International Dairy Journal 17 (2007) 481–487 Preparation of ingredients containing an ACE-inhibitory peptide by tryptic hydrolysis of whey protein concentrates I.M.P.L.V.O. Ferreira a,Ã , O. Pinho a,b , M.V. Mota a , P. Tavares c , A. Pereira c , M.P. Gonc - alves d , D. Torres d , C. Rocha e , J.A. Teixeira e a REQUIMTE—Servic - o de Bromatologia, Faculdade de Farma´cia, Universidade do Porto, R. Anı´bal Cunha 164, 4050-047 Porto, Portugal b Faculdade de Cieˆncias da Nutric - a˜o e Alimentac - a˜o da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal c REQUIMTE—Departamento de Quı´mica da Faculdade de Cieˆncias e Tecnologia da Universidade Nova de Lisboa, 2825 Monte da Caparica, Portugal d REQUIMTE—Departamento de Engenharia Quı´mica. Faculdade de Engenharia da Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal e Centro de Engenharia de Biolo´gica, IBQF, Universidade do Minho, Campus de Gualtar, 4710-057 Braga, Portugal Received 18 January 2006; accepted 15 June 2006 Abstract This study describes the characterisation of whey protein hydrolysates obtained from tryptic hydrolysis to assess their application as ingredients with angiotensin-converting-enzyme (ACE) inhibitory action. The levels of a-lactalbumin (a-la) and b-lactoglobulin (b-lg) remaining after hydrolysis were quantified. Peptides were separated by RP-HPLC, and Ala-Leu-Pro-Met-His-Ile-Arg (ALPMHIR), the most potent b-lg-derived ACE-inhibitory peptide was monitored. A correlation curve was established for the production of this peptide as a function of hydrolysis time. Heat-induced gelation of hydrolysates was studied by small-deformation rheology. The gelation times and the strength of the final gels were highly dependent on the degree of hydrolysis. Smaller peptides liberated by hydrolysis contributed to the inability of whey protein hydrolysates to gel. r 2006 Elsevier Ltd. All rights reserved. Keywords: Whey protein concentrates; Trypsin hydrolysis; ACE-inhibitory peptides; Gelation 1. Introduction Whey ingredients are used throughout the world in beverages, bars and other food systems. Newer whey ingredients include hydrolysed whey proteins that contain high levels of bioactive peptides (Foegeding, Davis, Doucet, & McGuffey, 2002; Gauthier & Pouliot, 2003; Meisel, 1998). These hydrolysates can be added to special foods to increase value, as enzymatic hydrolysis can optimise their functional properties (e.g., gelling, emulsify- ing and foaming capacities and solubility) (De Wit, 1998; Melachouris, 1984; Zydney, 1998). Thus, there is consider- able commercial interest in the preparation of whey proteins for food, nutraceutical, and therapeutic applica- tions (Torres, 2005). Bioactive peptides are often inactive within the sequence of the parent protein and can be released, for example, by enzymatic hydrolysis with digestive enzymes. Bioactive peptide fragments originating from whey proteins should be taken into account as components that have a positive effect on cardiovascular health (Clare & Swaisgood, 2000; Pihlanto-Leppala, Koskinen, Piilola, Tupasela, & Korho- nen, 2000; Seppo, Jauhiainen, Poussa, & Korpela, 2003; Yusuf, Lonn, Bosch, & Gerstein, 1999). For example, certain bioactive peptides may protect against hypertension through angiotensin-converting-enzyme (ACE)-inhibition and opioid-like activity, both in vitro and in animal experiments. The overall effect of an ACE inhibitor is the control of high blood pressure through dilation of blood vessels and its effect on blood volume (Belem, Gibbs, & ARTICLE IN PRESS www.elsevier.com/locate/idairyj 0958-6946/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.idairyj.2006.06.023 Ã Corresponding author. Tel.: +351 22 2078929; fax: +351 22 2003977. E-mail address: isabel.ferreira@ff.up.pt (I.M.P.L.V.O. Ferreira).