LEAF PROTEIN AVAILABILITY IN FOOD - SIGNIFICANCE OF THE BINDING OF PHENOLIC-COMPOUNDS TO RIBULOSE-1,5-DIPHOSPHATE CARBOXYLASE

The binding of phenolic compounds to ribulose-1,5-diphosphate carboxyl ase (RubisCO) is known to give rise to some digestive problems in huma n beings. In fact, the biological value of protein and hence the Prote in Efficiency Ratio and Net Protein Utilization decrease drastically. For this reason the binding of phenolic compounds (e.g. rutin and chlo rogenic acid) to ribulose-1,5-diphosphate carboxylase (RubisCO) was st udied by means of ultrafiltration techniques in order to better elucid ate the nature of this interaction and the factors influencing it in a n attempt to limit or avoid it. RubisCO behaviour was also compared wi th that of Bovine Serum Albumin. A multivariate approach was used to d etermine the most influencing variables and their effects on binding. A classical binding study with the aim of determining the binding stoi chiometry was also carried out. pH was found to be the most important variable affecting the binding of rutin to RubisCO as well as rutin to Bovine Serum Albumin while contact time became relevant when operatin g in sub-alkaline pH conditions. Classical binding analysis was carrie d out at pH 7.0 to 7.3 by both direct partition and diafiltration meth ods. A total number of five binding sites was determined with two kind s of binding mechanisms, one of which was hydrophobic. The diafiltrati on method can be considered a useful tool when high affinity interacti ons are studied; RubisCO protein stability was disturbed by stirring, but this allowed an increased affinity of aggregated RubisCO to chloro genic acid to be noted. This might have important consequences on Rubi sCO extraction technology since the most critical phase of phenolic co ntamination is the crystallization-precipitation step. (C) 1995 Academ ic Press Limited