Study on synergistic effects of curcumin and bixin against foodborne pathogens

Various studies have shown that natural colorants, in addition to their coloring attributes, have valuable biological effects such as antioxidant, anti-inflammation, and anticarcinogenic properties. Moreover, their use as a food colorant can restrict the potential disadvantages of synthetic additives and turn foods into functional products. In this study, in vitro antimicrobial activities of two natural colorants of bixin and curcumin against some important foodborne pathogens: Staphylococcus aureus (S. aureus), Listeria innocua (L. innocua), and Escherichia coli (E. coli) were investigated by disk diffusion method. Minimum inhibitory concentration and minimum bactericidal concentration values were determined by agar dilution and broth microdilution methods. The synergistic activity of the colorants against selected microorganisms was assayed by the checkerboard microdilution method. The results showed that the inhibitory effects of bixin against S. aureus were more pronounced than E. coli and L. innocua. The lowest concentration of curcumin (0.6 mg/mL) in the disk diffusion method was not inhibited by any tested bacteria. However, it was effective at the higher concentrations against three microorganisms, but its diameter of inhibition zones was lower than gentamicin in all concentrations. Synergetic effects were observed by curcumin and bixin combination against S. aureus (FICI ≤ 0.5), but they act as an antagonist against E. coli and L. innocua. The results of the synergy test were confirmed by the isobologram curves.

Determination of the anti-yeast activity of Lactobacillus spp. isolated from traditional Iranian cheeses in vitro and in yogurt drink (Doogh)

The objective of this study was to determine the anti-yeast effect of Lactobacillus spp. isolated from two popular Iranian cheeses known as Lighvan and Motal against food spoilage yeasts known as Rhodotorula mucilaginosa, Saccharomyces cerevisiae and Kluyveromyces lactis. Twenty strains of Lactobacillus were selected from Motal (16 isolates) and Lighvan cheeses (4 isolates). Anti-yeast activity was studied by Agar Spot and Well Diffusion Assay. Effect of pasteurization on inhibitory compounds was also investigated. Results showed that two strains of Lactobacillus brevis (M4 and M2) exhibited the highest anti- yeast activity in aforementioned methods, as well as tolerated pasteurization. M4 and M2 strains were inoculated into Doogh (a fermented yogurt drink) at two levels (10⁶ and 10⁸ cfu/ml). All samples were incubated in three storage temperatures (4, 25 and 37 °C) and were then examined for microbial parameters (Mold and yeast counts, Coliform, E. coli and Staphylococcus aureus) at specific intervals. Sample with M4 (10⁶cfu/ml) showed superiority rather than control sample in microbial point of view. At temperatures of 25 and 37 °C, inoculated samples were not contaminated up to day- 21 and day-14, respectively. The propionic acid content for M4 and M2, was 14576.11 and 11697.3 ppm, respectively. Results indicate that incorporation of strain M4 (Lb. brevis) at a level of 10⁶ cfu/ml can potentially postpone the yeast spoilage in Doogh and prolong the stability of this product. In conclusion, these strains had the highest activity against experimented yeasts.

Application of F⁺RNA Coliphages as Source Tracking Enteric Viruses on Parsley and Leek Using RT-PCR

The objective of this study was to identify sources of fecal contamination in leek and parsley, by using four different F(+)RNA coliphage genogroups (IV, I indicate animal fecal contamination and II, III indicate human fecal contamination). Three different concentrations (10(2), 10(4), 10(6) pfu/ml) of MS2 coliphage were inoculated on the surface of parsley and leek samples for detection of phage recovery efficiency among two methods of elution concentration (PEG-precipitation and Ultracentrifugation) by performing double agar layer (DAL) assay in three replications. Highest recovery of MS2 was observed in PEG method and in 10(6) inoculation concentration. Accordingly, the PEG method was used for washing and isolation of potentially contaminated phages of 30 collected samples (15 samples from the market and 15 samples from the farm). The final solutions of PEG method were tested for the enumeration of plaques by DAL assay. Total RNA was then extracted from recovered phages, and RT-PCR was performed by using four primer sets I, II, III, and IV. Incidence of F(+)RNA coliphages was observed in 12/15 (80 %) and 10/15 (66/6 %) of samples were obtained from farm and market, respectively, using both DAL and RT-PCR test methods. Different genotypes (I, II, and IV) of F(+)RNA coliphages were found in farm samples, while only genotype I was detected in market samples by using the primer sets. Due to the higher frequency of genotype I and IV, the absence of genotype III, and also the low frequency of genotype II, it is concluded that the contamination of vegetable (parsley and leek) in Neyshabour, Iran is most likely originated from animal sources.