Hygienic quality and incidence of histamine-forming Lactobacillus species in natural and processed cheese in Taiwan

Thirty-one natural cheese and 39 processed cheese products were collected from food markets in Taiwan and analyzed for bacterial content and histamine-related quality. The natural cheese samples had < 1 to 6.84 log colony forming unit (CFU)/g of aerobic plate count (APC) and < 3 to 60 most probable number (MPN)/g of total coliform (TC). On the other hand, the processed cheese products had < 1 to 4.57 log CFU`/g of APC and < 3 to 30 MPN/g of TC. None of the tested samples contained Escherichia coli. Only 2 of the natural cheese and 2 of the processed cheese products contained more than 10 MPN/g of TC, which is beyond the regulatory limit of hygienic quality. The tested natural cheese products had an average histamine content of 7.9 mg/100 g, while 17 of them (54.8%) had histamine content greater than the 5 mg/100 g limit set by the U.S. Food and Drug Administration for scombroid fish and/or product. In contrast, only 6 processed cheese products (15.4%) had histamine levels greater than this limit. The average content of the other 8 biogenic amines in all tested samples was lower than 2 mg/100 g. Among the 37 presumptive histamine-forming bacterial colonies isolated from the natural cheese products, 15 produced histamine, ranging from 6.4 to 16.4 ppm, in MRS broth supplemented with 0.25% L-histidine. These histamine-producing bacteria were identified as Lactobacillus spp. Of the 7 L. brevis identified, one produced 71.2 ppm of tyramine in histidine-supplemented MRS broth.