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 Solid Content and Lipid Content of Whey Protein Isolate-Beeswax Edible Coatings on Color Change of Fresh-cut Apples

ABSTRACT: Edible coatings from whey protein isolate (WPI)-beeswax (BW) were made with various total solid (8%, 12%, 16%, 20%) and BW content (0%, 20%, 40%, 60%, dry bases). Apple pieces were coated with the emulsion coatings; weight loss and color (CIE L*, a*, b* , and browning index [BI]) were measured during storage. Results show that coated apples had higher L* and presented lower BI than uncoated apples, indicating that whey proteins exert an antibrowning effect. The BI decreased as the solid content of the coating emulsions increased. Increasing BW content decreased enzymatic browning. Coating application did not reduce weight loss in fresh-cut apples, probably due to the product's high relative humidity.     

Starch-based coatings: effect on refrigerated strawberry (Fragaria ananassa) quality

Edible coatings can provide an alternative for extending post-harvest life of refrigerated fruit and vegetables. The influence of different starch-based coating formulations on quality attributes of strawberries stored at 0°C and a relative humidity of 84·8% was studied. Starch sources were classified according to the amylose content in starch, with medium amylose content (potato and corn) and high amylose content (amylomaize and amylose-rich product). Quality of fruits was evaluated by weight loss, firmness retention, microbial decay, surface colour development, titratable acidity and sugar content. The effects of starch amylose content and glycerol (plasticiser) concentration on coating properties were also analysed. The coatings reduced the number of infected fruits and extended storage life of strawberries by retarding senescence. The addition of glycerol improved coating performance, with 20 g litre⁻¹ the most effective concentration. The starch source had a significant effect on surface colour development, weight loss and firmness retention. Coated strawberries produced the lowest ratios of chromaticity parameters (a/b, red/yellow) with regard to the control fruits, thus retarding senescence. High amylose content starches reduced weight loss, maintained firmness and reduced decay better than medium amylose content starches. © 1998 SCI.     

Edible Coating Effects on Postharvest Quality of Green Bell Peppers

Green bell pepper fruits (Capsicum annuum L., cv. “Jupiter”) were coated with a mineral-oil-based coating or a cellulose-based coating. Three different milk-protein-based edible coatings (whey protein isolate, sodium caseinate, and sodium caseinate beeswax emulsion) plasticized with glycerol were also tested. The effects of these coatings were followed by measurement of changes in respiration, internal gases, color, firmness, and water loss during storage at 10°C, 80–85% RH for 20 days. None reduced respiration or affected color. Only the mineral-oil-based coating significantly reduced moisture loss, thus maintaining fruit firmness and thereby prolonging fruit freshness.     

Increasing shelf life of strawberries (Fragaria ssp) by using a banana starch-chitosan-Aloe vera gel composite edible coating

Strawberries are among the most consumed fruits in the world, however, they are highly susceptible to both microbial and fungal contamination during storage. In this study, we used composite films made from banana starch-chitosan and Aloe vera gel (AV gel) at different AV gel concentrations. Our results show that AV gel inclusion can significantly reduce fungal decay, increasing strawberries shelf life up to 15 day of storage at the highest AV gel concentration (20%), while maintaining their physicochemical properties, such as colour and firmness. Weight loss was reduced 5% with respect of the uncoated fruit. Our results can be attributed to the limited water vapour transfer allowed by the edible coating, this is the result of the crosslinking effect of the different AV gel and starch molecules that allows a more controlled decay of the strawberries in commercial storage conditions.     

Influence of nano-ZnO on microbial growth,bioactive content and postharvest quality of strawberries during storage

A rapid decline of quality causes economic loss of strawberries after harvest. Treatments based on nano-ZnO at different concentrations (0.03%, 0.07% and 0.5%) were used to prolong the shelf-life of strawberry fruit in cold storage. After treatments microbial growth, weight loss, firmness, titratable acidity, soluble solid content, pH value, vitamin C, anthocyanin and total phenolics and antioxidant activity were evaluated at 0, 3, 6, 9, 12, 15 and 18 days of storage. Furthermore, the levels of zinc and the sensory attributes of treated strawberries were evaluated three days after treatment. Nano-ZnO treatments decreased the microbial load during fruit storage (total mesophilic bacteria in control and 0.5% nano-ZnO treated strawberries were 4.35 and 3.67 Log CFU g^− 1, respectively). Treatments delayed weight loss, retained fruit firmness and maintained anthocyanin, vitamin C, phenol content and antioxidant activity at higher concentration than those of untreated fruit. Fruit sweetness and aftertaste attributes were not affected by treatments but the 0.5% ZnO treated fruit was less luminous (1.6) compared to control (5.6). 0.5% nano-ZnO was the most effective in delaying changes in the ripening and reducing microbial populations among the treatments. These findings indicated that the nano-ZnO might provide an alternative to maintain quality and control decay of fresh strawberries during extended storage.Industrial relevanceStrawberries are a highly perishable fruit and postharvest life is limited to 4 days or even shorter at room temperature or 2 weeks at cold storage, therefore finding a method to extend the shelf life of strawberries is important. Modified atmosphere packaging is a useful method but control of spoilage microorganisms is still a problem. Fruit coating has great potential to extend fruit postharvest life and maintain nutritional quality. Nano-ZnO may be an effective alternative.     

Antifungal Coatings on Fresh Strawberries (Fragaria × ananassa) to Control Mold Growth During Cold Storage

ABSTRACT: Chitosan (2%) -based or hydroxypropyl methylcellulose (HPMC) (1%) -based coatings were applied on fresh strawberries to evaluate their antifungal efficacies against Cladosporium sp. and Rhizopus sp. Potassium sorbate (PS) was also incorporated into coating formulas to evaluate any additional inhibitory effects on mold inhibition. Strawberries were inoculated with Cladosporium sp. or Rhizopus sp. at a level of approximately 10³ log colony-forming units (CFU) /g, coated with 2% chitosan, 2% chitosan containing 0.3% PS, or 1% HPMC containing 0.3% PS, and stored at about 5°C and about 50% RH up to 23 d for enumeration of mold, yeast, total aerobes, and coli forms. To assess antifungal activity of the coating materials in vitro, coating solutions were embedded into agar plates and the diameters of radial mold growth were measured after inoculation. In addition, weight loss of coated strawberries and water vapor permeability of the coatings were measured. No significant combined inhibitory effects between chitosan and PS on fungal growth on fresh strawberries were detected. However, significant combined inhibition activity was observed in in vitro testing when PS was formulated into chitosan. Antifungal activity of chitosan against Cladosporium sp. and Rhizopus sp. was not affected by the autoclaving process of coating solutions. Coating treatment also reduced total aerobic count, coliforms, and weight loss of strawberries during storage. Hence, chitosan can be used as a natural antimicrobial coating on fresh strawberries to control the growth of fungi, thus extending shelf-life of the fruits.     

Electrostatic and Conventional Spraying of Alginate-Based Edible Coating with Natural Antimicrobials for Preserving Fresh Strawberry Quality

Microbial contamination and mold growth are common causes of strawberry deterioration during storage. The growing need for extending shelf-life while enhancing the overall quality of perishable fruits has generated increasing interest in the development of novel preservation technologies. This study used electrostatic spraying (ES) technology as an innovative and efficient technique for the application of edible alginate coating enriched with carvacrol and methyl cinnamate (natural antimicrobials) on fresh strawberries. The efficiency of the electrostatic technology was compared to non-electrostatic (conventional) spray (NES) technology in terms of transfer efficiency and coating evenness. Furthermore, physicochemical and textural parameters (such as weight loss, visible decay, firmness, surface color, total soluble phenolic content, and antioxidant capacity) of ES and NES coated fruits were studied and compared to uncoated controls. ES technology demonstrated higher transfer efficiency and evenness than NES, which led to a significant reduction of visible decay over uncoated controls. The delay in microbial spoilage by ES (11 days) was greater than by NES (10 days) and uncoated strawberries (7 days). ES coating significantly inhibited strawberry decay with only 5.6 % of infected fruits, compared to 16.6 and 8.3 % for control and NES fruits after 13 days of storage, respectively. At the end of 13 days of storage, ES coating demonstrated superior performance on strawberry firmness, color retention, and weight loss reduction. Additionally, no differences were observed between uncoated and coated fruits with regard to their antioxidant and total soluble phenolics.     

Minimizing texture loss of frozen strawberries: effect of infusion with pectinmethylesterase and calcium combined with different freezing conditions and effect of subsequent storage/thawing conditions

Vacuum infusion (VI), freezing, frozen storage and thawing conditions were optimized in order to minimize the texture loss of frozen strawberries. Slow freezing caused severe loss in textural quality of the strawberries. This quality loss could not be prevented by the application of VI prior to slow freezing, or by the application of rapid, cryogenic or high-pressure shift freezing conditions on non-infused fruits. A remarkable texture improvement was noticed when infusion of pectinmethylesterase (PME) and calcium was combined with rapid or cryogenic freezing. The highly beneficial effect of PME/Ca-infusion followed by HPSF on the hardness retention of frozen strawberries was ascribed to the combined effect of the infused PME (53% reduction in degree of esterification (DE) of the strawberry pectin) and the high degree of supercooling during HPSF. During frozen storage, textural quality of PME/Ca-infused high-pressure frozen strawberries was maintained at temperatures below −8 °C, whereas the texture of PME/Ca-infused strawberries frozen under cryogenic freezing conditions was only preserved at temperatures below −18 °C. Thawing at room temperature seemed to be an appropriate method to thaw strawberries. Fast thawing by high-pressure induced thawing (HPIT) did not prevent textural quality loss of frozenstrawberries.     

不同强度DENBA+电场辅助处理冻结草莓后对其解冻品质影响的比较

DENBA+技术可利用高压静电,通过共振食品细胞中的水分子使其更为活性化,达到保持营养成分完整、延迟氧化、实现食材保鲜的目的,可与食品速冻保鲜配合使用。为系统地考察外加DENBA+静电场对冻藏草莓超声解冻后品质的影响,该实验以丹东九九草莓作为研究对象,通过对比分析感官评价、色差、硬度、汁液流失率、可溶性固形物、总糖、总酚等7项指标,探究草莓在外加不同强度DENBA+静电场条件下冻结对其解冻品质的影响。实验结果表明,经外加高低电场辅助草莓冻结解冻品质均优于空白对照组,且与2 000 V高强度DENBA+电场辅助冻结相比,经外加500 V低强度DENBA+电场辅助冻结后,感官评价综合分数最高,色差下降1.70%,硬度提高22.45%,汁液流失率下降27.72%;可溶性固形物含量提高8.16%、总糖含量提高4.79%、总酚含量提高9.90%,上述各项指标低电场辅助处理较高电场辅助处理效果更优且差异显著（P<0.05）,其解冻特性呈现相对较好的状态,综合分析得出500 V的低电场辅助冻藏草莓的品质较优。     

Edible coating affects physico‐functional properties and shelf life of chicken eggs during refrigerated and room temperature storage

Effects of chitosan, whey protein concentrate (WPC), mineral oil (MO) and/or soybean oil (SO) coating on egg quality were compared at 25 and 4 °C, respectively, during 5 and 20 weeks of storage. Storage time and temperature, and type of coating significantly affected Haugh unit, yolk index, weight loss, albumen pH and emulsifying capacity. Shelf life was extended 4 weeks by MO and SO and 2 weeks by chitosan and WPC longer than that observed for noncoated eggs at 25 °C. MO‐ and SO‐coated eggs maintained AA grade for 20 weeks at 4 °C. Weight loss of SO‐coated eggs was <1% after 5 weeks at 25 °C and after 20 weeks at 4 °C. Yolk index and emulsifying capacity were more correlated at 25 °C than at 4 °C. MO and SO were more effective coating materials, with SO providing a more cost‐effective coating for extending egg shelf life.     

The impact of delactosed whey permeate treatment on shelf‐life and antioxidant contents of strawberries

The aim of this study was to investigate the effect of delactosed whey permeate (DWP) treatment on antioxidant and physicochemical properties of strawberries. Fresh strawberries treated with 3% DWP were analysed for different quality, nutritional and microbiological markers during 10 days of storage at 5 °C. The results showed that DWP treatment significantly reduced incidences of decay (70%) and numbers of total aerobic counts (～1.4 Log₁₀ CFU g^?1) and yeast and moulds (～1.8 Log₁₀ CFU g^?1). DWP treatment also inhibited the loss of firmness (15%) and maintained significantly (P ≤ 0.05) higher levels of vitamin C, total phenols and antioxidant activity of strawberries. Sensory scores confirmed that the DWP‐treated strawberries retained a good appearance and overall quality. The aroma and colour attributes were not reduced during storage. These results suggest that DWP treatment has potential to extend the shelf‐life and maintain the quality of strawberries during storage.     

Application of waterborne rosin polymer coating for preserving strawberry during storage

A water-soluble rosin polymer (RP) was prepared via polymerization of rosin and maleic anhydride. The structure of the RP was characterized via Fourier-transform infrared spectroscopy, proton nuclear magnetic resonance spectroscopy, and gel permeation chromatography. The RP was used as a film-forming agent on strawberries to improve their postharvest quality at room temperature. The effectiveness of this treatment was evaluated based on the impact of the RP coating on the following parameters: weight loss, total soluble solids (TSS), firmness, respiration rate, malondialdehyde (MDA) content, anthocyanin content, and total phenolic content (TPC). The samples that coated with the RP exhibited delayed respiration and loss of firmness compared with the control. Correspondingly, the samples coated with the RP had lower weight loss (14.78%), MDA content (8.13 × 10⁻² μmol/g), anthocyanin content (37.86 mg/100 g), TPC (3.41 × 10⁻⁴ mg/100 g), and higher TSS (8.09%). The results indicated that the RP preservative could effectively maintain the freshness of fruits.     

Preservation of Strawberries with an Antifungal Edible Coating Using Peony Extracts in Chitosan

Strawberries represent a valuable source of bioactive compounds including vitamin C, E, β-carotene, and phenolic compounds, but they are fruits with an extremely short postharvest life. Therefore, the current study was conducted to investigate the effectiveness of an active coating consisting in antifungal microparticles obtained by spray drying of peony extracts (Paeonia rockii (PPR)) dispersed in chitosan (Ch) and subsequent addition to polysaccharide gels to slow the fungal attack of small highly perishable fruits, such as strawberries. The results of the antimicrobial assays indicate that the peony extracts in chitosan are able to counteract effectively the growth of different fungal isolates from deteriorated strawberries. In conclusion, through the treatment with this antifungal coating, it is possible to prolong the shelf life of delicate fruits, such as strawberries, to about 16 days, slowing down the weight loss, affecting the safeguard of important vitamins and antioxidant capacity during storage, without causing any significant alteration of the nutritional and sensorial properties of the product.     

Effect of Nanochitosan-Based Coating With and Without Copper Loaded on Physicochemical and Bioactive Components of Fresh Strawberry Fruit (Fragaria x ananassa Duchesne) During Storage

Edible coatings based on nanochitosan (50–110 nm) with and without copper loaded were evaluated on physicochemical and bioactive components of strawberry. Fresh fruits were coated with copper-free and copper-loaded nanochitosans and stored at 4?±?1 °C with 70 % relative humidity for 20 days. Both nanochitosan coatings provided an effective control in reducing weight loss and firmness as well as delayed changes in the respiration rate during 3 weeks. The antioxidant activity declined throughout the storage period of strawberries, although the decrease in antioxidant activity showed a slower rate in the strawberries coated with copper-free nanochitosan followed by copper-loaded nanochitosan compared with the control. Anthocyanin concentrations increased in fruits coated with copper free as well as copper-loaded nonochitosan at the first 12 days of storage followed by reduction in slow rates. However, no increase of anthocyanin was recorded for uncoated samples. Intensive reduction was recorded in ascorbic acid content of strawberries coated with copper-loaded nanochitosan, while the minimum loss of the ascorbic acid content was related to the copper-free nanochitosan. Also, both nanochitosans showed a significant suppression on the polyphenol oxidase and peroxidase activity, whereas a high rate of increase was recorded in control strawberry. The nanochitosan coatings with or without copper loaded significantly suppressed the visual loss and fungal decay of the strawberries during the storage compared with the control. The sensory evaluation of coated strawberries revealed that no effect on the consumer acceptability was detected as well as that copper-free nanochitosan showed better results in the point of preserving the overall flavor and appearance compared with the copper-loaded one.     

USE OF VACUUM IMPREGNATION TO DEVELOP HIGH QUALITY AND NUTRITIONALLY FORTIFIED FROZEN STRAWBERRIES

Strawberries (Totem) were vacuum impregnated (VI) before freezing with cryoprotectants of high fructose corn syrup (HFCS) or high methoxyl pectin (HMP) to improve quality, and with calcium and zinc salts to enhance the nutritional value of the product. The VI process consisted of a 15 min vacuum at 50 mm Hg and 30 min restoration at atmospheric pressure. VI pretreatment significantly increased the calcium and zinc content of frozen strawberries. VI with cryoprotectant improved the textural quality and reduced drip loss of frozen-thawed strawberries in comparison with untreated strawberries. Calcium in the VI solutions further increased the firmness of frozen-thawed strawberries, and zinc improved the color stability of the strawberries during the impregnation and freeze-thawing process.     

The effect of modified atmosphere packaging on the quality of Honeoye and Korona strawberries

Strawberries (cultivars Honeoye and Korona) were stored in perforated polypropylene bags at 5 °C for 10 days. Unpackaged strawberries were used as a reference. Several quality parameters were monitored during the storage period. The packaged strawberries retained their weight throughout the experiment as opposed to the unpackaged samples which lost 1.5% of their weight per day because of dehydration. The aroma profile of Honeoye strawberries was not affected by storage in modified atmospheres. In Korona fruits, on the other hand, there was a considerable increase in ethyl acetate levels, indicating unwanted metabolism caused by the altered gas composition. The production of potential off-odours was, however, not possible to distinguish in the sensory analyses of the strawberries. The results indicated that storage in a modified atmosphere (11–14% O₂ and 9–12% CO₂) can be used to maintain the quality of Honeoye and Korona strawberries for a longer time, than if kept in air in open containers.     

Effect of salep‐based edible coating enriched with grape seed extract on postharvest shelf life of fresh strawberries

Effects of novel edible coatings based on salep solution (SS) enriched with grape seed extract (GSE) (1.5% SS, 1.5% SS + 0.5% GSE, 1.5% SS + 1.5% GSE, 1.5% SS + 3% GSE) on the quality characteristics of fresh strawberries were monitored after 0, 4, 8, 12, 16, and 20 days of storage (1°C, 95% RH). The lowest growth of microorganisms, weight loss, softening and ascorbic acid, phenol and anthocyanin degradation was measured in strawberries coated with 1.5% SS + 3% GSE. The highest superoxide dismutase activity and the lowest peroxidase activity were determined in strawberries coated with 1.5% SS + 3% GSE. Moreover, they received the highest ranked sensory attributes. Incorporating GSE into the SS coating formulation as a new hurdle increased its antimicrobial properties and extended the shelf life of coated strawberries compared to uncoated by up to 20 days.     

Effect of native and acetylated‐crosslinked waxy corn starch‐beeswax coatings on quality attributes of raspberries during storage

Edible coatings (ECs) are a thin layer of a mixture of edible materials, applied in the liquid state and dried over the surface of a food product to maintain its quality during storage. This work was aimed to study the effect of ECs made from wx corn starch (WCS) or acetylated cross‐linked starch (ACLS) added with beeswax on fresh raspberry quality attributes during short‐term cold storage. Freshly harvested fruits were coated, dried, packed in plastic trays and stored up to 8 days at 4°C. During storage quality parameters such as firmness, respiration rate, anthocyanins content, total phenols, color changes, and weight loss were evaluated. A clear effect on control of respiration rate was observed in coated raspberries. Respiration rate of uncoated fruit was 4.5 ± 0.28 mmol/kg/h and decreased to 4.2 ± 0.27 for ACLS and to 4.1 ± 0.08 mmol/kg/h for WCS‐coated raspberries, after 56 h of storage at 15°C. Ethylene production followed a similar trend under these conditions decreasing from 0.043 ± 0.005 to 0.034 ± 0.004 mmol/kg/h for uncoated and ACLS coated fruits, respectively, indicating an effect on ripening control. Additionally, ACLS and WCS coatings permitted the preservation of color without affecting anthocyanins content. However, the presence of anaerobic metabolites and reduction of terpenes production in cold stored coated raspberries indicated hypoxic conditions, which can adversely affect shelf‐life quality attributes of raspberries such as firmness and weight loss.