Tailoring Preservation to Form: A Comparative Review of Postharvest Technologies for Three Types of Fresh Walnuts

Fresh walnut is an economically important nut variety, highly appreciated by consumers for its rich nutritional profile and desirable sensory qualities. However, its short postharvest shelf life and susceptibility to spoilage severely limit the market supply window, making fresh products available only within 1-2 months after harvest. Current preservation research primarily focuses on walnuts in a single form, such as fresh in-hull walnuts, fresh in-shell walnuts, or fresh walnut kernels, and lacks a systematic comparative study on the preservation characteristics across these different forms. To address this gap, this review begins by examining fresh walnuts from the perspective of these three distinct forms. It systematically compares their physiological structures, preservation traits, and physiological metabolic changes during storage. The analysis delves into how the unique physiological structure of each form regulates preservation efficacy, thereby clarifying the core technical challenges and divergent priorities for preserving different forms of fresh walnuts. The review summarizes universal, green, and safe preservation techniques applicable to all three forms while also outlining tailored strategies specific to the characteristics of each form. This perspective aims to guide the integrated innovation and practical application of preservation technologies throughout the fresh walnut industry chain. Future research should focus on constructing a segmented, multi-level preservation technology system for the three forms of fresh walnuts.