INFLUENCE OF EVAPORATIVE COOLING SYSTEM ON POSTHARVEST PHYSIOLOGICAL DETERIORATION AND QUALITY ATTRIBUTES OF PRODUCTS FROM BIOFORTIFIED CASSAVA

Abstract

A Metal-in-Block evaporative cooler was designed and constructed to investigate its efficiency for storage of fresh cassava roots. The study further investigated the quality of stored biofortified cassava roots in an Evaporative Cooling Structure (ECS) and the resulting biofortified cassava products (gari, fufu flour and HQCF) produced. The carotene retention of the biofortified products stored for 6 months in different packaging material (transparent HDPE, dark LDPE and dark HDPE) were also investigated. 150kg of freshly harvested 12 month old pro-vitamin A biofortified cassava variety (TMS 01/1368) was stored in an ECS for 12 weeks. Various observations were made on the evaporative cooling structure (temperature drop, humidity increase and cooling effectiveness); the stored cassava roots (physical loss indices, Postharvest Physiological Deterioration (PPD) quantification and scoring, enzymes activities, changes in soluble sugar, carotene, proximate composition, physicochemical composition, mineral composition, microbial loads and product yield); and on the selected stored and packed cassava products (proximate composition, physicochemical, carotenoid retention, colour parameters, mineral composition, functional properties, pasting properties and hedonic sensory evaluation). Results showed that cassava was still in good condition while the rate of weight loss decreased with increasing storage time with an average weight loss of 1.95% and 0.28% at the 1st week and 8th week respectively. The average cooling efficiency of the evaporative cooling structure was 102.7%. The result showed a drop in temperature from average of 31.97oC to 25.7oC and increase of relative humidity from average of 68.96% to 87.12%. No visual difference was observed in the stored cassava root during storage in ECS. Scopoletin (an indication of PPD) increased from 13.70-32.11 mmol/g though low compared to the control sample (103.47 mmol/g) at Day 8. The enzyme activities decreased across the storage period while the soluble sugars increased as the starch content decreased. Retention of carotene after 12 weeks of storage was 69.38% as against 22.09% at day 8 in the control sample. Changes in proximate composition were significantly different with increase in ash, fat, fibre and protein content. The pH and amylopectin increased from 5.00-6.38 and 78.82-94.38% while the cyanide content, starch and amylose decrease from 39.76-34.18mg/kg, 15.8-14.0g/100g and 21.19-5.62%. The mineral content of the cassava and products decreased as the storage period increased. The products yields and pulp:peel ratio’s decreased across the storage period. All biofortified cassava products (gari. fufu flour and HQCF) produced were within the range of published values. The carotenoid retention in gari, fufu flour and HQCF after 12 weeks were 41.30%, 71.92% and 41.17%. Organoleptic assessment of the gari samples from the stored cassava were done for dried gari, soaked gari and eba (stiff paste), while the fufu flour was evaluated for fufu dough. They were not different from each other (p>0.05) except for appearance and granularity in dried gari; retention capacity in soaked gari; and taste appearance and general acceptability in fufu dough. All sensory scores were above 6 indicating ‘like slightly’. The dark HDPE had the highest carotenoid retention in all the samples across the storage period. It can be concluded that cassava root can be stored successfully for at least 12 weeks in the ECS with minimal deterioration. Also the cassava roots stored produced gari, fufu flour and HQCF with acceptable utilization quality with appreciable retention of carotenoid.