134
where T, is the absolute temperature and h, is the dynamic viscosity coefficient
(Loncin and Merson 1979). Overall the factors that influence both the quality and
the quantity of the extracted pectin can be categorised as intrinsic, extrinsic and
techno functional ones. Intrinsic factors are related to matrix of polysaccharide like
particle size and moisture content. Extrinsic factors are based on the nature of solvent like its molecular weight, polarity, solid-liquid ratio, toxicity and volatility. The
techno functional factors like temperature, pressure, and optimal operating conditions are equally important. High temperatures can result in excessive depolymerisation and de-esterification of the protopectin, which can result in pectin extract
having inferior functional properties although yield per unit may be high at elevated
temperatures. Another important parameter that needs to be taken into consideration
is the pH of the extraction solvent while extracting pectin. Generally pH range
between 1 and 3 has been reported by most of the workers (Jensen et al. 2013). In
order to adjust the pH, small amount of base such as NaOH can be used although
time-temp combinations are also taken into account. Low acidic pH favours the
hydrolysis of the protopectin whereas high pH conditions can cause pectin degradation owing to β-eliminations (Kravtchenko et al. 1992a, b). So what we need is to
strike a balance between having a superior quality but low yield at high pH and
having an inferior quality extract but with higher yield at a lower pH. Talking about
particle size, El-Nawawi and Shehata (1987) reported that for smaller particle size
higher yields were obtained and the reason was that for increased surface area, the
area of contact between the solid and solvent increased and distance for diffusion
for the solute decreased. But for the particles which are too fine, problems may arise
as the fine particle size may jam within the cervices of adjacent coarser ones, which
may again pose a problem to the flow of the solvent. It was further reported by
El-Nawawi and Shehata (1987) that agitation of the solvent had no significant effect
on the yield of pectin. The workers explained this owing to the outward diffusion of
the solute within the solid matrix and the diffusion of solute from matrix surface to
the solvent. If it would have been vice-versa then agitation may have played a role
in increasing the extraction yield following the eddy diffusion induced by agitation.
Another significant factor attributing to the rate of mass transfer is time as with time
the concentration gradient decreases the rate of mass transfer decreases. As the
duration of the extraction increases, more and more pectin starts accumulating in
the solution. This makes the solution more viscous thereby declining the rate
(Richardson et al. 2002). Further the optimal duration for the process is important
as an extended period of extraction may cause the thermal degradation of the polysaccharide but also may stop the pectin dissolution. Thus control of the above mentioned parameters is very important to maintain the superior quality of the extracted
pectin. The role of the above mentioned factors have been studied in detail by
El-Nawawi and Shehata (1987).With respect to increasing both the quality and the
quantity of the extracted pectin, a number a non-conventional techniques have been
sorted to overcome the shortcomings of the conventional extraction techniques.
These aim to increase the yield in an environment friendly and energy conserving
way. A few of them have been described below:
N. Noor et al.
where T, is the absolute temperature and h, is the dynamic viscosity coefficient
(Loncin and Merson 1979). Overall the factors that influence both the quality and
the quantity of the extracted pectin can be categorised as intrinsic, extrinsic and
techno functional ones. Intrinsic factors are related to matrix of polysaccharide like
particle size and moisture content. Extrinsic factors are based on the nature of solvent like its molecular weight, polarity, solid-liquid ratio, toxicity and volatility. The
techno functional factors like temperature, pressure, and optimal operating conditions are equally important. High temperatures can result in excessive depolymerisation and de-esterification of the protopectin, which can result in pectin extract
having inferior functional properties although yield per unit may be high at elevated
temperatures. Another important parameter that needs to be taken into consideration
is the pH of the extraction solvent while extracting pectin. Generally pH range
between 1 and 3 has been reported by most of the workers (Jensen et al. 2013). In
order to adjust the pH, small amount of base such as NaOH can be used although
time-temp combinations are also taken into account. Low acidic pH favours the
hydrolysis of the protopectin whereas high pH conditions can cause pectin degradation owing to β-eliminations (Kravtchenko et al. 1992a, b). So what we need is to
strike a balance between having a superior quality but low yield at high pH and
having an inferior quality extract but with higher yield at a lower pH. Talking about
particle size, El-Nawawi and Shehata (1987) reported that for smaller particle size
higher yields were obtained and the reason was that for increased surface area, the
area of contact between the solid and solvent increased and distance for diffusion
for the solute decreased. But for the particles which are too fine, problems may arise
as the fine particle size may jam within the cervices of adjacent coarser ones, which
may again pose a problem to the flow of the solvent. It was further reported by
El-Nawawi and Shehata (1987) that agitation of the solvent had no significant effect
on the yield of pectin. The workers explained this owing to the outward diffusion of
the solute within the solid matrix and the diffusion of solute from matrix surface to
the solvent. If it would have been vice-versa then agitation may have played a role
in increasing the extraction yield following the eddy diffusion induced by agitation.
Another significant factor attributing to the rate of mass transfer is time as with time
the concentration gradient decreases the rate of mass transfer decreases. As the
duration of the extraction increases, more and more pectin starts accumulating in
the solution. This makes the solution more viscous thereby declining the rate
(Richardson et al. 2002). Further the optimal duration for the process is important
as an extended period of extraction may cause the thermal degradation of the polysaccharide but also may stop the pectin dissolution. Thus control of the above mentioned parameters is very important to maintain the superior quality of the extracted
pectin. The role of the above mentioned factors have been studied in detail by
El-Nawawi and Shehata (1987).With respect to increasing both the quality and the
quantity of the extracted pectin, a number a non-conventional techniques have been
sorted to overcome the shortcomings of the conventional extraction techniques.
These aim to increase the yield in an environment friendly and energy conserving
way. A few of them have been described below:
N. Noor et al.