Determination of decarboxylation activity and biogenic amines-producing ability of lactic acid bacteria isolated from shalgam

Serial dilutions from shalgam samples produced by traditional method were spread onto De Man Rogosa Sharpe (MRS) Agar and typical colonies were isolated. Out of 85 isolates, 56 confirmed as lactic acid bacteria (LAB). These isolates were identified as follow; 40 streptobacteria, 11 Lactobacillus spp., 3 Lactococcus spp., 1 Leuconostoc sp and 1 Streptococcus sp. Decarboxylase activity of isolates were tested using modified decarboxylase medium, added one of the histidine, ornithine, tyrosine, lysine, phenylalanine, arginine or tryptophan amino acids. Fifty three of 56 LAB isolates gave positive results for both arginine and tyrosine decarboxylase. One of the isolates (2C5) was tyrosine decarboxylase negative while two isolates (4C10 and 4E9) gave negative reaction for arginine decarboxylase. None of isolates could decarboxylate histidine, ornithine, lysine, phenylalanine or tryptophan. After LAB strains were grown in MRS Broth containing tyrosine and arginine, biogenic amines were detected quantitatively by HPLC (High Pressure Liquid Chromatography). All strains produced agmatine (105.78 ? 867.53 mg/l) and tyramine (24.52 ? 649.72 mg/l). Production of putrescine was not detected only for one isolate (0A8) while other isolates produced putrescine at the range from 2.09 to 33.34 mg/l. Tyrosine decarboxylase negative isolate (2C5) produced tyramine and arginine decarboxylase negative isolates (4C10 and 4E9) produced agmatine and putrescine. In other words, these three isolates gave false-negative results at decarboxylase test for corresponding amino acids. Although none of the isolates decarboxylated ornithine, almost all of the isolates produced putrescine suggesting these bacteria produced putrescine via agmatine deaminase or agmatinase and N-Carbomoylputrescine hydrolase enzymes. Therefore, it was concluded that during shalgam fermentation LAB were mainly responsible for tyramine and agmatine formation, as well as a small amount of putrescine.