Effect of vacuum cooling on physiological changes in the antioxidant system of mushroom under different storage conditions

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Abstract

The effects of vacuum cooling treatment and storage conditions on the activities of lipid oxidation, superoxide anion generation, superoxide dismutase (SOD), catalase (CAT), peroxidase (POD) and polyphenoloxidase (PPO) were investigated in the mushrooms. Mushrooms cooled to 5 °C by vacuum cooling induced 1.2-, 1.2-, 1.1- and 1.1-fold increase in the activities of SOD, CAT, POD and PPO. In contrast, malondialdehyde (MDA) levels and superoxide anion generation slightly decreased. During the storage, the highest expression of the enzymatic antioxidant system was found in the mushroom stored under modified atmosphere packaging (MAP) with vacuum cooling treatment. Additionally, the effects of vacuum cooling and storage conditions on mushroom firmness and browning were also investigated.

Introduction

Vacuum cooling is a rapid cooling technique extensively used for cooling some agricultural and food products (McDonald and Sun, 2000, McDonald et al., 2000, Sun and Wang, 2000, Thompson and Rumsey, 1984, Zheng and Sun, 2004). The evaporation is achieved by reducing the pressure to the point where boiling of water can be evaporated at a lower temperature (Tambunan, Sagara, Seo, Morishima, & Kawagoe, 1994). Vacuum cooling has been adopted commercially on some mushrooms farms in the United States (Lane, 1972), and investigated in the United Kingdom (Barnard, 1974); and more recently adopted on some British farms. Vacuum cooling can cool mushrooms uniformly and rapidly within a stack (Barger, 1963).

There are many research reports on the mushroom vacuum cooling technology (McDonald and Sun, 2000, Noble, 1985, Tao et al., in press). However, research of the vacuum cooling effect on enzyme systems of the materials is limited.

Mushroom senescence is an oxidative process that involves degradation of the cellular and sub-cellular structures and macromolecules, and the mobilization of the products of degradation to other parts of the fungus. Susceptibility to oxidative stress depends on the overall balance between production of oxidants and antioxidant capability of the cell (Rio et al., 1998). Changes in membrane permeability and loss in ability to retain solutes have been associated with fruit ripening (Sacher, 1973). Permeability changes during senescence have been linked with a simultaneous decline in membrane lipid (Ferguson & Simons, 1981).

Reactive oxygen species (ROS) such as superoxide radical, hydrogen peroxide and hydroxyl radical have a role in lipid peroxidation, membranes damage and consequently in senescence (Thompson, Legge, & Barber, 1987). Besides this, oxidative damage has been linked as the cause of damages experienced during various environmental stresses such as drought, air pollutant, temperatures, and herbicide (Prochazkova, Sairam, Srivastava, & Singh, 2001). Free radical reactions have been suggested to play an important role in the degradation process of membrane polar lipids in senescence (Lin & Kao, 1998). Antioxidant such as superoxide dismutase, peroxidase and catalase are involved in the scavenging of reactive oxygen radicals (Asada, 1992, Scandalios, 1993).

Enzymatic antioxidant systems provide protection against the toxic effects of ROS. The metabolism of ROS is dependent on several functionally interrelated antioxidant enzymes such as SOD, POD and CAT. SOD is believed to play a crucial role in antioxidant defense because it catalyzes the dismutation of O2- into H2O2, whereas CAT and POD destroy H2O2 (Jung, 2004).

Though a lot of works have been done on production of oxidants and antioxidant activity during senescence (Asada, 1992, Kerdnaimongkol and Woodson, 1999, Monk et al., 1989, Polidoros and Svandalios, 1999, Sang et al., 1991), little is known about the effect of vacuum cooling treatment as a factor that affects antioxidative mechanisms in mushrooms stored under different conditions.

The object of the study was to investigate whether the vacuum cooling treatment and storage conditions (cold room and modified atmosphere packaging) induces the changes in antioxidant enzyme activities of the mushroom.

Section snippets

Materials

Mushrooms (Agaricus bisporus, Monad, 2796) used in this study were harvested in the first week of May from a local field in Wuxi, China. The mushrooms were carried into the laboratory in one hour after picking and processed in 2 h. The replicate plots were arranged in a completely randomized pattern.

Treatment

The vacuum cooler used in the experiment was ZY0.1 vacuum cooler as shown in Fig. 1 (Qihong Cold-Making Co. LTD., Wuxi, China). The mushrooms were vacuum cooled to 5 °C and then stored under two

Effect of vacuum cooling and storage conditions on lipid oxidation

The level of lipid peroxides was measured in terms of MDA content (Fig. 2). Throughout the storage of 15 days, MDA content increased from the initial value (1.186–1.701 nmol g−1 FW) to 2.071–2.577 nmol g−1 FW under two storage conditions with vacuum cooling treatment, while 2.552–3.551 nmol g−1 FW under two storage conditions without vacuum cooling treatment, respectively. Under vacuum cooling treatments reduced level of lipid peroxides was observed both in cold room storage and MAP storage.

Conclusion

Mushrooms with or without vacuum cooling treatment were stored for 15 days at 4 °C under cold room and modified atmosphere packaging (MAP). Changes in lipid oxidation (MDA levels), superoxide anion generation, superoxide dismutase, catalase, peroxidase, polyphenoloxidase, firmness and browning were analyzed. The differences were observed among the mushrooms stored under different storage conditions with or without vacuum cooling treatment (P < 0.05). The results indicated that there were some

Acknowledgements

The authors would like to thank the Science and Technology Department of Jiangsu Province in China for its financial support (Program No. BE2003349); thanks also to Qihong Cold-Making Co. Ltd., Wuxi, China, for provision of mushrooms and facilities.

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