Comparison of Pectin Biosynthesis in Local Apple Cultivar 'Azayesh' and Some Commercial Cultivars as Affected by pH and Carbohydrates Content

In order to study the characteristics of commercial apple cultivars grown under climatic conditions in Karaj 32 different characters were evaluated in 30 native Iranian and introduced cultivars based on Apple Descriptor during 2008. Some of the important pomological characteristics such as: weight, shape, skin and flesh color and other physicochemical characteristic including: pectin content, carbohydrates, pH, TSS, TA, flesh firmness of 'Golden Delicious', 'Red Delicious', 'Granny Smith' and a very dwarf native Iranian crab 'Azayesh' were measured. All of the pomological evaluations were done at the fruit ripening phase. The results of mean comparison obtained from the collected data related to measurements of physicochemical variables under experiment showed that 'Granny Smith' and 'Azayesh' had the highest levels of pectin compared with 'Golden Delicious' and 'Red Delicious'. Further analyses confirmed that cultivars containing more pectin biosynthesis capacity present lower pH values, the difference showed to be statistically significant among cultivars. There was in fact significant difference between 'Golden Delicious' and 'Red Delicious'. Supplementary studies showed that pectin biosynthesis is positively correlated with lower pH of cell sap. Consequently, a pectin biosynthesis increase was always accompanied with a pH decrease. Contrarily, pectin biosynthesis was positively correlated with carbohydrates content. In fact, total carbohydrate measurements confirmed a higher content of carbohydrates in 'Azayesh', while the other cultivars show a low pectin producing capacity in contest of genetic variability. It is clearly known that the high economic value of 'Granny Smith' in the fresh consumption market is a limiting factor for being used as pectin source, while pectin may be abundantly extracted from 'Azayesh' because other researches showed the high fruit set percent in Karaj climatic conditions. 'Azayesh' is a well known dwarf rootstock, adapted to the typical compact and calcareous soils of Iran. Demonstrating its potential in pectin biosynthesis in this research, makes it more valuable and could be also recognized as a new cultivar to be used for pectin extraction.