The value-added challenge of nuts: antioxidant components, functions and applications in nut by-products

Large quantities of nut processing by products are generated worldwide and remain underutilized despite being rich sources of bioactive compounds. However, comparative integration of their antioxidant compositions and functional relevance is still limited. This review aims to summarize and compare the antioxidant compositions, functional properties, and potential food related applications of major nut by products generated during nut processing, with an emphasis on their relevance as nutritional and functional ingredients.

This review was conducted as a structured narrative synthesis. Relevant literature was retrieved from major academic databases, including Web of Science, Scopus, PubMed, and China National Knowledge Infrastructure (CNKI), covering publications from 2000 to 2025. Earlier foundational studies were also included when necessary to provide historical context. Search terms combined the names of major nut by-products with keywords related to polyphenols, flavonoids, polysaccharides, and antioxidant activity. Studies were selected based on relevance to compositional characterization, antioxidant activity evaluation, mechanistic investigation, and application-related research. Both international and regional peer-reviewed publications were considered to provide a comprehensive overview of current research progress.

Nut by products are rich in bioactive compounds such as polyphenols, flavonoids, and polysaccharides, which exhibit strong antioxidant capacity through scavenging reactive oxygen species and modulating oxidative processes. Comparative analysis indicates notable differences in antioxidant efficacy and functional performance among different nut residues. Beyond antioxidant activity, these by products show promising potential in food preservation, freshness maintenance, and natural coloring, as well as nutrition related functionalities including antimicrobial and anti inflammatory effects.

The findings highlight nut by products as valuable sources of antioxidant compounds for food and nutrition related applications. However, challenges including compositional variability, extraction efficiency, safety evaluation, and standardization remain key barriers to their large scale utilization. Addressing these issues may facilitate the development of value added functional ingredients and support the sustainable utilization of nut processing by products within food systems, thereby promoting circular economy strategies and enhancing the overall value chain of nut industries.