Original article Amino acid composition, foaming, emulsifying properties and surface hydrophobicity of mustard protein isolate as affected by pH and NaCl Mohammed Aider, 1,2 * Djamel Djenane 3 & Wassef B. Ounis 1,2 1 Institute of Nutraceuticals and Functional Foods (INAF), Universite´ Laval, Quebec G1V 0A6, Canada 2 Department of Food Engineering, Universite´ Laval, Quebec, Qc G1V 0A6, Canada 3 Department of Agricultural and Biological Sciences, University Mouloud Mammeri, Tizi-Ouzou, Algeria (Received 8 September 2011; Accepted in revised form 29 December 2011) Summary Amino acid composition, protein hydrophobicity, foaming and emulsifying properties of mustard protein isolate at pH 3, 5, 7 and in 0.05 and 0.1 m NaCl were studied. Glutamic (19.18 ± 0.30%) and aspartic (7.49 ± 0.11%) acids were the dominants. Foaming ability was enhanced by NaCl. Time to reach 75 mL foam was 23% higher in water than in NaCl. Drained volume after 10 min was concentration dependent and was the lowest in 0.05 and 0.1 m NaCl at protein concentration of 2.5% and 5%. The emulsifying properties were pH and concentration dependent, and the best results were obtained at pH 3, corresponding to the highest positive charge density of the protein surface. The highest emulsion stability (90.22 ± 3.52%) was obtained in 0.05 m NaCl and 5% protein concentration, whereas the lowest (63.00 ± 1.06%) was in water at all protein concentrations. Protein hydrophobicity was low and depended of pH but not of NaCl. Keywords Amino acids, emulsifying, foaming, hydrophobicity, mustard protein. Introduction Mustard (Brassica juncea) is one of the major oilseed crops of several countries such as India with an annual production of 5.0 million tonnes. The meal is rich in protein (38%). The protein is of excellent nutritional quality being rich in lysine with adequate amount of sulphur-containing amino acids–limiting amino acids in most of the cereals and oilseed proteins. Mustard is a widely grown crop throughout the world and plays an important role in the economies of several countries, including Canada. The primary use of mustard seeds is to produce edible oil (Alireza-Sadeghi et al., 2006). The meal remaining after oil extraction contains a high level of protein, which is estimated to be 30–38% on a dry basis (Newkirk et al., 1997). The first use of this protein source material was in animal feed (Alireza-Sadeghi et al., 2006). During the last two decades, extensive research has been carried out to identify the composition of the mustard meal residue and to find applications in human nutrition for mustard meal. This tendency is justified by the need for cheap and renewable protein sources, as well as the balanced amino acid score of mustard protein (Sen & Bhattacharyya, 2003) Mustard protein can be used to replace plant protein such as soy protein, which is commonly used to improve product quality and reduce production costs in many fields of the food industry, such as meat and bakery products (Aluko et al., 2005). It can be also used to replace the expensive whey protein (Das et al., 2009). Nutritional studies showed that mustard protein has a well-balanced amino acid composition and can be used to enhance the nutritional value of different foods made with plant ingredients. Mustard protein is rich in lysine and methionine, which are limiting essential amino acids in most of the cereals and other vegetable proteins. A mustard protein isolate (MPI) can be successfully used in conventional food applications in processed foods as protein fortifiers, oil emulsifiers and foaming agent that entrap gases to make volume (Newkirk et al., 1997). A mustard protein isolate has been shown to posses some interesting functional. Because of the potential of mustard proteins to be used as an ingredient in the food industry, knowledge of their functional properties is of great importance in the control of their use in manufactured foods and to increase the profit- ability of crops cultivated in Canada and worldwide. However, to ensure a successful use of mustard proteins *Correspondent: E-mail: mohammed.aider@fsaa.ulaval.ca International Journal of Food Science and Technology 2012 1 doi:10.1111/j.1365-2621.2012.02937.x Ó 2012 The Authors. International Journal of Food Science and Technology Ó 2012 Institute of Food Science and Technology