Development of effluent-free dry-peeling method for shallots (Allium cepa L. aggregatum): Spectral characterization of mid and long infrared peak wavelengths for maximizing the peeling performance.

Abstract

Different wavelength emitting infrared (IR) lamps (transparent quartz tungsten (TQT), ruby-coated quartz tungsten (RCQT), and ceramic) were used for dry peeling and evaluating the spectral characteristics of emitted radiations. The maximum temperatures for ceramic, RCQT, and TQT were 560, 662, and 861°C, respectively. The peak wavelength determined by Wien's law was between 3.37 and 21.47µm. Comparatively, longer wavelength was emitted by ceramic lamp. The spectral emissive power determined by Stefan Boltzmann's law was 1.14-37.49kWm-2 using the IR emitters at different power levels. The radiant efficiency was higher for the ceramic lamp. The peak wavelength and emissive power had a major influence on the peeling performance and quality during IR peeling. The optimized parameters for IR dry peeling of shallots are 60mm distance between lamp and product, 59.74% IR power level, 15min of heating time using the ceramic (peak wavelength 8.16µm) lamp. Practical Application: Infrared dry peeling of shallots is a sustainable alternative to traditional peeling methods that leaves adverse environmental footprints. Spectral characteristics of the infrared lamp can be used to determine the suitable emitter for the dry-peeling operation. It is necessary to check the wavelength emitted by the source for designing the IR system based on the food product and application. This study will be helpful in food processing industries to use an effective infrared lamp that can efficiently peel the agricultural product and sustainably maintain quality.