Granules starch

Starch granules exhibit hydrophilic properties and strong intermole-cular association via hydrogen bonding due to the hydroxyl groups on the granule surface. The hydrophUicity and thermal sensitivity render the starch polymer unsuitable for thermoplastic applications (6). 

Therefore, blends with other polymers have been proposed to optimize the properties of starch. However, most of such polymers are significantly more expensive than starch. This fact tends to increase the cost of such polymer blends in comparison to pure starch. Further, most of such compositions wiU alter the mechanical properties of these blends not significantly. 

Biodegradable trays from cassava starch, sugarcane fibers and sodium montmoriUonite have been developed by a baking process (7). A nanoclay dispersion, resulting in an exfoliated structure was obtained. The physical properties, the photodegradation and biodegradation of these trays have been studied. The formulations resulted in weU-shaped trays with densities in the range of 0.19-0.30 gcm.  

The addition of the fibers and sodium montmoriUonite reduce the density and the rigidity. UV stability tests of the trays for 336 h showed that a sample with 20% fiber and 5% nanoclay had the highest loss in stress at break of 91%. The results of degradation studies are shown in Table 5.1. 

At the end of the degradation experiment, i.e. after 90 d, aU of the samples showed an irregular texture with large pores and cracks. Their surfaces exhibited dense microbial colonization. 

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After cleaning to remove coarse material, ie, cobs, and fines (broken com, dust, etc), the com is steeped in a sulfurous acid solution to soften the com and render the starch granules separable from the protein matrix that envelopes them. About 7% of the kernel s dry substance is leached out during this step, forming protein-rich steep-water, a valuable feed ingredient and fermentation adjunct. 

Seeds. The seeds are produced in pods containing two or three seeds. The kernels are almost spherical to roughly cylindrical (0.4—1.1 g each) and consist of a thin coat (testa) containing two cotyledons and the embryo. Cotyledons contain protein bodies, Hpid bodies, and starch granules. 

The qua si-crystalline stmcture of natural starch granules causes them to be insoluble in water at normal room temperature and gives them relative resistance to carbohydrases other than a-amylase and glucoamylase unless the granules become swollen. Three-dimensional arrangements of crystalline and amorphous zones in starch granules have been suggested (2). 

Another likely commercial starch is that from amaranth seed, an expanding crop for food use, particularly its flour. Amaranth starch granules (1—3 micrometers dia) have potential for numerous food appHcations, one of which is as a fat replacer because of their small size and especially after minor surface hydrolysis with a-amylase or glucoamylase to produce a fluffy surface (see Fat replacers). 

Cold- Water Swelling Starches. Special physical treatment produces starch granules that will sweU in water without heating. Molecular dispersions can be formed by appHcation of shear to the swoUen granules. 

The minor content of impurities found ia the starch slurry are connected to the starch granules themselves. To faciUtate the purification of the starch duriag filtration, ceUulases, pentosanases, glucanases, proteases, and pectinases are sometimes used. Wheat starch is known to form precipitates or hazes that are difficult to filter. Arabiaoxylan, pentosanes, andlysophosphoHpids are claimed to be responsible for this problem (73). 

The performance of several Sephacryl gel combinations is illustrated by results achieved for glucans from different types of starch granules. The applied Sephacryl gels of Pharmacia Biotech (15) are cross-linked copolymers of allyl dextran and N,N -methylene bisacrylamide. The hydrophilic matrix minimizes nonspecific adsorption and thus guarantees maximum recovery. Depending on the pore size of the beads, ranging between 25 and 75 im in diameter, aqueous dissolved biopolymers up to particle diameters of 400 nm can be handled. 

FIGURE 16.1 Preparative SEC of short-chain (scb) branched glucans of small" (<3S /u.m) starch granules of potato species Ostara separated on Sephacryl S-1000 (88 X 2.6 cm) eluent 0.005 M NaOH the normalized chromatogram (area = 1.0) was constructed from an off-line determined carbohydrate content of succeeding 5-ml fractions flow rate 0.67 ml/mln V d = 185 ml, V, = 460 ml fraction I high dp fraction fraction 2 low dp fraction. 

Stftrke-kleister, m. starch paste, -kom, -korn chen, n. starch granule, -losung, /. starch solution, -mehl, n, starch flom. starch powder, starch. 

The subsequent advance was rather fortuitous and rested more with serendipity than with scientific logic. A search was made for cheaper more effective replacements for casein hydrolysate. Amongst the tested materials was com steep liquor (CSL). CSL is a by-product of the manufacture of starch from maize kemals. Whole maize is incubated in warm water, at 50°C acidified with SO2. Thermophilic bacteria hydrolyse proteins and other components of the kemals, thereby loosening the starch granules. These are removed, leaving behind the steep liquor which is used to treat further maize kemals. Ultimately, the liquor is too viscous to re-use and the liquor is concentrated and used as cattle feed. It was this material that was used for penicillin fermentation. Surprisingly, the yield of penicillin increased by a further 5-10 fold giving yields of 50-100 ig ml. 

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