Spray drying bioactive orange-peel extracts produced by Soxhlet extraction: Use of WPI, antioxidant activity and moisture sorption isotherms

Spray drying of orange peel extracts was performed using a laboratory-scale spray dryer in order to assess the best operating conditions to be used in a subsequent scale-up process. Addition of whey protein isolate (WPI) to the liquid feed enhanced the yield of the process significantly from 30 +/- 10% to 63 +/- 3%. The moisture sorption isotherms of the powders were also determined at 30 degrees C, 40 degrees C and 50 degrees C and fitted by the Guggenheim-Andersen-de Boer (GAB) equation. The average net isosteric heat of sorption for the powders was determined using the Clausius-Clapeyron equation to be 70.5 kJ/kg. The total phenolic content (TPC) and the free radical scavenging capacity (SC50) of the powders were retained by 95 +/- 5% and 95 +/- 15%, respectively, during small-scale spray drying at an inlet air temperature of 150 degrees C and a corresponding outlet temperature of 70 +/- 3 degrees C. Therefore, the best operating conditions for scale-up were suggested to be an inlet air temperature of 150 degrees C, a maximum allowable outlet temperature of 80 degrees C and a maximum allowable relative humidity for the exhaust air of 15%, while using a liquid feed containing 7.5% (w/w), dry basis WPI. (C) 2016 Elsevier Ltd. All rights reserved.