Visualization of Gluten, Starch, and Butter in Pie Pastry by Fluorescence Fingerprint Imaging

Abstract

The distribution of starches, proteins, and fat in baked foods determine their texture and palatability, and there is a great demand for techniques to visualize the distributions of these constituents. In this study, the distributions of gluten, starch, and butter in pie pastry were visualized without any staining, by using the fluorescence fingerprint (FF). The FF, also known as the excitation–emission matrix (EEM), is a set of fluorescence spectra acquired at consecutive excitation wavelengths. Fluorescence images of the sample were acquired with excitation and emission wavelengths in the ranges of 270–320 and 350–420 nm, respectively, at 10-nm increments. The FFs of each pixel were unmixed into the FFs and abundances of five constituents, gluten, starch, butter, ferulic acid, and the microscope slide, by using the least squares method coupled with constraints of non-negativity, full additivity, and quantum restraint on the abundances of the slide glass. The calculated abundances of butter, starch, and gluten at each pixel were converted to shades of red (R), green (G), and blue (B), respectively, and RGB images showing the distribution of these three constituents was composited. The composited images showed high correspondence with the images acquired with the conventional staining method. Furthermore, the ratio of gluten, starch, and butter in short pastry was calculated from the abundance images. The calculated ratio was 16.6:37.6:45.8, which was very close to the actual ratio of 12.7:38.8:48.5, and further proved the accuracy of this imaging method.