Refractance window drying: Influence of drying parameters on drying characteristics and quality attributes of orange pestil

Abstract

This study was focused on investigating drying traits and quality retention of orange pulp using Refractance Window Drying (RWD) method. The effect of RWD temperature (70, 80 and 90 °C) and orange pulp thickness (2mm and 3mm) on drying time, drying rate, moisture content, ascorbic acid and colour (L*, a*, b* and b*/a*) were studied. The moisture content of 15-25 % (wb) for intermediate moisture food like orange pestil was achieved within 50 minutes of drying. The moisture content of the final product was 18.5% (wb). The fastest and slowest drying rate was observed for the sample dried at 2mm thickness and 90°C (5.74 g/min) and the sample dried at 3mm thickness and 90°C (1.00g/min) respectively. The lowest ascorbic acid (57.15 mg/100g) was recorded for the sample dried at 2mm thickness and 70°C temperature and the highest ascorbic acid (62.05 mg/100g) was for the sample dried at 3mm thickness and 90°C temperature. The effect of pulp thickness (2mm and 3mm) and drying temperature had a considerable influence on the colour factors of orange pestil. The sample dried at 2mm thickness and 90°C has the least L* value of 57 and the samples appear brown or dark red dark in colour and sample dried at 3mm thickness and 90°C had a maximum L* value i.e., 62.96 with the bright yellow sample. Increased value of a* of orange pestil/sheet as compared to the a* value of orange pulp i.e., for orange sheet sample dried at 3mm and 90°C a* value was 10.69 showcasing an elevation in the level of redness of dried sample in comparison to the orange colour of orange puree. The b* value of dried orange pestil/sheet decreased maximum for sample dried at 3mm and 90°C i.e., 32.28. The findings revealed that RW drying is a suitable drying process that can be effectively used for the formulation of quality orange pestil preserving its nutritional as well as sensory attributes.