Evaluating the performance of low cost hydro-cooling system and calcium chloride application in maintaining postharvest quality of selected vegetables

Abstract

Fruits and vegetables constitute an important subsector in horticultural industry in Kenya a major part of human nutrition. However, due to their high perishability, limited postharvest technologies in most of the developing countries and inadequate cold storage, huge postharvest losses are incurred. Cool temperatures are essential in perishable produce for preservation of flavour, texture, aroma volatiles, appearance prolonging postharvest life. Use of chilled water to cool the produce otherwise referred to as hydrocooling allows high heat transfer rates, resulting in shorter cooling time of produce. The present study was undertaken with the objective of establishing the time required to cool specific fruits and vegetables to target temperatures using the low cost hydrocooling system designed and also assess its effects on postharvest characteristics in the selected produce. It also sought to establish the effect of hydrocooling, low temperature storage and use of calcium chloride as a sanitizer in maintaining the postharvest quality of selected perishables, i.e. tomatoes, African eggplants, carrots and courgettes. Fresh produce of tomatoes, African eggplants and carrots were harvested from the JKUAT experimental farm and courgettes from a farmer’s field in Ngarariga Limuru. The produce was transported to the laboratory in crates lined with moist paper towels within 3 hours, where sorting for uniformity in size grading and measurement was done. Fresh produce of each product were divided into 7 portions of equal number of fruits. Using a the hydrocooling system design constituting a water reservoir, electric powered pump, two identical shower heads, flow valve and polypropylene copolymer pipe, a shower type hydrocooling system was made and used to hydrocool the produce. Two portions were hydro cooled using the low cost hydrocooling system, with water at 2±10 C, another two were not hydrocooled. During hydrocooling, temperature monitoring at the core of the produce was done using a temperature data logger. From the four portions, one in each category was kept at low temperature (7 0 C or 10 0 C) while the other was stored at ambient conditions (25 C) in a room. The remaining three portions were hydrocooled with water at 2±1 0 C containing 0.5 %, 1.0% and 1.5% CaCl and subsequently stored at low temperature, all at constant relative humidity of 95%. Time required to hydro- 2cool the produce to target temperature was 10.5 ± 0.47, 4.9 ± 0.21, 7.42 ± 0.25, 3.33±0.34 minutes for tomatoes, carrots, courgettes and African eggplants respectively. The quality assessment carried out included weight loss, respiration rate, total soluble solids, colour, soluble sugar content, vitamin C, βcarotene, total titratable acidity, total viable count and spoilage during storage. Quality assessment done at two days intervals revealed progressive loss in weight in all the produce, ranging from 0.86±0.13 % to 4.43±0.46 %, 1.46±0.16 to 30.71±0.35 %, 1.32±0.19 to 20.45±0.68 % and 0.30±0.04 to 6.25±0.39 % for tomatoes, courgettes, carrots and African eggplants respectively. Hydrocooling coupled with low storage temperatures resulted in significantly (P≤0.05) superior postharvest quality characteristics with regard to throughout the storage period implying better postharvest quality. However, for the African eggplant produce stored at 10 C, both hydro-cooled and the control was significantly (P≤0.05) inferior in quality from 3 days after storage. More weight loss occurred and higher respiration rates were observed, this was accompanied by visible chilling injury symptoms such as shrivelling and darkening of the calyx. When calcium chloride (CaCl ) was added to the hydro-cooling water and produce subsequently stored at lower temperatures, retention of vitamins (beta carotene and ascorbic acid) was higher in all the produce. In tomatoes, African eggplants, carrots and courgettes, the highest retention was at 1.0 %, 1. 5%,0% and 1.5%, for both vitamin C and beta carotene. Microbial populations were also reduced by 78.2 %, 59.4% 63.9% and 71.6% for tomatoes, African eggplant, carrots and courgettes respectively in total plate count and by 63.1%, 46.2% 79.4% and 69.7% in yeast and moulds for all produce at 1.5% CaCl . In African eggplant, CaCl delayed the onset of chilling injury and lowered the respiration rates significantly. Keywords: Calcium Chloride, Low Cost hydro cooling, Postharvest Quality, Field heat, Specific Sugars, Microbial loads.