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Title: Studies on the pectic polysaccarides of wattakka cultivar (Cucurbita spp.) and some applications in food formulations
Authors: HERATH, HMT
Keywords: Carbohydrates
Issue Date: 2004
Publisher: University of Sri Jayawardenepura: USJ(Main).
Citation: HERATH, HMT, Studies on the pectic polysaccarides of wattakka cultivar (Cucurbita spp.) and some applications in food formulations, University of Sri Jayawardenepura USJ(Main), 2004: xv,98p.
Abstract: In this study, pectin from the fruits of Cucurbita spp, namely, Wattakka, Meemini and Butternut cultivara, was investigated as a potential souce for use in food industry. Towards this end, basic and applied research on the following work was carried out. (a) Isolation and characterization of the cell wall polysaccharides of Cucurbita moschata, Watakka cultivar, using non-degradative methods. The native pectin was purified and characterized to obtain its monimer sugar composition. (b) A comparison was also made on the non-starch polysaccharide compositions of the three cultivars of Cucurbita spp. As components of dietary fibre. (c) Extraction of pectin from the three cultivars of Cucurbita spp. Using an industrial process and determination of chemical and physical characteristics and (d) a study of the applications of pectin from the Wattakka cultivar in some food formulations. The pectic polysaccharides of the cell walls of Wattakka were isolated as alcohol insoluble residue using a modified method described by Ng et al. (1998). This alcohol insoluble residue, was sequentially extracted, under non-degradative methods, using CDTA (0.05 M, pH6.5) at 20§ - 22§ C, for 6 h (CDTA-1) and 2 h (CDTA-2), respectively. The residue thus obtained was further extracted with Na2CO3-2), respectively. The extracts of all fractions were filtered, neutralized and dialysed exhaustively and freeze dried. The monomer sugar compositions of the fractions wre determined after 12 M H2SO4 hydrolysis, neutralization and deivatization to alditol acetates and quantified by GC techniques. The uronic acid content was determined calorimetrically.The yield of the cell wall material of the edible portion of the Wattakka fruit was 29.6 percent, (as alcohol insoluble material), consisting of 91 percent carbohydrates, mainly pectic polysaccharides. The total CDTA and Na2CO3 fractions accounted for 24.7 percent and 3.7 percent respectively, of the original material. The monomer sugar composition of the fractions, showed that the branching points of pectic material (as indicated by the ratio of rhamnose; uronic acid) were high in CDTA-1 (1:38) and CDTA-2 fractions (1:30), while the Na2CO3-1 (1:22) and Na2CO3-2 (1:25) fractions contained less branching points. The major neutral sugar in all fractions was galactose , which was a significant characteristic of Cucurbita spp. The main fraction of the cell wall CDTA-1, was subjected to anion exchange chromatography (DEAE- Trisacryl column), more or less a homogenous individual polymer was obtained, when eluted with 0.25 M NaCI. This polymer contained 84 percent of uronic acid, with a rhamnose to uronic acid ratio of 1:44. The major neutral sugar of the polymer was galactose, with substantial amounts of arabinose and mannose. The non-starch polysaccharides (NSP) of all three cultivars were determined as dietary fibre. Wattakka contained 11.8 g/100g of NSP, of which 22 percent was soluble fibre. The NSP of the other two cultivars was less, Meemini containing 9.1g/100g (20 percent soluble fibre) and Butternut containing 8.9g/ 100g (18 percent soluble fibre). NSP of Cucurbita spp. May be of importance in terms of its physiological role in human systems. The pectin from all three cultivars of Cucurbita spp. Was extracted under industrial conditions (in HC1 at pH 1.3 for 2h, followed by alcohol precipitation), after pre-processing using three different methods. The yields of the pectin were in the range of 7.4 to 28.8 percent for all three cultivars and was found to be dependent on the method of pre-processing. These yields are in the same range of values reported for citrus ( 25 percent) and apple 15-18 percent). The chemical characterization of the industrially estracted Wattakka pectin was classified as a high mehoxyl (HM) pectin, as it had methoxyl content of over 7 percent. However, the Wattakka pectin showed weak gelling properties (gel grade 100) as compared to citrus pectin (gel grade 150), with a low rupture point (0.7K Pa) and a low compression ability (18 N). The presence of higher concentrations of neutral sugars in the pectic polymer may hinder the gel forming ability. Both other cultivars, Meemini and Butternut, did not demonstrate gel forming characteristics, probably due the high acetyl content (over 2 percent). Hence it could be concluded that the use of these two cultivars in food applications are limited. Wattakka pectin had an average molecular weight of 2927 daltons and its viscosity properties increasing markedly at a pH of 4.6 at a concentration of 1 percent (w/v). Wattakka pectin was applied to several food formulations and its technological characteristics were investigated as compared to that of citrus pectin. Wattakka pectin was incorporated into a dietetic fruit juice, showed a higher viscosity values (18-30 cP) as compared to citrus pectin (12-17 cP), at concentrations of 0.15-0.25 percent (w/v), imparting a body and texture to the product. Wattakka pectin when added to a formulation of stirred yoghurt (non-fat), demonstrated the formation of a stabilized milk-pectin complex by showing an increase in the viscosity, ranging from 2200 to 3800 cP, at pH 4-45 and at concentrations ranging from 0.15 - 0.25 percen (w/v). These stabilizing properties, however, were not demonstrated when Wattakka pectin was used in fat contining stirred yoghurt formulations. When Wattakka pectin was used in emulsions of oil-in-pectin solutions, an emulsion stability of 100 percent was obtained at a concentration of 2 percent (w/v), as compared to cirtrus pectin which showed a 40 per cent stability similar conditions.
Description: Dissertation: M.Phil., University of Sri Jayawardenepura: USJ(Main), 2004.
Appears in Collections:University of Sri Jayawardenepura

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