French bean is one of the major horticultural crops exported from Kenya into International markets. French bean production faces several challenges whose magnitude depend on whether the crop is produced in-house or with an out grower. Unlike with the large commercial growers who have well organized infrastructure to ensure quality food safety of the beans, small scale farmers have always struggled to keep up with the quality expectations of the markets.
This study was aimed at evaluating the performance of solar coolers in enhancing quality and shelf life stability of French beans with an overall of objective of developing a smart solar cooler to replace the use of charcoal coolers. A survey was done to understand the current knowledge and performance of charcoal coolers. Data were collected primarily from a household survey using a semi-structured questionnaire that was administered to 45 farmers that were selected at fixed interval purposively selected. To evaluate the effects of harvesting time and duration before cooling on the post-harvest quality and shelf-life stability of French beans, five harvesting times were evaluated; 7am, 9am, 11am, 1pm and 3pm. The harvested beans were then subjected to five different delay times before cooling; 0hr, 2 hours, 4 hours, 6 hours and 8 hours. The proximate compositions of the fresh French beans samples were determined using standard methods. The microbial quality of French harvested at different times of the day, 7am, 9am, 11am, 1pm and 3pm was also done using standard plate technique. The samples were later graded and packed in modified atmosphere packaging (MAP) bags.
The study revealed that majority (80%) of the farmers adopted evaporative cooling technology using charcoal coolers and stored their produce for one to six hours (68%).
The study revealed a significant loss of moisture and weight for every delay in start of cooling resulted in increase of protein by 18%, fat by 24%. Total viable counts (TVC) in these samples showed mean values ranging from 0.7 to 3.3×105 CFUs g-1 for total Enterobacteriaceae, Listeria monocytogenes, moulds and Staphylococcus aureus. Of the microorganisms isolated, Enterobacteriaceae (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 significantly (P≤0.05) affected the population of microorganisms with those harvested early in the morning recording the highest population.
The high presence of microbial load in samples harvested early morning can be attributed to poor hygiene of the harvesters and too much leaf wetness in the morning. The weight of the stored produce reduced by 5% and 2.8% after seven hours under conventional field shed and fabricated solar cooler respectively. The volume of carbon dioxide and oxygen released from produce stored in conventional shed and those stored in fabricated solar cooler prototype significantly differed. Higher volume of CO2 accumulation was detected in produce stored in the conventional cooling method than those stored in the fabricated solar-powered cooler. Further research should be carried out to understand the influence of solar radiation on the development and existence of Listeria monocytogenes. It was evident that the Listeria monocytogenes population decreased significantly with every delay in harvesting, which could also be attributed to dry leaf and pod surfaces.