sustainability Review Liquid Biphasic Systems for Oil-Rich Algae Bioproducts Processing 1, 2, 3 1, 4 Hui Yi Leong y, Chih-Kai Chang y, Jun Wei Lim , Pau Loke Show * , Dong-Qiang Lin and Jo-Shu Chang 5,6,7,* 1 Department of Chemical and Environmental Engineering, Faculty of Science and Engineering, University of Nottingham Malaysia, Jalan Broga, 43500 Semenyih, Selangor Darul Ehsan, Malaysia 2 Department of Chemical Engineering and Materials Science, Yuan Ze University, No. 135, Yuan-Tung Road, Chungli, Taoyuan 320, Taiwan 3 Department of Fundamental and Applied Sciences, Centre for Biofuel and Biochemical Research, Institute of Self-Sustainable Building, Universiti Teknologi PETRONAS, 32610 Seri Iskandar, Perak Darul Ridzuan, Malaysia 4 College of Chemical and Biological Engineering, Zhejiang University, Hangzhou 310027, China 5 Department of Chemical Engineering, National Cheng Kung University, Tainan 701, Taiwan 6 Research Center for Energy Technology and Strategy, National Cheng Kung University, Tainan 701, Taiwan 7 Research Center for Circular Economy, National Cheng Kung University, Tainan 701, Taiwan * Correspondence: [email protected] or [email protected] (P.L.S.); [email protected] (J.-S.C.) These authors contributed equally to this work and should be considered as co-first authors. y Received: 25 June 2019; Accepted: 16 July 2019; Published: 28 August 2019 Abstract: Oleaginous algae are nowadays of significance for industrial biotechnology applications and for the welfare of society. Tremendous efforts have been put into the development of economically feasible and effective downstream processing techniques in algae research. Currently, Liquid Biphasic Systems (LBSs) are receiving much attention from academia and industry for their potential as green and effective downstream processing methods. This article serves to review the applications of LBSs (LBS and Liquid Biphasic Flotation System (LBFS)) in the separation, recovery and purification of algae products, as well as their basic working principles. Moreover, cell disruptive technologies incorporated into LBSs in algae research are reported. This review provides insights into the downstream processing in algae industrial biotechnology which could be beneficial for algae biorefinement. Keywords: algae; cell disruption; downstream processing; liquid biphasic flotation system; liquid biphasic system; purification; recovery; separation 1. Introduction Over the years, algae (both macro- and microalgae) have received increasing levels of attention for the downstream processing of industrial biotechnology. Macroalgae (collectively known as seaweed) have two significant functions: (i) human consumption, and (ii) the production of gelatinous compounds such as agar, alginate and carrageenan. These compounds, known as hydrocolloids or phycocolloids, play a role as food additives. On the other hand, microalgae, to some degree, play an important role in algae biorefinement [1]. Microalgae biorefinement is of growing interest worldwide; the sustainable production of valuable microalgae-derived products can be attained through biorefinery processes. These products such as biofuels, carbohydrates, proteins, lipids, polyunsaturated fatty acids (PUFAs), vitamins, antioxidants, pigments, fertilizers and natural colorants, are valuable to the society. Moreover, most are generally associated with the manufacturing of biomedical, pharmaceutical and nutraceutical products [2–9]. Sustainability 2019, 11, 4682; doi:10.3390/su11174682 www.mdpi.com/journal/sustainability Sustainability 2019, 11, 4682 2 of 14 Oil-rich (oleaginous) microalgae such as Chlorella, Scenedesmus, Spirulina and Saccharina are potential biofuel feedstocks. Microalgae-derived biofuels, for example, bioethanol, biodiesel, biohydrogen, syngas and methane, are promising sources of green, renewable and sustainable energy globally [10–14]. Other than that, Chlorella and Spirulina were the first microalgae to have been commercialised as health food supplements worldwide, especially in Mexico, Taiwan and Japan. Later, β-carotene and astaxanthin from Dunaliella salina (also known as Dunaliella bardawil) and Haematoccus pluvialis, respectively, were marketed. Both β-carotene and astaxanthin are natural red pigments categorisedSustainability as carotenoids, 2019, 11, x FOR which PEER REVIEW are good for human health. Other carotenoids,2 of such 15 as lutein, canthaxanthin, zeaxanthin and fucoxanthin, are mostly synthesised by green algae (e.g., Scenedesmus Oil-rich (oleaginous) microalgae such as Chlorella, Scenedesmus, Spirulina and Saccharina are almeriensis, Scenedesmuspotential biofuel komareckii feedstocks., ChlorellaMicroalgae-derived zofigiensis biofuels,, Dunaliella for example, salina bioethanol,, Phaeodactylum biodiesel, tricornutum etc.). Moreover,biohydrogen,Crypthecodinium syngas and methane, cohnii aresuccessfully promising source produceds of green, docosahexaenoicrenewable and sustainable acid energy (DHA), and the product wasglobally subsequently [10–14]. Other commercialised. than that, Chlorella DHA and Spirulina is a type were of the PUFA first thatmicroalgae can beto have used been as a functional commercialised as health food supplements worldwide, especially in Mexico, Taiwan and Japan. food to improve health by preventing non-communicable diseases as well as improving cognitive and Later, β-carotene and astaxanthin from Dunaliella salina (also known as Dunaliella bardawil) and neurologicalHaematoccus functions. pluvialis Finally,, respectively,Isochrysis were, Nannochloropsis marketed. Both β-carotene, Chaetoceros and astaxanthin, Aurantiochytrium are natural red , Tetraselmis and Thalassiosirapigmentsare categorised among the as carotenoid PUFAs-producers, which are good microalgae for human [3 h,ealth.8,15]. Other carotenoids, such as The highlutein, operating canthaxanthin, costs ofzeaxanthin biorefining and fucoxanthin, algae mainly are comemostly fromsynthesised downstream by green algae processing (e.g., involving Scenedesmus almeriensis, Scenedesmus komareckii, Chlorella zofigiensis, Dunaliella salina, Phaeodactylum various stepstricornutum of recovery, etc.). isolation,Moreover, purificationCrypthecodinium and cohnii the successfully polishing produced of target docosahexaenoic products [16 ].acid Conventional separation and(DHA) purification, and the product methods was subsequently for the extraction commercialised. of valuable DHA is a algaetype of products,PUFA that can for be example, used Soxhlet extraction, maceration,as a functional high food pressure to improve heating healthand by preventing chemicals, non homogenisers-communicable diseases and bead as beating,well as contribute improving cognitive and neurological functions. Finally, Isochrysis, Nannochloropsis, Chaetoceros, to the high productionAurantiochytrium cost,, Tetraselmis impact and upon Thalassiosira the environment, are among the PUFAs and workload.-producer microalgae These [3,8,15] issues. illustrate the need to developThe new, high eff ective,operating and cost cost-savings of biorefining downstream algae mainly processingcome from downstream techniques processing [3,5,8,9 ,13]. Liquid biphasic systemsinvolving (LBSs) various o ffstepser a of unique, recovery, one-stepisolation, purification procedure andfor the downstreampolishing of target processing, products [16].which make Conventional separation and purification methods for the extraction of valuable algae products, for them attractiveexample, for theSoxhlet application extraction, maceration, of industrial high biotechnologypressure heating and [16 chemicals,]. LBSs homogenisers including Liquid and Biphasic Flotation Systemsbead beating, (LBFSs), contribute i.e., to a the type high of production bubble-assisted cost, impact LBS,upon the represent environment green, and andworkload highly-e. fficient separation, recoveryThese issues and illustrate purification the need to technologies develop new, effective for biomolecules., and cost-saving These downstream systems processing provide a gentle techniques [3,5,8,9,13]. Liquid biphasic systems (LBSs) offer a unique, one-step procedure for working environmentdownstream processing, for the recovery which make of them target attractive products for the whichapplication can of extractindustrial thebiotechnology products of interest without damaging[16]. LBSs other including fractions Liquid B [iphasic17,18]. Flotation Systems (LBFSs), i.e., a type of bubble-assisted LBS, This articlerepresent provides green and on ahigh comprehensively-efficient separation, review recovery (both and theoretical purification knowledgetechnologies for and empirical biomolecules. These systems provide a gentle working environment for the recovery of target research) ofproducts the separation, which can extract recovery the products and purificationof interest without of damaging algae products other fractions by di[17,18]fferent. types of LBSs (i.e., LBS and LBFS),This article as wellprovides as onon a the comprehensive basic principles review (both involved theoretical therein. knowledge In and addition, empirical di fferent cell disruptive technologiesresearch) of the integrated separation, recovery with LBSs and purification in algae research of algae products are well-discussed by different types (see of FigureLBSs 1). To the (i.e., LBS and LBFS), as well as on the basic principles involved therein. In addition, different cell best of the authors’disruptive knowledge,technologies integrated this is with the LBSs first in review