Functional properties and nutritional quality of acetylated and succinylated mung bean protein isolate Tarek A. El-Adawy * Food Science and Technology Department, Faculty of Agriculture, Meno®ya University, 32516-Shibin El-Kom, Egypt Received 18 September 1999; received in revised form 4 December 1999; accepted 4 December 1999 Abstract Mung bean protein isolate was acylated to various degrees by acetic and succinic anhydrides. Changes in functional properties (protein solubility index in dierent solutions, water and oil absorption capacities, emulsi®cation properties, foam capacity and stability), antinutritional factors (tannins, phytic acid and trypsin inhibitor) and in-vitro protein digestibility of acylated protein isolate were determined. The modi®cation rate with acetic anhydride was greater than with succinic anhydride. Succinylation sig- ni®cantly increased the protein solubility index in water and 1 M NaCl whereas acetylation decreased it in water. Acetylation and succinylation caused signi®cant increases in water and oil absorption capacities. Foam capacity and foam stability (up to 0.4 g anhydrides/g protein) were signi®cantly increased due to acylation. Signi®cant increase was observed in emulsi®cation capacity and emulsi®cation stability (up to 0.8 g acetic and 0.6 g succinic anhydrides/g protein) by acylation; however, emulsi®cation activity was signi®cantly decreased over 0.6 g anhydrides/g protein. Acetylation is more eective for reduction of antinutritional factors than succinylation. Also, acetylation is more eective in improving the in-vitro protein digestibility than is succinylation. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Mung bean; protein isolate; Chemical modi®cation; Functional properties; Antinutritional factors; In-vitro protein digestibility 1. Introduction In Egypt, mung bean (Phaseolus aureus) has been introduced recently by the Ministry of Agriculture. Mung bean is an excellent source of protein (27%), and its essential amino acid composition compares favour- ably with that of soybean, kidney bean and FAO/WHO reference protein ( El-Adawy, 1996; Evans & Bandermer, 1974; Fan & Sosulski, 1974; Thompson, Hung, Wang, Rapser & Gade, 1976). However, antinutritional factors and dark colour limit the food applications of mung bean. Therefore, dehulling of the seeds before milling as well as preparation of protein isolate have been used to overcome these problems (El-Adawy, 1996; Thompson et al., 1976). Mung bean protein isolate has been shown to perform many desirable functions in processed foods, such as foaming, emulsi®cation and water absorption (El-Adawy, 1996). However, improvements in those functions would make mung bean protein isolate more desirable as a food component. Chemical modi®cation is one method proposed to improve the functional properties of the proteins for food processing (Li-Chan, Helbig, Holbeck, Chan & Nakai, 1979; Matheis & Whitaker, 1984). Chemical modi®cation, particularly acylation with acetic and suc- cinic anhydrides, has been used to improve functional properties of many plant proteins including wheat (Grant, 1973), soybean (Franzen and Kinsella, 1976a), leaf protein (Franzen & Kinsella, 1976b; Sheen, 1991), peanut (Beuchat, 1977), sun¯ower (Kabirrullah & Wills, 1982; Schwenke & Rauschal, 1983), pea (Johnson & Brekke, 1983; Schwenke, Zirwer, Gast, GoÈrnitz, Linow & Gueguen, 1990), cottonseed (Choi, Lusas & Rhee, 1981; Rahma & Narasinga Rao, 1983), winged bean (Narayana & Narasinga Rao, 1984), faba bean (Krause, Mothes & Schwenke, 1996; Muschiolik, 1989; Muschiolik, Dickinson, Murray, & Stainsby, 1987; Rauschal, Linow, PaÈhtz & Schwenke, 1981; Schwenke, Dudek, Mothes; Raab & Seifert, 1993), soy glycinin (Kim & Rhee, 1990; Kim & Rhee, 1991), rapeseed (Dua, Mahajan & Mahajan, 1996; Gruener & Ismond, 1997; Gueguen, Bollecker, Schwenke & Raab, 1990), chickpea (Liu & Hung, 1998). 0308-8146/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0308-8146(00)00079-0 Food Chemistry 70 (2000) 83±91 www.elsevier.com/locate/foodchem * Tel.: +20-48-238788; fax: +20-2-5769495.