Correlation between Time of Harvesting and Duration before Cooling on the Microbial Quality of French Bean (Phaseolus vulgaris L.)

Abstract

French bean is a major export crop from Kenya into United Kingdom and Europe. It is usually consumed cooked. Food safety is one of the most important factors that influence success of fresh produce export. Microbial contamination is one of the food safety concerns in fresh produce industry. This study focused on understanding the correlation between harvesting time and duration before cooling on the microbial quality of French beans. To assess the microbial quality of French beans, samples of French beans were harvested at different times of the day, 7am, 9am, 11am , 1pm and 3pm. The harvested beans were then held in the produce shed before start of cooling for various durations; 0 hour, 2 hours, 4 hours, 6 hours and 8 hours. The samples were later graded and packed in modified atmosphere packaging (MAP) bags. The samples were analyzed following standard plate technique to determine the microbial qualities of French bean samples. Total viable counts (TVC) in these samples showed mean values ranging from 0.7 to 3.3×105 CFUs g-1 for total Enterobacteriacea, Listeria monocytogenes, moulds and Staphylococcus aureus. Of the microorganisms isolated, Enterobacteriacea (71.6%) was the highest, followed by Staphylococcus aureus (20.9%), Moulds (7.2%) and Listeria monocytogenes at 0.3%. The harvesting time and duration before cooling had significant effect on population of microorganisms with those harvested early in the morning having the highest population. The high presence of microbial load in samples harvested early morning can be attributed to poor personal hygiene of the food handlers and excessive leaf wetness in the morning. There is need to do further research on the effect of solar radiation on the growth and survival of Listeria monocytogenes, it was evident that the Listeria population decreased significantly with every delay in harvesting, which could also be attributed to dry leaf and pod surfaces. French bean contamination in the field may result from various sources, ranging from soil, irrigation water, contaminated harvesting tools and equipment and contamination from harvesters and food handlers. It is therefore important to know the possible sources of contamination and put in place measure to eliminate or reduce contamination. Hygiene practices like hand washing after using the toilet, before handling produce and avoiding touching of face, skin and nose can be useful in reducing contamination from food handlers. Use of gloves to protect hands during harvesting is necessary to reduce contamination.