficiency of lactic acid bacteria and Saccharomyces cerevisiae in reducing availability of AFM1 in Minas Frescal cheese. The determination of AFM1 of the first and second stages were performed by high performance liquid chromatography (HPLC - Shimadzu®, 10VP, Kyoto, Japan) with fluorescence detector (RF-10AXL). In the occurrence stage 34 samples (40%, n = 84) showed detectable levels of AFM1, including 11 (39%), 15 (54%) and 8 (29%) samples of raw, pasteurized milk and cheese, respectively. All samples were within the tolerance limits adopted in Brazil for AFM1 in milk (0.5 µg / L) and cheese (2.5 µg / kg). In the second stage, the binding capacity of two strains of lactic acid bacteria (BAL) was evaluated: 1) Lactobacillus rhamnosus (LRB, SACCO, Cadorago, Italy) and 2) Lactococcus lactis (MWO, SACCO, Cadorago, Italy) and one strain yeast, Saccharomyces cerevisiae (Fermentis K-97, SafALe, Belgium) to reduce the availability of AFM1. For this, Minas Frescal cheese was produced at the Dairy of the Faculty of Animal Science and Food Engineering (Campus Fernando Costa) and at the time of the addition of AFM1, starter culture or S. cerevisiae, due to the risk of contamination of the dairy, the curd was transferred to the Food Microbiology and Mycotoxicology Laboratory (LMMA) to finalize cheese production. The experimental design was completely randomized, in a 2 × 2 × 2 factorial scheme, corresponding to two levels of BAL starter culture (0 and L. rhamnosus 1010 cells/g + L. lactis 1010 cells/g), two levels of S. cerevisiae (0 and 1010 yeast cells/g) and two levels of AFM1 (0 and 0.5 µg/kg) in the cheese curd, totaling 8 treatments with three replicates per treatment. AFM1 was determined on days 2, 10, 20 and 30 after cheese production. The physical chemical (pH, fat content and protein percentage) and microbiological analyzes (Staphylococcus coagulase positive, Coliforms at 45 ° C, Salmonella sp. and Listeria monocytogenes) were performed on days 2 and 30 after cheese production. Only the pH decreased (P <0.05) in all treatments from day 2 to day 30 of storage. There was no presence of pathogenic bacteria in Minas Frescal cheese over the experimental period and the Coliform counts at 45 ° C were within the limits of the legislation. Therefore, the use of BAL and S. cerevisiae to reduce AFM1 in Minas Frescal cheese had no negative effect on the shelf life of this cheese. The AFM1 reduction varied according to the microorganisms used and S. cerevisiae showed greater capacity to bind AFM1. In the third stage, the interaction between the microorganisms used and AFM1 was evaluated by scanning electron microscopy. Analyzes were performed on days 2 and 30 after cheese production. A scanning electron microscope (HITACHI, TM 3000) with a backscattered electron detector was used at 15 kV to view each sample at 5000x magnification. The analysis by scanning electron microscopy allowed to verify the binding of both BAL and S. cerevisiae to AFM1 particles in Minas Frescal cheese. The addition of Saccharomyces cerevisiae or Lactobacillus rhamnosus and Lactococcus lactis cells inactivated by heat, alone or in combination, has the potential to reduce the levels of AFM1 in Minas Frescal cheese during the 30 days of storage without affecting the validity of this cheese. (AU)

FAPESP's process: 17/19683-1 - Evaluation of the efficiency of lactic acid bacteria and Saccharomyces cerevisiae in reducing the bioavailability of aflatoxin M1 in Minas frescal cheese
Grantee:Bruna Leonel Gonçalves
Support type: Scholarships in Brazil - Doctorate