Prof. Dr. Paul Struik

Especially Asian people have an umami tooth, and the umami flavour is highly valued in Asian cooking. The umami taste can best be characterized as savoury. The chemical background of the umami taste in boiled potatoes is diverse. The taste is associated with the occurrence of certain free amino acids (e.g., aspartic acid and glutamic acid or their respective ionic forms aspartate and glutamate), but also with small organic acids (e.g., succinic acid and gluconic acid), peptides (i.e., molecules, consisting of a small number of amino acids), 5’-nucleotides (adenosine-monophosphate: AMP and guanosine-monophosphate: GMP), products of the Maillard-reaction, etc. Moreover, research has demonstrated that the umami taste is not only relevant for boiled potatoes, where aspartate and glutamate are major triggers. Also in crisps, umami taste is important, and, in this product, the L- and D-forms of mono­sodium pyroglutamate, i.e., ionic forms of pyroglutamic acid, have recently been discovered as essential contri­butors to the umami taste. Pyroglutamic acid is derived from glutamic acid: the amino group has cyclized to form a lactam (i.e., a cyclic amide).

Environmental factors during potato production and storage influence the umami taste. For example, production year and storage temperature affect the intensity of the umami taste. Moreover, cultural practices are relevant: nitrogen fertilizer seems to negatively affect the taste of potato in general, whereas extra potassium fertilizer may result in high potassium levels in potato tubers that enhance the intensity of the umami taste. It has also been shown that the soil microbiome influences the flavour of potatoes.
There is also large genetic variation in the concentration of the compounds that are associated with the umami taste. For example, a two-fold range of glutamic acid has been found in a set of genotypes. In China and Japan, farmers still grow special landraces with poor agronomic and processing characteristics but great taste. Recently, Chinese researchers eva­luated 66 varieties of distinct tastes for sensory qualities, using a panel of 10 professional tasters, and conducted detailed research on chemical composition. They found large differences in concentrations of amino acids and many volatiles. They identified a Yunnan landrace, called Kai Hua Yang Yu, which had many agronomic and quality disadvantages (such as low yield, deep eyes, poor shape, rough skin), but stood out in texture, starch quality and umami taste of the cooked potato, and was therefore still very popular. The excellent umami taste in this particular case was associated with high concentrations of the free amino acids aspartic acid and glutamic acid.
For testing of the umami taste at scale, panels of tasters or complicated and advanced chemical analyses are not always possible. Nowadays, food scientists have access to modern equipment such as the electronic tongue. This is an analytical instrument that is capable of measuring and comparing tastes. It includes an array of non-selective chemical sensors with partial specificity to different components and has the capacity to recognize patterns. Such an instrument might be useful for breeding purposes and may help create highly productive, haute cuisi­ne potato cultivars. ●

Paul C. Struik