ACTIVE PACKAGING TECHNOLOGY

Active packaging is defined as packaging intended for deliberately improving the functionality of packaging system by inclusion of active ingredients in a packaging film or by modifying the headspace by these components. In other words, active packaging can also be defined as a system of food packaging which continuously optimize and maintain desired condition in the package which will improve the nutritive value, sensory appeal, longevity of the produce (Venneiren et al., 1999). Thus, active packaging systems are developed for improving the shelf life and quality of the fresh commodity. Active packaging technologies prevent the deteriorative changes between package and product by the virtue of various physical, chemical, or biological actions (Yam et al., 2005). Packaging may be termed active when it performs some desired role in food preservation other than providing an inert barrier to external conditions (Mane, 2016). Thus active packaging act as active barrier to manipulate the environment of package in order to allow improved microbiological or biochemical quality. Various active packaging systems employed are as follows (Fig. 6.4):

Types of active food packaging

FIGURE 6.4 Types of active food packaging.

OXYGEN SCAVENGERS

Increased level of oxygen in the headspace of package results in pronounced increase in respiration and ethylene production leading to detrimental effect on the quality of fruits. Oxygen is an enemy to variety of food components and often leads to their destruction high amount of oxygen brings about oxidation of vitamins, pigments, lipids, and flavor compounds. These changes are often accompanied by growth of aerobic microorganisms and browning reaction (Sanjeev and Rarnesh, 2006). By controlling the concentration of the oxygen in the headspace of the package we can control various deteriorative reaction associated with it including off-flavor, color change, and loss of nutritive value. Since rate of respiration and ethylene production has direct correlation with freshness of the produce. Utilization of oxygen scavenger in the package will allow the product to remain fresh for longer time by controlling the rate of product respiration and by absorption of oxygen that penetrates the package by the virtue of its permeability.

A variety of passive barriers are employed in the active packaging and these include high barrier materials like nanocomposites (Teixeira et al., 2011) and EVOH (Lagaron et al., 2004). However, such passive system does not allow sure short elimination of all the oxygen present. Therefore, oxygen scavengers are more appropriate technique in order to prevent various deteriorative reactions even due to small concentration of oxygen. The basic principle underlying the functioning of oxygen scavengers involves oxidation of active ingredients like iron powder, ascorbic acid, enzymes, unsaturated fatty acids, and photosensitive dyes (Floros et ah, 1997).

  • 6.3.1.1 DIFFERENT MECHANISMS OF ACTION OF OXYGEN SCAVENGERS
  • 6.3.1.1.1 Iron-based

Most of the commercially available oxygen scavenger present in the market are based on the oxidation of iron. The basic principle behind the oxygen scavenger is a moistening of iron due to the moisture present in the product package which results in the oxidation of iron and it is irreversible conversion into irreversible oxide. Reaction mechanism of Iron-based oxygen scavengers are as follows (Vermeiren et al., 2003):

For the effective functioning of iron-based, it is essential to have appropriate modeling of the process to calculate the required iron to maintain optimum level of oxygen in the package, which in turn is dictated by the rate of oxidation of the product and permeability of the package. As a thumb rule, 1 g of iron will react with 300 mL of O, (Labuza and Breene, 1987; Vermeiren et ah, 1999). Iron is known to have potent toxicity, so it is very essential to optimize the amount of iron in the sachet so largest commercially available sachet contains 7 g of iron so this would amount to only 0.1 g/kg for a person of 70 kg or 160x less than the lethal dose (Labuza and Breene, 1987). Some important iron-based oxygen absorbent sachets are listed in Table 6.2.

6.3.1.1.2 Ascorbic-acid based

Ascorbic acid is another oxygen scavenger component which is used in the active packaging of fruits and does not possess any health hazard. Ascorbic acid oxygen scavengers are based on the principle of oxidation of ascorbic acid to dehydroascorbic acid in the presence of Cu+ ions. It is basically a redox reaction, in which ascorbic acid reduces the Cu2+ to Cu+ to form the dehydroascorbic acid.

The oxygen absorption capacity of the sachet is dictated by the amount of ascorbic acid present. Usually, it requires 2 moles of ascorbic acid to reduce 1 mole of Oxygen (Cruz et al., 2012). Ascorbic acid and ascorbate salts both are congenial in both sachet and film technology. A technology developed by Pillsbury explains redox properties of these substances. The film containing ascorbic acid scavenger typically contain transitional metal (Co, Cu) which is activated by water; therefore it is essential to notice that such systems are successful in aqueous food packaging or in the packaged food which undergoes steam sterilization which is capable of providing trigger to the scavenging process (Brody et al., 2001).

6.3.1.1.3 Enzyme-based

Enzymes are preferred method in the active packaging due to being greener in nature. Enzyme-based scavenger typically contains combination of glucose oxidase and catalase in a water-mediated reaction. In the presence of water, the glucose oxidase will oxidize glucose to gluconic acid and hydrogen peroxide (Rooney, 1995; Vermeiren et al., 1999). Then catalase will convert the hydrogen peroxide to water and oxygen. According to the reaction, 1 mole of glucose oxidase reacts with 1 mole of Oxygen. So, in an impermeable packaging with 500 mL of headspace only 0.0043 mole of glucose (0.78 g) is necessary to obtain 0% of oxygen. Since action of enzymes is specific to reaction condition, the efficacy of this process will depend on number of factors namely, substrate concentration, oxygen transmission rate of the package, and enzymatic reaction velocity.

6.3.1.1.4 Unsaturated Hydrocarbon-based

A foresaid technology was particularly successful for moist or liquid foods due to need of presence of water for triggering the reaction. However, in most of the dry food where water is present in negligible amount or absent, oxygen scavenging reaction does not progress. The oxidation of PUFA is an excellent technique to scavenge oxygen in dry foods (Fig. 6.5).

Schematic of unsaturated hydrocarbon based oxygen scavengers

FIGURE 6.5 Schematic of unsaturated hydrocarbon based oxygen scavengers.

6.3.1.1.5 Photosensitive-based

This technique involves the inclusion of photosensitive dyes in the packaging film. This scavenger is based on UV-light and photosensitive dye mediated reaction. Reaction involving the conversion of ground state of oxygen to its singlet state, thereby making it more reactive. A photosensitive based oxygen scavenger contains sealing of ethyl cellulose film containing sensitizer (such as pigments and dyes) and a singlet oxygen acceptor. The ground state oxygen is also known as triple state oxygen (30,) which is excited to singlet state oxygen (Ю ) which is comparatively 1500 times more reactive than triple state oxygen. The basic principle underlying this oxygen scavenger includes activation of sensitizer by UV-light, activated sensitizer then reacts with ground state oxygen to produce singlet state oxygen. This singlet state oxygen accepted by the acceptor molecules and thereby consumed.

This technique is effective for wet as well as dry product and it does not require water for its activation. However as mentioned above, photosensitized reaction is triggered by UV-light, so scavenging action is initiated at processor’s packaging line by an illumination-triggering process (Vermeiren et al., 2003). Illumination-triggering process involves activation of multilayer oxygen scavenger layer by exposing it to UV-light (Fig. 6.6).

Oxygen scavengers can be incorporated in food packaging in the form of sachet or they can be directly incorporated into packaging material by extruding with polymer layer. Any substance used as an oxygen scavenger must meet several requirements and in particular, it must be safe, non-toxic, odorless, economical, easily handled, and should have high oxygen absorption rate. Oxygen scavenger sachets are classified based on their ability to scavenge the amount of oxygen and include: immediate type (0.5-1 day); general type (1-4 days); and slow type (4-6 days; Harima, 1990).

Illumination-triggering process of multi-layer oxygen scavenger layer by UV-light

FIGURE 6.6 Illumination-triggering process of multi-layer oxygen scavenger layer by UV-light.

Oxygen scavenging sachets sometime pose food safety hazard particularly when they are used in liquid foods. The spillage of sachet contents and their accidental consumption pose a risk to food safety. Thus, appropriate measure in the form of proper labeling “DO NOT EAT” and concealing in the secondary package should be practiced. For incorporation of any active substance in the food, it is very essential that it must not react the food, for such an approach we use multilayer oxygen scavenging system (Fig. 6.7). In such a packaging system the oxygen absorbing layer (inner) is made in such a way that it is permeable to oxygen present in the package but not permeable enough to allow the migration of these substances into the food. The outer barrier layer is oxygen impermeable to prevent permeation of the atmospheric oxygen to the oxygen absorbing layer. The rate of success of efficient execution depends on maintaining the appropriate oxygen concentration in the package. The heart of the process lies in the mathematical model of oxygen concentration which helps in selecting appropriate oxygen scavenger (Charles et al. 2003).

Schematic diagram of multilayer oxygen scavenging system

FIGURE 6.7 Schematic diagram of multilayer oxygen scavenging system.

Case study 1: Preservation of orange juice from oxidative degradation:

Johnson et al. (1995) conducted a study on preservation of color and ascorbic acid in orange juice during storage. Orange juice is filled in oxygen scavenger (OS) pouches. The scavenging in the packet resultant in significantly higher concentration of ascorbic acid and also helped in retaining the color of the juice. The reaction of non-enzymatic browning triggered by the virtue of loss of ascorbic acid was found to be decreased due to evidently low browning index in the orange juice during the storage.

Case study 2: Preservation of browning in Bananas:

Fresh-cut banana slices were wrapped in oxygen scavenging (OS) film, and they demonstrated 50% less browning as compared to the one packed in conventional PET film. Later on OS containing со-extruded multilayer films were developed to prevent banana from fast oxidation by sandwiching OS into two external layer of pure PET (PET/OS-PET/PET) in order to increase the reaction time (Galdi and Incamato, 2011).

 
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