Food Biochemistry and Food Processing (2 edition)

BLBS102-c09 BLBS102-Simpson March 21, 2012 11:15 Trim: 276mm X 219mm Printer Name: Yet to Come

9 Enzymes in Food Processing 201

and (iii) to participate in the reaction as co-reactant. When mois-

ture content is reduced by dehydration, there is conformational

destabilization and loss of catalytic activity. For example, most

enzymes such as proteases, carbohydrases, PPO, GOX, and per-

oxidases requireAw≥ 0 .85 to have functional activity, the well-

known exceptions being lipases that may actually gain in activity

and remain active atAwof 0.3, perhaps as low as 0.1 (Loncin

et al. 1968). The unusual behavior of lipases is observed in

lipase-catalyzed reactions with their water-insoluble substrates,

lipids, and is due to the interfacial phenomenon that proceeds

better in a reduced moisture milieu. Foodstuffs prepared based

onAwreduction to control the undesirable effects of enzymes

(and microorganisms) include the use of sugar in food spreads

(jams and jellies), salt in pickled vegetables, glycerol in cookies

and liqueurs, and gelatin in candies and confectioneries.

Effect of Irradiation

Irradiation of foods (also known as cold pasteurization) is a

process during which foods are subjected to ionizing radiations

to preserve them. Food irradiation methods entail the use of

gamma rays, X-rays, and accelerated electron beams, and can

preserve food by curtailing enzymatic (and microbial) activities.

However, the irradiation dosage needed to achieve complete and

irreversible inactivation of enzymes may be too high and could

elicit undesirable effects of their own (e.g., nutrient loss) in

food materials. The technique is used to some extent in meats,

seafood, fruits, and vegetables (especially, cereal grains) for

long-term preservation; however, the procedure has low appeal

and acceptability to consumers and, therefore, not extensively

used in food processing.

Effects of Pressure

High-pressure treatment, also known as high-pressure process-

ing (HPP) or ultra high-pressure processing, is a nonthermal

procedure based on the use of elevated pressures (400–700 MPa)

for processing foods. At the elevated pressures, there is inacti-

vation of both enzymes and microorganisms, the two foremost

causative agents of food spoilage, and the inactivation arises

from conformational changes in the 3D structure of the enzyme

protein molecules (Cheftel 1992). Enzymes in foodstuffs display

different sensitivities to pressure; while some may be inactivated

at relatively low pressures (few hundred MPa), others can toler-

ate pressures up to a thousand MPa. The pressure effects may

also be reversible in some enzymes and irreversible in others,

depending on the pressure intensity and the duration of the treat-

ment. Those enzymes that can tolerate extreme pressures may

be deactivated using appropriate pressure treatments in combi-

nation with other barriers to enzyme activity such as such as

temperature, pH, and/or inhibitors (Ashie and Simpson 1995,

Ashie et al. 1996, Sareevoravitkul et al. 1996, Katsaros et al.

2010).

HPP has minimal effects on the attributes of food, such as

flavor, appearance, and nutritive value, compared with other pro-

cedures like thermal processing, dehydration, or irradiation. In

contrast to those other processing methods, high-pressure treat-

ments keep foods fresher and highly nutritious, improve food

texture, make foods look better and taste better. The HPP ap-

proach also retains the native flavors associated with foods, pro-

tects heat-labile essential food components, and extends product

shelf life with minimum need for chemical preservatives. The

technology has been used mostly by companies in Japan and

the United States to process foods such as ready-to-eat meats

and meat products, food spreads (jams), fresh juices and bev-

erages (sake), processed fruits and vegetables, fresh salads, and

dips. HPP is also used to shuck and retrieve meats from shellfish

(oysters, clams, and lobster).

CONCLUDING REMARKS: FUTURE

PROSPECTS

Foodstuffs have naturally present enzymes as well as in-

tentionally added ones that produce significant effects on

food-processing operations. The actions of these enzymes may

improve food quality or promote food quality deterioration. The

use of enzymes as food-processing aids has increased steadily for

several years now, and this trend is expected to continue for the

foreseeable future due to the interest and need for more effective

strategies and greener technologies to curtail the reliance on ex-

isting technologies and protect the environment. The factors that

augur well for the expanded use of enzymes as food-processing

aids include: consumer preferences for their use instead of

chemicals, their use as food-processing aids is perceived to be

more innocuous and more environmental friendly, their capacity

to selectively and specifically remove toxic components in

foods (e.g., glucosinolates with sulfatases, acrylamide with

asparaginase, or phytates with phytases), and recent advances

in enzyme engineering, which is permitting the discovery and

design of new and superior enzymes tailored to suit specific

applications.

Recent developments in enzyme engineering are enabling

yields of particular enzymes to be improved by increasing the

number of gene copies that code for enzyme proteins in safe

host organisms, and this feature is particularly significant be-

cause they are permitting useful enzymes from plant and ani-

mal sources, and even their counterparts from uncertified mi-

croorganisms (including hazardous ones) to be produced in high

yields much more consistently, rapidly, and safely for food use. It

is also significant because the cultivation and growth of microor-

ganisms for the purpose of producing recombinant enzymes is

not dependent of weather conditions, proceeds much faster, and

require much lesser space and regulations compared with plants

or animals.

Enzyme engineering is also facilitating the design of new en-

zyme structures with superior performance characteristics with

respect to catalytic activity, thermal stability, tolerance to pH

and inhibitors, and other properties to make them more suited

for applications in several fields of endeavor. This capacity is

also expected to enhance the design and creation of synthetic or

artificial enzymes (Chaplin and Burke 1990) with superior prop-

erties for both food and nonfood uses. Recombinant enzymes

with improved stability would facilitate their use in producing