engleski

Effect of maturing and storage at 4oC and 22oC on pectin fractions of red haven peaches and gel strength of related marmalades

Peaches were harvested on three stages of maturity< (threshold mature, firm-mature and mature). Firm-mature peaches were stored 9 days at 4oC and 22oC. Basic physical and chemical parameters were determined for all peach samples. Water-soluble, chelate-soluble and alkaline-soluble pectin fractions were extracted and determined quantitatively by the colorimetric method. Pectin fractions are expressed quantitatively and as percentage of the total pectin content. Total pectin is expressed as the sum of the water-soluble + chelate-soluble + alkaline-soluble pectin fractions. Gels were made from extracted pectin fractions. Marmalades were made with all peach samples. Gel strength of gels and marmalades was measured by Sulc pectinometer. The results revealed the following changes in the basic physical and chemical parameters during maturing and storage of peaches. Amount of total pectin and the amount of alkaline-soluble pectin fraction dropped markedly after the first stages of maturity. The level of alkaline-soluble pectin decreased, the level of water soluble pectin increased and the level of oxalat soluble pectin in total pectin content was fairly constant during the maturing and storage at 22o C. Gel strength of marmalades made with these peach samples decreased more after first stages of maturity than between the second and the third stages of maturity and more than during storage. During storage at 4oC, the level of extracted pectin fractions was fairly constant in all peach samples, and there were no significant changes in gel strength of marmalades made with these peach samples. Only, the extracted alkaline-soluble pectin fraction was capable of forming an acid gel. Extracted chelate soluble pectin fraction form gel in presence of calcium but solid matter of this gel was more than 77%. It seems that the amount of alkaline-soluble pectin fraction in peach and ratio of level of alkaline-soluble pectin to water-soluble pectin are most responsible in producing peach marmalades according to gel strength.

Pectin; peach; gel strength; maturing; storage; marmalade

nije evidentirano