Introduction
Pecan (Carya illinoinensis ) is a woody oil crop of the Juglandaceae. The advantages of pecan kernel have been widely reported in the literature (Lv and Liu, 2005; Wang et al., 1998; Wang et al., 2012). Pecan kernel contains up to 65-75% oil and the dry matter remaining is rich in proteins. Pecan oil was considered a healthy specialty gourmet product (Cockerham et al., 2012; Al Juhaimi et al., 2018). The functional advantages of de-oiled pecan meal have also been reported in the literature (Marchetti et al., 2017). Furthermore, the advantages of vegetable proteins over animal proteins have been stated in the literature (Asgar et al., 2010).
A method which is able to simultaneously produce high quality oil and de-oiled meal is generally preferable to other methods for processing pecan kernels. Solvent extraction has the following disadvantages: 1) not environmental friendly, 2) explosion and fire risk, 3) not safe for consumption before the refinement of the crude oils extracted, 4) costly to operate, and 5) adverse effect of solvent on human health (Tu et al., 2017; Latif and Anwar, 2009; Environmental Protection Agency, 1999) though it can efficiently produce high quality oil and de-oiled meal on a commercial scale (Johnson, 2000; Lamsal et al., 2006; Pare et al., 2014). Conventional high temperature pressing produces dark de-oiled meal with high residual oil content (inadequate recovery of oils) and denatured proteins lacking functional properties and having limited application to the food industry. Enzyme-assisted aqueous methods (EAAM) using large amounts of water may simultaneously produce high quality oil and hydrolyzed proteins (Sharma and Gupta, 2004; Sharma and Gupta, 2006; Zhang et al., 2011; Liu et al., 2017). The mechanism of this method for the extracting oil is associated with the full dispersion or solubilization of proteins, free amino acids, free fatty acids, phospholipids, polyphenols, alkaloids, etc. which have both hydrophilic and hydrophobic groups to form an emulsion. However, four main disadvantages of this method are reported: 1) low oil recovery rate or even no free oil produced because of formation of a severe emulsion during the extraction process, 2) difficulty of treating large amounts of waste water generated with high cost, 3) removal of water from de-oiled meal is costly, and 4) use of expensive enzyme (Li et al., 2016; Ravber et al., 2015; Zhang et al., 2011; Jiang, 2010; Hanmoungjai et al., 2000).
The aim of this study was to develop a new aqueous method (NAM) for processing pecan kernels. The NAM established was compared with enzyme-assisted aqueous procedure using large quantities of water, and with hexane extraction in respect to oil recovery (OR) and the quality of de-oiled meal or oil obtained.