Xinguo Su

Identification of Major Phenolic Compounds of Chinese Water Chestnut and their Antioxidant Activity

Chinese water chestnut (CWC) is one of the most popular foods among Asian people due to its special taste and medical function. Experiments were conducted to test the antioxidant activity and then determine the major phenolic compound components present in CWC. CWC phenolic extract strongly inhibited linoleic acid oxidation and exhibited a dose-dependent free-radical scavenging activity against alpha,alpha-diphenyl-beta-picrylhydrazyl (DPPH) radicals, superoxide anions and hydroxyl radicals, which was superior to ascorbic acid and butylated hydroxytoluene (BHT), two commercial used antioxidants. Furthermore, the CWC extract was found to have a relatively higher reducing power, compared with BHT. The major phenolic compounds present in CWC tissues were extracted, purified and identified by high-performance liquid chromatograph (HPLC) as (-)-gallocatechin gallate, (-)-epicatechin gallate and (+)-catechin gallate. This study suggests that CWC tissues exhibit great potential for antioxidant activity and may be useful for their nutritional and medicinal functions.

Effects of anti-ethylene treatments on browning and energy metabolism of harvested litchi fruit

Litchi fruit were treated with 10 mL/L ethylene (C2H4), 0.1% cobalt chloride (CoCl2) and 1 mL/L 1-methylcyclopropene, respectively, packed individually in closed but vented containers, and then stored at ambient temperature (28–33°C). The effects of these treatments on the browning, energy metabolism and disease incidence of the fruit were investigated. Treatment with C2H4 enhanced the activities of polyphenol oxidase and phenylalanine ammonia-lyase. Ethylene also increased the accumulation of ADP and AMP, but decreased energy charge in fruit peel. Cobalt chloride treatment had an inhibitory effect on increases of peroxidase activity, ATP : ADP ratio, energy charge and ATP, ADP and AMP. Browning index was reduced by 8.4 and 10.4% and disease index was reduced by 10.7 and 12.7% in CoCl2 and 1-methylcyclopropene-treated fruit, respectively, suggesting a relationship between energy metabolism, browning and disease index.

Influence of the nitric oxide donor, sodium nitroprusside, on lipid peroxidation and anti-oxidant activity in pericarp tissue of longan fruit

Summary The effects of nitric oxide (NO) on lipid peroxidation and anti-oxidant activity in longan fruit were investigated during storage. Fruits were dipped for 5 min in a solution containing 1 mM sodium nitroprusside (SNP), an NO donor. They were then packed into polyethylene bags and stored for 6 d at 28°C. Changes in pericarp browning index, membrane permeability, malondialdehyde (MDA) content, the rate of superoxide production, the activities of lipoxygenase (LOX), superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT), α,αdiphenyl-βpicrylhydrazy (DPPH) radical scavenging activity, and reducing power were measured. Treatment with SNP inhibited pericarp browning and suppressed increases in membrane permeability and lipid peroxidation. These effects were associated with lower LOX activity, higher APX and CAT activities, better maintenance of DPPH radical scavenging activity and reducing power, and lower superoxide production rate. However, SOD activity was higher in control (non-SNP-treated) fruit than in SNP-treated fruit over the first 4 d of storage. Overall, these findings suggest that treatment with NO enhanced the anti-oxidant activity in pericarp tissue of longan fruit during storage, and contributed to reduced lipid peroxidation. Reduced lipid damage apparently maintained the compartmentation of enzymes and substrates and, thereby, lessened enzymatic browning.

Effects of adenosine triphosphate on the vase life of cut carnation flowers

The addition of adenosine triphosphate (ATP) to vase solutions at a concentration of 0.01−0.50 mmol/L markedly extended the vase life of cut carnation flowers at 25°C and 80−90% relative humidity. The most beneficial effect on vase life was observed at 0.1 mmol/L ATP, with a 28% extension over non-ATP-treated flowers. Furthermore, the addition of ATP at 0.1 mmol/L increased flower size by 12% by the end of the vase-holding period and significantly extended the time to maximum flower expansion by 1.7 days, compared with non-ATP-treated flowers held in distilled water. Our data suggest that exogenous ATP supply is an effective method to extend the vase life of cut carnation flowers.

Redox regulation of methionine in calmodulin affects the activity levels of senescence-related transcription factors in litchi

Reactive oxygen species (ROS) play a role in aging and senescence in organisms. The oxidation of methionine (Met) residues in proteins to Met sulfoxide by ROS can cause conformational alteration and functional impairments. Met oxidation is reversed by Met sulfoxide reductase (Msr) A and B. Currently, the repair of oxidized proteins by Msr and Msr-mediated physiological functions are not well understood, especially in higher plants. The down-regulated expression of LcMsrA1/B1 may be involved in the senescence of litchi (Litchi chinensis) fruit. We verified that LcCaM1 is a substrate of LcMsrA1 and LcMsrB1 in vitro and in vivo, and oxidized LcCaM1 could be repaired by LcMsrA1 in combination with LcMsrB1. Moreover, LcMsrA1 and LcMsrB1 play important roles in repairing oxidized Met110 and Met125 residues, respectively, in LcCaM1. Furthermore, the Met oxidation in LcCaM1 did not affect its physical interactions with two LcCaM1-binding senescence-related transcription factors LcNAC13 and LcWRKY1, but enhanced their DNA-binding activities. Therefore, we hypothesized that the down-regulated expression of LcMsrA1/B1 results in the accelerated oxidation of LcCaM1, which enhanced the DNA-binding activities of LcNAC13 and LcWRKY1, thereby activating or repressing the expression of senescence-related genes.