Food Biochemistry and Food Processing (2 edition)

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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.
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