MOLECULAR WEIGHT PROFILES OF DIETARY FIBER PRODUCTS OBTAINED BY CHEMICAL OR ENZYMATIC MODIFICATIONS OF Cucumis moschata, Duch. MESOCARP

FISSORE E.N.; RUMILLE SANDRA; MATKOVIC LAURA B; WIDER EVA A; ROJAS A.M.; GERSCHENSON LN

Conferencia; Dietary Fiber 2006; 2006

Fibre can be added to foods for nutritional or technological purposes. The aim of this study was to study the molecular weight (MW) profile of the cell wall polysaccharides (CWP) that constitute dietary fiber products obtained by chemical or enzymatic modification of pumpkin (Cucumis moschata, Duch) mesocarp.Water was removed from mesocarp through a juice extractor. Residue was washed twice, dried (85ºC, 2 h), milled and sieved. This powder was digested (20 h, 30ºC) under stirring into a 0.5 M-sodium citrate buffer (pH 5.2) without (B) or with a cell wall (CW) enzyme (hemicellulase H, or cellulase, C). Insolubles were separated and CWP precipated from supernatant after ethanol addition: B, H and C-products. They were filtrated, freeze-dried and dialysed. MW profiles were determined through a Sepharose column (0.4 ml/min) with 0.5 M-imidazol buffer (pH 7.0). Total carbohydrate content (TCC) into each collected fraction was determined by phenol-sulphuric method. Rheological characterization of fractions obtained were performed in a Brookfield viscometer (25ºC). C-product was constituted by polysaccharides of the highest (homogeneous) MW range (1200000-180000) determined (peak at 800000). On the other hand, H was constituted by CWP of the lowest MW range (4400-40000) determined, with a uniform MW-distribution. B-product was characterized by an heterogeneous MW distribution ranging from 20000 to 1600000 (peaks at 380000 and 86000), with a lower intensity between 80000 and 20000. C and B were essentially RGI and II, but B-fraction showed a higher proportion of galacturonic acid (GAC) to Rhamnose (17:1) than that observed for C (11:1). B, C and H-fractions were water soluble after swelling and the 1% (w/w)-B solution produced a transparent gel with thinning behavior (k=1.59 Pa.s; n=0.77) at room temperature, while C showed lower consistency (k=0.012 Pa.s; n=0.96) and acted as a thickener only after heating and addition of sucrose (60%, pH=3). Conversely, H-product showed newtonian behavior and a low viscosity ( 0.002 Pa.s). Although B presented CWP of lower MW than C, it showed the highest thickening behavior fact that can be attributed to a lower number of Rhamnose-kinks into homogalacturonan chains and/or to a lower number of hindering introduced by side chains into its CWP constituents (RGI, II). It can be concluded that cellulase or chemical modification of CW material of pumpkin mesocarp produced dietary fiber products (C, B) with interesting functional properties for food technological applications.