Analytical, Nutritional and Clinical Methods Section Response surface methodology for extraction optimization of pigeon pea protein Ivone Yurika Mizubuti a, *, Oswaldo Biondo JuÂnior a,1 , Luiz Waldemar de Oliveira Souza a,1 , Rui SeÂrgio dos Santos Ferreira da Silva b , Elza Iouko Ida b a Department of Animal Science, The State University of Londrina, PO Box 6001, CEP: 86051-990, Londrina, Brazil b Department of Food and Drugs Technology, The State University of Londrina, PO Box 6001, CEP: 86051-990, Londrina, Brazil Received 18 September 1999; received in revised form 7 January 2000; accepted 7 January 2000 Abstract Optimisation for pigeon pea protein extraction (Y)(Cajanus cajan (L) Millsp from the new IAPAR 43-ArataÄ variety) was inves- tigated using response surface methodology. A compound central design was used with variables (X 1 ) NaCl concentration (0.000; 0.025; 0.050; 0.075 and 0.100M); (X 2 ) pH (2.5; 4.0; 5.5; 7.0 and 8.5) and (X 3 ) liquid:solid ratio (5:1; 10:1; 15:1; 20:1; and 25:1, v/w). A model of the second degree equation was used to create the surface responses and con®rmative studies were carried out. The following equation: Y ^ =19.3733+8.6004x 2 0.508526x 2 2 shows optimum conditions for protein extraction of about 75% yield, at pH 8.5 without NaCl regardless of the liquid:solid ratio (v/w) under the experimental conditions studied. # 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction The guandu bean or pigeon pea (Cajanus cajan (L.) Millsp) is a leguminous plant of the Fabbaceae family and is grown in Asia, Africa and South America (Krishna & Bhatia, 1985; Salunkhe, Kadam & Chavan, 1985). However, there is no available information on its production in dierent regions of the world, as it is only cultivated to meet domestics needs, especially in the developing countries (Salunkhe et al., 1985). In Brazil, pigeon pea yield and market price have not been established, as this legume is produced only on small and medium-sized farms for subsistence. The Parana Agronomic Institute Ð IAPAR, put an early dwarf variety on the market in 1990 called ``Iapar 43- arataÄ'' whose yield varies from 1000 to 2000 kg/ha, and reaches 4000 kg grain under some cultivation condi- tions. The protein content of the pigeon pea varies from 15.5 to 28.8% (Oshodi & Ekperigin, 1989; Salunkhe, Chavan & Kadam, 1986; Vilela & El-Dash, 1985) and depends on genetic and environmental factors (Salunkhe et al., 1986). Traditional pigeon pea products involve hydration, cooking, peeling or grinding, tinning and freezing (Salunkhe et al., 1986). The pigeon pea can also be made into good quality ¯our by dry grinding (Vilela & El-Dash, 1985), or maceration for 12 h at 18  C (Batistuti & Freitas, 1995). Sant'anna Filho, Vilela and Gomes (1985) obtained protein isolates from pigeon peas with possible application in food. Singh, Jambunathan and Gurtu (1981) fractioned pigeon pea proteins using water-solubility properties (albumins), salts (globulins), alcohol (prolamins) and acid/alkali (glutelins) as well as residual proteins and non-protein nitrogen. Salunkhe et al. (1986) state that, as in other legumes, the pigeon pea gobulin were the largest proteins stored and their con- tents varied from 60 to 70%. A pigeon pea with 24.2% crude protein and 70% albumins and globulins was used for extraction with 0.5 M NaCl in a 0.01 M phosphate buer, and pH 7.0 (Gopala Krishna, Mitra & Bhatia, 1977; Morton, 1976). Various parameters, such as pH, temperature, ionic force, salt or solvent type, extraction time, solid-solvent ratio, presence of components causing linking, aect protein solubility. The solubility of a protein, as well as its functionality as a nutritional ingredient, may be aected by extraction conditions, solvent type and heat 0308-8146/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(00)00078-9 Food Chemistry 70 (2000) 259±265 www.elsevier.com/locate/foodchem * Corresponding author. 1 Undergraduate student, CNPq Scholarship Recipient.