Biotransformation of aflatoxin by lactic acid bacteria

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Title: Biotransformation of aflatoxin by lactic acid bacteria
Author: Bredehorst, Swantje
Other contributor: Helsingin yliopisto, Maatalous-metsätieteellinen tiedekunta
University of Helsinki, Faculty of Agriculture and Forestry
Helsingfors universitet, Agrikultur- och forstvetenskapliga fakulteten
Publisher: Helsingin yliopisto
Date: 2022
Language: eng
Thesis level: master's thesis
Degree program: Elintarviketieteiden maisteriohjelma
Master's Programme in Food Sciences
Magisterprogrammet i livsmedelsvetenskaper
Specialisation: ei opintosuuntaa
no specialization
ingen studieinriktning
Abstract: Aflatoxin B1 (AFB1) is among the most potent carcinogens and mutagens known and significantly contributes to liver cancer. Mycotoxin contaminated crops, such as maize, groundnuts, or cocoa beans, are often destroyed, leading to a waste of resources. Recently, biotransformation of AFB1 by lactic acid bacteria (LAB) has been receiving growing attention. Biotransformation refers to structural change induced by enzymes or bacteria and can yield modified compounds of lower toxicity or non-toxicity compared to their precursors. Despite this growing interest, previous studies have primarily focused on the AFB1-reduction potential of LAB and biotransformation products have not been studied extensively. Therefore, this work aimed to screen twelve LAB for AFB1 biotransformation properties and analyze its degradation products. LAB were incubated in growth media for 24, 48, or 72 hours and ultra-performance liquid chromatography with fluorescence detection (UPLC-FL) was employed to measure AFB1-reduction and determine whether new fluorescent compounds appeared. Ultra-performance liquid chromatography with quadrupole time-of-flight mass spectrometry (UPLC-QTOF-MS) was used to assess the structure of the degradation products. The highest biotransformation was achieved by Lactobacillus helveticus FAM22155 (28.9 % after 72 h) and Lactobacillus helveticus FAM19191 (19.7% after 72 h). Two new peaks at 2.0 and 3.3 min retention time were observed with UPLC-FL and considered as possible degradation products. As the amount of the latter compound was very low, it could not be further analyzed. The peak at 2.0 min had a mass-to-charge ratio of 207. Two possible structures for this compound were proposed, but due to low intensities, further studies to confirm the structure are needed. This study showed that Lactobacillus helveticus can reduce almost a third of the AFB1 concentration. However, this study highlighted the challenges of identifying degradation products, and it was concluded that the extraction prior to MS should be optimized to identify degradation products. Determining the structure of the degradation products is necessary in order to evaluate whether the biotransformation results in less toxic products. In addition to evaluating the biotransformation efficacy in complex food matrices, it should be studied to determine whether biotransformation represents a promising means of reducing AFB1.

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