β-Lactoglobulin as nanotransporter for bioactive compounds of garlic (Allium sativum L.)

The suitability of the whey protein β-lactoglobulin as nanotransporter for bioactive organosulfur compounds of garlic, i.e. allicin and diallyl disulfide, was investigated. Since allicin is relatively unstable and causes an intensive smell and pungency, a delivery system is necessary to enable its enrichment in a functional food. The interactions of allicin and diallyl disulfide with β-lactoglobulin were comprehensively analyzed, the physico-chemical and organoleptic properties of β-lactoglobulin modified with allicin were evaluated and the bioavailability of the bioactive compound transported by the protein was assessed. The binding reaction was analyzed by fluorescence quenching, high performance liquid chromatography and the spectrophotometric detection of free amino and thiol groups. Allicin and diallyl disulfide were covalently bound to the free thiol group of β-lactoglobulin under alkaline conditions. The binding resulted in moderate conformational changes of the protein structure, primarily on tertiary level. According to mass spectrometric analysis of the intact and hydrolyzed protein, the binding reaction with allicin and diallyl disulfide resulted in the formation of S-allylmercaptocysteine, a stable, non-volatile, bioactive compound. Through the binding of allicin by β-lactoglobulin, the typical smell and taste of garlic was significantly reduced. The food grade production of β-lactoglobulin modified with allicin resulted in a consumable beverage that delivered physiologically relevant amounts of bioactive organosulfur compounds without significant garlic like sensory properties. A double-blind, randomized, diet-controlled cross-over study with nine healthy volunteers showed that the bioavailability of S-allylmercaptocysteine was not impaired by the incorporation in the protein chain. Conclusively, the covalent binding of allicin to β-lactoglobulin provides an innovative approach for the delivery of bioactive compounds.