Glucose production from starch

Example 1.1 Glucose Production from Corn Starch ... 

It is not easy to show that a preparation of malt a-amylase is enzy-mically homogeneous and free from /3-amylase and maltase. As will be shown later, the enzyme liberates D-glucose as a primary product from starch. Thus the appearance of D-glucose is not evidence of the presence of maltase. But the absence of this enzyme is most easily demonstrated... 

In addition to ethanol from cellulose, cellulase enzymes play a minor role in the production of ethanol from corn. In this process, most of the glucose is from starch. Cellulase enzymes offer the opportunity to increase the glucose yield by hydrolyzing a portion of the cellulose to glucose, as well as decreasing the viscosity of the ground corn [25]. 

Starch is a renewable carbon source abundantly available from plant sources. However, it is usually hydrolysed to glucose via a two-step process, liquefaction and saccharification, before adding it into the polymer prodnction medium [26]. Kim [27] reported P(3HB) production from starch using Azotobacter chroococcum via a fed-batch fermentation. A PHA content of 46 and 20 wt% with a CDW of 54 g/1 and 71 g/1 were obtained with and without oxygen limitation, respectively. A halophilic bacterinm, Haloferax mediterrane was also reported to be able to produce P(3HB) from starch, but the strain was not favourable due to the salt required for its growth which contributed significantly to the PHA manufacturing cost. 

Glucose Glucose, commercial name dextrose, in the aldohexose form a-o-glucose [CsHizO ), is the major product from starch hydrolyzed by acid and/or enzymes. The major starch source in the USA and Japan is corn Zea mays) and in Europe, wheat and potato. There is some starch and starch hydrolyzate production from cassava in the tropics. Glucose is sold as anhydrous dextrose more commonly as dextrose monohydrate, as glucose syrup or corn syrup. 

Despite the efficiency of the manufacture of ethanol from petrochemical feedstocks, much of the world s production is based on a fermentation process. Over the past 75 years in the United States, where the total annual production now stands at just under 4 million tonnes, the source of this basic chemical feedstock has swung away from fermentation to petrochemistry and back again (Table 6.1). The carbon source for the fermentation is glucose derived from starch (see Section 6.6). An even larger quantity, about 9.5 million tonnes, is produced each year in Brazil from cane sugar. Nowadays the prime consumer is the motor car. 

Polysaccharides formed from a-glucose are called starches. A starch stores sugar until it is needed for energy production. Three important starches are glycogen, which animals produce in their livers, and amylose and amylopectin, produced by plants through photosynthesis. On average, plant starch is about 20% amylose and 80% amylopectin. Each of these polysaccharides contains glucose as its monomer, but they differ in how the monosaccharide units are linked. 

The main question is whether synthesis of PHA in plants can succeed in bringing the cost of the polymer down to the range of 0.5 -1 US /kg. Bacterial production of PHA typically relies on a carbon source, such as sucrose or glucose, which is produced from photosynthesis and extracted from plants. Synthesis of PHA directly in plants would, therefore, represent a saving in terms of the number of intermediary steps linking C02 fixation to PHA production. Furthermore, starch is one of the cheapest plant commodity product on the market, at about 0.25 US /kg [86]. It is, thus, likely that the production cost of PHA in plants will be substantially cheaper than bacterial fermentation. The final cost of producing PHA in plants will depend on a number of factors. 

A product manufactured in Japan as Alo mixture (Anomalously Linked Oligosaccharides) contains mainly a range of IMOS (glucose, isomaltose, and panose as principal constituents). It is produced from starch as substrate by the action of alpha-amylase, beta-amylase, and a transglucosidase. It is claimed to have favorable properties for application in the food industry.143... 

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