Effects and mechanisms of colour protectants combined with ultrasound treatment on colour enhancement in hot-air-dried green peppers (Piper nigrum L.)

The effects and influence mechanisms of l -ascorbic acid (AsA), L-glutathione (GSH), and their combination with ultrasound (US) treatment on the colour of hot-air-dried green peppers were investigated. The 0.10 %AsA − US (180 W) treatment resulted in the most favourable appearance, with a ⁎ , Δ E ⁎ , and BD values significantly decreasing by 145.3 %, 85.1 %, and 32.2 %, respectively. Additionally, the retention rates of AsA and total polyphenols in this group reached 134.53 % and 115.63 %, significantly higher than those of the control. Moreover, 5,7-dihydroxy-3,4,5-trimethoxyflavone was the monophenol most strongly negatively correlated with Δ E ⁎ ( R  = −0.94), contributing to a colour more closely resembling that of fresh green peppers. Importantly, AsA reacts with oxygen to inhibit polyphenol autoxidation and acts as a reducing agent to decrease quinone accumulation, while GSH inhibits browning by forming stable adducts with quinones. These results provide a theoretical basis and technical support for the processing of green peppers.