The effects of moisture sorption on physical properties of native and cross-linked starch films in the glassy state were studied. Water played a dual role as a plasticizer or an antiplasticizer, depending on the physical property measured. Plasticizing effects were clearly evident in the case of the calorimetric glass transition temperature (T g ), tensile modulus, linear expansion, and water vapor permeability. In contrast, antiplasticization by water resulted in maxima in tensile strength, strain-at-break, and toughness of films that were observed at an intermediate moisture content ranging from 4% to 8% (RVP 0.1 to 0.4). The seemingly contradictory effects of water on mechanical properties associated with lower and higher deformation of starch films were reconciled by assigning different roles to water operating primarily via opposite entropic/free volume effects. Relationships, if any, between DSC thermal events and mechanical antiplasticization were not apparent.

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Antiplasticization of synthetic glassy polymers by lowmolecular weight diluents at low concentrations is a wellknown phenomenon which leads to increased rigidity rather than flexibility of the polymer-diluent blends. Based on the food polymer science approach, we hypothesized that increases (rather than decreases) in modulus and brittleness, commonly observed when certain solid food systems are humidified from the dry state, are synonymous with antiplasticization by water. Sugars and polyols, important components of foods, behave in much the same manner as water in acting as either antiplasticizers or plasticizers of food polymer systems. Several mechanisms may be involved in antiplasticization by low-molecular mass diluents. Simultaneous changes in various physical properties, resulting from antiplasticization or plasticization by water and other diluents, may profoundly influence the quality and acceptability of food products.

Addition of citric acid (0.02%) inhibited the increased rate of lipid oxidation found in rendered pork fat following pressure treatment (650-800 MPa). This indicated that transition metal ions were probably released from complexes and became available to catalyze lipid oxidation in the pressure treated fat. In minced pork and washed fibers citric acid was less effective in inhibiting oxidation in pressure treated samples because of its pH lowering effects. However, the less acidic ethylenediaminetetraacetic-acid disodium salt (Na 2 EDTA) was an effective antioxidant in these pressure treated (400 MPa and 800 MPa) systems. This further indicated that metal catalysts (probably iron) were released from complexes during pressure treatment to catalyze lipid oxidation.

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