Available at: http://digitalcommons.calpoly.edu/theses/1559
Date of Award
MS in Agriculture - Food Science and Nutrition
Food Science and Nutrition
Dr. Amanda Lathrop
Growing consumer awareness of the health benefits associated with fruits and vegetables and demand for easy to prepare products has prompted the development of a wide variety of minimally processed fruits and vegetables. Minimally processed fruits and vegetables are often peeled, cut, or diced which compromise the produces’ natural protective barriers, exposing a nutrient rich medium and providing an ideal environment for the growth of microorganisms, including foodborne pathogens. The germination conditions of sprout vegetables consisting of relatively high temperatures and humidity, low light and abundance of nutrients are also conducive to the proliferation of foodborne pathogens. Recent outbreaks and recalls indicate additional measures are needed to improve food safety and maintain the integrity of the food industry.
The objective of this research was to evaluate the efficacy of Lactic Acid Bacteria (LAB) against E. coli O157:H7, L. monocytogenes, and Salmonella spp. on apple slices and alfalfa sprouts and it’s influence on product quality. Apple slices inoculated with E. coli O157:H7, L. monocytogenes, and Salmonella spp. (each at 104 CFU/g) were treated with Lb. plantarum alone and in combination with Pediococcus acidophilus and P. pentosaceus (LPP) (107 CFU/g) while alfalfa seeds were inoculated with L. monocytogenes and Salmonella spp. (each at 101 CFU/g and 103 CFU/g) and treated with LPP (107 CFU/g). The growth of the microorganisms on the apple slices was assessed during five and seven days of storage at 4◦C and 20◦C, respectively. Growth on alfalfa seeds was reported during five days of sprouting at 20◦C. Populations of LAB were maintained between 7.0 log CFU/g and 8.0 log CFU/g throughout storage and sprouting on the sliced apples and alfalfa seeds, respectively.
Although LAB had no significant effect on pathogen populations on apple slices during storage at 4°C (p > 0.05), populations were significantly different at 20°C (p < 0.05). Populations of L. monocytogenes in the presence of Lb. plantarum and LPP were 1.84 log CFU/g and 2.84 log CFU/g less than the controls after five days of storage at 20°C (p < 0.05). Populations of E. coli O157:H7 in the presence of Lb. plantarum and LPP were 1.83 log CFU/g and 1.86 log CFU/g less than the control after one and three days of storage, respectively. Finally, populations of Salmonella spp. were 0.86 log CFU/g less than populations in the absence of LPP after three days of storage.
LPP had a significant effect on the growth of L. monocytogenes and Salmonella spp. on alfalfa seeds (p < 0.05). After five days of sprouting, populations of L. monocytogenes at an initial concentration of 101 CFU/g and 103 CFU/g on seeds treated with LPP were approximately 4.5 log CFU/g and 1.0 log CFU/g less than the untreated seeds, respectively. Populations of Salmonella spp. at an initial concentration of 101 CFU/g and 103 CFU/g were 1.0 log CFU/g less than the control.
Overall, on apple slices the combination of Lb. plantarum with P. acidophilum and P. pentosaceus demonstrated greater efficacy than Lb. plantarum alone and reduction of L. monocytogenes by Lb. plantarum and LPP was greater than Salmonella spp. and E. coli O157:H7 on apple slices and alfalfa seeds, alike. LAB had a minimal effect on the quality of the apple slices and alfalfa seeds. LAB could be an effective strategy in reducing pathogen populations at abusive temperatures and germination conditions without influencing the quality of minimally processed fruit and vegetables.