Oregon State University, Corvallis, Oregon, U.S.A.
I. PACKAGING OF SEMISOLID FERMENTED DAIRY PRODUCTS A. Introduction
Packages play an important role in quality conservation of semisolid fermented dairy products. Packaging is very important and demanding for perishable cheese products such as fresh (cottage) cheeses. Well-designed packages help to extend shelf life, improve quality, and ensure safety of products. These benefits can be used to reach a higher level of flexibility in the distribution chain and to gain a better position in the market competition. As for any food product, the most important roles of a package include:
Protection of product from environment factors, including dirt or other foreign materials, microorganisms, gases (O2), and light; by preventing contamination, packaging serves a public health functions as well as reduces losses due to spoilage.
Reduction of moisture loss from the surface, thus increasing economic return.
Provision of relevant information to consumers—e.g., name and origin of the product, ingredients, nutritional information, instruction for use, and expiration date.
To meet these important roles for a package of semisolid fermented dairy products, including yogurt, sour cream, and fresh cheeses, the following aspects should be considered (1,2):
1. The packaging must successfully contain the product at low cost.
2. For most of these products, easy access with spoon or knife is essential. This indicates the use of wide-mouth containers for this product category.
3. A good advertising billboard must be provided by the package, which is one reason why the plastic construction are almost always pigmented.
4. Packaging materials must be highly resistant to attacks by fats and oils, proved a good barrier to moisture loss, and free of migration of plasticizers.
5. In most cases, a barrier to UV light is required to avoid oxidative rancidity development in these high-fat-content materials.
6. It is particularly important that the packaging materials do not contribute undesirable flavor or odor chemicals that could be easily detected or cause harm, because many of these products have delicate flavors.
7. Packaging has to provide convenience to consumers (e.g., single serve vs. institution bulk).
Design of packaging system to meet the above requirements involves several aspects, including selection of correct packaging material, package geometry and construction, and packaging equipment. This chapter emphasizes only packaging materials and package geometry and construction—not the equipment aspect.
B. Packaging Materials, Geometry and Construction
Semisolid fermented dairy products, including yogurt (drinkable yogurts are excluded in this chapter), sour creams, and fresh cheese, are always sold refrigerated and have a relatively short packaging shelf life of about 30 to 45 days under refrigeration. Products in this group are soft and thus require semirigid or rigid packaging. Containers are the most popular package type for these products. The container must be acid-resistant, prevent the loss of flavor volatiles, and be impermeable to oxygen, because the presence of oxygen can encourage the growth of contaminating yeasts and molds. Materials usually used for the manufacture of the containers include HDPE (high density polyethylene), PP (polypropylene), PS (polystyrene), PVC (polyvinyl chloride), and PVDC (polyvinylidene chloride). Chemical structures of these polymers are illustrated in Fig. 1, and their permeability to water and gas are listed in Table 1. These materials meet essential strength and low-cost requirements and are also inert, in the sense that they contribute no off-odors or off-flavors to the products. Except for the occasional use of clear PET (polyethylene terephthalate), containers are almost always pigmented, with the purposes of protecting the product from visible light, concealing the uneven clarity of these plastics, making the print more attractive, and adding additional market features by using color.
The finished containers can be cartons, tubs, or cups and can be manufactured in any shape or design to meet product requirements and attract consumer attention. Two different techniques are usually used to manufacture the plastics cups: injection-molding or thermo-forming. The injection-molding process involves melting the plastic in an extruder and using the extruder screw to inject the plastic into a mold, where it is cooled. After the cup is formed, it is ejected from the mold. This type of container has relatively thick walls and is characterized as a rigid cup. In the thermoforming process, the polymer is delivered to the dairy plant in the form of a continuous roll, one end of which is fed into the first section of the product filling/packaging machine. The polymer sheet is heat-softened and formed into or around a mold, so that the unit container is formed immediately prior to filling with the product. This packaging system is referred to as a form/fill/seal operation and is used mostly for yogurt packages. In the thermoforming process, the yogurt cups have a relatively lower wall thickness than those produced by the injection-molding system and are classified as semirigid cups (2,4).
The lids of the containers are also usually injection-molded or thermoformed using materials such as HIPS (high impact polystyrene) or LLDPE (linear low density polyethylene) sheetstock and are snapped on, rather than sealed, to provide easy opening/closing. The tamper-evidence rings that surround the lip of the top are usually made from a 50-75 Am PVC shrink film. The film is heat-shrunk in place after the package is filled and lidded (5). Paper-based lids have also been used lately for dairy applications such as yogurt cups
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