Pectic substances structure

As investigations with polysaccharides of microbiological, plant, and animal origin revealed the presence in these substances of uronic acids, it became necessary to know more about the acids. Moreover, the occurrence of uronic acids in plant gums and pectic substances, and the structures of urinary... 

This review will focus on pectic substances that have been shown to exhibit biological activity. Their structure, bioactivity and possible structure activity relations will be discussed. 

Pectins can generally be divided into neutral and acidic polymers, but certain structural features are common between the different types of pectic substances. These will be described below. Concerning the general chemistry of carbohydrate types of linkages, the reader can find details on this in general textbooks of chemistry and biochemistry and is for this reason not included. 

From the science performed mainly over the last ten years it is obvious that the role of pectic substances in health care has been substantiated. For some of the pectic substances, parts of the structure of the bioactive sites have been determined, but further studies of the relevant structures for the individual active polymers must be performed in order to find a possible common structure for the activities observed. It also appears that there are special structural features present in some of the polymers, which are not foimd in others, and which are important for their activity, and this may explain the different behaviour of the polymers in the same system. 

The structural features of ceU wall polysaccharides of carrots have been studied by Stevens and Selvendran (1984) and Massiot et al.(1988). Plat et al.(1991), Ben Shalom et al.(1992) and Massiot et al.(1992) investigated the changes in pectic substances of carrots after blanching, dehydration and extended heat treatment. Data on the changes in ceU waU polysaccharides of canned carrots are lacking. This study aims to investigate the effect of preheating time at low temperature and the addition of CaCL on texture and on the composition of various pectin fractions of carrots canned by conventional and by a new process. 

To date, the structural features of pectic polysaccharides and plant cell walls have been studied extensively using chemical analysis and enzymatic degradation. In addition, research on isolation and physicochemical characterisation of pectin from citrus peels, apple peels, sunflower head residues and sugar beet pulp has been reported (2). However, the pectic polysaccharides extracted from wheat straw have only previously been reported by Przeszlakowska (3). The author extracted 0.44% pectic substances from Author to whom correspondence should be addressed. 

Structural features of pectic substances during growth and ripening of apples... 

In contrast, a comparatively small proportion of recent researches dealing with the enzymes acting on pectic materials proceeded on classical lines involving purification and constitutional studies. With the exception of a few papers, most reports deal with the action and behavior of these enzymes without extensive purification and paying little attention to the chemical composition and constitution of the enzymes themselves. The reason for this might be the general preoccupation with the development of suitable methods for the exact determination of the action of pectic enzymes, which in turn is the result of our lack of knowledge of the exact structure of pectic substances. 

The role of the structural properties of pectins was described recently (1) where it was shown that interactions of calcium with pectic substances were directly related to the existence of unbranched and non-esterified galacturonic blocks. Calcium was able to ionically bind two or more chains... 

Desired organoleptic properties, particularly textural ones, are a direct consequence of these microstructural changes. A chip must be firm and snap easily when deformed, emitting a crunchy sound (Krokida et al., 2001a), whereas in thick products the better the contrast between a rich and soft inner structure and a crispy outside, the better the product (Moreira, 2006). Firmness is often related to starch swelling and gelatinization, as well as to the stability of pectic substances of the cell wall and middle lamellae. 

Enzymes. See also, Amylases, Galactosi-dases, /3-Glucuronidase, Glyco-enzymes, a-D-Mannosidase. acting on pectic substances, 5, 79-102 degradation by, of starch and glycogen, 3, 251-310 17, 407-430 of glycoprotein structure, 27, 301-341 specificity of, in the domain of carbohydrates, 5, 49-78... 

Pectic Substances. Part 111. Composition of Apple Pectin and the Molecular Structure of the Araban Component of Apple Pectin, E. L. Hirst and J. K. N. Jones,/. Chem. Soc., (1939) 454-460. 

Pectic substances are important structural components of the middle lamellea and the primary cell walls of higher plants, in particular fruits and vegetables. The extent and mode of their degradation by enzymes affect many aspects of the processing of fruits and vegetables and many quality attributes of fruit and vegetable products. 

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