Effect of added proteinases and level of starter culture on the formation of biogenic amines in raw milk Manchego cheese

The influence of two proteinases (Bacillus subtilis neutral proteinase and Micrococcus sp. cysteine proteinase) and two starter culture levels (0.1% a nd 1%) on biogenic amine formation has been studied in raw ewes' milk Manch ego cheese. Amino acid decarboxylating micro-organisms were determined on t yrosine enriched selective media. Biogenic amines were analysed by capillar y electrophoresis in citrate buffer at pH 3.6. Addition of proteinases and level of starter culture did not influence the population of micro-organism s with amino acid decarboxylating activity, which represented on average 1% of the bacterial population in 30-day-old cheeses. Tyramine and histamine were detected in all batches of cheese from day 30. Concentrations of tyram ine and histamine were higher in cheeses made from milk with neutral protei nase (up to 356 and 284 mg kg(-1), respectively, after 90 days) than in che eses made from milk with cysteine proteinase (up to 269 and 189 mg kg(-1) r espectively) or with no proteinase added (up to 305 and 226 mg kg(-1), resp ectively). Formation of tyramine and histamine was also favoured in cheeses made with 1% starter culture with respect to cheeses made with only 0.1% s tarter culture, probably due to the higher pH values of the former cheeses. After 90 days of ripening, concentrations of 10-20 mg kg(-1) phenylethylam ine were observed in 9 of the 12 batches, and levels < 10 mg kg(-1) tryptam ine were only detected in 3 batches, with no significant relationship betwe en the concentration of these amines and proteinase addition or level of st arter culture. (C) 1999 Elsevier Science B.V. All rights reserved.