Food Biochemistry and Food Processing (2 edition)

(Steven Felgate) #1

BLBS102-c01 BLBS102-Simpson March 21, 2012 11:8 Trim: 276mm X 219mm Printer Name: Yet to Come

8 Part 1: Principles/Food Analysis

Table 1.3.Changes in Carbohydrates in Cheese Manufacturing

Action, Enzyme or Enzyme System Reaction

Formation of lactic acid
Lactase (EC Lactose+H 2 O→d-Glucose+d-Galactose
Tagatose pathway Galactose-6-P→Lactic acid
Embden–Meyerhoff pathway Glucose→Pyruvate→Lactic acid
Formation of pyruvate from citric acid
Citrate (pro-3S)lyase (EC Citrate→Oxaloaceate
Oxaloacetate decarboxylase (EC Oxaloacetate→Pyruvate+CO 2
Formation of propionic and acetic acids
Propionate pathway 3 Lactate→2 Propionate+1 Acetate+CO 2 +H 2 O
3 Alanine→Propionic acid+1 Acetate+CO 2 +3 Ammonia
Formation of succinic acid
Mixed acid pathway Propionic acid+CO 2 →Succinic acid
Formation of butyric acid
Butyric acid pathway 2 Lactate→1 Butyrate+CO 2 +2H 2
Formation of ethanol
Phosphoketolase pathway Glucose→Acetylaldehyde→Ethanol
Pyruvate decarboxylase (EC Pyruvate→Acetylaldehyde+CO 2
Alcohol dehydrogenase (EC Acetylaldehyde+NAD+H+→Ethanol+NAD+
Formation of formic acid
Pyruvate-formate lyase (EC Pyruvate+CoA→Formic acid+Acetyl CoA
Formation of diacetyl, acetoin, 2,3-butylene glycol
Citrate fermentation pathway Citrate→Pyruvate→Acetyl CoA→Diacetyl→Acetoine→
2,3-Butylene glycol
Formation of acetic acid
Pyruvate-formate lyase (EC Pyruvate+CoA→Formic acid+Acetyl CoA
Acetyl-CoA hydrolase (EC Acetyl CoA+H 2 O→Acetic acid+CoA

lists some of the enzymes and their reactions related to these
complex carbohydrates.

Metabolism of Lactose in Cheese Production

Milk does not contain high-molecular weight carbohydrates;
however, it does contain lactose. Lactose can be enzymatically
degraded to glucose and galactose-6-phosphate by the enzyme
lactase, which can be produced by lactic acid bacteria. Glucose
and galactose-6-phosphate are then further metabolised to var-
ious smaller molecules through various biochemical reactions
that are important in the flavour development of various cheeses,
e.g. butyric acid via lactic acid decarboxylation. Table 1.3 lists
some of these enzymatic reactions.

Removal of Glucose in Egg Powder

Glucose is present in very small quantities in egg albumen and
egg yolk; however, it can undergo non-enzymatic reactions,
e.g. Maillard reactions, which lower the quality of the final
products. This problem can be overcome by using the glucose
oxidase–catalase system. Glucose oxidase converts glucose to
gluconic acid and hydrogen peroxide, which then decomposes

into water and oxygen by the action of catalase. This process is
used almost exclusively for whole egg and other yolk-containing
products. However, for dehydrated egg albumen, bacterial and/or
yeast fermentation is used to remove glucose.

Production of Starch Sugars and Syrups

The hydrolysis of starch by means of enzymes (α-andβ-
amylases) and/or acid to produce glucose (dextrose,d-glucose)
and maltose syrups has resulted in the availability of vari-
ous starch syrups, maltodextrins, maltose and glucose for the
food, pharmaceutical and other industries. In the 1950s, re-
searchers discovered that some xylose isomerase (d-xylose-
keto-isomerase, EC preparations possessed the ability to
convertd-glucose tod-fructose. In the early 1970s, researchers
developed immobilised enzyme technology for various applica-
tions. Since fructose is sweeter than glucose, xylose isomerase
was successfully applied to this new technology with the pro-
duction of high-fructose syrup (called high-fructose corn syrup
in the United States; Carasik and Carroll 1983). High-fructose
syrups have since replaced most of the glucose syrups in the soft
drink industry.
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