# The Oxidative Extraction of Starch from Chestnut (Castanea sativa Mill.) Byproducts: A Valorization Strategy for a Sustainable Food Industry

## TL;DR

This paper explores a method to extract usable starch from spoiled chestnuts to reduce waste and support a sustainable food industry.

## Contribution

A novel oxidative extraction method is proposed to produce functional starch from spoiled chestnuts.

## Key findings

- Oxidative extraction at pH 8 produced starch with moderate viscosity and good swelling capacity.
- Bleached starch retained a yellow hue but had higher crystallinity and similar lightness to native starch.
- Alkaline extraction conditions reduced gelatinization and retrogradation performance of the starch.

## Abstract

Global chestnut production is rising. However, the Portuguese chestnut industry still experiences annual post-harvest losses, largely due to microbial spoilage. Recovering high-value starch from spoiled chestnuts offers a promising strategy to reduce waste and increase economic returns. Yet, starch extracted from spoiled kernels is typically dark brown, limiting its industrial applications. This study aimed to enhance the sustainability of the chestnut sector by converting industrial byproducts into useful ingredients. We evaluated whether hypochlorite-mediated oxidative extraction at pHs around 8 and 12 could produce starch with functional properties suitable for industrial applications. Both native and bleached starches showed similar lightness (L* 84–91), though a slight yellow hue remained (ΔE* 12–19). The degree of crystallinity was higher in bleached starches (13–16%) while preserving the characteristic CB-type crystalline pattern of native chestnut starch. The degree of oxidation was 0.88% and 0.43% for bleached starches isolated at pHs 8 and 12, respectively. Starch bleached at pH 8 exhibited moderate viscosity (breakdown 0.103) and greater swelling capacity at 50 °C than corn starch. In contrast, extraction under alkaline conditions markedly reduced gelatinization and retrogradation performance. Therefore, oxidative extraction at middle pH proved to be the most effective method for recovering functional starch from spoiled chestnuts.