Processing And Storage Of Red Jujube Juice Concentrate Phenolics

Chinese jujube juice concentrate is a kind of concentrated beverages which are usually produced through a series of processing treatments such as squeezing, enzymolysis, ultrafiltration, concentration and pasteurization. Chinese jujube is rich in nutrients like vitamins, amino acids and minerals, and contains varieties of biologically active ingredients like cyclic nucleotides, triterpenic acids, alkaloids and phenolics. During processing and storage, these components are inevitably destroyed and lost. Phenolic compounds in fruits usually show strong antioxidant, anticancer, antiviral and anti-cardiovascular activities because of their special molecular structures. Nevertheless, some of these healthful compounds can bind to haze-active proteins, resulting in turbidity or haze, and lead to browning for its oxidative condensation. Despite of bearing positive or negative behaviors, distinctly, polyphenols have been paid more and more attentions. In order to control the loss of phenolic compounds in jujube concentrates and optimize the related processes, this study was performed by monitoring the variations of phenolics levels in jujube juice concentrate during processing and storage. The contents are mainly presented as followed:1. The effects of different pretreatment methods on phenolics levels were studied. The results showed that both peeling and denucleating could significantly reduce the content of jujube phenolic compounds. The loss rates of total phenols were12.3%and5.8%, respectively. When the solid-liquid ratio was fixed,50℃and12h is the best option for jujube rehydration.2. Based on the results of preliminary experiments, a four factor three level Box-Behnken design and the desirability function approach were used to optimize enzymatic conditions. The optimized conditions were0.13%for pectinase dosage,0.30%for protease dosage,55℃for incubation temperature and270min for incubation time. However, to shorten the producing time, the incubation time was down to2h. At this condition, the juice yield was86.7%and the turbidity was5.1NTU.3. The effects of enzyme treatment, ultrasonication, ultrafiltration, vacuum concentration and pasteurization on phenolics levels were evaluated. After enzyme treatment, total phenols were decreased by0.58%. Ultrasound-assisted extraction displays a positive effect on the increased levels of the phenolic compounds while total phenols were increased by4.2%. Ultrafiltration could significantly reduce all of the phenolic compounds and the loss rate of total phenols was42.0%. However, vacuum concentration and pasteurization did not have significant effects on the phenolics. After concentration, total phenols were0.80%while0.40%after pasteurization.4. During storage, turbidity and browning were increased to varying degrees at different temperatures. Higher storage temperature and longer storage time showed stronger effects on the enhancement of turbidity and browning.5. Storage temperature and storage time could significantly influence all the selected phenolic compounds. Gallic acid, ferulic acid, p-hydroxybenzoic acid, protocatechuic acid and rutin declined slightly at4℃, while visibly at25℃and37℃. The lowest stability of the5polyphenols was observed in the concentrates stored at37℃. The similar tendency was found in caffeic acid at4℃and25℃. However, the content of caffeic acid stored at37℃increased up to40days, and after that, decreased. At4℃, the amount of p-coumaric acid increased up to a point and then decreased. But at25℃and37℃,p-coumaric acid both increased until the end of storage. Chlorogenic acid, isochlorogenic acid and quercetin diminished rapidly at all storage temperatures and higher temperature promoted the reductions. After storage, they were even not detected. Galangin decreased also rapidly up to58days at4℃and25℃. From that on, gentle variations were observed. At37℃, content of galangin first decreased sharply till38days of the storage, and then began to ascend.6. When jujube juice concentrates were stored at4℃, all specific polyphenols except p-coumaric acid correlated highly to turbidity and browning with negative correlations. At25℃, all specific polyphenols were highly related to turbidity and browning. At37℃, turbidity was mainly correlated to gallic acid, ferulic acid, p-coumaric acid, caffeic acid, protocatechuic acid,p-hydroxybenzoic acid and rutin. All specific polyphenols except for caffeic acid had strong links with the browning of the concentrates. The results thus indicated that the alterations of the phenolic compounds made different contributions to the changes of turbidity and browning at varied temperatures.