Gianpiero Pataro

The influence of operating temperature on the dense phase properties of bubbling fluidized beds of solids

Abstract The paper analyses the dependence on process temperature of parameters that characterize the dense phase of a freely bubbling bed. Application of the bed collapse technique to beds of FCC, silica sand, and corundum in experiments covering a temperature field ranging from room level up to 700 °C demonstrates that the increase of interparticle forces at superambient temperatures leads to significant modifications of the fluidization dynamics. These include clear changes of the particulate phase voidage and dense phase velocity as well as of bubble hold-up. Changes induced in the partition of the total gas flow rate and, consequently, in the characteristics of the bubble phase of the fluidized bed are also discussed.

Energy-efficient biomass processing with pulsed electric fields for bioeconomy and sustainable development

Fossil resources-free sustainable development can be achieved through a transition to bioeconomy, an economy based on sustainable biomass-derived food, feed, chemicals, materials, and fuels. However, the transition to bioeconomy requires development of new energy-efficient technologies and processes to manipulate biomass feed stocks and their conversion into useful products, a collective term for which is biorefinery. One of the technological platforms that will enable various pathways of biomass conversion is based on pulsed electric fields applications (PEF). Energy efficiency of PEF treatment is achieved by specific increase of cell membrane permeability, a phenomenon known as membrane electroporation. Here, we review the opportunities that PEF and electroporation provide for the development of sustainable biorefineries. We describe the use of PEF treatment in biomass engineering, drying, deconstruction, extraction of phytochemicals, improvement of fermentations, and biogas production. These applications show the potential of PEF and consequent membrane electroporation to enable the bioeconomy and sustainable development.

Pulsed Electric Field-Assisted Vinification of Aglianico and Piedirosso Grapes

Pulsed electric field (PEF) treatments were applied to increase the polyphenolic content of fresh red wines made from Aglianico and Piedirosso grapes. Prior to the fermentation/maceration step, the grape skins were treated at different PEF intensities (field strengths from 0.5 to 1.5 kV/cm and energy inputs from 1 to 50 kJ/kg), with their permeabilization being characterized by electrical impedance measurements. Furthermore, the release kinetics of the total polyphenols and anthocyanins were characterized during the maceration stage by spectroscopic and Folin-Ciocalteu colorimetric methods, respectively. Finally, the fresh wine, obtained after pressing, was characterized for total acidity, pH, reducing sugar, color intensity, total polyphenols, anthocyanins content, antioxidant activity, and volatile compound composition. PEF treatment on Aglianico grapes induced a significantly higher release of polyphenols (+20%) and anthocyanins (+75%), thus improving the color intensity (+20%) and the antioxidant activity of the wine (+20%) while preserving the other organoleptic characteristics. In contrast, there was only a minor impact on the polyphenolic release kinetics of Piedirosso grapes, despite the significant degree of cell membrane permeabilization.

Innovative Alternative Technologies to Extract Carotenoids from Microalgae and Seaweeds

Marine microalgae and seaweeds (microalgae) represent a sustainable source of various bioactive natural carotenoids, including β-carotene, lutein, astaxanthin, zeaxanthin, violaxanthin and fucoxanthin. Recently, the large-scale production of carotenoids from algal sources has gained significant interest with respect to commercial and industrial applications for health, nutrition, and cosmetic applications. Although conventional processing technologies, based on solvent extraction, offer a simple approach to isolating carotenoids, they suffer several, inherent limitations, including low efficiency (extraction yield), selectivity (purity), high solvent consumption, and long treatment times, which have led to advancements in the search for innovative extraction technologies. This comprehensive review summarizes the recent trends in the extraction of carotenoids from microalgae and seaweeds through the assistance of different innovative techniques, such as pulsed electric fields, liquid pressurization, supercritical fluids, subcritical fluids, microwaves, ultrasounds, and high-pressure homogenization. In particular, the review critically analyzes technologies, characteristics, advantages, and shortcomings of the different innovative processes, highlighting the differences in terms of yield, selectivity, and economic and environmental sustainability.

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%.

Selective extraction of intracellular components from the microalga Chlorella vulgaris by combined pulsed electric field-temperature treatment.

The synergistic effect of temperature (25-65 °C) and total specific energy input (0.55-1.11 kWh kgDW(-1)) by pulsed electric field (PEF) on the release of intracellular components from the microalgae Chlorella vulgaris was studied. The combination of PEF with temperatures from 25 to 55 °C resulted in a conductivity increase of 75% as a result of cell membrane permeabilization. In this range of temperatures, 25-39% carbohydrates and 3-5% proteins release occurred and only for carbohydrate release a synergistic effect was observed at 55 °C. Above 55 °C spontaneous cell lysis occurred without PEF. Combined PEF-temperature treatment does not sufficiently disintegrate the algal cells to release both carbohydrates and proteins at yields comparable to the benchmark bead milling (40-45% protein, 48-58% carbohydrates).

Effect of pulsed light treatment on structural and functional properties of whey protein isolate

This work aimed at investigating the effects of Pulsed Light (PL) processing at different fluences (from 4 to 16J/cm2) on the structure and functional properties of Whey Protein Isolate (WPI) solution. The determination of the free and total sulfhydryl (SH) groups was used to detect the variation of WPI tertiary and quaternary structure. Additionally, PL-induced changes in secondary structure were determined by FT-IR spectroscopy and the differential scanning calorimetry (DSC), and primary structure by carbonyl content. The experimental data demonstrated that PL treatments increased the concentration of total and free sulfhydryl groups and protein carbonyls. A decrease of the denaturation temperature and enthalpy ratio with increasing the intensity of PL treatments was observed in DSC measurements. Small but significant changes in the secondary structure of PL treated WPI solution were also taking place and detected. The extent of whey protein structure modifications was fluence dependent. The results of this investigation demonstrated the potential of PL treatments to induce dissociation and partial unfolding of WPI, thus improving some of their functional properties, such as solubility and foaming ability.

Effect of pulsed electric fields – assisted extraction on anti-inflammatory and cytotoxic activity of brown rice bioactive compounds

The bioactive compounds of brown rice exhibit many beneficial health effects, ranging from antioxidant to cytotoxic activities. Pulsed Electric Field (PEF) pretreatment can significantly enhance their extraction, through the induction of the electro-permeabilization of the cell membranes. This paper aims to demonstrate that PEF-assisted extraction of brown rice enables not only enhanced yields of antioxidant compounds, such as γ-oryzanol, polyphenols and phenolic acids, and of saturated and unsaturated fatty acids, but also increased cytotoxic effects on cancer cells. Initially, the PEF-assisted extraction conditions have been defined by the assessment of the cell permeabilization index via impedance measurements and the DPPH antioxidant activity. Subsequently, the biological effects of PEF have been evaluated on the cytotoxicity and anti-inflammatory properties against human colon cancer cell line HT29. The results show that PEF-assisted extraction, enhancing the yield of bioactive compounds, with respect to untreated extracts, significantly promotes their antioxidant activity, which is correlated with an increased HT29 cells cytotoxicity. In addition, PEF extracts of brown rice substantially inhibit also gene expression and interleukin production in colon cancer cells, suggesting their exploitation as natural anti-inflammatory agents. The integration of PEF pretreatment in the solvent extraction process of bioactives from brown rice appears, therefore, as a promising practice to significantly enhance their biological activity.

Mass Transfer Enhancement by Means of Electroporation

PEF treatment involves the application of repetitive ultra-short pulses (from ns to s) of a high-strength electric field (0.1-10 kV/cm) through a material located between two electrodes. The application of the external electric field induces the permeabilization of cytoplasmatic membranes. The main advantages of PEF with respect to other treatments addressed to disrupt the cell membranes, such as the application of heat or the addition of pectolytic enzymes, are as follows:  Cost reduction due to lower energy consumption and unnecessary enzyme addition  Higher purity of the extracts, since upon the PEF treatment the permeabilized cell membranes maintain their structural integrity and are not disrupted in small fragments  Lower processing times thanks to the increased mass transfer rates. The application of PEF as a permeabilization treatment to increase the rates of mass transfer of valuable compounds from biological matrices was demonstrated to be effective in drying, extraction, and diffusion processes. This chapter reviews the basic mechanisms of PEF-induced permeabilization of plant tissues, discusses the methods of detection of electrically induced cell damages and analyses the influence of PEF process parameters on mass transfer. Furthermore, mathematical models to describe the mass transfer rates from PEF-treated vegetable tissue are discussed and some criteria of energy optimization are given as well as some examples on the recovery of polyphenolic compounds from food matrices and on the integration of PEF treatments in the winemaking industry.

Influence of pulsed light treatment on the aggregation of whey protein isolate

The effect of pulsed light (PL) on the aggregation of whey protein isolate (WPI) solutions was investigated. PL fluence values from 4 to 16J/cm2 were used to treat WPI (1% w/v) solutions in sodium phosphate buffer (pH=7.5). Whey protein structural modification and aggregation were assessed through the determination of free SH-groups and UV-absorption spectra. Additionally, covalent and non-covalently linked protein-protein interactions were identified through the measurement of turbidity, aggregation index, particle size distribution, and SDS-PAGE. WPI upon PL treatment showed structural changes as demonstrated by the immediate increase of free SH-group content (unfolding) and the subsequent formation of a small fraction of aggregation of unfolded proteins, due to both hydrophobic interactions and the formation of disulphide bonds. Turbidity, mean particle size, and aggregation index increased in samples treated at PL fluence from 4 to 16J/cm2. Furthermore, particle size distribution analysis of samples treated at higher fluence indicated that WPI dimer dissociation and formation of larger particles were likely to occur. The association of intermediate and larger protein molecules as well as the formation of soluble aggregates between β-lactoglobulin and α-lactalbumin were also observed in gel electrophoresis analysis. In conclusion, the results of this investigation demonstrated the potential of PL treatments to induce protein denaturation, with a minimal formation of soluble protein aggregates.