Melt reaction of zein with glyoxal to improve tensile strength and reduce solubility

Glyoxal, in the presence of base, has been used to crosslink zein in a melt process involving reaction in a melt state combined with compression molding. The resulting zein articles had improved tensile strength, increasing from 34.3 to 40.6 MPa, when the amount of glyoxal was 6% by zein weight. Reduced solubility in solvents, such as acetic acid, was achieved with glyoxal amounts as low as 1%. Derivitization of zein by glyoxal required the presence of base. As little as 0.00019 mmol of NaOH per gram of zein when using 6% glyoxal gave reduced solubility. Other bases such as KOH and Ca(OH)(2) also gave reduced solubility. However, these bases did not yield improvements in tensile strength. Decreases in melt temperature and processing time caused a corresponding decrease in tensile strength, but had little effect on solubility. (c) 2008 Wiley Periodicals, Inc.