Identification of lantibiotic producing lactic acid bacteria and its use combined with irradiation for food preservation

Abstract

The purpose of this study was to isolate lactic acid bacteria able to produce lantibiotics from dairy products containing them and evaluate their effects as food biopreservatives when combined with gamma irradiation. Twenty-five LAB isolates were isolated, among which fourteen proved to produce antibacterial substances at various levels. By using conventional methods, the two isolates that produced the highest yield were identified as Streptococcus thermophilus, and this identification was further verified by 16S ribosomal RNA (16S rRNA) sequence analysis. Lantibiotic was extracted from culture using chloroform. Liquid Chromatography Mass Spectrometry (LC/MS) and Gas chromatography–mass spectrometry (GC–MS) were used to characterize the extracted lantibiotic after it had been purified using Fast Protein Liquid Chromatography (FPLC). The resulting chromatograms indicated the presence of dehydrobutyrine amino acid, which is characteristic of lantibiotic compounds. Supernatant containing lantibiotics obtained from Streptococcus thermophilus was added to samples of minced meat and cut carrot at concentrations of 20 and 40 ml/kg, either separately or in combination with a dosage of 2 kGy gamma irradiation. Compared to the control samples, which had a storage life of only one week, these treatments effectively increased the samples' shelf life to two and three weeks at 4°C±1, respectively. To improve food preservation and microbiological safety, this study supports the use of natural biopreservatives as an alternative to chemical preservatives, either on their own or in combination with low doses of gamma irradiation.