Food Biochemistry and Food Processing (2 edition)

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 3.2.1.108) 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 4.1.3.6) Citrate→Oxaloaceate

Oxaloacetate decarboxylase (EC 4.1.1.3) 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 4.1.1.1) Pyruvate→Acetylaldehyde+CO 2

Alcohol dehydrogenase (EC 1.1.1.1) Acetylaldehyde+NAD+H+→Ethanol+NAD+

Formation of formic acid

Pyruvate-formate lyase (EC 2.3.1.54) 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 2.3.1.54) Pyruvate+CoA→Formic acid+Acetyl CoA

Acetyl-CoA hydrolase (EC 3.1.2.1) 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 5.3.1.5) 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.