Study of Structure – Property – Function Relations of Hawthorn Pectin

Pectins are a family of native heteropolysaccharides ubiquitously presenting in the primary cell wall and the middle lamella of higher plants, which have been commercialized for wide applications in food industry as gelling agent, emulsifier, stabilizer, and thickener. As a natural ingredient with both textural modification abilities and various health-benefit effects, the global market of pectin is expected to grow rapidly in the future, driven by the increasing demands for natural, clean label and functional ingredients. Currently commercial pectin products are mainly extracted from citrus and apple, which are difficult to adapt to the increasing and diversified demands for tailored applications of pectin in food, pharmaceutical, and hydrogel material industries. Finding new source of pectin with specific structure, property, and function is attracting both industry and academia. Hawthorn is a popular commercial fruit in China which is an important edible and medicinal source. Hawthorn fruits contain large amount of pectin resource which has been almost not exploited and utilized, due to the poor knowledge on the structure, property, and function of hawthorn pectin. The present thesis investigated in-depth on the structure characteristics of hawthorn pectin, and related them with the rheological property and function of inhibiting lipid digestion. The results showed that among natural pectins, hawthorn pectin is characterized by high degrees of methoxylation (DM), low molecular weight (MW), high proportion of homogalacturonan (HG) region, low proportion of rhamnogalacturonan (RG) region but with abundant side chains. These features of pectin structure are different among the hawthorn fruits which are mainly used for processing in different provinces of China, and significantly affected by heat processing and extraction temperature, thereby resulting in the different performances in rheological property and function of inhibiting lipid digestion. A dynamic alteration of pectin fractions involving solubilization and depolymerization occurred simultaneously during heat processing of hawthorn fruit. The solubilization mainly happened in chelator-soluble pectin (CSP) and Na2CO3-soluble pectin (NSP), inducing a shift from water-insoluble pectin to water-soluble pectin (WSP), meanwhile the depolymerization occurred in HG region of WSP, forming a large amount of pectic polysaccharide fragments with small MW. Long time heat processing at high temperature had negative effect on both rheological property and ability to inhibit lipid digestion of hawthorn pectin. The pectin (HP60) extracted from Hebei hawthorn at mild temperature (60 °C) presented a good rheological property and best inhibitory effect on lipid digestion. It can even can form gel-like structure by itself without the presence of sugar and calcium ion. The self-gelation property of HP60 owed to its unique structural and conformational characteristics including high DM, relatively lower MW, abundant side chains, an appropriate ratio of HG and RG-I regions and a balanced chain length between the main chain and side chains. Theoretically, the relation of structure–property–function of pectin is very complicated. Besides DM and MW, this thesis through systematic research into hawthorn pectin revealed that the other structural even conformational characteristics such as the abundance of RG-I region, the amount of side chains, and the length of main chain and side chains also affect pectin property and function. The property and function of pectin is a combined consequence of multiple effects of various structural even conformational features. This study provides novel knowledge and in-depth insight on understanding the structure–property–function relations of pectin. More importantly, this study described a typical structure of high methoxy pectin which can form gel without large amount of sugars as co-solute. It breaks the traditional knowledge on the gelling mechanism of high methoxy pectin. This typical structure of high methoxy pectin is worthy to be in-depth studied in the future. On the industrial relevance side, the results and finding of this thesis will facilitate the utilization and commercialization of hawthorn pectin.