Intelligent Packaging Technology Content and Form (5)

Active packaging is mainly used in food packaging. Compared with the past that used physical methods to block gas, water vapor and light, it plays an active and proactive role in extending the shelf life of foods, and can provide better protection. Therefore, active packaging is being widely used as an intelligent technology.

In order to control the specific gas in the package, a chemical substance that can absorb or release a specific gas is used. Its functional system includes the use of bactericides, deoxidants, odor absorbers or release agents, light barriers, anti-fogging agents, anti-sticking agents, stabilizers, and enzyme inhibitors.

(1) Absorb oxygen system

The presence of oxygen in food packaging can accelerate the spoilage and deterioration of many foods. Oxygen can cause many foods to produce odors, color changes and loss of nutritional value, and can accelerate bacterial growth. Deoxidizers are the most studied and patented areas of all active packaging technologies. A separate pouch containing a deoxidizer has been put into the package for commercial use. The deoxidizer in the pouch is usually finely ground iron oxide.

The deoxidizer can also be designed to combine directly with the packaging material. However, this deoxidizer consists of ethylenically unsaturated hydrocarbons and a transition metal catalyst. Its components are specially designed to overcome the disadvantage of slow oxygen absorption at low temperatures.

Mitsubishi Gas Chemicals Co., Ltd. solves one of the serious drawbacks of most known oxygen absorbers: their oxygen absorption reactions do not proceed smoothly in the absence of water. This deoxidizer system is composed of multiple unsaturated fatty acids (PUFAs). With some carrier oil (soybean oil, sesame oil, non-oleic acid in cotton seed oil, linoleic acid or linolenic acid, etc.) or PUFA mixed with a transition metal catalyst and an alkaline substance (calcium carbonate) to cure into a deoxidizer. Deoxygenation of enzyme-catalyzed oxidation systems has also been successfully explored.

(2) Carbon dioxide scavenger and generator

High levels of carbon dioxide are required in certain food packaging because they inhibit the proliferation of bacteria on the surface of foods and reduce the respiration rate of fresh crops such as fruits and vegetables. In conditioning atmosphere packaging, various concentrations of carbon dioxide need to be produced to suit specific food requirements. However, since most plastic films have a greater permeability for carbon dioxide than oxygen, in some packages it is necessary to step up production of carbon dioxide to maintain the necessary gas composition. In contrast, certain foods (such as coffee) emit carbon dioxide, and carbon dioxide must be absorbed to prevent food from spoiling or bursting through the package.

The carbon dioxide absorption system or generation system that has been completed has only a few commercial applications, so it is still an important research topic.

(3) Ethylene scavenger

Ethylene can act as a hormone and curing initiator for certain fresh and under-ripe fruits and vegetables. It can accelerate aging and reduce their shelf life. Ethylene absorption systems can irreversibly absorb ethylene produced by fruits or vegetables and require only a small amount of scavenger. A special scavenging system (CSIRO in Australia), when reacted with ethylene, appears pink and can be used to show the extent of the reaction and the presence of ethylene scavenger.

There are also more common ones that can serve similar effects: loading scavengers that facilitate the penetration of ethylene into bags; adding scavengers directly to the packaging film and reacting with potassium permanganate, which oxidizes ethylene to acetate And ethanol and passivation of alcohol and so on.

(4) Disinfection agent release system

Some preservatives can be used as active substances. They are added to the polymer packaging material or attached to the packaging material to achieve sterilization.

Active substances that can be used as sterilants include: ethanol and other alcohols, sorbates, benzoates, propionates, bacteriocins, and sulphur. In 1997 Ghosh et al. used a mixture of calcium sorbate and carboxymethyl cellulose as a sterilizing coating solution. Recently, Han (1996) studied the release system of potassium sorbate added to a plastic film and used a sterilizing agent. In other developments, the fungicide Imazalil chemically bonds with plastic films and is used to retard mold growth. Another example is a zeolite membrane, which impregnates the zeolite with an antimicrobial compound and then combines with the plastic matrix to slowly release the antimicrobial compound outwards.

Ethanol has been shown to spray onto bread and other baked food surfaces before packaging to extend shelf life. A new method developed by Japan to produce ethanol vapor to extend the shelf life of cakes is: Food-grade ethanol is first absorbed into an inert fine powder and then placed in a pouch that can penetrate water vapor. The inert powder absorbs moisture from the food and releases the ethanol vapor through the sachet and enters the remaining space of the package.

Other systems for active packaging that have been realized or are about to be realized include: antioxidant-containing films, odor absorption and release systems, anti-adhesive films, anti-fog films, light blocking and light-adjusting components, and the like.

Active packaging has a wide range of applications and it has an increasing momentum. In particular, the effectiveness of active packaging in extending shelf life of food products is significant. Just as Dr. Theodore Labuza of the University of Minnesota stated, “In the near future, changes in active packaging will not be general progress but revolutionary changes.” Active packaging as a kind of intelligent packaging is seen as a revolutionary change in the packaging industry and the hope of the new century.

(to be continued)