Pectic Substances
نویسندگان
چکیده
Pectins are a group of plant polysaccharides whose principal component is 1,4-linked a-d-galactosyluronic acid (O’Neill et al., 1990). Pectins are present in the primary cell walls of all seed-bearing plants and in the junction between cells called the middle lamella. The primary wall surrounds growing plant cells, meristematic cells and cells in succulent tissue such as fruit. The secondary walls of differentiated plant cells (e.g. xylem tracheids) are often lignified and cellulose-rich, and contain little pectin. Pectins are major components (20–30%) of the primary walls of dicotyledons (e.g. tomato, soybean and apple), nongraminaceous monocotyledons (e.g. onion and garlic) and gymnosperms (e.g. Douglas Fir). In contrast, pectin accounts for 5 10% of the primary wall of the Poaceae (e.g. wheat, maize, and rice). The limited data available suggest that pectins are present in the walls of lower plants (e.g. ferns) and some green algae (e.g. Nitella and Coloechaete). Some plants also produce water-soluble polysaccharides that contain galactosyluronic acid residues. These polysaccharides are structurally related to pectins but are usually referred to as gums andmucilages in the literature. Recent studies of cell wall pectins have provided evidence that the pectic polysaccharides are structurally modified during the growth anddevelopment of plant cells. Pectin fragments are signal molecules that can activate plant defence responses to pathogens and modify the growth and development of plant tissue. Pectins are a major component of dietary fibre and have been reported to lower serumcholesterol levels to bind toxicmetals and to have immunostimulating and antiulcer activities. Pectins effect the texture and processing characteristics of fruits and vegetables. The ability of pectins to form gels (‘pectin’ is derived from the Greek ‘pektos’ – ‘coagulated’) has been exploited by man for centuries and these polysaccharides have been used in various commercial applications, especially in the food industry (Visser and Voragen, 1996). Molecular Structure
منابع مشابه
The isolation of pectic substances from softwoods.
Branfoot (1) has summarised the early work on pectic substances. Bonner (2), Norman (3), and Hirst and Jones (4) have reviewed later work on the structure of these substances. Pectic materials that approximate the composition and have some of the properties of pectic acid are widely distributed but in small amounts in mature hardwoods. In 1925 O’Dwyer (5) isolated such a material from beechwood...
متن کاملXxvi. the Nature of the Pectic Substances of Flax
As the result of recent researches our knowledge of the pectic substances of plants has become more systematic, and it is proposed in the present paper to adhere to the nomenclature adopted by the American Pectin Symposium of 1925. Thus we are now acquainted with protopectin, the naturally occurring pectic substance; pectin, the substance extracted from the plant by chemical or other means with...
متن کاملThe Isolation of Pectic Substances from Wood* by Ernest Anderson
Pectin is considered by many investigators to be the tetramethyl ester of an acid composed of 4 molecules of d-galacturonic acid, 1 molecule of d-galactose, and 1 molecule of Larabinose (1). However, experimental work described by Morell, Baur, and Link (2) indicates that the pectin molecule is more complex and contains between 8 and 10 molecules of d-galacturonic acid. The data obtained by rep...
متن کاملEffects of Cutting Direction on the Changes of Microorganisms and Pectic Substances in the Partially Processed Carrot during Storage (Studies on Physiological and Chemical Changes of Partially Processed Carrot-Part IV) ABE
The changes of microorganisms and pectic substances of partially processed carrots (PPC) were determined with respect to cutting direction. The increase of microbial counts occurred in all tissues and both lengthwise cut sections (LCS)and crosswise cut sections (CCS). The microbial count in the xylem of LCS increased at a greater rate than those of phloem at 20•Ž. The counts in both tissues of ...
متن کاملSeason-controlled changes in biochemical constituents and oxidase enzyme activities in tomato (Lycopersicon esculentum Mill.).
Season-controlled changes in biochemical constituents viz. carotenoids (carotene and xanthophyll) and pectic substances along with IAA-oxidase and polyphenol oxidase (PPO) enzyme activities were estimated/assayed in leaves of Lycopersicon esculentum Mill. (tomato) in two developmental stages--pre-flowering (35 days after sowing) and post-flowering (75 days after sowing) in three different seaso...
متن کامل