Structure and composition changes in the cell wall in relation to texture of shiitake mushrooms (Lentinula edodes) stored in modified atmosphere packaging

BACKGROUND: Firmness in shiitake mushroom (Lentinula edodes) is an important textural attribute affecting consumer attitudes toward freshness and quality. In this study, the effects of modified atmosphere packaging (MAP) treatments on structure and composition changes in cell walls in relation to the texture of mushrooms were investigated. RESULTS: Shiitake mushrooms were packaged in low density polyethylene bags with no holes (M₀₎, two microholes (M₁), four macroholes (M₂), stored at 4 °C for 16 days with non‐wrapped mushrooms as control. Control mushrooms showed the highest firmness value due to significant increase of cellulose and chitin. All three MAP treatments reduced losses of protein and polysaccharides; the M₂ treatment can best preserve the original texture while mushrooms in M₀ became soft and deteriorated, possibly due to higher CO₂ accumulation, lower cellulose and chitin content. Transmission electron microscopy performed on caps at harvest and after 16 days indicated that disintegration of plasmalemma had been alleviated by M₂ treatment, leading to better preservation of the cell wall. CONCLUSION: Our results suggest that differences in firmness of shiitake mushrooms during storage may be due to differences in cellulose and chitin concentrations. M₂ treatment may be a useful way of maintaining shiitake mushrooms texture during storage at 4 °C. Copyright © 2010 Society of Chemical Industry     

Maintaining quality of wild vegetables (Aster glehni and Aruncus dioicus var. kamtschaticus) from Ulleungdo(Island), Korea by modified atmosphere packaging

Wild vegetables, Aster glehni and Aruncus dioicus var. kamtschaticus, produced from Ulleungdo (Island), Korea were packaged with 30 μm polypropylene (PP), 30 μm antifogging oriented polypropylene (A-OPP), 30 μm microperforated antifogging oriented polypropylene (MiA-OPP), 30 μm macroperforated low density polyethylene (Ma-LDPE), and 20 μm macroperforated high density polyethylene (Ma-HDPE), stored at 4, 10, and 20°C. Concentrations of O₂ and CO₂ in the packages were not modified by Ma-LDPE and Ma-HDPE. Weight loss was retarded by PP, A-OPP, MiA-OPP, especially as storage temperature decreased. Soluble solids were not affected by packaging materials. pH slightly decreased in LDPE and Ma-HDPE. Appearance, color, and overall acceptability of both vegetables stored at 4°C in PP or MiA-OPP showed the highest sensory score. These results suggest that packaging with PP or MiA-OPP films and storage at 4°C could be a useful method to maintain quality of the wild vegetables.     

Keeping quality and safety of minimally fresh processed melon

Fresh-cut Amarillo melon was stored under passive modified atmosphere packaging (MAP) for 14 days at 5 °C. Three commercial films were tested: microperforated polypropylene (MPP), bioriented PP (BPP), and oriented PP (OPP). As a control, a macroperforated PP film was used. The effect of a citric acid dip treatment (0.52 mM) on the quality of the melon pieces packaged in OPP film was also evaluated. A similar final gas composition (4 kPa O2 plus 12–13 kPa CO2) within packages was achieved by using the three tested films. This atmosphere was effective for maintaining sensorial quality and microbial safety and for avoiding weight loss and translucency. When citric acid dip was applied, a reduction of microbial counts, a low discoloration, an increase of lightness, and a general improvement of visual appearance were found. However, after 14 days of storage, neither MAP treatments nor citric acid dip were enough to avoid softening of at least 23%, although the highest value (32%) was found in control pieces. Taking into account safety, quality attributes and consumer acceptance, shelf life of fresh processed melon stored under the studied MAP conditions could be stabilised for 10 days.     

Quality of enoki mushrooms as affected by packaging conditions

Fresh enoki mushrooms (100 g) were packaged under various conditions and stored at 10 °C for 14 days. Package atmosphere, weight loss, stipe elongation, surface colour and sensory quality of the mushrooms were measured during storage. Different levels of initial vacuum application did not have a significant influence on the in‐package atmosphere after 2 days. The half‐vacuum package was best in terms of quality preservation of the fresh mushrooms. A polyolefin film with respective gas permeabilities of 166 and 731 ml m⁻² h⁻¹ atm⁻¹ to O₂ and CO₂ established an equilibrated atmosphere of 1.7–2.4% O₂ and 4.1–5.6% CO₂ inside the package at 10 °C. This polyolefin film was shown to contribute to preserving the freshness of the mushrooms. Temperature fluctuations between 5 and 15 °C did not induce a harmful atmosphere inside the polyolefin package, though high temperatures accelerated the quality loss. © 2000 Society of Chemical Industry     

QUALITY CHANGES IN FRESH‐CUT SPINACH (SPINACIA OLERACEA) UNDER MODIFIED ATMOSPHERES WITH PERFORATIONS

ABSTRACT

Fresh‐cut spinach leaves were stored for 4 days at 15C and 75% relative humidity under modified atmosphere packaging to assess the impact of differential in‐pack gas atmospheres generated through different packaging films and variable in‐pack weight on the quality of stored produce. After 4 days of storage, retention of chlorophyll, β‐carotene and ascorbic acid was better in low‐density polyethylene (LDPE) packages than in polypropylene (PP) packages. LDPE film‐packaged samples had higher phenolic content than PP film‐packaged samples. Low in‐pack O₂ (1–2 kPa) along with the buildup of CO₂ (8–10 kPa) seems to have enhanced the retention of antioxidant components, i.e., β‐carotene and ascorbic acid, in LDPE packages. This helped in chlorophyll retention and also prevented formation of oxidation compounds of phenols that otherwise caused browning of cut surfaces. Thus, O₂ and CO₂ permeability of packaging film or in‐pack weight of produce might be such that equilibrated O₂ partial pressures remain near to 1–2 kPa so as to affect a beneficial increase in the phenolic content along with concomitant retention of chlorophyll.

PRACTICAL APPLICATIONS

Fresh‐cut spinach leaves have received an enormous demand due to their utility in various traditional Indian preparations. Shelf life and quality of fresh‐cut produce may be greatly reduced due to high rates of respiration. Traditional packaging and handling techniques reduce the shelf life and sensory quality of fresh‐cut spinach. Temperature control and atmospheric modifications help to maintain produce quality by reducing respiration rate and enhance shelf life by minimizing the adverse effects of cutting. This research focused on evaluation of respiratory behavior of fresh‐cut spinach leaves at a temperature commonly encountered during transportation and retail distribution, i.e., 15C, and the effect of different polymeric films and in‐pack weights on produce quality. The results of the study suggest that packaging of fresh‐cut spinach in polymeric film packages could maintain the sensory quality and reduce degradation of various physicochemical constituents. Utilization of the results for proper design of modified atmosphere packages for this highly perishable produce can prove to be extremely beneficial for safe storage and transportation to urban retail markets.     

Microbiological,physicochemical and sensory characteristics of Cameros cheese packaged under modified atmospheres

This study evaluated the shelf-life quality of Cameros cheeses packaged under modified atmospheres. Five different modified atmosphere conditions were studied (carbon dioxide/nitrogen mixtures and vacuum). Control cheeses were packaged in air. The product stored at 3–4°C was evaluated periodically to investigate its sensory quality, microbiological condition and physicochemical characteristics. Weight loss and pH evolution were similar in vacuum and air packaging. Cheeses packaged in 100% CO₂showed the greatest weight losses and lower pH values. CO₂reduced proteolysis and lipolysis during storage in all conditions studied. Fat acidity and NPN/TN values were slightly higher in vacuum than in CO₂, but lower than in air. Modified atmosphere packaging presented an extended shelf life. Those containing CO₂reduced the growth rate of mesophiles, psychrotrophs, Enterobacteriaceae and coliforms, which was lower when the CO₂concentration increased. The lowest microbial counts were at 100% CO₂while vacuum conditions presented microbial counts only slightly lower than the controls. Salmonella spp.,Staphylococcus aureus and Listeria spp. were not found in any of the samples. Faecal coliforms, moulds and yeasts were not detected under CO₂atmospheres or in vacuum. After 7 days of storage, the sensory characteristics of the control cheeses were unacceptable in all the parameters studied. However, the overall score for cheeses stored in 40% and 50% CO₂did not change substantially, retaining a reasonable acceptability until the end of the storage period. The 100% CO₂atmosphere had a very negative effect on sensory quality. With regard to Cameros cheese, packaging in 50%CO₂/50%N₂and 40%CO₂/60%N₂are the most effective for extending shelf life and retaining good sensory characteristics.     

Storage of mushrooms in pre-packs: The effect of changes in carbon dioxide and oxygen on quality

Mushrooms (Agaricus bisporus) were picked at the “button” stage (velum differentiated but unbroken) and stored for 3 to 5 days at 2 or 18 °C in styrene punnets (pre-packs) overwrapped with one of a range of plastic films. Concentrations of carbon dioxide and oxygen were measured inside the pre-packs at intervals. When the packs were opened, internal and external browning, loss of weight and diameter of the mushrooms were measured and subjective assessments of quality were made. These parameters were compared with those of mushrooms stored in unwrapped punnets. As a result of the mushroom respiration, the internal atmosphere of the prepack was rapidly modified until, after about 24 h, a rough equilibrium concentration of CO₂ and O₂ was established in the range 4 to 10% CO₂ and 11 to 17% O₂ at 2 °C or 8 to 15% CO₂ and 1 to 2% O₂ at 18 °C; the mean concentration was dependent on the type of film. An equation, applicable to five out of six films that were tested, is proposed to describe the relationship between the equilibrium CO₂ concentrations at 18 °C and the permeability data of the film. At 18 °C, the gas changes inside the pre-packs prevented opening of the pileus and, in combination with prevention of water loss by the film, slowed down deterioration of the mushrooms. However, concentrations of CO₂ much above or below 10 to 12% were associated with increased internal browning. At 2 °C overwrapping generally caused slight external browning of the pileus. The relevance of the results are discussed in relation to the commercial marketing of pre-packed mushrooms.     

Minimally processed butternut squash shelf life

The effects of dipping in antimicrobial solution and efficacy of proper film and modified atmosphere packaging conditions (MAP) on the quality decay of packaged fresh-cut butternut squash were investigated. The work was divided into three subsequent experimental trials: the first two were aimed to select the optimal packaging film mass transport properties, being micro-perforated and no-perforated films been tested. In the third experimental step, the best film (i.e., no-perforated oriented polypropylene, OPP40) was used to package sliced butternut squash under passive and active MAP. Each slice of product was dipped in aqueous solution of potassium sorbate, while no dipped samples were stored as the controls. During storage at refrigerated temperature (4 ± 1 °C) headspace gas concentrations, mass loss, microbiological and sensory quality were monitored. Results obtained from the preliminary pre-screening showed that micro-perforated films did not match fresh-cut butternut squash respiratory requirements. In these films a high proliferation of moulds occurred, probably due to elevated oxygen levels. Among the no-perforated films with different thickness, the OPP40 showed better performances. In the third trial samples dipped in potassium sorbate and packaged in OPP40 under active MAP recorded a shelf-life of about 22 days respect to the no-dipped samples packaged under both passive and active MAP that reached a shelf life of about 2 weeks.     

Shelf‐life extension of refrigerated seabass slices under modified atmosphere packaging

The effect of CO₂‐enriched atmosphere in combination with either oxygen or nitrogen on the keeping quality of seabass slices stored at 4 °C was investigated. The inhibitory effect on bacterial growth increased proportionally to the CO₂ concentration in the packaging, maximum inhibition being achieved with 100% CO₂ (P < 0.05). Seabass slices stored in CO₂‐enriched atmosphere had lower total volatile base, trimethylamine, ammonia and formaldehyde contents than those stored in air (P < 0.05). However, increases in lightness and exudate loss were observed for samples packaged in high‐CO₂ atmosphere, suggesting the denaturation of both muscle and pigment proteins by carbonic acid formed. Thiobarbituric acid‐reactive substances (TBARS) increased as the CO₂ concentration increased (P < 0.05). However, odour, flavour and overall acceptability of CO₂‐enriched packaged samples, particularly with 80 and 100% CO₂, were acceptable throughout storage for 21 days. Chemical and microbial changes in all samples were generally in agreement with sensory panel evaluations. The shelf‐life of seabass slices packaged in 80–100% CO₂ atmosphere could be extended to more than 20 days at 4 °C, compared with 9 days for those packaged in air. © 2002 Society of Chemical Industry     

The sensory and microbiological quality of fresh sliced mushroom (Agaricus bisporus L.) packaged in modified atmospheres

The effect of modified atmospheres, generated by using different packaging films, on the quality of sliced mushrooms was evaluated. The carbon dioxide and oxygen content inside the packages as well as the colour, texture, weight loss, sensory attributes, mesophiles, psychrotrophs, Pseudomonas fluorescens, faecal coliforms, Escherichia coli and anaerobic spores were determined. Modified atmospheres containing 2.5% CO₂ and 10–20% O₂ reduced the microbial counts and improved the mushrooms’ appearance when compared with an air atmosphere. Modified atmospheres containing 15% CO₂ and <0.1% O₂ inhibited mushroom development and toughening and reduced microbial growth. Although these atmospheres had no effect on colour, they did allow the development of off odours and anaerobic spores were detected. No differences in microbial growth or mushroom spoilage were observed under the different moisture contents generated in the packages at 4 °C. Aerobic bacteria counts were considered very high even at the beginning.     

Storage studies of tomato and bell pepper using eco‐friendly films

Tomato (Lycopersicon esculentum) and bell pepper (Capsicum annuum), packaged in cartons (approximately 0.35 kg per box) covered with either eco‐friendly chitosan film or synthetic petroleum‐based low‐density polyethylene (LDPE) film, were stored at room temperature (27 ± 1 °C) and 65 ± 3% relative humidity (RH). Fruits were withdrawn periodically and changes in physico‐chemical, instrumental and sensory characteristics were analysed. During storage, oxygen levels showed only marginal changes, while CO₂ levels showed a gradual increase, especially so in LDPE film‐covered cartons. The fresh weight loss, colour, firmness, formation of defective spots and shrivelling showed greater changes for unpackaged fruits as well as for those in LDPE film‐covered cartons, in comparison with fruits stored in chitosan film‐covered cartons, which retained many of the desirable attributes. Principle component analysis of data from sensory or instrumental sensory analyses indicated segregation of samples stored under different conditions with respect to both desirable and undesirable attributes. The fruits showed greater deterioration, including the loss of characteristic bell pepper odour, when packaged in cartons covered with LDPE films, while those packaged in chitosan film retained more of the desirable quality attributes for a longer period. Copyright © 2006 Society of Chemical Industry     

Atmospheric Composition and Quality of Fresh Mushrooms in Modified Atmosphere Packages As Affected by Storage Temperature Abuse

Mushrooms (Agaricus bisporus) were packaged in 4-liter modified atmosphere (MA) containers, and a steady-state atmosphere of 5% and 10% was maintained at 4 °C. Temperature was fluctuated from 4 °C to 20 °C during 12-d storage period in cycles: 2 d at 4 °C followed by 2 d at 20 °C. Temperature increase during fluctuations caused anoxic atmospheres both in O₂ (1.5%) and CO₂ (22% to 10%). The quality of mushrooms stored under temperature fluctuating regime was severely affected as indicated by extensive browning, loss of firmness, and the level of ethanol in the tissue compared to mushrooms stored at constant temperature. It was clear that temperature fluctuation, even if it should occur once, can seriously compromise the benefits of MA packaging and safety of the packaged produce.     

Evaluation of different varieties of cauliflower for minimal processing

The impact of minimal processing technology on the sensory quality and the growth of micro‐organisms in eight varieties of cauliflower packaged in four different films (one PVC and three P‐Plus) was measured and quantified during more than 25 days of storage at 4 °C. Other important parameters such as weight loss and gas concentration in the packages were also determined. The composition of the atmosphere in the packages of minimally processed cauliflower depended on both the permeability of the film used for the packaging and the variety of cauliflower. When establishing shelf‐life, loss of sensory quality was the deciding factor rather than loss of microbiological quality. The initial microbial load proved more important than the composition of the atmosphere inside the packages. In sensory evaluation the most important aspect was colour. In instrumental evaluation, coordinate b* was the main means of estimating shelf‐life. The combination of P‐Plus 120 film and varieties of cauliflower of large size and great vigour allowed the atmosphere inside the packages to have an O₂ level below 10% and a CO₂ level above 10%. That atmosphere composition proved essential for maintaining the sensory quality of minimally processed cauliflower. In these conditions, samples attained a shelf‐life of more than 25 days. However, the different behaviours of the cauliflower varieties make it necessary to establish particular packaging conditions. The use of less permeable films than those used in this study, or the use of actively modified atmospheres, could be an alternative for those varieties that require special packaging conditions when processed using this technology. Copyright © 2006 Society of Chemical Industry     

Effect of Modified Atmosphere Pakaging on the Shelf-life of Common Carp (Cyprinus carpio) Steaks

The effect of modified atmosphere packaging (MAP 1: 40%CO₂+60%N₂ and MAP 2: 100%CO₂) on the shelf-life of carp steaks was studied. Carp steaks were stored at +3±0.5˚C and on days 1, 3, 6, 9, 13 and 15, microbiological, chemical and sensory testing was performed. Based primarily on odour scores it was observed that carp steaks packaged in MAP1 remained acceptable up to 13 days of storage, while carp steaks packaged in MAP2 remained unchanged until the end of the study. By using MAP, especially 100% CO₂, products shelf-life can be significantly prolonged.     

Storage of Morwong (Nemadactylus macropterus Bloch and Schneider) in Combinations of Polyphosphate, Potassium Sorbate and Carbon Dioxide at 4o C

Combinations of potassium sorbate and polyphosphate, in conjunction with vacuum or modified atmosphere packaging, were assessed for their preservative effects on morwong fillets (pH 6.75) stored at 4°C. Vacuum packaged and/or frozen fillets were used as comparisons for microbiological and taste panel analysis. A combination of potassium sorbate, polyphosphate and 100% CO₂ was the most effective packaging regime. Potassium sorbate on vacuum packaged fish was more effective than a 100% CO₂ atmosphere alone. Polyphosphate had no apparent additional effect on fillets stored under vacuum with or without potassium sorbate.     

The effects of packaging film and storage temperature on the quality of a dry coleslaw mix packaged in a modified atmosphere

Summary The effects of six packaging treatments on the quality of dry coleslaw packaged in modified atmospheres and stored at 4 and 8 °C for 9 days were determined. The coleslaw was packaged within either oriented polypropylene (OPP) or one of four microperforated OPP films, PA‐120, PA‐160, PA‐190, and PA‐210. It was also stored within punctured OPP (i.e. in air). Packaging within OPP resulted in an atmosphere with very low O₂ (<1%) and extremely high CO₂ (25–35%) levels. These storage conditions had detrimental effects on the quality of coleslaw: loss of firmness, falling pH, high cell permeability and exudate, high surface moisture and poor acceptability of aroma. By contrast, the microperforated films generated less atmosphere modification; in some cases this was insufficiently modified to be technically useful. The relatively high O₂ levels in these microperforated packs resulted in lower appearance and colour scores, increased surface dryness and higher firmness values. Increasing storage temperature from 4 to 8 °C resulted in a reduction in shelf‐life for all film types. While still not optimal, packaging within microperforated films allowed better preservation of quality and reduced cell membrane damage.     

Effect of some thermal and chemical pretreatments on smoked Oyster mushroom quality

The effect of different thermal and chemical pretreatments on quality and enzyme activities of smoked mushroom was investigated. Mushrooms were blanched (water and steam) and dipped in different concentrations of sulphites (SO₂), hydrogen peroxide (H₂O₂), ethylene‐di‐amine tetra‐acetic acid (EDTA) and citric acid for 10 min before smoking. Enzyme activities, colour characteristics, microbiological and sensory examinations were carried out every 2 weeks up to 8 weeks of storage in refrigerator at 4 °C. Results could be concluded that smoked mushroom pretreated with SO₂, H₂O₂ and steam blanching had the best colour values, the better score for all sensory characteristics and lower non‐enzymatic browning compared with other pretreatments. The most effective pretreatment against total aerobic bacteria and yeast & moulds were citric acid, EDTA and steam, and then smoking of mushroom can be attributed to the reduction of microbial counts. The most effective pretreatments on quality and safety of smoked mushrooms were H₂O₂ and steam. It can be concluded that thermal and chemical treatments, rather than smoking of mushroom, reduce enzyme activities and are suitable to preserve mushrooms.     

Spoilage and shelf life of sardines (Sardina pilchardus) packed in modified atmosphere

The effect of modified atmosphere packing (MAP) (O₂/CO₂/N₂, 5/35/60 (%) and O₂/CO₂/N₂, 5/70/25 (%)) on the quality of sardine stored in refrigerator was investigated in terms of sensory, chemical and microbiological analysis. Although chemical and microbiological analyses indicated that modified atmosphere packing prolonged the shelf life of sardine compared with that of air packing, sensory analysis showed that the extension of shelf life was (condition: O₂/CO₂/N₂, 5/70/25 (%)) 8 days and in air (condition: O₂/CO₂/ N₂, 5/35/60 (%)) 6 days. The results showed significant differences (p <0.05) between air and MAP storage conditions.     

Synergistic antimicrobial effect of pyrophosphate on Listeria monocytogenes and Escherichia coli O157 in modified atmosphere packaged and refrigerated seabass slices

Effect of pyrophosphate (PP) in combination with modified atmosphere (MAP) (80% CO₂, 10% O₂ and 10% N₂) on the survival of Listeria monocytogenes and Escherichia coli O157 inoculated on seabass slices stored at 4 °C was investigated. PP pretreatment showed the synergistic effect on microbiological inhibition with MAP as evidenced by the lowered TVC and LAB counts, compared with samples stored in air and those kept under MAP. Microbiological changes of seabass slices inoculated with different levels of L. monocytogenes or E.coli O157 (10³ and 10⁵ cfu/g) were monitored during storage. PP pretreatment reduced colony count of E. coli O157 and extended the lag phase of L. monocytogenes. Therefore, MAP in combination with PP pretreatment not only retarded microbiological deterioration of seabass slices but also reduced or inactivated some pathogenic bacteria to some extent.