Surrogates for validation of electron beam irradiation of foods

The aim of this study was to identify a potential surrogate to describe the radiation sensitivity of the most common pathogens encountered in fruits. Three pathogens: Escherichia coli O157:H7 933, Listeria monocytogenes ATCC 51414, and Salmonella Poona, and five non-pathogens: E. coli K-12 MG1655, Listeria innocua Seeliger 1983 (NRRL B-33003 and NRRl B-33014), Enterobacter aerogenes, and Salmonella LT2 were inoculated (populations of 10(7)-10(9) CFU/ml) into model food systems (10% w/w gelatin) and exposed to doses up to 1.0 kGy using a 2 MeV Van der Graaf linear accelerator. The non-pathogen E. coli K-12 MG1655 was highly resistant to radiation (D(10)=0.88 kGy) in comparison to the other strains while L. monocytogenes was the more radiation-resistant pathogen (D(10)=1.09 kGy). Thus, E. coli K-12 MG1655 could be a suitable surrogate for e-beam studies with L. monocytogenes as the indicator pathogen. L. innocua strains were more radiation-sensitive (D(10)=0.66, 0.72 kGy) than their pathogenic counterpart. S. Poona and E. coli O157:H7 were even more radiation-sensitive (D(10)=0.38, 0.36 kGy, respectively). S. LT2 was the least radiation-resistant pathogen with D(10)=0.12 kGy. In a later study, the radiation resistance of the pathogens and the surrogate was evaluated when inoculated in a real food (i.e., fresh cantaloupe). The D(10) values obtained in this experiment were higher than those obtained with the model foods. However, the surrogate was still more radiation-resistant and could therefore be used to indicate decontamination of the target pathogens under electron beam irradiation.     

Antioxidant and antibacterial activities of Nephelium lappaceum L. extracts

Ether, methanolic and aqueous extracts of lyophilized rambutan (Nephelium lappaceum L.) peels and seeds were evaluated for phenolic contents, antioxidant and antibacterial activities. High amounts of phenolic compounds were found in the peel extracts and the highest content was in the methanolic fraction (542.2 mg/g dry extract). Several potential antioxidant activities, including reducing power, β-carotene bleaching, linoleic peroxidation and free radical scavenging activity, were evaluated. The peel extracts exhibited higher antioxidant activity than the seed extracts in all methods determined (P < 0.05). The methanolic fraction was found to be the most active antioxidant as shown by their 50% DPPH inhibition concentration, 4.94 μg/mL. The results indicated this fraction exhibited greater DPPH radical scavenging activity than BHT and ascorbic acid (0.32 g dry extract/g BHT or ascorbic acid). Antibacterial activity against eight bacterial strains was assessed by disc diffusion and broth macrodilution methods. All peel extracts exhibited antibacterial activity against five pathogenic bacteria. The most sensitive strain, Staphylococcus epidermidis, was inhibited by the methanolic extract (MIC 2.0 mg/mL).