Valorization of Peel-Based Agro-Waste Flour for Food Products: A Systematic Review on Proximate Composition and Functional Properties

Abstract

With the steadily growing world population, effective methods are needed to alleviate food shortages. One possible strategy could be to utilize agro-waste materials that accumulate in large quantities at every stage of the economic chain during harvesting, food production, and consumption. Peel-based agro-waste consists of promising materials that can be utilized to potentially substitute commonly used raw materials in products traditionally made from wheat, tapioca, and rice flours. In this systematic review, we aim at establishing prospective proximate components as basic nutrients and their valorization potential as substitutes in traditional flour products (bread, biscuits, etc.). Generally, the peel contains high levels of fiber and relatively low digestible carbohydrates, providing a healthier food ingredient. In terms of protein, it should be pointed out that seeds such as wheat utilize insoluble gluten as their major storage protein, while proteins in peel were found in quite high percentage although they were not yet well characterized. However, the general effect of using peel to substitute wheat in food products are the reduction of dough elasticity, increased hardness of the end-products, faster water absorption rate of the products, and in some cases, bitter taste and darker colors. The latter two could have been contributed by the secondary metabolites such as phenolic compounds. On the other hand, substitution of peel into food products can have valuable health benefits, e.g., retention of antioxidant activity due to the phenolic compounds or simply adding fiber. In this review, literature on the composition of promising agro-waste raw materials is being discussed in the relationship with physical properties and appearance of potential end-products. Antinutritional compounds and pretreatment processes are also being considered. It is hoped that a critical discussion will lead to a better understanding and higher acceptance of the incorporation of peel into food products.