Faculty of Applied Sciences
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Item Inactivation of heat adapted and chlorine adapted Listeria monocytogenes ATCC 7644 on tomatoes using sodium dodecyl sulphate, levulinic acid and sodium hypochlorite solution(PAGEpress, 2017-04) Ijabadeniyi, Oluwatosin Ademola; Mnyandu, ElizabethThe effectiveness of sodium dodecyl sulphate (SDS), sodium hypochlorite solution and levulinic acid in reducing the survival of heat adapted and chlorine adapted Listeria monocytogenes ATCC 7644 was evaluated. The results against heat adapted L. monocytognes revealed that sodium hypochlorite solution was the least effective, achieving log reduction of 2.75, 2.94 and 3.97 log CFU/mL for 1, 3 e and 5 minutes, respectively. SDS was able to achieve 8 log reduction for both heat adapted and chlorine adapted bacteria. When used against chlorine adapted L. monocytogenes sodium hypochlorite solution achieved log reduction of 2.76, 2.93 and 3.65 log CFU/mL for 1, 3 and 5 minutes, respectively. Using levulinic acid on heat adapted bacteria achieved log reduction of 3.07, 2.78 and 4.97 log CFU/mL for 1, 3, 5 minutes, respectively. On chlorine adapted bacteria levulinic acid achieved log reduction of 2.77, 3.07 and 5.21 log CFU/mL for 1, 3 and 5 minutes, respectively. Using a mixture of 0.05% SDS and 0.5% o levulinic acid on heat adapted bacteria achieved log reduction of 3.13, 3.32 and 4.79 log CFU/mL for 1, 3 and 5 minutes while on chlorine adapted bacteria it achieved 3.20, 3.33 and 5.66 log CFU/mL, respectively. Increasing contact time also increased log reduction for both test pathogens. A storage period of up to 72 hours resulted in progressive log reduction for both test pathogens. Results also revealed that there was a significant difference (P ≤ 0.05) between contact times, storage times and sanitizers. Findings from this study can be used to select suitable sanitizers and contact times for heat adapted and chlorine adapted L. monocytogenes in the fresh produce industry.Item Biocontrol of Listeria monocytogenes ATCC 7644 in fresh tomato with Probiotics(MN Khan, 2014-10) Ijabadeniyi, Oluwatosin Ademola; Naidoo, ShaniceThe effectiveness of probiotics Lactobacillus bulgarius and Streptococcus salivarius as biocontrol agents against Listeria monocytogenes ATCC 7644 in fresh tomato throughout storage and their effect on the physicochemical properties of tomato was evaluated. Tomato samples were cut into wedges and inoculated with 108 CFU/ml of Listeria monocytogenes ATCC 7644, thereafter inoculated with L.bulgaricus and S.salivarius separately. Tomato was also inoculated with probiotics L.bulgaricus and S.salivarius without inoculation of L.monocytogenes. Nutrient broth was prepared and inoculated with 108 CFU/ml of L.monocytogenes ATCC 7644 and thereafter inoculated with L.bulgaricus and S.salivarius separately after which all treatments were stored at 4°C for 72 hours. Chlorine was used as a control and compared against probiotics. L. monocytogenes counts taken during storage period in nutrient broth showed that L. bulgaricus had a 2.19 log reduction and S. salivarius had a 1.65 log reduction. The tomato study showed that L. bulgaricus had a 3.15 log reduction and S.salivarius had a 3.01 log reduction. Physicochemical properties of tomato were not affected (p > 0.05) by treatment with probiotics when compared to control. Statistical analysis showed a significant difference between both probiotics and chlorine in tomato. This research indicated that L.bulgaricus and S. salivarius could potentially be used as eco-friendly biocontrol agents in the produce industry.