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Quality and safety of fermented meat products

The project involves determining the relative role of muscle and bacterial (starter) enzymes in the hydrolysis and further metabolism of protein and fat during meat fermentation. The breakdown products of protein and fat are of key importance for product flavour. A better understanding of these will allow the development of guidelines for improving/standardizing the flavour and safety of fermented meat products. Some preliminary results are as follows: The relative importance of bacterial and meat enzymes in lipolysis (fat breakdown) and carbonyl production (flavour compounds) was evaluated during dry sausage ripening. It was concluded that the meat enzymes were more involved in this process than the bacterial lipases. In the case of protein breakdown in fermented sausages, it was confirmed that the muscle enzyme cathepsin D, activated by pH drop, was responsible for nearly all myosin and actin breakdown. However, up to 70% of further metabolism of peptides to amino acids was achieved by bacterial enzymes. The production of biogenic amines, such as tyramine and histamine, by over 30 starter culture bacteria is also being investigated as these amines are highly undesirable in dry sausages. The production of histamine was between 0 and 20 mg per ml while tyramine production is still being evaluated; currently high pressure liquid chromatography procedures are being developed to facilitate a better separation and quantification of the amines. Model systems are being used to evaluate bacteria strains as producers of volatile flavour components from amino acids. Preliminary results on two strains show specific differences. For example, strain A degrades isoleucine to 2-methylbutanal and the production of ethanol is stimulated; strain B gives 2-methylbutanal and 2-methylbutanol from isoleucine. In general, strain B produces more volatile compounds than A and is more active than a commercial starter.

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