Label-Free Fried Starchy Matrix: Investigation by Harmonic Generation Microscopy.

Agathe Chouët,Catherine Loisel,Romain Fleurisson,Laurence Dubreil,Sylvie Chevallier

doi:10.3390/s19092024

Abstract

An innovative methodology based on non-destructive observation by using harmonic generation microscopy is proposed for detection and location of starch granules and oil in a fried starchy matrix and topography analysis of food products. Specific fluorescent probes were used to label the main biochemical components of the starchy fried matrix, namely starch and oil. Fluorescence of starch and oil respectively stained with Safranin O and Nile red was observed from non-linear microscopy. By using sequential scanning and specific emission filters, it was possible to merge fluorescence and harmonic generation signals. Second harmonic generation (SHG) generated by starch granules was superposed with safranin fluorescence, whereas third harmonic generation (THG), not restricted to the superposition with Nile red fluorescent signal, was used to investigate the topography of the fried product. By these experiments, starch granule mapping and topography of the starchy fried product were obtained without any destructive preparation of the sample. This label-free approach using harmonic generation microscopy is a very promising methodology for microstructure investigation of a large panel of starchy food products.

Highlights

The distribution of constituents in the matrix of fried foods and the topography of the product are important information to understand phenomena occurring during the frying process
Imaging of oil in the starchy fried matrix was performed by using Nile red staining and Starch granules were quantified from second harmonic generation (SHG) and Safranin detection by image analysis with Fiji multiphoton microscopy on an area of 0.3 mm2 and 0.36 mm in depth (Figure 4a), The third harmonic generation (THG) signal software [35]. 2D projection was performed to get Zmax projection
SHG from native starch granule was observed in the blue channel from non-linear microscopy at 820 nm

Summary

Introduction

The distribution of constituents in the matrix of fried foods and the topography of the product are important information to understand phenomena occurring during the frying process. Bouchon and Pyle [1] highlighted a relationship between those two components and their importance on the quality of fried products They demonstrated that presence of native starch in potato snacks could cause the increase of oil in the product, and the decrease of the surface roughness. Bouchon et al [3] showed that three different absorption mechanisms exist for fried potato cylinder that lead to three different oil fractions. These three fractions are (i) oil absorbed during frying, (ii) oil absorbed during cooling by a pressure gradient created by vapor condensation and surface tension forces, and (iii) oil on the surface favored by product roughness [1]. Oil absorption is essentially a surface phenomenon: Rubnov and Saguy [4] demonstrated the relationship between this phenomenon and the surface roughness of the fried restructured potato products, and Rahimi and

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