Effect of γ-irradiation on the microbial quality and the biological activity of mixed spices powder

Abstract

The effect of γ- irradiation on both the microbial and chemical quality of the mixed spices powder (MSP) as well as the antimicrobial and the antioxidant activities of the MSP essential oil were evaluated. Irradiation at a dose of 10.0 kGy eliminated yeast and molds, pathogenic bacteria and reduced the total mesophillic and thermophillic bacteria to the permissible limits of WHO. The antibacterial and antifungal activities of the MSP essential oil as well as the minimum inhibitory concentration (MIC) values were recorded. The MSP essential oil was generally more effective against bacteria than molds and the gram-positive Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalies and Bacillus cereus were more sensitive than the gram-negative Escherichia coli and Proteus.sp. Aspergillus paraseticus was the most resistant mold to MSP essential oil, while A. niger 1 was the least. The inhibitory effect of the MSP essential oil against bacteria was dependent on the type of microorganisms and it mainly acted upon decreasing the final cell concentration, while it acted upon increasing the lag phase, the generation time and decreasing the final cell mass in the case of molds. Gamma irradiation (10 kGy) did not significantly affect the antimicrobial activity of the MSP essential oil. Application of BHA, BHT, essential oil of non-irradiated and irradiated MSP significantly delayed the oxidation rate in sunflower oil and the shelf life of the oil was enhanced by 4, 5, 9.5 and 9.5 days, respectively. γ-irradiation (10 kGy) showed no significant effect on the antioxidant activity of the essential oil of MSP. Also, storage of one year decreased the percentage of the MSP essential oil in both nonirradiated and irradiated samples

New Egyptian Journal of Microbiology Vol. 17 (2) 2007: pp. 191-213