Shelf life extension of minimally processed water caltrop (Trapa acornis Nakano) fruits coated with chitosan

Freshwater caltrop (Trapa acornis Nakano) fruits are very perishable and susceptible to browning, and thus have a short shelf life. In this study, minimally processed water caltrop (MPWC) fruits were treated with 0.0% (control), 0.5%, 1.0% and 2.0% of chitosan aqueous solutions, respectively, and stored at 4 ± 1 °C, 80–85% relative humidity for 15 day. Effects of the chitosan coating on MPWC fruit shelf life and qualitative attributes were evaluated by investigating fresh weight loss, browning index, phytochemicals and browning‐related enzymes activities. Results showed that 1.0% and 2.0% chitosan coating significantly extended shelf life of MPWC fruit by reducing browning occurrence and fresh weight loss, preserving ascorbic acid, soluble solid and titratable acidity as well as total phenol content, also inhibiting the increase in phenylalanine ammonia lyase, polyphenol oxidase and peroxidase activities compared to the control during storage. However, 0.5% chitosan coating seemed to be ineffective in prolonging shelf life and conserving quality of MPWC fruit except for keeping more total phenols during storage in comparison with the control.     

Ultrasound-Assisted Chitosan–Surfactant Nanostructure Assemblies: Towards Maintaining Postharvest Quality of Tomatoes

A novel ultrasound-assisted chitosan–surfactant nanostructure assembly was developed to allow better delivery of chitosan particles into intact fruit tissues for extension of postharvest life. Three solutions of 1 % chitosan–surfactant nanostructure assembly with micelle sizes of 400, 600 and 800 nm were prepared and applied as an edible coating on tomatoes. The fruits were stored at 15?±?2 °C and 70–80 % relative humidity for 20 days. The indicators of tomato ripening, which included loss of firmness, decline of titratable acidity, decline of chlorophyll content and increase in soluble solid content, were delayed in the treated fruits in comparison to the control (p?<?0.05). A delay of approximately 5 days in ripening was observed by evaluating the colour evolution from green to red. The treatment significantly (p?<?0.05) enhanced the phenolic content while maintaining a lower level of respiration in comparison to the control, throughout most of the storage duration. However, weight loss was higher in the treated fruits in comparison to the control. No significant difference in the resultant effects was observed by using chitosan–surfactant nanostructure assemblies of different micelle sizes (p?>?0.05).     

Effects of chitosan coating on postharvest life and quality of longan fruit

The effects of chitosan coating in extending postharvest life of longan fruits and maintaining their quality were investigated. The fruits were treated with aqueous solutions of 0.5, 1.0 and 2.0% chitosan, respectively, and then stored at 2°C and 90% relative humidity. Changes in respiration rate, polyphenol oxidase (PPO) activity, colour, eating quality, and weight loss were measured. The effect of chitosan coating on disease incidence was also evaluated. The application of chitosan coating reduced respiration rate and weight loss, delayed the increase in PPO activity and the changes in colour, and eating quality, and partially inhibited decay of fruit during storage. Furthermore, increasing the concentration of chitosan coating enhanced the beneficial effects of chitosan on postharvest life and quality of the fruit.     

Influences of preharvest spraying Cryptococcus laurentii combined with postharvest chitosan coating on postharvest diseases and quality of table grapes in storage

The effects of preharvest spray with Cryptococcus laurentii combined with chitosan coating after harvest on decay and quality of table grapes during storage periods were evaluated in the present study. Preharvest spray with C. laurentii (PreA) significantly decreased decay index (DI), and postharvest chitosan coating (PCC) enhanced the effectiveness of the pre-harvest spray when fruits were stored at 0 °C. PreA combination with PCC increased the activities of polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) of fruit in storage. PreA + PCC treatment was effective in reducing weight loss of fruits by 85% at 17 d storage and 38% at 42 d storage as compared to PreA alone at the same stage. In addition, PreA enhanced the ratio of soluble solids content (SSC) to titratable acid (TA) by 12% at harvest time, 7% at 17 d storage and 25% at 42 d storage, mainly by increasing SSC and decreasing TA in fruit stored at 0 °C. These results suggested that integration of preharvest spray with C. laurentii and postharvest chitosan coating treatment may be a promising management strategy for decay control and quality maintenance of table grapes.     

Effect of shrimp chitosan coatings as affected by chitosan extraction processes on postharvest quality of strawberry

Edible coatings as affected by chitosan extraction processes were used to preserve the quality of strawberries (Fragaria × ananssa) during their storage at ambient temperature (20–25 °C). Thus, three different chitosans were prepared from shrimp shell and were designated as the following: C1 by classical method, C2 without the decoloration step, and C3 without the decoloration step and the deproteinization step. In order to study the effectiveness of coatings, changes in physicochemical parameters and mold spoilage were studied. Chitosan coatings had no significant effects on titrable acidity, pH and soluble solids content (SSC) of strawberries throughout the storage, while the SSC content of control fruits increased with the storage time. In contrast, chitosan coatings delayed changes in weight loss and the appearance of fungal infection. Coated samples had greater visual acceptability than had the untreated fruits. By visual analysis, it was possible to verify that the best quality was maintained until the day 12, for the strawberries coated with C3 (1 %).     

Combination of heat treatment and chitosan coating to improve postharvest quality of wolfberry (Lycium barbarum)

The synergistic application of hot water dip at 42 °C for 30 min and 1% chitosan coating on differentiation in postharvest quality traits, microstructure as well as microbiological evolution of wolfberry fruits was investigated. Fresh wolfberry fruits were stored at 2 ± 0.5 °C and 90% relative humidity (RH) for 28 days. Results indicated the combination of prestorage heat treatment and chitosan coating maintained higher levels of ascorbic acid, total phenolic contents and antioxidant capacity as well as lower decay, compared with untreated wolfberry fruits. The possible mechanism was that the heat treatment almost sealed open stomata to limit the sites of pathogen penetration into fruits independently, followed by the biofilm formed by chitosan which controlled secondary infections as well as slowed changes in fruit respiration and metabolic activity in wolfberries. The synergistically treated fruit also exhibited a higher acceptability obtained by sensory analysis after cold storage. In this sense, the integrated application of heat treatment and chitosan coating could be regarded as an effective strategy to extend storage life and maintain the postharvest quality of wolfberry fruits.     

Double Layer Coatings: A New Technique for Maintaining Physico-Chemical Characteristics and Antioxidant Properties of Dragon Fruit During Storage

A double layer coating was evaluated for maintenance of quality of dragon fruit during storage at 10?±?2 °C and 80?±?5 % RH for 28 days. Significant differences (p?<?0.05) were observed between control and the treated fruit. However, a double layer coating with 600 nm droplet size?+?1.0 % conventional chitosan showed promising results in all the tested parameters, while the fruit treated with 1,000 nm droplet size?+?1.0 % conventional chitosan showed some negative effects on fruit surface. Increase in weight loss was 12.0 % in fruit treated with 600 nm droplet size and 1.0 % conventional chitosan as compared to the control. Antioxidants and gaseous analysis also proved the efficacy of double layer coatings with 600 nm droplet size?+?1.0 % conventional chitosan. Thus it can be concluded from the present investigation that double layer coating could be used for maintaining quality in dragon fruit for up to 28 days without any off-flavours.     

Effect of chitosan/nano-silica coating on the physicochemical characteristics of longan fruit under ambient temperature

A novel chitosan/nano-silica hybrid film was prepared using tetraethoxysilane as precursor by in situ sol–gel process, and characterized by transmission electron microscopy. Its effect on preservation quality of longan fruits (Dimocarpus longan Lour. cv Shijia) was investigated under ambient temperature. The present study revealed that the excellent semi-permeable film of chitosan/nano-silica markedly extended shelf life, reduced browning index, retarded weight loss and inhibited the increase of malondialdehyde amount and polyphenoloxidase activity in fresh longan fruit. In addition, the peroxidase activity of longan fruit coated with hybrid film was lower than that in other treatment fruits. Decreases in the contents of total soluble solids, titratable acidity and ascorbic acid were also significantly inhibited by hybrid films. These data indicated that the chitosan/nano-silica coating might provide an attractive alternative to improve preservation quality of fresh longan fruits during extended storage.     

Combined effects of postharvest heat treatment and chitosan coating on quality of fresh‐cut mangoes (Mangifera indica L.)

The influence of heat treatment combined with coating on sensory quality, physico‐chemicals characteristics (firmness, colour, pH, titratable acidity, total soluble solids and total carotenoids content) and microbiological quality of fresh‐cut mangoes were studied. Whole mangoes (Mangifera indica cv ‘Tommy Atkins’) were subjected to hot water dipping (HWD) at 50 °C for 30 min and cooled for 15 min. Heated and unheated fruits were minimally processed and mango cubes were coated with chitosan solution (0.25% w/v) dissolved in 0.5% (w/v) citric acid, and stored for 9 days at 6 °C under ambient atmosphere. This study showed that both HWD 50 °C for 30 min and chitosan coating, either alone or combined, did not affect the taste and the flavour of mangoes slices. The chitosan coating combined with HWD or not inhibited the microbial growth for 9 days at 6 °C. Indeed chitosan coating was used for his antimicrobial proprieties. HWD 50 °C for 30 min was the beneficial treatment to maintain firmness and colour during 9 days at 6 °C.     

Effect of chitosan coating combined with postharvest calcium treatment on strawberry (Fragaria × ananassa) quality during refrigerated storage

Strawberries (Fragaria × ananassa Duch.) were coated with either 1% or 1.5% chitosan (CS) or chitosan combined with calcium gluconate (CaGlu). Following treatment, strawberries were stored at 10 °C and 70 ± 5% RH for one week. The effectiveness of the treatments in extending fruit shelf-life was evaluated by determining fungal decay, respiration rate, quality attributes and overall visual appearance. No sign of fungal decay was observed during the storage period for fruit coated with 1.5% CS (with or without the addition of CaGlu) or 1% CS + 0.5% CaGlu. By contrast, 12.5% of the strawberries coated with 1% CS lacking calcium salt were infected after five days of storage. The chitosan coating reduced respiration activity, thus delaying ripening and the progress of fruit decay due to senescence. Chitosan coatings delayed changes in weight loss, firmness and external colour compared to untreated samples. Strawberries coated with 1.5% chitosan exhibited less weight loss and reduced darkening than did those treated with 1% chitosan, independently of the presence or absence of CaGlu. However, addition of calcium to the 1% chitosan solution increased the firmness of the fruit. Coated samples had greater visual acceptability than had untreated fruits. The addition of calcium gluconate to the chitosan coating formulation increased the nutritional value by incrementing the calcium content of the fruit.     

Effect of chitosan coating on maintenance of aril quality,microbial population and PPO activity of pomegranate (Punica granatum L. cv. Tarom) at cold storage temperature

BACKGROUND: Chitosan edible coating was used in an attempt to extend the storage life of pomegranate arils during 12 days at 4 °C. Prior to storage, treated arils were dipped in 0.25, 0.5 and 1% (w/v) chitosan aqueous solutions and 1% (v/v) acetic acid for 1 min, while control arils were dipped in distilled water with 1% (v/v) acetic acid. RESULTS: Chitosan coating inhibited bacterial and fungal growth on the surface of arils. The water content of arils coated with 0.5 and 1% chitosan was maintained during 12 days of storage. Chitosan reduced the increase in total soluble solids (TSS) and titratable acidity (TA) of arils during storage. The lowest TSS and TA were detected in arils coated with 0.5 and 1% chitosan, which maintained the highest TSS/TA ratio after 12 days of storage. In contrast, application of chitosan delayed the decrease in total phenolics, total anthocyanins and antioxidant capacity during storage. The results also showed that chitosan coating suppressed the monophenolase activity of polyphenol oxidase (PPO) with pyrogallol substrate and the diphenolase activity of PPO with dopamine hydrochloride substrate, but the diphenolase activity of PPO with pyrocatechol substrate increased during storage. CONCLUSION: The results suggest that chitosan coating has the potential to extend the storage life of pomegranate arils by reducing the microbial population on their surface. Copyright © 2012 Society of Chemical Industry     

Physico-mechanical properties of chitosan films with carvacrol and grape seed extract

The physico-mechanical properties of 3 films composed by carvacrol, grape seed extract (GSE) and chitosan in different proportions were studied. The films, prepared by solvent casting technique with the following compositions of the casting solutions in carvacrol, GSE and chitosan: film-1: 9.6 ppm–684 ppm–1.25% w/v, film-2: 60 ppm–400 ppm–1.2% w/v and film-3: 90 ppm–160 ppm–1.24% w/v and were compared to a control (1.25% w/v chitosan) film. Mechanical, structural, barrier and colour properties of the films were evaluated. Film-3 presented the lowest water vapour and carbon dioxide permeabilities (WVP and CO₂P) and tensile strength (TS) values and the highest oxygen permeability (O₂P), whereas film-1 presented the highest water content and the lowest crystallinity, CO₂P, TS and luminosity. These results suggest that in the range studied, carvacrol and GSE affect the film structure and its mechanical properties due to hydrophilic (GSE) and hydrophobic (carvacrol) compounds. This work will help the development of edible films, based on physico-mechanical properties, contributing to food preservation and shelf-life extension.     

Antifungal activity of chitosan and its application to control post‐harvest quality and fungal rotting of Tankan citrus fruit (Citrus tankan Hayata)

In this study, the antifungal activity of chitosan A (MW = 92.1 kDa) and B (MW = 357.3 kDa), with 94.2% N‐deacetylation were examined at various concentrations against fungi including Penicillium digitatum, Penicillium italicum, Botrydiplodia lecanidion and Botrytis cinerea. The effectiveness of these chitosans to control the post‐harvest quality of Tankan fruit, a popular sub‐tropical citrus fruit, was investigated. It was found that chitosan, depending on type and concentration, caused 25.0–90.5% growth inhibition on test organisms after 5 days of cultivation at 24 °C. Chitosan treatment significantly reduced (P < 0.05) the percentage decay of Tankan fruit during storage at 24 °C. After 42 days of storage at 13 °C, chitosan‐coated Tankan fruits were firmer, exhibited less decay and weight loss, and showed higher titratable acidity, ascorbic acid, and total soluble solids than the control fruit. Weight loss of Tankan fruits decreased as the concentration of chitosan was increased. On the other hand, chitosan A, regardless of concentration tested, was found to be more effective in retaining the firmness, titratable acidity and water content, total solid content and ascorbic acid content of Tankan fruits than chitosan B. Copyright © 2006 Society of Chemical Industry     

黄皮精油-壳聚糖复合涂膜对番木瓜果实常温贮藏品质及生理的影响

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The nutraceutical quality of tomato fruit during domestic storage is affected by chitosan coating

Fruits and vegetables are highly perishable foods which usually undergo a gradual loss of nutraceuticals during storage. Chitosan‐based edible coatings are extensively studied thanks to antimicrobial activity and great potential to extend the shelf life. However, little information is presently available on the nutraceutical quality of chitosan‐coated products. The present study is addressed to evaluate accompanied by a delayed degradation of some phenolic compounds during storage. These results indicate that chitosan coating is effective in maintaining the quality parameters, the coated fruit showed less weight loss (?16%) and more firmer (+40%) than control fruit, chitosan‐coated tomato emitted significantly lower ethylene (?41%) than control, and slowing down the nutraceutical loss occurring in postharvest, mainly of the lycopene, main carotenoid, found in tomato fruits. These results indicate that chitosan coating is effective in slowing down the nutraceutical loss occurring in postharvest, thus representing a promising tool to preserve bio‐protective phytochemicals during fruit conservation.

Practical applications

During storage and domestic conservation, the nutraceutical quality of fruits and vegetables usually decreases and can undergo deterioration due to physiological disorders and mechanical damages. In the last decade, use of edible coatings has attracted interest as a promising technology to prolong the shelf life of particularly perishable foods. These coatings act as protective barriers decreasing transpiration rate and gas transfer across the product surface, thus promoting the maintenance of nutritional quality.     

Resistance of rubberwood (<Emphasis Type="Italic">Hevea brasiliensis</Emphasis>) treated with chitosan or silane against surface molds

The aim of this study was to determine the efficacy of chitosan and methoxysilane in the prevention of surface mold growth on rubberwood. Three different chitosan samples were tested; C1 (Mw 37 kDa), C2 (Mw 5.4 kDa) and C3 (Mw 3.5 kDa). Radial growth inhibition assay of the chitosan samples was investigated at concentrations ranging from 0.063 to 0.5 %w/v against Aspergillus niger BAM 4 and Penicillium decumbens CBS 121928. Chitosan samples C1 and C3 exhibited strong antifungal activity against both molds. Rubberwood samples were either vacuum or dip treated with varying concentrations of chitosan or silane solution. The content of chitosan in wood showed that after the leaching test, chitosan was well retained in both vacuum and dip treated wood. The concentration of silicon in wood showed similar results. The vacuum treated wood samples with chitosan C1 and C3 at 1 %w/v concentration had strong resistance against A. niger BAM 4. However, dip treated rubberwood samples with 2 %w/v chitosan solutions showed lower resistance against A. niger BAM 4. On the other hand, both vacuum and dip treated rubberwood samples with chitosan had no resistance against P. decumbens CBS 121928. The silane treated wood samples showed no resistance to fungal growth.     

Effect of chitosan coatings enriched with cinnamon oil on the quality of refrigerated rainbow trout

The effects of a chitosan (Ch) coating enriched with cinnamon oil (Ch + C) on quality of rainbow trout (Oncorhynchus mykiss) during refrigerated storage (4 ± 1 °C) were examined over a period of 16 days. A solution of Ch (2%, w/v) and Ch + C (2%, w/v Ch + 1.5%, v/v C) was used for the coating. The control and the coated fish samples were analysed periodically for microbiological (total viable count, psychrotrophic count), chemical (TVB-N, PV, TBA), and sensory (raw and cooked fish) characteristics. The results indicated that the effect of the Ch + C coating on the fish samples was to enable the good quality characteristics to be retained longer and to extend the shelf life during the refrigerated storage.     

Cellulose Nanocrystal Reinforced Chitosan Coatings for Improving the Storability of Postharvest Pears Under Both Ambient and Cold Storages

Cellulose nanocrystal (CNC, 0%, 5%, and 10% w/w, in chitosan, dry basis) reinforced 2% chitosan aqueous coatings were evaluated for delaying the ripening and quality deterioration of postharvest green D'Anjou (Pyrus communis L.) and Bartlett (Pyrus communis L.) pears during 3 wk of ambient storage (20 ± 2 °C and 30 ± 2% RH) or 5 mo of cold storage (–1.1 °C and 90% RH), respectively. Ethylene and CO₂ production, color, firmness, and internal fruit quality were monitored during both storage conditions. Moisture and gas barrier, antibacterial activity, and surface morphology of the derived films were also evaluated to investigate the mechanisms of delayed fruit ripening and quality deterioration. In the ambient storage study, the 5% CNC reinforced chitosan coating significantly (P < 0.05) delayed green chlorophyll degradation of pear peels, prevented internal browning, reduced senescence scalding, and improved retained fruit firmness. During cold storage, the 5% CNC reinforced chitosan coating showed a competitive effect on delaying fruit postharvest quality deterioration compared to a commercial product (Semperfresh?, Pace International, Wapato, Wash., U.S.A.). The 5% CNC coating strongly adhered to the pear surface, provided a superior gas barrier and a more homogenous matrix in comparison with the other coatings tested. Hence, it was effective in delaying ripening and improving the storability of postharvest pears during both ambient and cold storage.     

Effects of chitosan coating on shelf life of cold-stored litchi fruit at ambient temperature

Postharvest pericarp browning of litchi fruit results in an accelerated loss in shelf life and a reduced commercial value. Visual quality was lost in only 6 h at ambient temperature when fruit were removed from storage at 2 °C, due to browning. The experiment was conducted to test the role of chitosan coating in inhibiting skin browning and extending shelf life of cold-stored litchi fruit at ambient temperature. Litchi fruit were treated with 2 g chitosan/100 g solution and then stored for 20 days at 2 °C and 90–95% relative humidity (RH), prior to shelf life evaluation at 25 °C and 80–90% RH. Changes in polyphenol oxidase (PPO) activity, anthocyanin concentration, colour index, eating quality and concentrations of total soluble solids and titratable acidity were measured. The effects of chitosan coating on disease incidence were also evaluated. Application of chitosan coating delayed the decrease in anthocyanin content, the increase in PPO activity and the changes in colour index and eating quality, reduced the decrease in concentrations of total soluble solids and titratable acidity, and partially inhibited decay. The results suggested that treatment with chitosan coating exhibited a potential for shelf life extension at ambient temperature when litchi fruit were removed from cold storage.     

壳聚糖-纳米纤维素复合涂膜对砂糖橘贮藏保鲜效果的影响

为探究纳米纤维素（nanocrystal cellulose,NCC）的添加对壳聚糖涂膜保鲜效果的影响,本研究采用纯壳聚糖（chitosan,CS）涂膜液以及NCC质量分数为2%和4%的CS-NCC复合涂膜液（CS-2% NCC和CS-4% NCC）分别对砂糖橘进行涂膜,并以咪酰胺（prochloraz,PCZ）处理组和未处理组（CK组）为对照,测定各组果实在贮藏期间的质量损失率、腐烂率、营养品质指标、果皮中丙二醛含量以及抗氧化酶活力,并进行果皮表面微观形态的观察。结果表明,复合涂膜不能降低果实的质量损失率,但其对腐烂的抑制效果总体好于CS组和PCZ组;在贮藏24 d时,与CK组相比,CS-4% NCC组的腐烂率降低了50%;同时,涂膜可有效保持可滴定酸、可溶性固形物、总酚和可溶性蛋白等营养物质的含量;CS-4% NCC组果皮中的丙二醛含量最低,且该组在贮藏期间可维持较高的过氧化物酶与过氧化氢酶活力,说明CS-4% NCC复合涂膜可明显延缓果实的膜脂过氧化,从而使果实保持较好的抗衰老能力;从涂膜的微观形态可看出,果皮表面的涂膜在贮藏第1天便出现微孔,添加4%的NCC有助于减少微孔的出现,增强涂膜的结构稳定性。综上,添加NCC可改善CS涂膜的结构和性能,显著增强其对果实的保鲜效果。添加4% NCC的复合涂膜在抑制果实腐烂和保持果实品质方面与PCZ处理的效果接近,因此该复合涂膜有望替代化学保鲜剂在砂糖橘等柑橘果实的保鲜中进行应用。