Overall quality and oxidative damage in packaged freshly shelled walnut kernels during cold storage

In this study, the effect of passive- and active-modified atmosphere packaging (PMA and MAP with 70% N2 and 30% CO2) using semipermeable and barrier films on physicochemical and enzymatic properties and quality of freshly shelled walnut kernels stored at 6 °C for 18 days were investigated. Changes in physicochemical such as free fatty acidity content, peroxide value, colour and enzymatic traits such as polyphenol oxidase, lipoxygenase were tracked in the fresh kernels during cold storage in different packaging systems. The MAP system inhibited polyphenol oxidase activity, delayed browning of tegumented kernels, and helped in maintaining a high total polyphenol content. The PMA system preserved membrane integrity by inhibiting lipoxygenase activity and malondialdehyde accumulation with values of 3.26 ± 0.05 nmol hydroperoxides min−1 g−1 dry weight and 10.90 ± 0.50 nmol g−1 dry weight, respectively after 18 days of cold storage. Moreover, this system inhibited free fatty acid formation and it was characterised by lower peroxide values with 5.17 ± 0.04 mEq O2 kg−1 oil at the end of storage. Principal component analysis provided a global view of the differential qualitative responses of fresh walnut kernels in different packaging systems during cold storage. Our results show that packaging systems could be utilised to extend postharvest shelf life, improve qualitative traits, and inhibit enzyme-mediated browning of fresh kernel walnuts during cold storage.