Ultra-high pressure effects on color, volatile organic compounds and antioxidants of wholegrain brown rice (Oryza sativa L.) during storage: A comparative study with high-intensity ultrasound and germination pretreatments

Abstract

Abstract Wholegrain brown rice (WBR) with significantly enhanced quality attributes has been recently achieved after ultra-high pressure (UHP) processing, but the process-induced changes in physicochemical parameters following subsequent storage for UHP-treated WBR are scarcely documented. So this work was designed to investigate the effects of UHP treatments (0.1–450 MPa/10 min) on chemical composition, microstructure, and the changes in chemical reactions during storage (20 days/30 °C) as indicated by volatile profiling, color development, and antioxidant activities for WBR grains, compared to high-intensity ultrasound (HIU) and germination (GER) pretreatments. Results showed that significant variation in physicochemical properties was caused by both processing approaches and storage duration. Color changes (a*, b*, L*, and ΔE) were slightly noticeable after storage for all WBR samples, and UHP-treated grains represented clearly visible browning reactions. In addition, hierarchically clustered heatmap suggested that volatile fingerprinting could be preliminarily separated according to different pretreatments and storage duration. After immediate treatments, total antioxidant activities presented a decrease by 14–28% for all treated grains compared to the unprocessed samples. Within storage process, GER and HIU samples showed steadily declining trends for antioxidant activities whereas a fluctuation was observed in UHP-treated grains. Besides, samples treated by 350/450 MPa maintained more antioxidants (91–102%) than the control (83–87%), GER (64–76%) and HIU (76–88%) samples at the end of storage. Multivariate analysis revealed a close relationship between color changes and antioxidant activity. These results indicated the necessity of a complete evaluation for possible processing effects on physicochemical and nutritional characteristics of WBR grains within the entire process extending immediate treatments to its prolonged storage and consumption, in order to achieve better quality control using the optimized processing parameters. Industrial relevance The selected emerging techniques including UHP, HIU and GER allow the acquisition of WBR products with improved texture and cooking properties as well as the enrichment of bioactive components. Nevertheless, the processed WBR grains must be subjected to a storage process before consumption. A more comprehensive understanding of the effects of newly-developed techniques on quality characteristics of WBR grains contributes to better control of products quality, particularly extending from immediate effects to the prolonged storage.