138
Besides it also increases production, reduces equipment size and has very few process steps. Apart from these, it also improves the bioactive profile of polysaccharides, by modifying their molecular properties. As we know that unmodified pectin
is not easily absorbed by the body, so modification of pectin using UAE can break
these molecules into smaller fragments. Shear forces are responsible for decreasing
the molecular weight of pectin and this force is generated as a result of relative
motion between solvent and polymer chains, as the bubbles collapse. The effect is
more pronounced in long chains as compared to chains below a certain critical size.
Various researchers have reported the synergistic application of the ultrasound and
the other novel techniques for obtaining better yield of pectin e.g. the workers in
china reported that an ultrasound-/microwave- assisted acid method’ (abridged
UMAAM) not only helped to achieve higher yields of pectin but also the pectin
obtained was having much higher MW (636.20 vs. 295.95 kDa) in comparison to
pectin obtained by traditional means. It has been reported that grapefruit pectin
obtained from UAHE had lower molecular weight, viscosity and degree of esterification as compared to the conventional heating extraction (CHE).On the contrary it
had higher degree of branching and purity and yield comparable to CHE. Two
modes of the UAE system exists in two forms: namely bath and probe units. In the
former, there are limitations of reproducibility and lack of uniformity in distribution
of ultrasound energy. On the other hand, ultrasonic probes are much efficient as the
ultrasound energy can be focussed on specific sample zones which can result in better cavitation. Probes are better suited to laboratory works.
Purification of Pectin
The industrial production of pectins mostly consists of HMP. Although LMP occurs
naturally in plants but can also be obtained from HMP by its de-esterification using
acid, alkaline and/or enzymes. Short extraction time at a temperature close to boiling yields rapid-setting HMP as the high temperature- short extraction time combinations reduce de-esterification. This is reverse in case of long extraction time with
low temperatures which favour de-esterification to yield slow-setting HMP or even
LMP (Nussinovitch and Hirashima 2013). Therefore, by selecting the suitable timetemperature combinations, the pectin with desired properties can be obtained (Chan
and Choo 2013). In case of acid de-esterification, inorganic acids such as hydrochloric acid is used to bring out the de-esterification. The method has a major disadvantage that it can lead to the pectin degradation via hydrolysis and β-elimination.
In case of hydrolysis, which is a pH-dependent reaction, and occurs mainly in acidic
environment (Krall and McFeeters 1998; Smidsrød et al. 1966), neutral polysaccharides (ballast) are removed. A lesser portion of proteins and phenolic compounds
are also removed (Constenla and Lozano 2003; Kravtchenko et al. 1992a, b). The
pH of the plant cell wall lies in the range of 4–6 and as the pH decreases, the rate of
the reaction of acid hydrolysis increases (Brett and Waldron 1990). But for the pH
range of 4–6, acid hydrolysis was found negligible by Fraeye et al. (2007). Again,
N. Noor et al.
Besides it also increases production, reduces equipment size and has very few process steps. Apart from these, it also improves the bioactive profile of polysaccharides, by modifying their molecular properties. As we know that unmodified pectin
is not easily absorbed by the body, so modification of pectin using UAE can break
these molecules into smaller fragments. Shear forces are responsible for decreasing
the molecular weight of pectin and this force is generated as a result of relative
motion between solvent and polymer chains, as the bubbles collapse. The effect is
more pronounced in long chains as compared to chains below a certain critical size.
Various researchers have reported the synergistic application of the ultrasound and
the other novel techniques for obtaining better yield of pectin e.g. the workers in
china reported that an ultrasound-/microwave- assisted acid method’ (abridged
UMAAM) not only helped to achieve higher yields of pectin but also the pectin
obtained was having much higher MW (636.20 vs. 295.95 kDa) in comparison to
pectin obtained by traditional means. It has been reported that grapefruit pectin
obtained from UAHE had lower molecular weight, viscosity and degree of esterification as compared to the conventional heating extraction (CHE).On the contrary it
had higher degree of branching and purity and yield comparable to CHE. Two
modes of the UAE system exists in two forms: namely bath and probe units. In the
former, there are limitations of reproducibility and lack of uniformity in distribution
of ultrasound energy. On the other hand, ultrasonic probes are much efficient as the
ultrasound energy can be focussed on specific sample zones which can result in better cavitation. Probes are better suited to laboratory works.
Purification of Pectin
The industrial production of pectins mostly consists of HMP. Although LMP occurs
naturally in plants but can also be obtained from HMP by its de-esterification using
acid, alkaline and/or enzymes. Short extraction time at a temperature close to boiling yields rapid-setting HMP as the high temperature- short extraction time combinations reduce de-esterification. This is reverse in case of long extraction time with
low temperatures which favour de-esterification to yield slow-setting HMP or even
LMP (Nussinovitch and Hirashima 2013). Therefore, by selecting the suitable timetemperature combinations, the pectin with desired properties can be obtained (Chan
and Choo 2013). In case of acid de-esterification, inorganic acids such as hydrochloric acid is used to bring out the de-esterification. The method has a major disadvantage that it can lead to the pectin degradation via hydrolysis and β-elimination.
In case of hydrolysis, which is a pH-dependent reaction, and occurs mainly in acidic
environment (Krall and McFeeters 1998; Smidsrød et al. 1966), neutral polysaccharides (ballast) are removed. A lesser portion of proteins and phenolic compounds
are also removed (Constenla and Lozano 2003; Kravtchenko et al. 1992a, b). The
pH of the plant cell wall lies in the range of 4–6 and as the pH decreases, the rate of
the reaction of acid hydrolysis increases (Brett and Waldron 1990). But for the pH
range of 4–6, acid hydrolysis was found negligible by Fraeye et al. (2007). Again,
N. Noor et al.