Determination of the polyphenoloxidase enzyme activity in cultivated blueberry : diploma thesis

Fenolni spojevi su ključni za prehrambena i organoleptička svojstva hrane poput boje, okusa, mirisa te njenog učinka na zdravlje čovjeka. Borovnice se smatraju jednim od najvažnijih prirodnih izvora polifenolnih spojeva među kojima dominiraju antocijani. Ovi visokovrijedni spojevi nalaze se najvećim dijelom u kožici ploda pa je njihova biodostupnost potrošačima velika. Borovnice, kao voće koje je izrazito bogato fenolnim spojevima, izuzetno su podložne procesu enzimskog posmeđivanja što znatno umanjuje njihovu nutritivnu vrijednost i skraćuje period konzumacije. U ovom radu uspoređen je utjecaj različitih tehnika obrade uzoraka borovnice na aktivnost enzima polifenoloksidaze, koji je odgovoran za proces posmeđivanja. Uspoređena je aktivnost enzima polifenoloksidaze u uzorcima svježe borovnice, uzorcima podvrgnutima termičkoj obradi – pasterizacija, liofiliziranim uzorcima te uzorcima tretiranima ultrazvukom visokog intenziteta. Aktivnost enzima polifenoloksidaze određena je uz pomoć brze spektrofotometrijske metode. Aktivnost enzima polifenoloksidaze pokazala se najnižom u liofiliziranim uzorcima borovnice što znači da je taj proces optimalan za očuvanje stabilnosti biološki aktivnih spojeva iz borovnicePhenolic compunds are crucial for nutritional and organoleptic food traits, such as colour, taste, odour and due to their impact on human health. Blueberries are considered as one of the most important natural sources of polyphenolic compounds, amongst which anthocyanins are found as dominant ones. These valued compounds can mostly be found in the fruit membrane, which makes them being easily accessible to the consumers. Due to the fact that they are extremely rich in phenolic compounds , blueberries are susceptible to becoming brown by enzymatic activity, which leads to decreasing their nutritional value and shelf-life.This thesis compares the effect of different techniques of processing blueberry samples on the activity of polyphenoloxidase enzyme, which is responsible for the process of enzymatic browing. The activity of polyphenoloxidase enzyme in fresh blueberry samples which were subjected to thermal treatment such as pasterization, is compared to lyophilized samples and to ones which were treated with high intensity ultrasound. Activity of polyphenoloxidase enzyme was determined by quick spectrophotometric method. It has been shown that the activity of poliphenoloxidase enzyme is the lowest in lyophilized blueberry samples, which makes that process optimal for preserving stability of biologically active compounds from blueberry