Oil composition in stored walnut cultivars—quality and nutritional value

Abstract

The effects of temperature and O2 availability on quality attributes and nutritional value of oil in four walnut (Juglans regia L.) cultivars (Chandler, Hartley, Franquette, and Ioli) were investigated. Dried kernels, all of initial high quality, were packaged under air or N2 or CO2 and stored at 1 °C or 20 °C for 12 months. Results showed that the saturated fatty acids (SFA) myristic, palmitic, stearic, and arachidic remained stable during storage, whereas the unsaturated palmitoleic, oleic (OL), gondoic, linoleic (LL) and linolenic (LN) decreased, with the stable vaccenic being the exception. Rancidity, assessed as free fatty acids and peroxide value, increased after 12 months, and rancidity evolution found to be correlated with LL and LN, but not with OL. In all cultivars, low temperature and N2 or CO2 prevented additively the fatty acid (FA) losses and rancidity increases. The best results were obtained in walnuts stored at 1 °C under N2 or CO2, while storage at 20 °C under air led to the greatest product deterioration. However, storage at 20 °C under N2 or CO2 and at 1 °C under air showed intermediate results and similar among them. The cultivar affected the kernel oil content and FA profile initially, as well as, the FA decreases and rancidity development during storage. The omega‐6/omega‐3 ratio largely depended on cultivar and was affected by storage conditions. Overall, the storability of the studied cultivars in descending order was Chandler > Hartley, Franquette > Ioli. Practical applications: Storage at 1 °C under N2 or CO2 for 12 months retained the peroxide value (PV) lower than 3 meq O2 kg−1 oil and the free fatty acids (FFA) up to 0.6%, cut‐off values for acceptable walnuts, as suggested by the walnut industry in California. Storage at 20 °C under N2 or CO2 increased the PV value up to 10 meq O2 kg−1 oil, being the upper acceptable limit according to panel tests in studies. For energy savings, the 12‐months storage at 20 °C with low O2 availability can substitute the storage at 1 °C under air. Rancidity development and nutritional value related to fatty acids largely depended on cultivar. Thus, the cultivar factor should also be considered for storage purposes and according to the destination markets. Effects of temperature and packaging atmosphere on rancidity and nutritional value related to oil composition in stored dried kernels of walnut (Juglans regia L.) cultivars. The present results are summarized in the bi‐plot (combination of score and load plots) of Principal Component Analysis. Each color corresponds to each cultivar. Rhombuses, circles, squares, and triangles, corresponding to different storage conditions, indicate the position of each walnut sample in score plot. Daggers indicate the position of major fatty acids and indicators of rancidity in load plot.

Kernel oil content and oil composition in walnut (Juglans regia L.) accessions from north‐eastern Italy

“…Although the kernel moisture could vary as a function of season, harvest time and environmental conditions, both wild accessions and commercial cultivars had the same moisture content of about 3.5% (w/w) (data not shown) after drying, suitable for long storage . This value was in agreement with those reported by Amaral et al and Pereira et al and lower than those reported in other studies …”

“…Commercial varieties generally showed a higher mean oil content than wild genotypes, but the difference was quite small (∼4% w/w) (Table ). The oil content of the commercial varieties was comparable to the literature data for the same cultivars . However, there were some differences between commercial varieties.…”

“…21 This value was in agreement with those reported by Amaral et al 3 and Pereira et al 4 and lower than those reported in other studies. 22,23 Oil content Oil content is reported in Table 2. Commercial varieties generally showed a higher mean oil content than wild genotypes, but the difference was quite small (∼4% w/w) ( Table 2).…”

Effects Of Storage Conditions On The Quality Of Unripe Hazelnuts In The Husk

“…Consumers also feel convinced that nuts in the husk are fresh and were harvested in the same year. An argument supporting the consumption of unripe hazelnuts sold in the husk is their higher content of polyphenols and some fatty acids, as well as better palatability (Ebrahem et al 1994;Farinelli et al 2001;Ciemniewska-Żytkiewicz et al 2015). The higher water content, reflected in higher weight, with 41% share of the husk, is an advantage, important for producers (Ebrahem et al 1994;Zdyb 2012;Ciemniewska-Żytkiewicz et al 2015).…”

“…The results of numerous experiments on the storage of different kinds of ripe nuts suggest that controlled and modified atmosphere, aside from having a positive effect on the sensory features and chemical composition, can reduce nut weight losses, thus enabling longer storage (Maté et al 1996;Maskan & Karataş 1998;Mexis et al 2009;Christopoulos & Tsantili 2011;Ghirardello et al 2014, Christopoulos & Tsantili 2015.…”