Stability of the hop bitter acids during long-term storage of cones with different maturity degree

Abstrakt

The aim of the study was to assess the dynamics
of changes in the content of hop bitter acids during long-term
storage of cones that vary in maturity degree under different
temperature conditions. The impact of the degree of maturity
of hop cones on the stability of bitter acids during storage is
little known so far, and it is important, because due to the systematic
increase of the hop growing area on individual farms, the
cone harvesting period is extended beyond the optimal phase of
technological maturity. Hop cultivars belonging to two groups
were included in the study: bitter (Magnat, Magnum) and aroma
(Puławski, Sybilla). Cones were collected on a few dates during
vegetation season, starting from the phase in which they reached
maximum size until the beginning of physiological maturity.
The dried cones were stored at +5 °C and +20 °C for 12 months
and tested every three months for alpha and beta acid content
using HPLC. Studies have shown that too early a hop harvest
adversely affected bitter acid content. Storage temperature had
significant impact on the degradation of alpha and beta acids. At
a higher temperature the decrease in the content of these compounds
was greater. The tested hop cultivars were characterized by
different stability of bitter acids. The highest stability of alpha
acids was observed for Sybilla, while the lowest for Magnat.
The stability of alpha and beta acids during long-term storage
of the raw material, especially at + 20oC, depended on the degree
of cones maturity. The aging rate of hop cones was not the
same throughout the storage period. For the first 3–6 months at
a temperature of +5oC, the bitter acid content remained at a level
similar to the initial one, later a relatively rapid decrease in the
content of these metabolites occurred. At higher temperatures,
the bitter acid stabilization period was shorter.