ELSEVIER PII: SO308-8146(97)00158-l Food Chemistry, Vol. 62, No. 1, pp. 2747, 1998 0 1998 Elsevier Science Ltd. All rights reserved Printed in Great Britain 0308-8146/98 $19.00+0.00 Salt-soluble seed globulins of various dicotyledonous and monocotyledonous plants-I. Isolation/purification and characterization Massimo F. Marcone*, Yukio Kakuda & Rickey Y. Yada Department of Food Science, University of Guelph, Guelph, Ontario, Canada NIG 2W1 (Received 20 February 1997; revised version received and accepted 28 June 1997) Detailed characterization of 21 purified seed globulins derived from both mono- cotyledonous and dicotyledonous plants indicated that globulins from both class types (as well as within the same class type) lay within a narrow molecular weight range between 300 000 and 370 000 Da and were composed of multiple subunits. In all cases, purified globulins could be classified as hetero-oligomers being com- posed of a non-equimolar ratio of various subunits. The vast majority of subunits forming these globulins were shown to be held together by non-covalent bond forces. A small percentage of linkages between subunits were also shown to be disulfide linked, in the case of dicotyledonous seed globulins. It was also found that the majority of subunits composing the dicotyledonous and mono- cotyledonous seed globulins examined fell within two very narrow molecular weight ranges, i.e. 20 00&27 000 and 30 00&39 000 Da and were believed to cor- respond to basic and acidic subunits, respectively. Unlike monocotyledonous seed globulins, globulins derived from dicotyledonous plants were found to undergo alkaline-induced dissociation due to electrostatic repulsion between subunits. The amino acid composition of both dicotyledonous and mono- cotyledonous seed globulins suggests that they have a storage role and may be similar proteins based on a high content of amides (glutamic acids-glutamine and aspartic acid-asparagine and arginine). From the results of the structural and chemical data obtained in this study, it is concluded that the 11s storage globulin, having several similar properties, exists in many leguminous and non- leguminous dicotyledonous plants as well as monocotyledonous plants. This similarity among 11s storage globulins could be due either to convergent evolu- tion in response to a common functional need, or to common ancestry. 0 1998 Elsevier Science Ltd. All rights reserved. INTRODUCTION It has been estimated that directly or indirectly plants comprise up to 95% of the present world’s food supply (Walsh, 1984) with cereal/grains providing in excess of 50% of man’s basic protein requirement (Johnson, 1984). Presently, cereal crops still predominate in pro- viding both calories and proteins; however, the utiliza- tion of other grains such as the legume family is gaining in overall popularity (Massecaa and Baudet, 1983; Lambert and Yarwood, 1992). This increased popular- ity in the utilization of non-cereal grains stems not only from the fact that these grains commonly possess two to four times more protein than traditionally used cereal grains but that their proteins are often of higher nutri- *To whom correspondence should be addressed. tional quality (Lambert and Yarwood, 1992). Of the three types of protein commonly associated with seeds, i.e. the structural, metabolically active and storage-type proteins, it is the storage-type proteins which are found in most abundance and, therefore, are considered responsible for the nutritional as well as technological properties of the whole grain (Boulter, 1983). In cereal grains the main storage proteins are usually the alcohol- soluble prolamins, whereas in non-cereal grains they are usually predominated by the more nutritiously balanced salt-soluble globulins (Waggle et al., 1989) (Table 1). Although researchers have shown that globulins can be subdivided into two distinct classes, termed 7 and 11 S, on the basis of their sedimentation coefficients (Wright, 1988), the 11s globulin is the predominant protein in dicotyledonous plants (Pernollet and Moss&, 1983; Derbyshire et al., 1976). 27