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.     

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 %).     

Edible Active Coatings Based on Pectin,Pullulan, and Chitosan Increase Quality and Shelf Life of Strawberries (Fragaria ananassa)

Edible active coatings (EACs) based on pectin, pullulan, and chitosan incorporated with sodium benzoate and potassium sorbate were employed to improve the quality and shelf life of strawberries. Fruits were washed, disinfected, coated by dipping, packed, and stored at 4 °C for 15 d. Application of EACs reduced (P < 0.05) weight loss and fruit softening and delayed alteration of color (redness) and total soluble solids content. In contrast, pH and titratable acidity were not affected (P > 0.05) throughout storage, and ascorbic acid content was maintained in pectin‐EAC coated strawberries. Microbiological analyses showed that application of EACs reduced (P < 0.05) microbial growth (total aerobic counts, molds, and yeasts) on strawberries. Chitosan‐EAC coated strawberries presented the best results in microbial growth assays. Sensory quality (color, flavor, texture, and acceptance) improved and decay rate decreased (P < 0.05) in pectin‐EAC, pullulan‐EAC, and chitosan‐EAC coated strawberries. In conclusion, EACs based on polysaccharides improved the physicochemical, microbiological, and sensory characteristics, increasing the shelf life of strawberries from 6 (control) to 15 d (coated fruits).     

Effects of Antimicrobial Edible Coating of Thymol Nanoemulsion/Quinoa Protein/Chitosan on the Safety,Sensorial Properties,and Quality of Refrigerated Strawberries (<Emphasis Type="Italic">Fragaria × ananassa</Emphasis>) Under Commercial Storage Environment

The effectiveness of the edible coating with thymol nanoemulsion on the safety, sensorial properties, and quality of refrigerated strawberries was investigated under commercial storage conditions. Spontaneous emulsification was used to obtain the thymol nanoemulsion that was included on quinoa protein/chitosan coatings. During the entire storage time, strawberries coated with thymol-antimicrobial packaging had a lower fungal and yeast load compared with the controls (uncoated and coated with quinoa protein/chitosan). The flavour and aroma of the coated strawberries was initially affected, although this sensory appreciation was improved from the fifth day of storage and showed similar scores than the controls, and presenting better aroma score at day 12 of storage. Furthermore, the shelf life of the thymol nanoemulsion-coated strawberries increased in 4 days, unlike that in the both controls. Further, the application of these biocoatings on strawberries significantly decreased the weight loss relative to that in the control, during 16 days of storage at 5 °C and 90% relative humidity, and did not alter the quality parameters (pH, titrable acidity, and percentage of soluble solids). These results suggest that the application of thymol/nanomulsion-loaded edible films is an effective strategy to increase the shelf life of highly perishable products such as strawberries.     

Postharvest Quality of Strawberry Fruit (<Emphasis Type="Italic">Fragaria x Ananassa</Emphasis> Duch cv. Albion) as Affected by Ozone Washing: Fungal Spoilage,Mechanical Properties,and Structure

Storage life of strawberry fruit is limited due to its high softening rate and susceptibility to fungal attack. Thus, it is of interest to develop and improve preservation techniques to reduce postharvest losses. The aim of this study was to evaluate the effect of ozonized water washing (maximum concentration of 3.5 mg L^?1; 5–15 min) on fungal spoilage, water loss, mechanical properties, and structure of strawberries (cv. Albion) harvested in different years and stored at 5 °C. The effect of ozone treatment on decontamination and weight loss was dose-dependent. Ozonization for 5 min significantly reduced fungal incidence (~?22–25% lesser than control) and weight loss of strawberries throughout storage. High doses (10 or 15 min) did not reduce significantly fungal growth in relation to control, although weight loss in fruit treated for 15 min was higher than control. In both harvest years studied, cold storage provoked a diminution in deformability modulus and an increase in deformation but a significant effect of treatment was not observed. These changes were correlated with alteration of cell walls and turgor loss. Otherwise, cuticular membrane of strawberries treated for 5 min was observed thicker and more electron dense than in fruit ozonized for 15 min or control. It could partially explain the lower moisture loss observed in 5-min treated fruit. Results showed that ozonized water washing for 5 min can be an alternative strategy for extending postharvest strawberry shelf-life by decreasing fungal decay and water loss along cold storage, without affecting mechanical parameters.     

Phytochemical composition of everbearing strawberries and storage quality of strawberry fruit treated by precooling

This study was conducted to investigate the nutrient composition of everbearing strawberry cultivar grown on highlands of Gangwon province after harvest. Various phytochemical compositions such as ascorbic acid, anthocyanin, malondialdehyde, and phenolic compounds were analyzed in strawberry fruits from five different cultivars (cv. Albion, Flamenco, Goha, San Andreas, and Seascape). Ascorbic acid content was similar among five cultivars at 20 mg 100 g^?1, whereas major pigment anthocyanin in Seascape was higher than in any other cultivars. Goha and San Andreas showed higher total phenolic compound contents. The effect of room or forced-air precooling on Flamenco and Goha was studied. Higher weight loss was observed in Flamenco treated with forced-air cooling, while in Goha both precooling treatments induced weight loss. Both precooling treatments were effective to maintain firmness in two strawberry cultivars. Forced air cooling maintained total phenolic contents until 12 days of storage, and the efficiency accelerated by low temperature storage.     

Postharvest Physiology and Quality Maintenance of Sliced Pear and Strawberry Fruits

Sliced strawberries (cvs.‘Pajaro’ and 'G-3′) and partially ripe pears (cv.‘Bartlett’) were dipped in various solutions (citric acid, ascorbic acid, and/or calcium chloride) and stored in air or in controlled atmospheres (CA) for 7 days at 2.5°C followed by one day at 20°C. Fruit slices respired at a higher rate than whole fruits at both temperatures. CA storage suppressed respiration and ethylene production rates of sliced fruits. Firmness of strawberry and pear slices was maintained by storage in air + 12% CO₂ and in a 0.5% O₂ atmosphere, respectively, or by dipping in 1% calcium chloride. These treatments also resulted in lighter colored pear slices than the air control treatment.     

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.     

Characterization and Antifungal Activity of Pomegranate Peel Extract and its Use in Polysaccharide-Based Edible Coatings to Extend the Shelf-Life of Capsicum (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.)

Effect of pomegranate peel extract (PPE) in two polysaccharide-based edible coatings namely chitosan and alginate on capsicum (Capsicum annuum L.) was studied during storage at 10 °C. The characterization of PPE confirmed the presence of polyphenols such as punicalagin, catechin, and rutin. PPE also demonstrated antifungal activity against the fungal strain of Colletotrichum gloeosporioides. Incorporation of PPE in chitosan coating recorded significant (P?<?0.05) retention of physiological loss in weight, firmness, color, and ascorbic acid in the samples as compared to the control. The restricted losses in total chlorophyll were found to be 22, 29, 38, and 48 in the samples coated with PPE-enriched chitosan, chitosan alone, PPE-enriched alginate, and alginate alone respectively as compared to higher loss of around 71% in control samples during storage. The addition of PPE in these two coatings could also inhibit the microbial growth, maintain sensory scores, and extend the shelf-life up to 25 days at 10 °C.     

Postharvest Changes in Antioxidant Capacity,Enzymatic Activity,and Microbial Profile of Strawberry Fruits Treated with Enzymatic and Divalent Ions

Strawberry fruits are highly perishable and cannot be stored for more than 1–2 days at ambient condition. Therefore, it was thought desirable to enhance the shelf-life of harvested strawberry using pectin methyl esterase and divalent ions. The freshly harvested fruits of strawberry were treated with different concentrations of pectin methyl esterase (50–300 units) and divalent calcium ions (calcium chloride) for 5–30 min using response surface methodology—Box–Behnken design. The treated and untreated (control) fruits were packed in plastic punnets and stored at two different temperature conditions, viz., 7 °C with 80 % relative humidity (RH) and 25 °C with 60 % RH, for evaluating the shelf-life. Appropriate physico-chemical and microbiological parameters were determined at alternate days during their storage. Overall firmness and color values (L, a, b) decreased, while physiological weight loss (percent) increased during their storage. No food-borne pathogens, viz., Salmonella, Staphylococcus, and coliforms, were observed during storage. Total antioxidant capacity and ferric reducing antioxidant power decreased, while lipoxygenase and polyphenol oxidase activities increased during storage at 7 and 25 °C. The shelf-life of treated strawberry was found to be 10 days at 7 °C as against 6 days for control fruits under similar conditions. The treated strawberry had shelf-life of 2 days compared to 1 day for control maintained at 25 °C.     

Effect of Osmotic Dehydration and Pectin Edible Coatings on Quality and Shelf Life of Fresh-Cut Melon

The aim of this work was to investigate the influence of osmotic dehydration and pectin edible coating on quality parameters of fresh-cut melon. Fruits were osmodehydrated in 40°Bx sucrose solution containing 0.5% calcium lactate or dipped in 0.5% calcium lactate solutions. Then, samples were coated with 1% pectin. Melon pieces dipped in sanitizing solution (nontreated sample) were used as control. Weight loss, respiration rate, firmness, color parameters (lightness, chroma, and whiteness index), sensory acceptance, microbial growth, and structural changes of fruits were evaluated during storage at 5 °C for 14 days. The shelf life of the control sample was limited to 9 days due to microbial growth and sensory rejection, while treated samples showed a shelf life of 14 days. Higher preservation of firmness in coated samples was attributed to the action of calcium salt on melon structure, causing a strengthening of the cell wall. Calcium lactate also inhibited microbial growth along storage, improving microbiological stability of fresh-cut melon. The use of calcium lactate dips and pectin edible coatings hindered weight loss and maintained fruit color characteristics during the storage time. However, these pretreatments probably masked melon taste, reducing the sensory acceptance scores at the end of shelf life study. The combination of osmotic dehydration and pectin coatings was a good preservation alternative for fresh-cut melon, since it improved fruit sensory acceptance, promoting the reduction of product respiration rate, as well as the maintenance of quality parameters during 14 days.     

Composite starch‐based coatings applied to strawberries (Fragaria ananassa)

Starch‐based coatings were used to the extend storage life of strawberries (Fragaria ananassa) stored at 0°C and 84.8% relative humidity. Effects of coating formulation (including starch type, plasticizer, lipid and antimicrobial agent) were analysed with respect to fruit quality. Plasticizer addition was necessary for film and coating integrity to avoid pores and cracks. Plasticizer presence reduced weight losses and maintained surface colour of fruits. Amylomaize coatings showed lower water vapour and gas permeabilities and decreased weight losses for longer periods than corn starch ones. Coatings with sorbitol showed lower permeabilities than glycerol ones. Coatings with antimicrobial agents decreased microbial counts, extending storage life of coated fruits by 10 to 14 days in comparison to the control. The addition of 2 g/l sunflower oil to the formulations decreased the water vapour permeability of starch‐based films, maintained the surface colour of coated fruits and controlled effectively fruit weight losses during storage. Lipid addition minimized the effects of starch and plasticizer types. Composite starch‐based coatings showed selective gas permeability (CO₂ higher than O₂) which helps to delay senescence of fruits.     

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.     

Combined high pressure-mild temperature processing for optimal retention of physical and nutritional quality of strawberries (Fragaria × ananassa)

Response surface methodology was used to determine the optimal high pressure-temperature condition for the processing of strawberries for maximal inactivation of oxidative enzymes as well as best retention of nutritional and physicochemical quality following processing and during storage. High pressure treatment at 20–40 °C resulted in visual quality closest to the fresh product. High pressure combined with mild temperature caused substantial inactivation of peroxidase in strawberries with a maximum of 58% inactivation after 10 min treatment at 600 MPa and 60 °C. No significant inactivation of polyphenol oxidase was observed in strawberries under the studied condition. Combined high pressure-mild temperature processing did not have significant effect on the total polyphenol and total anthocyanin content of strawberries. However, an average of 22 ± 13% loss of total polyphenol content and 27 ± 10% loss of total anthocyanin contents was observed after 3 months of refrigerated storage.Industrial relevanceThe work described in this research is relevant to the high pressure processing of strawberries and other berry fruits. The results of the study have shown that best quality retention of strawberry products is obtained when high pressure processing is combined with vacuum packaging in high barrier packaging material and refrigerated storage since strawberry polyphenol oxidase is highly resistant to high pressure inactivation.     

Use of alginate or zein as edible coatings to delay postharvest ripening process and to maintain tomato (Solanum lycopersicon Mill) quality

BACKGROUND: Edible coatings could be effective tools for delaying the ripening process of fruits. Alginate or zein as edible coatings were assayed in tomato in order to maintain parameters related to quality during postharvest storage. RESULTS: Coated tomatoes showed lower respiration rate and ethylene production than control ones, with a twofold lower concentration of ethylene precursor. In addition, the evolution of parameters related to tomato quality losses, such as softening, colour evolution and weight loss, was significantly delayed (4–6 days on average) in coated tomatoes as compared to controls. Thereafter, sugars, organic acids (and especially ascorbic acid) and scores from sensory analysis remained at much higher levels at the end of storage in treated than in control tomatoes. CONCLUSIONS: Coatings based on alginate or zein could be effective tools for delaying the tomato‐ripening process during postharvest storage, and in turn maintaining tomato quality and its acceptability by consumers. Copyright © 2008 Society of Chemical Industry     

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.     

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.     

Composite starch-based coatings applied to strawberries (Fragaria ananassa)

Starch-based coatings were used to the extend storage life of strawberries (Fragaria ananassa) stored at 0 degree C and 84.8% relative humidity. Effects of coating formulation (including starch type, plasticizer, lipid and antimicrobial agent) were analysed with respect to fruit quality. Plasticizer addition was necessary for film and coating integrity to avoid pores and cracks. Plasticizer presence reduced weight losses and maintained surface colour of fruits. Amylomaize coatings showed lower water vapour and gas permeabilities and decreased weight losses for longer periods than corn starch ones. Coatings with sorbitol showed lower permeabilities than glycerol ones. Coatings with antimicrobial agents decreased microbial counts, extending storage life of coated fruits by 10 to 14 days in comparison to the control. The addition of 2 g/l sunflower oil to the formulations decreased the water vapour permeability of starch-based films, maintained the surface colour of coated fruits and controlled effectively fruit weight losses during storage. Lipid addition minimized the effects of starch and plasticizer types. Composite starch-based coatings showed selective gas permeability (CO2 higher than O2) which helps to delay senescence of fruits.     

Storage quality of strawberry fruit treated by pulsed light: Fungal decay,water loss and mechanical properties

The effect of different pulsed light (PL) doses (2.4–47.8 J/cm²) on water loss, fungal spoilage, mechanical properties and structure of strawberries stored for up to 8 days at 6 °C was studied. Incidence of postharvest molds on strawberry fruits was reduced by over 16–42% with PL application. There were no significant differences in maximal rupture force (F_R), mechanical work (W) and deformability modulus (E_d) values between treated and untreated fruits immediately after treatments. After 8 days storage at 6 °C, untreated strawberries showed a pronounced softening (≈ 48% reduction in F_R), but stored strawberries exposed for 10 s and 40 s to PL presented slight or not significant changes in the mechanical parameters regarding day 0, while F_R and W values of 20 s-PL treated samples were increased by 35% and 88% compared to those at 0 day storage. Micro and ultrastructure changes evaluated by LM and TEM images demonstrated ITW cell wall strengthening and a major integrity of walls of hypodermis cells induced by PL stress, while cell wall disassembly and reduction of cell-to-cell contact were detected in stored untreated fruit. There were no significant differences in weight loss among untreated and PL treated fruits after storage, excepting at the highest PL dose. PL technique would be able to simultaneously provide disinfection and delete softening of the tissues along cold storage. Present results make this non-thermal, residue-free alternative promising for extending shelf-life of traditional and organic strawberry production.Industrial relevanceThe present results demonstrated that pulsed light (PL) treatment is a promising alternative for extending the shelf-life of strawberries. A decrease in fungal incidence and a depletion of softening, important factors which limit the strawberry postharvest storage life, were achieved by the application of PL.     

柑橘精油熏蒸对草莓贮藏品质的影响

为研究柑橘精油对草莓贮藏品质的影响,以柑橘精油为熏蒸剂,研究不同熏蒸时间（4h、6h、8h）对草莓贮藏品质的影响。结果表明：与对照相比,熏蒸处理能够抑制腐烂率,延缓VC、可溶性糖损失,抑制花青素类黄酮含量变化,减缓丙二醛（MDA）的累积,抑制脂氧合酶（LOX）活性,减缓膜脂过氧化作用,延缓果实的后熟衰老进程;通过提高苯丙氨酸解胺酶（PAL）、过氧化氢酶（CAT）活性、过氧化物酶（POD）含量,使草莓保持较高的清除活性氧能力和抗病力,从而达到保持品质、延长货架期的目的。其中,6h柑橘精油熏蒸处理对于草莓品质保持效果最好。