The kinetics of heat inactivation and reactivation of peroxidase were examined in extracts of carrots, spinach and apricots. The enzyme from carrots was the most heatstable and showed the highest reactivation during storage whereas the peroxidase from apricots was the most heat-sensitive and showed no reactivation during storage. Higher rates of reactivation were generally observed for samples stored at -5'C compared to those stored at 4 and 18°C. The optimal pH for reactivation of peroxidase from spinach and apricots was pH 8.0. The presence of sodium chloride resulted in higher rates of reactivation during storage whereas sucrose had no significant effect.
The study aimed to evaluate the efficacy of plant essential oils and their mixtures and to investigate the effect of g-irradiation on their antibacterial activity. About 2 kGy (C2) and 4 kGy (C4) in cumin essential oil, 4 kGy (T4) in thyme essential oil, and 6 kGy (R6) in rosemary essential oil were the effective antibacterial dose against Escherichia coli, Salmonella typhimurium, Bacillus cereus and Staphylococcus aureus. The checkerboard method was used to quantify the efficacy of mixtures made from cumin, thyme and rosemary. Fractional inhibitory concentrations were calculated and interpreted as synergy, addition, indifference or antagonism. Most of the mixtures showed indifference efficacy against selected strains. (R6 ¥ T4) and (C4 ¥ R6) represented additive efficacy against B. cereus and S. typhimurium, respectively. Synergistic effect was observed against B. cereus and E. coli in (C0 ¥ R0). (C2 ¥ T4) represented a higher minimum inhibitory concentration than (C0 ¥ T0). The mixtures of essential oils either irradiated or nonirradiated could be used to minimize essential oil concentrations and to reduce any adverse sensory impact on food.
The effect of mint (Mentha viridis) essential oil (EO) on Aspergillus flavus growth and aflatoxin production was investigated in stored corn and evaluated. A. flavus was isolated from stored corn and identified as an aflatoxigenic strain. Conical flasks of 250 mL each containing 100 g of corn were sterilized by autoclave (121C, 15 lbs/in2 for 15 min) and artificially inoculated with A. flavus approximately 106 cfu/mL (control sample). Other samples were inoculated in the same manner as the control, but with the addition of different values of mint EO (50, 100, 200, 300, 500 and 700 µL/100 g corn). Mint EO was fungistatic at all concentrations, fungicidal and antiaflatoxigenic at 300, 500 and 700 µL/100 g corn from 7 days storage up to the end of storage at 21 days. Minimum inhibitory concentration for A. flavus was found to be 200 µL/100 g corn, and also limited the aflatoxin production to be under the safety level of 20 ppb determined by the Food and Agricultural Organization and World Health Organization. Mint EO could be used as fungicidal and antiaflatoxigenic agents for A. flavus in stored corn especially in granaries. Mint EO is safe, acceptable and extends the storage period of corn.
PRACTICAL APPLICATION
It could be applied to preserve cereals, especially in granaries for a long storage period, that mint essential oil Mentha viridis can be used as antifungal and antiaflatoxigenic and a safe alternative instead of chemicals, which have hazardous effects on human and animal health.
Chitosan (COS) is a natural safe biopolymer that received great attention in agriculture, food, biomedical, pharmaceutical and environmental industries because their biocompatible, biodegradable, non-toxic and non-allergenic natures. The aims of the current study were to synthesize and characterize chitosan nanoparticles (COS-NPs), to evaluate their antifungal activity against phytopathogenic fungi and inhibition of zearalenone (ZEN) production by Fusarium graminearum. The results revealed that the deacetylation degree of COS was 86.9 0.44 %, the average of molar mass was 171.41 ± 0.29 g/mol, molecular weight was 244 ± 7 kDa and the concentration of free amino groups was 0.05 ± 0.019 mol L-1. COS-NPs showed the nanorod form with rough nature and particle size was around 180 nm. COS-NPs showed an excellent antifungal activity against Alternaria tenuis, Aspergillus niger, A. flavus, Baeuvaria bassiana, Fusarium graminearum, Fusarium oxysporum, Penicillium sp. and Sclerotium rolfsii in dose dependent manner. At a concentration of 800 ppm, it inhibits ZEN production by Fusarium graminearum. It could be concluded that COS-NPs are promise candidate as safe antifungal capable for the prevention of ZEN production.
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