Methoxyl content Pectin Characterization

18

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

Methoxyl content defined as the amount of methanol that containedin the pectin. Pectin is categorized as high methoxyl pectin HMP if it has a value methoxyl content equal to 7 or more. If the a bc b c d d 0,00 200,00 400,00 600,00 800,00 1000,00 1200,00 1400,00 1600,00 1800,00 600 800 Eq ui va le nt W ei gh t Microwave Power Watt 3 min 5 min 7 min 19 methoxyl content is less than 7, the pectin is categorized as low methoxyl pectin LMP Goycoolea and Adriana 2003. Methoxyl content of extracted pectin ranged from 4.07-6.43. Based on the value of methoxyl content, the resulted pectin in this study was relatively low in methoxyl. Graph showing the relationship of microwave power and time of extraction treatment on methoxyl level of pectin can be seen in Figure 13. The graph showed that the methoxyl content will become higher with increasing microwave power and the length of extraction time. Figure 13. The relationship between microwave power and extraction time to methoxyl content. Results of analysis of variance showed that the microwave power and extraction time significantly affected the methoxyl content of pectin, but interaction between microwave power and extraction time was not significantly affect the methoxyl content of pectin Appendix 5b. The highest methoxyl content was pectin with treatment microwave power of 800 W for 7 minutes, while the lowest methoxyl content was obtained from pectin with treatment microwave power of 600 W for 3 minutes. The range of methoxyl content from this pectin was 4.07-6.43 which was under 7. Because of the methoxyl pectin was under 7, so the pectin extracted from sugar palm seed was belongs to Low Methoxyl Pectin LMP category. Methoxyl content of pectin has an important role in determining functional properties of pectin solution and can affect the structure and texture of pectin gel Constenla and Lozano 2006. High methoxyl pectin forms a gel in the presence of sugar and acid. Conditions required for gel formation is 58- 75 sugar content with a pH 2.8-3.5. Low methoxyl pectin does not have the ability to form gel in the presence of sugars and acids, but it can forms a gel with presence of polyvalent cations Cruess 1958. LMP on industry can be used as a thickener in manufacturing of low calories beverage, jelly for diabetic, and others healthy food. The pectin industry normally produces high methoxyl pectin though there are some plants that produce low methoxyl pectin. There are four methods of demethylation including the use of acid, alkali, enzyme and ammonia in ethanol. Demethylation using acidis commonly used to produce low methoxyl pectin Kertesz 1951. Extraction of high methoxyl pectin is easier to do with lower cost. In addition, most of the sources of raw materials produce high methoxyl pectin. High methoxyl pectin is more considered to meet the market needs. If the market want slow methoxyl pectin, the high methoxyl pectin can be easily converted into low methoxyl pectin. But low methoxyl pectin is more difficult to be converted to high methoxyl pectin Kertesz 1951.

5. Galacturonic content