Pectins
Functionality
In the fruit, pectin has a very high degree of esterification (DE). During the acid hydrolysis used to extract it, some of the esters are converted into the free acid form (that is to say they are saponified). By careful control of this process, high methoxyl (HM) pectins with different degrees of esterification are obtained. The higher the DE, the faster the setting rate, so these pectins are classified as Rapid Set (RS), or Slow Set (SS) (for example).
In general, low methoxl (LM) Pectins can be obtained either by acid or alkaline hydrolysis. However, amidated LM Pectins can only be produced by hydrolyzing under alkaline conditions using an ammonia solution. Under these conditions, some of the esters are converted to amide groups, which alter the pectin's rheology and calcium reactivity.
Correct preparation of the pectin solution is a key first step in its use, with incomplete dissolution a frequent cause of unsatisfactory performance. To be easy to handle, a pectin must have good dispensability, high dissolution rate and maximum solubility.
Pectin solutions are stable under acid conditions (between pH 3.2 and 4.5), even at high temperatures. They are also stable for several hours at room temperature under more alkaline conditions, but degrade rapidly at high temperature.
HM pectins form thermostable gels when the pH is low (less than 3.5) and the sugar concentration is high (dry matter content greater than 60%). When the dry matter is less than 60%, LM pectins have to be used. The pH and the dry matter content affect the rate of gelation, more than the gel strength. LM pectins are generally thermoreversible. However, non-amidated LM pectins can form thermostable gels.
Gel formation is not the only function of Pectins: HM Pectins are excellent stabilizers of acid milk drinks. They coat the casein particles, stopping them form aggregating and so preventing sedimentation problems. LM Pectins can provide a wide range of textures and rheological properties, depending on the calcium concentration and the calcium reactivity of the Pectin chosen.