J Food Process Preserv. 2019;e13923. wileyonlinelibrary.com/journal/jfpp | 1 of 8 https://doi.org/10.1111/jfpp.13923 © 2019 Wiley Periodicals, Inc. 1 | INTRODUCTION Fruit cultivation is important to obtain food, fiber, biofuel, med‐ icine and other products, and fruit trees used to sustain and en‐ hance human life. Fruit cultivation was also the key development in the rise of sedentary human civilization (Oztemiz, Kuden, Nas, & Lavkor, 2017; Vijayan, Chakraborti, Ercisli, & Ghosh, 2008). All over the world, peanuts ( Arachis hypogaea L.) are used to produce peanut butter. Botanically, they are legumes; however, due to their chemi‐ cal composition, including the fatty acid profile, they are considered as nuts. In China, which is a leader in their production, grow nearly 8,000 varieties of Arachis hypogaea L. In 2017, their production in this region of the world was more than 17.40 million tonnes. About 40% of the global production of peanut butter takes place in the United States (Gong et al., 2018), where its mean annual consump‐ tion is 1.5 kg per person (Ewers, 2016). Peanuts butter is produced by mixing crushed and roasted peanuts, which proportion in the product reaches as much as 81% (Ewers, 2016). The remaining ingre‐ dients are sugar, salt, and food additives. The unique taste and odor of the product made it a favorite snack in the world. Walnut ( Juglans regia L.) is a plant belonging to the Juglandaceae family. The native region of walnut origin is Asia Minor, the Himalayan chain, and Kyrgyzstan. This plant arrived in Europe before the ad‐ vent of Roman times (1,000 BC). Their leading producers are China, Received: 7 November 2018 | Revised: 23 January 2019 | Accepted: 24 February 2019 DOI: 10.1111/jfpp.13923 INVITED REVIEW Type of heat treatments on walnut fruits affects physicochemical content of walnut butter Karolina Pycia 1 | Ireneusz Kapusta 1 | Grażyna Jaworska 1 | Piotr Kuźniar 2 | Joanna Kaszuba 1 1 Faculty of Biology and Agriculture, Department of Food Technology and Human Nutrition, University of Rzeszow, Rzeszow, Poland 2 Faculty of Biology and Agriculture, Department of Food and Agriculture Production Engineering, University of Rzeszow, Rzeszow, Poland Correspondence Karolina Pycia, Faculty of Biology and Agriculture, Department of Food Technology and Human Nutrition, University of Rzeszow, Zelwerowicza 4 St., 35‐601 Rzeszow, Poland. Email: kpycia@ur.edu.pl Abstract The experimental material was walnut butter obtained from walnut fruits subjected to baking, roasting, and heating in the microwave field. It was found that heat treat‐ ment of walnut fruits increased the contents of fat, antioxidant capacity, total poly‐ phenol content, color and tocopherol content in walnut butter. Butter prepared from the microwaved walnut fruits was characterized by the lowest hardness (0.16 N), ad‐ hesiveness (0.03 mJ), and gumminess (0.15 N). The content of total polyphenols was the highest in butter from the microwaved walnut fruits (970.2 mg GAE/100 g d.m.) and the smallest in the raw walnut butter (557.9 mg GAE/100 g d.m.). In the polyphe‐ nol profile, 18 compounds were identified, mainly from the ellagitannin class. Their content ranged from 2.68 mg/g DM (raw) up to 7.55 mg/g d.m. (microwayed) depend‐ ing on the heat treatment applied. In turn, four tocopherol isoforms: α, β, γ, and δ were identified. Practical applications In the world, the raw material for the production of peanut butter are hazelnuts. In contrast, walnuts compared to hazelnuts are much more valuable under the nutri‐ tional value, and the cream based on them has interesting sensory properties. In ad‐ dition, health‐related properties and quality of walnut‐based butter may depend to a large extent on the type of heat treatment the nuts have undergone. Therefore, the authors of the study decided to investigate this issue. The results of the research described in the article can be used to develop a new food product.