A Comparative Study of the Drying Rate Constant, Drying Efficiency, Nutrients and Sensory Qualities of Dried Vegetables using Solar Dryer and Open-Air Sun Drying Methods

Abstract

The study estimated and compared some drying parameters of bitter leaf (Vernonia amagdalina) and black pepper (Piper guinenses) using solar dryer and open- air sun drying methods. Two hundred grams (200g) of each sample were dried under the two different conditions. Their respective weight losses were used to determine the reduction in moisture contents. Drying was assumed to have taken place in the falling- rate period, which enabled the use of only one drying rate constant, K. Graphs of ln(M₀-M) versus time were plotted in each case and used to obtain the drying rate constants, K for the two drying conditions. The drying rate constants for the solar dryer and open- air sun dried bitter leaf were 0.8 and 0.7, respectively. Similarly, the values for black pepper were 0 2 and 0.3, respectively. Free moisture versus time graphs of both samples were also plotted which showed that the assumption of one falling- rate period is justifiable. The above information would be very critical to farmers as well as to industrial applications because specified levels of moisture content could be linked with a specified time in the process equation. The solar dryer was more efficient but also more expensive and so would be more appropriate to industrial application, whereas open-air sun drying would be more suited for village scale drying of these vegetables. Both the nutritional and sensory qualities of the dried products were enhanced by the process. The adoption of the drying techniques would ensure steady availability of these vegetables all the year round as well as reduce carbon emissions from the conventional drying methods and hence mitigate global warming.

KEYWORDS: Solar drying, open- air sun drying, drying rate constant, falling rate, climate change, food ingredients.