Antifungal activity stability of flaxseed protein extract using response surface methodology

The stability of the antifungal activity of flaxseed (Linum usitatissimum) protein extract was evaluated in this study. Response surface methodology (RSM) using Box-Behnken factorial design was used to evaluate the effects of treatment variables, that is, temperature (50 to 90 degrees C), time (1 to 29 min), and pH (2 to 8), on the residual antifungal activity (RAA) against Penicillium chrysogenum, Fusarium graminearum, Aspergillus flavus, and a Penicillium sp. isolated from moldy noodles. Regression analyses suggested that the linear terms of the temperature and time had significant (P < 0.05) negative effects on the RAA against all test fungi, whereas that of pH had a significant (P < 0.1) positive role on the RAA of all 3 fungi. In addition, the RAA was significantly (P < 0.05) affected by the quadratic terms of time for all fungi, and the quadratic term of temperature played a significant (P < 0.1) role on RAA against F. graminearum. One interaction term (temperature-pH) was found to significantly (P < 0.1) affect the RAA against both Penicillium strains tested. The results indicated that >or= 90% antifungal activity was lost after the protein extracts were heated at 90 degrees C for 8 min except for F. graminearum. At pasteurization condition, >or= 50% activity was retained except for P. chrysogenum. The results also suggested that neutral and alkaline pH favored the antifungal activity stability of the protein extracts. Thus, flaxseed protein might be promising if used as a preservative in foods with neutral or alkaline pH requiring mild heat treatments.