Combined effects of pulsed electric field pre-treatment and partial osmotic dehydration on air drying behaviour of red bell pepper.

Pulsed electric fields (PEF) using varying field strengths (1.0,1.5 and 2.0 kV/cm with application of 20 pulses having duration of
400 ls each) and pulse numbers (10–80) at a constant field strength of 2.0 kV/cm were applied to bell peppers as a pre-treatment to
study their influence on the products� air drying kinetics. Air drying characteristics of PEF pre-treated pepper samples immersed in
sucrose/sodium chloride solutions for either 30 or 60 min were also evaluated. Air drying was carried out at 60 �C in a fluidised bed
dryer with an air velocity of 1 m2/s.
Cell membrane permeabilisation increased with increasing field strength and higher pulse number. However,the increase became
marginal after application of more than 30 pulses. Pre-treating pepper with PEF enhanced initial drying rates significantly. The
initial rates of drying of all the PEF pre-treated samples (0.18–0.052 kg/kg min) were consistently higher than the untreated ones
(0.13–0.051 kg/kg min) until average moisture content of 3.12 kg/kg in untreated and approximately 2.2 kg/kg in the treated samples
(75 min of drying) beyond which the rate of losing water was faster in the untreated than the treated ones. Effective water diffusivity
(Deff ) values for PEF pre-treated samples pre-concentrated in osmotic solution for 30 or 60 min ranged from 0.94 to 1.36�10�9 m2/s
depending on the treatment conditions while untreated samples immersed in osmotic solution for 30 or 60 min had 0.87 and
0.99�10�9 m2/s respectively. Partial osmotic dehydration before air drying resulted in minimal decrease in Deff values in all cases
studied. The results also showed that the air drying of untreated,PEF pre-treated and partially osmotically PEF pre-treated pepper
samples occurred in the falling rate period having two different slopes.