The Effect of Thermal Pretreatment and Packaging Conditions on the Shelf-life of Walnut Kernels

Subject Areas : Walnut

Seyedhamidreza Ziaolhagh ¹ , Hamed Fatemian ² , Farzad Goodarzi ³

1 - Agricultural Engineering Research Department, Agricultural and Natural Resources Research Center of Semnan Province (Shahrood), AREEO, Shahrood, Iran
2 - 2Agricultural Engineering Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Karaj, Iran
3 - Agricultural Engineering Research Department, Hamedan Agricultural and Natural Resources Research and Education Center, AREEO, Shahrood, Iran

Received: 2019-11-12 Accepted : 2020-06-23 Published : 2020-06-30

Keywords: Oxidation, Walnuts, shelf life, Packaging, Nuts,

Abstract :

This study aimed to extend the shelf life of walnut kernels by appropriate packaging conditions and physical methods. For this purpose, the kernels were heated at 50 or 70°C for 2 or 10 minutes. About 100g of walnuts were packed in low-density polyethylene (LDPE) packages under ordinary, vacuum or nitrogen conditions. Samples were stored for 18 months at room temperature. Peroxide value and acidy number were determined after 6, 12 and 18 months of storage. The results of the variance analysis showed that the effect of packaging conditions on peroxide value, and the effect of all factors on the acidity of the samples were significant (p < 0.01) for the 6- month storage. Walnuts packaged under nitrogen conditions had lower peroxide value than others, and the samples preheated at 70˚C had a lower acidity. After 12 months of storage, the effect of all factors on peroxide and the acidy number of walnuts were significant (p < 0.01). The lowest peroxide value and acidity were observed for walnuts preheated at 50˚C for two minutes. Finally, based on the obtained results, we recommend that walnut kernels should be preheated at 70˚C for two minutes and packaged under nitrogen or vacuum conditions. In this way, they could be stored for six months without perceived oxidation. The oxidation of walnuts would increase during storage for 12 to 18 months gradually, and their peroxide value and the acidity would exceed the desirable limits.

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