Equivalent weight Pectin Characterization

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3. Equivalent weight

Equivalent weight is a measurement of of free galacturonic acid group non-esterified content in the pectin chain molecules Ranganna 1977. Pure pectic acid is a substance that its composition is entirely composed of polygalacturonic acid that free from methyl ester group or did not undergo esterification. Pure pectic acid has equivalent weight of 176. The high degree of esterification between galacturonic acid with methanol showed the low number of free acid which means that the higher equivalent weight Rouse 1977. Equivalent weight of resulted pectin powder ranged between 847.95 and 1431.69. Relationship between treatment time and extraction temperature on equivalent weight can be seen in Figure 12. Figure 12. The relationship between microwave power and extraction time to equivalent weight The equivalent weight will decrease when microwave power and extraction time increased. The highest equivalent weight was pectin with treatment microwave power of 600 W for 3 minutes, while the lowest equivalent weight was obtained from pectin with treatment microwave power of 800 W for 7 minutes. Results of analysis of variance showed that the microwave power and extraction time significantly affected the equivalent weight of pectin, but interaction between microwave power and extraction time was not significantly affect the equivalent weight of pectin Appendix 4b. Kim et al. 1978 explain the low temperatures used on the extraction will minimize the occurrence of depolymerization and demethylation. According to Padival et al 1979, characteristics of the gel and molecular weight will decrease with increasing extraction temperature. The higher the temperature and the longer extraction time will increase the depolymerization or deesterification of pectin so the value of equivalent weight would be lower. If deesterification increase, it means that free acid group is also increase and it make the equivalent weight decrease because the amount of pectic acid that has equivalent weight increase. According to Doesburg in Rouse 1977, pure pectinic acid has low equivalent weight value of 1886, while pure pectic acid has equivalent weight value of 176. Increase in microwave power will make extraction temperature increase, so the equivalent weight will decrease if microwave power is increased. Molecular weight of pectin depends on the type of plants, the quality of raw materials, extraction methods, and treatment in the extraction process. Generally, high molecular weight pectin is preferable due to its better gel formation Constenla and Lozano, 2006. The best pectin is pectin which has a high equivalent weight. The higher microwave power and extraction time, will obtained the lower quality pectin according to the equivalent weight value.

4. Methoxyl content