Dry Sterilization of Paprika (Capsicum annuum L.) by Short Time-Intensive Microwave-Infrared Radiation: Establishment of Process Using Glass Transition, Sorption, and Quality Degradation Kinetic Parameters

The present study was undertaken for inactivation of S. Typhimurium and A. flavus in paprika by short time intensive microwave-infrared (MW-IR) radiation. The MW-IR heating experiments were carried out using the central composite design with the microwave power density, infrared heater temperature, the distance between the infrared heater and paprika layer, and heating time in the range of 4–12 W g⁻¹, 75–375 °C, 6–14 cm and 15–75 s, respectively. It was observed that whenever the temperature of paprika was exceeded its corresponding glass transition temperature, it resulted in accelerated moisture diffusion and quality degradation. Also, the correlation of overall color degradation with sorption and thermal characteristics of paprika was established. The spatial changes in the temperature and water activity of paprika during short time intensive MW-IR heating resulted in 8.849 log reduction of total plate count (S. Typhimurium) and 7.372 log reduction of yeast and mold count (A. flavus) in presence of natural microbial flora.India is the largest producer, consumer, and exporter of spices in the world. The steam-assisted sterilization is widely practiced in Indian spice industry but steam treatment is problematic particularly for paprika because of moisture condensation and additional drying cycle resulting in excess quality degradation which fetches a low price in the export market. The present work has been carried out based on industry demand for alternative technology considering spice growers and processors with the special requirement on the quality profile, bactericidal efficacy, ease of operations, cost-effectiveness, and affordability. The results of the present study showed that the short time intensive MW-IR assisted heating process would be an alternative method for finish drying, microbial and enzyme inactivation, and restriction of moisture deteriorative reactions in low moisture products like spices considering demand of spice growers, processors, and exporters.