Effect of long term cold storage and microwave extraction time on the physical and chemical properties of citrus pectins

Authors: Fishman, Marshall; Chau, Hoa - Rose; Hotchkiss, Arland; Garcia, Rafael; COOKE, PETER - New Mexico State University; White, Andre

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2018
Publication Date: 1/1/2019
Citation: Fishman, M., Chau, H.K., Hotchkiss, A.T., Garcia, R.A., Cooke, P.H., White, A.K. 2019. Effect of long term cold storage and microwave extraction time on the physical and chemical properties of citrus pectins. Food Hydrocolloids. 92:104-116. https://doi.org/10.1016/j.foodhyd.2018.12.047.
DOI: https://doi.org/10.1016/j.foodhyd.2018.12.047

Interpretive Summary: Carbohydrates such as pectin are common food ingredients with health benefits as dietary fiber. The quality of pectin is determined by its chemical and physical properties with degree of methyl-esterification the most important for gelling and emulsification. While freezer storage is typically used to preserve pectin properties, the degree of methyl-esterification for orange and lime pectin was observed to decrease by 50% following 14 years of freezer storage. These results will alert pectin manufacturers and customers that degree of methyl-esterification changes with storage time and if pectin is not used close to the manufacture date, then the degree of methyl-esterification must be determined for optimal food and health promoting applications.

Technical Abstract: The physical and chemical properties of pectin determine its food and non-food uses. To determine the effect of cold storage on these properties, multi detector HPSEC and compositional analysis were performed on fresh and 14 year old cold (-20C) stored, microwave-extracted pectin. The weight average molar mass (Mw), intrinsic viscosity ('w) and radius of gyration (Rgz) decreased with time of extraction for both orange and lime pectin, regardless of whether they were analyzed before or after long term cold storage. Mw and Rgz generally increased following cold storage compared to pectins before storage with a few exceptions. AFM images showed that both large extended and small spherical molecules were present in lime and orange pectins following cold storage. Amino acid analysis indicated that phenylalanine and tyrosine were present in pectin fractions following cold storage. UV traces of HPSEC chromatograms for both pectins samples revealed that more protein was associated with higher rather than with lower molar mass pectin at 2.5 minutes of extraction time. At 10 minutes of extraction time, there is a larger breakdown of high molar mass pectin containing protein compared to pectin not containing protein. All pectin samples had little or no appreciable difference in galacturonic acid content following cold storage. Most significantly, the degree of esterification decreased by approximately 50% following cold storage for both orange and lime pectin. Pectins consisted mostly of homogalacturonan with some rhamnogalacturon I containing arabinogalactan side chains.