Abstract
The objectives of this study were based on screening for presence of decarboxylase producing microorganisms (Enterobacteriaceae, Enterococci and Lactobacilli) in sour milk, yoghurt and labenh, collected from supermarkets in Ismailia City. The isolated strains were tested for decarboxylase activity and the levels of histamine, tyramine, putrescine and cadaverine were determined in the examined samples. The results revealed that all the examined samples were contaminated with EnterobacteriaceaeandEnterococci at variable counts. All the isolated strains of Enterobacteriaceae, Enterococci and Lactobacillus spp. have the potential to release decarboxylase enzymes with biogenic amines formation. The examined samples were found to contain the estimated amines with variable levels, expect yoghurt that didn't contain tyramine. In conclusion, there was a positive correlation between the type of microorganisms present in fermented milk and the type of biogenic amines formed. The prevention of biogenic amines formation in fermented milks could be achieved by following good hygienic measures and careful screening of lactic acid bacteria for amino acid decarboxylase activity before selecting as starter or probiotic strains in dairy industry.
Highlights
Fermented milk products such as buttermilk, sour cream, yoghurt, sour milk and labenh are popular dairy products
Biogenic amines can be formed in food primarily due to the release of specific amino acids and by the action of decarboxylases enzymes produced by certain microorganisms such as Enterobacteriaceae and Enterococci (Priyadarshani and Rakshit, 2011)
The ability of microorganisms to form biogenic amines was considered as strain specific property rather than a species related property
Summary
Fermented milk products such as buttermilk, sour cream, yoghurt, sour milk and labenh are popular dairy products. Biogenic amines can be formed in food primarily due to the release of specific amino acids and by the action of decarboxylases enzymes produced by certain microorganisms such as Enterobacteriaceae and Enterococci (Priyadarshani and Rakshit, 2011). The production property and storage period of fermented milk help the formation of biogenic amines by enhancing the activity of proteolytic microorganisms that increases the amount of free amino acids (Linares et al, 2011). The levels of existence of biogenic amines are related to numerous factors, such as the composition and availability of free amino acids, water activity, storage time, storage temperature, pH of the product and the presence of decarboxylase-positive microorganisms. The levels of the most prevalent biogenic amines such as histamine, tyramine, putrescine and cadaverine in the fermented milk samples were estimated
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