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 C, 40 C and 50 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 ClausiuseClapeyron 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 C and a corresponding outlet temperature of 70 ± 3 C. Therefore, the best operating conditions for
scale-up were suggested to be an inlet air temperature of 150 C, a maximum allowable outlet temperature
of 80 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.