Walnut (Juglans regia L.) Volatile Compounds Indicate Kernel and Oil Oxidation

Area of Science:

• Food Science and Technology
• Agricultural Chemistry
• Nutritional Biochemistry

Background:

• Walnut quality is significantly impacted by kernel oxidation and pellicle darkening.
• Effective monitoring of oxidation is essential throughout the supply chain, from production to consumption.

Purpose of the Study:

• To identify reliable chemical and volatile markers for assessing walnut kernel oxidation during storage.
• To compare the oxidative stability of 'Chandler' and 'Howard' walnut varieties.

Main Methods:

• Analysis of chemical oxidation parameters (peroxide value, UV absorbances), fatty acid profile, tocopherols, phenols, and volatiles in walnut kernels over 28 weeks.
• Utilized multivariate analysis to group samples based on oxidative levels.
• Evaluated specific volatile compounds as potential oxidation markers.

Main Results:

• Oxidation increased over storage, indicated by rising peroxide values, UV absorbances, and volatile concentrations, while phenols and tocopherols decreased.
• 'Chandler' walnuts exhibited better oxidative stability with lower peroxide values and higher stability compared to 'Howard'.
• Specific volatile compounds, including aldehydes, ketones, alcohols, and acids, were identified as effective markers for distinguishing oxidation levels in walnut kernels.

Conclusions:

• Kernel volatile analysis provides a practical and efficient method for monitoring walnut oxidation during storage, eliminating the need for prior fat extraction.
• The identified volatile compounds serve as valuable biomarkers for predicting and managing walnut quality.