6 Interactive packaging involving sachet technology J.P. SMITH, J. HOSHINO and Y. ABE 6.1 Introduction Over the past decade, there has been a tremendous growth in interactive packaging for shelf-life extension of food. Packaging can be defined as 'interactive' when it 'performs some role in the preservation of the food other than providing an inert barrier to outside influences' (Rooney, 1992), There are many examples of interactive packaging technologies including antimicrobial and antioxidant films, ethylene absorbing sachets and tem- perature control indicators, some of which have been discussed in previous chapters of this text. However, perhaps one of the best examples of interactive packaging, and one which fulfils the above definition in all aspects, is modified atmosphere packaging (MAP). MAP has been defined as 'the enclosure of food products in a high gas barrier film in which the gaseous environment has been changed or modified to slow respiration rates, reduce microbiological growth and retard enzymatic spoilage with the intent of extending shelf-life' (Young et aL, 1988). The growth in MAP technology has resulted from advances in packaging technology, the food industry's need for less energy-intensive forms of food preservation than drying, freezing or thermal processing, and consumer needs for convenience foods with extended shelf-life yet retaining their fresh characteristics. The atmosphere in MAP foods has traditionally been modified by vacuum or gas packaging, the latter involving various mixtures of CO2, either alone or in conjunction with nitrogen and sometimes oxygen depending on the product gas packaged, e.g., meat or fruits and vegetables (Smith et al., 1990). Although this form of interactive packaging can be used to extend the shelf life and keeping quality of food, aerobic spoilage can still occur in these packaged products depending on the level of residual oxygen in the package headspace. The level of residual oxygen in vacuum/gas packaged products could be due to a number of factors such as oxygen permeability of the packaging material; ability of the food to trap air; leakage of air through poor sealing; and inadequate evacuation and/or gas flushing (Smith et ai, 1986). In recent years, novel methods of oxygen control and atmosphere modification have been developed, primarily by the Japanese. These include oxygen/carbon dioxide absorbents, oxygen absorbents/carbon dioxide gen- erators, and ethanol vapor generators. This technology involves the use of sachets which can be placed alongside the food and actively modify the package headspace thereby extending product shelf-life. This chapter will review the various types of absorbent/generator sachets available in the marketplace, the methods by which these sachets actively modify the gas atmosphere in the packaged product, and their uses, advantages and disadvantages for shelf-life extension of food. 6.2 Oxygen absorbents One novel and innovative method of oxygen control and of atmosphere modification involves the use of oxygen absorbents. Oxygen absorbents can be defined as 'a range of chemical compounds introduced into the MAP package (not the product) to alter the atmosphere within the package' (Agri- Food Canada, personal communication). Developed in Japan in 1976, oxygen absorbents were first marketed by the Mitsubishi Gas Chemical Co., under the trade name Ageless (Table 6.1). Several other Japanese companies also produce oxygen absorbents with the best known being the Toppan Printing Company which produces a range of oxygen absorbents under the label Freshilizer Series (Smith et al., 1990). In 1989, almost 7000 million sachets were sold in Japan with sales of absorbents growing at a rate of 20% annually. The Mitsubishi Gas Chemical Co. dominates the oxygen absorbent market (73%) while the Toppan Printing Co. has about 11% of the market with nine other companies sharing the remaining 16% of the market. Oxygen absorbent technology has been successful in Japan for a variety of reasons, including the hot and humid climate during the summer months which is conducive to mold spoilage of food products. Another important factor for their success is that Japanese consumers are willing to pay higher prices for preservative-free products with an increased shelf-life. Several years after the Mitsubishi Gas Chemical Co., successfully launched oxygen absorbent technology onto the marketplace, Multiform Desiccants in the United States introduced FreshPax, the first North American oxygen scavenger (Table 6.1). Like its predecessors, FreshPax is extremely effective in lowering package oxygen from 20% to less then 0.05% in about 36 hours. However, unlike the Japanese market, acceptance of oxygen scavengers in Table 6.1 Major companies producing oxygen absorbents Company Product name Mitsubishi Gas Chemical Co., Japan Ageless Toppan Printing Co., Japan Freshilizer Multiform Desiccants, US Freshpax North America and Europe has been slow, although several major companies in both continents are now using this technology. Oxygen absorbents comprise of easily oxidizable substances usually contained in sachets made of air-permeable material. These sachets come in a variety of sizes capable of absorbing 20-2000ml of headspace oxygen. When placed inside the packaged food, they actively modify the package headspace and reduce the oxygen levels to < 0.01% within 1-4 days at room temperature. However, some are designed to scavenge oxygen at refrigerated or frozen storage temperatures and are used to further extend the shelf-life and keeping quality of muscle foods. This oxygen-free environ- ment protects the food from microbiological and chemical spoilage and is also effective in preventing damage by insects. A combination of some or all of these factors helps maintain the quality and freshness of food, which facilitates the marketing of oxygen absorbents. The classification and the main types of oxygen absorbents will now be briefly reviewed. 6.2.7 Classification of oxygen absorbents Oxygen absorbents can be classified into several different categories as shown in Table 6.2. Each category will be briefly reviewed. 6.2.1.1 Classification according to material. In theory, any material that reacts easily with oxygen can be used as an oxygen scavenger. However, because the technology involved is used mainly for food preservation, the material used inside the sachet must meet the following criteria prior to approval by regulatory agencies. • It must be safe. • It must be handled easily. • It must not produce toxic substances or offensive odors/gases. • It must be compact in size. • It must absorb a large amount of oxygen. • It must have an appropriate oxygen absorption speed; and • It must be economically priced (Harima, 1990). Iron powder and ascorbic acid are commonly used in existing oxygen absorbers with powdered iron being most frequently used either alone or in conjunction with other specific chemical compounds in dual function absorbents (Table 6.2). 6.2.1.2 Classification according to reaction style. Water is essential for oxygen absorbents to function. In the self-reaction types, water required for the chemical reaction is added and the absorbents must be handled carefully as the oxygen absorbing reaction commences as soon as the self-reacting absorbent is exposed to air. In moisture dependent types, the oxygen absorption reaction only takes place after moisture has been absorbed from the food; these type of absorbents are easier to handle as they do not react immediately upon exposure to air. However, they absorb oxygen quickly after sealing and oxygen can be absorbed within 0.5-1 day in certain products. Examples of self-reacting and moisture dependent types of oxygen absorbents are shown in Table 6.2. 62.13 Classification according to reaction speed.. Oxygen absorbents can be classified as immediate effect, general effect, and slow effect types (Harima, 1990). The average time for oxygen absorption is 0.5-1 day for the immediate type; 1-4 days for the general type; and 4-6 days for the slow Table 6.2 Classification of oxygen absorbents Absorption Function Reactant Application speed Product O2I Iron Self-working type Dry 4 to 7 days Ageless Z-PK aw < 0.3 Vitalon T Tea; nuts Medium aw 1 to 3 days Ageless Z aw < 0.65 Keplon TS Dried beef High aw 0.5 days Ageless S aw > 0.65 Sequl CA Cakes Bakeries Frozen temp 3 days at Ageless SS + 3 to - 25°C - 25°C Raw fish Moisture High aw 0.5 days Ageless FX dependent type aw > 0.85 Vitalon LTM Pastas Catechol Self-working type Medium aw Tamotsu A aw < 0.65 Nuts High aw Tamotsu P aw > 0.65 Cakes O2I & Iron + Calcium Self-working type Roasted coffee 3 to 8 days Ageless E CO2I O2I & Ascorbic acid Self-working type Medium aw 1 to 4 days Ageless G CO2T 0.3 < aw < 0.5 Toppan C Nuts Ascorbic acid + Moisture High a w Vitalon GMA Iron dependent type aw > 0.85 Cakes O I & Iron + Moisture High a 2 w Negamold EthanolT Ethanol/Zeolite dependent type aw > 0.85 Cakes (%) n concentratio 2 O Time (day) Figure 6.1 Effect of storage temperature on oxygen absorbing speed of Ageless S-IOO, a self working type (fast working type) of oxygen absorber. reacting type (Harima, 1990). The reaction time depends on storage temperature and water activity (aw) of the food. The effect of storage temperature on oxygen absorbing speed is shown in Figures 6.1 and 6.2. Most oxygen absorbents are used with foods stored at ambient temperature. (%) n concentratio 2 O Time (day) Figure 6.2 Effect of storage temperature on oxygen absorbing speed of Ageless Z-100, a self working type (medium working type) of oxygen absorber. However, if used with refrigerated or frozen products these absorbents react very slowly. To overcome this problem, some absorbents can now scavenge oxygen rapidly from the package headspace of food stored under low- temperature conditions.