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 °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 ≥ 90% antifungal activity was lost after the protein extracts were heated at 90 °C for 8 min except for F. graminearum . At pasteurization condition, ≥ 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.