Physico-Chemical Properties of Pectins in the Cell Walls and After Extraction
Pectins are present as structural polysaccharides in the middle lamella and the primary cell-walls of higher plants. They are part of our diet either as additives in some food products or as constituants of the raw materials used in the food products. Their physico-chemical properties, within the cell wall matrix or after extraction, are of prime importance both from a functional and a nutritional point of view.
Industrial pectins are extracted from by-products of the fruit juice industry (apple pomace or citrus peels). They are extracted in acidic conditions and chemically modified to give High Methoxy (HM) pectins and Low Methoxy (LM) pectins (some may be also amidated). The properties of these two main types of differ widely. The HM pectins form gels in acidic conditions and in presence of sugars whereas the LM pectins needs calcium for gelation. The gelation mechanisms are directly linked to the conformation of the molecules, to their polyelectrolyte nature, and to the amount and distribution of the substituents (methyl, amid ...). The characteristics of the surrounding solutions (pH, ionic strength, nature of the ions, presence of cosolutes, temperature..) may also play key roles. The application areas of these gels are mainly in the food industries: jams, marmelades, jellies, confectionery...Their stabilizing properties are now more and more used, for instance in acid milk products.
Within the cell wall, the pectins may have another range of important properties in relation to ion-binding and to hydration which depend on numerous parameters. Furthermore, the physical structure of the matrix is also very important and particle size, surface area, porosity have to be considered in the dietary fibre context.
KeywordsDietary Fibre Apple Pomace Hydration Property Divalent Metal Cation Citrus Peel
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