Summary module 5 - Predicting Food Quality (31306)

Module 5:

 Enzymes may both have negative and positive effects on food quality.

Amylase:
 Enzyme that hydrolyzes/synthesizes carbohydrates, depending on the conditions.
o In bread, amylase breaks down starch to provide food to the yeast 
successful fermentation, loaf volume & softness.

Proteases:
 Enzymes that hydrolyze proteins into peptides. This results in improved digestibility.
o Protein hydrolysates are used in sports drink.
o Enzyme activity of proteases must be controlled  extensive hydrolysis
makes the products unpleasant for the consumer (bitter taste).

Lipases:
 Enzymes that hydrolyze oils = lipid oxidation.
o Occurs in nuts and oils.
o Activity must be controlled to minimize rancidity.

Trans-glutaminase:
 Enzyme that is used in meat  protein crosslinking.

 Enzymes can affect different properties of food:
o Texture.
 Formation of cheese from milk (+).
 Wilting of vegetables (-).
o Taste.
 Oil  soapy taste (-).
o Color.
 Fruit browning (-).

 For the before-mentioned proteins, it is important to describe the kinetics, to control
the reactions!

 Both temperature and pH influence enzymatic reactions.

 In foods, enzymes and substrates are often stored in different compartments  they
cannot react. However, upon cutting, the structure is altered  cells break down 
enzymes get in contact with substrate.

 Enzyme activity is often undesired. Enzyme activity may be suppressed in various
ways:
 Without treatment:
o Products with a low/high pH.
o Products that are stored at a low temperature.
o Products with low-intermediate water activity.
 With treatment:
o Heat treatment for a short time (traditional method).

, o Ultra High Pressure (UHP) or Pulsed Electric Field (PEF) (alternative
methods).

 Treatment does not only affect enzymes, but also bacteria and spores. Depending on
the most heat-sensitive organism, a heat treatment will be selected.
o However, there is a limit, as the structure of food cannot be affected too much
 temperature and duration should be balanced properly.

 Currently, enzymes are considered very mild tools for the food industry:
o They may be used to produce food components (e.g., prebiotics).
o They may be used to improve food products’ properties.
o Green chemistry.
 Some reactions are convenient to use, as they are highly
selective in terms of substrate  not many side reactions 
reaction is performed efficiently (= green chemistry).

 Temperature can be used as a tool to control enzyme activity.
o Low temperature  reactions proceed slowly.
o High temperature  faster reaction, but also inactivation of enzymes.

 Generally, the Arrhenius equation is used to describe the effect of temperature on
enzyme activity. However, keep in mind that the exact behavior depends on the
specific reaction mechanism.
o The Arrhenius equation should thus be used with caution!
o Enzyme heating inactivation can be treated as microbial inactivation.

 Upon applying a certain high temperature,
the reaction will proceed fast at the start.
However, as time proceeds, the situation
reverses  the extent of the reaction is
stabilized at higher temperatures (i.e., the
enzyme is inactivated faster than that the
product is formed).
o Inactivation kinetics thus needs to
be desribed at increasing
temperatures.

 The reaction rate strongly varies with time and temperature. It is thus important to
specify the exact conditions when referring to enzyme activity.
o To determine the enzymatic reaction rates, the initial slopes must be straight.
This is the case <10% conversion.
o When using higher conversions, a non-liner
approach is advisable.

 At high values of water activity (aw), the reaction rate is
very high  reaction rate depends on the hydration state
of the enzyme, which requires water molecules to react.