Antibacterial activity of plant essential oils and extracts: The role of thyme essential oil, nisin, and their combination to control Listeria monocytogenes inoculated in minced fish meat

Effect of nisin and perilla oil combination against Listeria monocytogenes and Staphylococcus aureus in milk

In the present study, in vitro interaction of nisin and perilla oil (PO) against 20 food-borne isolates of L. monocytogenes and S. aureus were assessed using a checkerboard microdilution method. Synergism was observed in tested strains with the fractional inhibitory concentration indexs (FICIs) ranges from 0.125-0.25 and 0.19-0.375, respectively. Scanning electron microscopy was carried out to investigate the effect of nisin and PO on the integrity of cell wall and membrane of L. monocytogenes and S. aureus. The results showed that nisin and PO were more effective in damaging cell wall and membrane in combination.

Comparing the effect of encapsulated and unencapsulated fennel extracts on the shelf life of minced common kilka (Clupeonella cultriventris caspia) and Pseudomonas aeruginosa inoculated in the mince

The quality of minced kilka (Clupeonella cultriventris caspia) with gum arabic encapsulated (0.3% and 0.5% w/w) and unencapsulated fennel extract (FE) (0.3% and 0.5% w/w) stored at 4°C was examined over a storage period of 15 days. The control and the treated fish samples were analyzed periodically for microbiological (total viable count [TVC] and total psychrotrophic count [TPC]) and chemical (peroxide value (PV) and total volatile nitrogen (TVB-N)) parameters. Also the inhibitory effect of encapsulated and unencapsulated FE was evaluated against Pseudomonas aeruginosa, inoculated in minced kilka. According to the results, encapsulated FE samples showed the lowest amount of lipid oxidation and microbial deterioration during the storage period compared with the control and pure extract treatments. Although, the encapsulated FE at 0.5% showed drastic bacterial effect against Pseudomonas aeruginosa compared to others. Generally, gum arabic encapsulation could help to obtain higher antimicrobial and antioxidant activity in lower FE concentrations in minced fish.

Effects of chitosan combined with nisin treatment on storage quality of large yellow croaker (Pseudosciaena crocea)

Effects of chitosan combined with different concentrations of nisin on quality enhancement of large yellow croaker (Pseudosciaena crocea) stored at 4 °C were evaluated for 8 days. Changes in sensory score and volatile spoilage products, total viable counts (TVC), and physiochemical indexes including weight loss, colour, pH, total volatile basic nitrogen (TVB-N), and K-value were examined. Results demonstrated that nisin-treated samples presented better quality preservation effects than chitosan alone. 1% chitosan combined with 0.6% nisin presented optimal quality enhancement effects, such as moisture loss control, volatile spoilage inhibition, TVB-N reduction, TVC growth control, and colour and sensory acceptability maintenance. Therefore, chitosan combined with nisin is promising in large yellow croaker shelf life extension.

Antilisterial Peptides Released by Enzymatic Hydrolysis from Grass Carp Proteins and Activity on Controlling L. monocytogenes Inoculated in Surimi Noodle

The primary objective of this study was to prepare the antilisterial peptides by enzymatic (pepsin, trypsin, protamex, neutrase, flavourzyme, papain, alcalase, and acid protease) hydrolysis of grass carp proteins with various degree of hydrolysis. The second objective was to evaluate the antilisterial activity of grass carp proteins hydrolysates (GCPH) at differnet levels in the surimi noodle samples with or without boiling treatment inoculated with 10(4) CFU/g of Listeria monocytogenes for storage at 4 and 25 °C up to 20 d. These results revealed that GCPH, obtained by treatment with the neutrase hydrolysates at degree of hydrolysis of 19% (NSH19), showed the highest antilisterial activity reaching up to 64.8% inhibition of bacterial growth. The antilisterial activity of NSH19 in the raw surimi noodle was stronger than that of the boiled group, and the samples treated by NSH19 at 10 g/100 g level had no-detectable numbers of L. monocytogenes for both raw and boiled noodle samples within 20 d of storage at 4 and 25 °C. The results of this study indicated that antilisterial peptides generated via neutrase from grass carp proteins can efficiently inhibit the growth of L. monocytogenes in surimi noodle, which was useful as natural preservatives for storage and distribution of meat based products.

PRACTICAL APPLICATION

The results of this study indicated that antilisterial peptides generated via neutrase from grass carp proteins can efficiently inhibit the growth of L. monocytogenes in surimi noodle, which was useful as natural preservatives for storage and distribution of meat based products.

Antimicrobial Effects of Nisin, Essential Oil, and γ-Irradiation Treatments against High Load of Salmonella typhimurium on Mini-carrots

This study aimed at using essential oil (EO) alone or combined EO with nisin and γ-irradiation to control Salmonella Typhimurium during the refrigerated storage of mini-carrots. Peeled mini-carrots were inoculated with S. Typhimurium at a final concentration of approximately 7 log CFU/g. Inoculated samples were coated by 5 different coating solutions: (i) nisin solution at final concentration of 10(3) IU/mL; (ii) mountain savory EO solution at 0.35%; (iii) carvacrol solution at 0.35%; (iv) mountain savory EO at 0.35% plus nisin solution of 10(3) IU/mL; or (v) carvacrol at 0.35% plus nisin solution of 10(3) IU/mL. Coated mini-carrots were then irradiated at 0.5 or 1.0 kGy and compared to an unirradiated control sample. Samples were kept at 4 °C and microbial analyses were conducted at days 1, 3, 6, and 9. The results showed that mini-carrots coated by carvacrol plus nisin solution or mountain savory EO plus nisin solution in combination with irradiation at 1.0 kGy completely eliminated S. Typhimurium to under the detection limit during the storage. Thus, the combined treatments using carvacrol plus nisin or mountain savory EO plus nisin coating solution and irradiation at 1.0 kGy could be used as an effective method for controlling S. Typhimurium in mini-carrots.

PRACTICAL APPLICATION

This study shows the effect of using γ irradiation at low dose (1 kGy) to reduce significantly the growth of Salmonella typhimurium in mini-carrots. It also shows that combination of nisin, essential oils with γ irradiation have the best antibacterial effects against S. Typhimurium during the storage of mini-carrots. The results can be used for practical application in food industry in terms of food safety.

Antimicrobial activity of turmeric extract and its potential use in food industry

The present study investigates the antimicrobial and preservative potentials of turmeric extracts for food industry. Turmeric extracts prepared in n-hexane, water, chloroform and ethanol were applied to meals as preservatives and antibacterial agent. The samples were assessed microbiologically (total bacterial, total fungal and total coliform counts) and organoleptically (color, odor, taste) at day zero and after 15 days intervals. Meals autoclaved for shorter time (5 min) and treated with combination of 1 % or 2 % turmeric extract preserved for longer period. These results were comparable with samples autoclaved for longer period (15 min) with out turmeric extract. The antibacterial activities of different turmeric extracts were also tested against Escherichia coli, Staphylococcus aureus, Salmonella typhi and Candida albicans by disc diffusion method. Water extracted samples of turmeric stored at room temperature inhibited the growth of Escherichia coli and Salmonella typhi while aqueous extract autoclaved at 121 °C for 30 min reduced the growth of Escherichia coli and Staphylococcus aureus. Methanol extracted samples stored at room temperature or autoclaved at 121 °C was effective to control the growth of all microbes under study. Chloroform and n-hexane extracts (stored at room temperature) showed weak activity against all tested microbes.