Lactic from carbohydrates

Lactic acid and levulinic acid are two key intermediates prepared from carbohydrates [7]. Lipinsky [7] compared the properties of the lactide copolymers [130] obtained from lactic acid with those of polystyrene and polyvinyl chloride (see Scheme 4 and Table 5) and showed that the lactide polymer can effectively replace the synthetics if the cost of production of lactic acid is made viable. Poly(lactic acid) and poly(l-lactide) have been shown to be good candidates for biodegradeable biomaterials. Tsuji [131] and Kaspercejk [132] have recently reported studies concerning their microstructure and morphology. 

The fermentative production of lactic acid from carbohydrates has repeatedly been reviewed recently [36, 41, 42]. Two classes of lactic acid producers are discerned the homofermentative lactic acid bacteria, which produce lactic acid as the sole product, and the heterofermentative ones, which also produce ethanol, acetic acid etc. [43]. Recently, the focus has been on (S)-L-lactic acid producing, homofermentative Lactobacillus ddbrueckii subspecies [42]. 

Problem 22.34 Polylactic add (PLA) has received much recent attention because the lactic acid monomer [CH3CH(0H)C00H] from which it is made can be obtained from carbohydrates rather than petroleum. This makes PLA a more environmentally friendly polyester. (A more in-depth discussion of green polymer synthesis is presented in Section 30.8.) Draw the structure of PLA. 

The formation of acetyl CoA from carbohydrates is less direct than from fat. Recall that carbohydrates, most notably glucose, are processed by glycolysis into pyruvate (Chapter 16). Under anaerobic conditions, the pyruvate is converted into lactic acid or ethanol, depending on the organism. Under aerobic conditions, the pyruvate is transported into mitochondria in exchange for OH by the pyruvate carrier, an antiporter (Section 13.4). In the mitochondrial matrix, pyruvate is oxidatively decarboxylated by the pyruvate dehydrogenase complex to form acetyl CoA. 

For the reasons mentioned, lactic acid has the potential to become a very large-volume, commodity-chemical green product that can be produced biologically from carbohydrates to serve as the feedstock for polylactate. This potential demand is estimated at 5.5 to 5.7 billion Ib/year (or 2.5 to 3.4 million tons). Due to this potential, many large corporations have been involved in product and process development of lactic acid and polylactate production Chemical Market Reporter, October 28 1996). 

Although most synthetic approaches to L-daunosamine start from carbohydrate precursors, some routes employ chiral synthons derived from other sources. The aldehydes 213 obtained through reaction of cinnamaldehyde with acetaldehyde in the presence of Baker s yeast followed by ozonolysis [157], and 214 obtained from L-tartaric acid [158-160] have been utilised in the synthesis of daunosamine derivatives, and protected daunosamines and acosamines have been synthesised from (synthetic approaches have employed lactic acid as a chiral starting material [162, 163] and the (S)-amine 215 obtained by resolution has been converted to V-benzoyl daunosamine together with its 3-epimer [164]. Wovkulich and Uskokovic have... 

PLA can be produced by condensation polymerization directly from its basic building block lactic acid, which is derived by fermentation of sugars from carbohydrate sources such as com, sugarcane, or tapioca, as will be discussed later in this chapter. Most commercial routes, however, utilize the more efficient conversion of lactide—the cyclic dimer of lactic acid— to PLA via ring-opening polymerization (ROP) catalyzed by a Sn(ll)-based catalyst rather than polycondensation [2-6]. Both polymerization concepts rely on highly concentrated polymer-grade lactic acid of excellent quality... 

When the concentration of HCl is low, its antiseptic action is weak, and secondary fermentations are liable to occur in the stomach. These are due to organisms swallowed along with the food, and the usual end-products are butyric acid and lactic acid (derived from carbohydrates). Butyric acid causes the characteristic sour smell of regurgitated gastric contents lactic acid has no odour. 

The ROP of lactones can also be achieved by the application of much milder organic acids. Several reports have detailed the ROP of e-caprolactone and 8-valerolactone where the polymerization has been catalyzed by additional lactic add [52, 53], fumaric acid [44], maleic add [44], tartaric acid [52], dtric add [52] and a range of amino acids [52, 54]. Tartaric acid was shown to the most active catalyst for the ROP of e-caproladone in a comparative study performed by Cordova and colleagues [52], The application of this methodology, in which the polymerizations are carried out in neat lactone at either 120 or 160 °C, results in the synthesis of polymers with molecular weights that agreed weU with the initial monomer initiator ratio, and with polydispersities ranging from 1.2 to 1.9. Extension to the synthesis of dendrimers such as star poly(ester)s [55] and the polymerization of e-caprolactone from carbohydrates [56] has also been reported. 

Lactic Acid B cteri. The lactic acid bacteria are ubiquitous in nature from plant surfaces to gastrointestinal tracts of many animals. These gram-positive facultative anaerobes convert carbohydrates (qv) to lactic acid and are used extensively in the food industry, for example, for the production of yogurt, cheese, sour dough bread, etc. The sour aromatic flavor imparted upon fermentation appears to be a desirable food trait. In addition, certain species produce a variety of antibiotics. 

Some of the economic hurdles and process cost centers of this conventional carbohydrate fermentation process, schematically shown in Eigure 1, are in the complex separation steps which are needed to recover and purify the product from the cmde fermentation broths. Eurthermore, approximately a ton of gypsum, CaSO, by-product is produced and needs to be disposed of for every ton of lactic acid produced by the conventional fermentation and recovery process (30). These factors have made large-scale production by this conventional route economically and ecologically unattractive. 

In spite of the number of different structural types, lipids shar e a common biosynthetic origin in that they are ultimately derived from glucose. During one stage of carbohydrate metabolism, called glycolysis, glucose is converted to lactic acid. Pyruvic acid is an intermediate. 

Several carbohydrates such as corn and potato starch, molasses and whey can be used to produce lactic acid. Starch must fust be hydrolysed to glucose by enzymatic hydrolysis then fermentation is performed in the second stage. The choice of carbohydrate material depends upon its availability, and pretreatment is required before fermentation. We shall describe the bioprocess for the production of lactic acid from whey. 

Dry bean curd refuse was used as the substrate in the lactic acid fermentation with simultaneous saccharification (SSF). The dry bean curd refuse was preliminarily sieved under a mesh size of 250 II m. It contained 12.3% water, 4.0% ash, 0.8% lipid, 29.3% protein, 53.6% carbohydrate, respectively, in weight basis. The cellulase derived from Aspergilltis niger with an enzymatic activity of 25,000 units/g (Tokyo Kasei Industry Inc.) was employed as the saccharification enzyme. 

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