Hetong Lin

Inhibitory Effects of Propyl Gallate on Tyrosinase and Its Application in Controlling Pericarp Browning of Harvested Longan Fruits

Tyrosinase (EC 1.14.18.1), also known as polyphenol oxidase (PPO), is a key enzyme in pigment biosynthesis of organisms. The inhibitory effects of propyl gallate on the activity of mushroom tyrosinase and effects of propyl gallate on pericarp browning of harvested longan fruits in relation to phenolic metabolism were investigated. The results showed that propyl gallate could potently inhibit diphenolase activity of tyrosinase. The inhibitor concentration leading to 50% activity lost (IC50) was determined to be 0.685 mM. Kinetic analyses showed that propyl gallate was a reversible and mixed type inhibitor on this enzyme. The inhibition constants (K(IS) and K(I)) were determined to be 2.135 and 0.661 mM, respectively. Furthermore, the results also showed that propyl gallate treatment inhibited activities of PPO and POD in pericarp of harvested longan fruits, and maintained higher contents of total phenol and flavonoid of longan pericarp. Moreover, propyl gallate treatment also delayed the increases of browning index and browning degree in pericarp of harvested longan fruits. Therefore, application of propyl gallate may be a promising method for inhibiting tyrosinase activity, controlling pericarp browning, and extending shelf life of harvested longan fruits.

Role of hydroxyl radical in modification of cell wall polysaccharides and aril breakdown during senescence of harvested longan fruit.

The effects of reactive oxygen species (ROS), especially hydroxyl radical (OH), on cellular wall disassembly in vitro and in vivo, and aril breakdown in longan fruit, were investigated. OH caused the disassembly of cell wall material (CWM) in vitro, demonstrated by the increases of total sugars and uronic acid released, and the downshift in molecular mass of CDTA soluble pectin (CSP) and Na2CO3 soluble pectin (CO3-SP). In addition, OH resulted in decreased CO3-SP content and increased CSP content in CWM suspension, suggesting the conversion of CO3-SP to CSP. Application of exogenous OH accelerated aril breakdown in longan fruit while the process was delayed by l-cysteine·HCl, a ROS scavenger. Furthermore, lower CWM content and decreased molecular mass of pectins were observed in OH-treated fruit. These results indicated that OH contributed to the degradation of cell wall polysaccharides, resulting in aril breakdown in longan fruit.

Inhibitory effects of propyl gallate on membrane lipids metabolism and its relation to increasing storability of harvested longan fruit

Effects of propyl gallate on membrane lipids metabolism and its relation to storability of harvested longan fruits were studied. The results showed that the propyl gallate-treated longans maintained lower activities of pericarp phospholipase D (PLD), lipase and lipoxygenase (LOX) than those in control fruits. Such treatments could maintain higher levels of pericarp unsaturated fatty acids (USFAs), higher pericarp indices of unsaturated fatty acids (IUFA), and higher pericarp ratio of unsaturated fatty acids to saturated fatty acids (U/S) than those in control fruits. Furthermore, propyl gallate also delayed color changes of pericarp in the harvested longans. Therefore, the postharvest treatments of longan fruits with propyl gallate for increasing storability of longan fruits might be explained by a decrease in activities of PLD, lipase and LOX, and an the increased unsaturation of fatty acids, which could delay membrane lipids metabolism and maintain cell membrane characteristics.

DNP and ATP induced alteration in disease development of Phomopsis longanae Chi-inoculated longan fruit by acting on energy status and reactive oxygen species production-scavenging system

As compared with P. longanae-inoculated longans, DNP treatment for P. longanae-inoculated longans exhibited higher fruit disease index and pericarp browning index, lower ATP amount and energy charge level, lower activities of SOD, CAT and APX, lower amounts of AsA and GSH, lower levels of DPPH radical scavenging activity and reducing power, higher O2- generating rate and MDA amount. However, supply of ATP for P. longanae-inoculated longans showed the contrary effects. These results gave convincing evidence that DNP treatment for accelerating pericarp browning and disease development of harvested longans caused by P. longanae was due to decreases of energy production and ROS scavenging capacity, and increases of O2- accumulation and membrane lipid peroxidation. Whereas, supply of ATP for retarding pericarp browning and disease development of harvested longans caused by P. longanae was due to increases of energy production and ROS scavenging capacity, and reductions of O2- accumulation and membrane lipid peroxidation.

Inhibitory effects of naphthols on the activity of mushroom tyrosinase

Tyrosinase (EC 1.14.18.1), a copper-containing multifunctional oxidase, was known to be a key enzyme for biosynthesis in fungi, plants and animals. In this work, the inhibition properties α-naphthol and β-naphthol toward the activity of tyrosinase have been evaluated, and the effects of α-naphthol and β-naphthol on monophenolase and diphenolase activity of tyrosinase have been investigated. The results showed that both α-naphthol and β-naphthol could potently inhibit both monophenolase activity and diphenolase activity of mushroom tyrosinase, and that β-naphthol exhibited stronger inhibitory effect against tyrosinase than α-naphthol. For monophenolase activity, β-naphthol could not only lengthen the lag time but also decrease the steady-state activity, while α-naphthol just only decreased the steady-state activity. For diphenolase activity, both α-naphthol and β-naphthol displayed revisible inhibition. Kinetic analyses showed that both α-naphthol and β-naphthol were competetive inhibitors.

Paper-based 1-MCP treatment suppresses cell wall metabolism and delays softening of Huanghua pears during storage

BACKGROUND Huanghua pear will lose its firmness quickly during postharvest storage at ambient temperature, and hence has limited storage and marketing potential. In this study, Huanghua pears treated with paper containing 0 (control) or 0.9 μL L-1 1-methylcyclopropene (1-MCP) for 12 h, and then stored at (25 ± 1) °C for 30 days, were investigated for the effect on fruit firmness, cell wall composition and activities of cell wall-degrading enzymes. RESULTS Huanghua pears without 1-MCP treatment softened rapidly during room-temperature storage and cell wall composition analyses showed an increase in water-soluble pectin (WSP) and decreases in cell wall materials (CWM) and cell wall components such as Na2 CO3 -soluble pectin (NSP), cellulose and hemicellulose. In contrast, the 1-MCP-treated fruits maintained higher firmness than the control; also, the treatment prevented the formation of WSP and reduced the degradation of CWM and cell wall components including NSP, cellulose and hemicellulose. 1-MCP treatment also significantly lowered the activities of cell wall-degrading enzymes such as pectinesterase, polygalacturonase, β-galactosidase and cellulase during storage. CONCLUSION 1-MCP treatment can slow down the softening of Huanghua pears through reducing cell wall-degrading enzyme activities and hence maintain the integrity of the cell wall structure.

Longan (Dimocarpus longan Lour.).

While products such as bananas, pineapples, kiwifruit and citrus have long been available to consumers in temperate zones, new fruits such as lychee, longan, carambola, and mangosteen are now also entering the market. Confirmation of the health benefits of tropical and subtropical fruit may also promote consumption further. Tropical and subtropical fruits are particularly vulnerable to postharvest losses, and are also transported long distances for sale. Therefore maximizing their quality postharvest is essential and there have been many recent advances in this area. Many tropical fruits are processed further into purees, juices and other value-added products, so quality optimization of processed products is also important. The books cover current state-of-the-art and emerging post-harvest and processing technologies. Volume 1 contains chapters on particular production stages and issues, whereas Volumes 2, 3 and 4 contain chapters focused on particular fruit. Volume 1 focuses on key issues of fruit physiology, quality, safety and handling relevant to all those in the tropical and subtropical fruits supply chain. [Book summary from Google]

Phomopsis longanae Chi-induced Changes in Activities of Cell Wall-degrading Enzymes and Contents of Cell Wall Components in Pericarp of Harvested Longan Fruit and its Relation to Disease Development

The main goal of this study was to investigate the influences of Phomopsis longanae Chi infection on activities of cell wall-degrading enzymes (CWDEs), and contents of cell wall components in pericarp of harvested “Fuyan” longan (Dimocarpus longan Lour. cv. Fuyan) fruit and its relation to disease development. The results showed that, compared with the control samples, P. longanae-inoculated longans showed higher fruit disease index, lower content of pericarp cell wall materials (CWMs), as well as lower contents of pericarp cell wall components (chelate-soluble pectin (CSP), sodium carbonate-soluble pectin, hemicelluloses, and cellulose), but higher content of pericarp water-soluble pectin (WSP). In addition, the inoculation treatment with P. longanae significantly promoted the activities of CWDEs including pectinesterase, polygalacturonase, β-galactosidase, and cellulase. The results suggested that the P. longanae stimulated-disease development of harvested longans was due to increase in activities of pericarp CWDEs, which might accelerate the disassembly of pericarp cell wall components. In turn, resulting in the degradation of pericarp cell wall, reduction of pericarp mechanical strength, and subsequently leading to the breakdown of longan pericarp tissues. Eventually resulting in development of disease development and fruit decay in harvested longans during storage at 28°C.

Phomopsis longanae Chi-Induced Disease Development and Pericarp Browning of Harvested Longan Fruit in Association With Energy Metabolism

Longan fruit is a popular subtropical fruit with a relatively short shelf life at room temperature mainly due to pericarp browning and fungal infection. This study aimed to investigate the infection of Phomopsis longanae Chi in longan fruit and its effects on the storability and shelf life of longan fruit. The relationship between the energy metabolism of harvested longan fruit and disease development and pericarp browning was elucidated. Results show that P. longanae-inoculation accelerated the deterioration of longan fruit and caused pericarp browning. It also led to the energy deficit in pericarp of longan fruit, which was reflected as lower contents of ATP and ADP, higher AMP content, and lower energy charge as compared to the control samples. Additionally, P. longanae-infection reduced the activities of H+-ATPase, Ca2+-ATPase, and Mg2+-ATPase in plasma, vacuolar, and mitochondrial membranes during the storage period. The results demonstrate that P. longanae-infection led to disease development and pericarp browning in harvested longan fruit, which were due to the infection-induced energy deficit and low ATPase activity that caused disorders of ion transport and distribution, and damaged the structure and function of vacuole, mitochondria, and eventually the whole cells of fruit tissues.

Rapid determination of thiabendazole in juice by SERS coupled with novel gold nanosubstrates

The aim of this study was to develop surface-enhanced Raman spectroscopy (SERS) methods in combination with novel gold nanomaterial-based substrates for rapid measurement and quantification of pesticides extracted from lemon, carrot, and mango juice. Facile synthesis of a sensitive and robust SERS substrate was achieved by assembling gold nanorods (AuNRs) into vertically aligned arrays on silicon slides. The nanorod arrays were orderly aligned and can induce vigorous electromagnetic field for SERS measurement. The synthesized SERS substrate was utilized for detection and quantification of thiabendazole in juice samples using partial least squares analysis with R values of 0.99, 0.98, and 0.99 for lemon, carrot, and mango juice, respectively. The detection limits of thiabendazole were 149, 216, and 179 μg/L in lemon, carrot, and mango juice, respectively. These results demonstrate that SERS combined with AuNR substrates is a quick, convenient, and highly sensitive technique for detection of thiabendazole residues in fruits juice.