Submitted to: Food Hydrocolloids Journal
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/18/2006
Publication Date: 3/9/2006
Citation: Fishman, M.L., Chau, H.K., Hoagland, P.D., Hotchkiss, A.T. 2006. Microwave assisted extraction of lime pectin. Food Hydrocolloids Journal 20, p.1170-1177. Interpretive Summary: The need to increase utilization of low valued co-products derived from the processing of fruit has prompted us to investigate the structure of pectin. Pectin is a polysaccharide found in citrus peels. In this work we show that high quality food grade pectin can be extracted rapidly from various parts of limes after the juice is removed by microwave heating under pressure in a dilute acid solution. The quality of the lime pectin is demonstrated by its molecular weight and viscosity which is higher than that of commercial pectin. This research should be of help to fruit growers and processors by increasing the demand and value of their by-products without increasing the cost of the basic commodity to the consumer.
Technical Abstract: Pectin was extracted from lime flavedo, albedo and pulp by employing microwave assisted extraction (MAE) under pressure. Advantages of MAE over conventional heating methods in the extraction of pectin from citrus residues include 10 fold or better reduction in heating time, better control of extraction conditions and more narrow molar mass distributions. Heating times ranged from 1 to 10 minutes. Optimal time of heating was 3 minutes. A unique feature of MAE under pressure as compared to conventional heating methods is that high methoxyl pectins with a wide range of molar masses can be produced. Pectins dissolved in 0.05 M sodium nitrate were characterized by HPSEC with online static light scattering, dynamic light scattering and viscosity detection. Molar mass, viscosity, radius of gyration and hydrated radius were found to decrease with heating time. At 3 minute heating time, depending on the lime fraction which was extracted weight average molar mass ranged from about 310,000-515,000 Daltons, and weight average intrinsic viscosities ranged from about 9.5-13 dL/g. Molar mass polydispersity passed through maximum at 4 minutes. Molecules of pectin became less compact with increasing heating time. The results obtained here are consistent with previous evidence that extracted pectins may exist in solution as networks, partially formed networks, i.e. branched molecules or linear molecules depending on extraction conditions and the solvent in which they are dissolved.