Changes in antioxidant activity and postharvest quality of sweet pomegranates cv. Hicrannar under modified atmosphere packaging

The effects of different modified atmosphere packaging (MAP) on antioxidant compounds and storage quality of ‘Hicrannar’ sweet pomegranates were investigated during long term storage. Pomegranates were harvested at the commercial harvest stage and packed in two different types of MAP (MAP1 and MAP2). After packaging, all fruit were stored at 6 °C and 90–95% RH for 120 days, then removed from storage for different quality analyses. Some fruit were kept at 20 °C for 3 days to simulate a period of shelf-life. Fruit weight loss, decay index, skin color, total titratable acidity, total soluble solids content, total phenolics, total anthocyanins and antioxidant activity were determined. Internal atmospheres created by the MAP were periodically assessed during cold storage, and CO₂ concentrations increased and O₂ concentrations decreased inside the MAP. MAP significantly reduced weight loss after both 120 days of cold storage and shelf-life. MAP2 was the most effective packaging in reducing weight loss. Storage of pomegranates in MAP also reduced decay and the decay index, and maintained visual appearance compared to control fruit. During storage, a decrease in L* and C* values and an increase in h° values were observed in all treatments. However, fruit stored in MAP2 had higher L*, C* and lower h° values than in other treatments. Titratable acidity and total soluble solids decreased after cold storage and shelf-life, and no significant differences among treatments were found. Total phenolics, total anthocyanin contents and antioxidant activity increased during the storage period in control fruit.     

Influence of modified atmosphere packaging on sensory quality of shiitake mushrooms

Shiitake mushrooms (Lentinus edodes) were packaged under air in two macroperforated packages (A—9.0 × 10³ perforations/m², 0.1 mm² surface and B—17 perforations/m², 0.1 mm² surface) and under two gas mixtures (15% and 25% O₂) in polyethylene packages, and stored at 5 °C for 18 d. The sensory quality of the mushrooms was evaluated using a trained assessors panel.

Mushrooms packaged in macroperforated packages A showed the smallest deterioration rate. However, weight loss after 6 d of storage reached 15%, which is unacceptable. Besides, shelf life of shiitake mushrooms in active modified atmosphere was limited by off-odour development. Mushrooms in these packages developed off-odour after 12 d of storage due to the fact that O₂ concentrations fall bellow 5%.

On the other hand, the shelf life of mushrooms packaged in macroperforated packages B was limited by their sensory deterioration, particularly by changes in the colour and uniformity of their gills. In this film, mushrooms could be stored for approximately 10 d with a weight loss lower than 2%.

Results from the present work suggest that during the first 6 d of storage all the evaluated packaging conditions were useful for reducing mushroom deterioration rate.     

Perforation-mediated modified atmosphere packaging: Part I. Development of a mathematical model

A space-and-time dependent mathematical model describing perforation-mediated modified atmosphere packages was developed for respiring commodities. The model is based primarily on fundamental laws, with empirical relations used only when no other approach can be devised or when there is a significant advantage from using an empirical approach. The computational domain is divided into four subdomains: a part of the ambient storage environment; the perforation, allowing gas exchange between the package and the ambient; the commodity layer, inside the package; and the headspace above the commodity, but also contained in the package. The package walls are rigid and impermeable to gases but heat conducting. The commodity is treated as a homogenous porous medium with distributed sinks for oxygen consumption and distributed sources for carbon dioxide production due to commodity respiration. The commodity model also accounts for water vapour production due to transpiration and removal caused by possible condensation. The effects of commodity temperature and headspace gas composition on oxygen consumption and carbon dioxide production are accounted through a respiration model. The model permits the determination of the gas mixture velocity as the solution of Darcy's law in the commodity layer and the Navier–Stokes equations in the headspace, perforation, and surrounding ambient storage area. Transport of oxygen, carbon dioxide, water vapour and nitrogen is modelled based on Maxwell–Stefan equations coupled with the Navier–Stokes equations and Darcy's law. Solubility of carbon dioxide within the commodity has been included in the model. Commodity temperature and gas mixture temperature are modelled as solutions of the energy equation in the appropriate subdomains, coupled through transpiration, condensation, and convective heat transfer at the commodity surface.     

Maintenance of broccoli quality and functional properties during cold storage as affected by modified atmosphere packaging

Broccoli (Brassica oleracea L. var. Italica) heads were packaged using 3 types of polypropylene films: macro-perforated (Ma-P), micro-perforated (Mi-P) and non-perforated (No-P), and then stored at 1 °C for 28 days to study the effects of modified atmosphere packaging (MAP) on the maintenance of quality and functional properties by comparison with non-wrapped heads. Results revealed that deterioration occurred quickly in control broccoli, manifested mainly by weight loss, yellowing, chlorophyll degradation and stem hardening. Also, a rapid decrease in total antioxidant activity (TAA), ascorbic acid and total phenolic compound concentration was observed. Conversely, in those heads packaged under MAP, especially for Mi-P and No-P, all changes related with loss of quality were significantly reduced and delayed with time. Additionally, TAA, ascorbic acid and total phenolic compounds remained almost unchanged during the whole period. Thus, broccoli packaged with Mi-P and No-P films had prolonged storability up to 28 days with high quality attributes and health-promoting compounds, this period being only 5 days in unwrapped control broccoli.     

Perforation-mediated modified atmosphere packaging. Part II. Implementation and numerical solution of a mathematical model

The present article describes the numerical implementation of a space-and-time dependent mathematical model of perforation-mediated modified atmosphere packaging for respiring commodities as Part II of a study in which the mathematical model is described in Part I. The model includes species transport of CO₂, H₂O, N₂, and O₂ through the Maxwell–Stefan equations, velocity and pressure through Darcy's law and the Navier–Stokes equations, and temperature of the gas mixture and the commodity through the energy equation. Numerical solutions of the coupled system of equations were obtained using the finite-element method. To illustrate the capabilities of the general approach, simulations of a package of strawberries have been presented, for which experimental results are available in the literature. Comparison of the measurements and the model predictions were fair, considering the uncertainty of the available information. The sensitivities of the solution to the respiration rate model, respiration rates, porosity, package aspect ratio, relative humidity, transpiration coefficients, storage temperature, CO₂ solubility and volume of ambient storage area considered were examined. The steady-state concentrations of O₂ and CO₂ in the package were found to be very sensitive to the value of respiration rate, but much less so to changes of other input parameters within the ranges considered. The steady-state commodity temperature depended on the aspect ratio of the package. Including the CO₂ solubility in the commodity did not affect the steady-state gas concentrations, but it increased the time required for the CO₂ concentration to reach equilibrium in the package. It was shown that neglecting the ambient space beyond the perforation overpredicted the steady-state O₂ concentration. Approximately 80% of the resistance to diffusion was found to occur within the perforation, with the remainder equally divided between the spaces beyond each end of the perforation.     

Combined effect of chemical treatment and/or modified atmosphere packaging (MAP) on quality of fresh-cut papaya

The efficacy of chemical dips and modified atmosphere packaging (MAP), alone and in combinations, on the quality of fresh-cut papaya were studied throughout 25 days at 5 °C. Fresh-cut papaya were dipped in a solution of calcium chloride (1% w/v) and citric acid (2% w/v), packed in an atmosphere of 5% O₂, 10% CO₂, 85% N₂ and stored at 5 °C for 25 days. Physico-chemical analysis (package atmosphere, weight loss, pH, total soluble solids, firmness and color) and microbial quality along with a sensory analysis were measured at regular intervals throughout the storage period. Significant differences were found among the chemically treated and non-treated fresh-cut papaya in all the parameters considered. Chemical treatment followed by MAP, showed the best results among the treatment in terms of retaining sensory and quality characteristics and extending the shelf-life of 25 d for fresh-cut papaya.     

Quality retention of oyster mushrooms (Pleurotus florida) by a combination of chemical treatments and modified atmosphere packaging

Three preservation techniques, chemical treatment, modified atmosphere packaging (MAP) and low temperature storage were used to improve physico-chemical attributes of oyster mushrooms. Mushrooms were treated with a solution of sorbitol (0.05%, w/v), citric acid (3%, w/v) and CaCl₂ (1%, w/v). Chemically treated mushrooms were packed under two different gas compositions. Physico-chemical, textural and sensory properties of the samples were assessed during storage at 4 °C for 25 d. Chemical treatment of mushrooms followed by modified atmosphere packaging using 10% O₂ and 5% CO₂ provided better retention of quality characteristics and received higher sensory ratings compared to other samples, resulting in a storage life of 25 d. Material with this treatment underwent minimal changes in weight, pH and TSS. Radical scavenging activity and total polyphenol contents were retained at 85 and 91% levels, respectively. Control samples without chemical treatment and with chemical treatment, kept under similar packaging conditions, underwent spoilage after 5 and 15 d, respectively.     

Apparent synergism between the positive effects of 1-MCP and modified atmosphere on storage life of banana fruit

Fruit of cv. Gros Michel banana were treated with 1-MCP (1000 nL L⁻¹ for 4 h at 25 °C) and then packed in non-perforated polyethylene (PE) bags for modified atmosphere storage (MAP). The bags were placed in corrugated cardboard boxes and stored at 14 °C. Fruit were removed from cool storage and ripened at room temperature using ethephon. The length of storage life was determined by the change in peel color to yellow, after this ethephon treatment. Fruit treated with 1-MCP + MAP had a storage life of 100 days. The storage life of control fruit (no 1-MCP and no MAP) was 20 days. Fruit held in PE bags without 1-MCP treatment had a 40 day storage life, and the same was found in fruit treated with 1-MCP but without PE bags. 1-MCP is an inhibitor of ethylene action, but also inhibited ethylene production, mainly through inhibition of ACC oxidase activity in the peel. MAP inhibited ethylene production mainly through inhibition of ACC oxidase, both in the peel and pulp. The combination of 1-MCP treatment and MAP storage resulted in much lower ethylene production due to inhibition of both ACC synthase and ACC oxidase activity.     

Effect of non-conventional modified atmosphere packaging on fresh cut watercress (Nasturtium officinale R. Br.) quality

In recent years, the minimally processed food industry has increased due to a consumer trend toward healthier eating. Among these products, watercress represents an interesting alternative due to its high content of functional compounds. The aim of this study was to investigate the effect of non-conventional modified atmosphere packaging (nitrogen (89.7% N₂, 10.3% O₂), argon (89.9% Ar, 10.1% O₂), helium (90.1% He, 9.9% O₂), nitric dioxide (89.3% N₂O, 10.7% O₂) and air (0.03% CO₂, 21% O₂)) on fresh-cut watercress leaves preserved for 13 days at 5 °C. The respiratory rate was reduced by the non-conventional atmosphere up to 3 days of storage, and no significant effects were observed on C₂H₄ production. In addition, mesophilic microbial growth was reduced up to 3 days of storage, and no effect was observed on psychrotrophic and Enterobactericeae counts. He and N₂O atmospheres increased the antioxidant activity of watercress at the end of the storage period. Nevertheless, there was no clear effect of non-conventional gases on the color parameters, polyphenol contents and sensory parameters of fresh-cut watercress.     

Modified atmosphere packaging for long-term storage of astringent persimmons

The maximum storage life ‘Triumph’ persimmons in modified atmosphere (MA) packs of 0.08 mm low-density polyethylene was 8 weeks when packed under vacuum and 20 weeks when packed under nitrogen. The storage life could be extended to 7 months by storing ggibberellin-treated fruit in air at −1C°C prior to MA packaging. The factor which limited further extension of the storage life of the fruit under these conditions was the accumulation of ethanol and acetaldehyde, which caused development of off-flavors and tissue browning, respectively.     

Partial purification and some properties of polyphenol oxidase extracted from litchi fruit pericarp

Litchi (Litchi chinensis Sonn.) fruit peel polyphenol oxidase (PPO) was partially purified 21 fold by ammonium sulfate fractionation and gel filtration. Pyrogallol, catechol, and 4-methylcatechol were good substrates for the enzyme; with no activity observed with chlorogenic acid, p-cresol, resorcinol, or tyrosine. The optimal pH for PPO activity was 7.0 with 4-methylcatechol, with the enzyme being most stable at pH 7.4. The enzyme was relatively temperature stable with maximum activity at 70 °C and requiring a little less than 10 min at 90 °C for 50% loss of activity. The K_m and V_max for the enzyme, with 4-methylcatechol, were 10 mM and 1.47 × 10⁴ units/min per mg protein, respectively. The enzyme was not activated by SDS. Reduced glutathione, -cysteine, tropolone, thiourea, FeSO₄, and SnCl₂ markedly inhibited PPO activity, whereas MnSO₄ and CaCl₂ enhanced PPO activity. Data obtained in this study might help to better understand and control commercially, litchi fruit peel browning.     

Effects of modified atmosphere packaging with a silicon gum film as a window for gas exchange on Agrocybe chaxingu storage

The edible mushroom Agrocybe chaxingu was stored in packages with or without silicon gum film windows in three different modified atmosphere systems (5% O₂, with 5%, 10% and 15% CO₂) at a temperature of 3 ± 1 °C. The results showed that there were significant differences between the packages with and without the silicon gum film windows on O₂, CO₂, and ethylene concentrations, respiration rate, ascorbic acid content, electrolyte leakage and sensory characteristics. Compared to the packages without the silicon gum film windows, the packages with the windows were more effective for quality keeping of the stored mushrooms. This window kept the gas compositions of the packages at levels which avoided anaerobic respiration and resulting off-odors. Among three different modified atmosphere systems, the packages with the silicon gum film window with initial gas concentrations of 5% O₂ and 10% CO₂ were the most effective for maintaining mushroom quality.     

Effect of active modified atmosphere packaging with different initial gas compositions on nutritional compounds of shiitake mushrooms (Lentinus edodes)

The effect of active modified atmosphere packaging with different initial gas compositions on fresh shiitake mushrooms was investigated. Shiitake mushrooms were packaged under each of the following conditions: (1) high oxygen packaging (HOP), 100% oxygen initially; (2) medium oxygen packaging (MOP), 50% O₂ and balanced with N₂ initially; (3) low oxygen packaging (LOP), 3% O₂/5% CO₂, balanced with N₂ initially. Passive modified atmosphere packaging with air inside initially (AIR) was used as the control treatment. All the packaged samples were stored at 10 °C with 90% RH for 7 days. During storage, gas compositions, electrolyte leakage, crude water-soluble polysaccharides, total phenolic content and free amino acid content were determined. The results showed that ethanol release was high in LOP and AIR but retarded in MOP and HOP. No packaging could prevent the decrease in polysaccharide content decreasing. Both the active and passive modified atmosphere packaging maintained the color and integrity of the mushrooms. The active modified atmosphere packaging had a significant effect on the increase of total phenolic content and total amount of free amino acids. LOP had a harmful impact on mushrooms with high levels of electrolyte leakage. In conclusion, HOP and MOP had a better effect on maintaining the nutritional compounds of shiitake mushrooms.     

Effects of a phospholipase D inhibitor on postharvest enzymatic browning and oxidative stress of litchi fruit

Membrane lipid degradation catalyzed by phospholipase D (PLD) results in postharvest browning and senescence of litchi fruit. The effects of n-butanol, a specific PLD inhibitor, on enzymatic browning and oxidative stress during storage of litchi fruit at room temperature were evaluated. n-Butanol-treated fruit had a lower browning index and disease index than untreated fruit. n-Butanol treatment also decreased PLD activity. As a result, the decompartmentalization of litchi polyphenoloxidase and substrates was reduced. The conversion of substrates (−)-epicatechin and procyanidin A₂ into quinones was slowed down and enzymatic browning of litchi pericarp tissues was lower after 6 d storage. Additionally, n-butanol-treated fruit possessed significantly lower malondialdehyde contents than untreated fruit after 4 d storage. Analysis of antioxidative enzyme activities showed that n-butanol treatment inhibited oxidative stress mainly by maintaining high catalase activity in litchi pericarp tissues. Consequently, senescence of litchi fruit during storage was moderated.     

Modified atmosphere packaging of fresh produce with a biodegradable laminate of chitosan-cellulose and polycaprolactone

Use of a biodegradable laminate of a chitosan-cellulose and polycaprolactone as a film for modified atmosphere packaging (MAP) of fresh produce was tested. The temperature dependence of O₂, CO₂ and N₂ gas permeability coefficients for the biodegradable laminate was examined. The coefficients increased linearly with increasing temperature in the range 10–25 °C. The coefficients were validated by experiments on MAP with shredded lettuce and shredded cabbage. MAP systems with head lettuce, cut broccoli, whole broccoli, tomatoes, sweet corn and blueberries were designed using the gas permeability coefficients. The gas composition in each biodegradable package including the fresh produce was simulated to be close to the optimal composition. The biodegradable laminate was found suitable as a packaging material for storage of fresh produce.     

Physiological and biochemical dissection of fiber development in colored cotton

Colored cotton is a very attractive proposition for the textile industry as it reduces the cost for dying. However, inferior fiber quality and non uniform color make it unsuitable for heavy machine spinning. Due to this reason cultivation of colored cotton on commercial scale has been restricted by cotton growers. The current study was planned to unveil the process of fiber development in isogenic lines of brown, green and white cotton by comparing their fiber length, flavonoid, cellulose, carbohydrate and enzyme activities (SuSy, SPS, acid invertase, Cox, NAD+, NADH, NADP+, and NADPH). White cotton fiber exhibited high cellulose contents (915.81 mg g^?1) and long fibers (3.07 cm) as compared to colored cotton fibers with low cellulose content (787.63 and 780.66 mg g^?1) and shorter fiber length (2.54 and 2.48 cm). Similarly the amount of flavonoids also varied significantly with maximum concentration (8.67 and 7.13 mg g^?1) in brown and green cotton fiber at 5 DPA as compared to white cotton fiber (3.12 mg g^?1) at 0 DPA. This high concentration of flavonoid not only lowered the total amount of carbohydrates but also lowered the sucrose transformation rate to developing cotton fiber in colored cotton. The activity of different enzymes (AI, SuSy and SPS, Cox, NAD+/NADH and coenzymes NADP+/NADPH involved in the metabolism of carbohydrates was higher in brown cotton fiber than green cotton fiber. However, high activity of these enzymes did not always correlated with higher amount of cellulose thus indicated the involvement of complex mechanisms for cellulose and flavonoid synthesis during the development of cotton fiber.     

铬胁迫对罗汉果幼苗生理生化指标的影响

重金属铬对植物的生长发育有非常重要的抑制作用。但是至今为止还没有铬对我国特有药用植物罗汉果植物影响的生理生化机理研究的报道。本实验以罗汉果幼苗为材料,对生长在添加0、50、100、150、200μmol?L-1浓度的重金属铬离子的培养基中生长15天的罗汉果幼苗的相关生理生化变化进行了详尽的分析变化。结果表明,随着铬离子浓度的增加,植株叶片的叶绿素含量、蛋白质含量、可溶性糖含量、超氧物歧化酶活性、过氧化氢酶活性一直下降;过氧化物酶活性先上升后下降;相反,脯氨酸和丙二醛含量则一直上升。表明铬离子 的毒害导致体内保护酶活性受到抑制,膜系统受到伤害,从而影响罗汉果幼苗生长。     

Physiological and biochemical changes during banana ripening and finger drop

Fruit drop of banana is due to breaking at the junction of the pedicel and pulp, and we found no true abscission zone. The breakage seems therefore due to weakening of the peel. We investigated pectin hydrolysis and some properties at the rupture zone, using ‘Hom Thong’ (Musa acuminata, AAA Group) and ‘Namwa’ (Musa x paradisiaca, ABB Group) fruit, which show massive drop and no drop, respectively. During the period of finger drop, the water content of the peel in ‘Namwa’ was similar to that of ‘Hom Thong’ and thus water content does not account for the high breakage in ‘Hom Thong’. The peel thickness at the rupture area in the two cultivars was not significantly different. During the period of finger drop, the level of water-soluble pectin in the peel at the rupture area of ‘Hom Thong’ was higher than that of ‘Namwa’, indicating pectin degradation. CDTA soluble pectin and insoluble pectin was lower in ‘Hom Thong’, also indicating more pectin breakdown in this cultivar. Polygalacturonase activity in the peel at the rupture area of ‘Hom Thong’ bananas rapidly increased, but not clearly more than in ‘Namwa’ bananas. Pectinesterase activity in the peel at the rupture area of ‘Hom Thong’ was much lower than that of ‘Namwa’ bananas, and thus does not account for the breakage. Pectate lyase in the peel of ‘Hom Thong’ was considerably higher than in that of ‘Namwa’. The present data indicate that the much higher pectate lyase activity in ‘Hom Thong’ might be responsible, at least partially, for the finger drop.     

Physiological and quality responses of Chinese chive leaves to low oxygen atmosphere

Harvested leaves of Chinese chive were stored in 0, 1 or 3% O₂ (balance N₂), or air for 7 days at 20 °C to determine the effects of low O₂ atmospheres on their physiology and quality. Leaf yellowing was visible at day 5 in air, whereas low O₂ treatment delayed yellowing and retarded chlorophyll and protein degradation that accompanied leaf senescence. The respiration rates of leaves stored at low O₂ atmospheres were substantially lower than those of the control during storage. However, at 0% O₂, undesirable off-odors were induced and visible anaerobic injury appeared in stored leaves, presumably due to a high accumulation of acetaldehyde and ethanol in the tissue. The contents of acetaldehyde and ethanol were very low during storage at 1% O₂, 3% O₂, or air. At 0% O₂, ethanol and to a lesser extent acetaldehyde, rapidly accumulated in the leaf tissue. Pyruvate decarboxylase (PDC) activity greatly increased in leaves exposed to 0 or 1% O₂, while its activity in leaves exposed to 3% O₂ was only slightly higher than that of the control. Alcohol dehydrogenase (ADH) activity greatly increased in leaves exposed to 1 or 3% O₂, while its activity in leaves exposed to 0% O₂ was only slightly higher than that of the control. The activity of ADH was about 250 times that of PDC during storage. Changes in ADH isozymes correlated well with changes in ADH activity. The potential for using low O₂ atmospheres to help in maintaining the quality of Chinese chive leaves is discussed.