* To whom correspondence should be addressed. Tel:# 33 0240675064; Fax:# 33 0240675066; E-mail: ralet@nantes.inra.fr Lebensm.-Wiss. u.-Technol., 34, 266 } 269 (2001) Research Note Foaming Properties of Potato Raw Proteins and Isolated Fractions Marie-Christine Ralet* and Jacques Gue H guen Unite H de Recherche sur les Polysaccharides, leurs Organisations et Interactions Unite H de Biochimie et Technologie des Prote H ines, Institut National de la Recherche Agronomique, rue de la Ge H raudie`re, B.P. 71627, 44316 Nantes Cedex 03 (France) (Received April 11, 2000; accepted June 8, 2000) The foaming properties of undenaturated potato raw proteins and of isolated patatin and 16}25 kDa fraction are investigated over a pH range of 4}8 with and without added NaCl. The patatin fraction was shown to be a very promising foaming agent with a foamability and foam stability equivalent or even superior to that of egg-white powder.  2001 Academic Press Keywords: potato; Solanum tuberosum; protein; foam; patatin Introduction A foam can be de"ned as a &two-phase system in which a distinct gas bubble phase is surrounded by a continu- ous phase' (Phillips et al., 1990). Foams are present in numerous colloidal systems prepared by the food and cosmetic industries, and proteins are often used in their stabilisation. The molecular properties that are relevant for foaming are (i) solubility (enabling rapid di!usion to the interface); (ii) amphipathicity (for enhanced interfacial interactions); (iii) segmental #exibility (facilitating unfold- ing at the interface); (iv) interactive segments (to enable secondary interactions in the gaseous, aqueous and inter- facial phases); (v) disposition of charged and polar groups (to prevent the close approach of bubbles and to allow hydration) and also (vi) steric e!ects (Panyam & Kilara, 1996). Evaluation of the foaming properties of proteins requires the characterisation of both foam formation and stability. Most frequently, foam volume and liquid drain- age kinetics are measured (Fains et al., 1997). The potato starch factory e%uents, called potato juice, have a high water polluting capacity (De Noord, 1976). One possible means of reducing this pollution problem is the recovery of proteins, which can represent up to 250 g/kg of the soluble dry solids of potato juice. Potato proteins can tentatively be divided into three classes (i) the patatin family, highly homologous acidic 43 kDa glycoproteins (40 }50%), (ii) basic 22 kDa proteins family (30 } 40%) and (iii) basic protease inhibitors (20 }30%) (Ralet & Gueguen, 1999). The nutritional quality of potato proteins is known to be comparable to that of whole egg (van Gelder & Vonk, 1980). Therefore, potato proteins have a high potential for food utilisation. Presently, potato proteins are obtained by a combined acid and heat treatment of the potato juice, resulting in irreversibly precipitated proteins which have lost func- tional properties (Pots et al., 1998). In this study, the foaming properties of undenatured potato raw proteins and of two proteic fractions isolated on a charge criteria (patatin and 16}25 kDa fractions) were investigated over a pH range of 4 } 8 with and without added NaCl. Materials and Methods Protein samples Potato raw proteins were recovered after aqueous extrac- tion and dialysis as described elsewhere (8). An acidic (patatin fraction) and a basic (16}25 kDa fraction) popu- lation were isolated by ion-exchange chromatography (Ralet & Gueguen, 2000). Ovomousse M (ref. 251), a spray-dried hen egg-white powder from EPI Bretagne (Plaintel, France) was chosen as a reference considering its good foaming properties (Baniel et al., 1997). Foam analyses The foaming properties at 1 mg/mL in 50 mM phos- phate/citrate (pH 4 and 5) or phosphate (pH 6} 8) and for 0023-6438/01/060266 #04 $35.00/0 doi:10.1006/fstl.2000.0684  2001 Academic Press All articles available online at http://www.idealibrary.com on 266