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    Changes in oxidative stability, antioxidant capacity and phytochemical composition of Pistacia terebinthus oil with roasting
    (Elsevier Sci Ltd, 2011) Durmaz, Gokhan; Gokmen, Vural
    The effect of roasting on oxidative stability, antioxidant capacity and the content of antioxidant phytochemicals in Pistacia terebinthus oil was investigated. Oils were extracted from P. terebinthus fruits roasted at 180 degrees C for 0-40 min. Roasting was found to cause an increase in the passage of phenolic compounds to the oil whereas the level of tocopherols, lutein and beta-carotene was decreased. Antioxidant capacity and oxidative stability of P. terebinthus oil increased with roasting. As an indicator of the presence of Maillard reaction products in oil, hydroxymethylfurfural (HMF) level and colour intensity was measured and found to increase with increasing roasting time. Fatty acid composition was not affected significantly by roasting. (C) 2011 Elsevier Ltd. All rights reserved.
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    Effect of refining on bioactive composition and oxidative stability of hazelnut oil
    (Elsevier Science Bv, 2019) Durmaz, Gokhan; Gokmen, Vural
    In this study, the effect of refining process on the content of phytochemicals, antioxidant capacity and oxidative stability of hazelnut oil was investigated. The oil samples were taken at the consecutive steps of hazelnut refining process and analyzed for some compositional properties along with the antioxidant capacity and oxidative stability. The results have shown that, carotenoid content of the hazelnut oil was decreased during the refining process. The main carotenoids of hazelnut oil were found to be lutein and zeaxanthin and these compounds were lost completely during bleaching step of the refining. On the other hand, phenolic compounds and tocopherols were also partly removed from hazelnut oil to a degree. Loses in antioxidant compounds caused a clear decrease in antioxidant capacity measured in either the oils or polar extract of oils. Oxidative stability of the oil samples was measured by Rancimat method and it was found that neutralization caused an increase in oxidative stability compared to the crude oil. However, deodorization step caused a slight decrease in oxidative stability probably as a result of partial removal of tocopherols at this stage.
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    Hazelnut skin powder: A new brown colored functional ingredient
    (Elsevier Science Bv, 2014) Ozdemir, Kubra S.; Yilmaz, Cemile; Durmaz, Gokhan; Gokmen, Vural
    Hazelnut skin arises as a by-product in the roasting process of hazelnuts. This study aimed to investigate the potential of its utilization as a brown colored functional ingredient. Chemical composition analyses revealed that hazelnut skin is a very rich source of dietary fibers (67.7%) and phenolic compounds (233 mg GAE/g). Its oil fraction (14.5%) was found to contain very high amounts of tocopherols (2.77 mu g/g) and oleic acid (75.2%). After defatting, coarse and fine hazelnut skin powders were obtained by low and high shear homogenization. High shear homogenization was performed at different pressures (10, 20 and 30 ksi) for different pass cycles (1, 3, 5 and 10). The powder samples were analyzed for particle size distribution, color, individual phenolic compounds, total phenolic content, and total antioxidant capacity. A desirable low micron particle size for the hazelnut skin for incorporation into food formulations was achieved by means of high shear homogenization, meanwhile there was no significant change in phenolic composition and antioxidant capacity. (C) 2014 Elsevier Ltd. All rights reserved.