Efeito de diferentes açucares, pectinas e ligações de agua na formação de geis pecticos

AUTOR(ES)

Carlos Ferreira Grosso

DATA DE PUBLICAÇÃO

1992

RESUMO

Pectin gels were made with HMP and LMP using sucrose glucose fructose and sorbitol as sweetening agents. The absorption of water at controlled aw, the different water association forms and the values for SAG in each gel were measured and correlated with gel formation mechanisms. Polygalacturonic acid partially and methylated derivative as well were exaustively methylated HMP were studied too. The absorptions of water by LMP and HMP, and the sugars used in preparing gels follow the same pattern. Water absorption for the purified pectins, free of added sugars, had the same values as for water curves absorption but among the sugars absorption values were different. The amount of total water absorbed by the lyphylized gels or monolayer water was in all cases greather than the sum of water absorbed for each component individually indicating that the gel matrix has a larger area of exposure to which water molecules can associate. Results from DSC revealed different amount of decrease for the melting points of the ice when different sugars were used. Equilibration of a gel to different levels of humidity produced ice that melted at a lower temperature than pure water. In LMP gels, BET values, combined water and total water have no correlation with SAG values while for HMP good correlation was observed. When the above values were calculated on a mol/mol basis, correlation ceased, indicating the water holding capacity of the sugars is not the only cause of rigidity for the gel and pectin-sugar interaction must be a determining factor. The results for LMP demonstrated the non correlation between water absorption of the sugars and gel rigidity. The effects of the different sugars are associated with the competition between each sugar and the pectin for the calcium ions. This explanation was supported by the results of the NMR for the sugar showing the formation of sugar-metallic ion complex.

ASSUNTO(S)

polissacarideos alimentos

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