Histo-cytochemistry and scanning electron microscopy for studying spatial and temporal extraction of metabolites induced by ultrasound. Towards chain detexturation mechanism

Abstract

There are more than 1300 articles in scientific literature dealing with positive impacts of Ultrasound-Assisted Extraction (UAE) such as reduction of extraction time, diminution of solvent and energy used, enhancement in yield and even selectivity, intensification of diffusion, and eliminating wastes. This present study aims to understand what are the mechanism(s) behind these positive impacts which will help to design a decision tool for UAE of natural products. Different microscopic observations (Scanning Electron Microscopy (SEM), Environmental Scanning Electron Microscopy (e-SEM), Cyto-histochemistry) have been used for spacial and temporal localization of metabolites in rosemary leaves, which is one of the most studied and most important plant for its antioxidant metabolites used in food industry, during conventional and ultrasound extraction. The study permits to highlight that ultrasound impacted rosemary leaves not by a single or different mechanisms in function of ultrasound power, as described by previous studies, but by a chain detexturation mechanism in a special order: local erosion, shear forces, sonoporation, fragmentation, capillary effect, and detexturation. These detexturation impacts followed a special order during ultrasound treatment leading at the end to the total detexturation of rosemary leaves. These mechanisms and detexturation impacts were identified in glandular trichomes, non-glandular-trichomes and the layer adaxial and abaxial cuticle. Modelling metabolites diffusion phenomenon during conventional and ultrasound extraction with the second Fick's law allowed the estimation of diffusivities and solvent penetration into the inner tissues and in meantime to accelerate the release of valuable metabolites.

The effect of ultrasound pretreatment on some selected physicochemical properties of black cumin (Nigella Sativa)

“…The study permits to highlight that ultrasound-impacted rosemary leaves not by a single or different mechanisms in function of ultrasound power, as described by previous studies, but by a chain detexturation mechanism in a special order: local erosion, shear forces, sonoporation, fragmentation, capillary effect, and detexturation. These detexturation impacts followed a special order during ultrasound treatment leading at the end to the total detexturation of rosemary leaves [32].…”

Effects of ultrasound treatment and concentration of ethanol on selectivity of phenolic extraction from apple pomace

“…The different extraction processes in recovery of total polyphenols from apple pomace by ultrasound were identified (Pingret et al, 2012). The extraction mechanism induced by ultrasound may include combination of many effects related with fragmentation, local erosion, sonocapillarity, capillary effect, detexturation and sonoporation (Chemat et al, 2017b;Khadhraoui et al, 2018). It can be speculated that manifestation of these effects is quite different in dependence on structure of flesh and peel tissues, ability of their swelling and rehydration and distribution of phenolic compounds inside these tissues.…”

“…Nowadays, the ultrasound-assisted extraction (UAE) is widely recognised as green technique with reduced energy consumption, processing time and low quantity of wastes (Jacotet-Navarro et al, 2016;Chemat et al, 2017aChemat et al, , 2017bKhadhraoui et al, 2018). Particularly, in several works, an application of UAE for recovery of polyphenols from apple pomace has been reported (Virot et al, 2010;Pingret et al, 2012;Lohani & Muthukumarappan, 2016;Chemat et al, 2017b).…”

Recovery of bioactive anthocyanin pigments from Ficus carica L. peel by heat, microwave, and ultrasound based extraction techniques

“…Nevertheless, along with the scarcity of studies on the evaluation of anthocyanin content in F. carica (entire infructescence, pulp, or peel), to the best of our knowledge none of these studies has previously optimized their extraction from these matrices, which hinders results comparison for this particular matrix. Consequently, the reported total anthocyanin values in the fig peel will be compared with bibliographic results in which the entire infructescence was used, as well as with those that have been reported as the major natural sources of anthocyanins (Khadhraoui et al, 2018).…”