The effect of ripening and storage on peach pectin and gel strength of related jams

Levaj, B. and Dragovic-Uzelac, V. and Dancevic, A. and Frlan, J. (2003) The effect of ripening and storage on peach pectin and gel strength of related jams. Acta Alimentaria, 32 (4). pp. 329-340. ISSN 0139-3006

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Abstract

Peaches were harvested in three stages of ripeness (threshold-mature - I, firm-ripe - II and ripe - III). Firm-ripe (II) peaches were stored for 9 days at 4 and 22 C. The amount of water-soluble, oxalate-soluble and alkali-soluble pectin were extracted and quantitatively determined as galacturonic acid, neutral sugars were determined as glucose. Jams were made with all peach samples as well as gels from extracted fractions. Gel strength of jams and gels was measured.  Dry matter, sugar composition (amount of sucrose and reducing sugars) and pH value were determined and very little change was found during the ripening period and storage, too.  Alkali-soluble fraction was more abounding than water-soluble fraction. The oxalate-soluble pectic fraction was found to be a minor fraction in all peach samples. The amount of total pectin and the amount of alkali-soluble pectin fraction dropped markedly after the 1st stage of ripening, after the 2 nd day of storage at 22 C and slightly after the 6th day of storage at 4 C. The level of alkali-soluble pectin in total pectin was inversely proportional to the level of water-soluble pectic fraction, and the level of oxalate-soluble pectic fraction in total pectin content was fairly constant during the ripening and storage. Gel strength of jams and gels correlated very well with changes of the amount of alkali-soluble pectic fraction.  The extracted alkali-soluble pectic fraction was capable of forming an acidic gel. Extracted oxalate-soluble pectic fraction forms a gel in the presence of calcium and solid matter more than 77%.  It seems that the amount of alkali-soluble pectic fraction in peaches is responsible in producing peach jams according to gel strength.

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