Enhancement of colour density and anthocyanin stability in pomegranate juice against 5-hydroxymethylfurfural at different concentrations by amino acid copigmentation during storage

This study investigated the effect of amino acid [aspartic acid (Asp), phenylalanine (Phe) and valine (Val)] copigmentation on pomegranate juice (PJ) anthocyanins in the presence of 5-hydroxymethylfurfural (HMF) at different concentrations (2.3–15.2 mg/L) during storage at 20°C. A decrease in stabilities of anthocyanin and colour density (CD) was observed at 5.2–8.2 mg HMF/L. However, 15.2 mg HMF/L prevented the decrease in anthocyanin stability. In this sample, copigmentation occurred when ratios of "cyanidin-3,5-diglucoside to HMF" and "cyanidin-3-glucoside to HMF" were 1.82–2.67 and 1.91–2.85, respectively. The highest reduction in HMF content resulted from addition of Val. As number of –CH₃ groups in an amino acid increased, HMF reducing effect of amino acid increased. In PJ containing 8.2 mg HMF/L, Val provided the highest stabilities for individual anthocyanins, CD and hyperchromic effect (HE). Asp increased the stability of CD and HE in PJ containing 5.2 mg HMF/L, while Phe increased the stability of CD at a concentration of 15.2 mg HMF/L. Depending on the amount of HMF, the effect of adding amino acids to PJ to improve colour stability and reduce HMF content varies. Therefore, after determining the initial HMF content of PJ, the amino acid to be added to PJ should be decided.