Reactive extrusion process to obtain a multifunctional fiber-rich ingredient from coffee hull

Abstract

Brazil is a country with strong agricultural production, annually producing a large amount of lignocellulosic residues. The valorization of these residues as ingredients for the food industry aims at environmental, social, and economic sustainability. Coffee hull is a by-product generated by the coffee industry that can be used to produce new food ingredients with high added value. This study aimed to obtain a multifunctional fiber-rich ingredient from a coffee hull using a one-step process based on reactive extrusion with alkaline hydrogen peroxide or sulfuric acid. For this purpose, we submitted a coffee hull to extrusion with sulfuric (1% and 3%) acid or alkaline hydrogen peroxide (1% and 3%) in one-step processes. Then, the obtained materials were characterized through their physicochemical and techno-functional properties. All treated samples had an increase in their cellulose and insoluble dietary fiber contents and also presented an increase in their porosity as observed by scanning electron microscopy. The sample modified with 3% alkaline hydrogen peroxide (AHP3) had the highest cellulose content (45.17%), insoluble dietary fiber (78.20%), density (3.54), water absorption capacity (1.96 g/g), and oil absorption capacity (0.86 g/g). All samples had thermal stability from room temperature to 300 °C and in all samples, the crystallinity indexes decreased after treatment. Reactive extrusion was effective in modifying the coffee hull. Our study proposes a green route to obtain a higher value-added product from lignocellulosic waste, with some advantages including short reaction times, low reagents concentrations, little or no effluent generation, and the possibility of scaling to industrial scale.

Keywords

• alkaline hydrogen peroxide
• coffee hull
• insoluble fibers
• sulfuric acid