Potato Flavor - The Potato: Botany, Production and Uses - page 350

Tuberosum, so that the substrate (RNA) and
degradative enzymes come into contact more
readily during cooking of the Phureja tubers.
Other recent work has investigated the
effects of adding umami compounds to differ-
ent model food matrices and measuring the
hedonic effects (Barylko-Pikielna and Kostyra,
2007). Glutamate, either on its own or in com-
bination with 5¢- IMP and 5¢- GMP, was added
to a range of soups and broths, or to mashed
potato. There were significant increases in the
degree of acceptability of most of the foods
when the umami compounds were added, as
assessed by a taste panel. For mashed potato,
the increase was smaller than for the soups
and broths, and the authors of this report
concluded that potato as a food matrix was
insensitive to supplementation with umami
substances. Although this approach was inter-
esting, little further analysis of the potato samples
was carried out, and there was no comparison
of different potato cultivars.

19.3 Volatile Compounds

The volatiles produced by raw and cooked pota-
toes have been studied extensively (reviewed by
Maga, 1994), and over 250 compounds have
been identified in potato volatile fractions. Since
then, attempts have been made to discriminate
which of these components are important for
potato flavor and which are specific to the method
of cooking, cultivar differences, the effects of
agronomic conditions, and the effects of storage
(Duckham et al ., 2001, 2002; Oruna-Concha
et al ., 2001, 2002; Dobson et al ., 2004). Although
many different volatiles can be detected in cooked
potato, it is necessary to consider the odor activity
value (OAV) for each when assessing whether a
compound is likely to impact on sensory assess-
ment. OAV is the ratio of concentration of the
odorant in the material to the odor threshold
(the lowest concentration of a vapor in air that
can be detected by smell). In some foods, only a
small fraction of volatile compounds contribute
to aroma (Grosch, 2001). For example, although
more than 400 aroma volatiles have been identi-
fied in tomato, only 15-20 are present in suffi-
cient quantities to have an impact on flavor
(Buttery, 1993; Baldwin et al ., 2000). These
compounds are derived from a diverse set of
amino acid, carotenoid, and fatty acid precursors
(Klee, 2010).
Recent advances in analytical technology
have facilitated the study of flavor volatiles
greatly. In particular, relatively high throughput
methods for the profiling of flavor volatiles using
GC-MS have been reported (Thybo et al ., 2006;
Shepherd et al ., 2007). A particularly useful and
sensitive method is the analysis of head-space
volatiles by solid phase micro extraction. In this
process, samples of tuber are cooked in a sealed
vial prior to analysis (Morris et al ., 2010).

Glycoalkaloids and flavor

Potato tubers are well known to contain gly-
coalkaloids, the major forms being a-chaconine
and a-solanine, which represent approximately
95% of the total (Slanina, 1990). The level of
tuber glycoalkaloids varies according to culti-
var (Ramsay et al ., 2004), and is also influenced
by growth and storage conditions (Sengul et al .,
2004). Tuber glycoalkaloids are toxic to hu-
mans if present at levels in excess of 20 mg
100 g - 1 (Osman, 1983). Additionally, high
levels of glycoalkaloids are responsible for
off-flavors in potato tubers (Zitnak, 1961; Sin-
den et al ., 1976; Ross et al ., 1978). The emer-
ging consensus is that potato glycoalkaloids
at elevated levels are responsible for flavors
described as bitter, burning, scratchy, or acrid,
and are thus generally undesirable compo-
nents of flavor. In one study, taste panels cor-
related glycoalkaloid content in excess of
10 mg 100 g - 1 fresh weight with a burning
taste. However, at levels between 0.76 and
4.98 mg 100 g - 1 , no correlation was found
(Ross et al ., 1978). Other taste panel studies
described how tubers with glycoalkaloid con-
tents greater than 14 mg 100 g - 1 had a bitter
taste (Sinden et al ., 1976).

The origins of potato flavor volatiles

The volatile profile obtained from cooked pota-
toes contains many process-derived compounds
originating from a range of metabolite pre-
cursors (Maarse, 1991). Many flavor volatiles,
including aldehydes, alcohols, and alkyl furans,
are derived from lipids in reactions that have
both enzymic and non-enzymic steps. Enzymic