Solar tunnel assisted drying of parchment coffee (Coffea. Araica L) for better quality and safety of raw beans and beverage

Abstract

This study was conducted to investigate the combined effect of solar tunnel dryer zones and layer thicknesses on the drying characteristics, quality and safety of washed Arabica parchment coffee. The experimental design was 4 x 3 factorial arrangements in a randomized complete block design with three replications. The first factor was solar tunnel drier zones (zone 1, zone 2, zone 3 and open sun drying) and the second factor was a layer of drying thicknesses (2, 4 and 6 cm). Parameters such as moisture ratio, effective diffusivity, hours to drying, were collected to determine drying characteristics of parchment coffee. Then physicochemical quality parameters such as titratable acidity, total soluble solid, PH, Crude fat, total polyphenol contents, total Antioxidant capacity, IC50, raw and cup quality) and fungal load were determined. During the drying, drying air temperature and relative humidity were measured continuously at one-hour interval. Moisture ratio was examined by moisture loss at a given time per initial moisture content at every one hour interval. Selected 7 different thin-layer drying models were compared to determine drying kinetics. According to statistical analysis results, the Modified Midilli model has shown a better fit to the experimental drying data as compared to other models. The effective diffusivity varied between (1.2 to 5.0*10-6 ) and increased with increasing temperature along the drying zones. All collected parameters except TA differed significantly (p<0.05) concerning drying zones and layer thicknesses. There was no significant variation among the treatments concerning cup quality and all the coffee scored grade one and grade two for the total quality score referring to very good quality for all the coffees. Higher fungal fungal were found for the sun-dried coffee beans with aspergillus genera being the most abundant. The study concluded that drying parchment coffee under zone 2 (solar tunnel drier 50-60 0 C and 18-28% RH) at a drying depth of 4 cm resulted in desirable effects. Consequently, in the absence of a mechanical drier due to the unavailability of its basic materials, the solar tunnel drier could be a worthy substitute without compromising on coffee bean and cup qualities as compared to traditional open sun drying