Module 6. Modern packaging techniques

Lesson 24

24.1 Introduction

Packaging is an essential component in the complex distribution system. The main aim of packaging is to safeguard the food material from microbial attack and other contaminants and prevent damage during the distribution. There is huge demand for the packaging material, which will be causing huge environmental concerns as they are majorly plastics which will degrade very slowly. In order to overcome this problem “Biodegradable Packaging” has emerged.

24.2 Definition of Bio-Packaging Materials

“Biobased food packaging materials are materials derived from renewable sources. These materials can be used for food applications”. The renewable sources are from plants, marine life and animals.

24.3 Degradable Plastic

Plastic designed to undergo significant change in its chemical structure under specific environmental conditions, resulting in loss of some properties that may be measured by standard methods appropriate to the plastic and application in a period of time that determines its classification.

24.4 Biodegradable Plastic

Degradable plastic in which the degradation must result from the action of naturally occurring micro organisms.

24.5 Compostable Plastic

Plastic that undergoes biological degradation during composting to yield carbon dioxide, water, inorganic compounds and biomass at a rate consistent with other known compostable materials and leaves with no visually distinguishable or toxic residues.

24.6 Polymers Directly Extracted From Biomass

These are the material, which find their origin from the marine and agriculture, animals and plants. They are having very good “Gas barrier property”. These materials are hydrophilic, by nature and are crystalline, because of which they cause problems to certain extent, mainly in the Packaging of moist food products.

24.6.1 Polysaccharides

The polysaccharides of interest from Packaging material point of view are cellulose, starch, gums, and chitosan. The more complex polysaccharides produced by fungi and bacteria such as xanthan, curdlan, pullan and hyaluronic acid are of greater interest in the future.

24.6.2 Starch and its derivatives

The principle source of starch is Corn and Potatoes. The starch is a very competitive material as compared to the other plastics. As a packaging material, starch alone does not form films with adequate mechanical properties unless it is first treated by either plasticization, blending with other materials, genetic or chemical modification or combinations of the above approaches.

24.6.3 Cellulose and its derivatives

Cellulose is the most commonly available polymer on the earth. Because of its regular structure and array of hydroxyl groups, it tends to form strongly hydrogen bonded crystalline microfibrils and fibres and is most familiar in the form of paper or cardboard in the packaging industries. Cellulose is a cheap raw material, but difficult to use because of its hydrophilic nature, insolubility and crystalline structure.

24.7 The Biobased Polymers and their Sources

24.7.1 Biobased polymers

Cellophane film; it is very hydrophilic in nature and has good mechanical Properties. In order to improve the barrier properties of the packaging material the cellophane is coated with other plastic materials like Saran etc.

24.7.2 Nitrocellulose, wax or PVC or PVDC (Poly vinylidene chloride)

Cellulose acetate (C.A), is the most commonly used Packaging material in food industry. Uses of packaging material in foods
  • Baked Goods.
  • Processed Meat.
  • Cheese and its products.
  • Candies.
24.7.3 Chitin

Chitin is chemically composed of repeating units of 1,4-linked deoxy-2- acetoamido-D-glucose, and chitosan refers to a family of partially N-acetylated 2-deoxy-2-amino-.-glucan polymers derived from chitin. It is the second most abundant polysaccharide material available after cellulose.

24.7.4 Chitosan

Chitosan also readily forms films and, in general, produces materials with very high gas barrier properties. It is widely used for the production of edible coating. The cationic properties of chitosan offer good opportunities to take advantage of electron interactions with numerous compounds during processing and incorporating specific properties into the material. The advantages of this material include antimicrobial property and their ability to absorb the heavy metals. The application of laminates made of chitosan, cellulose, and polycaprolactone in Modified Atmospheric Packaging (MAP) have been tested and was effectively performed.

24.7.5 Proteins

A protein is considered to be a random copolymer of amino acids and the side chains are highly suitable for chemical modification which is helpful to the material engineering, for getting required properties of the Packaging material. The proteins can be divided into two categories, 1) Plant origin and 2) Animal origin.
  • Plant origin: Gluten, Soya, Pea, Potato.
  • Animal origin: Casein, Whey, Collagen, Keratin.
The Properties of Proteins used in Packaging material:

1. High gas barrier property.

2. Efficient and suitable application for packaging of foods.

The major drawback of these protein polymers is their sensitivity to relative humidity.

24.7.6 Animal Origin Casein

Casein is a milk-derived protein. It is easily processable due to its random coil structure. Upon processing with suitable plasticizers at temperatures of 80- 100ºC, materials can be made with mechanical performance varying from stiff and brittle to flexible and tough performance. Casein melts are highly stretchable making them suitable for film blowing. In general, casein films have an opaque appearance. Casein materials do not dissolve directly in water. The main drawback of casein is its relatively high price. Casein was used as a thermoset plastic for buttons in the 1940’s and 50’s. Whey

Whey proteins are by-products from the cheese production. They have relatively high nutritional value, are available in large amounts worldwide and have been extensively investigated as edible coatings and films. Whey proteins are readily processable and have some potential as exterior films, if, used with gelatin, suitable modification strategies can be developed to reduce moisture sensitivity. Collagen

Collagen is a fibrous, structural protein in animal tissue, particularly skin, bones and tendons. Collagen is a flexible polymer. However, because of its complex helical and fibrous structure, collagen is very insoluble and difficult to process. Collagen is the basic raw material for the production of gelatine, a common food additive with potential for film and foam production. Gelatine is a very processable material, but it is extremely moisture sensitive. Keratin

Keratin is by far the cheapest protein. It can be extracted from waste streams such as hair, nails and feathers. Due to its structure and a high content of cysteine groups, keratin is also the most difficult protein to process. After processing, a fully biodegradable, water-insoluble-plastic is obtained. However, mechanical properties of this plastic are still poor compared to the proteins mentioned above. The main drawback of all protein plastics, apart from keratin, is their sensitivity to relative humidity. Either blending or lamination can circumvent this problem.

24.7.7 Plant origin Gluten

Gluten is the main storage protein in wheat and corn. Gluten plastics exhibit high gloss (polypropylene like) and show good resistance to water under certain conditions. They do not dissolve in water, but they do absorb water during immersion. Due to its abundance and low price, research on the use of gluten in edible films, adhesives, or for thermoplastic applications is currently being carried out. Soy protein

Soy proteins are commercially available as soy flour, soy concentrate and soy isolate, all differing in protein content. Soy protein consists of two major protein fractions referred to as the 7S (conglycinin, 35%) and 11S (glycinin, 52%) fraction. Both 7S and 11S contain cysteine residues leading to disulphide bridge formation and processing is, therefore, similar to gluten with similar mechanical properties. The best results are obtained with soy isolate (approx.90% protein). This behaviour in water is similar to that of gluten plastics. The most successful applications of soy proteins are paper coatings. Potato

Potato starch produces a more translucent plastic. The potato starch plastic display significantly greater water absorption than those made from other sources. Zein

Zein comprises a group of alcohol soluble proteins (prolamines) found in corn endosperm. Film-forming properties of zein have been recognized for decades and are the basis for most commercial utilization of zein. Films may be formed by casting, drawing or extrusion techniques (Reiners et al., 1973). The films are brittle and need plasticizers to make them flexible. Zein-based films show a great potential for uses in edible coatings and biobased packaging.

24.8 Polymers Produced from Classical Chemical Synthesis from Biobased Monomers

Using classical chemical synthesis for the production of polymers gives a wide spectrum of possible “bio-polyesters”. To date, polylactic acid is the polymer with the highest potential for a commercial major scale production of renewable packaging materials. However, a wide range of other bio polyesters can be made. In theory, all the conventional packaging materials derived from mineral oil today can in the future be produced from renewable monomers gained by e.g. fermentation.

24.8.1 Polylactic acid (PLA)

Lactic acid, the monomer of polylactic acid (PLA), may easily be produced by fermentation of carbohydrate feedstock. The carbohydrate feedstock may be agricultural products such as maize, wheat or alternatively may consist of waste products from agriculture or the food industry, such as molasses, whey, green juice, etc.
PLA is polyester with a high potential for packaging applications. The properties of the PLA material are highly related to the ratio between the two meso-forms (L or D) of the lactic acid monomer. Using 100% L-PLA results in a material with a very high melting point and high crystallinity. If a mixture of D- and L-PLA is used instead of just the L-isomer, an amorphous polymer is obtained with a Tg (Temperature gradient) of 60°C, which will be too low for some packaging purposes. A 90/10% D/L copolymer gives a material which can be polymerized in the melt, oriented above its Tg and is easy processable showing very high potential of meeting the requirements of a food packaging. Furthermore, PLA may be plasticized with its monomer or, alternatively, oligomeric lactic acid and the presence of plasticizers lower the Tg.

24.9 Polymers Produced Directly by Natural Or Genetically Modified Organisms

Polyhydroxyalkanoates (PHAS) are the polyester compounds that are accumulated by a major group of bacteria as carbon reserve (Energy source), of which the main polyester is Polyhydroxybutyrate (PHB). Two more PHAS were discovered namely 3- hydroxy butyrate (PHB) and 3- hydroxyl valerate (PHBV). As these both are known for their compositability and biodegradability they are generally used for packaging material production. The very important property of the PHAS, is their low water vapour permeability which is essential requirement in food packaging. Medium chain length PHAS, behave as elastomers with crystals acting as physical crosslinks and, therefore, can be regarded specific of its mechanical properties. Elongation to break up to 250-350% has been reported and a Young’s modulus up to 17 MPa. These materials have a much lower melting point and Tg than their PHBS. The major application of medium chain length PHAS are biodegradable cheese coatings and biodegradable rubbers.

24.9.1 PHAS from bacteria

The major packaging compounds of the bacteria are “Bacterial Cellulose”. Strains of Acetobacter xylinum, Acetobacter pasteurianus are capable of producing cellulose (homo â 1-4 glucane). The cellulose thus produced from bacteria is processed at ambient conditions where the degree of polymerization is 15000, crystalline in nature. This technique is not that successful on the economic terms as its production cost is very high.

24.10 Bio Packaging of Foods

Most commonly used food packages clearly fall into primary, secondary or tertiary packaging categories. For a variety of food products, however, conventional packaging does not provide optimal conditions for product storage and a number of approaches are used to design packages for specific products. Such product-specific packaging includes applying of edible films and coatings, active packaging, modified atmosphere packaging (MAP), and using combinations of packaging materials. Of these packaging techniques specified above bio films or edible films are of importance.

24.10.1 Edible films

Edible coatings and films comprise a unique category of packaging materials differing from other biobased packaging materials and from conventional packaging by being edible. Edible coatings are applied and formed directly on the food product either by addition of a liquid film-forming solution or molten compounds. They may be applied with a paintbrush, by spraying, dipping or fluidising. Edible coatings form an integral part of the food product, and hence should not have impact on the sensory characteristics of the food. Edible films, on the other hand, are freestanding structures, formed and later applied to foods. They are formed by casting and drying film-forming solutions on a levelled surface, drying a film-forming solution on a drum drier, or using traditional plastic processing techniques, such as extrusion. Edible films and coatings may provide barriers towards moisture, oxygen (O2), carbon dioxide (CO2), aromas, lipids, etc., carry food ingredients (e.g. antimicrobial, antioxidants, and flavour components).Edible films and coatings may be used to separate different components in multi-component foods thereby improving the quality of the product.

They may be used to reduce the amount of primary synthetic packaging material used in a product or allow conversion from a multi-layer, multi-component packaging material to a single component material. Edible coatings may also help maintain food quality by preventing moisture and aroma uptake or loss, etc. after opening of the primary packaging.
Biobased packaging materials must meet the criteria that apply to conventional packaging materials associated with foods. These relate to barrier properties water, gases, light, aroma, optical properties, strength, welding and moulding properties, marking and printing properties, migration requirements, chemical and temperature resistance, disposal requirements, antistatic properties besides being user-friendly and cheap.

Biobased packaging materials must also comply with food and packaging legislation, and interactions between the food and packaging material must not compromise food quality or safety.

24.11 Application of Biodegradable Packaging in Dairy Industry

The potential biobased packaging materials which are tested for dairy products are as follows:

1. Cheese and Varieties: The packaging materials which can be used are starch laminates and nitrocellulose lacquered cellophanes as they have good moisture and gas barrier properties.

2. Yoghurt, Fermented foods: The packaging material can be Biodegradable plastics, PLA , as they have good mechanical, CO2 and moisture barrier properties.

3. Butter and Fat rich products: The packaging material can be Laminate, Butter paper, PLA, PLA + PCL which possess good moisture and Light barrier properties.

4. Ice Cream: The packaging materials which can be used are Acetylated monoglycerides as they posses good moisture barrier properties.

24.12 Recent Technologies for Producing Biodegradable Plastics

Bio – degradable plastics are being produced from plants by Fermentation, Recombinant DNA engineering etc.

Last modified: Friday, 12 October 2012, 5:25 AM