In this work, a valorization of the starch stemming from downgraded potatoes was approached through the preparation of starch nanoparticles using different physical methods, namely liquid and supercritical carbon dioxide, high energy ball milling (HEBM), and ultrasonication on the one hand and enzymatic hydrolysis on the other hand. Starch nanoparticles are beneficial as a reinforcement in food packaging technology as they enhance the mechanical and water vapor resistance of polymers. Also, starch nanoparticles are appropriate for medical applications as carriers for the delivery of bioactive or therapeutic agents. The obtained materials were characterized using X-ray diffraction as well as scanning and transmission electron microscopies (SEM and TEM), whereas the hydrolysates were analyzed using size exclusion chromatography coupled with pulsed amperometric detection (SEC-PAD). The acquired results revealed that the physical modification methods led to moderate alterations of the potato starch granules’ size and crystallinity. However, enzymatic hydrolysis conducted using Pullulanase enzyme followed by nanoprecipitation of the hydrolysates allowed us to obtain very tiny starch nanoparticles sized between 20 and 50 nm, much smaller than the native starch granules, which have an average size of 10 μm. The effects of enzyme concentration, temperature, and reaction medium pH on the extent of hydrolysis in terms of the polymer carbohydrates’ fractions were investigated. The most promising results were obtained with a Pullulanase enzyme concentration of 160 npun/g of starch, at a temperature of 60 °C in a pH 4 phosphate buffer solution resulting in the production of hydrolysates containing starch polymers with low molecular weights corresponding mainly to P-10, P-5, and fractions with molecular weights lower than P-5 Pullulan standards.

Flax fibres are an agro‐industrial waste available in large quantities in several countries around the world. This resource can be properly used. The goal of this work was to extract lignocellulosic nanosized flax fibres using an environmentally friendly process based on a combination of supercritical carbon dioxide (SC‐CO2) pre‐treatment and enzymatic hydrolysis. Raw flax fibres (RFF) were submitted to a SC‐CO2 pre‐treatment at various temperatures (ie, 70°C and 80°C) and pressures (ie, 20 and 37.7 MPa) for 60 minutes. The enzymatic hydrolysis was performed at 40°C for 24 hours in a pH 4.0 buffer. Cellulase, xylanase, pectinase, and viscozyme were used as hydrolytic enzymes. The as‐received raw flax fibres, SC‐CO2 pretreated flax fibres, and extracted lignocellulosic nanofibrils (LCNF) were characterized by Fourier transformed infrared spectroscopy (FTIR), x‐ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). It was shown that the effect of the SC‐CO2 pre‐treatment of flax fibres was two‐fold. It helped to disorganize biomass without changing its chemical composition and it increased access to enzymes to extract LCNF. The FTIR analysis showed no changes in the functional groups after SC‐CO2 pre‐treatment. The XRD characterization revealed that the crystallinity increased with the SC‐CO2 pre‐treatment and LCNF extraction. SEM images showed holes, cracks, and erosion on the surface of the SC‐CO2 pretreated flax fibres (SC‐CO2‐PFF). TEM evidenced the production of nano/micro‐sized fibril and fibril aggregates.

In this work, starch nanocrystals were successfully produced from downgraded potatoes using enzymatic hydrolysis combined with a supercritical carbon dioxide pretreatment to improve the accessibility of the enzyme to the starches. Enzymatic hydrolysis was carried out using the pullulanase enzyme at a temperature of 60 °C and a pH of 4. Following hydrolysis, the starch nanoparticles were recovered via precipitation and recrystallization. Comparative characterization of the native, supercritical carbon dioxide-pretreated, and hydrolyzed-recrystallized starch materials was conducted via transmission electron microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction. The scanning electron microscopy images revealed alterations, e.g., layered strips, on the surface of the potato starch granules after the supercritical carbon dioxide pretreatment. The transmission electron microscopy images revealed that spherical nanostructures from 80 nm to 150 nm were successfully produced. The Fourier transform infrared spectroscopy spectra displayed several absorption bands corresponding to the molecular structure of starches. The X-ray diffractograms exhibited a typical B-type scattering pattern for all the samples. In addition, it was found that the crystallinity of the potato starch nanoparticles was considerably increased compared with native starch.

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