Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
The staling of ground roasted coffee blend was studied over one year of storage. Solid phase microextraction-gas chromatography-mass spectrometry analysis was carried out to identify and semi-quantify 40 volatile compounds. We focused on volatile compounds related to the ageing of coffee: methanethiol, propanal, 2-methylfuran, 2-butanone, 2,3-butanedione, 2-furfurylthiol and hexanal. Changes in sensory properties of coffee beverage prepared from the ground roasted coffee samples during storage in laminate packages (PET/ aluminium foil/PE) under air atmosphere, under nitrogen or in punctured packages were determined. Samples were stored at (23±2) °C and (40±10) % relative humidity. The reference coffee was packed similarly in laminate packages under nitrogen and stored at (-20±1) °C. Applying a statistical assessment of the results, we found the loss of most volatile compounds from all stored coffee samples, including even those stored under freezing conditions. The ratios of 2-methylfuran/2-butanone and methanethiol/hexanal proved useful indicators of staling. Our new proposed aroma index, the ratio of 2-furfurylthiol/ hexanal, proved to be the most effective, giving high correlation coefficients (R≥0.80) with aroma freshness for coffee brews prepared from the ground roasted coffee stored under different conditions at room temperature.U radu je istraženo starenje mješavine mljevene pržene kave tijekom jedne godine. Mikroekstrakcijom na čvrstoj fazi i plinskom kromatografijom u kombinaciji s masenom spektrometrijom identificirano je i djelomično kvantificirano 40 hlapljivih spojeva. Težište je rada na hlapljivim spojevima (metantiol, propanal, 2-metilfuran, 2-butanon, 2,3-butandion, 2-furfuriltiol i heksanal), povezanim sa starenjem kave. Tijekom skladištenja uočene su promjene senzorskih svojstava napitaka pripremljenih od mljevene pržene kave, pakirane u višeslojnu ambalažu (PET/aluminijska folija/PE) u atmosferi zraka ili dušika, te u probušenu ambalažu. Uzorci su skladišteni pri temperaturi od (23±2) °C i relativnoj vlažnosti od (40±10) %. Referentni je uzorak slično pakiran u višeslojnu ambalažu u atmosferi dušika i skladišten pri temperaturi od (-20±1) °C. Statističkom obradom podataka utvrđeno je da se u svim skladištenim uzorcima, pa čak i u zamrznutim, izgubio veliki dio hlapljivih spojeva. Omjeri 2-metilfurana i 2-butanona, te metantiola i heksanala pokazali su se kao korisni pokazatelji starenja. Novi predloženi indeks arome (omjer 2-furfuriltiola i heksanala najdjelotvorniji je pokazatelj, s velikim koeficijentom korelacije (R≥0.80) u usporedbi sa svježinom arome napitaka pripremljenih od mljevene pržene kave, skladištene pri različitim uvjetima na sobnoj temperaturi
