Steam treatment of whole red chillies at various water activity levels: Microbial and enzyme inactivation, and bioactive retention
摘要
Red chillies have high water activity (aw = 0.85), which leads to rapid microbial growth and spoilage, making moisture control essential for preserving quality and safety. To address this, water activity was reduced using sequential tray drying: 60 °C/5 h + 40 °C/2 h (aw from 0.85 to 0.60) and 70 °C/11 h + 55 °C/4 h + 40 °C/2 h (aw from 0.85 to 0.35), respectively. While these drying methods successfully reduced the moisture content, they were not sufficient to fully inactivate or prevent the regrowth of microorganisms, which remain a critical concern in ensuring the microbial safety of chillies. Steam treatment was employed as supplementary control for microbial growth and to enhance enzyme stability. The steam treatment up to 300 s at a saturation temperature of 100 to 120 °C was highly effective in achieving more than an 8-log reduction in microbial count, over 99% enzyme inactivation, and improved bioactive retention. However, the steam treatment caused slight changes in the physicochemical properties of the chillies, particularly affecting their colour, weight, and surface morphology. Post-treatment analysis revealed notable shrinkage and surface roughness in the structural integrity of the chilli surfaces. The combined strategy of sequential drying (70 °C/11 h + 55 °C/4 h + 40 °C/2 h) followed by steam treatment (120 °C/300 s) represents a promising approach to producing microbially safe and enzymatically stable red chillies.