Microbiological quality of walnut kernels and apple juice concentrate

Abstract

In the present study, we have evaluated the microbiological quality of walnut kernels and pasteurized apple juice concentrate and the application of PCR for quality control of these important horticultural products. PCR assays for the detection of Bacillus cereus, Salmonella, Escherichia coli and E. coli O157:H7 were standardized using minimum time for each step of the reaction. The protocols were effective for their detection in these products after pre-enrichment for 6–12 h. 2, 68 and 30% of the samples of walnut kernels were respectively found satisfactory, acceptable and unsatisfactory on the basis of their viable count. Only 15% of the samples of pasteurized apple juice concentrate were found to possess the desired viable count of less than 100 c.f.u./ml. The predominant contaminants of walnut kernels were found to be the species of Bacillus, Klebsiella, Enterobacter and Staphylococcus. Samples of apple juice concentrate were predominantly found contaminated with species of Bacillus, Staphylococcus and Micrococcus. However, B. cereus, Salmonella and E. coli were also isolated from some of the samples of walnut kernels. Bacillus cereus was also obtained from some of the samples of pasteurized apple juice concentrate in high numbers. Among the moulds Penicillium, Aspergillus, Cladosporium, Rhizopus and Mucor were isolated from these products.