Morphometric Analysis of Paramylon Particles Produced by <i>Euglena gracilis</i> EOD-1 Using FIB/SEM Tomography

Abstract

Euglena gracilis EOD-1, a microalgal strain, produces large quantities of paramylon, a class of polymers known as β-1,3-glucans and has been reported to function as a dietary fiber and to improve the metabolic syndrome including obesity. However, despite its importance, the morphometric analysis of paramylon has not been conducted so far. In this study, we attempted to observe the detailed three-dimensional structure of paramylon by focused ion beam/scanning electron microscopy (FIB/SEM). Paramylon samples were fixed and three-dimensional image reconstruction and segmentation of the image stack were created using computer software (Amira v6.0.1, FEI). The results indicated that the inside of paramylon particles (diameter: 5 µm, thickness: 3 µm) was comprised of a dense structure with no evidence of the presence of large pores and gaps, although a small 100 nm crack was observed. The specific surface area of paramylon particles measured by the Brunauer-Emmet-Teller (BET) method, was not as large as activated charcoal, but similar to those of plant starches, indicating that the cholesterol-lowering effect of paramylon cannot be simply attributed to its adsorption ability. The FIB/SEM method was found to be useful for elucidating the internal structure of small solid particles.

Effect of Food Containing Paramylon Derived from Euglena gracilis EOD-1 on Fatigue in Healthy Adults: A Randomized, Double-Blind, Placebo-Controlled, Parallel-Group Trial

“…It has been speculated that EOD-1PM is less susceptible to degradation by intestinal bacteria and is less likely to be absorbed through the intestines in mice [ 19 , 21 ]. Therefore, EOD-1PM may not be directly involved in improving serum antioxidant potential.…”

“…Euglena gracilis is a kind of microalgae that produces a β-1,3-glucan called paramylon. E. gracilis EOD-1 containing a high proportion (70–80%) of paramylon is known to proliferate depending on culture conditions [ 18 , 19 ]. Moreover, E. gracilis EOD-1, which has been suggested to have various functionalities, has recently drawn attention as a health food.…”

A review of paramylon processing routes from microalga biomass to non-derivatized and chemically modified products

“…At least six different morphological variations have been reported, from disks to rods (Monfils et al, 2011). For E. gracilis, the shape is typically flat cylindrical with reported diameters around 5m and thicknesses about 3 m (Anraku et al, 2020). The granules are actually surrounded by a biomembrane.…”

“…It is assumed that paramylon is first biosynthesized as elementary microfibrils with low crystallinity (Kiss et al, 1987(Kiss et al, , 1988: as the granule matures, the microfibrils assemble to form the final highly ordered crystalline structure with concentric deposition of aggregates of elemental nanofibers of 4-10 nm. Recently, morphometric characterizations by focused ion beam/scanning electron microscopy (FIB/SEM) tomography (Anraku et al, 2020) confirmed that the paramylon particles have a very dense structure without large void spaces. A specific surface area (SSA) of 2.438 m 2 /g was measured by BET which is close to starch granules from potatoes and corn.…”