Pulsed vacuum drying of wolfberry: Effects of infrared radiation heating and electronic panel contact heating methods on drying kinetics, color profile, and volatile compounds

ABSTRACT

The drying kinetics and quality attributes of wolfberry were investigated under pulsed vacuum drying based on two different heating ways of far-infrared radiation (PVD-FIR) and electronic panel contact (PVD-EPC) heating. They were operated at different drying values of heating panel temperatures (60, 65, and 70°C) with 15 and 2 min as the constant vacuum pressure and atmospheric pressure duration, respectively. Drying time for wolfberry dried by PVD-FIR was lower by 17–19% compared with that by PVD-EPC at the same drying temperature. The effective moisture diffusivity (D_eff) determined by Weibull distribution model ranged from 3.72 × 10⁻¹⁰ to 6.59 × 10⁻¹⁰ m²/s and 3.34 × 10⁻¹⁰ to 6.88 × 10⁻¹⁰ m²/s for PVD-FIR and PVD-EPC, respectively. The drying activation energy was 54.30 and 68.59 kJ/mol for the samples dried by PVD-FIR and PVD-EPC, respectively. The color parameters L*, a*, and b* of wolfberry dried by PVD-FIR were higher than those dried by PVD-EPC. The product dried by PVD-FIR contained more vivid luster compared to that dried by PVD-EPC. The contents of aldehydes, esters, phenols, and the heterocyclic compound in PVD-FIR sample were higher than those in PVD-EPC samples. Additionally, the alcohols, ketones, and acid contents in PVD-FIR sample were lower than those in PVD-EPC sample. In summary, PVD-FIR is more suitable for wolfberry drying as it enhances drying rate and product’s quality compared with PVD-EPC.

KEYWORDS:

• Color parameters
• PVD-EPC
• PVD-FIR
• volatile compounds
• Weibull distribution model
• wolfberry

Acknowledgment

In addition, Dr. Long Xie thanks China Scholarship Council (File No. 201506350206) for supporting his overseas research in Washington State University.