Increase in Color Stability through Amino Acid Copigmentation in Pomegranate Juice during Storage

Pomegranate juice (PJ) loses its impressive purple-red color during storage. Exploiting the copigmentation effect of amino acids could be a solution to this problem. This study was the first to investigate the effect of amino acids with different chemical structures (aspartic acid, phenylalanine, valine, asparagine, and lysine) on the storage stability of anthocyanins (ACNs) and color in PJ. All amino acids formed complexes with anthocyanins [r = (−0.615)–(−0.968)]. Aspartic acid was the only amino acid to show a significant increase in the stability of total monomeric anthocyanin (4.7%) and cyanidin-3-glucoside (Cy-3-glu, 7.4%) and in Amax value (4.7%). Cy-3-glu, major anthocyanin in PJ, showed the greatest increase in stability in the presence of aspartic acid, followed by asparagine (3.7%), valine (3.1%), and phenylalanine (2.9%). Lysine reacted with all anthocyanins [r = (−0.921)–(−0.991)] and caused a strong decrease in Amax (19.2%). Amino acids prevented browning before storage by forming a chelate with Cu (II) or inhibiting the oxidation of quinones. Aspartic acid is recommended for color stabilization, especially in juices rich in Cy-3-glu, due to its high copigmentation with Cy-3-glu and inhibition of browning.