Nabil Grimi

Selective extraction from microalgae Nannochloropsis sp. using different methods of cell disruption.

This work studies the extraction of intracellular components from microalgae Nannochloropsis sp. with application of different cell disruption techniques, including pulsed electric field (PEF) (20kV/cm, 1-4ms, 13.3-53.1kJ/kg), high voltage electrical discharge (HVED) (40kV/cm, 1-4ms, 13.3-53.1kJ/kg), ultrasonication (USN) (200W, 1-8min, 12-96kJ/kg), and high pressure homogenization (HPH) (150MPa, 1-10 passes, 150-1500kJ/kg). The data evidence that electrically based disruption techniques (PEF and HVED) allowed selective extraction of water soluble ionic components and microelements, small molecular weight organic compounds and water soluble proteins. Microscopic and sedimentation stability analyses have shown that microalgae cells in HVED-treated suspension were noticeably agglomerated and could be easily settled in centrifuge. The electrically based disruption techniques were ineffective for delivery of pigments (e.g., chlorophylls or carotenoids) and their extraction required subsequent application of more potent disruption techniques. The obtained data have shown that HPH disruption technique was the most effective; however, this mode required the highest power consumption.

The Effects of Conventional and Non-conventional Processing on Glucosinolates and Its Derived Forms, Isothiocyanates: Extraction, Degradation, and Applications

Abstract In recent decades, glucosinolates and isothiocyanates have attracted the interest of scientific community due to healthy properties of these bioactive compounds and their role as natural antimicrobials and anticarcinogenic agents. However, these compounds can lose their properties and transform into antinutrients depending on processing conditions. At this stage of investigation, there is a need in evaluation of the commonly accepted and new emerging methods in order to establish the optimum conditions for preserving healthy glucosinolates and isothiocyanates. This paper reviews the conventional and new promising technologies that can be useful for extraction of appropriate glucosinolates and isothiocyanates from natural sources (i.e., Brassica vegetables). The impact of different preservation processes on degradation of glucosinolates and isothiocyanates is also discussed.

New Approaches for the Use of Non-conventional Cell Disruption Technologies to Extract Potential Food Additives and Nutraceuticals from Microalgae

In recent decades, microalgae species have focused the attention of several research groups and food industry as they are a great source of nutritionally valuable compounds. The use of environmentally friendly technologies has led to researchers and food industry to develop new alternative processes that can extract nutritionally valuable compounds from different sources, including microalgae. This note describes the potential use of some non-conventional methods including sub- and supercritical fluid extraction, pulsed electric fields, high-voltage electric discharges, high-pressure homogenization, ultrasound- and microwave-assisted extraction, which involve cell disruption to recover nutritionally valuable compounds from microalgae and can help to comply with criteria of green chemistry concepts and sustainability.

Enhanced Extraction of Phenolic Compounds from Merlot Grapes by Pulsed Electric Field Treatment

The objective of this investigation was to study the influence of pulsed electric field application on fermentation process and wine characteristics. Investigations were related, in particular, to the effects of pulsed electric field pretreatment (500–700 V/cm) of grapes with a short treatment duration (40–100 ms) on the evolution of color intensity, anthocyanins, and phenolic content during the alcoholic fermentation of Merlot grapes and seven months after bottling. The kinetics of the extraction of valuable compounds during the vinification stage was established. Sensory analyses of untreated wines were compared to those of pulsed electric field-treated wines. These results showed that the permeabilization of Merlot skin by a pulsed electric field treatment resulted in increased extraction of polyphenols and anthocyanins. Pulsed electric field of moderate intensity and short duration accelerated the flow kinetics of phenolic compounds through the cell membranes. Compared to the classical process, pulsed electric field treatment has the advantage of nonthermal selective extraction (<5°C) involving no loss of product quality. Phenolic compounds have an important role in enology owing to their contribution to the sensory properties of wine and to their participation in various phenomena during the vinification and aging processes. Sensory analysis indicated that pulsed electric field treatment contributes to the enhancement of the sensory attributes of wine. This technique seems to be an interesting alternative to current prefermentative techniques.

Structural and biochemical changes induced by pulsed electric field treatments on Cabernet Sauvignon grape berry skins: impact on cell wall total tannins and polysaccharides.

Pulsed electric field (PEF) treatment is an emerging technology that is arousing increasing interest in vinification processes for its ability to enhance polyphenol extraction performance. The aim of this study was to investigate the effects of PEF treatment on grape skin histocytological structures and on the organization of skin cell wall polysaccharides and tannins, which, until now, have been little investigated. This study relates to the effects of two PEF treatments on harvested Cabernet Sauvignon berries: PEF1 (medium strength (4 kV/cm); short duration (1 ms)) and PEF2 (low intensity (0.7 kV/cm); longer duration (200 ms)). Histocytological observations and the study of levels of polysaccharidic fractions and total amounts of tannins allowed differentiation between the two treatments. Whereas PEF1 had little effect on the polyphenol structure and pectic fraction, PEF2 profoundly modified the organization of skin cell walls. Depending on the PEF parameters, cell wall structure was differently affected, providing variable performance in terms of polyphenol extraction and wine quality.

Application of Non-conventional Extraction Methods: Toward a Sustainable and Green Production of Valuable Compounds from Mushrooms

Mushrooms are a great source of nutritionally valuable compounds, including proteins, lipids, polysaccharides, polyphenols, micronutrients and vitamins. In particular, they are a significant dietary source of B group vitamins and can be an ideal vehicle in order to supply these vitamins for vegetarians. Conventional extraction methods usually involve water or organic solvents and may results in the noticeable degradation of components. This review describes the potential use of the novel non-conventional methods including enzyme-assisted extraction, pulsed electric fields, ultrasounds, microwaves, subcritical and supercritical fluid extraction for recovery of valuable compounds from mushrooms. Recent studies have shown the great potential of these environmentally friendly methods for green production of specific compounds for use as nutraceuticals or as ingredients for functional foods.

Extraction assisted by pulsed electric energy as a potential tool for green and sustainable recovery of nutritionally valuable compounds from mango peels.

The study compares the efficiency of conventional aqueous extraction at different temperatures (20-60 °C) and pH (2.5-11) and extraction assisted by pulsed electric energy (pulsed electric fields, PEF or high voltage electrical discharges, HVED) of nutritionally valuable compounds found in mango peels. Exponential decay pulses with initial electric field strengths of ≈ 13.3 kV/cm and ≈ 40 kV/cm for PEF and HVED treatments were used, respectively. The impact of temperature on aqueous extraction of proteins and carbohydrates was not significant. The highest values of nutritionally valuable and antioxidant compounds (7.5mM TE) were obtained for aqueous extraction (T = 60 °C, pH 6) but extracts were unstable and cloudy. The application of two-stage procedure PEF+supplementary aqueous extraction (+SE) that include PEF-assisted extraction as the first step, and +SE at 50 °C, pH 6 during 3h as the second step, allowed a noticeable enhancement of the yields of TPC (+400%) even at normal pH.

Ultrasound-assisted green solvent extraction of high-added value compounds from microalgae Nannochloropsis spp.

The aim of this work was to investigate ultrasound (US)-assisted green solvent extraction of valuable compounds from the microalgae Nannochloropsis spp. Individual green solvents (water, ethanol (EtOH), dimethyl sulfoxide (DMSO)) and binary mixture of solvents (water-DMSO and water-EtOH) were used for the extraction procedures. Maximum total phenolic compounds yield (Yp ≈ 0.33) was obtained after US pre-treatment (W=400 W, 15 min), being almost 5-folds higher compared to that found for the untreated samples and aqueous extraction (Yp ≈ 0.06). The highest yield of total chlorophylls (Yc ≈ 0.043) was obtained after US (W=400 W, 7.5 min), being more than 9-folds higher than those obtained for the untreated samples and aqueous extraction (Yc ≈ 0.004). The recovery efficiency decreased as DMSO>EtOH>H2O. The optimal conditions to recover phenolic compounds and chlorophylls from microalgae were obtained after US pre-treatment (400 W, 5 min), binary mixtures of solvents (water-DMSO and water-EtOH) at 25-30%, and microalgae concentration of 10%.

Changes in polyphenol profiles and color composition of freshly fermented model wine due to pulsed electric field, enzymes and thermovinification pretreatments.

This work compares the effects of three pretreatments techniques: pulsed electric fields (PEFs), enzymes treatment (ET) and thermovinification (TV) on the improving of extraction of main phenolic compounds, color characteristics (L(∗)a(∗)b(∗)), and composition (copigmentation, non-discolored pigments) of freshly fermented model wine from Cabernet Sauvignon variety. The pretreatments produced differences in the wines, with the color of the freshly fermented model wine obtained from PEF and TV pretreated musts being the most different with an increase of 56% and 62%, respectively, compared to the control, while the color only increased by 22% for ET. At the end of the alcoholic fermentation, the contents of anthocyanins for all the pretreatments were not statistically different. However, for the content of total phenolics and total flavonols, PEF and TV were statistically different, but ET was not statistically different. The contents of flavonols in musts pretreated by PEF and TV were significantly higher comparing to the control. An increase of 48% and 97% was noted respectively, and only 4% for ET. A similar result was observed for the total phenolics with an increase by 18% and 32% respectively for PEF and TV, and only 3% for ET comparing to the control. The results suggest that the higher intensity and the difference of color composition between the control and pretreated freshly fermented model wines were not related only to a higher content of residual native polyphenols in these freshly fermented model wines. Other phenomena such as copigmentation and formation of derived pigments may be favored by these pretreatments.

Pulsed electric field pretreatment of rapeseed green biomass (stems) to enhance pressing and extractives recovery

The objective of this study was to investigate the effects of pulsed electric field (PEF) pretreatment on the valorization of extractives (proteins and polyphenols) from rapeseed green biomass (stems) by pressing. The effect of pressure, electric field strength and pulse number on the juice expression yield, total polyphenols and total proteins content in the expressed juices were studied. Experiments conducted under optimal conditions (E = 8 kV/cm, tPEF = 2 ms, P = 10 bar) permitted to increase the juice expressed yield from 34% to 81%. Significant increases in total polyphenols content (0.48 vs. 0.10 g GAE/100g DM), in total proteins content (0.14 vs. 0.07 g BSA/100g DM) and in consolidation coefficient (9.0 × 10(-8) vs. 2.2 × 10(-8)m(2)/s) were also observed after PEF pretreatment. The recovered press cake was well dehydrated with an increase of dry matter content from 8.8% to 53.0%.