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Catabolite repression, transient repression and catabolite inhibition regulate the utilization of many carbohydrates.[1] Catabolite repression is a reduction in the rate of synthesis of certain enzymes in the presence of glucose or other easily metabolized carbon sources. In addition to this repression during steady-state growth in glucose, a period of more intense repression may occur immediately after the cells have been exposed to very high levels of glucose. This effect may last up to one generation or until glucose levels have been reduced to more acceptable levels. This is transient repression. Catabolite inhibition is a control exerted by glucose on enzyme activity rather than on enzyme formation, analogous to the feedback inhibition in biosyn-thetic pathways. Enzymes involved in the utilization of other carbohydrates are inhibited by glucose.

Simple sugars are available in powder or in liquid form and in a variety of purities. Glucose is usually made from corn starch through hydrolysis and sucrose from sugar cane or sugar beets. Sucrose is most often purchased in the form of molasses. Sugar beet molasses is the main by-product of table sugar production. Blackstrap molasses is the remaining by-product of raw sugar production from sugar cane, it is the prevailing type of cane molasses. High test molasses or inverted cane syrup is a by-product of the refineries in which raw sugar is refined into white or table sugar. Both blackstrap and beet molasses are widely used in the fermentation industry. Their approximate composition differs considerably, as indicated in Table 3.[51 The data on sugar beet molasses are averages from two (2) samples each of Dutch and French molasses from the 1990 campaign (column A). The US beet molasses data are averages from five (5) factories belonging to American Crystal Sugar over the 1991 season (Column B). The blackstrap molasses data are averages from several samples from Brazil, Dominican Republic and Haiti, over the period 1975-1983. Table 4 is an indication of how complex a medium blackstrap molasses is. Upon diluting to 25%, it was stripped under reduced pressure (40 mm Hg) at 38°C. The distillate was extracted with an ether/pentane (1:1) mixture. Separation and identification was done with a capillary column and mass spectrometer.'51

Molasses is produced through nonsugar accumulation during the sugar production process and the accompanying increased solubility of sucrose. Of the non-sugars, the mineral salts have a much greater influence on sucrose solubility than the organic compounds. As a rule of thumb, one gram of mineral salts present in normal molasses will retain five grams of non-crystallizable sucrose. Through chromatographic separation processes, it is possible to recover up to approximately 85 percent of this sucrose.

Table 3. Average composition (%) of European (A) and U. S. (B) beet molasses versus Brazilian/Caribbean blackstrap molasses samples^51

Component Beet Molasses Blackstrap

Column A Column B

water 16.5 19.2 18.0

sucrose 51.0 48.9 32.0

glucose + fructose 1.0 0.5 27.0

organic non-sugars 19.0 18.0 14.0

Ash components:

Sulfates as S03 0.55 0.74 1.8

Vitamins (mg/100 g):

Nicotinic acid 51.0 8.0 21.0

Folic acid 2.1 0.025 0.04

The average viscosity of sample B was 1,062 cP at 45°C.

Table 4. Isolation Of Some Volatile Compounds In Blackstrap Molasses[5]

methanol

acetic acid

methylformate

propionic acid

2-methyl-furamidon-3

isobutyric acid

furfurylacetate

n-butyric acid

methylfurfural

isovaleric acid

2-acetylfuran

n-valeric acid

phenol

isocaproic acid

quaiacol

n-caproic acid

benzaldehyde

alanine

2.5-dimethylpyrazine (1,4)

aspartic acid

2, 6-dimethylpyrazine (1, 4)

glutamic acid

2-methyl-6-ethylpyrazine (1, 4)

leucine

2-methyl-5-ethylpyrazine (1, 4)

isoleucine

trimethylpyrazine (1, 4)

glycine

syringic acid

methionine

vanillic acid

asparagine

p-hydroxy benzoic acid

glutamine

p-coumaric acid (trans-)

valine

p-coumaric acid (cis-)

tyrosine

p-hydroxphenylacetic acid

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