ESIPT-exhibiting protein probes: a sensitive method for rice proteins detection during starch extraction.

The 2-(4'-isothiocyanate-2'-hydroxyphenyl)benzoxazole dye was successfully applied as label of rice proteins during the alkaline extraction of starch. Direct fluorescence measurements were used to observe the presence of proteins labelled in different steps of rice starch extraction. The results were compared to those obtained with the well-known biuret colorimetric test. Whereas the colorimetric test indicates the absence of protein after the third extraction step, the fluorescence emission of the conjugate could be observed in all extraction steps. The separation of different rice proteins could also be observed.