Effects of maceration with phenolic additives on the physicochemical properties and antioxidant activity of blackened jujube (Ziziphus jujuba Mill.)

Ziziphus jujuba cv. Goutouzao (GTZ) was pretreated by macerating with phenolic additives (green tea powder, tea polyphenols, EGCG and pomegranate peel ellagic acid) before the blackening process to improve the functional quality. The antioxidant capacity and physicochemical properties during the process of different treatment groups were evaluated by high-performance liquid chromatography (HPLC) and spectrophotometric assays. The results showed that the total phenolic content and antioxidant capacity were higher with each tested additive than the blank control group. Among them, the EGCG group had the highest total phenolic content and the strongest antioxidant capacity, whereby the total phenolic content of the blackened jujube was 24.59 times higher than the control group at the end of blackening (84 h). The scavenging of DPPH radicals, scavenging of ABTS radicals and total reducing capacity were 26.36, 5.51 and 4.58 times higher than those of the control group, respectively. The 5-hydroxymethylfurfural (5-HMF) content of blackened jujube in the EGCG and tea polyphenol groups was significantly reduced, and was 72.36 and 36.47% lower than the control group at the end of blackening, respectively. The green tea powder, EGCG and ellagic acid groups had the highest cyclic adenosine monophosphate (cAMP) content at the end of blackening, which was 50, 70 and 87% higher than in the control group, respectively. Correlation analysis showed a highly significant negative correlation between total phenolic content and 5-HMF content (p < 0.01). The heatmap showed that the EGCG-macerated blackened jujube had the best comprehensive medicinal profile, with low 5-HMF, high residual cAMP, and increases total phenolic content, resulting in high antioxidant activity.