Abstract
In this study, a cascaded cell disintegration process, based on pulsed electric fields (PEF - 20 kV/cm, 100 kJ/kgSUSP.) and high-pressure homogenization (HPH - 150 MPa, 5 passes) was designed for the efficient and selective release of intracellular compounds (water-soluble proteins, carbohydrates, and lipids) from C. vulgaris suspensions during extraction in water (25 °C, 1 h) and ethyl acetate (25 °C, 3 h). Recovery yields of target compounds from cascaded treatments (PEF + HPH) were compared with those observed when applying PEF and HPH treatments individually. Particle size distribution and scanning electron microscopy analyses showed that PEF treatment alone did not induce any measurable effect on cell shape/structure, whereas HPH caused complete cell fragmentation and debris formation, with an undifferentiated release of intracellular matter. Spectra measurements demonstrated that, in comparison with HPH alone, cascaded treatments increased the selectivity of extraction and improved the yields of carbohydrates and lipids, while higher yields of water-soluble proteins were measured for HPH alone. This work, therefore, demonstrates the feasibility of sequentially applying PEF and HPH treatments in the biorefinery of microalgae, projecting a beneficial impact in terms of process economics due to the potential reduction of the energy requirements for separation/purification stages.
Highlights
In the last decades, microalgae have attracted increasing attention from the industry, because of their exploitation as an alternative source of different nutrient and non-nutrient compounds, to be used in replacement of increasingly depleted conventional sources of natural foodstuff [1,2,3,4]
The authors reported a significant alteration in the shape of the Particle Size Distribution (PSD) curve associated with untreated samples when subjected to high-pressure homogenization (HPH) treatments (P = 100 MPa, nP = 4), which correlated well with the observed 1.6-fold reduction in the mean particle size over control samples
In the case of the cascaded treatments, the mean diameter lays in between the values recorded for the individual treatments by pulsed electric fields (PEF) and HPH (Figure 2)
Summary
Microalgae have attracted increasing attention from the industry, because of their exploitation as an alternative source of different nutrient and non-nutrient compounds, to be used in replacement of increasingly depleted conventional sources of natural foodstuff [1,2,3,4]. Microalgae are capable of synthesizing high amounts of lipids, proteins, carbohydrates, and pigments, which could find large applications in the food sector and in other markets [5,6,7,8]. Microalgal proteins, carbohydrates, and pigments may find application in the food, feed, health, and bulk chemical market, or for the production of ethanol and chemicals [11,12,13,14,15]. The first and most crucial step after microalgae harvesting is the cell disintegration pre-treatment, through which damages to the cell wall/membrane system are induced, to reduce the mass transfer resistance in the extraction of valuable compounds from both cytoplasm and internal organelles [5,18,23], while maintaining high quality and purity of the extracts, as well as to prevent the reduction of the product value [24]
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