IRRADIATION DOSE AND CALCIUM EFFECT ON THE MECHANICAL-PROPERTIES OF CROSS-LINKED CASEINATE FILMS

The effect of irradiation dose on the formation of cross-links in calc ium caseinate solutions was investigated. The formation of bityrosine was found to increase with the irradiation dose for the basic formulat ion containing calcium caseinate, carboxymethylcellulose, and glycerol . Addition of CaCl2 to the basic formulation increased the fluorescenc e signal of bityrosine for all irradiation doses suggesting that CaCl2 can have an indirect effect on the formation of bityrosine by shorten ing molecular distances between polypeptides, thus making easier the f ormation of bityrosine. Furthermore, gels were formed for solutions co ntaining CaCl2 at irradiation doses greater than or equal to 16 kGy. T he formation of gels was found to be accountable for the increased mec hanical strength in the corresponding films. A maximum gel strength wa s obtained at an irradiation dose of 64 kGy for all formulations, sugg esting a maximum cross-linking density. Such a feature was also noted when poly(ethylene glycol), mannitol, and sorbitol were added to the f ormulations. Although bityrosine cross-links increase with irradiation dose, some damage can occur in another part of the protein structure, accounting for the overall loss of puncture strength at doses >64 kGy .