Aloe vera based edible coatings improve the quality of minimally processed ‘Hayward’ kiwifruit

This article studies the efficacy of an edible coating based on Aloe vera gel at four different concentrations (0, 1, 5, 15% (v/v)) in maintaining the quality of fresh-cut kiwifruit. The kiwifruit slices were packaged under passive atmosphere and stored at 4 ± 1 °C. Quality attributes such as colour and texture (firmness and texture profile analysis), titratable acidity, total soluble solids, pectin content, microbial load and sensory parameters were evaluated during storage. In general, Aloe vera coating reduced respiration rates and microbial spoilage in sliced kiwifruit. After seven days of storage, the mesophilic load dropped by approximately one logarithmic unit for slices coated with 15% and 5% Aloe vera. Total pectin depolymerization was also lower in the treated samples and the texture of the uncoated samples deteriorated more rapidly than the treated slices during storage. Furthermore, due to the atmospheric composition and the microbial load, the quality of the control samples declined after six days of storage. Our results show that an Aloe vera coating improved the quality of stored kiwifruit slices. The best results obtained in the instrumental texture profile and in the preference panel test were with the 5% coating, indicating that this may be a healthy alternative coating for fresh-cut kiwifruit.     

Impact of edible coatings and mild heat shocks on quality of minimally processed broccoli (Brassica oleracea L.) during refrigerated storage

The effects of edible coatings and mild heat shocks on quality aspects of refrigerated broccoli were studied. Minimally processed broccoli was coated with either chitosan or carboxymethyl-cellulose with or without a previous application of a mild heat shock of 1.5 min at 50 °C. Product was packaged in multilayered polyolefin bags and stored at 5 °C for 18 d. Quality parameters such as weight loss, texture, colour, ascorbic acid content, total chlorophyll content, oxygen concentration inside the bags, browning potential, mesophilic aerobic counts, and sensory quality, were evaluated during storage. Edible coatings exhibited a beneficial impact on broccoli quality. The weight loss in uncoated broccoli was found to be between 2 and 5 times higher compared to coated samples. During storage, coated florets from both thermally and non-thermally treated samples, presented higher retention of the (?a*/b*) ratio indicating better green colour retention and a reduced rate of floret yellowing. Chitosan coating always presented the lower ascorbic acid degradation rates (twofold lower compared with control samples). Broccoli texture for uncoated samples increased significantly during storage. However, for carboxymethyl-cellulose coated broccoli a slight increase in texture was observed while for chitosan coated broccoli no significant changes in texture were observed throughout the storage period. After the edible coating application the microbial broccoli load dropped by around 1.5 and 0.9 logarithmic units in chitosan and carboxymethyl-cellulose films, respectively. During storage, the application of chitosan coating significantly reduced total microbial counts in the thermally and non-thermally treated uncoated samples. Among the assayed edible coatings, chitosan effectively maintained quality attributes and extended shelf life of minimally processed broccoli. The single application of a mild heat shock had a measurable influence in reducing weight loss, enzymatic browning in broccoli stems, and in delaying yellowing of broccoli florets. Moreover, chitosan coating combined with a mild heat shock showed the best performance for long-term refrigerated storage of minimally processed broccoli.     

Effects of pulsed light treatments on quality and antioxidant properties of fresh-cut mushrooms (Agaricus bisporus)

This study investigated the impact of pulsed light treatments on microbial quality, enzymatic browning, texture and antioxidant properties of fresh-cut mushrooms. The reduction of the native microflora of sliced mushrooms ranged from 0.6 to 2.2 log after 15 days of refrigerated storage by flashing at 4.8, 12 and 28 J cm⁻². Pulsed light treatments allowed extension of the microbiological shelf life of fresh-cut mushrooms by 2–3 days in comparison to untreated samples, while providing a high quality product. The use of high pulsed light fluencies (12 and 28 J cm⁻²) dramatically affected the texture of sliced mushrooms due to thermal damage induced by the treatments. Enzymatic browning was also promoted by an increase in polyphenol oxidase activity when the highest dose of pulsed light was applied. At 28 J cm⁻², phenolic compounds, vitamin C and antioxidant capacity were significantly reduced. Our results suggest that the application of pulsed light at doses of 4.8 J cm⁻² could extend the shelf life of fresh-cut mushrooms without dramatically affecting texture and antioxidant properties.     

Lemongrass essential oil incorporated into alginate-based edible coating for shelf-life extension and quality retention of fresh-cut pineapple

The effects of different concentrations (0.1%, 0.3% and 0.5%, w/v) of lemongrass essential oil incorporated into an alginate-based [sodium alginate 1.29% (w/v), glycerol 1.16% (w/v) and sunflower oil 0.025% (w/v)] edible coating on the respiration rate, physico-chemical properties, and microbiological and sensory quality of fresh-cut pineapple during 16 days of storage (10 ± 1 °C, 65 ± 10% RH) were evaluated. Coated fresh-cut pineapple without lemongrass and uncoated fresh-cut pineapple were stored under the same conditions and served as the controls. The results show that yeast and mould counts and total plate counts of coated samples containing 0.3 and 0.5% (w/v) lemongrass were significantly (p < 0.05) lower than other samples. However, the incorporation of 0.5% (w/v) lemongrass in coating formulation significantly (p < 0.05) decreased the firmness and sensory scores (taste, texture and overall acceptability) of fresh-cut pineapples. Therefore, the results indicate that an alginate-based edible coating formulation incorporated with 0.3% (w/v) lemongrass has potential to extend the shelf-life and maintain quality of fresh-cut pineapple.     

Some conventional and latent anti-listerial effects of essential oils,herbs, carrot and cabbage in fresh-cut vegetable systems

The anti-listerial effectiveness of selected essential oils (EOs) and shredded fresh herbs (thyme, oregano and rosemary) was examined on a range of modified atmosphere packaged fresh-cut vegetables (lettuce, carrot discs, cabbage and dry coleslaw mix). Anti-listerial effects were in the order: thyme EO > oregano EO > rosemary herb > rosemary EO. While thyme EO demonstrated the best anti-listerial effect, direct application of all the EOs damaged product appearance. Shredded fresh rosemary herb appeared to have a major anti-listerial effect, but shredded fresh thyme and oregano showed no anti-listerial effects. However, fresh rosemary herb was only effective in fresh-cut products when it was stomached with the product prior to microbial analysis. The effectiveness of these antimicrobials varied depending on the product type. Greater anti-listerial effects were recorded on carrot discs and shredded cabbage than on shredded lettuce. Adding shredded carrot to packages enhanced the apparent anti-listerial effects, suggesting a synergistic effect between carrot and rosemary.     

Postharvest shelf-life extension of green chillies (Capsicum annuum L.) using shellac-based edible surface coatings

Shellac-based coatings were developed in combination with starch, EDTA and sodium alginate and were evaluated for shelf-life extension of fresh green chillies during storage at ambient temperature (26 ± 2 °C, RH 68 ± 4%) for 12 days. The developed composite coatings were found to be effective in extending the shelf-life of chillies. The control samples showed a higher weight loss (12.35%) compared to coated ones (5.60-6.90%). The coated samples showed significantly (p < 0.05) higher retention of ascorbic acid, firmness and chlorophyll content, whereas, total phenolic content was found to be significantly (p < 0.05) higher in uncoated samples after 12 days of storage. Shellac-sodium alginate based coating was found to be the most effective in maintaining the quality of fresh green chillies during ambient storage as compared to other coatings.     

Low-intensity light cycles improve the quality of lamb's lettuce (Valerianella olitoria [L.] Pollich) during storage at low temperature

The influence of light on fresh-cut vegetables during storage is controversial, since both positive and negative effects on shelf-life and quality of such products have been observed. In this work, the effect of low-intensity light treatments on lamb's lettuce, a fresh-cut leafy and ready-to-eat vegetable, was investigated during storage at low temperature (6 °C), in comparison with conventional storage (in the dark at 4 °C). Although continuous light treatment (1 cycle of 8 h per day) was deleterious, cycles of light treatments (8 cycles of 1 h per day; 16 cycles of 0.5 h per day) showed positive effects, assessed by evaluating the content of chlorophylls, carotenoids, ATP, glucose and ascorbate. These analyses were performed at the beginning and after 6 days of storage, in comparison with samples stored in the dark at 4 °C. Under low-intensity light treatments, even if performed at a higher temperature (6 °C), the content of such bioactive compounds increased or was at least similar to that found in samples stored in the dark at the same temperature. We suggest that continuous low-intensity light treatments during cold storage of lamb's lettuce are able to promote photosynthesis but, at the same time, induce photo-damage. On the contrary, under intermittent low-intensity light cycles, photosynthesis is only partially activated, while the metabolism of the green tissues is still able to provide carbon moieties for the synthesis of bioactive molecules involved in delaying senescence. Therefore, low-intensity light cycles at 6 °C could contribute to maintain quality of lamb's lettuce, with respect to samples stored in the dark at both 6 and 4 °C. Finally, setting the temperature at 6 °C allows reduction of refrigerator energy consumption during storage.     

Effect of antifungal hydroxypropyl methylcellulose-beeswax edible coatings on gray mold development and quality attributes of cold-stored cherry tomato fruit

Edible composite coatings based on hydroxypropyl methylcellulose (HPMC), beeswax (BW), and food preservatives with antifungal properties, were evaluated on cherry tomatoes during cold storage. Food preservatives selected from previous research work included sodium propionate (SP), potassium carbonate (PC), ammonium phosphate (APh) and ammonium carbonate (AC). Cherry tomatoes artificially inoculated with Botrytis cinerea were coated and stored up to 15 d at 5 °C followed by 7 d of shelf-life at 20 °C. All antifungal HPMC-BW coatings significantly reduced gray mold development on inoculated and cold-stored cherry tomatoes, the SP-based coating being the most effective. Analytical and sensory fruit quality was also evaluated after cold storage and shelf-life. The AC-based coating was the most effective to control weight loss and maintain the firmness of coated cherry tomatoes. Respiration rate, firmness, color, sensory flavor, off-flavor, and fruit appearance were not adversely affected by the application of the antifungal coatings. Overall, the application of HPMC-BW edible composite coatings containing AC could be a promising treatment to extend the postharvest life of cherry tomatoes. Further studies should focus on the modification of some physical characteristics of the coatings in order to enhance the general performance and provide higher peel gloss.     

Biopreservation of fresh-cut melon using the strain Pseudomonas graminis CPA-7

The use of biopreservation is a promising technique to ensure microbial safety of fresh-cut produce. The objective of this work was to test the effectiveness of the strain CPA-7 of Pseudomonas graminis against a cocktail of Salmonella spp. and Listeria monocytogenes on fresh-cut melon, and evaluate its effect on its quality during shelf-life when tested in conditions simulating commercial application.Fresh-cut melon was artificially inoculated with Salmonella spp. and L. monocytogenes and with or without the biopreservative strain at different concentrations and stored at 20, 10 and 5 °C. Moreover, the effect of the strain was tested in conditions simulating commercial application. Fresh-cut melon was packaged using passive modified atmosphere (MAP) and AIR conditions and stored at 5 and 10 °C. Quality of fresh-cut melon was evaluated in CPA-7 treated and untreated samples. At laboratory scale trials, P. graminis reduced Salmonella and L. monocytogenes growth on fresh-cut melon stored at 5, 10 and 20 °C. Effectiveness depended on their concentration and on storage temperature. At low pathogen concentration and 20 °C, L. monocytogenes growth was reduced between 2.1 and 5.3 log cfu g⁻¹ units after 2 days of storage and Salmonella growth between 2.0 and 7.3 log cfu g⁻¹ depending on CPA-7 dose. At 10 °C, similar reductions of pathogens were observed after 5 days of storage. In studies simulating commercial conditions, packaging atmosphere and temperature influenced P. graminis effectiveness, with better results in samples packaged under AIR conditions and 10 °C. Reduction of pathogen growth was <1-log unit in fresh-cut melon stored in MAP whilst it was >4-log units in AIR. Soluble solids content, titratable acidity, pH and firmness of fresh-cut melon were not significantly different in CPA-7 treated and untreated (control) melon. In general, lightness, chroma and hue values of fresh-cut melon stored in AIR decreased faster in CPA-7 samples than on control ones. At 5 °C, CPA-7 treated melon was visually scored lower than untreated melon. P. graminis has demonstrated promising results at 10 °C, which is a temperature more compromised for safety. Nevertheless more detailed studies on the modified atmosphere are required because AIR packaging is not recommended due to the rapid loss of quality.     

Effect of minimal processing on bioactive compounds and antioxidant activity of fresh-cut ‘Kent’ mango (Mangifera indica L.)

The influence of dipping in ascorbic acid, citric acid and calcium chloride (AA + CA + CaCl₂) solution and storage time on color, bioactive compounds content and antioxidant activity of fresh-cut mango ‘Kent’ stored at 5 °C was evaluated. The treated mangoes showed better color retention during storage than control mangoes. The dipping treatments with AA + CA + CaCl₂ significantly increased the vitamin C values compared with untreated mango cubes. β-Carotene was not affected by dipping treatments and vitamin E showed a significant decline over storage time for both treated and untreated mango cubes. However, higher vitamin E values were found in treated mangoes. Dipped cubes had higher antioxidant activity measured as TEAC and %RSA than controls. In general, addition of ascorbic acid as an anti-browning agent not only retarded quality loss of fresh-cut mango cubes but also promoted significant increases in antioxidant activity in comparison with control samples.     

Storage temperature and type of cut affect the biochemical and physiological characteristics of fresh-cut purple onions

Minimal processing of onion (Allium cepa L.) results in convenience and freshness in a single product. However, inappropriate storage of fresh-cut onion results in losses of nutritional and sensory characteristics. To further understand this phenomenon, we evaluated the effect of the storage temperature and type of cut on the quality of fresh-cut purple onions. Purple onions (cv. Crioula Roxa) were minimally processed using two types of cut (10 mm cubes and 3–5 mm thick slices) and stored at different temperatures (0, 5, 10 and 15 °C) with 85–90% relative humidity (RH) for 15 days. The following analyses were performed to evaluate the shelf life of the purple onion: pungency, total phenolic content, anthocyanin content, quercetin content, respiratory rate, color, soluble solids content, titratable acidity, pH, dryness and deterioration index (DDI), and decay index (DI). Fresh-cut onions stored at 0 °C showed less pungency, lower respiratory rate levels and less variation of total phenolic, anthocyanin and quercetin contents. In addition, the physicochemical aspects and appearance changed less with fresh-cut onions stored at 0 °C. Moreover, slicing enabled a higher stability of the physicochemical and biochemical aspects in comparison to dicing. Storage of slices at 0 °C allowed preservation for up to 15 days.     

Extending the shelf life of fresh-cut eggplant with a soy protein–cysteine based edible coating and modified atmosphere packaging

The effect of a soy protein-based edible coating with antioxidant activity, and conventional and superatmospheric modified atmosphere (MA) packaging, on the quality of fresh-cut ‘Telma’ eggplants, was evaluated during storage. In a first experiment, eggplant pieces were dipped in either a coating composed of soy protein isolate (SPI) and 0.5% cysteine (Cys), or water as an uncoated control. Samples were packed in trays under atmospheric conditions to reach a passive MA (MA-P) or two gas mixtures (MA-A: 15 kPa CO₂ + 5 kPa O₂; MA-B: 80 kPa O₂) and were stored at 5 °C. Atmospheric conditions were used as the control conditions (Control). The coated samples packed under MA-B and Control conditions resulted in the highest whiteness index (WI) values during storage, whereas MA-A did not improve the shelf-life of minimally processed eggplants and had the lowest WI values. The MA-B and atmospheric control conditions helped to maintain firmness, whereas the coating helped to maintain the weight loss under MA-A and MA-B. The maximum commercial shelf-life was reached on day 6 for the coated samples packed under atmospheric conditions. In a second experiment, the commercial shelf-life of fresh-cut eggplants was extended to 8 and 9 storage days by increasing the Cys content in the edible coating from 0.5 to 1% under MA-B and Control storage conditions, respectively.     

Effects of a composite chitosan–gelatin edible coating on postharvest quality and storability of red bell peppers

For the first time, a composite chitosan–gelatin (CH–GL) coating was applied to peppers and its effects on fruit quality and storability were examined. Pure chitosan (CH) and gelatin (GL) coatings were studied for comparison. The CH coating inhibited microbial spoilage and prolonged the possible storage period. The GL coating contributed to fruit firmness, but did not allow for prolonged storage. The composite CH–GL coating was associated with a two-fold decrease in microbial decay, significantly (p ≤ 0.05) enhanced fruit texture and prolonged the possible period of cold storage up to 21 days and fruit shelf-life up to 14 days, without affecting the respiration or nutritional content of the fruit.     

Hexanal reduces infection of tomatoes by Botrytis cinerea whilst maintaining quality

Hexanal vapour and intact tomatoes were used as models to assess the opportunities for control of Botrytis cinerea rots by controlled release of organic vapours. Hexanal vapour concentrations in the ranges 5–270 μL L⁻¹ were applied continuously or as a single dose at the start of storage. The postharvest microbiological, physiological and quality attributes of control and hexanal treated tomatoes were investigated during storage for 7 days at 20 ± 1 °C and ∼99% RH. Continuous hexanal exposure effectively suppressed grey mould with the minimum inhibitory concentration (MIC) being 40–70 μL L⁻¹; the single-dose treatment showed minimal antifungal activity. During continuous exposure at the MIC the fruit respiration rate was increased ∼50% and reddening was slowed. No clear trend was observed in ethylene production and treated fruit did not differ from the controls in firmness or mass loss. The controlled release of low concentrations of hexanal vapour into a packaging headspace appears a feasible mechanism for prolonging tomato storage life.     

Edible coatings containing chitosan and moderate modified atmospheres maintain quality and enhance phytochemicals of carrot sticks

Carrot sticks are increasingly in demand as ready-to-eat products, with a major quality problem in the development of white discoloration. Modified atmosphere packaging (MAP) and edible coating have been proposed as postharvest treatments to maintain quality and prolong shelf-life. The combined application of an edible coating containing 5 mL L^?1 of chitosan under two different MAP conditions (10 kPa O₂ + 10 kPa CO₂ in Pack A and 2 kPa O₂ + 15–25 kPa CO₂ in Pack B) over 12 d at 4 °C was studied. Respiration rate, microbial and sensory qualities as well as the contents of vitamin C, carotenoids and phenolics of coated and uncoated carrot sticks were evaluated. The use of the edible coating containing chitosan preserved the overall visual quality and reduced surface whiteness during storage. Microbial populations were very low and not influenced by coating or MAP. Edible coating increased respiration rates of carrot sticks, although this was only noticeable in the package with the less permeable film (Pack B). Vitamin C and carotenoids decreased during storage particularly in coated carrot sticks. In contrast, the content of total phenolics markedly increased in coated carrot sticks stored under moderate O₂ and CO₂ levels, while it was controlled under low O₂ and high CO₂ levels. The combined application of edible coating containing chitosan and moderate O₂ and CO₂ levels maintained quality and enhanced phenolic content in carrot sticks.     

Salinity of nutrient solution influences the shelf-life of fresh-cut lettuce grown in floating system

Quality, microbiological and enzymatic characteristics of fresh-cut lettuce (Lactuca sativa var. longifolia, ‘Duende’), grown in floating system with three electrical conductivities of nutrient solutions (2.8, 3.8 and 4.8 mS cm^?1), were investigated in order to evaluate the effect of salinity on product shelf-life during cold storage (9 d at 4 °C). Pre-harvest salinity of 3.8 and 4.8 mS cm^?1 improved the properties of fresh-cut lettuce, since CO₂ production was reduced with a subsequent control of the decay process. Fresh-cut processing caused an activation of polyphenol oxidase and peroxidase; in all cases the product obtained by salinity treatments was less subject to oxidase activity and browning phenomena during storage. Increased salinity reduced the number of mesophilic bacteria and of moulds and yeasts, assessed by plate counts on different culture media; in contrast, Enterobacteriaceae levels were unaffected by pre-harvest treatments. The research demonstrated that an increase in nutrient solution electrical conductivity, through the use of floating system, affects fresh-cut lettuce characteristics, improving shelf-life of the product.     

Effects of alginate edible coating on preserving fruit quality in four plum cultivars during postharvest storage

Four plum (Prunus salicina Lindl.) cultivars (“Blackamber”, “Larry Ann”, “Golden Globe” and “Songold”), were treated with 1 or 3% alginate as an edible coating before storage. Analytical determinations were made after 7, 14, 21, 28 and 35 days at 2 °C and after a 3 day period at 20 °C (shelf-life). Both treatments were effective in inhibiting ethylene production for all cultivars, especially when 3% alginate was used. The changes in fruit quality parameters related to plum postharvest ripening, such as weight and acidity losses, softening and colour changes, were significantly delayed by the use of both edible coatings. The delay of the ripening process was also related to lower anthocyanin and carotenoid accumulation. Overall results suggest that these treatments could increase the plum storage period with optimum quality, 2 weeks for “Larry Ann” and “Songold” and 3 weeks for “Blackamber” and “Golden Globe” more than controls.     

Responses of 1-MCP application in plums stored under air and controlled atmospheres

The potential of 1-MCP for controlling ripening in ‘Angeleno’ plum fruit under air and controlled atmosphere (CA) storage was explored, and the possibility that 1-MCP can inhibit development of brown rot caused by Monilinia laxa and internal breakdown in ‘Fortune’ and ‘Angeleno’ plums tested. After harvest, fruit were exposed to 300 and 500 nl l⁻¹ (in 2003) and 500 nl l⁻¹ 1-MCP (in 2004) at low temperatures (0–3 °C) for 24 h. After treatment the plums were stored in air at 0 °C and ‘Angeleno’ fruit were also stored in CA storage (1.8% O₂ + 2.5% CO₂). Following storage, fruit were kept at 20 °C. In ‘Angeleno’ fruit, 1-MCP was effective in delaying the loss of firmness and colour changes during holding at 20 °C. 1-MCP reduced brown rot in fruit stored in CA but no significant reduction was found in air storage. Internal breakdown, a major physiological storage disorder in plums, was inhibited by 1-MCP treatment. Furthermore, since 1-MCP applied in air storage showed better results than the control in CA conditions, an application of 1-MCP before air storage could be the best way to reduce the ripening process for short or medium storage periods (40 and 60 days). CA storage plus 1-MCP treatment could be used for long periods (80 days).     

Effect of new sanitizing formulations on quality of fresh-cut iceberg lettuce

In the present study, three recently patented decontamination agents: peroxyacetic acid combined with lactic acid, and two different combinations of hydrogen peroxide with citric acid (with and without propylene glycol), were compared with sodium hypochlorite and tap water washing regarding their effect on equilibrium modified atmosphere packaged (EMAP) fresh-cut iceberg lettuce. Effects of these sanitizers on respiration rate, electrolyte leakage, microbial levels, and sensory quality of the product after decontamination and during storage (3 d at 4 °C followed by 4 d at 7 °C) were elucidated. Hydrogen peroxide based sanitizers provoked a significant increase in the respiration rate and the electrolyte leakage of fresh-cut iceberg lettuce compared with tap water washing. Peroxyacetic acid combined with lactic acid resulted in similar results to those of tap water washing for all the parameters analyzed. However, other aspects of the combination of peroxyacetic and lactic acids (e.g. efficacy for cross-contamination avoidance) should be assessed in the future in order to determine its suitability for fresh-cut iceberg lettuce processing.     

Effect of 1-MCP treatment and N2O MAP on physiological and quality changes of fresh-cut pineapple

The effects of both 1-MCP treatment of pineapples and packaging of their fresh-cut products with an alternative modified atmosphere (MA: 86.13 kPa N₂O, 10.13 kPa O₂ and 5.07 kPa CO₂) on physiological and quality changes of these minimally processed products were investigated. Fresh-cut fruit treated or not with 1-MCP were packed in Air or in MA and were stored at 4 °C for 10 d. The following parameters were monitored during storage: ripening index; O₂, CO₂ and C₂H₄ in the package headspace; firmness and colour. Microbial spoilage of MP pineapple samples was also investigated and a mathematical model based on the Zwietering modified Gompertz equation was used to obtain growth parameters of mesophilic bacteria, yeasts and moulds.The results showed that 1-MCP treatment and MAP in a N₂O enriched atmosphere had a positive combined effect on the inhibition of respiration and ethylene production of fresh-cut pineapple and on its softening delay, confirming previous findings about 1-MCP and N₂O preservative effects on fresh-cut fruit quality. This combined effect was not extended to the ripening index and colour maintenance, as MAP at 86.13 kPa of N₂O did not add any benefit to that of the 1-MCP treatment. From a microbiological point of view, N₂O MAP extended the shelf-life of the products of 3–4 d by increasing the lag phase of microbial growth.