# Prediction of Walnut Deterioration Using Kernel Oxidative Stability
## 1 Introduction  
Walnuts are known to contain not only high levels of triglycerides, but also high proportions of unsaturated fatty acids (oleic acid, linoleic, and linoleic acids), which have long been considered as relevant health-promoting components. Unsaturated fatty acids can be easily oxidized in the presence of oxygen, light, moisture, and heat [1]. Fatty acid oxidation is initiated by reactive oxygen species, which lead to the formation of various primary and secondary products [2]. These products result in the modification of major quality characteristics such as color, flavor, aroma, and nutritional value, affecting the suitability of a food product [1].  
Fatty acid compositions of walnuts contribute to a shorter shelf life compared to other nuts, which presents challenges during storage and limits the usage as a snack mix product [1]. Since lipid oxidation occur slowly at room temperature, accelerated methods can be applied to estimate the oxidative stability of a product in a more rapid time frame, particularly if the temperature is exponentially related to the rate of reaction [3]. Common accelerated oxidation methods include the active oxygen method, Schaal Oven method, and Rancimat method [4]. Rancimat method observes the production of volatile organic compounds while the other two methods look at peroxide formation during oxidation. Rancimat instrument is simple to use and has good reproducibility [5; 6].  
Rancimat method was developed by [PERSON] and [PERSON] (1974) [7] to measure oxidative stability and has been widely used to determine lipid oxidation and predict the shelf life of oils and fats [8].  
This method has been vastly used to study the effects of antioxidants, edible coatings, and storage conditions of nut oils [9; 10; 11]. However, measuring oxidative stability through an accelerated method can lead to an over or underprediction of the actual shelf life due to different mechanisms of peroxidation that occur at room temperature [4; 12]. Consequently, the study and use of the proper operational parameters is essential to avoid misleading results in accelerated oxidation methods. Nut oxidation depends on fat content, moisture, fatty acid composition, and antioxidant content; these characteristics may vary significantly with cultivar and year of production [13; 14; 15].  
The use of Rancimat for high-fat solid-foods is not commonly used [16], and there are no studies on the effect of temperature and flow parameters on oxidative stability index (OSI) values for walnut kernels. The aim of this work was to study the capability of this accelerated oxidation method in differentiating oxidative stability of walnut kernels and evaluate different operating parameters of the instrument. Four walnut cultivars were analyzed using Rancimat at three airflow rates and three temperatures to allow the identification of the operational parameters with the least variance coefficient to measure oxidative stability. To study the relationships between oxidation levels and OSI values of walnut sample, we also measured kernel OSI, quality parameters, and oxidative markers over six months of storage. Findings from this study would help monitor the oxidative quality of walnut kernels without the need for oil extraction prior to analysis.