Food Biochemistry and Food Processing (2 edition)

BLBS102-c03 BLBS102-Simpson March 21, 2012 11:56 Trim: 276mm X 219mm Printer Name: Yet to Come

46 Part 1: Principles/Food Analysis

Amylose

Amylase

Dextrin

Pullulanase

Maltose units

Glucoamylase Maltose units

Glucose

Glucoamylase

Glucose

(A) (B)

Figure 3.5.Schematic of enzymatic breakdown of starch (amylose and amylopectin) to glucose. (A) With amylose as substrate, amylase

hydrolyzes the starch to maltose units, which are further simplified to glucose units. (B) With amylopectin substrate, pullulanase hydrolyzes

the limit dextrin resulting from amylase activity. The products are further simplified by the amylase and glucoamylase to release glucose units.

cardiovascular disease has generated strong interest in the level

of cholesterol in foods. Some foods characterized by high lev-

els of cholesterol are cheese, egg yolk, beef, poultry, shrimps,

and pork. The earliest enzymatic methods for cholesterol anal-

ysis were based on colorimetric assays involving initial de-

esterification of cholesterol esters by cholesterol esterase to

release free cholesterol, which is further oxidized by choles-

terol oxidase to generate hydrogen peroxide. The peroxide pro-

duced is subsequently coupled to a colored or fluorescent reagent

in a peroxidase-catalyzed reaction (Satoh et al. 1977, Hamada

et al. 1980, Omodeo et al. 1984, Van Veldhoven et al. 2002). A

commercial kit (Boehringer’s Monotest cholesterol or CHOD-

PAP method) for the colorimetric assay is available, in which

4-aminoantipyrine and phenol are converted to a red cyanogen-

imine dye in the presence of the peroxide released. New and

more sensitive electrochemical biosensors have since been de-

veloped involving immobilization of the enzymes (cholesterol

esterase and cholesterol oxidase) on electrode surfaces and car-

bon nanotubes (Wisitsoraat et al. 2009). Similarly, a number of

other enzyme-immobilized biosensors originally developed for

analysis of serum cholesterol may also be applicable to food

analysis. These include immobilization on polyvinyl chloride

with glutaraldehyde as a coupling agent (Hooda et al. 2009),

agarose gel and activation with cyanogen bromide (Karube et al.

1982), and pyrrole membrane coupled with flow injection for

hydrogen peroxide analysis (Wolfgang et al. 1993).

Antioxidants

Oxidation of lipids in foods has been an age-old problem of the

food industry due to the free-radical-induced off-flavors and the

implication of these free radicals in cell damage and a number

of pathogenetic conditions. Controlling such oxidation has been

largely achieved by a number of process modifications as well

Glycerol

Glycerokinase

Glycerol-1- NADH + Dihydroxyacetone

Glycerol-1-phosphate

dehydrogenase

AT P phosphate

phosphate .............. (1)

NAD+

Glycerol

Glycerol

dehydrogenase Dihydroxyacetone phosphate + NADH .........(2)

NAD+

Figure 3.6.Glycerolkinase and glycerol dehydrogenase for glycerol analysis in foods.