Extraction of pectin from skin and cap of pumpkin by microwave

Introduction: Pectin is a complex sugar soluble and it use widely as a gelling and stabilizing agent, texturizer and emulsifier in the food industry with increasing production and processing of fruits and vegetables, is created many byproducts. Pumpkin skin and cap, often discarded as waste, are a valuable source of pectin. Therefore, its use for pectin production, in addition to producing a valuable product, can be beneficial from the aspect of economically and environmentally and it also reduces problems related to exclusion of waste. The use of acidified hot water with mineral acids is a traditional and widely used method of pectin extraction. The use of mineral acids not only causes corrosion of equipment and apparatus, it also follow environmental damage. Also this method be time- consuming and it reduces the quality of produced pectin. Therefore, it is necessary to replace this method with a better and newer method that minimizes the problems arising from it. The use of microwave waves has been one of the new methods of extraction that recently, it has received the much attention of researchers. This method has many advantages compared to traditional methods such as shorter process time, lower consumed solvent, higher production efficiency, producing higher quality product and spend of lower cost. The use of microwaves is one of the new methods of effective extraction of certain compounds. This method has many advantages over traditional methods, including a shorter process time, less solvent consumption, higher production efficiency, higher quality product production and lower cost. Purpose: In this study, pectin was extracted from the skin and cap of pumpkin by microwave waves and then its yield and physicochemical properties were compared.

Material and methods: In this study, the cap and skin of pumpkin were cut and crushed and was exposed to sunlight for 4 days to dry against air flow. Then was grinded the dried cap and uniformity powder was made from it. The obtained powder in packed containers, keep away from moisture. Extraction of pectin from pumpkin skin and cap using microwave done at 80 and 90 °C, with power of 20 watt and times of 10, 15, 20 and 30 min, pH 1.5 and 2 and ratio of sample to solvent 20 and 30 % w/v. Determination of galacturonic acid content of extracted pectin by colorimetric method, degree of esterification by titration, emulsion properties, rheological properties using rotational viscometer and FTIR spectroscopy to determine the presence of functional groups (such as OH, C- O- H, C- O- C gropes) to confirm the quality of extracted pectin was performed on selected treatments with higher yield. The results were analyzed based on a completely random design by ANOVA and in binary comparisons of t tests. Data analysis was performed at 5% confidence level using software of SPSS 16.
Results and discussion: The treatment obtained at constant power of 20 W, 90 °C for 30 minutes, 30 % w/v, was determined as theselected treatment, its extraction efficiency was 24.21 % in pumpkin skin and 3.24 % in cap. The extraction efficiency of pectin has been increased by increasing the temperature from 80 ℃ to 90. The extraction efficiency increased by increasing the extraction time, So that the highest extraction efficiency occurred in 30 minutes. The extraction efficiency for pH= 1.5 is more than a condition that was used of pH= 2. The extraction efficiency increased by increasing the ratio of solid to liquid from 20% to 30%. The percentage of galacturonic acid in pumpkin skin and cap was 38.04% and 46.6%, respectively. The cap pectin has a higher purity than the pumpkin skin pectin. According to the degree of obtained esterification for the samples, pumpkin pectin is a low ester group. The highest degree of esterification was in the extracted sample from pumpkin skin (44.3). Using higher temperature for extraction reduces the degree of esterification, this is due to the pectin de- esterification at high temperatures. What ever the pH of the extraction solution be lower, the resulting pectin will have a lower degree of esterification. Emulsion stability of pumpkin skin at 4 °C on first day and tenth day was 90.2% and 77.2%, respectively, indicating high emulsion stability, which indicates the high stability of the emulsion. But emulsion stability at 23 °C on the first day of the tenth day is 85.5% and 49.2% respectively, that indicates a decrease in emulsion stability at higher temperatures. The extracted pectin solution from the pumpkin is not different at different concentrations, so that pectin had newtonian behavior (flow index (n) equal 1) at four concentrations of 0.1, 0.5, 1 and 2% w/v and the viscosity remains constant with increasing shear rate. The obtained solution from cap pectin has a higher viscosity than obtained pectin from pumpkin skin. The reason for this viscosity difference can know presence of structures with higher molecular weight in the cap pectin. Because compounds with high molecular weight have more ability to absorb water and create viscosity. The suggested model in this study was the newtonian model because for all samples, R2 had a value above 0.9. That's mean, this model had the ability to predict 90% from changes in rheological traits related to the studied samples. FT- IR results showed that the peaks of extracted pectin from the cap and skin were different together. That can be concluded that the produced pectin from the pumpkin cap has different structure from the extracted pectin from the pumpkin skin. The cap pectin has structurally more similar to the standard pectin.
Conclusion: Therefore, from this kind of agricultural waste can use as a promising source in pectin production for provide the needs of the food industry.