Oil permeability Grease resistance is an important property of paper packaging materials used for foods containing fats or oils. Limited research has been done on quantifying the oil permeability of packaging materials. Coated paper or paperboard with a good grease barrier is important for packaging used in fast-food restaurants, as well as food-packaging applications such as cereal boxes, donut boxes, and pizza boxes. Corn zein was shown to have excellent grease resistance, both as a film and as a coating on paper. Zein coating on paper for grease barrier was compared to quick-service sandwich packaging, and it was found that zein-coated papers were as effective as polyethylene laminates used for quick-service restaurant sandwich packaging (Trezza and Vergano 1994). In their study, the zein-coated papers were not heat-sealed to a 2nd sheet of paper, as were the commercial polyethylene-laminated samples. Further research is required to evaluate the effects of heat sealing of zein coating and storage on grease properties of the coated papers.
Research results also showed that a whey protein film (De Mulder-Johnston 1999) and whey protein coating on paper (Chan 2000) provided excellent oil-barrier properties. Rhim and others (1998) showed that the grease resistance of carrageenan-coated papers was comparable to polyethylene-laminated papers, and Park and others (2000) reported that soy-protein-coated papers imparted gas and lipid barrier, as well as adequate mechanical properties.
Chan and Krochta (2001a) studied the grease barrier property of WPI-coated paperboard. They found that a good grease barrier was obtained with paperboard coated with WPI and glycerol as plasticizer. However, glycerol plasticizer may migrate into the paperboard during storage. Lin and Krochta (2003) concluded that WPC with about 80% protein coatings on paperboard gave a grease barrier comparable to WPI coatings. Sucrose-plasticized whey-protein coatings on paperboard imparted excellent grease resistance, similar to glycerol-plasticized coatings. Long-term ambient storage of WPC-coated paperboard indicated that the use of sucrose as plasticizer imparted good grease resistance and minimized plasticizer migration. On the other hand, Ham-Pichavant and others (2005) explored the ability of bilayer chitosan-coated paper as fat barrier. They also investigated the nature of interactions between fatty acids, chosen as model lipids, and chitosan. Their experiments showed a strong pH-dependent chitosan-lipid interaction. The chitosan layer could act as a lipid trap coating to decrease fat transfer if the pH of the chitosan film-forming solution was adjusted to 5.5 to 6 prior to coating. Chitosan-coated papers can be used as fat barrier packaging with a chitosan level of 5.41%. However, treatment costs remain high compared with fluorinated resins. In an attempt to decrease both treatment cost and fat transfer, chitosan was associated with various polymers. Incorporation of sodium alginate considerably increased the fat barrier of coated papers. Kjellgren and others (2006) reported that chitosan-coated greaseproof papers exhibited excellent grease resistance within the coat weight range of 2.4 to 5.2 g/m2. The air permeability of the coated material had a great influence on grease resistance.