Alkaline-extracted thinned young apple polyphenols as an effective scavenger against nitrite in pickles: A comparative study with ethanol-extracted polyphenols

Abstract Pickles are popular fermented vegetable products worldwide. However, nitrite residue in pickles has caused a major safety concern. In this study, we adopted 80% ethanol solution (v/v) and 4N NaOH solution as solvents to extract polyphenols from thinned young apples, and the resulting polyphenols were designated EEP (ethanol-extracted polyphenols) and AEP (alkaline-extracted polyphenols), respectively. The results showed that AEP had a higher extraction yield than EEP, and the main individual phenolic components in AEP and EEP were different. Additionally, the DPPH scavenging capacity (1,1-diphenyl-2-picrylhydrazyl free radical) of AEP was slightly higher than that of EEP, indicating that the antioxidant activity of AEP was better than that of EEP. Further experiments suggested that both AEP and EEP exhibited good nitrite-scavenging capacity under simulated acidic conditions (pH ~3.8, close to the pH of real pickle products), with AEP showing a more pronounced effect. Moreover, in a real pickle system, the nitrite-scavenging capacity of AEP was also better than that of EEP, possibly because AEP contained a higher caffeic acid content, which was proven more effective in reacting with nitrite than chlorogenic acid (the main individual polyphenol in EEP). In addition, the EEP and AEP addition did not significantly affect the original flavor and taste of the pickle, which highlights the potential application of thinned apple polyphenols in pickle production.