Optimization of lentil protein extraction and the influence of process pH on protein structure and functionality M. Jarpa-Parra a , F. Bamdad a , Y. Wang a , Z. Tian a , F. Temelli a , Jay Han b , L. Chen a, * a Department of Agricultural, Food and Nutritional Science, University of Alberta, Edmonton, AB, Canada T6G 2P5 b Food Processing Development Centre, Alberta Agriculture and Rural Development, Leduc, AB, Canada T9E 7C5 article info Article history: Received 23 October 2013 Received in revised form 16 February 2014 Accepted 17 February 2014 Keywords: Lentil protein RSM Structure characterizations Functional properties abstract Response surface methodology was used to optimize alkaline extraction of protein from lentil flour to maximize both protein content and yield. Solid/solvent ratio and pH were the significant factors that determined protein extraction efficiency. At the optimized condition of pH 9.0 and solid/solvent ratio of 1:10 (g:mL), a yield of 14.5 g of protein extract/100 g of flour was obtained with a protein content of 82 g/ 100 g at (22  C) after 1 h of extraction. The impact of extraction pH on the molecular structures and functionalities of lentil protein was investigated. Increasing the extraction pH to 10 caused partial protein hydrolysis and unfolding as suggested by size exclusion high performance liquid chromatography and Fourier transform infrared spectroscopy analysis, leading to improved protein solubility and gelling property. Environmental pH influenced protein solubility and surface charge, and subsequently the gelling and foaming properties. The foaming capacity was especially strong, comparable to whey and egg proteins. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Lentil (Lens culinaris) is a leguminous plant high in fiber and low in fat. Like most legumes, lentil is a rich source of protein (Urbano, Porres, Frias, & Vidal-Valverde, 2007), with a protein content be- tween 20.6 and 31.4 g/100 g. According to Osborne’s classification, lentil proteins are mainly globulins (w50 g/100 g) consisting of legumin and vicilin-like proteins with a molecular mass of about 60 kDa and 50e80 kDa, respectively (Barbana & Boye, 2011). In- terest in lentil protein has recently grown due to its high nutritional value, good Leu/Ile and Leu/Lys ratios (1.24e1.98 and 1.08e2.03, respectively) (Urbano et al., 2007), high digestibility (w83%) (Barbana & Boye, 2013), and its potential use in food product ap- plications (Alsohaymi, Sitohy, & El-Masry, 2007; Barbana & Boye, 2011; Bora, 2002; Boye et al., 2010). Usually, preparation of lentil protein concentrates involves alkaline extraction followed by an isoelectric precipitation step. Although there are several protocols described in the literature on alkaline extraction of lentil protein, they differ in pH, varying from 7.2 to 11, solid to solvent ratio, from 1:5 to 1:20, and temperature, from 25  C to 40  C, and there is a lack of systematic studies showing how extraction parameters impact lentil protein yield and purity. The limited work includes study of the effect of temperature and pH on lentil starch and protein yields by Lee, Htoon, Uthayakumaran, and Paterson (2007), and investi- gation of the impact of pH on purity of isolates by Alsohaymi et al. (2007). On the other hand, great progress has been made recently to reveal the good functionality of lentil proteins such as solubility and emulsifying, foaming and gelation capacities (Alsohaymi et al., 2007; Bora, 2002; Boye et al., 2010). Nevertheless, these studies have focused on lentil proteins extracted under one condition and evaluated their functionality at neutral pH. Studies are limited regarding the influence of extraction conditions on lentil protein structure and subsequent functional properties of these extracts. Since protein functional properties are dictated to a large extent by protein’s physicochemical and structural properties as influenced by the treatment and environmental conditions (Fang & Dalgleish, 1997), more fundamental research that addresses this gap is critical to facilitate wider applications of lentil proteins. Therefore, this study aims to optimize the lentil protein extraction process using response surface methodology to maxi- mize both protein content and yield of the extract. The extracts, obtained at different pH treatments, were characterized for composition and structure using Sodium dodecyl Sulphate Poly- acrylamide gel electrophoresis (SDS-PAGE), Size exclusion high performance liquid chromatography (SE-HPLC) and Fourier trans- form infrared spectroscopy (FTIR). Functional properties were * Corresponding author. Tel.: þ1 780 492 0038; fax: þ1 780 492 4265. E-mail addresses: lingyun.chen@ualberta.ca, Lingyun.Chen@ales.ualberta.ca (L. Chen). Contents lists available at ScienceDirect LWT - Food Science and Technology journal homepage: www.elsevier.com/locate/lwt http://dx.doi.org/10.1016/j.lwt.2014.02.035 0023-6438/Ó 2014 Elsevier Ltd. All rights reserved. LWT - Food Science and Technology 57 (2014) 461e469