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HIGHLIGHTS  Review of pressurized hot water extraction of bioactive compounds, 2009-14  Chemical and physical properties of pressurized hot liquid water  Equipment, method optimization, applications, coupling and future prospects  Challenges with degradation and other chemical reactions during extraction ABSTRACT The purpose of this review is to give the reader a thorough background to the fundamentals and applications of pressurized hot water extraction (PHWE) for the analysis of bioactive compounds. We summarize the field in the period 2009-14, and include fundamentals of water as a solvent: equipment; method optimization; applications; coupling; and, future prospects. We highlight that solvent properties of water are tunable by changing the temperature, particularly self-ionization, dielectric constant, viscosity, diffusivity, density and surface tension. Furthermore, important aspects to consider are the risk of degradation of the analytes and other potential reactions, such as hydrolysis, caramelization and Maillard reactions that may lead to erroneous results. For the extraction of bioactive compounds, we report PHWE methods based on using water of 80-175°C and short extraction times. In conclusion, PHWE provides advantages over conventional extraction methods, such as being "greener", faster and more efficient. Why another review article on pressurized hot water extraction?Pressurized hot water extraction (PHWE) is an extraction technique that uses liquid water as extractant (extraction solvent) at temperatures above the atmospheric boiling point of water (100°C/273 K, 0.1 MPa), but below the critical point of water (374°C/647 K, 22.1 MPa) (Fig. 1). The use of PHWE in analytical chemistry started with the work in environmental analysis by Hawthorne and colleagues in the mid-1990s [1,2], and can also be referred to as subcritical water extraction (SWE), superheated water extraction and pressurized liquid extraction or accelerated solvent extraction with water as a solvent. There are a few relatively recent review articles on analytical PHWE, which the reader is recommended to read [3][4][5][6][7].The aim of this review article is to give a thorough background on the fundamental properties of water -an aspect that has been virtually overlooked in most review articles written so far about analytical PHWE. Hence, the first part of this review article concerns the fundamentals of chemical/physical properties of water and how these change with the increase in temperature, as well as how these affect the extraction performance both positively and negatively in different analytical applications.The second part deals with technical solutions of PHWE and how to conduct the experiment in practice. This technical part includes discussions on using commercially available and home-built equipment. The third part includes aspects on method optimization in PHWE. The fourth part summarizes some of the key applications and related publications mainly in the field of extraction of bioactive compounds from plants, food, ...

Lignin is a major component of lignocellulosic biomass and as such, it is processed in enormous amounts in the pulp and paper industry worldwide. In such industry it mainly serves the purpose of a fuel to provide process steam and electricity, and to a minor extent to provide low grade heat for external purposes. Also from other biorefinery concepts, including 2nd generation ethanol, increasing amounts of lignin will be generated. Other uses for lignin - apart from fuel production - are of increasing interest not least in these new biorefinery concepts. These new uses can broadly be divided into application of the polymer as such, native or modified, or the use of lignin as a feedstock for the production of chemicals. The present review focuses on the latter and in particular the advances in the biological routes for chemicals production from lignin. Such a biological route will likely involve an initial depolymerization, which is followed by biological conversion of the obtained smaller lignin fragments. The conversion can be either a short catalytic conversion into desired chemicals, or a longer metabolic conversion. In this review, we give a brief summary of sources of lignin, methods of depolymerization, biological pathways for conversion of the lignin monomers and the analytical tools necessary for characterizing and evaluating key lignin attributes.

The seed oil derived from the tung (Aleurites fordii Hemsl.) tree contains approximately 80% ␣-eleostearic acid (18: 3⌬ 9cis,11trans,13trans ), an unusual conjugated fatty acid that imparts industrially important drying qualities to tung oil. Here, we describe the cloning and functional analysis of two closely related ⌬ 12 oleate desaturase-like enzymes that constitute consecutive steps in the biosynthetic pathway of eleostearic acid. Polymerase chain reaction screening of a tung seed cDNA library using degenerate oligonucleotide primers resulted in identification of two desaturases, FAD2 and FADX, that shared 73% amino acid identity. Both enzymes were localized to the endoplasmic reticulum of tobacco (Nicotiana tabacum cv Bright-Yellow 2) cells, and reverse transcriptase-polymerase chain reaction revealed that FADX was expressed exclusively within developing tung seeds. Expression of the cDNAs encoding these enzymes in yeast (Saccharomyces cerevisiae) revealed that FAD2 converted oleic acid (18:1⌬ 9cis ) into linoleic acid (18:2⌬ 9cis,12cis ) and that FADX converted linoleic acid into ␣-eleostearic acid. Additional characterization revealed that FADX exhibited remarkable enzymatic plasticity, capable of generating a variety of alternative conjugated and ⌬ 12 -desaturated fatty acid products in yeast cells cultured in the presence of exogenously supplied fatty acid substrates. Unlike other desaturases reported to date, the double bond introduced by FADX during fatty acid desaturation was in the trans, rather than cis, configuration. Phylogenetic analysis revealed that tung FADX is grouped with ⌬ 12 fatty acid desaturases and hydroxylases rather than conjugases, which is consistent with its desaturase activity. Comparison of FADX and other lipid-modifying enzymes (desaturase, hydroxylase, epoxygenase, acetylenase, and conjugase) revealed several amino acid positions near the active site that may be important determinants of enzymatic activity.Conjugated fatty acids are naturally occurring compounds that have specialized uses in nutraceutical and industrial applications. For example, conjugated linoleic acid (CLA) is a potent anticancer compound present in foods derived from ruminant animals (Belury, 2002). This bioactive fatty acid (predominantly the 18:2⌬ 9cis,11trans isomer) is synthesized by rumen bacteria and then absorbed by the animal and concentrated in milk fat or adipose tissue. Rumen bacteria also synthesize 18:1⌬ 11trans , which can be absorbed and then desaturated by an animal stearoyl-CoA desaturase to produce CLA (Corl et al., 2001). Conjugated fatty acids such as ␣-eleostearic acid (18:3⌬ 9cis,11trans,13trans ) have recently shown promise for anticancer applications (Igarashi and Miyazawa, 2000;Kohno et al., 2002), as well as serum lipidlowering effects in mammals (Koba et al., 2002). Oils containing ␣-eleostearic acid may also be used for industrial drying applications. Tung oil, which is derived from seeds of the tung tree (Aleurites fordii Hemsl.), is commonly used in formulations of inks, dyes,...

Onion waste is a renewable raw material, rich in different molecular species of the antioxidant quercetin. To utilize this resource, an environmentally sustainable procedure has been developed, using pressurized hot water to extract the quercetin species, followed by biocatalytic conversion of the quercetin glycosides to quercetin and carbohydrates. Two different recombinantly expressed thermostable b-glucosidases, Thermotoga neapolitana b-glucosidase A and B, were utilized as catalysts. These enzymes maintain activity at temperatures around 90 uC, and are therefore ideal to use in combination with hot water extraction. Our results, based on experimental design, showed that they converted quercetin glycosides to active quercetin in less than 10 min reaction time in water at 90 uC, pH 5.0. Experimental design showed that the optimal extraction conditions included three 5 min extraction cycles with water at 120 uC and 50 bars, giving a total extraction time of 15 min. Several different types of quercetin and isorhamnetin glycosides as well as kaempferol were detected in onion waste using LC-MS/MS analysis. After converting the different glycosidic compounds to their respective aglycones, the quercetin content was 10 to 50 mg g 21 dry weight of onion waste (RSD 8%). In summary, our research demonstrates that subcritical water extraction followed by b-glucosidase-catalyzed hydrolysis is a rapid method to determine the content of quercetin and isorhamnetin in onion samples, and is environmentally sustainable as it only uses water as solvent and enzymes as catalysts.

Antioxidants are widely used by humans, both as dietary supplements and as additives to different types of products. The desired properties of an antioxidant often include a balance between the antioxidizing capacity, stability, and solubility. This review focuses on flavonoids, which are naturally occurring antioxidants, and different common substituent groups on flavonoids and how these affect the properties of the molecules in vitro. Hydroxyl groups on flavonoids are both important for the antioxidizing capacity and key points for further modification resulting in O-methylation, -glycosylation, -sulfation, or -acylation. The effects of O-glycosylation and acylation are discussed as these types of substitutions have been most explored in vitro concerning antioxidizing properties as well as stability and solubility. Possibilities to control the properties by enzymatic acylation and glycosylation are also reviewed, showing that depending on the choice of enzyme and substrate, regioselective results can be obtained, introducing possibilities for more targeted production of antioxidants with predesigned properties.

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In this study, we analyzed fatty acid and carotenoid composition of fruit tissues, including seed (which are surrounded by a bright red, oily aril) of Momordica cochinchinensis Spreng, known as gac in Vietnam. Carotenoid content was analyzed by reversed-phase HPLC, using a C(30) column and a method separating cis- and trans-isomers of the major carotenoids in this fruit. Mean values obtained in aril tissues were 1342 microg trans-, 204 microg cis-, and 2227 microg total lycopene; 597 microg trans-, 39 microg cis-, and 718 microg total beta-carotene; and 107 microg alpha-carotene/g FW. Mesocarp contained 11 microg trans-, 5 microg cis-beta-carotene/g FW, trace amounts of alpha-carotene, and no lycopene. Gac aril contained 22% fatty acids by weight, composed of 32% oleic, 29% palmitic, and 28% linoleic acids. Seeds contained primarily stearic acid (60.5%), smaller amounts of linoleic (20%), oleic (9%), and palmitic (5-6%) acids, and trace amounts of arachidic, cis-vaccenic, linolenic, and palmitoleic, eicosa-11-enoic acids, and eicosa-13-enoic (in one fruit only) acids.