Serap Cosansu

Some growth parameters and antimicrobial activity of a bacteriocin-producing strain Pediococcus acidilactici 13

Some growth parameters and bacteriocin production by the strain Pediococcus acidilactici 13, were screened in this study. The inhibitor substance produced by this strain showed strong antimicrobial activity at 204,800 AU/mL (Activity Units/mL) against the gram positive food borne pathogen, Listeria monocytogenes, when the incubation temperature was 37 degrees C and the initial pH of the medium, TGE (Trypton Glucose Yeast Extract), was 6.0. The bacteriocin-producing strain had considerable resistance NaCl, since the strain maintained to growth up to 10% NaCl concentrations at TGE broth and was able to grow in a wide temperature range (25-50 degrees C). The strain was identified as P. acidilactici with API 50 CHL, as well as with 16S rRNA gene sequencing.

Survival of Salmonella Enteritidis during salting and drying of horse mackerel (Trachurus trachurus) fillets

Survival of Salmonella Enteritidis inoculated (5-6 log cfu/g) on horse mackerel fillets was studied during salting and/or drying processes at 4 degrees C for up to 70days. Sample groups were as follows: group A (salt/fish=80/100), group B (salt/fish=30/100), group C (salted as group A and dried after 15days), group D (salted as group B and dried after 15days), and group E (dried without salting). The salt content increased in all groups with a maximum level of 29.36%. Final salt contents (%) were higher (P<0.05) in salted-dried groups (C and D) than the salted groups (A and B). Total reductions in a(w) values were found as group E>group D>group C>groups A and B (P<0.05). Salmonella survived 60days in group A, 65days in group B, 35days in group C, 45days in group D and 20days in group E. Drying process following salting accelerated the elimination of this pathogen. Salmonella survived longer in salted samples than in salted-dried and dried samples. This work demonstrated that Salmonella may be inhibited by one of salting, drying and salting-drying techniques; however, processing periods should be long enough to reduce a(w) sufficient to inhibit this pathogen.

Amino acid decarboxylase activities and biogenic amine formation abilities of lactic acid bacteria isolated from shalgam

ABSTRACT 56 lactic acid bacteria were isolated during shalgam fermentation and identified as Lactobacillus spp. (51 isolates), Lactococcus spp. (3 isolates), Streptococcus sp. (one isolate), and Leuconostoc sp. (one isolate). 53 of all isolates decarboxylated both arginine and tyrosine, while others decarboxylated one of arginine or tyrosine. None of the isolates could decarboxylate histidine, ornithine, lysine, phenylalanine, or tryptophan. All isolates produced both agmatine (105.8–867.5 mg L–1) and tyramine (24.5–649.7 mg L–1). Although none of the isolates displayed ornithine decarboxylase activity, putrescine was produced (2.1–33.3 mg L–1) by all isolates, except one Lactobacillus strain. Therefore, lactic acid bacteria seem to be responsible mainly for tyramine and agmatine formation during shalgam fermentation, as well as a small amount of putrescine.

Growth of Clostridium perfringens in sous vide cooked ground beef with added grape seed extract

The growth of Clostridium perfringens from spore inocula was studied in sous vide cooked ground beef with added 0 to 3% grape seed extract (GSE). C. perfringens did not grow at 4 °C with or without GSE present. Lag time (LT) was 95 h in control samples at 15 °C, whereas 1-3% GSE addition significantly (p < .05) extended LT to 244 h or longer. Generation time (GT) in 3% GSE added beef was similar to that of control (19 h, 3% GSE versus 18 h, control) at 15 °C. At 20 °C, GT was 1.5 h in samples without GSE; however, 1-3% GSE addition extended GT about 2-3 folds (p < .05). Lag time at 20 °C was 23 h in control samples, while LT was 40-59 h in samples containing GSE. Interestingly, GSE did not affect LT at 25 °C; however, significantly (p < .05) longer GT was observed in 3% GSE added samples than the other sample groups. Additionally, GSE from 1 to 3% in beef extended the period needed to reach 6 log cfu/g at 15 or 20 °C, while 3% GSE was required at 25 °C. The findings suggest that GSE exhibits concentration and temperature dependent inhibitory effect on growth of C. perfringens in sous vide cooked ground beef. Grape seed extract can be used to extend the shelf-life and ensure the microbiological safety of sous vide cooked meat products.