The effect of a plant glutathion/thioredoxin on the tryptic digestibility of milk Β-lactoglobulin

Β-lactoglobulin (BLG) is a member of lipocalin superfamily. BLG structure has 2 intramolecular disulfide bonds and one free cysteine in cys121. BLG is one of the major bovine milk allergen that disulfide bonds are responsible for its low digestibility. It seems that the digestibility of BLG will be increased via the reduction of disulfide bonds. In the present work, we aim to study the effect of plant glutathione/thioredoxin systems on the digestibility of milk BLG. Thioredoxins (Trxs) are small and abundant disulfide reductase in all organisms. That themselves are reduced with Trx reductase or glutathione reductase or glutathione. Previously the genes encoding plant Trx, OsTrx20 was cloned and heterologously expressed in E.coli. In this work this protein was produced and purified in considerable amounts. The interaction of Trx with glutathione (GSH) was confirmed by insulin assay. The result of this assay showed that GSH was able to reduce OsTrx20. Therefore, in this work the effect of GSH/OsTrx20 on the digestibility of BLG was studied. To this end BLG was pre-treated by GSH/OsTrx20 at 4, 25 and 37°C and then digested with trypsin. The digestibility was studied by using SDS-PAGE and HPLC and allergenicity was studied by ELISA. The results revealed that GSH/Trx system significantly effect on the BLG digestibility and allergenicity.