Management Strategies for the Anti-nutrient Oxalic Acid in Foods: A Comprehensive Overview of Its Dietary Sources, Roles, Metabolism, and Processing

Abstract

Oxalic acid is among the most abundant organic acids found in different biospheres, including plants, as an end product of metabolism. It forms either soluble or insoluble salts with monovalent or divalent cations, respectively. Then, consumption of oxalic acid-rich foods in human diets, particularly leafy vegetables (e.g., spinach, tea, and rhubarb), affects minerals absorption such as calcium. Meanwhile, its high level in blood is associated with many diseases such as hyperoxaluria systemic oxalosis and is thus classified among potential anti-nutrients. Various factors have affected oxalic acid levels in foods, including agricultural traits and consumption practices. Hence, the current review aimed at rediscovering oxalic acid dietary sources, metabolism, and the various processes employed to reduce its content in foods, and consequently, health harmful effects. Among them are physical/cooking, chemical, fermentation, and biotechnological processing. Recent biotechnological approaches have been attempted to produce transgenic crops remodeling oxalate metabolism, particularly its degradation. The soluble form of oxalate seems to be better absorbed and more harmful than insoluble salts in foods aiding in kidney stones formation. Cooking (e.g., boiling, microwaving, and steaming) appears as a useful management strategy to reduce soluble oxalate and, therefore, lowering oxaluria. The present review provides new perspectives on different processing methods to lower oxalate in essential vegetables highlighting their advantages or any limitations to aid improve these foods nutritional value and consumption.