Fermentation as a strategy to improve the bioactive and antioxidant properties of walnuts and their derived products

Oxidative stress is a significant factor in the development of many chronic illnesses, and antioxidants play a vital role in mitigating its effects. The walnut ( Juglans regia L .) is widely recognized for its diverse range of bioactive compounds, particularly polyphenols, flavonoids, and tocopherols, which exhibit notable antioxidant properties. These beneficial compounds are found in various walnut-based products, including milk, yogurt, cheese substitutes, flowers, protein meals, oils, and extracts from components such as the husk, pellicle, and leaves. Previous studies demonstrated that microbial fermentation using probiotic or non-probiotic starter cultures may significantly enhance the antioxidant capacity of walnut-based products. Outcomes are influenced by factors such as the type of walnut tissue used, the fermentation conditions, the choice of microbial strain, and the extraction method. This review critically summarizes and evaluates current findings on the impact of fermentation on the antioxidant properties of walnuts and walnut-derived products.