Influence of Near Infrared Reflection and Evaporative Cooling on Mango Fruit Storage

Abstract

Mango (Mangifera indica L.) fruit is valuable in Kenya due to its nutritive and economic value. However, at least 40 to 45% of mango fruit is lost during postharvest handling primarily due to inadequate availability of storage facilities during the peak harvest seasons. As a result, farmers are often forced to sell their fruits at a throw away price in fear of spoilage. Thus, this study is aimed at developing and evaluating the performance of an improved store for mangoes. The improved store combined reflection of near infrared radiation and evaporative cooling to lower the temperature inside the storage chamber. A computer simulation model was developed in a Java programming language and was used to predict the performance of the improved store. The input parameters of the model were ambient conditions (dry and wet bulb temperature, specific humidity and air velocity), coolant conditions (coolant temperature and flow rate), cooler characteristics (length, thickness and height of the evaporative pad, wetted area per unit volume of the evaporative medium) and air properties (specific heat of air and water vapour, thermal conductivity of air, Prandtl number, kinematic viscosity of air and density of air). The performance parameters of the cooler which included saturation efficiency and cooling capacity were evaluated at various inlet air velocities ranging from 3.0 to 4.0 m/s at a regular interval of 0.2 m/s. The effect of storage conditions on the shelf-life and properties of two mango varieties namely Apple and Kent were evaluated. Room conditions were used as a control during the experiment. The physical (weight, colour, and firmness) and chemical (total soluble solids, total titratable acids, and pH) properties were monitored on daily basis. Results from the simulation model did indicate that actual saturation efficiency of the near infrared reflecting store (SNR) ranged from 66.9 to 68.9 % while the simulated was 66.9 to 69.0% which was highly correlated to the actual measurements (R2 = 0.999). The actual cooling capacity of the SNR ranged from 105.67 to 136.48 mJ/h while the simulated was 105.73 to 136.68 mJ/h which was strongly correlated to the actual data (R2 = 0.998). The SNR lowered ambient temperature by 11.4oC and increased relative humidity by 6.7%. In addition, a 3.2 oC temperature difference was recorded between the SNR and non-near infrared reflecting store (SNNR). The difference was significant (P<0.05). The SNR increased the shelf-life for both mango varieties by 3 and 9 days compared to the SNNR and room conditions (RC), respectively. The SNR reduced weight loss in Apple mangoes by 4.64 and 9.77% compared to SNNR and RC, respectively while the weight loss in Kent mangoes was decreased by 4.09 and 8.82% compared to SNNR and RC, respectively. The difference was significant (P<0.05). Except for the colour of the flesh for Kent, the storage environment did not have any significant effect (P>0.05) on the colour of the peel or flesh of the Apple. Moreover, the storage environment had no significant effect (P>0.05) on the firmness of the peel or flesh for Apple except for Kent. In addition, the effect of storage environment on the total soluble solids (TSS), total titratable acids (TTA), and pH for both mango varieties were not significant (P>0.05). The results from this study therefore indicate that the combination of near infrared reflection and evaporative cooling has a potential of improving the shelf-life and preserving the quality of the mango fruits. Thus, this technology can provide an applicable solution to storage challenges in mangoes.