Most packaging materials traditionally used are polymers and are not easily degradable. Barrier properties of the packaging material are also important to determine the shelf life of the product. For an instance, for a fatty food Oxygen barrier properties are important. The empty space over the product in packaged food is called as head space. A proper packaging material protects preserves, promotes and informs the food item.
Polymers used for packaging include polyethylene, polypropylene, Polyvinyl chloride, Polyvinilydine chloride and Polyethylene terephthalate etc. PET and HDPE are recyclable. For respiring food items, packaging material with high barrier properties are not suitable as it leads to rotting due to moisture accumulation. Triple laminates are used to package dried products to prevent it from moisture and to prevent escape of volatile aroma compounds. Food items with pigments/dyes important for the quality of the product; are packed in light protective containers.
Apart from these traditional methods of packaging, new trends such as active packaging, intelligent packaging has scope. In active packaging, subsidiary constituents have been deliberately included in or either the packaging material or the package headspace to enhance the performance of packaging material. In this, active compounds are filled into sachets or pads which are placed inside packages or active compounds can be directly incorporated into the packaging material. These active compounds include Oxygen scavengers/absorbers that include powdered iron, ascorbic acid. Iron powder reduces the Oxygen concentration in the headspace to less than 0.01%. Water is essential for Oxygen absorbers to function. Nonmetallic absorbers include ascorbic acid, ascorbate salt and catechol. Enzymatic oxygen scavengers include glucose oxidase, ethanol oxidase incorporated into sachets, adhesive labels or immobilized onto package surface. Apart from these vacuum packaging and Nitrogen flushing is used to remove Oxygen from the package.
As Oxygen, Carbon dioxide also can be problematic to the packaged food item as it can lead to an anaerobic environment with an acidic pH. Carbon dioxide absorbers are used to remove this. Sometimes Carbon dioxide emitters are inserted into food packaging to create anaerobic conditions. Generally used Carbon dioxide emitters are Ascorbic acid with Ferrous carbonate, Ascorbic acid with Sodium bicarbonate. These chemicals absorb Oxygen and generate equivalent amount of Carbon dioxide. CO2 emitters avoid package collapse and development of a partial vacuum. Ethylene absorbers such as Potassium permanganate oxidize ethylene to Carbon dioxide and water.
Ethanol emitters show antimicrobial effects even at lower concentrations. The substance is filled into a paper copolymer sachet. Some sachets contain traces of vanilla and other aroma compounds to mask the alcohol odour. The sachet contents absorb moisture from the food and releases ethanol vapour. Water activity of the food is an important factor in this type of packaging. This is widely used in Japan to extend the shelf life of high moisture bakery products upto 20 times the normal. Moisture absorbers are also heavily used which include Polyacrylate salts, activated clay, silica gel. Moisture accumulation can result from temperature fluctuations, drip of tissue fluid from flesh and during respiration of horticultural products. This can lead to growth of molds and bacteria.
Intelligent packaging is a great advantage of food biotechnology. In this, different sensors are used in food package which indicates about the quality of the food to the consumer. These sensors are coupled with biochemical reaction taking place inside the food when deterioration of the quality of food such as lipid oxidation, rotting of fruits etc. Gas indicators are one type of intelligent packaging. Thermochromic inks which are sensitive to temperature and microwave doness indicators (MDI) which emit audible signals when the food is ready to serve are some advance applications.