www.ejlst.com European Journal of Lipid Science and Technology Review Article Nutritional Composition, Extraction and Utilization of Wheat Germ Oil: A Review† Kashif Ghafoor*,1, Mehmet Musa Özcan2, Fahad AL-Juhaımı1, Elfadıl E. Babıker1, Zaidul Islam Sarker3, Isam A. Mohamed Ahmed1, Mohammed Asif Ahmed1 1 Department of Food Science & Nutrition, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia. 2 Department of Food Engineering, Faculty of Agriculture, Selcuk Universty, 42031 Konya, Turkey 3 Faculty of Pharmacy, International Islamic University Malaysia (IIUM), Kuantan Campus, Kuantan 25200, Pahang, Malaysia Running title: Nutritional components in wheat germ oil Key words: Wheat germ oil, extraction, composition, fatty acids, tocopherol, health benefits Article *Correspondence: Associate Professor Dr Kashif Ghafoor, PO Box 2460, Department of Food d Science & Nutrition, College of Food and Agricultural Sciences, King Saud University, Riyadh 11451, Saudi Arabia E-mail: [email protected]; [email protected] Fax: +966 11 4618394 Phone: +966 11 4678403 †This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to ccepte differences etween this version and the Version of Record. Please cite this article as doi: [10.1002/ejlt.201600160]. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim A Received: April 7, 2016 / Revised: November 10, 2016 / Accepted: December 16, 2016 1 www.ejlst.com European Journal of Lipid Science and Technology Abstract Wheat germ is a by-product of wheat milling from which wheat germ oil (WGO) can be obtained using different techniques. For a better quality WGO, techniques such supercritical fluid fractionation, molecular distillation and other innovative methods can be adopted. WGO is composed of nonpolar lipids, glycolipids, phospholipids, alcohols, esters, alkene, aldehydes, tocopherols, n-alkanols, sterols, 4-methyl sterols, triterpenols, hydrocarbons, pigments and volatile components. The most abundant WGO fatty acid is linoleic acid which composes 42-59% of total triglycerides followed by palmitic (16:0) and oleic acids (18:1). The stearic acid, a saturated fatty acid, is usually less than 2%. WGO is rich in tocopherols particularly vitamin E. It contains α-tocopherol and β-tocopherol which gives various health benefits to it. It is being used in medicine, cosmetic, agricultural and food industry. Some of its applications include production of vitamins and food supplements, annimal feed and biological insect control and for treating circulatory/cardiac disorders and weaknesses. More studies are required for producing better quality WGO such as application of more innovative and optimized techniques that can increase its health benefits and hence utilization. More Article mechanistic approaches for extraction, evaluation and utilization of WGO can help in making this by-product of wheat processing more valuable. d Practical Application Wheat is a major food crop around the globe and produced and processed in large quantities. Its by-products such as wheat germ can be used to obtain value added products. Oil obtained from wheat germ is found to be a good source of various nutritionally beneficial constituents and carry important health benefits and functional properties. The review will help researchers to carry out further research to improve processing and the quality of oil besides emphasizing on its beneficial aspects. It will also assist in better utilization of this wheat by-product to develop value added products and nutraceuticals after carrying out further studies. 1. Introduction Wheat is one the most important food crops which is usually milled to produce flour and other ccepte products. Wheat germ (2-3% of grain) can be separated as a by-product during wheat milling. It is considered an important by-product and can be used in different applications such as food, pharmaceutical and other biological purposes [1]. Naturally, there exists a separation A line between endosperm and scab of the germ due to which its separation from wheat grain is 2 www.ejlst.com European Journal of Lipid Science and Technology considered easy [2, 3]. The embryo consists of two parts, the embryonic axis and the scutellum which is a storage organ [3, 4]. The germ contains high amounts of protein (25%), sugar (18%), oil (16% of the embryonic axis and 32% of the scutellum) and ash (5%). The wheat germ oil (WGO) is rich in phosphorus (1.4 g/kg), contains no starch but high vitamins B contents. Vitamin E can also be as high as 500 ppm [4, 5]. The longitudinal section of a wheat grain is shown in Figure 1 to demonstrate the general structure and location of germ in the grain. The general chemical composition of the commercially available wheat germ is shown in Table 1. In another study it was stated that germ constitutes about 2.5-3.5% of the kernel and its oil contents range between 10 to 15% [4], of which 2-6% are unsaponifiable matters [6], containing mainly phytosterol and tocopherol [7]. The tocopherol content of WGO is the highest among vegetable oils; can reach up to 2500 mg/kg and α-tocopherol (60%) is predominant [8]. Phytosterols (mainly sitosterol and campesterol) contents of WGO are also generally higher than other commercial oils [7]. It is also contains high levels of unsaturated fatty acids of which 80% is linolenic and linoleic acids. The consumption of these fatty acids Article is important for human health as they are considered as essential (cannot be synthesized in the organism). They also help in synthesis of a group of hormones called prostaglandins that are d important for their role in muscle contractions and for anti-inflammatory properties [8]. WGO, due to its bioactive compounds, is associated with different nutritional and health benefits such as reduction of plasma and liver cholesterol levels, improving physical endurance and delaying aging effects. Some of the positive health effects are also due to polycosanol and especially octacosanol contents of WGO [7]. The higher amount of vitamin E acts as stabilizer for cell membrane by protection of unsaturated fatty acids from peroxidase cleavage [6]. WGO is also used in foods, biological insect control agents and pharmaceutical formulations [9]. The aim of current review is to discuss physico-chemical, compositional and bioactive properties of WGO so as to promote better utilization in formation of different value added products and further research. The review also discuss the current and potential utilization of WGO. ccepte 2. The Characteristics, Composition and Bioactive Contents of Wheat Germ Oil 2.1. Physico-Chemical Properties The values for refractive index, specific gravity, iodine value, saponification value and A unsaponifiable matter of WGO are 1.4700-1.4800, 0.9000-0.9300, 120-130, 184-185 and 1.5- 7.8, respectively. The free fatty acid content is usually lower than 60 g/kg if oil is stored 3 www.ejlst.com European Journal of Lipid Science and Technology without stabilizing. The free fatty acid content of solvent extracted WGO is lower than that obtained by pressing. The free fatty acid content also depends on oil refining process [10, 11]. The lipase enzyme produce free fatty acids by converting triglyceride into diglyceride and monoglyceride [12]. Megahed [12] carried out a study about lipase activity of WGO during periodical storage and observed that the acid value of oil gradually increased and reached up to maximum of 23.46 (mg/g) by comparison with initial value (14.88 mg/g). However, during lipase inhibition at 70°C for 15, 30 and 60 minutes, the acid value decreased from 14.88 mg/g to 12.02 mg/g after 60 minutes. It was determined that the acid value reached to a suitable value by repressing of enzyme activity at 70°C for 30 minutes. Jha et. al [13] studied inactivation of lipase enzyme in WG using γ-irradiation and observed 16.75% lipase inhibition at 12 kGy radiation dose which was increased up to 31.2% at 30 kGy dose. The total lipase inactivation could be achieved at radiation doses above 35 kGy that can enhance the shelf life of WG products. Other treatments have also been studied in relation to improving the shelf life of WG which include treatments using antioxidants, infra- red, epoxy compounds, moisture reduction and microwave [14-17]. However these treatments may Article negatively affect the nutritive value of WG products. Hence, selection of a suitable method for enzyme inactivation and germ stabilization might be important for commercialization of d WGO and other WG products. The constituents isolated from WGO and identified are alcohols, esters, alkene and aldehydes. The volatile compounds present in oil are responsible for the flavor of oil and play their role in consumer preference. The main volatile components are hexanal (15.97%), 2-methyl-2-butene (10.43%), 2.4-heptadienal (8.53%) and limonene (6.83%) [18]. Due to the presence of polyunsaturated fatty acid, mineral and elemental contents in high quantities, WGO is dietetically valuable. The nutritionally important macro and micro elements constitute a substantial part of oil composition [19]. Niu et al. [18] studied the thermal behavior of WGO and found that the values for onset temperature of melting, the peak temperature and ΔH were -29.03°C, -14.61°C and 21.54 J/g, respectively. While the weight loss substantially occurred in the 280-500°C range, the complete weight loss occurred at 516.02°C. The oxidative stability is important for WGO as for all other oils. Niu et al. [18] specified the oxidative induction time of WGO which was 3.81 h. The oils being rich in ccepte unsaturated fatty acid are easily soluble, prone to oxidation and can become rancid. WGO melts easily, however it is more stable due to its high amount of tocopherol compared to the oils with high amounts of unsaturated fatty acid.