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. (Authors abstract)

Flaxseed meal, the main by-product of the flaxseed oil extraction  process, is primarily used as ruminant feed. However, the meal may serve as an excellent protein source since it contains high protein content (over 30% on a dry weight basis). The amino acid composition of the flaxseed protein is ideal based on its percentage ratios of the essential to total amino acids according to the recommendation by FAO/WHO (1973). Flaxseed protein contains abundant arginine and glutamine. Flaxseed protein was previously reported to possess fungistatic activity against the growth of agronomically important pathogens Alternaria solani and Alternaria alternata, the human pathogen Candida albicans and common food spoilage fungi Penicillium chrysogenum, Fusarium graminearum, and Aspergillus flavus. The application of flaxseed protein extract as a food preservative requires information about the heat stability of the protein and the effect of heating on the fungistatic activity of the protein.  Thus, the objective of this investigation was to study the effects of temperature, time, and pH on the fungistatic activity of flaxseed protein extract using RSM design. The results showed considerable variations in the residual antifungal activity (RAA) when the flaxseed protein extracts were subjected to various heat and pH combinations. RAA against P. chrysogenum ranged from 68.2% to 0% and those for the other 3 fungi all ranged from 100% to 0%. This suggested that heat and pH greatly affected the fungistatic activity of the flaxseed protein extracts. Statistical modelling indicated that the temperature and time had a negative effect, whereas pH had a positive effect on the RAA against all 3 fungi.  Results showed that heating flaxseed protein for 8 min at 90◦C destroyed the majority of the fungistatic activity of the protein, which is consistent with the reported denaturation temperature (91.3◦C) of flaxseed protein. The authors postulate that the antifungal activity of the extracts was due to the protein based on the loss of antifungal activity of the extract observed under heating conditions. (Editors comments)