pH-driven formation of soy protein isolate-thymol nanoparticles for improved the shelf life of fresh-cut lettuce

Plant essential oils as natural preservatives are attracting attention for their non-toxic and antibacterial properties, and are gradually being used in food preservation. In this study, thymol was encapsulated in Soy protein isolate (SPI) via pH-driven method to construct a convenient, efficient and safe thymol delivery system without the need of adding other substances. The loading efficiency of thymol in complexes formed in 10 mg/mL SPI and 6 mg/mL thymol was 37.3 %, and the particles were spherical with a z-average diameter less than 120 nm. Results of antibacterial activity showed that SPI-thymol nanoparticles effectively inhibited growth of Escherichia coli and Bacillus subtilis. Applying on fresh-cut lettuce, the nanoparticles also reduced weight loss, retain ascorbic acid and chlorophyll contents during shelf-life. Additionally, SPI-thymol nanoparticles effectively inhibited growth of bacteria, mold, and yeast during storage. The sensory evaluation results indicated that the nanoparticles had a satisfactory impact on the sensory characteristics of lettuce. These results illustrated that SPIthymol nanoparticles are a simple and promising composite transportation system and have the potential to be applied to the preservation of postharvest fruits and vegetables.