Influence of sucrose and trehalose addition on phenols, antioxidant activity and apple juice colour

U prvom dijelu ovog rada ispitivana je aktivnost polifenoloksidaze, sadržaj fenola, antioksidativna aktivnost i boja svježeg soka jabuke. Sok jabuke je dobiven od sorata Golden Delicious, Pink Lady i Fuji. Najveću aktivnost polifenoloksidaze imao je sok jabuke sorte Fuji, potom sorte Golden Delicious i Pink Lady. Sok jabuke sorte Pink Lady imao je najveći udio fenola kao i antioksidativnu aktivnost, potom sokovi jabuke sorte Fuji i Golden Delicious. Tijekom skladištenja aktivnost polifenoloksidaze se smanjila a smanjio se je i udio fenola. Cilj drugog dijela ovog rada bio je istražiti utjecaj dodataka trehaloze i saharoze (10%) na udio fenola, antioksidativnu aktivnost i boju soka u termički tretiranom soku jabuke tijekom skladištenja pri 4 °C i sobnoj temperaturi. Kontrolni uzorak bio je sok od jabuke bez dodatka šećera. Najveći udio fenola imao je sok jabuke sorte Pink Lady, potom sorte Fuji i Golden Delicious (828,25, 796,01 i 749,67 mg/L). Tijekom skladištenja degradacija fenola je bila veća u uzorcima čuvanim pri sobnoj temperaturi. Dodatak šećera imao je utjecaj na udio fenola. Uzorci s dodatkom saharoze su imali manji, a uzorci s dodatkom trehaloze veći udio fenola u odnosu na kontrolni uzorak. Za određivanje antioksidativne aktivnosti koristile su se DPPH i ABTS metode. Sok jabuke sorte Pink Lady imao je najmanju antioksidativnu aktivnost (5,8 i 8,48 μmol TE/100 mL određenu s DPPH i ABTS metodom). Sokovi jabuke sorte Fuji i Golden Delicious imali su slične vrijednosti za antioksidativnu aktivnost bez obzira na metodu koja se koristila (~ 7,3 i ~ 10,2 μmol TE/100 mL određena s DPPH i ABTS metodom). Tijekom skladištenja došlo je do povećanja antioksidativne aktivnosti u svim uzorcima.First part of this study was to evaluate phenoloxidase activity, phenol content, antioxidant activity and colour of fresh apple juice. Apple juice was obtained from Golden Delicious, Pink Lady and Fuji varieties. The highest phenoloxidase activity had juice from Fuji variety, than Golden Delicious and Pink Lady. The highest phenol content and antioxidant activity had juice from Pink Lady variety, than Fuji and Golden Delicious. During storage phenoloxidase activity decreased and degradation of phenols occurred. The objective of second part of study was to investigate influence of trehalose and sucrose addition (10 %) on phenol content, antioxidant activity and colour in thermally treated apple juice during storage at 4 °C and room temperature. Control sample was apple juice without sugar addition. The highest phenol content had juice from Pink Lady variety, than Fuji and Golden Delicious (828.25, 796.01 and 749.67 mg/L, respectively). During storage, degradation of phenols was higher in samples stored at room temperature. Addition of sugars had high influence on phenol content in comparison to control sample. Samples with addition of sucrose had lower, while samples with addition of trehalose had higher phenol content in contrast to control sample. DPPH and ABTS methods were used for antioxidant activity determination. The lowest antioxidant activity had juice from Pink Lady variety (5.82 and 8.48 μmol TE/100 mL obtained with DPPH and ABTS method). Juice from Fuji and Golden Delicious variety had similar values of antioxidant activity regardless of used method (~7.3 and ~10.2 μmol TE/100 mL obtained with DPPH and ABTS method). During storage, increase of antioxidant activity in all samples occurred