Bacteriocin-like inhibitory substances as green bio-preservatives; nanoliposomal encapsulation and evaluation of their in vitro/in situ anti-Listerial activity

Abstract

In this study, predominant lactic acid bacteria (LAB) isolated from a traditional pickle (Persian pickled Litteh) were screened based on their ability to produce bacteriocin-like inhibitory substances (BLIS) with inhibitory effects on foodborne bacteria tested. The isolated BLIS was also characterized using liquid chromatography-mass spectrometry (LC-MS), and loaded into nanoliposomes; then, it's in vitro and in situ inhibitory effects were evaluated. Sequencing results of the PCR products led to the identification of Lactococcus lactis LI04 as the selected BLIS-producing LAB. The highest inhibitory activity of the BLIS was observed against Listeria monocytogenes PTCC 1298, which was significantly (P < 0.05) higher than the other foodborne bacteria studied. According to LC-MS analysis, presence of two peptides with retention times of 1.45 and 1.76 min corresponding to mass to charge ratio of 456.45 and 194.79 was approved in the BLIS. Produced empty and BLIS-loaded nanoliposomes had diameters of 92.99 and 139.10 nm, respectively. Results of Fourier transform infrared analysis showed that BLIS loading induced high degree of hydration in nanoliposomes. The increased Tm of loaded nanoliposomes (verified by differential scanning calorimetry) implied that the rigidity of liposomal membrane was enhanced. The loaded nanoliposomes were also able to maintain their inhibitory activity after treatment in simulated gastrointestinal conditions and commercial sterilization; whereas, the free (non-encapsulated) BLIS lost its effect. Furthermore, anti-Listerial activity of nanoliposomal BLIS after pasteurization was higher than the free BLIS. The highest release of the BLIS from nanoliposomes at 4 °C was observed after 16 days' storage. After this period, anti-Listerial activity of nanoliposomal BLIS was significantly higher than the free BLIS in the produced homemade beef steak.