Effect of modified atmosphere packaging on the shelf-life of coated, whole and sliced mushrooms

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Abstract

Whole and sliced fresh mushrooms (Agaricus bisporus) were packaged with PVC wrap or two polyolefins (PD-941 and PD-961) films after coating with CaCl2 and chitosan. Package gas composition, color, weight loss and maturity were measured during storage at 12 °C and 80%RH. For PD-961, the highest in-package concentration occurred during the first day of storage regardless of treatments, while wrap and PD-941 showed varying degrees in-package concentration with different processes and coatings. The whiteness of whole mushrooms varied significantly with the type of coating, but not with the type of films. The extent of darkening was greater in coated whole mushrooms than in sliced ones. Weight loss occurred in all packages and varied from 3 (g/100 g) to about 7 (g/100 g) after 6 days of storage. Due to a lower permeability, PD-961 packages had the lowest weight loss. The type of packaging films significantly affected the maturity index, where PD-961 most effectively lowered maturity index for both whole and sliced mushrooms, thus extending the shelf-life. The type of coating did not appear to affect maturity index except for the wrap package where chitosan coating markedly lowered the maturity index of sliced mushrooms.

Introduction

Due to their thin and porous epidermal structure, the respiration rate of mushrooms is relatively high (200–500 mg/kg h at 20 °C) compared to other vegetables and fruits (Kader, 1985; Warwick & Tsureda, 1997). Mushrooms are highly perishable and tend to lose quality right after harvest. Shelf-life of mushrooms is less than 3 days under usual shipping and marketing conditions (Lee, 1999). Therefore, mushrooms need special care to retain freshness.

There are several indicators that determine the quality of mushrooms such as whiteness, cap development, stripe elongation, number of ripe spores, texture, respiration rate, mannitol content, weight loss and microbial deterioration (Gormley, 1975; Bartley, Beelman, & Winnett, 1991; Lopez-Briones et al., 1992). There are many methods to extend the shelf-life of mushrooms. They include modified atmosphere packaging (MAP) (Roy, Anantheswaran, & Beelman, 1995), controlled atmosphere storage (CA) (Lopez-Briones et al., 1992), coating (Nussinovitch & Kampf, 1993), refrigeration (Gormley, 1975; Mau, Miklus, & Beelman, 1993), cultivating with CaCl2 solution (Miklus & Beelman, 1996) and using sorbitol (Roy et al., 1995). Although CA storage is effective to lower respiration rate and increases shelf-life of fruits and vegetables, it is not appropriate for vegetables, as mushrooms, which have extremely high respiration rates (Roy et al., 1995). MAP is the most simple, economical, and effective way of extending shelf-life of fresh mushrooms. Nichols and Hammond (1973) reported that over-wrapping with polyvinyl chloride (PVC) film increased the shelf-life of mushrooms by retarding cap opening, discoloration, and reducing weight loss. Roy et al. (1995) determined the proper O2 and CO2 concentrations for MAP of mushrooms. They found that 6% O2 was effective in reducing cap development. Sveine, Klougart, and Rasmussen, (1967) reported that 0.1% O2 and 5% CO2 were optimum conditions for prolonging shelf-life of mushrooms. Low O2 reduced respiration rate and retarded cap development, reduced aerobic deterioration and weight loss. Also, low O2 decreased tyrosinase activity reducing enzymatic browning. Although a low concentration of O2 may have many advantages, less than 2% could cause anaerobic microbial growth significantly, such as Clostridium botulinum (Herr, 1991) and Staphylococcus aureus (Martin & Beelman, 1996).

Coating vegetables and fruits with semi-permeable film has the beneficial effect of delaying ripening and prolonging the storage life of fresh produce (El Ghaouth, Ponnampalam, Castaigne, & Arul, 1992a; Park, Bunn, Vergano, & Testin, 1994). Chitosan appears to be an ideal preservative coating for fresh produce because of antifungal activity and film foaming property (Hirano & Nagao, 1989). Chitosan coating has been used to extend the shelf-life of tomatoes, cucumbers, bell peppers, and strawberries (El Ghaouth et al., 1992a; El Ghaouth, Arul, & Ponnampalam, 1992b; Zhang & Quantick, 1997). Alginate and calcium-alginate films were used as coating materials for mushrooms by Nussinovitch and Kampf (1993) and Hershko and Nussinovitch (1998), but there has been no research on chitosan as a mushroom coating.

Recently consumers have been more interested in readily available fruits and vegetables. For the food service industry in particular, there are some advantages of using minimally processed food to save cost and labor (Hoover, 1997). It can be assumed that if sliced mushrooms can be preserved as long as fresh mushrooms, the market share of sliced mushroom will increase. The objectives of this study were to determine the suitable commercial MAP film and the effect of chitosan coating on the quality of sliced mushrooms (Agaricus bisporus), determining CO2/O2 concentrations, color, weight loss and maturity as indicators of mushrooms quality.

Section snippets

Materials and sample treatment

Fresh mushrooms (Agaricus bisporus) were purchased from a local farmer in Seoul, Korea and brought to the laboratory within 1 h after harvest. Mushrooms with pileus (cap) size of 30–40 mm and a maturity index of stage 1 were selected and refrigerated at 4 °C before slicing. The films for mushroom packaging were PVC wrap (Lucky Co, Naju, Korea), and polyolefin PD-941 and PD-961 (Cryovac Division, Sealed Air Corp, Duncan, SC, USA). Chitosan was purchased from Biotech Co. (Mokpo, Korea). It was

In-package CO2 and O2 concentration

The patterns of changes in the CO2 concentration in both whole and sliced mushrooms during storage were similar for the three films. Two patterns of changes in the CO2 concentration were observed, namely, a transitional state characterized by a peak of CO2 concentration and a steady state where the CO2 concentration remained relatively constant. The CO2 concentration in containers with whole mushrooms increased sharply within 24 h except for the wrap packaging (Fig. 1). The peak in 24 h is

Conclusions

The gas composition of MAP was highly related to the quality of both whole and sliced mushrooms. PD-961 provided a successful MAP that extended shelf-life up to 6 days, regardless of coating treatment. Coating treatment could be considered with films that are moderate gas barriers such as a PD-941 film. Coating treatment is a parameter, beside temperature, film permeability and weight of tissue, that affects the gas composition of a package. Coating treatment stimulated respiration of the

Acknowledgments

Journal Series No. 14614, Agricultural Research Division, Institute of Agriculture and Natural Resources, University of Nebraska-Lincoln.

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