Functional properties of pectin
It is the hydrocolloid character of pectin which makes it such important and versatile adduct in certain food system. Most important raw material for the production of commercial pectin is apple pomace, peels of various citrus fruits. Apple pomace have low content of pectin [15%] and on the other hand lime peel have to the extend of 50%.
Degree of methoxylation of pectin
It has been found that galactouronic acid unit of pectin is partially esterified with methyl group. The DM of pectin decides the sped of gelation and pectins with high DM also set at higher temperature which will influence their end use. The pectin having DM of more than 50% is called as high methoxyl [HM] pectin and pectin with DM of less than 50% is called as low methoxyl
[LM] pectin. HM have quite specific gelling property as it require high soluble solids i.e. above 55% and low pH. LM are able to form thermo- reversible gels and need Ca ions for gel formation.
Measurement of grades of pectin
Initially pectin was graded as per SAG value but now a days it is being estimated as breaking strength and as internal strength as being measured by pektionometer and Stevens- LFRA Texture
Pectin and gel formation
Pectin is readily soluble in water when the concentration of soluble solids is below 25%. As the sugar or total solids [TS %] content increases through processing, the available free moisture is removed and pectin will dehydrate. The precipitated macromolecule will form a lattice through the gel and being negatively charged, pectin molecules in solution will repel one another. By lowering the pH [increasing the hydrogen ion concentration], the repulsion effect will be reduced and gel
Theories of gel formation
Jelly formation is due to the precipitation of pectin rather than its swelling. Only when the pectin, acid, sugar and water are in definite equilibrium range, the precipitation of pectin takes place. The
rate of precipitation depends on
According to Cruess, when sugar is added to pectin solution, it destabilizes the pectin-water equilibrium and the pectin conglomerates forming a network of fibrils holds the sugar solution in the interfibrillar spaces. The strength of the jelly depends on the strength of fibrils, their continuity and rigidity. The greater the amount of pectin, greater number of fibrils formed and the network will be more continue and dense. The firmness of network depends on concentration of sugar and acidity. Increasing amount of sugar reduces the of water to be supported by pectin firbrils, lower amount of sugar can be compensated by using additional amount of pectin. The fibrils of the pectin become tough in the presence of acid and thus hold sugar. If a larger amount of acid is present, fibrils lose their elasticity with the result that the jelly becomes syrupy, due to hydroxylation of pectin. If acid is present in smaller amount, a weak fibril is formed which is unable to support the sugar solution. It can be made up by adding more pectin. Ultimately, the maximum amount of acid which can be added to the pectin solution, without any undesirable effect, is determined by the degree of decomposition of the pectin.
Pectin particles are negatively charged. A pectin solution is most stable at the neutral pH . Thus increase in acidity or alkanity decreases the stability of pectin solution. In jelly formation , sugar
acts as a precipitating gent, and the presence of acid helps it. Some salts also help in the precipitation of pectin, while others hinder t according to their capacity to increase or decrease the
stability. Thus, more the acid present lesser will be the sugar requirement.
If pectin is taken to be a negatively charged hydrophilic colloid, the following may be assumed.
It s based upon the assumption that pectins are complex mixtures of variables composition. According to it, gelations of pectin are a type of coagulation in which the coagulated particles form
a continuous network. It is only the non ionized, and not the ionized pectin, which enters into jelly formation. To form a jelly, therefore, the concentration of non ionized pectin must exceed a certain saturation limit, which varies with the concentration of total solids in the mixture.
Strength of Pectin Jellies