Development and Evaluation of Greenhouse Type Solar Dryer for Coriander Leaves

Abstract

The proper drying techniques are the most important aspect of leafy vegetable preservation. The use of solar dryer helps not only to reduce the loss<'s and improves the quality of product but also helps in conserving the conventional energy sources. A greenhouse type solar dryer which is based on greenhouse effect was dcvt"loped :md 'he cxpt ·riments were · mduc! ed to clr.v<"lop dchydral\·d coriander l€'~wes so as to enhance the awulnbility of coriander leaves during orr season. In the present study, fresh coriander leaves were pretreated 10 two ways viz. (i) dipping in a solution (!raves to water I :5 (w fw)J containing 0.1% MgCIJ + 0.1 o/o NaHC03 + 2% KMS in distilled water for 15 min at room lemperatutT. and (ii) blanching in boiling water containing 0.5<\o sodium metabisulphite for 2 min. The leaves were dried nt 2.0, 2.5 and 3.0 kgjmJ loading density, under greenhouse type solar dryer and in open sun. Untreated coriander leaves were also dried as control samples. The .S(')('Cted drying models wt·re attempted on cxpt"rimentaJ data to describe the phenomena of drying process using linearized rl'gi"Cssion technique. Performance C'\~luation of greenhOUSl" type solar dryer in terms Of capacity, efficiency, thermal and €'COnomic analysis were canicd out. Experim<'nts wen· also conducted to study the effect of drying conditions on st·nsory quality, chlorophyll content, vitamin C and rehydration characteristics. Storage bt•haviour of thre<" best samples sek<:tt·d from sensory analysis was studied for a period of 120 days. A greenhoust• type solar dryer of modified quonset shape to a size 3m width x Sm length x 2m side height and 2.3m central height covered with 200 micron W stabilized polyethylene sheet was developt"d .. There was the provision of insulated black painted pucca floor, shade net, insect proof inlet and outlets to remove humid air. Total drying Hme considerably reduced with the increase in drying air temperature from 29 •c under open sun drying to 42 °C under greenhouse type solar drying condWons. Major drying took place in falling rate period except some accelerating period initially. The average drying rate increased with increase in temperature and decreased with increase in time and loading density. The Page's model was found most suitable to describe lhe drying behaviour of coriander leaves as compared to other models. Chemically treated samples dried under greenhouse type solar dryer took lesser lime than blanched and untreated samples. The capacity and efficiency of the dryer for leafy vegetables are 55 kg per batch and 95%, respectively. The rehydration ratio, chlorophyll content and ascorbic acid content increased under greenhouse type solar dryer as compared to open sun drying. The product quality was found to be most acceptable of coriander leaves treated in the solution of 0.1% MgCI, ~ O. l'?o NaHCO. • 2"·o KMS. were dried under GSD using 2.5 kgjm2 loading density. Economic analysis revealed that different economic indicators such as B:C ratio, IRR and Pay back period were 1.3, 94%, and 1 year respectively. The net present valve of the net receipts over the entire project period was positive. The greenhouse type solar dryer can be successfully used for drying of coriander leaves which can be safely ust"d for 4 months.