CROSS REFERENCE TO RELATED APPLICATIONS

This application is a National Stage of International Application No. PCT/KR2019/011509 filed Sep. 5, 2019, claiming priority based on Korean Patent Application No. 10-2018-0106552 filed Sep. 6, 2018, the entire disclosures of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a method of chemically producing novel sugar alcohols, 3,6-anhydro-L-galactitol (L-AHGol) and agarobititol (ABol) which is a disaccharide having the L-AHGol as a reducing end, from marine algae.

BACKGROUND ART

The ocean has a unique environment different from land, such as high pressure, low temperature, low oxygen content, and a small amount of light. For this reason, unlike terrestrial organisms, marine organisms have their own unique characteristics. Among marine organisms, marine algae, unlike land plants, have very unique characteristics such as absorbing and preserving moisture well because they inhabit the ocean. Among marine algae, especially, agar, which is obtained from red algae, retains moisture to form a gel, and therefore, it has been widely used in the food and pharmaceutical industry. Agarose, which is a major polysaccharide constituting the agar, is a polymer consisting of 3,6-anhydro-L-galactose (L-AHG) and D-galactose alternately linked by an α-1,3-bond and a β-1,4-bond. In this case, L-AHG, which is a rare sugar that does not exist in terrestrial organisms, can be used as a cosmetic material due to having excellent whitening and moisturizing effects and is a multifunctional high value-added material with anti-inflammatory, anti-caries, and colon cancer prevention effects. Due to the functionality of L-AHG, many studies have been conducted to produce L-AHG from red algae for use as a high value-added material. In addition, agarobiose (AB) which is a disaccharide having L-AHG as a reducing end is known to have an excellent anti-inflammatory effect.

However, since L-AHG and AB are very unstable under conditions of high temperatures and acids, they are easily converted into 5-hydroxymethyl furfural and thus lose the functionality thereof.

Sugar alcohols generally refer to all types of sugars whose aldehyde group or ketone group is substituted with an alcohol group by adding hydrogen. Sugar alcohols have a variety of functions that natural sugars do not have and also have lower sweetness than natural sugars and a refreshing feeling. For this reason, various sugar alcohols such as sorbitol, xylitol, mannitol, and the like have been used as food additives, and maltitol, lactitol, erythritol, and the like are themselves treated as foods. In addition, sugar alcohols may be converted into useful chemicals through chemical and biological catalytic reactions. In this way, sugar alcohols are potential high value-added materials, and there is a need for production of novel sugar alcohols.

The inventors of the present invention have attempted to compensate for the disadvantages of L-AHG and AB and confirm multifunctionality by producing L-AHGol and ABol which are the sugar alcohols of L-AHG and AB.

RELATED-ART DOCUMENTS

Patent Documents

Korean Registered Patent No. 10-1864800 (2018May 30)

Non-Patent Documents (Non-Patent Document 1) H T Kim et al.,Bioresour. Technol. (2012) 107: 301-306

(Non-Patent Document 2) H T Kim et al.,Bioresour. Technol. (2013) 136: 582-587

(Non-Patent Document 3) C H Lee et al.,Appl. Environ. Microbiol. (2014) 80: 5965-5973 (Non-Patent Document 4) C H Lee et al.,Process Biochem. (2015) 50: 1629-1633

DISCLOSURE

Technical Problem

The present invention is directed to providing a method of producing a sugar alcohol from agarose or agar by acid hydrolysis and chemical reduction with a reductant.

The present invention is also directed to providing a method of producing a sugar alcohol from agarose or agar by enzymatic saccharification and chemical reduction with a reductant.

Technical Solution

One aspect of the present invention provides a method of producing one or more sugar alcohols of agarobititol (ABol) and 3,6-anhydro-L-galactitol (L-AHGol) from agarose or agar, which includes the steps of: (1) acid-hydrolyzing 5 to 30% (w/w) of agarose or agar based on dry weight, which is a substrate, using a strong acid with a concentration of 0.1 to 5% (w/v) at 80 to 140° C. for 5 minutes to 500 minutes to produce one or more sugars of agarobiose and 3,6-anhydro-L-galactose (L-AHG); and (2) treating the produced sugars with a reductant.

Another aspect of the present invention provides a method of producing 3,6-anhydro-L-galactitol (L-AHGol) from agarose or agar, which includes the steps of: (1) saccharifying agarose or agar, which is a substrate, using endo-β-agarase, exoβ-agarase, and neoagarobiose hydrolase to produce 3,6-anhydro-L-galactose (L-AHG); and (2) treating the produced L-AHG with a reductant to induce reduction.

The material to be finally produced in the present invention is a sugar alcohol derived from agarose or agar, which is referred to as agarobititol (ABol) or 3,6-anhydro-L-galactitol (L-AHGol). The two types of sugar alcohols are in the form in which agarobiose (AB) and 3,6-anhydro-L-galactose (L-AHG) are reduced with a reductant, respectively. The AB or L-AHG is produced from agar or agarose largely in three ways through previous studies described in the Related-Art Documents of the present invention. First, there is a method of hydrolyzing agarose or agar using a strong acid at high temperature, and this method has a problem of degraded L-AHG yield but is economical due to a relatively simple process. Second, there is a method of using a β-agarase system, and endo- and exo-β-agarase and neoagarobiose hydrolase are used. This method has a problem of a complex process caused by using various enzymes, but the use of the enzymes results in high yield. Third, there is a method of liquefying agarose or agar using an acid or chemical catalyst and then saccharifying the liquefied agarose or agar using various enzymes to produce L-AHG. This method also has a problem of a complex process caused by performing saccharification using β-agarases after the liquefaction process, like the second method, but results in high yield. Therefore, the present invention has been completed by producing AB and L-AHG using the methods and then reducing the products with a reductant to convert the products into ABol and L-AHGol.

In addition, the method of the present invention is largely divided into a step of hydrolysis or saccharification of agarose or agar and a reduction step, and the steps are characterized in that they are performed simultaneously in a single reactor, and the specific reaction conditions of each step may vary.

In the method of the present invention, which uses acid hydrolysis, when agarose or agar is treated with a strong acid, the strong acid with a concentration of 0.1 to 5% (w/v), and specifically, 0.5 to 3% (w/v), may be used. Within the above-described concentration range, the production of 5-HMF caused by treatment of agarose or agar with a strong acid can be minimized, and simultaneously, a high concentration of AB can be produced, resulting in the production of L-AHG with high yield.

In addition, the treatment of agarose or agar with a strong acid may be performed using a strong acid with a concentration of 0.1 to 5% (w/v) at 80 to 140° C. for 5 minutes to 300 minutes. Specifically, the treatment may be performed using a strong acid with a concentration of 2% (w/v) at 90° C. for 5 minutes to 300 minutes, and, under the above-described conditions, most of the agarose or agar may be acid-hydrolyzed to produce AB.

Furthermore, to further hydrolyze the AB to produce L-AHG, more intensive reaction conditions are required. Specifically, the reaction may be performed using a strong acid with a concentration of 2% (w/v) at 120° C. for 10 minutes to 30 minutes.

The strong acid may be phosphoric acid, sulfuric acid, hydrochloric acid, nitric acid, or the like. More specifically, phosphoric acid may be used.

The amount of agarose or agar used in the treatment with the strong acid may be 5 to 20% (w/v), and more specifically, 10% (w/w) based on dry weight. Within the above-described content range, a liquefaction rate of 90%, 95%, or 98% or more may be achieved. Outside of the above-described content range, the hydrolysis rate of a substrate may be substantially degraded.

In the method of producing L-AHG from agarose or agar according to another embodiment of the present invention, agarose or agar may be directly saccharified into L-AHG, without passing through AB, using endo-β-agarase, exo-β-agarase, and neoagarobiose hydrolase, and this enzymatic method may increase the production yield of L-AHG compared to the acid hydrolysis method.

The endo-β-agarase, exo-β-agarase, and neoagarobiose hydrolase may be represented by amino acid sequences set forth in SEQ ID NO: 1, SEQ ID NO: 2, and SEQ ID NO: 3, respectively.

The endo-β-agarase, exo-β-agarase, and neoagarobiose hydrolase may be transcribed and translated through a DNA segment, that is, a coding gene involved in producing a polypeptide, having an intervening sequence between individual coding segments as well as regions before and after the coding region of the enzyme. For example, each enzyme may be transcribed and translated from base sequences set forth in SEQ ID NO: 4, SEQ ID NO: 5, and SEQ ID NO: 6, but the present invention is not limited thereto. In addition, one or more mutant proteins of the enzymes by transition, deletion, transposition, addition, and the like, which have hydrolysis activity with respect to the agarobiose, are also encompassed in the scope of the present invention for an enzyme, and preferably, an amino acid sequence having a sequence identity of 80% or more, 85% or more, 90% or more, 93% or more, 94% or more, 95% or more, 96% or more, 97% or more, 98% or more, or 99% or more with amino acid sequences set forth in SEQ ID NOS: 1 to 3 is included.

The endo-β-agarase may be derived fromBacteroides plebeius, and the exo-β-agarase and the neoagarobiose hydrolase may be derived fromSaccharophagus degradans2-40T, but the present invention is not limited thereto.

The endo-β-agarase, exo-β-agarase, and neoagarobiose hydrolase may be isolated from cell lysates or supernatants ofBacteroides plebeiusandSaccharophagus degradans2-40Tand purified and may also be produced and isolated by strains other than the above strains or artificial chemical synthesis using a genetic engineering recombination technique. In the case of using the recombination technique, the lysate or culture medium of transformedE. colimay be used as an alternative, but the present invention is not limited thereto. According to an embodiment, the enzymes may be obtained fromE. colitransformed with recombinant vectors including base sequences set forth in SEQ ID NO: 4, SEQ ID NO: 5, and SEQ ID NO: 6, or a culture medium thereof.

The reaction of agar or agarose with endo-β-agarase, exo-β-agarase, and neoagarobiose hydrolase may be sequentially performed. Specifically, the reaction of agar or agarose, which is a substrate, with endo-β-agarase may be performed at 40 to 60° C. for 5 hours to 48 hours. More specifically, the reaction may be performed at 50° C. for 6 hours. Then, the reaction of the resulting product, which is a substrate, with exo-D-agarase may be performed at 20 to 40° C. for 1 hour to 10 hours. More specifically the reaction may be performed at 30° C. for 2 hours. Then, the reaction of the resulting product, which is a substrate, with neoagarobiose hydrolase may be performed at 20 to 40° C. for 1 hour to 10 hours. More specifically, the reaction may be performed at 30° C. for 2 hours.

As used herein, the terms “enzyme”, “protein”, and “polypeptide” are used interchangeably.

In the present invention, the fact that polypeptide has a specific ratio (e.g., 80%, 85%, 90%, 95%, or 99%) of sequence identity with another sequence means that when the two sequences are aligned and compared, the above-described ratio of amino acid residues are identical. The alignment and percent homology or identity may be determined using any suitable software program known in the art, for example, those described in the document [CURRENT PROTOCOLS IN MOLECULAR BIOLOGY (F. M. Ausubel et al. (eds) 1987 Supplement 30 section 7.7.18)]. As desirable programs, the GCG Pileup program, FASTA (Pearson et al.

1988Proc. Natl Acad. SciUSA 85: 2444-2448), and BLAST (BLAST Manual, Altschul et al., Natl. Cent. Biotechnol. Inf., Natl Lib. Med. (NCIB NLM NIH), Bethesda, Md., and Altschul et al. 1997 NAR25: 3389-3402) may be used. As another desirable alignment program, ALIGN Plus (Scientific and Educational Software, PA) may be used, and preferably, a basic parameter may be used. As another available sequence software program, TFASTA Data Searching Program (Sequence Software Package Version 6.0, Genetics Computer Group, University of Wisconsin, Madison, Wis.) may be used.

As used herein, the term “recombination”, when used in relation to a cell, nucleic acid, protein, or vector, means that the cell, nucleic acid, protein, or vector is modified by the introduction of a heterologous nucleic acid or protein or the alteration of the original nucleic acid or protein, or that the cell is derived from the modified cell. That is, for example, a recombinant cell expresses a gene that is not found in the original (non-recombinant) form of the cell, or otherwise expresses an original gene that is abnormally expressed or not expressed at all.

As used herein, the term “nucleic acid” encompasses single-stranded or double-stranded DNA, RNA, and chemical modifications thereof. “Nucleic acid” and “polynucleotide” may be used interchangeably herein. Since the genetic code is degenerated, one or more codons may be used to encode a specific amino acid, and polynucleotides encoding a specific amino acid sequence are encompassed in the present invention.

The term “introduction” for inserting a nucleic acid sequence into a cell means “transfection”, “transformation”, or “transduction” and encompasses the integration of a nucleic acid sequence into a eukaryotic or prokaryotic cell. In this case, the nucleic acid sequence is integrated into the genome of the cell (e.g., chromosome, plasmid, plastid, or mitochondrial DNA) and thus converted into an autonomous replicon or transiently expressed.

In the present invention, the step of reducing one or more sugars of agarobiose and 3,6-anhydro-L-galactose (L-AHG) with a reductant may be performed at the same time as or in the middle of the step of acid-hydrolyzing or enzymatically saccharifying agar or agarose, or at the time the step is terminated. According to a specific embodiment, when reduction is performed with a reductant at the terminal time the final product is sufficiently produced by performing acid hydrolysis or enzymatic saccharification of agar or agarose, the final product is produced with excellent yield.

Examples of the reductant include morpholine borane, piperidine borane, pyridine borane, piperazine borane, 2,6-lutidine borane, N,N-diethylaniline borane, 4-methylmorpholine borane (MMB), 1,4-oxathiane borane, ammonium, alkali and alkaline earth metal borohydrides, hypophosphites, sulfites, bisulfites, hydrosulfites, metabisulfites, dithionates, tetrathionates, thiosulfates, thioureas, hydrazines, hydroxylamines, aldehydes (including formaldehyde and glyoxal], glyoxylic acid, reducing sugars, and a combination thereof, but the present invention is not limited thereto. According to a specific embodiment, the reductant of the present invention may be 4-methylmorpholine borane (MMB), sodium borohydride, and a combination thereof.

Advantageous Effects

According to the present invention, optimal conditions that allow a sugar alcohol, which is a novel biomaterial, to be mass-produced from agarose or agar are established, particularly, agarose or agar can be easily and efficiently converted into a sugar alcohol by chemical reduction with a reductant, and a process of producing a sugar alcohol of the present invention is simplified by simultaneously performing acid hydrolysis and reduction in a single reactor.

