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196 Application of Alternative Food-Preservation Technologies to Enhance Food Safety & Stability, 2010, 196-204 Alternative Modified Atmosphere for Fresh Food Packaging Maria Rosaria Corbo* and Antonio Bevilacqua Department of Food Science, Faculty of Agricultural Science, University of Foggia, Italy Antonio Bevilacqua, Maria Rosaria Corbo and Milena Sinigaglia (Eds) All rights reserved - © 2010 Bentham Science Publishers Ltd. APPENDIX II Abstract: Modified atmosphere packaging (MAP) has a long history of safe and effective use to prolong the shelf life of foods; it involves the change of gas composition inside the bag, mainly an increase of CO2 content and the lowering of O2. In recent years, many authors have proposed the use of some non-conventional gases, like argon (Ar) and other noble gases, or the use of volatiles in the head space (hexanal, hexenal, essential oils from citrus) to improve the safety and quality of fresh products. This appendix offers a short overview of the most recent findings in the application of these novel approaches for food preservation, along with a proposal for some possible ways to improve the use of these methods for an effective scale up in food industry. Key-concepts: Noble gases , Aroma compounds, Modified atmosphere packaging, Fresh-products. INTRODUCTION TO MODIFIED ATMOSPHERE PACKAGING (MAP) Definitions and Overview of MAP Food packaging serves to protect products against deteriorative effects, contain the products, communicate to the consumers as a marketing tool and provide consumers with ease of use and convenience [1]. The display of fresh product in plastic materials allows consumer evaluation of the product in an attractive, hygienic and convenient package [2]. Therefore, food packaging now performs beyond the conventional protection properties and provides many functions for the container product [3]. Modified atmosphere packaging (MAP) is a technique used for prolonging the shelf-life of fresh or minimally processed foods. In this preservation technique the atmosphere surrounding the food in the package is changed to another composition before sealing in vapour-barrier materials [3]. MAP can be vacuum packaging (VP), which removes most of the air before the product is enclosed in barrier materials, or forms of gas replacement, where air is removed by vacuum or flushing and replaced with another gas mixture before packaging sealing in barrier materials. The headspace environment and product may change during storage in MAP, but there is no additional manipulation of the internal environment, while controlled atmosphere packaging (CAP) uses continuous monitoring and control of the environment to maintain a stable gas atmosphere and other conditions such as temperature and humidity within the package. CAP has most often been used to control ripening and spoilage of fruits and vegetables [4], usually in containers larger than retail-sized packages although some research has been conducted on packaging for individual fruits and vegetables. The use of MAP allows the prolonging of the initial fresh state of the perishable products like meat, fish, fruits and vegetables, since it slows the natural deterioration of the product. MAP is used with various types of products, where the mixture of gases in the package depends on the type of product, packaging materials and storage temperature. But fruits and vegetables are respiring products where the interaction of the packaging material with the product is important. If the permeability (for O2 and CO2) of the packaging film is adapted to the product respiration, an equilibrium modified atmosphere will establish in the package and the shelf-life of the product will increase. Among fresh-cut produce equilibrium modified atmosphere packaging (EMAP) is the most commonly used packaging technology. When packaging vegetables and fruits the gas atmosphere of package is not air (O2 – 21%; CO2 – 0.01%; N2 – 78%) but consists usually of a lowered level of O2 and a heightened level of CO2. This kind of package slows down the normal respiration of the product, thus prolonging the shelf life of the product. There are many factors which affect modified atmosphere packaging of fresh produce: *Address correspondence to this author Maria Rosaria Corbo at: Department of Food Science, Faculty of Agricultural Science, University of Foggia, Italy; E-mail: m.corbo@unifg.it
Alternative MAPs Application of Alternative Food-Preservation Technologies 197 1. Movement of O2, CO2, and C2H4 in produce tissues is carried out by the diffusion of the gas molecules under a concentration gradient. Different commodities have different amounts of internal air space (for example, potatoes 1–2%, tomatoes 15–20%, apples 25–30%). A limited amount of air space leads to increase in resistance to gas diffusion. 2. Ethylene (C2H4), a natural plant hormone, plays a central role in the initiation of ripening, and is physiologically active in trace amounts (0.1 ppm). C2H4 production is reduced by about half at O2 levels of around 2.5%. This low O2 retards ripening by inhibiting both the production and action of C2H4. 3. Metabolic processes such as respiration and ripening rates are sensitive to temperature. Biological reactions generally increase two to three-fold for every 10°C rise in temperature. Therefore temperature control is important to achieve an effective work of MAP system. 4. Film permeability also increases as temperature increases, with CO2 permeability responding more than O2 permeability. Low RH (relative humidity) can increase transpiration damage and lead to desiccation, increased respiration, and ultimately to an unmarketable product. A serious problem associated with high in-package humidity is condensation on the film driven by temperature fluctuations. A mathematical model was developed for estimating the changes in the atmosphere and humidity within perforated packages of fresh produce [5]. The model was based on the mass balances of O2, CO2, N2 and H2O vapours in the package. Also a procedure to maintain desired levels of O2 and CO2 inside packages that are exposed to different surrounding temperatures was designed and tested [6]. 5. For most commodities light is not an important factor in their post-harvest handling. However green vegetables, in the presence of sufficient light, could consume substantial amounts of CO2 and produce O2 through photosynthesis. Finally, shock and vibration leads to damage to produce cells which causes an increase in respiration, the release of enzymes and the beginning of browning reactions. Gases Used in MAP The main gases used in modified atmosphere packaging are CO2, O2 and N2. The choice of gas depends upon the food product being packed. Used singly or in combination, these gases are commonly used to balance safe shelflife extension with optimal sensorial properties of the food. Noble or ‘inert’ gases, such as argon, are used for products such as coffee and snack products, although their use for minimally processed apples and kiwifruit has been recently proposed [7, 8]. Experimental use of carbon monoxide (CO) and sulphur dioxide (SO2) has also been reported. Carbon Dioxide Carbon dioxide is a colourless gas with a slight pungent odour at very high concentrations. It is an asphyxiant and slightly corrosive in the presence of moisture. CO2 dissolves readily in water (1.57 g/kg at 100 kPa, 20°C) to produce carbonic acid (H2CO3) that increases the acidity of the solution and reduces the pH. This has significant implications on the microbiology of packed foods. Oxygen Oxygen is a colourless and odourless gas, that is highly reactive and supports combustion. It has a low solubility in water (0.040 g/kg at 100 kPa, 20°C) and promotes several types of deteriorative reactions in foods including fat oxidation, browning reactions and pigment oxidation. Most of the common spoilage bacteria and fungi require oxygen for growth. Therefore, the pack atmosphere should contain a low concentration of residual oxygen to increase shelf life of foods; however, superatmospheric O2 concentrations (> 70 kPa) have been proposed as an alternative to low O2 modified atmospheres in order to inhibit the growth of typical spoilage microorganisms of fresh-cut produce (strawberries, raspberries, pears), prevent undesired anoxic fermentation and maintain fresh sensory quality [9, 10, 11, 12, 13, 14]. Nitrogen Nitrogen is a relatively un-reactive gas with no odour, taste, or colour. It has a lower density than air, nonflammable and has a low solubility in water (0.018 g/kg at 100 kPa, 20°C) and other food constituents. Nitrogen does not support the growth of aerobic microorganisms and therefore inhibits the growth of aerobic spoilage microorganisms, without affecting the growth of anaerobic bacteria.
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