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

22 Part 1: Principles/Food Analysis

Table 1.20.Selected Commercial

Biotechnology-derived Food Enzymes

Enzyme Application

Acetolactate decarboxylase (EC

4.1.1.5)

Beer aging and diacetyl

reduction

α-Amylase (EC 3.2.1.1) High-fructose corn syrup

production

Amylo-1,6-glucosidase (EC

3.2.1.33)

High-fructose corn syrup

production

Chymosin (EC 3.4.23.4) Milk clotting in cheese

manufacturing

Lactase (EC 3.2.1.108) Lactose hydrolysis

Glucan-1,4-α-maltogenic

α-amylase (EC 3.2.1.133)

Anti-stalling in bread

Source: Roller and Goodenough 1999, Anonymous 2004, IUBMB-NC

website (www.iubmb.org).

very complex due to degradation of genetic material as the re-

sult of processing conditions. Detecting misrepresentation of

food components is a task well-suited for DNA-based detec-

tion in the case of meat species of origin, especially when the

meat product is processed such that appearance and physical

traits cannot easily cue experts as to product identity. Gene se-

quences within mitochondrial DNA are usually used as the PCR

targets for such purposes (Wiseman 2009). For example, differ-

ent tuna species can be differentiated (Michelini et al. 2007).

Likewise, the presence of meat in cattle feed can be assayed

(Rensen 2005). Such tests can be done for high-heat-processed

samples at a low cost, and such tests can be highly automated

for steps post sample collection. Lastly, another example of a

food authentication application for PCR is the case of detecting

the presence and/or the quantity of genetically modified ingredi-

ents in a food. For the purposes of quantification, real-time PCR

must be used (Wiseman 2009), the most modern type of PCR

technology, because it is capable of highly precise, quantitative

determinations. This capability is due to real-time PCR’s ability

to very quickly and accurately modulate PCR reaction tempera-

ture via the use of low-volume reactions. Jurisdictions that have

Table 1.21.Selected Genetically Modified

Microorganisms Useful in Food Processing

Microorganism Application

Lactobacillus lactis Phage resistance, lactose

metabolism, proteolytic activity,

bacteriocin production

Saccharomyces

cerevisiae(Baker’s

yeast, Brewer’s yeast)

Gas (carbon dioxide) production

in sweet, high-sugar dough

Manufacture of low-calorie beer

(starch degradation)

Source: Hill and Ross 1999, Roller and Goodenough 1999,

Anonymous 2004.

GM labelling laws (e.g. the European Union) can thus verify the

correct labelling of incoming ingredients.

In the authentication process, DNA within foods can also be

characterised and differentiated by use ofDNA probes, an earlier

food authentication technology that dates back to at least 1990,

where it was used to distinguish between heat-processed rumi-

nant (goat, sheep and beef), chicken and pig meat (Chicuni et al.

1990). DNA probes are short pieces of DNA (Rensen et al. 2005)

that contain a detectable feature (usually fluorescence) and that

are complementary to a DNA sequence of interest. Thus, a signal

is produced only if the probed sequence is present in the food,

since the probe will bind only to its complement in a manner

that yields a signal. In order to probe a food product, genetic

material is isolated and immobilised on a piece of nitrocellulose

(blotting), which is then ‘probed’ with a DNA complementary

probe. The information from the above types of DNA-based au-

thentication tests can aid in processing quality control to ensure

both authenticity and safety at relatively cheap cost.

NATURAL TOXICANTS

The contamination of various foods by toxicants may occur

as a result of microbial production, crop plant production or

ingestion by animals for human consumption. Microbial sources

of toxins are mycotoxin-producing fungi and toxin-producing

bacteria. Notable examples of microbially derived toxins are

botulinum toxin produced byClostridium botulinumand the

Staphylococcus aureustoxin. These toxins are produced in the

food itself and result in food poisoning. Both toxins are heat-

labile; however, the extreme toxicity of the botulinum toxin,

potent at 10−^9 g per kg body weight, makes it of particular

concern for food processing of anaerobically stored foods.

Mycotoxins are extremely toxic compounds produced by cer-

tain filamentous fungi in many crop plants (Richard 2007). In-

gestion of mycotoxins can be harmful to humans via contami-

nated foods or feed animals via their feed, particularly in maize,

wheat, barley, rye and most oilseeds. Mycotoxins produce symp-

toms that include nervous system disorders, limb loss and death.

Aflatoxins are a well-studied type of mycotoxin that are known

carcinogens. An example of a mycotoxin structure, aflatoxin

B1, is shown in Figure 1.6. Mycotoxin poisoning can take place

either directly or indirectly, through consumption of a contam-

inated food or by a food ingredient that may be contaminated

and subsequently eaten as part of a final product.

O

O

O

O O

O

Figure 1.6.The structure of aflatoxin B1, produced byAspergillus

flavusandA. parasiticus.