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

1 Introduction to Food Biochemistry 7

Table 1.1.Starch Degradation During Cereal Grain Germination

Enzyme Reaction

α-Amylase (EC 3.2.1.1) Starch→Glucose+Maltose+Maltotriose+α-Limit

dextrins+Linear maltosaccharides

Hexokinase (EC 2.7.1.1) Glucose+ATP→Glucose-6-phosphate+ADP

α-Glucosidase (maltase, EC 3.2.1.20) Hydrolysis of terminal, non-reducing 1,4-linkedα-d-glucose

residues releasingα-d-glucose

Oligo-1,6 glucosidase (limit dextrinase, isomaltase,

EC 3.2.1.10)

α-Limit dextrin→Linear maltosaccharides

β-Amylase (EC 3.2.1.2) Linear maltosaccharides→Maltose

Phosphorylase (EC 2.4.1.1) Linear maltosaccharides+Phosphate→

α-d-Glucose-1-phosphate

Phosphoglucomutase (EC 5.4.2.2) α-d-Glucose-1-phosphaate→α-d-Glucose-6-phosphate

Glucosephosphate isomerase (EC 5.3.1.9) d-Glucose-6-phosphate→d-Fructose-6-phosphate

UTP-glucose-1-phosphate uridyl transferase (UDP-glucose

pyrophosphorylase, EC 2.7.7.9)

UTP+α-d-Glucose-1-phosphate→UDP-glucose+

Pyrophosphate

Sucrose phosphate synthetase (EC 2.4.1.14) UDP-glucose+d-Fructose-6-phosphate→Sucrose

phosphate+UDP

Sugar phosphate phosphohydrolase (sugar phosphatase,

EC 3.1.3.23)

Sugar phosphate (fructose-6-phosphate)→Sugar (fructose)

+Inorganic phosphate

Sucrose phosphatase (EC 3.1.3.24) Sucrose-6-F-phosphate→Sucrose+Inorganic phosphate

Sucrose synthetase (EC2.4.1.13) NDP-glucose+d-Fructose→Sucrose+NDP

β-Fructose-furanosidase (invertase, succharase, EC 3.2.1.26) Sucrose→Glucose+Fructose

Source:Duffus 1987, Kruger and Lineback 1987, Kruger et al. 1987, Eskin 1990, Hoseney 1994, IUBMB-NC website (www.iubmb.org).

Table 1.2.Degradation of Complex Carbohydrates

Enzyme Reaction

Cellulose degradation during seed germinationa

Cellulase (EC 3.2.1.4) Endohydrolysis of 1,4-β-glucosidic linkages in cellulose and cereal

β-d-glucans

Glucan 1,4-β-glucosidase (exo-1,4,β-glucosidase, EC

3.2.1.74)

Hydrolysis of 1,4 linkages in 1,4-β-d-glucan so as to remove

successive glucose units

Cellulose 1,4-β-cellubiosidase (EC 3.2.1.91) Hydrolysis of 1,4-β-d-glucosidic linkages in cellulose and

cellotetraose releasing cellubiose from the non-reducing ends of the

chains

β-Galactosan degradationa

β-Galactosidase (EC 3.21.1.23) β-(1→4)-linked galactan→d-Galactose

β-Glucan degradationb

Glucan endo-1,6,β-glucosidase (EC 3.2.1.75) Random hydrolysis of 1,6 linkages in 1,6-β-d-glucans

Glucan endo-1,4,β-glucosidase (EC 3.2.1.74) Hydrolysis of 1,4 linkages in 1,4-β-d-glucans so as to remove

successive glucose units

Glucan endo-1,3-β-d-glucanase (EC 3.2.1.58) Successive hydrolysis ofβ-d-glucose units from the non-reducing ends

of 1,3-β-d-glucans, releasingα-glucose

Glucan 1,3-β-glucosidase (EC 3.2.1.39) 1,3-β-d-glucans→α-d-glucose

Pectin degradationb

Polygalacturonase (EC 3.2.1.15) Random hydrolysis of 1,4-α-d-galactosiduronic linkages in pectate

and other galacturonans

Galacturan 1,4-α-galacturonidase (EC 3.2.1.67) (1,4-α-d-Galacturoniside)n+H 2 O→(1,4-α-d-Galacturoniside)n-1+

d-Galacturonate

Pectate lyase (pectate transeliminase, EC 4.2.2.2) Eliminative cleavage of pectate to give oligosaccharides with

4-deoxy-α-d-galact-4-enuronosyl groups at their non-reducing ends

Pectin lyase (EC 4.2.2.10) Eliminative cleavage of pectin to give oligosaccharides with terminal

4-deoxy-6-methyl-α-d-galact-4-enduronosyl groups

Source:aDuffus 1987, Kruger and Lineback 1987, Kruger et al. 1987, Smith 1999,bEskin 1990, IUBMB-NC website (www.iubmb.org).