Storage Temperature, Relative Humidity, and Time Effects on the Organoleptic Profile of Walnut Kernels

Abstract

Four cultivars of English walnut (Juglans regia) were evaluated by a trained taste panel after 6 and 12 months of storage. English walnuts were stored at 5, 15, or 25 °C, and at 40%, 60%, or 80% relative humidity within each temperature. Principal component analysis was used to compare taste, texture, and aroma attributes evaluated by the taste panel to objective indicators of English walnut quality including water activity, moisture content, free fatty acids, peroxide value, hexanal content, and kernel color. Temperature was found to significantly impact English walnut oxidation and perceived rancidity, whereas storage at high relative humidity affected English walnut texture and accelerated quality loss. Water activity was more strongly correlated to textural changes than moisture content. The effect of relative humidity was more pronounced at lower temperatures, leading to increased hydrolytic rancidity and free fatty acids. Peroxide value had higher and more significant correlation to sensory attributes related to rancidity than hexanal. Free fatty acids were not correlated to the rancid sensory attribute, but were significantly correlated to bitter. English walnuts stored at 5 °C with 40% or 60% relative humidity were associated with the sweet sensory attribute and L* value (light color). Kernel darkening was associated with bitter and rancid, but a causal relationship is unknown. Sensory quality of English walnuts is complex and requires further study to establish thresholds for chemical indices of English walnut quality loss based on organoleptic perception.