Oxygen can cause to food deterioration by microbiological reactions and/or chemical reactions as a result of growth of aerobic microorganisms, enzymatic reactions, nonenzymatic chemical reactions such as Maillard reactions between amino acids and reducing sugars or chemical reactions such as oxidation of lipids and proteins. Oxidation may facilitate the growth of yeasts, molds, aerobic bacteria, and insects and cause changes in flavor, odor, and color, as well as nutritional losses in foods (Suppakul et al., 2003a; Ozdemir and Floros, 2004; Gomes et al., 2009). Thus, oxygen becomes an important factor to be controlled for many quality losses and deteriorations in food and to extend the shelf life of food, and it is necessary that oxygen level in a food package should be controlled to retard these deterioration reactions.
As with many foods, milk and dairy products are very susceptible to oxidation because of the fat content and in particular, light oxidation, due to the presence of photosensitizers (such as riboflavin, porphyrins and chlorophyll derivatives), which are able to absorb visible and UV light and transfer this energy into highly reactive forms of oxygen such as singlet oxygen (Mestdagh et al., 2005; Granda-Restrepo, 2009a). Lipid oxidation plays a major role in the quality deterioration of most of the dairy products such as milk, cheese, and butter. Lipid oxidation in the milk produces methyl ketones and saturated aldehydes, which contribute to stale flavor (Valero et al., 2001; Perkins et al., 2007; Intawiwat et al., 2011). The amount of dissolved oxygen in the package should also be reduced in order to control the growth of spoilage microorganisms in dairy products such as cheese and yogurt (L'opez-Rubio et al., 2008).
Oxygen can be found in headspace of package or in pores of food products like bread, bakery products, and powdered food products. Although oxygen can be removed from the package by modified atmosphere packaging technology, this technology does not always remove the oxygen completely, and deterioration reactions may occur even when a very small amount of residual oxygen exists.
Oxygen scavengers can be used to reduce the oxygen concentration in a package to less than 0.01% in several hours and to maintain those levels, they are to be used alone or in combination with modified atmosphere packaging (MAP) technology (Vermeiren et al., 1999; Brody et al., 2001; Suppakul et al., 2003a; Ozdemir and Floros, 2004; Uquncu, 2011). MAP technology brings extra costs due to needs of different gas formulations according to each product and the use of specialized and expensive equipment. When MAP technology is applied to eliminate the oxygen in package, if oxygen scavengers are used alone instead of MAP technology, these economic problems can be eliminated. In oxygen scavenger and MAP combination, the efficiency of MAP is increased by eliminating all residual oxygen in very short time with oxygen absorbents.
Oxygen scavengers can be directly added to the package in sachet or label form, incorporated in to packaging film material, or can be integrated under bottle closures. Existing O2 scavenging technologies are based on oxidation of one or more of the following substances: iron powder, ferrous carbonate, catechol, ascorbic acid, photosensitive dyes, enzymes (such as glucose oxidase-glucose alcohol oxidase), unsaturated fatty acids (such as oleic, linoleic, and linolenic acids), rice extract, or immobilized yeast on a solid substrate (Suppakul et al., 2003a; Ozdemir and Floros, 2004; Uquncu, 2011). The most commonly used oxygen scavengers are iron-based powder. The iron powder is separated from the food by keeping it in a small sachet that is highly permeable and is labeled as “Do not eat” because of possible toxicity and includes a diagram illustrating this warning (Brody et al., 2001; Vermeiren et al., 2003; Lopez-Rubio et al., 2008).
Oxygen scavengers can be used in most of food packages except fresh red meat packaging, where higher than 50% oxygen is necessary to maintain the bright red color. Dairy products are one of the main food products that can be extensively used with oxygen scavengers to extend the shelf life and to maintain the product quality because dairy products are very susceptible to deterioration reactions related with oxygen, such as aerobic spoilage, lipid oxidation, and nonenzymatic browning reactions. In the literature, there are many studies related to the use of oxygen scavengers with or without MAP technology in dairy products.
The degree of lipid oxidation was reduced in modified atmosphere (30% CO2 and 70% N2) packaged Danbo cheese (Danish semi-hard cheese contained 25% fat) with PLA (Polylactic acid) by applying iron-based oxygen scavenger in sachet form in package (Holm et al., 2006). In another study related to application of iron powder-based oxygen-absorbing sachets in white cheese packaging (Panfil-Kuncewicz et al. 2006), oxygen concentration reduced approximately to a level of zero and the growth of yeasts and molds were inhibited over the storage period. Mexis et al. (2011) investigated the effect of active packaging [oxygen absorber+ethanol emitter sachet (OA+EE)] or modified atmosphere (100% Nitrogen) packaging in combination with a high-barrier experimental PET-silicon oxides/LDPE film on shelf-life extension of grated Graviera cheese. The active material in OA sachet is not expressed here. The O2 concentration inside the package was reduced to less than 0.01% by OA+EE sachet for samples stored at 12°C and 4°C, respectively, after 12 and 16 hours of storage, and these O2 levels were maintained throughout a 10-week storage period. The use of oxygen scavenger sachets in packaging substantially extended the shelf life of grated Graviera cheese to 8 to
- 8.5 weeks, whereas shelf life of cheese packaged in modified atmosphere was only 4 to
- 4.5 weeks.
Although the sachets are extensively used in active packaging technology, especially for oxygen scavengers, the sachets may cause food product distortion and may be ingested accidentally by the consumer due to the fact that they could leak out or contaminate the product. They are not appropriate for liquid food (Brody et al., 2001; Vermeiren et al., 2003; Ozdemir and Floros, 2004). Because of these problems related with sachets, oxygen scavenger film is a better way to limit oxygen levels in packages. Gomes et al. (2009) evaluated the effect of oxygen-absorbing laminate (PET/Al-foil/ LDPE+LLDPE with iron-based oxygen absorber) on the shelf life of hot-filled meal- ready-to-eat cheese spread. O2-absorbing laminate efficiently reduced headspace oxygen concentration from 20.4% to 6.82% within 24 hours, and this active packaging material significantly reduced rancidity in cheese-spread samples.
The dissolved oxygen in a package also poses a problem for probiotic foods, including dairy products, because of the negative effect on the viability of probiotic bacteria (Dave and Sahah, 1996; Tamime et al., 2005; Kuorwel et al., 2011). Miller et al. (2003) examined different packaging materials with/without active packaging technology for producing probiotic yogurt with minimal oxygen content. High-impact polystyrene (HIPS) was compared with Nupak”(HIPS/EVOH-Ethylene Vinyl alcohol/LDPE) as oxygen- barrier material and oxygen scavenger was incorporated into Nupak”(ZerO2-reducible organic compound such as a substituted anthraquinone) for determining their effect on the dissolved oxygen content of set type and stirred type probiotic yogurt. It was found that Nupak™ container plus oxygen scavenger was the most effective system particularly for set-type yogurt.
The stale flavor in UHT milk caused by aldehydes and ketones can be associated with lipid oxidation together with Maillard reactions (Valero et al., 2001; Zabbia et al., 2012; Richards et al., 2014). In a study performed by Perkins et al. (2007), to be able to reduce the stale flavor in UHT milk, the oxygen-scavenging film laminate (ZerO2TM) was inserted into the laminate of packaging film of metalized PET/LLDPE//LLDPE of aseptic pouches, and significant reductions were observed in some stale flavor volatiles of UHT milk by lowering the amount of dissolved oxygen at room-temperature storage.
Light-induced milk off-flavor caused by photo-oxidation of milk proteins, fat, and other nutrients is a serious problem for the dairy industry because of the severity of the taste deterioration noticed by consumers. These oxidation reactions are initiated when photo sensitizers present in milk are activated by light energy (Zygoura et al., 2004; Granda-Restrepo et al., 2009a; Intawiwat et al., 2010; Intawiwat et al., 2011; Intawiwat et al., 2013).
Mestdagh et al. (2005) studied the use of oxygen-scavenging technology to prevent light-induced off-flavor in UHT semi-skimmed milk. They used three types of bottles, with one transparent bottle having an oxygen-scavenging layer, a second bottle with perfect light barrier, and the third a transparent bottle with UV-filter. Although the decline of dissolved O2 concentration during milk storage was most explicit for the transparent bottle provided with an active oxygen-binding inner layer, this layer could not remove the relatively large quantity of oxygen and photo-degradation of the milk could occur. The results showed that if the milk package has adequate light barrier, there is no need to use the oxygen-scavenging technology in transparent packaging material. It is also well documented in the literature that transparent packaging provides poor protection against photo-oxidation (Moyssiadi et al., 2004; Zygoura et al., 2004; Intawiwat et al., 2011; Intawiwat et al., 2013).