engleski

EFFECT OF STORAGE ON COMPOSITION AND PROPERTIES OF PEACH PECTIC SUBSTANCES

Changes in the amount and composition of pectic substances during storage of Red Haven peaches were observed, as well as influence of these changes on the gel strenght of peach jams and gels made from stored peaches. Peaches were stored for 1, 2, 3, 4, 6 i 9 days at 4 oC. Amount of pectic substances were expressed as content of total pectin. The proportion of water-soluble (WSPF), oxalate-soluble (OSPF) and alkali-soluble (ASPF) pectic fractions were determined to etablish the composition of pectic substances. Those fractions were extracted and quantitatively determined as galacturonic acid (GalA) by colorimetric Internationale Fruchtsaft-Union method. Furthermore, the composition of the extracted pectic fractions was determined to etablish the proportion of GalA and neutral sugars (NS) by using phenol-sulphate method and Scott's method. Gel strenght of peach jams and gels was measured by Sulc pectinometer. During the storage there were some changes of total pectin amount and ASPF, and the highest values were determined between the third and the sixth day of storage. There were no significant changes in amount of WSPF and OSPF during the storage. ASPF was a major fraction and OSPF was a minor pectic fraction found in Red Haven peaches. The highest concentrations of GalA were determined in ASPF and the lowest concentrations were determined in WSPF. Furthermore, the highest concentrations of NS were determined in WSPF and the lowest concentrations were determined in OSPF. Duration of peaches storaging had not significant negative influence on gel strenght of jams and gels. It was established that there was a correlation between ASPF amount with gel strenght of peach jams and gels made from stored peaches.

peach; pectic substances; storage; jam; gel strenght

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