Converted starches enzymatic conversion

Prior to fermentation, the wort is then cooled to temperatures below 85°F (30°C), and the pH is adjusted to about 5. Yeast such as Saccharomyces cerevisiae, Saccharomyces carlsbergensis or Candida brassicae are added and fermentation proceeds for 2 to 3 days under batch processing conditions. Yeast produces the enzymes maltase, zymase, and invertase. Maltase converts maltose to glucose. Zymase converts glucose to ethanol. Invertase converts any sucrose present to fermentable sugar. The following equations illustrate the enzymatic conversion of starch to ethanol ... 

As mentioned above, this process now serves mainly as an adjunct to enzymatic conversion of starch and is rarely used alone. A starch slurry containing 35-45 percent solids is acidified with hydrochloric acid to about pH 1.8-1.9. The suspension is pumped into an autoclave (converter) where live steam is gradually admitted to a pressure of 30-45 psi. The conversion time largely determines the DE of the hydrolyzate for example, eight min... 

Size press starch may be non-ionic, from in-mill enzymatic conversion or thermo-chemical conversion of native starch. It may be anionie if an oxidised starch is used. (Note this refers to chemically modified oxidised starch. Many American texts wrongly refer to any viscosity-reduced starch - including enzyme-converted and thermo-chetnically converted stareh - as oxidised stareh. Such processes do not form any carboxyl or carbonyl groups on the starch.) Furthermore, cationic and amphoteric starches are frequently tpplied on multi-purpose office paper for improved ink-jet printability. 

In the enzymatic conversion process the depolymerization of starch, i.e., the cleavage of the 1,4- and 1,6-bridges is performed by hydrolases, specifically by glycosidase enzymes. Naturally occurring hydrolases capable of converting starch into specific products are... 

Eurther conversion (saccharification) to dextrose can be done using glucoamylase. Starch consists of polymeric linear a-1,4 linked dextrose units (amylose, 25 % of the starch) and polymeric mixed a-l,4/a-l,6 linked dextrose units (amylopectin, 75 % of the starch). Eor enzymatic degradation besides a-1,4 specific amylases also a-1,6 specific amylases (pullulanases) are required. A portion of the dextrose can be converted into fructose with a glucose isomerase yielding a high fructose com symp (MFCS). 

A membrane cell recycle reactor with continuous ethanol extraction by dibutyl phthalate increased the productivity fourfold with increased conversion of glucose from 45 to 91%.249 The ethanol was then removed from the dibutyl phthalate with water. It would be better to do this second step with a membrane. In another process, microencapsulated yeast converted glucose to ethanol, which was removed by an oleic acid phase containing a lipase that formed ethyl oleate.250 This could be used as biodiesel fuel. Continuous ultrafiltration has been used to separate the propionic acid produced from glycerol by a Propionibacterium.251 Whey proteins have been hydrolyzed enzymatically and continuously in an ultrafiltration reactor, with improved yields, productivity, and elimination of peptide coproducts.252 Continuous hydrolysis of a starch slurry has been carried out with a-amylase immobilized in a hollow fiber reactor.253 Oils have been hydrolyzed by a lipase immobilized on an aromatic polyamide ultrafiltration membrane with continuous separation of one product through the membrane to shift the equilibrium toward the desired products.254 Such a process could supplant the current energy-intensive industrial one that takes 3-24 h at 150-260X. Lipases have also been used to prepare esters. A lipase-surfactant complex in hexane was used to prepare a wax ester found in whale oil, by the esterification of 1 hexadecanol with palmitic acid in a membrane reactor.255 After 1 h, the yield was 96%. The current industrial process runs at 250°C for up to 20 h. 

The advantage of starch as a carbon source is that its price is lower than that of glucose. Choi and Lee (1999) estimated that on a production scale of 100,000 tons of PHB per year, production costs would decrease from US 4.91 to 3.72 kg if hydrolysed com starch (US 0.22 kg" ) were used instead of glucose (US 0.49 kg ). Most processes for PHA production based on starch require the conversion of starch to easily convertible substrates such as glucose by enzymatic or chemical hydrolysis (Chen et al. 2006 Huang et al. 2006). Alternatively, VFAs can be produced as fermentation substrates by acidogenesis (Yu et al. 2002). The production of P(3HB-co-3HV) by H. mediterranei on extruded starch in a pH-stat fed-batch mode was recently described by Chen et al. (2006). Here, an exogenous source of a-amylases was used. 

A more spectacular example is the possible conversion of fossil fuel (oil) derivatives to edible carbohydrates. This transformation needs an industrial breakdown of petroleum products to glyceraldehyde. Then glyceraldelyde can be enzymatically converted to fructose, glucose, and starch. 

Enzymatically hydrolyzed potato processing waste has been studied as a possible source of a fermentable substrate for the production of PHB by R. eutropha. The results indicated that potato starch waste could be converted with high yield to a concentrated glucose solution. The most economical process used barley malt as a source of amylase enzyme with an optimal ratio of 10 90 g g of potato waste. A conversion efficiency of 96% of the theoretical value was obtained with a final glucose concentration of 208 g L After dilution and addition of mineral salts the hydrolysate was converted by a batch culture to 5.0 g L of PHB, comprising 77% of the cell dry weight [241]. 

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