Presentation on theme: "Gelling polysaccharides"— Presentation transcript:
1 Gelling polysaccharides What is a gelLook atAlginatesPectinCarrageenansSynergyXanthanLBGMechanisms for gelationNotes can be found on ;sbw5f/APPS/APPS/WINAPPS/Data/Slides and Lectures/SEHill/INDEX.HTM??????????????????????
2 X Gelation of proteins Polysaccharides Said to occur when a small amount of solid is dispersed in a relatively large amount of solvent (usually water), by the property of mechanical rigidity.Defined as a protein aggregation phenomenon – attractive and repulsive forces are so balanced that a well ordered tertiary network or matrix is formed.Protein gels are composed of three dimensional matrices or networks of interwined, partially associated polypeptides in which water is entrapped.Is a continuous network of macroscopic dimensions immersed in a liquid medium and exhibiting no steady flow.
23 Low ester pectin High ester pectin Pectin with degree of esterification > 50% is referred to as high ester pectin.High ester pectins gel in the presence of high concentrations of cosolutes (e.g. 60% sugar) and at pH values < 3.4.Rapid set pectins have DE ~70% and slow set pectins have DE ~65%.Gelation is believed to occur through association of the pectin chains by hydrophobic bonding.Gels are thermally irreversible.Low ester pectins have DE < 50%.Low ester pectins gel in the presence of calcium ions. The reactivity increases as DE decreases.Gelation occurs as a consequence of calcium ion crosslinking.
24 Mixed gels Often more than one polymer exists This can enhance to reduce gel quality
25 Two component gel types Swollen networkInterpenetrating network
29 Gel Textures Firm, Brittle Low Acyl Gellan Gum Agar k-Carrageenan High “G” AlginatePectinGel TexturesHigh “M” AlginateGelatinXanthan/LBGHigh Acyl Gellan GumSoft, Flexible
30 Useful references http://www.lsbu.ac.uk/water/ E-learning hydrocolloid program on BlackboardJournals: Food Hydrocolloids and Carbohydrate PolymersSeries of Books: Gums and Stabilisers for the Food IndustryBook :Functional Properties of Food Macromolecules (Chapter by Morris on gelation)Anything in the TX55-, QD4--, QP section of the library