Walnut browning and rancidity as affected by N2 and CO2-containing control atmospheres

VICENTE AR, ORTIZ CM, FIELDS RP, LAMPINEN B, LABAVITCH JM, CRISOSTO, CH.

Congreso; Congreso AITEP; 2017

Nitrogen atmospheres are known to extend the postharvest life of Europeans walnuts. More recent studies have suggested that CO2 could exert beneficial effects on walnut shelf life. However, the relative effects of CO2 and N2 under constant control atmosphere storage has not been univocally established. The aim of this work was to evaluate the effect of air, 100% N2 and 100% CO2 on quality maintenance of Chandler and Howard shelled walnuts. Samp;les were stored at 35˚C for 0, 4 and 6 weeks and evaluated for visual (DFA) and instrumental (L*, Hue) color, ethanol soluble phenolics, free fatty acids (FFA), and peroxide value (PV). We also determined volatile aldehydes production by using Kitagawa testing tubes and gas chromatography coupled to mass spectrometry (CG-MS). Storage under both 100% N2 and 100% CO2 were highly effective in delaying browning, phenolic compounds degradation, and lipids hydrolysis, oxidation and cleavage as compared to air stored walnuts. However, CO2 atmospheres were more effective in delaying surface browning than storage under N2. Oil FFA increased during storage in nuts held in air and showed no clear trend in walnuts stored in CO2 and N2. Storage under either CO2 or N2 delayed the increase in PV. However, the inhibition of lipid peroxidation was more marked in CO2 controlled atmospheres. Results from this work support the need of fully anaerobic atmospheres to maximize shelled walnuts storage life. Full O2 removal was particularly beneficial for preventing phenolic antioxidant degradation in Howard walnuts. CO2 superseded N2 storage in terms of maintaining walnut color and oil stability. Further studies at normal storage temperatures are needed to fully establish the technological potential of the use of CO2 for shelled walnut CA storage.