Effect of Drying Method and Irradiation on the Microbiological Quality of Moringa Leaves

Abstract

Effect of drying method and irradiation on the microbiological quality of dried moringa leaves (DML) was investigated. Moringa leaves dried by 3 methods (mechanical, solar and room drying) was assessed for microbiological quality in addition to 6 different retail samples of DML. Mechanical, solar and room-dried moringa leaves were irradiated at doses of 0, 2.5, 5.0, 7.5, 10.0 kGy with gamma radiation from a Co-60 source and the microbiological quality was assessed using the methods of serial dilution and pour plating. Range of mean counts of total viable cells, coliforms, moulds and yeasts, E. coli and Pseudomonas spp. of the retail samples of DML were respectively 5.92 – 8.44, 4.85 – 7.25, 1.65 – 3.69, 3.71 – 4.78 and 1.84 - 4.22 log10cfu/g. Salmonella spp. was detected in 2 out of the 6 retail samples analysed. Room-dried moringa leaves relatively had high counts of total viable cells (6.45); coliforms (6.18); moulds and yeasts (3.46); E. coli (1.58) and Pseudomonas spp. (3.32) compared to samples dried by mechanical or solar methods. Irradiation dose of 2.5 kGy reduced the counts of all microorganisms to ≤ 3.57 and no survivors were detected in the samples of DML at 5, 7.5 and 10 kGy. High counts of total viable cells, coliforms, E. coli, Pseudomonas spp. and presence of Salmonella spp. in retail samples of DML raise food safety concerns. Solar-dried moringa leaves had improved microbiological quality compared to mechanical or room-dried leaves. Gamma irradiation significantly improved the microbiological quality of DML. A minimum irradiation dose of 5 kGy is recommended to enhance the quality of dried moringa leaves to meet standards of domestic and export markets.