Jian Sun

Comparison on characterization of longan (Dimocarpus longan Lour.) polyphenoloxidase using endogenous and exogenous substrates.

Longan polyphenoloxidase (PPO) was extracted and partially purified using ammonium sulfate precipitation and dialysis. The PPO characterizations were compared using endogenous substrate (-)-epicatechin and exogenous substrate catechol. The optimal pH and optimal temperature for the PPO activity were different when reacting with both substrates. The addition of ethylenediaminetetraacetic acid disodium salt into both substrate-enzyme systems exhibited the same lowest inhibition of the PPO activity. L-ascorbic acid and L-cysteine were the best inhibitors to endogenous substrate-enzyme system, while L-ascorbic acid and glutathione were most effective inhibitors to exogenous substrate-enzyme system. Cupric (Cu2+), ferric (Fe3+), and ferrous (Fe2+) ions accelerated the enzymatic-catalyzed reactions of both substrates. Kinetic analysis indicated that longan PPO strongly bound endogenous substrate but possessed a higher catalytic efficiency to exogenous substrate, and moreover, (-)-epicatechin was determined as the optimal substrate for longan PPO. This study is useful to exactly illuminate the enzymatic-catalyzed browning mechanism of postharvest longan fruit.

Production and Characteristics of High Quality Vinegar from Sugarcane Juice

A high quality sugarcane original vinegar drink was produced from fresh sugarcane juice using the wine yeast and LB acetate bacteria by submerged alcoholic fermentation followed by acetic fermentation at room temperature. The quality parameters of vinegar was investigated during the process of submerged fermentation. It was observed that the alcoholic fermentation period of 9 to 20 days and an acetic fermentation period of 15 to 21 days each in succession, produced the sugarcane quality vinegar with 3.04xa0% (w/v) total acid and 4° alcoholicity. Besides the vinegar consisted of many saccharides (fructose, glucose, sucrose) and organic acids (oxalic acid, tartaric acid, citric acid, acetic acid). The prominent ingredient of acetic acid ranged from 8.16 to 13.65xa0mg/g. Vinegar produced by this process yielded a yellow–brown colour with full wine aromas and cane flavour, mild and mellow, low-alcohol and strong odour of vinegar. The present study provides a new approach to process sugarcane byproducts, which contributes to the value-added production and processing of sugarcane.

Phenolics and polysaccharides in major tropical fruits: chemical compositions, analytical methods and bioactivities

Tropical fruits are important sources of phenolics and polysaccharides which are of great benefit to human health and have already been used in foodstuff, drugs and cosmetics. This review attempts to summarize the current research on phenolics and polysaccharides in major tropical fruits with large-scale production. Chemical composition, analytical methods, bioactivities and therapeutic functions of main phenolics and polysaccharides in pericarps, pulps and/or seeds of lychee (Litchi chinensis Sonn.), longan (Dimocarpus longan Lour.), mango (Mangifera indica L.), banana (Musa acuminata L.), pineapple (Ananas comosus L.) and papaya (Carica papaya L.) fruits are elucidated. The future research trends on phenolics and polysaccharides in tropical fruits are also suggested. This review indicates potential applications of phenolics and polysaccharides in tropical fruits, which is an important reference for effectively utilizing these bioactive components in tropical food systems.

Effects of Polysaccharide-Based Edible Coatings on Quality and Antioxidant Enzyme System of Strawberry during Cold Storage

Strawberry is a nutritious, but highly perishable fruit. Three polysaccharide-based edible coatings (alginate, chitosan, and pullulan) were applied to postharvest strawberry fruit during cold storage (4°C), and their effects on fruit quality and antioxidant enzyme system were investigated in the present study. The results showed that polysaccharide coatings showed a significant delay in fruit softening and rot and reduced changes in total soluble solid and titratable acidity content during 16u2009d storage. Polysaccharide coatings also maintained higher ascorbic acid and total phenolic contents than control from day 2 and significantly inhibited fruit decay and respiration after 12u2009d storage ( ). Polysaccharide treatments enhanced the activities of antioxidant enzymes (peroxidase, catalase, superoxide dismutase, and ascorbate peroxidase) so as to prevent lipid peroxidation and reduce membrane damage. Additionally, chitosan coating had the most positive effects on fruit quality amongst three polysaccharide-based edible coatings and presented the highest relative activities of antioxidant enzymes. These results indicated that polysaccharide-based edible coatings were helpful in postharvest quality maintenance of strawberry fruit.

Cloning, Characterization, and Functional Expression of Phospholipase Dα cDNA from Banana (Musa acuminate L.)

Phospholipase D (PLD) plays a key role in adaptive responses of postharvest fruits. A cDNA clone of banana (Musa acuminate L.) PLDα () was obtained by RT-PCR in this study. The MaPLDα gene contains a complete open reading frame (ORF) encoding a 92-kDa protein composed of 832 amino acid residues and possesses a characteristic C2 domain and two catalytic H×K×××D (abbr. HKD) motifs. The two HKD motifs are separated by 341 amino acid residues in the primary structure. Relatively higher PLD activity and expression of MaPLDα mRNA were detected in developing tissues compared to senescent or mature tissues in individual leaves, flower, stem, and fruit organs, respectively. The expression profile of PLDα mRNA in postharvest banana fruits at different temperatures was determined, and the MaPLDα mRNA reached the highest expression peak on day 5 at 25°C and on day 7 at 12°C. The results provide useful information for maintaining postharvest quality and extending the storage life of banana fruit.

Responses of Phospholipase D and Antioxidant System to Mechanical Wounding in Postharvest Banana Fruits

Banana fruits are susceptible to mechanical damage. The present study was to investigate the responses of phospholipase D (PLD) and antioxidant system to mechanical wounding in postharvest banana fruits. During 16u2009d storage at 25°C and 90% relative humidity, PLD activity in wounded fruits was significantly higher than that in control (without artificial wounding fruits). The higher value of PLD mRNA was found in wounded fruits than in control. PLD mRNA expression reached the highest peak on day 4 in both groups, but it was 2.67 times in wounded fruits compared to control at that time, indicating that PLD gene expression was activated in response to wounding stress. In response to wounding stress, the higher lipoxygenase (LOX) activity was observed and malondialdehyde (MDA) production was accelerated. The activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) in wounded fruits were significantly higher than those in control. The concentrations of reactive oxygen species (ROS) such as superoxide anion () and hydrogen peroxide (H2O2) in fruits increased under mechanical wounding. The above results provided a basis for further investigating the mechanism of postharvest banana fruits adapting to environmental stress.