Food Biochemistry and Food Processing (2 edition)

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


1 Introduction to Food Biochemistry 15

Figure 1.4.SDS-PAGE gel with protein standards of known masses
(right lane), impure target protein (left lane) and pure target protein
(middle lane;∗∗∗). The target protein was calculated to have a
molecular mass of 11,700 Daltons (Da) or 11.7 kDa.

(Sampson 2004). Such reactions are thought to result from an
abnormal response of the mucosal immune system towards nor-
mally harmless dietary proteins (antigens; Bischoff and Crowe
2005). Allergic reactions are distinct from food intolerances that
do not involve the immune system (Sampson and Cooke 1990).
One of the biggest problems with food allergy management
is that avoidance of antigen is the primary means of preventing
allergic reactions; however, minute amounts of so-called ‘hidden
allergens’ in the form of nut, milk and egg contaminants occur
in many processed foods. To avoid allergens entirely may pose
the risk of avoiding nutritionally important foods, resulting in
malnutrition, especially in the young, a problem highlighting the
need for control of allergens in foods including the making of
hypoallergenic food products (Mine and Yang 2007). Allergic
reactions to food components that are mediated by IgE are the
best understood and most common type (Type I; Ebo and Stevens
2001).
In general, glycosyl biomolecules are often important elic-
itors of immunogenic responses (Berg 2002), e.g. bacterial
lipopolysaccharides. Many proteins contain carbohydrate moi-
eties and are termed ‘glycoproteins’. IgE specific to glycans has
been reported (van Ree et al. 1995), and it was originally re-

ported that the carbohydrate portion of ovomucoid contributed
to binding human IgE (Matsuda et al. 1985); however, subse-
quent investigation suggested that it did not participate in protein
allergenicity (Besler et al. 1997).
As a means of reducing the allergenicity of egg proteins, en-
zymatic treatments have been studied. The major limitations or
potential hurdles to such an approach are the need for the aller-
gen epitope(s) to be directly impacted, i.e. cleavage upon enzyme
treatment, and the retaining of the unique functional properties
of egg proteins in foods, e.g. foaming and gelling (Mine et
al. 2008). A combination of thermal treatments and enzymatic
hydrolyses resulted in a hydrolysed liquid egg product with
100 times less IgE-binding activity than the starting material,
determined by analysis of human subjects having egg allergies
(Hildebrt et al. 2008 ). Flavour and texturising properties were
not altered when incorporated into various food products, sug-
gesting potential to manufacture customised products accessible
to egg-allergy sufferers (Mine et al. 2008).

Enzyme Biotechnology in Foods

Various enzymes are used as processing aids in the food indus-
try. Examples include acetolactate decarboxylase,α-amylase,
amylo-l,6-glucosidase, chymosin, lactase and maltogenic
α-amylase (Table 1.11), many of which are produced as recom-
binant proteins using genetic engineering techniques. Recombi-
nant expression has the advantage of providing consistent en-
zyme preparations since expression cultures can be maintained
indefinitely, and it is not dependent on natural sources (e.g. chy-
mosin from calf stomachs). In addition to recombinant enzymes,
microbial enzymes are also used, e.g. microbial rennets are used
in cheese production from several organisms:Rhizomucor pusil-
lus, R. miehei, Endothia parasitica, Aspergillus oryzae and Irpex
lactis. Trade names of microbial milk-clotting enzymes include
Rennilase, Fromase, Marzyme and Hanilase. Other enzymes in-
clude lactase, which is well accepted by the dairy industry for the
production of lactose-free milk for lactose-intolerant consumers,
and amylases, which are used for the production of high-fructose
corn syrup and as an anti-stalling agent for bread.

FOOD LIPID BIOCHEMISTRY


Fatty Acids

Lipids are organic compounds characterised by little or no sol-
ubility in water and are the basic units of all organisms’ mem-
branes, the substituent of lipoproteins and the energy storage
form of all animals. The basic units of lipids are fatty acids
(FAs), simple hydrocarbon chains of varying length with a car-
boxylic acid group at one end.

CH 3 −[CH 2 ]n−COOH

The carboxylic carbon is designated as carbon 1 (C1). FAs
are characteristically named using hydrocarbon chain length.
For example, a four carbon FA is butanoic acid, a five carbon
FA is pentanoic acid, a six carbon FA is hexanoic acid etc.,
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