Effects of concentration method and storage time on some bioactive compounds and color of jujube (Ziziphus jujuba var vulgaris) concentrate.

Jujube extract was concentrated by various heating methods including vacuum, microwave and conventional heating. The effect of concentration methods and storage time (for 90 days at 4 °C) on total phenolic and total monomeric anthocyanin contents, individual anthocyanins, individual organic acids, and color values of jujube concentrate was investigated separately. The desired level of concentration (65.0 °Brix) was achieved in 45, 96 and 117 min by the microwave, vacuum and conventional heating methods, respectively. The concentrate obtained with microwave method had the highest total phenolic content (159.32 mg GAE/g DW) and total monomeric anthocyanin content (48.84 mg cyn-3-glu/100 g DW) in comparison to the other methods at the beginning of storage. Hunter color parameters (L*, a* and b*) decreased significantly with increasing the time of storage in all cases; however, this effect was more obvious in the vacuum heating. Cyanidin-3,5-diglucoside was determined as the major anthocyanin in all concentrates, while its degradation was more pronounced in the conventional heating (25.59%) comparing to the microwave (11.14%) and vacuum methods (17.59%) during the 90-day storage. The jujube concentrate prepared with the microwave method had the highest organic acid contents (e.g. malic, citric, succinic and ascorbic acids) as compared to the other methods. Thus, according to the results, the heating method and storage time had significant effects on the bioactive compounds and color values of jujube concentrate. In general, microwave energy could be successfully used in production of jujube concentrate followed by 90-day storage.