Food Chemistry

5.2 Aroma Analysis 345

Fig. 5.3.The cause of aroma defects in food

5.2 AromaAnalysis.........................................

The aroma substances consist of highly di-
versified classes of compounds, some of them
being highly reactive and are present in food
in extremely low concentrations. The diffi-
culties usually encountered in qualitative and
quantitative analysis of aroma compounds are
based on these features. Other difficulties are
associated with identification of aroma com-
pounds, elucidation of their chemical structure
and characterization of sensory properties.
The results of an aroma analysis can serve as
an objective guide in food processing for assess-
ing the suitability of individual processing steps,
and for assessing the quality of raw material,
intermediate- and endproducts. In addition, inves-
tigation of food aroma broadens the possibility of
food flavoring with substances that are prepared
synthetically, but are chemically identical to those
found in nature, i. e. the so-called “nature identi-
cal flavors” (cf. 5.5).
The elucidation of the aroma of any food is car-
ried out stepwise; the following instrumental and
sensory analyses are conducted:

• Isolation of the volatile compounds


• Differentiation of the aroma substances from
  the remaining components of the volatile frac-
  tion by dilution analyses


• Concentration and identification


• Quantification and calculation of aroma values
  
  
  • Simulation of the aroma on the basis of the
    analytical results
  
  
  • Omission experiments
  
  
  
  

5.2.1 AromaIsolation.........................................

The amount of starting material must be selected

to detect even those aroma substances which are

present in very low concentrations (ppb range),

but contribute considerably to the aroma because

of still lower odor thresholds. The volatile com-

pounds should be isolated from food using gentle

methods because otherwise artifacts can easily be

produced by the reactions listed in Table 5.6.

Additional difficulties are encountered in foods

which retain fully-active enzymes, which can

alter the aroma. For example, during the homoge-

nization of fruits and vegetables, hydrolases split

the aroma ester constituents, while lipoxygenase,

together with hydroperoxide lyase, enrich the

aroma with newly-formed volatile compounds.

To avoid such interferences, tissue disintegration

is done in the presence of enzyme inhibitors,

e. g., CaCl 2 or, when possible, by rapid sample

preparation. It is useful in some cases to inhibit

enzyme-catalyzed reactions by the addition of

methanol or ethanol. However, this can result

in a change in aroma due to the formation of

esters and acetals from acids and aldehydes

respectively.