Pectic Fractions Research Articles

Irradiation Effects on the Ripening of Kent Mangoes

SUMMARY— Kent mango fruit irradiated with 0, 100, 200, and 300 Krad were ripened at 20°C for 0, 4, and 8 days.Irradiated mangoes were less firm than control fruit immediately after irradiation, but fruit softening due to ripeness was more pronounced than softening induced by irradiation. Irradiated fruit contained higher water‐soluble and lower Versene‐vinsoluble pectic fractions as compared to unirradiated fruit. NO differences were observed in the content of the Versene‐soluble fraction among all irradiation dosages. Higher PE activities were exhibited by the irradiated fruit throughout the ripening period. Irradiated fruit contained higher AIS and lower soluble solids than control fruit. No differences in sucrose content due to irradiation were observed, but there were less reducing and total sugars at the 300 Krad dose as compared to other dosages.Changes in pectic fractions and PE activity were more pronounced immediately following irradiation in comparison to those occurring during ripening. The increase in soluble solids as well as sucrose, and the decrease in AIS, titratable acidity, reducing sugars and firmness during ripening proceeded at faster rates in control fruit than in the irradiated fruit. These variable rates of change were reflected by the significant irradiation dose and storage duration interactions.Results suggest that irradiation induces a delay in ripening of Kent mangoes.

STRUCTURE OF A GALACTURONAN FROM SUNFLOWER PECTIC ACID

Fractions of sunflower pectic acid containing 89.8%, 94.2%, and 91.4% of D-galacturonic acid were carboxyl reduced as their methyl or ethylene glycol esters by potassium borohydride. Critical assessment of the effects of three different solvents (water, 80% aqueous dimethyl sulfoxide, and 80% aqueous methanol) on the efficiency of reduction showed that the latter solvent was best. The reductions caused a decrease in the degree of polymerization from 270 to 21. Measurement of the rates of hydrolysis of partially reduced pectic acids containing 90%, 41.6%, 19.9%, 11.0%, and 0.65% of D-galacturonic acid showed that the rate of hydrolysis was directly related to the proportion of galacturonosidic linkages present. Methylation and hydrolysis of the carboxyl-reduced pectic acid fractions yielded 2,3,4,6-tetra-O-methyl-D-galactose and 2,3,6-tri-O-methyl-D-galactose in an approximate molar ratio of 1:20. Results of the periodate oxidation of the carboxyl-reduced pectic acid supported the conclusion inferred from the methylation results that the pectic acid was a linear polymer of 1 → 4 linked α-D-galacturonic acid units.

Polysaccharides and germination: Some chemical changes that occur during the germination of white mustard

AbstractInformation has been obtained about the general nature of some chemical changes that occur during the germination of white mustard, with the object of providing background information for a detailed study of the role of cell wall polysaccharides.(1) During the germination of mustard seeds a number of reserve materials are used which occur largely in the cotyledons; the most important of them would appear to be proteins (during the first few days) and fats (during the later stages).(2) Although sucrose, stachyose and raffinose are present in only small amounts in mustard seeds, they seem to have a reserve function. During germination, the galactose units of the raffinose and stachyose are utilised rapidly and virtually completely, whereas the net utilisation of glucose and fructose units is very incomplete and relatively large amounts of free glucose and fructose accumulate.(3) The chemical character of the polysaccharides present in the cotyledons suggests that they have functions in the cell walls, rather than as reserves. Chemical analysis showed only minor fluctuations in the total amount of these polysaccharides during germination.(4) 14C‐Sucrose supplied to the germinating seed was utilised in a variety of ways. Some of the radioactivity was incorporated into the pectic fraction of the cotyledon polysaccharides, showing that this component of the cotyledon cell walls is not inert during germination.

Seasonal Changes Occurring in the Pectinesterase Activity and Pectic Constituents of the Component Parts of Citrus Fruits II. Pineapple Orangesa

SUMMARYPectinesterase activity, 3 pectic fractions, and other characteristics were determined periodically on 5 component parts of Pineapple oranges during a 9.month maturation cycle for 2 seasons. Generally, PE activity was greatest in the peel, membrane, and juice sacs in March, April, and May, when the Brix/acid ratio was highest. However, the activity varied in similar components for like months during the 2 seasons. The order of component parts for PE in most cases, from highest to lowest activity, was juice sacs, membrane, peel, seeds, and juice. Total PE in the average whole orange attained maximum activity in March and April. Over 52% of the activity present was found in the juice sacs, which represented about 22.5% of the whole fruit. Water‐soluble pectin increased slightly in the peel and membrane, remained somewhat irregular in the juice sacs, and decreased to a constant level in the seeds throughout the growing season. Ammonium‐oxalate‐soluble pectin in the peel decreased slightly, and in the other components was either irregular or increased slightly, during maturation. Quantity of protopectin was greatest in the membrane and generally decreased toward the end of the sampling period in the various components. Total pectin and weight of the average whole orange was greater in the 1961–62 season than in the preceding season.

A CHEMICAL STUDY OF THE CELL WALLS OF JERUSALEM ARTICHOKE TUBER TISSUE UNDER DIFFERENT GROWTH CONDITIONS

Slices of tissue from Jerusalem artichoke tubers were maintained under different growth conditions for periods of between 40 and 60 hours, when they were harvested and the walls isolated. The wall preparations were fractionated into the main polysaccharide components and the contents of uronic acid and sugar residues estimated in these components and in the whole wall preparations. Concentrations of plant hormones, optimal for cell enlargement, caused an increase in the water solubility of the pectic fractions of the walls compared to the situation in the water controls where enlargement was negligible. No differences could be detected in wall composition between ray, pith, and cortex tissue in the tuber. In the presence of plant hormones, tissue enlargement was inhibited by calcium ions for about 30 hours, after which it proceeded at a reduced rate. Such calcium treatment appeared to cause no change in wall deposition or composition. The results are discussed in relation to current ideas concerning the plasticity of primary cell walls.

Seasonal Changes Occurring in the Pectinesterase Activity and Pectic Constituents of the Component Parts of Citrus Fruits.

SUMMARYPectinesterase activity, 3 pectic fractions, and other characteristics were determined periodically on 5 component parts of Valencia oranges during a 7‐month maturation cycle for 2 seasons. Usually, PE activity for peel, membrane, and juice sacs was least in December, when the Brix/acid ratio was low, and highest in June, when this ratio was greatest. The order of component parts for PE in most cases, from highest to lowest activity, was juice sacs, membrane, peel, seeds, and juice. Water‐soluble pectin generally remained constant in peel and juice sacs, increased slightly and then remained constant in the membrane, and was irregular throughout the cycle in the seeds. The trend of ammonium‐oxalate‐soluble pectin in the components was to increase during maturation. Protopectin in the component parts usually increased to a peak and then gradually decreased for the remainder of the season, except that protopectin in the juice sacs decreased throughout the sampling period. In this component, protopectin evidently was at its maximum by the first picking in December. Total pectin remained constant in the juice and seeds, and slowly declined in the other 3 components with maturation. Membrane contained the highest source of protopectin and total pectin throughout the season.

Polysaccharides of the characeae II. The carbohydrate content of Nitella translucens

The chemical constitution of cells of Nitella translucens has been studied. A graded extraction procedure gave 22 fractions, which have been analysed. The free sugars include galacturoc acid, galactose, glucose, arabinose, sucrose, and fructose; a small amount (4%) of an iodophilic, starch-type, glucan is present. The pectic fractions have a very small methoxyl content. The uronic acid content of the cells accounts for the ion-exchange capacity previously reported for the cell walls. The outer cell wall appears to contain an almost pure cellulose as well as hemicellulosic materials.

PECTIC CONTENT OF PLANT MATERIALS

Many plants and plant materials such as wood (2), tea (25), tobacco (15), cotton (16), hops (13), ramie (11), flax (12), grass (6), potato (10), plantain seed (20), celery (9), limes (22), guava (1), bergamot (23), and root hairs (21), have been shown to contain pectic compounds. Because different methods of extraction and analysis were employed, it is impossible to make comparative studies from these data of the pectic composition, types of pectic materials, and distribution of pectic compounds in these plants. A systematic study, employing uniform treatment of the pectic materials of leaves, cereal grains, apples, and citrus fruits, was conducted by Nanji and Norman (18). They determined water-soluble pectin, oxalic-acid-soluble pectin and ammonium-oxalate-soluble pectin. These data were interpreted as representing pectic material present as pectin, pectin in combination with metallic ions, and pectic acid. This interpretation was based on the theory that protopectin is an insoluble calcium, magnesium, or iron salt (19), and that treatment with oxalic acid and ammonium oxalate dissolved the pectin and pectates combined in this manner. More recent studies, however, (3, 4, 14^ 17, 24), lead to the conclusion that the pectic molecule is essentially a long-chain, poly-galacturonic molecule combined through intermolecular forces and anhydride structure to form the insoluble protopectin layers of the cell wall and middle lamella. Single treatment with water or acid does not remove any definite pectic compound, but yields a part of a series of pectic substances; continued hydrolysis progressively dissolves the entire protopectin layer. The lack of quantitative data for comparison of the distribution of pectin in the plant phyla has led to the present study. A large number of plants and plant materials have been included, and in order to obtain comparative data for the concentrations of each pectic fraction present, a system of extraction involving successive stages of hydrolysis was employed. The first stage involves the removal of the water soluble pectin ; the second, the easily hydrolyzable protopectin; and the third, the difficultly hydrolyzable protopectin. These analyses have been supplemented by data on gelling power of the pectic material. Extraction and analyses One hundred grams of the material was ground in a sausage mill ; 500 ml. of water were added, and the mixture was heated for one hour at 90? C, evaporated water being replaced during the heating. The pulp was then pressed free of the liquid and returned for a second extraction with 500 ml. of water containing 0.155 ml. H2S04 (pH = 1.5). The pulp was again