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Antioxidants are compounds that are employed to enhance shelf life and preserve the quality of fats and oils and lipid‐containing foods by suppressing oxidation reactions of their unsaturated components. These compounds could be naturally present, deliberately added, or generated during processing. Antioxidants are needed in small quantities to participate or interfere in the lipid autoxidation reaction cascade via various mechanisms. They should not impart any undesirable characters to the food, they should be stable, and they should be nontoxic. Application of these antioxidation differs depending on the nature of the food, conditions of intended processing, and storage. However, antioxidants that are deliberately added to foods are thoroughly scrutinized for their safety and toxicology aspects. Their usage in food is regulated under different legislatures in various countries. This chapter examines the purpose of antioxidant use, chemistry of antioxidant activity, and natural synthetic compounds that exert antioxidative activity in foods, as well as the relevant technological, toxicological, and regulatory considerations.

Flaxseed protein isolates were prepared by sodium hexametaphosphate complexation and acylated with acetic or succinic anhydride to improve their functional properties. The degree of acylation of free amino groups was lower when succinic anhydride was used in place of acetic anhydride. The color of the acylated proteins became lighter as the degree of acylation was increased. Emulsification properties of protein preparations were improved due to acylation, particularly for succinylated products. While foaming properties of flax protein isolates were not improved by acylation, their solubility was markedly improved. Low degrees of acetylation improved fat binding capacity of flax protein isolates, but succinylation did not exhibit such an effect. Acylation also increased aromatic or surface hydrophobicity of the products, and the highest value was observed at the lowest degree of acetylation. The in-vitro enzymic hydrolysis of the isolated proteins was reduced due to the acylation process. Keywords: Acylation; acetylation; succinylation; flaxseed; functional properties; protein isolate

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Total proteins of defatted low-mucilage flaxseed meals were isolated by extraction with aqueous sodium hexametaphosphate (SHMP). A composite central rotatable design was used to study effects of pH (X 1 ), meal-to-solvent ratio (X 2 ) and concentration of SHMP (X 3 ) on nitrogen extractability (Y 1 ) and protein recovery (Y 2 ). Using RSM, quadratic polynomial equations were obtained for Y 1 and Y 2 by multiple regression analysis. All three variables significantly affected nitrogen solubility and protein extractability. The pH was the most effective factor and mealto-solvent ratio was least. Verification experiments confirmed validity of predicted models. Stationary points for response surfaces were characterized as maxima and they were Y 1 ϭ77.6% at X 1 ϭ8.90, X 2 ϭ1:33.6 and X 3 ϭ2.75% and Y 2 ϭ57.5% at X 1 ϭ9.00, X 2 ϭ1:33.3 and X 3 ϭ2.85%, for nitrogen extractability and protein recovery, respectively.