Studies on the preservation of okra (Hibiscus esculentus) by solar drying and) packaging of the dried products

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Solar drying technology as an alternate drying method for the preservation of okra (Hibiscus esculentus L) was investigated in this study. Experiments were carried out to study the effects of three factors, namely: slice thickness and drying time; dipping and blanching pretreatments prior to drying; and type of packaging material and storage time on some nutritional and sensory quality attributes of solar dried okra. Results show that drying time significantly (p<0.01) affected all quality parameters monitored, while slice thickness significantly influenced the moisture, crude fibre and ash contents of the solar dried okra. Also the combined effects of slice thickness and drying time had a significant effect (p<0.0 1) on ash, moisture and crude fibre contents, as well as on viscosity and microbial load (p<0.05) of dried samples. The study revealed that with the exception of vitamin C, most other nutrients increased in concentration upon drying up to a maximum at about 48hrs, after which no significant changes were observed. Although some of the original green colour of okra was lost during drying, solar-dried okra had a better appearance than traditionally-dried okra. Of much significance was the increase in viscosity upon drying. Under the conditions of this study, a slice thickness of 10mm and a drying time of 48hrs were most suitable for solar drying of okra. With respect to application of pretreatments the results showed that, certain nutritional and sensory quality attributes of dried okra were enhanced or lost depending on the particular pretreatment used. Blanching or dipping in NaC1 resulted in products with the least viscosity and acceptable colour among other quality losses. Though dipping in lemon juice and ascorbic acid solutions did produce dried okra of acceptable colour and viscosity, none of these pretreatments surpassed the control (no pretreatments applied) in producing dried okra with comparatively higher nutritional and sensory quality attributes. Drying sliced okra without any pretreatments is thus recommended. During storage of solar dried okra, the packaging material and storage time significantly (p<0.0l) affected viscosity, colour, ash and moisture contents, while physical form only affected (p<0.05) product colour. The combined effect of package material and storage time also had a significant effect (p<0.01) on moisture content and green colour of solar dried okra. From this study, rehydration of dried okra during storage through absorption of water from the surrounding air appeared to be the single most important quality deteriorating factor. Storing dried and milled okra in polyethylene films or other high moisture barrier materials is therefore recommended.
A thesis submitted to the Board of Postgraduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirement for the award of the Degree of Master of Science in Food Science and Technology, 1996