Abstract
Proteins extracted from microalgae for food, personal care products and cosmetics must be of high purity, requiring solvent-free extraction techniques despite their generally considerably lower protein yield and higher energy consumption. Here, three such approaches for green extraction of proteins from Chlorella vulgaris were evaluated: ultrasound, freeze-thawing, and electroporation; chemical lysis was used as positive control (maximal achievable extraction), and no extraction treatment as negative control. Compared to chemical lysis, electroporation yielded the highest fraction of extracted protein mass in the supernatant (≤27%), ultrasound ≤24%, and freeze-thawing ≤15%. After a growth lag of several days, electroporated groups of algal cells started to exhibit growth dynamics similar to the negative control group, while no growth regeneration was detected in groups exposed to ultrasound, freeze-thawing, or chemical lysis. For electroporation as the most efficient and the only non-destructive among the considered solvent-free protein extraction techniques, simultaneous extraction of intracellular algal lipids into supernatant was then investigated by HPLC, proving relatively low-yield (≤7% of the total algal lipid mass), yet feasible for glycerides (tri-, di-, and mono-) as well as other fatty acid derivatives. Our results show that electroporation, though lower in extraction yields than chemical lysis or mechanical disintegration, is in contrast to them a technique for largely debris-free extraction of proteins from microalgae, with no need for prior concentration or drying, with feasible growth regeneration, and with potential for simultaneous extraction of intracellular algal lipids into the supernatant.
Highlights
Green, solvent-free, and preferably non-destructive extraction of natural chemical compounds from microorganisms is among the key concepts in meeting the 21st century challenges of protecting both the environment and the consumers
We investigate, evaluate and compare ultrasound, freeze-thawing, and electroporation as three non-thermal, solvent-free approaches for extraction of proteins from the microalga Chlorella vulgaris; we use chemical lysis as the positive control, and absence of extraction treatment as the negative control
We demonstrate that electroporation allows largely debris-free extraction of proteins and lipids from microalgae, with feasible growth regeneration
Summary
Solvent-free, and preferably non-destructive extraction of natural chemical compounds from microorganisms is among the key concepts in meeting the 21st century challenges of protecting both the environment and the consumers. The proteins extracted from microalgae for food – as well as for personal care products and cosmetics – must be of high purity, requiring solventfree extraction techniques despite their generally lower protein yield and higher energy consumption. Bead-milling, highpressure homogenization, ultrasonication, and freeze-thawing have all proved effective in protein extraction from microalgae (Hopkins, 1991; Middelberg, 1995; Doucha and Livansky, 2008; Günerken et al, 2015; Postma et al, 2015), and ultrasonication was found effective in lipid extraction (Prabakaran and Ravindran, 2011) All these approaches generally result in cell lysis and disintegration. We demonstrate that electroporation allows largely debris-free extraction of proteins and lipids from microalgae, with feasible growth regeneration
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