DEVELOPMENT OF COOL STORAGE SYSTEM USING LOCALLY AVAILABLE MATERIALS FOR QUALITY PRESERVATION OF DRIED VEGETABLES

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Author

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Department of Engineering

ABSTRACT
Food and Agricultural Organization of United Nations projected that Nigeria on the average loses $9billion annually to postharvest loss and waste of food. This losses and wastages occur as a result of in-adequacy of affordable and sustainable processing and storage mechanization technology. Among the food products, fruits and vegetables were found to be the most vulnerable .A cool storage system was designed and constructed with aim of mitigating dried vegetables losses and wastage. Surveys on dried vegetables and agricultural cold storages were conducted in the North Western region of Nigeria. Two cool rooms of 500kg dried vegetable capacity each were built using Laterite soils and Thatch grasses, soil classification and Atterberg limits tests were conducted using standard methods. A standard British mould (230x110x100mm) was used in moulding laterite soil blocks after 6% cement stabilization; the blocks were cured both in the shed and the sun for 14months in which its strengths were measured. Physical properties of the Thatch materials were determined, thermal conductivity of both Thatch and the stabilized blocks were also measured. Natural and artificial cooling methods were designed as a cooling medium for the rooms. Temperature and humidity mapping was carried out on the constructed rooms as no load test. Three dried vegetables; Baobab leaves, Okra and Tomato were dried using traditional method and a solar dryer then packaged in food grade polypropylene sheet and loaded into the rooms for load test after a statistical design, similar samples were kept in ordinary room as control. Room1 was set at air conditioner temperature of 20oC while Room2 was set at a temperature of 25oC, five quality indicating parameters: color, water activity, rehydration ratio, solid content and moisture contents were traced and tracked for four months starting from May using standard laboratory procedures. The survey results indicated that only fresh fish were stored in the region’s cold rooms and baobab leaves, okra and tomato are the most produced and stored dried vegetables in the region. The no load test showed that the inside Room1 temperature remains at 25oC while the outside room temperature ranges between 18oC to 41oC, similarly Room2 inside temperature stood at 23oC at the same condition of outside temperatures. That is at all outside temperature the inside temperature remains constant. The inside relative humidity of the rooms varies as that of the outside. By DMRT ranking, tomato and okra did not show significant color difference (5%level) for both storage temperatures and drying methods within the storage period but significant differences exist when compared with the controls. Baobab leaves colour differences were significant for all the storage samples (5% levels). The moisture content ranges between 6.5% and 9.0 %within the storage period of three months and then shot up to 13.9% in the month of August for Tomato and Okra. There was no significant difference in Fungal and Bacterial load on Tomato and Baobab but it existed in Okra (5% level) for the two storages. Water activity, rehydration ratio and solid content indicated stability at 0.05level of significance for all stored products except their controls. Within the storage period there was no significant difference in the quality indicating parameters measured for all the crops stored at 20oC and 25oC in the designed rooms at their packaging condition. During temperature mapping at natural cooling condition the rooms temperature remains constant (25oC) for all outside temperatures, therefore the products can be stored without the need of artificial cooling (air conditioner). The research cost of storage per kilogramme of products was N20.56.