Effect of thermal treatment on physicochemical, phytochemical, and microbiological characteristics of brown Spanish onion paste

Onion paste is a commercially used processed product that reduces cooking time. Industrial processing of onion paste involves various treatments that affect the overall nutritional profile of the final product. In this study, effect of various thermal treatment conditions was evaluated, with temperature and time ranging between 70 and 90°C for 8 to 22 min, respectively. Changes in quercetin, pyruvic acid, and quality characteristics of fresh onion paste were investigated. A negative linear trend was observed in quercetin, pyruvic acid, viscosity, ascorbic acid, and total plate count, with an increase in temperature and time. An interactive and combined effect of time and tem-perature showed a positive linear relationship with color difference. For all the quality parameters investigated in this study, thermal treatment at 87°C for 15 min was found to be optimum for development of shelf-stable onion paste. Quercetin and pyruvic acid content were found to be 2.587±0.03 g kg–1 and 0.086±0.004 µmol kg–1, respectively. Optimum conditions depicted better retention of principal compounds as compared to the other experimental conditions and exhibited safer quality product as compared to the untreated sample.Industrial relevance: Brown Spanish onion is a perishable produce due to high moisture content. In order to reduce its postharvest losses at domestic and commercial levels, optimized processing parameters for the production of onion paste can be economically beneficial, and it is a highly acclaimed product for consumer usage.