Evaluation of Irradiated Galangal Rhizomes (Alpinia galanga) as natural foodpreservatives (Antioxidant and Antimicrobial)

摘要

Spoiled food is considered as that food which has been damaged or injured so as to make it undesirable for human consumption. The primary causative agents of microbial spoilage such as bacteria, yeast and molds, can be inhibited using plant derived products. This study aims to evaluate the antioxidant and antimicrobial activities of methanolic extracts from non-irradiated and irradiated galangal rhizomes powder at dose levels 3, 5 and 7 kGy. The data revealed that, the methanolic extracts of galangal samples irradiated showed the highest antioxidant activity and phenolic compounds compared with those from non- irradiated samples. The major compounds of galangal methanol extract were analyzed by GC-MS before and after exposure of galangal to γ- irradiation. The main compound was 1/-acetoxychavicol acetate (ACA) (9.48 %) with non irradiated sample whereas, the percentage of this compound increases with exposure of spice to γ- irradiation to reach 14.44, 13.46 and 11.12 % with 3, 5, and 7 kGy respectively. Also, the results concluded that, some compounds disappeared and others appeared after treatment with γ- irradiation. Antimicrobial activity of methanolic extracts from non-irradiated and irradiated galangal exposed to different doses of γ- irradiation against six pathogenic strains E. faecalis, S. aureus, S. faecalis. E. coli, Pseudomonas aeruginosa and S. typhi by using disc diffusion assay has been evaluated. Methanolic extracts have been shown excellent activity towards all the pathogen under study. It is interesting to note that the extract from irradiated galangal powder at 3.0 kGy showed the significant strongest inhibitory activity (p<0.05) against all tested pathogen with zone of inhibition ranging from (12-29 mm).While other doses ranged from (10-20 mm) compared to non-irradiated galangal (8- 16 mm). In refrigerated minced chicken all the concentrations of irradiated galangal powder at 3 kGy (1, 3, 5, 7 mg/g) additives reduced significantly (p< 0.05) total bacterial, total mold-and- yeast counts. It is noticed that, all the concentrations used had considerable effectiveness in decreasing aerobic plate count (APC) of inoculated S. typhi, E. coli, E. fecalis and S. aureus. Also, the results indicated that, the bacterial counts, decrease as the concentration of the spice increases since the concentration (7 mg/g) gives the best effectiveness. The treated minced chicken samples extend the shelf life of the treated samples more than the control samples by 9 days. In conclusion, galangal can play an important role as antioxidant and antibacterial agents in refrigerated minced chicken. The irradiation treatment of galangal powder at 3.0 kGy ameliorates the effectiveness of its antioxidant and antimicrobial activity.