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Effects of Highpressure Argon and Nitrogen Treatments on Respiration

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Effects of Highpressure Argon and Nitrogen Treatments on Respiration Research Article Received: 6 March 2011 Revised: 20 October 2011 Accepted: 21 December 2011 Published online in Wiley Online Library: 24 February 2012 (wileyonlinelibrary.com) DOI 10.1002/jsfa.5612 Effects of high-pressure argon and nitrogen treatments on respiration, browning and antioxidant potential of minimally processed pineapples during shelf life Zhi-shuang Wu,a Min Zhanga∗ and Shao-jin Wangb Abstract BACKGROUND: High-pressure (HP) inert gas processing causes inert gas and water molecules to form clathrate hydrates that restrict intracellular water activity and enzymatic reactions. This technique can be used to preserve fruits and vegetables. In this study, minimally processed (MP) pineapples were treated with HP (∼10 MPa) argon (Ar) and nitrogen (N) for 20 min. The effects of these treatments on respiration, browning and antioxidant potential of MP pineapples were investigated after cutting and ◦ during 20 days of storage at 4 C. RESULTS: Lower respiration rate and ethylene production were found in HP Ar- and HP N-treated samples compared with control samples. HP Ar and HP N treatments effectively reduced browning and loss of total phenols and ascorbic acid and maintained antioxidant capacity of MP pineapples. They did not cause a significant decline in tissue firmness or increase in juice leakage. HP Ar treatments had greater effects than HP N treatments on reduction of respiration rate and ethylene production and maintenance of phenolic compounds and DPPH• and ABTS•+ radical-scavenging activities. ◦ CONCLUSION: Both HP Ar and HP N processing had beneficial effects on MP pineapples throughout 20 days of storage at 4 C. c 2012 Society of Chemical Industry Keywords: minimally processed pineapples; argon; nitrogen; high pressure; gas hydrate INTRODUCTION malic dehydrogenase, which are specific key enzymes related Minimally processed (MP) fruits represent one of the most rapidly to browning of fresh fruits and vegetables and respiratory expandingsegmentsofthelightlytreatedrefrigeratedfoodmarket metabolism.16 It was found that both nitrogen and argon reduced owing to their increased functionality.1 Minimal processing offers tyrosinase and malic dehydrogenase activities, with argon having consumers highly nutritious, convenient and healthful fruits while a more significant effect than nitrogen. A gaseous inhibitor of maintaining freshness of the non-processed products.2 However, the enzymes related to browning and respiration could have MP fruits are perishable and have shorter a shelf life than an important role in maintaining the quality of fresh fruits and whole produce, because ethylene production, respiratory activity, vegetables as a replacement for some chemical treatments with 16 enzymatic and non-enzymatic browning and nutrient release from their potential health risks. cells are stimulated by plant injuries.3–6 Pineapple is a very popular When certain gases such as neon, argon, krypton, xenon, fruit throughout the world for its nutritive and health-promoting nitrogen and oxygen are in contact with water under favourable properties.7,8 MP pineapple has a commercial advantage in terms temperature and pressure conditions, they can form ice-like of weight reduction for transport, since bulky inedible crown and crystals called clathrate hydrates or gas hydrates in which the peel tissues are removed,9 and MP product is the main form at gas molecules are trapped within a framework of cages of water ∼ molecules stabilised by physical bonding via van der Waals retail. However, its shelf life is very limited ( 2–3 days) because 17–19 of quality loss, including pulp browning, accumulation of liquid in forces. These gas hydrates are stabilised relative to the the packaging, off-flavours and microbial growth.4,10,11 structureofpurewatericeandcanexistattemperatureswellabove Argon and nitrogen as major components of the atmosphere in modified atmosphere packaging (MAP) have been reported ∗ to reduce microbial growth and improve quality retention of Correspondence to: Min Zhang, School of Food Science and Technology, Jiang- nan University, 214122 Wuxi, Jiangsu, China. E-mail: [email protected] fresh produce.12–14 Argon is reported to be biochemically active, probably owing to its enhanced solubility in water compared a School of Food Science and Technology, Jiangnan University, 214122 Wuxi, with nitrogen and its possible interference with enzymatic oxygen Jiangsu, China 2250 15 receptor sites. A comparative study has been carried out on the b Department of Biological Systems Engineering, Washington State University, effects of nitrogen and argon on the activities of tyrosinase and Pullman, WA 99164-6120, USA J Sci Food Agric 2012; 92: 2250–2259 www.soci.org c 2012 Society of Chemical Industry Effects of HP Ar and N treatments on shelf life of MP pineapples www.soci.org ◦ ◦ 0 C.14,20,21 At 0 C, argon and nitrogen clathrate hydrates can form 0) and after storage for 2, 5, 8, 11, 14, 17 and 20 days. Approximately and remain stable at more than 8.7 and 14.3 MPa respectively.22 900 g of MP pineapples for each treatment were used for day 0 The gas hydrate structures are identified as I, II and the recently evaluations and 70 trays per sample were prepared, resulting in a determined structure H.19 Argon and nitrogen form structure II total of 420 trays. Ten trays per sample were randomly taken and hydrates.23 Four conditions must be met simultaneously within analysed at each storage time (2, 5, 8, 11, 14, 17 and 20 days). The one region in order for a gas hydrate to be formed: presence of gas, whole process was conducted in triplicate as replications. water, high pressure and low temperature.22 Behnke24 suggested that high-pressure inert gases inhibit tyrosinase in non-fluid (e.g. Experimental apparatus and procedure gelatin) systems by decreasing oxygen availability rather than by The high-pressure gas treatment apparatus was designed by 25 physically altering the enzyme. Fujii et al. reported that argon Jiangnan University (Jiangsu, China) and manufactured by Huaan addition accelerated the inactivation of Bacillus cereus spores at Scientific Research Instrument Co. Ltd (Jiangsu, China). The ◦ ◦ 20 Cunderapressureof600 MPaowingtoargonclathratehydrate apparatus had an operating temperature range from 0 to 50 C 26 formation. Oshita et al. found that pressurised xenon treatments at a maximum working pressure of 30 MPa. A diagram of the were efficient in maintaining the quality of fresh-cut carnation and high-pressure gas treatment system is shown in Fig. 1. The broccoli owing to xenon clathrate hydrate formation. Clathrate primary components of the apparatus were a 500 mL stainless hydration restrains the activity of intracellular water and inhibits steel treatment vessel, a plunger pump, a vacuum pump and a enzymatic reactions, so vegetable metabolism is retarded. Zhang thermally controlled bath. The sample treatment vessel had two et al.14 reported that the shelf life of asparagus spears could ◦ circular viewing windows made of Plexiglas on the front and be extended to 12 days at 4 C by treatment with mixtures of back and was submerged in a water bath to ensure the desired compressed (1.1 MPa absolute) argon and xenon (2 : 9 v/v) under operating temperature. The water in the bath was recirculated partial pressure. They also found that many micropores appeared through a plastic tube to a small thermally controlled bath, where in the asparagus microstructure after the treatment process, the temperature of the water was stabilised by cooling via a with argon and xenon remaining in the structure as micropores, refrigerator or heating via a heater. A plunger pump with a suggesting a positive connection with keeping asparagus spears maximum pressure of 32 MPa was used to pressurise the vessel. 14 fresh during the whole storage time. It is desirable to use A pressure transducer was fixed in the vessel lid to monitor a pressurised low-cost inert gas such as argon or nitrogen to the vessel pressure. All temperature and pressure data were preserve MP fruits. displayed on a control panel. All parts of the system exposed There have been few reports dealing with the application of to high pressure were made of stainless steel. The vessel had high-pressure (HP) argon (Ar) or nitrogen (N) treatment to preserve gas-tight connections to the gas inlet and outlet. The vessel lid MP fruits. The aim of this study was to investigate the effects of HP could be sealed by screwed flanges and neoprene O-ring gaskets Ar and HP N treatments on respiration, browning and antioxidant ◦ during high-pressure gas processing. A vacuum pump (2XZ-4, potential of MP pineapples during 20 days of storage at 4 C. Huangyan Qiujing Vacuum Pump Factory, Zhejiang, China) was connected to the vessel for evacuating the air in the vessel and building the vacuum state of the vessel. Commercially available MATERIALS AND METHODS Ar and N2 of 99.7% purity were purchased from Wuxi Xinnan Raw material and sample preparation Gas Co. (Jiangsu, China). Gas was injected into the plunger of the Pineapples (Ananas comosus L.) harvested in Hainan (China) were pressuriser from a gas cylinder and then entered the pressure supplied by a local distributor and transferred to the laboratory vessel. The on–off valve on the feed line between the pump and ◦ and stored at 10 ± 1 C overnight before processing. the vessel was turned off after the required pressure level had been Fruitsweresortedtoeliminatedamagedordefectivespecimens. reached, then the pressure was held for the required treatment The shell colour stage was that where several to most of the shell time. At the end of the experiments the system could be easily eyes were partially filled with yellow colour, all of them surrounded depressurised by opening the on–off valve on the vessel outlet by green.27 Pineapple crown leaves were removed and fruits were line. − washed in an aqueous solution of 200 µLL 1 sodium hypochlorite The pressure vessel was rinsed and sanitised with 200 µLL−1 ◦ at 4 C for 5 min, rinsed with tap water and drained on a clean sodium hypochlorite solution.
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