A comparison of methods to quantify prolamin contents in cereals

Hydrophobic prolamins are endosperm storage proteins accounting for about 40% of the total protein in most cereal seeds. Despite the absence of a reference method, several procedures have been periodically published to quantify prolamins in cereals. The aim of this study was to compare a conventional fractionation assay (LND) vs three other methods: one based on sequential extractions (HAM) and two rapid turbidimetric procedures (L&H and DRO). Prolamins were extracted in duplicate on barley, corn and wheat samples. For the turbidimetric prolamin evaluation in barley and wheat, a universally available purified gliadin, as alternative to purified zein, was also tested as standard reference material (SRM). The extraction prolamin values were different among grain types (P<0.01) and methods (P<0.01) without interaction (P>0.05). LND agreed sufficiently well both with HAM and with L&H methods (R-2=0.664 and R-2=0.703, respectively, P<0.01). On all tested cereals, LND and L&H gave similar prolamin extraction values (P>0.05), whereas a higher prolamin quantification was obtained using HAM (P<0.05). Overall, DRO did not provide similar comparison and performance parameters with respect to other method comparisons. The effect of changing purified zein with purified gliadin was noteworthy only for L&H, both for wheat and barley samples (P<0.01). Considering the increasing attention of animal nutritionists on prolamins, our results could get useful information for routine laboratory analysis.