Prediction of Walnut Deterioration Using Kernel Oxidative Stability

Abstract

Monitoring walnut oxidation is essential to control walnut quality during storage. An accelerated oxidation method for differentiating the oxidative stability index (OSI) of walnut kernels was examined and the effects of instrument operational parameters such as temperature and airflow were evaluated. Four cultivars, Chandler, Solano, Durham, and Howard were analyzed at 110, 120, and 130 °C with 15, 20, and 25 L h−1 airflow. Analysis using 110 °C with 25 L h−1 yielded the lowest coefficients of variance (4.4) than other operational parameters; analysis using the same temperature at lower airflow, 15 L h−1, yield the highest coefficient of variance (10.5). Kernel OSI values were independent of airflow, however, dependence of temperature coefficient and Q10 were demonstrated. The results from selected parameters were correlated with fat and moisture content, peroxide value, UV absorbances, oil oxidative stability, hexanal, and rancidity to establish the relationships between OSI values and quality changes during storage. Using 0.5 g of ground kernels, at 110 °C with 25 L h−1 airflow gave a lower coefficient of variance and higher correlation with kernel quality and oxidative markers comparing to other combinations of operating parameters.

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

“…‘Howard’ presented an average of 3.5 and all kernels were classified as ‘amber’ or ‘dark amber’. Although no differences were found between cultivars before and during the first 4 weeks of storage, our results are consistent with previous reports where ‘Chandler’ was described as the brightest cultivar derived from the Californian breeding program [ 33 ] and ‘Howard’ demonstrated a higher predisposition to dark kernels during storage when compared to ‘Chandler’ [ 29 , 34 ].…”

“…Oxidative stability gives an estimation of food susceptibility to oxidation; it can be used to provide information on the hypothetical stability of a product as it generally correlates with shelf life [ 24 ]. Walnut oil and kernels oxidative stability has been reported in previous studies, and different parameters of temperature and airflow have been applied [ 25 , 26 , 27 , 28 , 29 ]. We used the parameters advised by Metrohm Instruments specifically for walnut oil; the same method was applied to the oil and kernel to allow a comparison of both matrixes.…”

“…Differences between cultivars in PV, K 268 , and kernel oxidative stability were significant before storage, showing that these methods can be used to predict samples susceptibility to oxidation and to evaluate storage time and conditions. As we recently demonstrated [ 29 ], direct measurements of oxidative stability using walnut kernels can open the possibility of a shelf-life assessment considering all nut matrix.…”

Synergistic rosemary extract with TBHQ and citric acid improves oxidative stability and shelf life of peanut

“…The oxidative stability index (OSI) was measured using Rancimat 892 (Metrohm Ltd., Herisau, Switzerland). The accurately weighed oil sample of 2.5 ± 0.1 g was placed in a reaction tube, and the OSI of the oil sample was tested at 120 • C with an airflow rate of 25 mL/min (Simoes Grilo et al, 2020).…”

Oxidative Stability of Walnut Kernel and Oil: Chemical Compositions and Sensory Aroma Compounds

“…According to Phatanayindee [10], the high susceptibility of unsaturated fatty acids to free-radical chain reactions in the presence of heat and oxygen leads to the formation of secondary products (e.g., hydroperoxides, malonaldehyde, and ketones) responsible for oxidative rancidity, discoloration, and poor nutritional value. For instance, a recent study from our group established positive correlations between storage conditions, oxygen availability, oxidative stability, and rancidity in four walnut cultivars [11]. Additionally, Jensen et al [12] investigated walnut oxidative rancidity under different storage conditions (i.e., light/darkness and 5/21 • C) for 25 weeks.…”