Stability of the hop bitter acids during long-term storage of cones with different maturity degree
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Instytut Uprawy Nawożenia i Gleboznawstwa – Państwowy Instytut Badawczy w Puławach
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The aim of the study was to assess the dynamicsof changes in the content of hop bitter acids during long-termstorage of cones that vary in maturity degree under differenttemperature conditions. The impact of the degree of maturityof hop cones on the stability of bitter acids during storage islittle known so far, and it is important, because due to the systematicincrease of the hop growing area on individual farms, thecone harvesting period is extended beyond the optimal phase oftechnological maturity. Hop cultivars belonging to two groupswere included in the study: bitter (Magnat, Magnum) and aroma(Puławski, Sybilla). Cones were collected on a few dates duringvegetation season, starting from the phase in which they reachedmaximum size until the beginning of physiological maturity.The dried cones were stored at +5 °C and +20 °C for 12 monthsand tested every three months for alpha and beta acid contentusing HPLC. Studies have shown that too early a hop harvestadversely affected bitter acid content. Storage temperature hadsignificant impact on the degradation of alpha and beta acids. Ata higher temperature the decrease in the content of these compoundswas greater. The tested hop cultivars were characterized bydifferent stability of bitter acids. The highest stability of alphaacids was observed for Sybilla, while the lowest for Magnat.The stability of alpha and beta acids during long-term storageof the raw material, especially at + 20oC, depended on the degreeof cones maturity. The aging rate of hop cones was not thesame throughout the storage period. For the first 3–6 months ata temperature of +5oC, the bitter acid content remained at a levelsimilar to the initial one, later a relatively rapid decrease in thecontent of these metabolites occurred. At higher temperatures,the bitter acid stabilization period was shorter.
Keywords
hop, alpha acids, beta acids, storage temperature, cones maturity