Comparison of the Conformation of Tomato Pectins With Apple and Citrus Pectins

Abstract

7'he conformation of hot break tomato pectins in water/glycerol solutions as afinction of degree esteriflcation was studied and compared with the conformation of apple and citrus pectin using reduced storage [GYR and loss [G'YR moduli and the theories of Marvin and McKinney for rod-like behavior and those of Rouse as well as Zimm for random coil conformation. In all three cases the theory of Zimm implying dominant hydrodynamic interactions p t the experimenal data best. This is consistent with current knowledge on chemical structure of pectin where the charged uronides clearly readily interact with each other. 0 Copyright 1593 by Food & Nutrition Press, Inc.. Trumbull, Connecticut. 117 118 J.L. KOIUNI and T.C. CHOU et al. 1973). They can undergo deesterification and depolymerization in aqueous solution. The pH of greatest stability is around 4 (Smith and Bryant 1968; Pedersen 1980; BeMiller and Whistler 1958).Several factors affect the rheological properties of pectins in solution. These are electrolyte concentration, molecular weight, the degree of esterification, and the pH (Nelson el al. 1977). Paoletti et af. (1986) hypothesized that monovalent cation salts of pectins are highly ionized in solution, and the distribution of ionic charges along the molecule tends to keep it in an extended form. Ionization also prevents aggregation between the polymer chains resulting in solutions of stable viscosity because each polymer chain is hydrated, extended and independent (BeMiller and Whistler 1958). However, Thibault and Rinaudo (1986) found that monovalent cations caused a decrease in viscosity, the degree of which was greater with decreasing DE. Addition of salts of di-and tri-valent cations had the op posite effect.Tomato pectic substances extracted according to their solubility in water, 0.2% ammonium oxalate, 0.05N hydrochloric acid and 0.05N sodium hydroxide were found to be highly polydisperse, with the majority having a molecular weight of 2 X lo5 using gel filtration (Stein and Brown 1975) . Luh et af. (1984) found that the weight average molecular weights of pectinic acids isolated from fresh tomatoes of six cultures ranged from 7870-26,800. This calculation was based on measurement of intrinsic viscosity and Mark-Houwink constants obtained by Owens et al. (1946). The Mark-Houwink exponents were in the range of 1.38-1.42. If the assumption of random coil type molecule was made, the molecular weights would be larger approximately by a power of 1.5, since the Owens approximation uses a Mark-Houwink exponent of 1.38 and a random coil molecule would have an exponent between 0.8-0.9 (Luh et al. 1984). In that case the weight average molecular weights would range from approximately 7 x lo5 to 5 x lo6. These values would then be consistent with those obtained by Stein and Brown (1975).Fishman et al. (1984) showed that the radii of gyration of pectin molecules were significantly affected by the degree of methylation, with 57% being an o p timal value where steric hindrance would prevent further aggregation. Pippen e...

Analysis of cell-wall pectin from hot and cold break tomato preparations

“…Past work has suggested that hot break processing inactivates pectolytic enzymes (EPG and PME), and therefore, prevents the breakdown of pectin, which is often important in product viscosity (Chou & Kokini, 1987;Goodman et al, 2002;Kokini & Chou, 1993;Xu, Shoemaker, & Luh, 1986). Our results showed that a 24 min hold time at 22°C did not allow for observable endogenous pectolytic activity on the cell-wall pectin.…”

Conformational Changes in Serum Pectins during Industrial Tomato Paste Production

“…Measurements of rms radii showed that, during processing, serum pectins assumed a more compact conformation (Figures and ). It has previously been shown that the conformation of tomato paste pectins is different from other unheated pectins , . While depolymerization alone may cause conformational changes in pectins , we did not find substantial changes in serum pectin weighted average molecular weight during tomato juice concentration.…”

Changes in Cell Wall Pectins Accompanying Tomato (Lycopersicon esculentum Mill.) Paste Manufacture

“…Only the fruit and paste samples are included in Figures 7-9 to make it easier to see differences. Analysis of the pectins from the intermediate samples (2)(3)(4); not shown) generally shows trends intermediate to those depicted for paste pectins.…”

“…Texture, particularly in relationship to flow characteristics, is among the important quality attributes of processed tomato products. Several authors ( − ) have reported that the most important factor in determining the viscosity and consistency of tomato paste and products derived from it is the high molar mass polymeric substances derived from cell wall polysaccharides during processing.…”