Abstract
The in vitro digestibility of rice glutelin and wheat glutenin was investigated with a view to assessing their nutritional qualities, using casein and bovine serum albumin (BSA) as references. The following hydrolytic processes were adopted: pepsin-pancreation digestion (a model system before intestinal absorption) and aminopeptidase-prolidase hydrolysis [a model system for the intestinal mucosa (membrane digestion) and after intestinal absorption (intracellular hydrolysis)]. The pepsin-pancreatin digests were first examined. The degree of amino acid released from the proteins was 30% (glutelin), 23% (glutenin), 24% (casein) and 30% (BSA). A similar release pattern of individual amino acids was observed for all the proteins. The amounts of large peptide fractions increased in the order: glutelin < glutenin < casein < BSA. Glutelin was highly digestible. Apart from containing high amounts of glutamic acid (glutamine), cystine and proline, the large peptide fractions of glutelin were also rich in threonine, glycine and isoleucine while those of glutenin were only rich in glycine. The aminopeptidase-prolidase digests were examined next. Glutelin was almost completely hydrolyzed to amino acid, except for a low release of cystine, suggesting that the amino acid residues constituting glutelin could be easily utilized as nutrients in the living tissues. The degree of amino acid released from the proteins was 97% (glutelin), 93% (glutenin), 90% (casein) and 79% (BSA).
The convenient application of these model systems for the assessment of the in vitro digestibility of food proteins have been discussed.
