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 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.,