Polysaccharides fermentation methods

The connective tissues and liquids of HA, as a rule, exist firstly as chondroitin sulfates in association with collagen [27,28] and other glycosaminoglycans. Purification methods must therefore include the purification of HA from these impurities. An extraction of hyaluronate with water and aqueous salt solutions is accompanied with the presence of a large amount of impurities of protein nature, other polysaccharides, nucleic acids, lipids and lipoproteins. The limitation of the protein removal fermentative methods... 

The same methods (chemicals, enzymes, physical treatments) can be also applied on the cell wall materials not with the aim of extracting polysaccharides but with the aim of obtaining modified fibres. New properties concerning for exemple fermentability, ratio soluble/insoluble dietary fibre, hydration., can be obtained (1). 

Fine and specialty chemicals can be obtained from renewable resonrces via multi-step catalytic conversion from platform molecules obtained by fermentation. An alternative method decreasing the processing cost is to carry out one-pot catalytic conversion to final product without intermediate product recovery. This latter option is illustrated by an iimovative oxidation method developed in our laboratory to oxidize native polysaccharides to obtain valuable hydrophilic end-products useful for various technical applications. 

For monitoring the extent of polysaccharide hydrolysis, l.c. methods that sepeu ate and analyze the non-fermentable oligosaccharides (d.p. 3-30) derived from cellulose, hemicellulose, and pectins are useful, and have already been described (see Section III,l,c). For determination of the monosaccharide composition of completely hydrolyzed, plant polysaccharides, l.c. is especially useful and has been applied to the compositional analysis of hydrolyzed plant fiber,wood pulps,plant cell-walls,and cotton fibers.In these representative examples, the major sugars of interest, namely, glucose, xylose, galactose, arabinose, and mannose, have traditionally been difficult to resolve by l.c. The separa-... 

The polysaccharides in the raw materials need to be hydrolyzed before the sugar monomers canbe fermented to ethanol. Today, enzymatic hydrolysis is regarded as a method with great potential. One major obstacle to overcome is the high cost of cellulolytic enzymes. In 2001, the United States Department of Energy formed a contract with two commercial producers of cellulolytic enzymes in an attempt to achieve a 10-fold decrease in the cost of the cellulolytic enzymes (www.ott.doe.gov/ biofuels/research partnerships.html). 

The saccharification-fermentation (SF) method for the derivation of fuels and chemicals from wood is based on the breakdown or hydrolysis of the polysaccharides in wood to the constituent monomeric sugars. The six carbon or hexose sugars (glucose, galactose, and mannose) then are fermentable to ethyl alcohol... 

Fermentation products include the cells themselves, solvents and chemicals, organic and amino acids, antibiotics, polysaccharides, lipids, RNA and DNA, vaccines, bulk and fine diagnostic and therapeutic proteins, food and feed ingredients, and enzymes. These biomolecules can differ substantially in nature and require a large variety of methods to separate and purify them. They are often produced in low concentrations in complex media together with many other components. 

The hydrolysis of polysaccharides into monomeric sugars is a well-studied process its mechanism is still believed to be accurately described by the work of Saeman in 1945.432 Its significance is linked to the production of fermentable sugars for ethanol manufacture. Many of these processes are based on acid catalysis and overlap closely the pretreatment methods described earlier.363,364,373 Treatments with both concentrated and dilute acids are well known as methods for the hydrolysis of cellulose and hemicellulose, as is the use of organic dicarboxylic acids as alternative catalysts to mineral acids.433... 

There are many publications and comprehensive handbooks on the thin-layer chromatography (TLC) of carbohydrates (e.g., Refs. 1 and 2). The reason is their great importance in life science and the great diversity of cases monosaccharide, disaccharide, trisaccharide, oligosaccharide, polysaccharide, aldose, ke-tose, triose, tetrose, pentose, hexose, as well as reducing and nonreducing sugars. In addition, when extracted from natural products or produced by fermentation, carbohydrates are accompanied by many impurities. That is why separation methods are used predominantly for their analysis. 

With few exceptions, enzymatic processes in carbohydrates cause degradation. Enzymes are used in the form of pure or semipure preparations or together with their producers, i.e., microorganisms. Currently, semisynthetic enzymes are also in use. Alcoholic fermentation is the most common method of utilization of monosaccharides, sucrose, and some polysaccharides, e.g., starch. Lactic acid fermentation is another important enzymatic process. Lactic acid bacteria metabolize mono- and disaccharides into lactic acid. This acid has a chiral center thus either D(-), L(+), or racemic products can be formed. In the human organism, only the L(+) enantiomer is metabolized, whereas the D(-) enantiomer is concentrated in blood and excreted with urine. Among lactic acid bacteria, only Streptococcus shows specificity in the formation of particular enantiomers, and only the L(+) enantiomer is produced. 

The second method is direet fermentation of wood sugars, recovered from the polysaccharides, cellulose and the hemicelluloses, by aeid hydrolysis to produee ethanol. This is a proven teehnology whereas synthesis gas fermentation is as yet successful at only a small seale. The main advantage of synthesis gas fermentation is that all the wood components, ineluding lignin, beeome a potential souree of ethanol. In direct fermentation lignin must be separated out from the feed to the fermentor. 

Microbial polysaccharides from Xanthomonas campestris, notably xanthan gum for use in food industry, have been studied. Other polysaccharides like dextrans, pullulans, scleroglucan were isolated from several microbial sources. Incorporation of xanthan gum in traditional Indian fermented foods like Idli and Dosa has been investigated in elaborate details. Other products with supplementation of xanthan gum which have been investigated include orange and lemon squash, commercial tomato soup, yogurt preparations with or without CMC. Immunological methods for detection of xanthan gum in... 

Polymers derived from renewable resources (biopolymers) are broadly classified according to the method of production (1) Polymers directly extracted/ removed from natural materials (mainly plants) (e.g. polysaccharides such as starch and cellulose and proteins such as casein and wheat gluten), (2) polymers produced by "classical" chemical synthesis from renewable bio-derived monomers [e.g. poly(lactic acid), poly(glycolic acid) and their biopolyesters polymerized from lactic/glycolic acid monomers, which are produced by fermentation of carbohydrate feedstock] and (3) polymers produced by microorganisms or genetically transformed bacteria [e.g. the polyhydroxyalkanoates, mainly poly(hydroxybutyrates) and copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV)] [4]. 

The exocellular polysaccharides released by yeast during fermentation and aging on the lees may be isolated by precipitation with ethanol, or membrane ultrafiltration at a cutoff of 10 000. They may be fractionated by two processes precipitation with hexadecyltrimethylammonium bromide (Cetavlon) and affinity chromatography on a Concanavaline A-Sepharose gel column. The composition of the fractions obtained by these two methods is very similar, consisting of the following ... 

In order to improve microbial production, serious attention was given to determine the effect of fermentation conditions on the production yield and on the polymers physicochemical properties. Generally, the yield and composition of the polysaccharide depend on the microbial species used, age of the producing microbial cells and growth, cultivation medium, and conditions. The chitinous compounds content also depends on the type of fermentation and extraction method. An increase in chitinous material can be obtained either by increased biomass yield or by an increase in the cell wall content of chitin/chitosan. A summary of the advantages and disadvantages of several biotechnological possibilities to produce chitin/chitosan can be found in Table 3.1. 

A wide variety of products can be produced by fermentation. In some cases the microorganism itself is the product, for example, in the manufacturing of active dry yeast (ADY). Well-known pharmaceutical fermentation products are insulin and penicillin G. Fermentation processes are also used to produce various commodity bioproducts like organic and amino acids, polysaccharides, lipids, chemical compounds like isoprene (Whited et al., 2010), 1,3-propanediol (Nakamura and Whited, 2003), RNA, DNA, enzymes, and other proteins. The large variety of commodity bioproducts produced by fermentation requires an equally large variety of different methods to separate and purify them. Compared to fermentation processes, where usually one unit, the fermenter vessel, is used, several different steps and unit operations are necessary to achieve purification and formulation of bioproducts. 

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