Evaluation of the Quality Changes of Kales and Tomatoes Stored in an Improved Zero Energy Cooler

Abstract

The world is faced with myriad challenges like climate change and ever-increasing population making the achievement of global food security a challenge. Although highly perishable, tomatoes and kales are popular food commodities, farmers must sell the commodities soon after harvest for fear of deterioration. For longer storage, the two crops require an environment with low temperature and high relative humidity. Cooling systems such as refrigeration are not accessible to most small-scale farmers because they require connection to the grid. In this study, a zero-energy cooler was developed and evaluated for the storage of ripe tomatoes and mature kales. The system adopted the principle of evaporative cooling and comprised of walls filled with pumice coupled with a pond filled with water on the roof and below the storage space. A full factorial experimental design was employed. This design allowed water to drip from an elevated tank through the pumice walls and drain into the reservoir below the storage space before recirculation using a solar powered pump. The tomatoes (cultivar Ann F1) were harvested at the turning stage and kales (cultivar thousand headed) were harvest at mature stage. At different times, the two crops were stored in the cooler (treatment) and in the ambient condition (control). The relative humidity in the cooler was significantly higher than in the ambient environment while the temperature in the cooler was generally lower than the temperature at the ambient environment. Data was analysed using ANOVA at p≤0.05. For tomatoes, quality attributes namely firmness, colour, pH, total soluble solids (TSS) and shelf life were evaluated on a seven-day interval for 28 days. For kales the same quality attributes were evaluated on daily basis for ten days. For tomatoes, results showed a significant (p≤0.05) difference for pH, TSS, and firmness between tomatoes stored in the treatment and control. However, there was no significant (p>0.05) difference in the colour (hue angle) for the fruits under the treatment and control. Compared to the control, the developed solar powered storage system increased the shelf life of tomatoes from 14 days to 28 days. On the other hand, kales results showed a significant (p≤0.05) difference for a* colour parameter, and in b* colour parameter. However, comparing the quality parameters between kales stored in the cooler and in the ambient environment, there was no significant (p>0.05) difference between quality parameters; ∆E, TSS and pH. The cooler improved the shelf life of kales from 5 days (control) to 9 days (cooler). The results from this study indicate that pumice padded zero energy evaporative cooler preserves the quality of perishable tomatoes. However, the notable effect of the cooler on kales was maintenance of green colour (a*) and prevention of yellowing (b*). The Cost Benefit Analysis of the cooler under tomatoes was 10.6 and 4.21 for storage of tomatoes and kales respectively. The pay back periods for the cooler under kales and tomatoes were 7.2 Months and 1.9 months respectively. The findings of this study shows that the developed pumice-padded/roof pond zero-energy cooler provides an accessible solution for off grid and resources constrained small-scale farmers. By extending the shelf life of kales and tomatoes without reliance on electricity, the cooler directly addresses the major cause of post harvest losses in fruits and vegetables. The resultant reduction in spoilage will not only minimize economic losses but will also allow farmers greater flexibility in marketing their produce and further enabling them to avoid distress sales and hence access better prices. From a food security angle, the ability to preserve vegetables for a longer period contributes to enhanced availability and stability of nutritious foods in the local markets. The system under study supports eco-friendly agriculture by utilizing zero-energy xviii evaporative, thereby reducing traditional dependence on fossil fuel-based refrigeration and hence lowering negative environmental impact. The low-cost design of the cooler based on use of locally available materials such as pumice, proves its adaptability and scalability across different regions facing post-harvest challenges. Overall, the technology demonstrates a sustainable and economically viable innovation with a high potentiality of wide utilization among smallholder farmers, rural communities and cooperatives. This innovation will contribute to enhancement of agricultural systems, reduced post-harvest losses and improved livelihoods. The zero-energy cooler is recommended for use with other crops besides kales and tomatoes. Key words: Zero energy cooler, Combined cooling mode, Post harvest losses, Kales, Tomatoes, solar powered cooling system