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

Analyser respectively.

 

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

  • Concentration of pectin in solution
  • Constitution of pectin
  • pH of the pectin solution
  • Concentration of sugar in solution
  • Temperature of mixture

 

Fibril theory

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.

 

Spencer’s theory

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.

 

Olsen’s theory

If pectin is taken to be a negatively charged hydrophilic colloid, the following may be assumed.

  • Sugar acts as dehydrating agent, which disturbs the equilibrium existing between water and pectin.
  • Sugar does not dehydrate the pectin micelles instantaneously, but requires the time to bring about an equilibrium
  • If the negative charge on pectin is reduced, with the help of H+ concentration, pectin precipitates and form a network of insoluble fibers provided that the sugar is present in sufficient concentration.
  • The rate of hydration and precipitation of pectin increases with the addition of acid upto an optimum of about pH 2.0, in direct proportion to H+ concentration
  • As the system reaches an equilibrium, the jelly strength becomes the maximum
  • Salt and other components which cause a change in the ultimate jelly strength of the system, may function either by changing the rate of gelation or by affecting the ultimate structure f the jelly or by combination of both

 

Hinton’s theory

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

  • Quantity of pectin   : the larger the amount of pectin present, the higher is the jelly strength
  • Quantity of acid      : the larger the amount of acid presents, the lower the pH and higher is the jelly strength.
  • Quantity of salts      : Jelly strength is affected by the presence of salt as also by the temperature of gelation and the tie elapsing between the additions of sugar and pouring of equally into containers
  • Quantity of sugar    : the higher the sugar concentration, the greater is the jelly strength
  • Temperature of gelation: more jelly strength is obtained when sugar + pectin is heated upto 21 to 100 °C

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Comment by Ms. ALKA KUMARI on April 22, 2016 at 12:13pm

It's really well explained, Thanks for this info

Sir can you add some figures showing the structure of pectin and changes that takes place during gel formation,

Hope this will help us to understand the topic in a better way

Comment by Pankaj Kumar Jha on September 12, 2011 at 10:35am

Dear Sanjeev,

 

very informative posting... Thanks...

 

Can you throw some light on Thermoreversible pectin, what is low methoxy amidated pectin, and how does amidation of low methoxy pectin helps in thermoreversibility??

 

Regards,

Pankaj

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