Pectin for use in food is defined as a polymer containing at least 65% galacturonic acid units. The acid groups may either be free or be methylesterified, sodium, potassium, calcium or ammonium salts. In some commercial pectins amide groups also may be present.
The regular structure is interrupted by the presence of L-rhamnose, which causes deviations called "pectic elbows". The L-rhamnose is linked by carbons 1 and 2.
The proportion of the galacturonic acids that are in the methyl ester form, is called the “degree of esterification” (DE) or “degree of methoxylation” and is quoted as a percentage. DE affects the behavior of pectin.
High methoxyl (HM) pectins are defined as those with a DE equal to or above 50, while low methoxyl (LM) pectins have a DE of less than 50. LM pectins can be acid or alkali-treated. LM pectins also can be either amidated (LMA) or non-amidated (LMC).
The % level of substitution of the amide group is defined as the “degree of amidation” (DA) and also is very important to the performance of a pectin.
DE and DA provide a good classification of pectins, and while these values can help identify the expected behavior of a pectin, additional properties are more suited to define its functionality, e.g. SAG, setting temperature and viscosity.
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, or saponified. By careful control of this process, HM pectins with different degrees of esterification are obtained. The higher the DE, the faster the setting rate, so depending on the DE these pectins are classified as Rapid Set (RS), or Slow Set (SS) for example.
In general, 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, a process which alters the pectin's rheology and calcium reactivity.
Correct preparation of the pectin solution is a key initial preparatory step. Incomplete dissolution is a frequent cause of unsatisfactory performance. A pectin which is easy to handle must have the following characteristics: good dispersibility, 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 also are 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, more than the gel strength affect the rate of gelation. LMA 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 from aggregating to prevent 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.
HM pectins also are very attractive viscosifiers for soft drinks. Here the pectin builds a similar mouthfeel to that of fruit juices, and is therefore useful in juice drinks and in low calorie or diet drinks. In addition, HM pectins have the advantage of delivering a very clean flavor release. In this case, the viscosity is created simply by the behavior of the pectin in the solution.
From a nutritional point of view, pectin is an interesting dietary fiber. Early research indicates that it has physicochemical properties which may positively influence several biomarkers that influence cardio-vascular and digestive functions. It may act as a cholesterol-lowering agent and preliminary research shows that it can impact gut health. Our scientific team will be glad to provide the necessary information.