Sinapis alba seed meal as a feedstock for extracting the natural tyrosinase inhibitor 4-hydroxybenzyl alcohol

Although mustards are ideal rotational crops in moisture-limited environments, biofuels production from mustard seed isn't economically feasible unless the de-oiled seed meal is used to generate co-products. 4-Hydroxybenzyl alcohol (HBA) derived from Sinapis alba (yellow mustard) seed meal is a potentially high value co-product that acts as a skin lightening agent. With increasing demand for skin lightening agents, there is need for the development of alternative products preferably derived from what are perceived as renewable, safer natural materials. Although HBA is known to have inhibitory activity on the tyrosinase reaction by reducing melanin production, the use of HBA from S. alba, a widely grown agricultural crop, has not been described. Our objective was to evaluate the potential of an HBA-containing S. alba extract to act as an inhibitor for the tyrosinase reaction by 1) optimizing the conditions for production and recovery of HBA from S. alba seed meal and 2) quantifying the inhibitory effect of S. alba seed meal extracts on the tyrosinase-activated reaction of L-3,4-dihydroxyphenylalanine (L-DOPA). The optimized procedure to produce an S. elba mustard seed meal extract with an HBA concentration of 2 mM included using ground mustard meal, 100 mM citrate-phosphate buffer (pH 3.8), and a 24-h incubation. The calculated IC50 value for the S. alba extract is equivalent to 6.0 mu M demonstrating that potency of the extract is comparable to that achieved using standard skin lightening agents. The procedure for HBA extraction from seed meal is relatively rapid and does not require sophisticated equipment or solvent systems, making it easily adapted to large scale industrial processing facilities. The potential thus exists to use a feedstock that is readily available from an agriculturally important oilseed crop to produce HBA as a natural tyrosinase inhibitor.