Infrared Processing of Chili Oil at Different Exposure Times for Enhanced Biological Performance and Phytochemical Modulation

Abstract

Infrared (IR) processing of chili oil significantly modulated its phytochemical composition and biological activity. GC–MS analysis revealed that unexposed chili oil was rich in eugenol (32.73%), caryophyllene (8.21%), and polyunsaturated fatty acids (PUFAs) such as 9,12-octadecadienoyl chloride (16.86%). Short-term IR exposure (5 min) reduced eugenol to 25.90% and generated a positional isomer (phenol, 2-methoxy-3-(2-propenyl), 10.93%) along with diynoic acid esters and alkyne fatty-acid derivatives, indicating isomerization and partial PUFA degradation. Prolonged IR exposure (10 min) further decreasd volatile phenolics and PUFA esters while enriching high-molecular-weight alcohols (1-heptatriacotanol, 7.65%) and chlorinated derivatives (9,12-octadecadienoyl chloride, 21.04%). The 5-min IR treatment produced the highest antimicrobial activity, with inhibition zones increasing for B. subtilis (25 ± 0.2 mm), S. aureus (23 ± 0.7 mm), E. coli (18 ± 0.5 mm), S. typhi (19 ± 0.2 mm), and C. albicans (25 ± 0.3 mm), and MIC/MBC values notably reduced (15.62 µg/mL for B. subtilis and C. albicans). IR-treated chili oil also displayed strong dose- and time-dependent biofilm inhibition, reaching up to 95.23 ± 2.0% at 75% MBC. 5-min IR-treated chili oil reduced B. subtilis from 3.2×10⁵ to 2.1×10³ and S. aureus from 2.4×10⁵ to 2.6×10³ CFU/mL. Furthermore, antioxidant activity peaked at 5 min exposure (96.4 ± 1.91% DPPH scavenging; IC₅₀ = 5.65 ± 0.20 µg/mL), while anti-inflammatory activity was enhanced (IC₅₀ = 2.72 ± 0.14 µg/g).