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.     

Antimicrobial effect of electrolyzed oxidizing water against Escherichia coli O157:H7 and Listeria monocytogenes on fresh strawberries (Fragaria x ananassa)

ABSTRACT:  Antibacterial activity of electrolyzed oxidizing (EO) water prepared from 0.05% or 0.10% (w/v) sodium chloride (NaCl) solutions against indigenous bacteria associated with fresh strawberries ( Fragaria × ananassa ) was evaluated. The efficacy of EO water and sodium hypochlorite (NaOCl) solution in eliminating and controlling the growth of Listeria monocytogenes and Escherichia coli O157:H7 inoculated onto strawberries stored at 4 ± 1 °C up to 15 d was investigated at exposure time of 1, 5, or 10 min. Posttreatment neutralization of fruit surfaces was also determined. More than 2 log₁₀ CFU/g reductions of aerobic mesophiles were obtained in fruits washed for 10 or 15 min in EO water prepared from 0.10% (w/v) NaCl solution. Bactericidal activity of the disinfectants against L. monocytogenes and E. coli O157:H7 was not affected by posttreatment neutralization, and increasing exposure time did not significantly increase the antibacterial efficacy against both pathogens. While washing fruit surfaces with distilled water resulted in 1.90 and 1.27 log₁₀ CFU/mL of rinse fluid reduction of L. monocytogenes and E. coli O157:H7, respectively, ≥ 2.60 log₁₀ CFU/mL of rinse fluid reduction of L. monocytogenes and up to 2.35 and 3.12 log₁₀ CFU/mL of rinse fluid reduction of E. coli O157:H7 were observed on fruit surfaces washed with EO water and NaOCl solution, respectively. Listeria monocytogenes and E. coli O157:H7 populations decreased over storage regardless of prior treatment. However, EO water and aqueous NaOCl did not show higher antimicrobial potential than water treatment during refrigeration storage.     

气调包装对草莓货架期延长保鲜内在品质的影响

植物组织或器官在衰老过程中常伴随细胞膜结构的破坏,导致组织结构和细胞区域化的丧失。研究经过气调包装(MAP)处理后草莓超微结构的变化,结果表明经过MAP处理能较好地维持草莓细胞形状。果胶酯酶(PE)活性是影响草莓货架期的内在因素之一。采用NaCl盐析法得到了草莓果胶酯酶粗提液,对草莓果胶酯酶的特性进行了探索。试验结果表明,氯化钙溶液对果胶酯酶的活性影响很大,植酸同样可抑制果胶酯酶的活性,以0.05%效果最好。     

Effect of nitrogen fertilization on quality markers of strawberry (Fragaria × ananassa Duch. cv. Aromas)

BACKGROUND: Nitrogen is an indispensable element for fruit metabolism and low or excessive N levels can affect the accumulation of the most important components that contribute to the flavour and aroma of the fruit. Among them, sugars, acids and volatile compounds can be considered quality markers. The objective of this study was to evaluate the effect of N fertilization on these quality markers of the fruit at two harvest dates. RESULTS: Strawberry plants were grown in a hydroponic system and N was applied as Ca(NO₃)₂ at concentrations of 0.3, 3 and 6 mmol L^?1 in the nutrient solution. Total soluble solids, soluble carbohydrates, amino acids and organic acids and volatile compounds of the fruit were analyzed. The fruits produced at 3 and 6 mmol L^?1 N had higher contents of esters, soluble carbohydrates and amino acids. The hexanal content increased with the 6 mmol L^?1 dose. The effect of fertilization was more marked at the second harvest date. CONCLUSION: The availability of N in strawberry plants affected the accumulation of quality markers. The fruits expected to have the best flavour and aroma, with both high levels of soluble carbohydrate and esters and low levels of hexanal, were obtained with 3 mmol L^?1 nitrate in the solution. Copyright © 2009 Society of Chemical Industry     

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.     

The aroma of strawberry (Fragaria ananassa): Characterisation of some cultivars and influence of freezing

The volatiles of six strawberry (Fragaria ananassa Duch) cultivars, both fresh and deep-frozen, were isolated by direct dichloromethane extraction. Sixty compounds were identified and quantified by GC—MS. Characterisation of cultivars was achieved by applying principal component analysis to the chromatographic data. Great differences were observed. Maxim and Directeur Paul Wallbaum are rather low in volatiles while Gariguette and Tioga are rich in mesifurane (2,5-dimethyl-4-methoxy-2,3-dihydrofuran-3-one), furaneol' (2,5-dimethyl-4-hydroxy-2,3-dihydrofuran-3-one) and nerolidol. Esters are the major compounds in Senga Sengana and Vicomtesse Hericart de Thury. This last cultivar is also characterised by high concentrations of γ-decalactone. Trans-hex-2-enal and hexanal are found mainly in fresh fruits. Determinations of volatiles in stored frozen fruits have shown only slight influence on mesifurane and furaneol while the concentration of nerolidol increases and that of esters decreases.     

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.     

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).     

草莓复合涂膜保鲜效果的研究

以草莓为实验原料,采用魔芋精粉、丁香提取物和氯化钙复合涂膜方法对草莓进行涂膜保鲜实验。选择失重率和Vc含量为指标,以单因素实验和正交实验优化保鲜膜配方,结果表明,常温下,魔芋精粉浓度0.5%、丁香提取物浓度2.0%、氯化钙浓度1.2%的复合涂膜剂对草莓的保鲜效果最好,有效地延长了保质期。该最佳配比的复合涂膜剂在低温下对草莓的保鲜效果比在室温下更显著,相关指标明显优于室温下的涂膜组。     

Nitrogen availability drives the effect of Glomus intraradices on the growth of strawberry (Fragaria x ananassa Duch.) plants

BACKGROUND: On the one hand, the critical nitrogen (N) content curve allows the minimal N content necessary for maximum growth rate at any stage of crop development to be predicted. On the other hand, arbuscular mycorrhizal fungi (AMF) transfer N from the soil to the plants and its growth and activity depends on the availability of soil N. Our objective was to investigate how the availability of N in the soil affects growth and the accumulation of N in inoculated strawberry plants. Root colonisation, dry matter accumulation and the critical N% curve were studied during growth of inoculated and non‐inoculated strawberry plants grown at several N levels. RESULTS: (1) The increase in the availability of N augmented root colonisation by AMF. (2) The effect of AMF on plant growth depended on N availability and the plant developmental status. (3) The critical %N curves were fitted by the following equations: %N = 2.81× (DM)^−0.21 (r² = 0.81) and %N = 2.89× (DM)^−0.32 (r² = 0.80) for inoculated and non‐inoculated plants, respectively (where DM is the weight of leaf dry matter, in g plant⁻¹). CONCLUSION: N availability was a key factor for root colonisation by AMF and for its contribution to plant growth. The patterns of the critical %N curves suggest that AMF modified the photosynthetic N use efficiency. Copyright © 2012 Society of Chemical Industry     

Root colonisation by the arbuscular mycorrhizal fungus Glomus intraradices alters the quality of strawberry fruits (Fragaria × ananassa Duch.) at different nitrogen levels

BACKGROUND: Arbuscular mycorrhizal fungi (AMF) increase the uptake of minerals from the soil, thus improving the growth of the host plant. Nitrogen (N) is a main mineral element for plant growth, as it is an essential component of numerous plant compounds affecting fruit quality. The availability of N to plants also affects the AMF–plant interaction, which suggests that the quality of fruits could be affected by both factors. The objective of this study was to evaluate the influence of three N treatments (3, 6 and 18 mmol L^?1) in combination with inoculation with the AMF Glomus intraradices on the quality of strawberry fruits. The effects of each factor and their interaction were analysed. RESULTS: Nitrogen treatment significantly modified the concentrations of minerals and some phenolic compounds, while mycorrhization significantly affected some colour parameters and the concentrations of most phenolic compounds. Significant differences between fruits of mycorrhizal and non‐mycorrhizal plants were found for the majority of phenolic compounds and for some minerals in plants treated with 6 mmol L^?1 N. The respective values of fruits of mycorrhizal plants were higher. CONCLUSION: Nitrogen application modified the effect of mycorrhization on strawberry fruit quality. Copyright © 2010 Society of Chemical Industry     

Effect of edible coating and gamma irradiation on inhibition of mould growth and quality retention of strawberry during refrigerated storage

The aim of this study was to investigate the effect of edible coating and gamma irradiation treatment on mould growth and storage quality of strawberry. Strawberry fruit after harvest were treated with 0.5–1.0% (w/v) carboxymethyl cellulose (CMC) coating followed by irradiation at 2.0 kGy and subsequent storage under refrigerated conditions for 21 days. The investigations revealed that CMC coating alone at levels 0.5% and 0.75% w/v was not effective in delaying the decay and inhibiting the appearance of mould growth in strawberry fruit. Treatment of irradiation in combination with 1.0% w/v CMC coating was found significantly (P ≤ 0.05) effective compared with other treatments in maintaining the quality and delaying the decay and appearance of the mould growth in strawberry up to 18 days of refrigerated storage. Combinatory treatment of irradiation and coating can help to a greater extent in facilitating the marketing of the strawberry fruit to distant markets other than the local market, thereby benefiting growers and consumers.     

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.