Effect of acetylation and succinylation on solubility profile, water absorption capacity, oil absorption capacity and emulsifying properties of mucuna bean (Mucuna pruriens) protein concentrate O. S. Lawal 1 and K. O. Adebowale 2 1 Introduction There is a growing interest in the utilisation of plant proteins in the formulation of new food products or in conventional foods. In Africa and the other developing countries, there is inadequate supply and shortage of food protein because animal protein such as meat, milk and eggs are expensive and rela- tively difficult to acquire [1]. There has been a constant search for unconventional legumes as new protein source for use in both functional food ingredients and nutritional supplement [2]. The seeds of mucuna beans (Mucuna pruriens) are less exploited as protein source in Africa. The seeds are tradition- ally used as soup thickener by Ibos in south eastern Nigeria. Outside Africa, the seeds are eaten by Indian tribal sects, Mun- dari and Dravidian groups [3]. In addition to providing essential amino acids, seed proteins should possess requisite functional properties for their success- ful utilisation in various food products [4]. Critical functional properties necessary in protein ingredients include solubility, water and fat absorption, emulsion capacity, stability and activ- ity, whippability, gelation and good organoleptic properties [5]. The effective utilisation of proteins entails matching a variety of functional and nutritional characteristics to the com- plex needs of manufactured food products. This is often elu- sive because many native protein possess limited functionality. There is technical need for developments of methodology to manipulate plant proteins and endow them with desirable func- tional characteristics. During the last decade, extensive litera- ture has been published on different modification methods of various proteins, for example, by physical [6], genetic [7], enzymatic [8] and chemical [9, 10] methods. Chemical derivatization through acylation of amino acid residues with acetic and succinic anhydride has been used to improve functional properties of many plant proteins including wheat [11], soybean [4], leaf protein [12], peanut [13], sun- flower [14], pea [15], cotton seed [16], winged bean [17], Faba bean [18–20], soy glycinin [21, 22], rapeseed [23–25], and chick pea [26]. So far, no literature is available on acylation of mucuna beans. Acylated proteins have been applied in prepara- tion of some products such as coffee whiteners [27], carbo- nated beverages [28], mayonnaise [29], and margarine [30]. A reversible acylation could have advantages in that during digestion amino groups such as those of lysine would be de- acylated and the lysine would become nutritionally available. Deacylation of soy protein after modification has been studied [31] and it was established that substantial reversibility took place under mild acidic condition. The purpose of this research was to evaluate the effect of acylation with succinic and acetic anhydride on some func- tional properties of mucuna bean protein concentrate. The solubility, water absorption capacity, oil absorption capacity and emulsifying properties were monitored in relation to influ- ence of pH, ionic strength of solvent, and presence of other i 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/food.200300384 Nahrung/Food 48 (2004) No. 2, pp. 129 – 136 129 Mucuna protein concentrate was acylated with succinic and acetic anhydride. The effects of acylation on solubility, water absorption capacity, oil absorption capacity and emulsifying properties were inves- tigated. The pH-dependent solubility profile of unmodified mucuna protein concentrate (U-mpc) showed a decrease in solubility with decrease in pH and resolubilisation at pH values acidic to isoelectric pH (pH 4). Apart from pH 2, both acetylated mucuna protein concentrates (A-mpc) and succinylated mucuna protein concentrate (S-mpc) had improved solubility over the unmodified derivative. Acylation increased the water absorption capacity (WAC) at all levels of ionic strength (0.1– 1.0 M). WAC of the protein samples increased with increase in ionic strength up to 0.2 M after which a decline occurred with increase in ionic strength from 0.4–1.0 M. When protein solutions were prepared in salts of various ions, increase in WAC followed the Hofmeister series in the order: NaSCN a NaClO 4 a NaI a NaBr a NaCl a Na 2 SO. Acetyla- tion improved the oil absorption capacity while the lipophilic tendency reduced the following succinylation. Emulsifying capacity increased with increase in concentration up to 2, 4 and 5% w/v for U-mpc, A-mpc and S-mpc, respectively, after which an increase in concentration reduced the emulsifying capacity. Both acetylation and succinylation significantly (P a 0.05) improved the emulsifying capacity at pH 4– 10. Initial increase in ionic strength up to 0.4 M for U-mpc and 0.4 M for A-mpc and S-mpc increased the emulsion capacity progressively. Further increase in ionic strength reduced emulsion capacity (EC). Con- trary to the effect of various salts on WAC, increase in EC generally fol- lows the series Na 2 SO 4 a NaCl a NaBr a NaI a NaClO 4 a NaSCN. At all levels of ionic strength studied, S-mpc had a better emulsifying activity (EA) than both A-mpc and U-mpc. EA and emulsifying stability (ES) were pH-dependent. Maximum EA and ES were recorded at pH 10. ES of protein derivatives were higher than those of U-mpc in the range of pH 4–10 but lower at pH 2. Studies revealed that both A-mpc and S-mpc had better ES and EA than the unmodified derivative when pro- tein solutions were prepared in salts of various anions. Correspondence: Dr. K. O. Adebowale, Department of Chemistry, University of Ibadan, Ibadan, Nigeria E-mail: adebowal@ictp.trieste.it 1 Department of Chemical Sciences, Olabisi Onabanjo University, Ago-Iwoye, Nigeria 2 Department of Chemistry, University of Ibadan, Ibadan, Nigeria Abbreviations: A-mpc, acetylated mucuna protein concentrate; EA, emulsifying activity; EC, emulsifying capacity; ES, emulsifying stability; S-mpc, succinylated mpc; U-mpc, unmodified mpc; WAC, water absorption capacity Keywords: Acetylation / Mucuna bean / Succinylation /