Potato Flavor - The Potato: Botany, Production and Uses - page 351

reactions in lipid degradation are likely to be im-
portant if results from tomato fruit can be ex-
trapolated to potato. Lipoxygenases catalyze the
dioxygenation of polysaturated fatty acids con-
taining cis , cis - 1,4- pentadiene moieties (such as
linoleic and linolenic acids), converting them
into corresponding fatty-acid hydroperoxides
(HPOs). In tomato, five lipoxygenase genes have
been identified, and one ( TomloxC ) has a critical
role in the generation of important six-carbon
aldehyde and alcohol fatty-acid-derived flavor
volatiles (Chen et al ., 2004). Autooxidation (Fran-
kel, 1998) and enzymic (hydroperoxide lyase) ac-
tion on hydroperoxides derived from linoleic and
a-linolenic acids (Gardner, 1995) are also involved
in the production of lipid-derived, flavor-active
volatiles such as aldehydes, ketones, alcohols, and
alkyl furans.
Thermally driven reactions are important in
the development of many flavor volatiles. Major
examples include the Maillard reaction between
reducing sugars and amino acids, and the Streck-
er degradation of methionine to produce me-
thional. The Maillard reaction takes place when
compounds possessing a carbonyl group, typic-
ally reducing sugars, react with components
with a free amino group such as amino acids
to form heterocyclic compounds. The Maillard
reaction occurs under more forcing conditions
such as baking or roasting (Shepherd et al .,
2007). The Strecker degradation of methionine
involves the interaction of α-dicarbonyl com-
pounds, intermediates in the Maillard reaction,
with methionine, resulting in the formation of
methional (Lindsay, 1996). The other major clas-
ses of cooked potato volatiles include meth-
oxypyrazines and terpenes. In addition, several
specific compounds have been related directly to
desirable flavor and aroma characteristics with
methional (Lindsay, 1996), methoxypyrazines
(Murray and Whitfield, 1975), and the lipid deg-
radation product, cis - 4- heptenal (Josephson and
Lindsay, 1987), all reported to exhibit “a cooked
potato odor”. This provides some evidence that
these compounds may be significant contribu-
tors to potato flavor. To generalize the findings of
several studies, in boiled potatoes, the most im-
portant volatile constituents are likely to be those
derived from lipid degradation, the Maillard reac-
tion, and the Strecker reaction, and include me-
thional, aliphatic alcohols and aldehydes, thiols
and sulfides and methoxypyrazines.

The types and amounts of volatiles derived
from potato tubers vary significantly according
to the processing method. Distinctive quantita-
tive and qualitative differences in volatile profile
were observed in a comparison of tubers (culti-
vars Estima and Maris Piper) cooked by boiling,
baking, or microwaving (Oruna-Concha et al .,
2002). For the three methods of cooking, the
main sources of flavor compounds were from
lipid degradation and the Maillard reaction and/
or sugar degradation; however, there was a
characteristically different ratio of the contribu-
tion of each class to the total volatile fraction.
For boiled potatoes, volatiles formed by lipid deg-
radation were judged to be the most important,
whereas for baked potatoes, those arising from
amino acids contributed more significantly
(Oruna-Concha et al ., 2002). A much lower
amount of volatile aroma compounds was pro-
duced from microwave-cooked potatoes than for
the other cooking methods, possibly indicating
that microwave-cooked potato products are
blander in flavor than potato products produced
by boiling or conventional baking. The cooking-
dependent differences in volatile profiles have
been attributed to variations in heat and mass
transfer processes associated with the different
cooking methods (Wilson et al ., 2002a,b).
In order to determine which, of the many
volatiles present in cooked potato, are the main
contributors to flavor, comparisons have been
made between potato germplasm with different
sensory attributes. As with studies on umami
compounds, accessions of Phureja have been
compared with Tuberosum. The study of Win-
ield et al . showed that, in general, boiled tubers
from a range of Phureja accessions were more
acceptable than those from a wide range of Tu-
berosum (Winfield et al ., 2005). Head-space
volatile analysis from these samples identified 70
compounds, and principal component analysis
revealed that hexenal, pentanal, pentyl-furan,
and the sesquiterpene, α-copaene, accounted for
most of the variability in the data set.
This type of approach was extended to in-
vestigate in detail the correlation between vola-
tile and non-volatile tuber components and sensory
attributes. The resulting correlation matrix re-
vealed new associations between flavor attributes,
most notably between flavor intensity, flavor
creaminess, and flavor savoriness ( Fig. 19.3 ) . Inter-
estingly, there was an almost inverse relationship