Infrared (IR) heat penetration profile in pigeon pea (Cajanus cajan L.) grains
摘要
Infrared (IR) heating results in loosening of hull over pigeon pea grains, thus, emerging as a promising and energy-efficient alternative to conventional pre-milling treatments for grain legumes. This study investigated the effect of IR radiation at different voltages (200–240 V), exposure times (1–5 min), and grain moisture levels (8–16%, w.b.) on the thermal properties and heat penetration in pigeon pea (Cajanus cajan L.) grains. Spatial temperature distributions were recorded using K-type thermocouples at depths of 1–4 mm beneath the IR lamp. Results demonstrated that mean IR intensity increased with voltage, indicating a strong dependence of the heating rate on the applied energy input. Specific heat (Cp) and thermal conductivity (k) of the grains increased linearly with moisture content, showing strong correlations (R² = 0.9661 and 0.9775, respectively), which reflects enhanced heat conduction at higher moisture levels. Temperature profiles followed a logarithmic trend up to 3 mm depth (R² > 0.95), with minimal inconsistent heat penetration beyond 4 mm, indicating predominant surface absorption of IR energy. No significant (p > 0.05) differences in temperature were observed between 10 and 12% moisture contents at 210–220 V for 1–2 mm depths, corresponding to standard industrial milling conditions in India and hull thickness of pigeon pea grains. The findings of this research plug the gap of fixing parametric levels for controlled IR pretreatment of pigeon pea grains for enhanced pigeon pea milling efficiency.
Graphical abstract