Monitoring the changes in the content of low molecular weight organic acids, free amino acids, and oligopeptides during the ripening of Krk cheese by high performance liquid chromatography methods

Istraživanje metaboličkih promjena u siru tijekom zrenja važno je zbog boljeg razumijevanja procesa nastajanja arome i teksture sira. U tom smislu tradicionalni sirevi proizvedeni od toplinski neobrađenog mlijeka, kakav je i Krčki sir istraživan u ovom radu, predstavljaju još uvijek nedovoljno istraženo područje od velikog interesa za prehrambenu industriju. Metabolizam proteina, ugljikohidrata i masti uvelike doprinosi razvoju arome, a definiranje obrasca promjene tih metabolita može poslužiti kao dobra metoda praćenja zrenja sira. U ovom radu praćena je promjena sadržaja 19 slobodnih aminokiselina, 7 organskih kiselina te sastava vodotopljivih oligopeptida tijekom tromjesečnog perioda zrenja Krčkog sira. Određivanje slobodnih aminokiselina i oligopeptida u vodenim ekstraktima sira provedeno je reverzno-faznom tekućinskom kromatografijom visoke djelotvornosti, pri čemu su slobodne aminokiseline prethodno derivatizirane dabsil-kloridom. Za određivanje niskomolekulskih organskih kiselina korištena je podvrsta ionsko-izmjenjivačke kromatografije temeljena na isključenju po naboju. Navedene metode pokazale su se učinkovitima za analizu ciljanih metaboličkih intermedijera i produkata te je dobiveno dobro slaganje s literaturnim podacima za ovčje sireve.The investigation of metabolic changes in cheese during ripening gives an important perspective to understanding the aroma and texture development. Traditional cheese varieties, made from non-pasteurized milk, represent an insufficiently investigated area of food technology. The metabolic changes of proteins, carbohydrates and fat greatly contribute to aroma development. Defining the pattern which characterizes those changes can be a good method for monitoring cheese ripening. This thesis analyses the changes in the content of 19 aminoacids, 7 organic acids and the composition of water soluble oligopeptides during three months of Krk cheese ripening. Free aminoacids and oligopeptides were determined by RP-HPLC in cheese water extracts, where free aminoacids where previously derivatized with dabsyl-chloride. Low molecular weight organic acids were determined by ion exclusion chromatography. Applied methods were efficient for the analysis of metabolic intermediates and the obtained results show a good concordance with previous researches of ovine cheese varieties