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

Document Type : Research Article


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


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.


Buranasompob A, Tang J, Powers JR, Reyes J, Clark S, Swanson BG (2007) Lipoxygenase activity in walnuts and almonds. LWT - Food Science and Technology. 40(5), 893–899.
Buransompob A, Tang J, Mao R, Swanson BG (2003) Rancidity of walnuts and almonds affected by short time heat treatments for insect control. Journal of Food Processing and Preservation. 27(6), 445–464.
Cam S, Kilic M (2009) Effect of blanching on storage stability of hazelnut meal. Journal of Food Quality. 32(3), 369-380.
Cheniany M, Ebrahimzadeh H, Masoudi-Nejad A, Vahdati K, Leslie CA (2010) Effect of endogenous phenols and some antioxidant enzyme activities on rooting of Persian walnut (Juglans regia L.). African Journal of Plant Science. 4(12):479-487.
Christopoulos MV, Tsantili E, Papageorgiou Komaitis VMR (2008) Effects of package atmosphere and temperature on phenolics, total antioxidant capacity and colour in kernels of “franquette” walnuts during 8-month storage. ISHS Acta Horticulturae 858: III International Conference Postharvest Unlimited 2008.
Christopoulos MV, Tsantili E (2011) Effects of temperature and packaging atmosphere on total antioxidants and colour of walnut (Juglans regia L.) kernels during storage. Scientia Horticulturae. 131, 49-57.
FAOSTAT (2014) Retrieved September 27, (2014), Accessed 24 June 2019.
Farsi M, Fatahi Moghadam MR, Zamani Z, Hassani D (2018) Effects of scion cultivar, rootstock age and hormonal treatment on minigrafting of Persian walnut. International Journal of Horticultural Science and Technology. 5(2), 185-197.
Golzari M, Rahemi M, Hassani D,Vahdati K, Dalalpour Mohammadi N (2013) Protein content, fat and fatty acids of kernel in some persian walnut (Juglans regia L.) Cultivars affected by kind of pollen. Iranian Journal of Food Science and Technology. 10(38), 21-31. [In Persian]
Grosso AL, Asensio CM, Grosso NR, Nepote V (2020) Increase of walnuts' shelf life using a walnut flour protein-based edible coating. LWT Food Science and Technology. 118, 108712.
Gutteridge JMC (1986) Aspects to consider when detecting and measuring lipid peroxidation. Free Radical Research Communications. 1(3), 173–184.
Habibie A, Yazdani N, Kooshesh Saba M, Vahdati K (2019) Ascorbic acid incorporated with walnut green husk extract for preserving the postharvest quality of cold storage fresh walnut kernels. Scientia Horticulturae, 245, 193–199.
Han Y, Zheng Y, Li S, Mo R, Long X, Liu Y (2019) Effects of drying process with different temperature on the nutritional qualities of walnut (Juglans regia L.). Food Science and Technology Research. 25(2), 167-177.
Hassankhah A, Vahdati K, Rahemi M, Hassani D, Sarikhani Khorami S (2017) Persian walnut phenology: effect of chilling and heat requirements on budbreak and flowering date. International Journal of Horticultural Science and Technology. 4(2), 259-271.
Hosseini H, Ghorbani M, Sadeghi Mahoonak A and Maghsoudloo Y (2014) Effect of atmospheric contact surface and two normal storage temperatures on the oxidative stability of walnut kernels. Iranian Food Science and Technology Research Journal. 9(4), 348-358. [In persian]
Jaleh Rezaei H (1999) Effective factors in preserving almond kernels.  Proceeding of the first national conference on Almond (Abstract book), August 24-27, 1999 Shahrekord - Iran. [In Persian]
Jensen PN, Sørensen G, Engelsen SB, Bertelsen G (2001) Evaluation of quality changes in walnut kernels (Juglans regia L.) by Vis/NIR spectroscopy. Journal of Agricultural and Food Chemistry. 49(12), 5790–6.
Koyuncu M, Koyuncu F, Bakir N (2003) Selected drying conditions and storage period and quality of walnut selections. Journal of Food Processing and Preservation. 27(2), 87–99.
Laskawy G, Senser F and Grosch W (1983) Storage stability of roasted hazelnuts. Review for Chocolate, Confectionery and Bakery. 8(3), 21-23.
Leahu A, Oroian M, Ropciuc S (2016) The quality and stability of walnut oil under the influence of storage conditions. book: Scientific papers of Animal Science Series, University of Agricultural Sciences and Veterinary Medicine, Iasi, Romania. 65, 230-236.
Ling B, Hou L, Li R, Wang S (2014) Thermal treatment and storage condition effects on walnut paste quality associated with enzyme inactivation. LWT-Food Science and Technology. 59(2), 786-793.
Mate JI, Saltveit ME, Krochta JM (1996) Peanut and walnut rancidity: effects of oxygen concentration and relative humidity. Journal of Food Science. 61(2), 465-469.
Mazinani S, Elhamirad AH, Piravi Vanak Z, Naghavi MR (2011) Evaluation of the thermal stability, antioxidant activity, total phenolics and fatty acids profile in some edible nut oils (pistachio, walnut, almond). 3(2), 45-52. [In persian]
Mexis SF, Badeka  AV, Riganakos KA, Karakostas KX and Kontominas MG (2009) Effect of packaging and storage conditions on quality of shelled walnuts. Food Control. 20(8), 743–751.
Mitchell JH, Malphrus RK (1977) Lipid oxidation in spanish peanuts: the effect of moist heat treatments. Journal of Food Science. 42(6), 1457-1461.
Parvaneh V (2006) Quality control and the chemical analysis of food.University of Tehran Press. pp. 2,11-13, 212-215, 217-219. [In persian]
Prabhakar JV, Hemavathy J (1979) Influence of antioxidants, inert atmosphere and polyethilene packing on shelf life of walnut kernels. In First symposium of Association of Food scientists and Technologists. pp. 48.
Salajegheh F, Tajeddin B (2020) The Effect of Modified Atmosphere Packaging and Packaging Material on Walnut Kernel Shelf-life. Journal of Research and Innovation in Food Science and Technology. 8(4), 357-368.
Senter S, Forbus W, Nelson S, Wilson R, Horvat R (1984) Effects of dielectric and steam heating treatments on the storage stability of pecan kernels. Journal of Food Science. 49(3), 893-895.
Severini C, Pill TDE, Baiano A, Gomes T, Agro-zootecnici S (2003) Autoxidation of packed roasted almonds as affected by two packaging films. Journal of Food Processing Preservation. 27, 321–335.
Tajeddin B (2004) The effect of polymer films on walnut packaging. Pajouhash and Sazandegi. 62, 2-8. [In Persian]
Talebi Habashi R, Zomorodi S, Talaie A, Kalateh Jari S (2019) Evaluation of shelf life of walnut kernel coated by antioxidants in combination with packaging under different storage conditions. Journal of Postharvest Technology. 7(3), 87-95.
Tatarov P, Sandulachi E, Ivanova R, Baerle A (2017) Quality changes in oil of walnut (Juglans regia L.) during storage. Lucrări tiinifice. Editura “Ion Ionescu de la Brad. 187-190.
Young CK, CS (1991) Exploring the partnership of almonds with cereal foods. Cereal Foods World. 36(5), 412–418.
Zacheo G, Cappello MS, Gallo A, Santino A, Cappello AR, Agroalimentari B, Prunus A (2000) Changes Associated with Post-harvest Ageing in Almond Seeds. LWT-Food Science and Technology. 33, 415–423.
Ziaolhagh H (2011, September) Study on the best packaging material and packaging conditions on the rancidity of almond kernels. In 1 International Symposium on Mycotoxins in Nuts and Dried Fruits. 963. 113-118.
Ziaolhagh H (2013) Effect of packaging on shelf life of almond kernels. International Journal of Agriculture and Crop Sciences. 5(1), 15-20.
Ziaolhagh S, Mazaheri Tehrani M, Razavi SMA, Rashidi H (2017) Roasting process optimization of walnut kernels for the preparation of walnut cream using response surface methodology. Journal of Nuts. 8(1), 31-40.