Effect of nitric oxide on pericarp browning of harvested longan fruit in relation to phenolic metabolism

The effects of nitric oxide (NO) on enzymatic browning of harvested longan fruit in relation to phenolic metabolisms were investigated. Fruits were dipped for 5 min in 1 mM sodium nitroprusside (SNP), a nitric oxide donor, then packed in 0.03 mm thick polyethylene bags, and finally stored for 6 days at 28 °C. Changes in pericarp browning and pulp breakdown were evaluated, while total phenol content, activities of phenolic-associated enzymes, polyphenol oxidase (PPO), peroxidase (POD) and phenylalanine ammonia lyase (PAL), and concentrations of total soluble solids, titratable acidity and ascorbic acid were measured. SNP treatment delayed pericarp browning, inhibited activities of PPO, POD and PAL and maintained a high total phenol content of longan fruit during storage. Furthermore, NO showed a significant inhibition of the in vitro activities of PPO and POD, indicating that the beneficial effect of NO was direct. Moreover, application of NO resulted in a lower pulp breakdown and maintained relatively high levels of total soluble solids and ascorbic acid.     

Browning on the surface of cut lettuce slices inhibited by short term exposure to nitric oxide (NO)

Freshly cut lettuce slices (Latuca sativa L.) were fumigated with nitric oxide (NO) gas at concentrations between 5 and 1000 μl/l in air at 20 °C for 1–4 h or dipped in an aqueous solution of the NO-donor compound, 2,2′-(hydroxynitrosohydrazino)-bisethanamine (DETANO) at concentrations between 10 and 1000 mg/l for 15 s to 60 min at 20 °C. Development of browning on the cut surfaces was inhibited during subsequent storage at 0 °C. The most effective treatments for extending postharvest life of lettuce slices were fumigation with 500 μl/l NO for 1 h, and dipping in 500 mg/l DETANO for 5 min. Dipping in DETANO solution was, however, more effective as it generated a 100% increase in postharvest life compared with a 70% increase due to NO gas. Solutions of DETANO in water were found to be relatively stable as the same extension in postharvest life was obtained for five batches of lettuce sequentially dipped in the same solution.     

久保桃贮期褐变抑制的研究

研究了自制核果类果蔬保鲜剂抑制久保桃贮期果肉褐变的问题。结果表明,久保桃果实采后室温下衰老进程较快,采后第3d和第9d出现呼吸高峰,经自制核果类果实保鲜剂处理后,呼吸高峰明显下降。0℃贮藏到48d,褐变指数为6.9%,褐变度仍能保持较优水平,比对照降低89.7%,室温(25℃)贮藏到15d,褐变指数为12.8%,褐变度也能保持较高水平,比对照降低41.8%。自制核果类果实保鲜剂在桃贮藏期防止果肉褐变方面效果显著。     

鲜切果蔬酶促褐变机理及控制研究进展

介绍酶促褐变的机理及与褐变相关的酶,并从物理、化学等方面介绍了一些新近发展的酶促褐变抑制方法.     

一氧化氮对采后水蜜桃果实衰老和清除自由基酶系影响

为研究一氧化氮(NO)处理对采后水蜜桃果实衰老和清除自由基相关酶的影响,分别采用0、5、10、20和30μL/L的NO气体熏蒸水蜜桃,然后置于20℃下贮藏10 d。结果表明:10μL/L的NO处理可有效地抑制水蜜桃果实软化。对自由基清除酶系影响研究表明,NO处理提高了贮藏期果实超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)、脱氢抗坏血酸还原酶(DHAR)和单脱氢抗坏血酸还原酶(MDHAR)活性,保持了较高抗坏血酸(ASC)含量。因此,适宜浓度(10μL/L)的NO处理能提高桃果实清除自由基酶系能力,抑制膜脂过氧化并保持细胞膜完整性,进而改善贮藏品质。      

Effect of a combination of nitric oxide treatment and intermittent warming on prevention of chilling injury of ‘Feicheng’ peach fruit during storage

Effects of fumigation with 15 μl l⁻¹ of nitric oxide gas (NO), intermittent warming (IW) and a combination of NO and IW (NO + IW) in preventing chilling injury of ‘Feicheng’ peaches were investigated. Chilling injury index, firmness, ethylene production, cell wall fractions and cell wall metabolism-associated enzymes were evaluated. These results indicated that three treatments significantly prevented the mealiness of ‘Feicheng’ peaches. Further, NO fumigation could counteract the side effect of IW. Trans-1,2-diaminocyclohexane – N,N,N′,N′-tetraacetic acid (CDTA)-soluble fractions in control peaches significantly increased, but maintained lower contents in the three treatments. IW obviously increased the activity of polygalacturonase (PG) and endo-1,4-glucanase. NO fumigation preserved lower PG activity in early 20 days of storage, and endo-PG activity was significantly higher than that of control peaches during the later storage time. Exo-PG and endo-PG activity of the fruits treated with NO + IW was midway between those single treatments with NO and IW.     

Nonenzymatic browning of selected fruit juices affected by D-galacturonic acid

This work studies the effect of d ‐galacturonic acid (AGA) on the non‐enzymatic browning of three types of clarified concentrated fruit juices (apple, pear and peach). It was observed that the presence of AGA increases the browning of juices. This was evaluated by the evolution of the absorbance at 420 nm (A₄₂₀) with the treatment time that these juices show. The evolution at A₄₂₀ over time was fitted to first‐order kinetics and it was observed that the kinetic constant values increased with both the increase in the AGA content and the rise in the treatment. The effect of the temperature treatment on the non‐enzymatic browning of these juices was quantified by fitting the variation of the kinetic constants with the Arrehnius equation, thus obtaining the corresponding activation energies. In the case of apple juice, it was observed that for the increase in AGA content the activation energy increases considerably, while for the pear and peach juices, a slight increase of the activation energy was observed with the increase in AGA.     

Dual effectiveness of sodium chlorite for enzymatic browning inhibition and microbial inactivation on fresh-cut apples

The dual effectiveness of sodium chlorite for browning inhibition and microbial inactivation on fresh-cut apples was investigated and compared to other anti-browning and antimicrobial agents. Results indicate that sodium chlorite significantly (P < 0.001) inhibited the browning reaction of fresh-cut Red Delicious apples stored at 5 °C for 14 days. This treatment also significantly reduced polyphenol oxidase activities. Treatments with acidified sodium chlorite, calcium chloride, or calcium ascorbate exhibited strong inhibition on apple browning during the early storage, these treatment effects diminished after 7 days in storage. Combining calcium chloride with sodium chlorite further significantly (P < 0.001) improved the firmness of apple slices, and browning inhibition during storage. Additionally, treatments with acidified sodium chlorite, sodium chlorite, or the combination of sodium chlorite and calcium chloride significantly (P < 0.001) reduced Escherichia coli populations on fresh-cut apples by 3.0, 3.6, and 3.9 log cfu g⁻¹ over the water control. The dual effectiveness of sodium chlorite to inhibit enzymatic browning and inactivate E. coli may allow this compound to achieve a prominent role in improving the quality and safety of products in the fresh-cut apple and other food industries.     

Light exposure inhibiting tissue browning and improving antioxidant capacity of fresh-cut celery (Apium graveolens var. dulce)

Fresh-cut celery is perishable and susceptible to tissue browning during storage. In this study, the effect of continuous light exposure (2000 lux) on browning related enzyme activity of fresh-cut celery was investigated during 8 d storage at 7 °C using darkness (0.2 lux) as control. Light exposure significantly suppressed polyphenol oxidase (PPO) and peroxidase (POD) activities, and subsequently decreased soluble quinone accumulation and browning index (BI) evolution during storage. In addition, phenylalanine ammonia lyase (PAL) activity, total phenol (TP) content, and antioxidant capacity (AC) values were all higher when the fresh-cut celery samples were exposed to light than in darkness during storage. A significant positive correlation between TP and AC was observed at both light (R = 0.884, P < 0.01) and dark (R = 0.705, P < 0.01) conditions.     

The effect of ascorbic acid on oxidative browning of white wines and model wines

The effects of ascorbic acid addition to white wines and model wines were either anti-oxidative or pro-oxidative, and depended, inter alia , on the duration of storage. Soon after its addition, ascorbic acid decreased the redox potential and brown colour of model wines and white wines. However, with time, these effects were reversed, and redox potential, SO₂ consumption and browning were greater in samples with added ascorbic acid. The point at which the net effect of ascorbic acid addition was to increase browning occurred earlier at higher SO₂ levels. Under a variety of accelerated (45®), or prolonged (ranging from three months to five years) storage conditions, the browning of model wines and white wines was invariably enhanced by ascorbic acid addition, and this enhancement took place whether or not SO₂ was present. The addition of SO₂ alone, rather than ascorbic acid alone or SO₂ plus ascorbic acid, appears to be the most effective and least expensive way of protecting white wine from browning during bottle conservation.     

Non-enzymatic browning and ascorbic acid degradation of orange juice subjected to electroreduction and electro-oxidation treatments

Orange juice was submitted to electroreduction and electro-oxidation treatments prior to pasteurization and compared to a control juice for oxido-reduction potential (ORP), dissolved oxygen and ascorbic acid contents. Evolution of non-enzymatic browning reactions and ascorbic acid degradation was evaluated at 4, 21 and 37 °C storage temperatures. Electroreduction treatment of the juice at 6 V (cell length of 1.58 cm) created a substantial reducing reservoir as ORP decreased from + 161 to −406 mV and it decreased dissolved oxygen by more than 90% of its initial content while the ascorbic acid content was not altered. In contrast, the electro-oxidation treatment raised the final ORP of the juice by 15 to 20 mV, increased substantially the dissolved oxygen content and decreased significantly the ascorbic acid retention. Electro-oxidation treatment resulted in an increase of non-enzymatic browning reactions during storage. Both the control and electroreduced juice showed very similar trends in ascorbic acid degradation over the 3 months storage period whereas the anions, cations and amino acids profiles of the juice remain unchanged. Contrary to the control and electroreduced juices, the electro-oxidation process decreased severely the orange flavor intensity and character being characterized as musty with sour-bitter aftertaste.

Industrial relevance of electrolytic treatment to modulate the oxidation-reduction potential of comestible food systems

The limitation of shelf life imposed on comestible beverage systems (juice, beer, milk, wine, etc.) is an important and common issue for food manufactures and consumers. The shelf life is shortened by the time-dependent development of off-flavors, browning, change of colors, and deterioration of nutrients, caused by the oxidative reactions of chemical and nutrient components in the food systems. Consequently, the food is becoming unattractive to consumers. The electrochemical technique by means of an electrochemical cell has the potential in inhibiting or accelerating these deterioration reactions through reduction or oxidation of organic and inorganic compounds inherent to the products, as well as effectively controlling the oxygen content in the products. This technique can be used as an alternative to the deliberate addition of chemical compounds (sulfite and others reducing substances) to inhibit the deterioration reactions (electroreduction) as well as to accelerate the aging process of the comestible products via accelerated oxidation process (electro-oxidation).     

Suppression of arachidonic acid metabolism and nitric oxide formation by kudzu isoflavones in murine macrophages

Inhibitory effect of kudzu isoflavones on arachidonic acid metabolism and nitric oxide (NO) production in lipopolysaccharide activated RAW 264.7 macrophages were investigated. Isoflavone aglycones, such as daidzein, genistein, biochanin A, and formononetin significantly suppressed arachidonic acid release (50 microM). Biochanin A, which displayed the most active inhibition on arachidonic acid release in HT-29 human colon cancer cells, exhibited its most potent suppression in RAW 264.7 cell (by 86%) without showing cytotoxicity. However, isoflavone glucosides, puerarin and daidzin, showed lower inhibitory activities on the release of arachidonic acid and its metabolites. In NO formation, biochanin A showed marked inhibition, by 62% (50 microM), followed by genistein, daidzein, formononetin, and daidzin, 56, 39, 33, and 8%, respectively. 5,7-Dihydroxyl group in the A-ring of isoflavones could be a key functional group responsible for the strong inhibitory activity of biochanin A and genistein on NO production. These activities may contribute to the antiinflammatory and anticarcinogenic properties of kudzu isoflavones.     

Inhibition of polyphenol oxidase and peroxidase activities on fresh-cut apple by simultaneous treatment of ultrasound and ascorbic acid

The effects of ultrasound and ascorbic acid on activity changes of polyphenol oxidase and peroxidase, of fresh-cut apple during storage, were investigated. The combined treatment of ultrasound and ascorbic acid inactivated monophenolase, diphenolase, and peroxidase, whilst the individual treatment of ultrasound or ascorbic acid had inverse and limited inhibitory effect on the enzymes. The main protein bands had a molecular weight of approximately 63 kDa. A diffuse band, lacking the electrophoretic mobility of proteins, was observed after combined treatment. This investigation revealed that simultaneous treatment with ultrasound and ascorbic acid had synergistic inhibitory effects on several enzymes related to enzymatic browning.     

Evaluation of browning effect on avocado purée preserved by combined methods

The inhibition of enzymatic browning catalyzed by polyphenol oxidase is still an important challenge in food processing. The aim of this work was to evaluate the feasibility of using combined methods in reducing browning of avocado purée through the evolution of PPO activity and CIELab color parameters. Higher reductions of activity were achieved when EDTA was added as an antioxidant and stored under N₂ conditions. Purées with greater activity decays were less sensitive to colour changes. These changes occurred in avocado, thus losing the original lightness and greenness of the pulp. The antioxidant utilised was the factor that most affected the initial color, EDTA being the more effective additive in order to avoid browning reactions. The combination of factors had to be taken into account to evaluate these changes. The influence of combined methods over PPO activity was also assessed. Greater activity inhibition was reflected in better color maintenance.     

Quantitative modelling approaches for ascorbic acid degradation and non-enzymatic browning of orange juice during ultrasound processing

The objective of this study was to develop a deterministic modelling approach for non-enzymatic browning (NEB) and ascorbic acid (AA) degradation in orange juice during ultrasound processing. Freshly squeezed orange juice was sonicated using a 1500 W ultrasonic processor at a constant frequency of 20 kHz and processing variables of amplitude level (24.4–61.0 μm), temperature (5–30 °C) and time (0–10 min). The rate constants of the NEB and AA were estimated by a primary model (zero and first order) while their relationship with respect to the processing factors was tested for a number of models, i.e., second order polynomial, different types of Ratkowsky-type model, and an Arrhenius-type model. The non-monotonic behaviour of NEB has been described more accurately by the use of a polynomial model. The rate constants of AA were described by a similar type of model having a monotonic behaviour. A synergistic effect of temperature for different amplitudes on the rate constant of both NEB and AA was observed, while an antagonistic effect of amplitude on the rate of NEB was evident. The models with the best fit were integrated to produce contour plots for the combined amplitude and temperature. The constructed contour plots illustrate that low temperatures and intermediate amplitudes, i.e., 42.7 μm, result in lower NEB and AA deterioration and consequently better quality orange juice. The overall developed modelling approaches exploit quality data in order to identify the optimal processing regions for eliminating quality deterioration of orange juice during ultrasound processing which is of high importance to the food industry.