Effects of cold plasma treatment on antioxidants activity, phenolic contents and shelf life of fresh and dried walnut (Juglans regia L.) cultivars during storage

• Plasma jet treatment is effective for decontamination of fresh and dried walnuts.
• Cold plasma treatment had no significant effect on phenolic content & antioxidant activity of cultivars after treatment & during storage.
• For decontamination of walnuts by cold plasma the cultivars of walnuts should be considered.

The present study investigated the effect of cold plasma on the stability of the total phenolic content, antioxidant activity, and inhibition of microbial growth in dried and fresh walnut cultivars during storage. In this study four walnut cultivars named Mazandaran, Toyeserkan, Taleghan and Shahmirzad was used for comparison. The results indicated that, although 11 min of plasma jet treatment caused complete elimination of Aspergillus flavus that had been inoculated onto fresh walnut cultivars, the amount of decrease on the inoculated walnuts was different for different cultivars. This difference may be caused by the differing volumes and thickness of the walnut cultivars. In addition, 10 min of plasma jet treatment eliminated Aspergillus flavus from the dried walnuts. After 15 and 30 d of storage (4 °C), the number of survivors in the samples for 11 min was negligible. The 11 min plasma jet treatment had no effect on the total phenolic content and antioxidant activity of the dried and fresh walnuts. The effect of plasma jet treatment on the total phenolic and antioxidant activity of all cultivars was the same. An increase in the total phenolic content and antioxidant activity after 15 and 30 d of storage (4 °C) was observed in the control and treated samples. Changes in the total phenolic content and antioxidant activity in the control sample and treated walnuts showed a similar pattern.