(544bh) Criteria for a Unique Steady State for Guava Juice Depectinization in a Continuous Stirred Tank Reactor

Fruits
have several health benefits, which has led to an increased consumption of the
same throughout the world. Packaged fruit juices devoid of preservatives are
particularly preferred, as they offer convenience with regards to portability.
If preservatives are not added, there is degradation of the juice with time.
Pectins, a class of polysaccharides, are responsible for the same [1]. Therefore,
the key to obtaining a high shelf life of fruit juice devoid of preservatives
is to significantly reduce the pectin content. Enzymes like pectinase are used
for hydrolysis of pectin and subsequent flocculation of the pectin-protein
complexes, resulting in a juice having insignificant pectin concentration [2].
Enzymatic treatment also leads to a substantial lowering of viscosity,
essential for subsequent clarification step [3].  According to earlier studies,
enzymatic depectinization of fruit juice with pectinase demonstrated
Michaelis-Menten reaction kinetics [4, 5]. In all these studies, the pectin was
first isolated from the juice, followed by subsequent depectinization. But, for
large-scale fruit juice processing, it seems viable to undertake
depectinization of the actual fruit juice, instead of the two-step process of
protein isolation and subsequent depectinization. However, it is observed that
depectinization of actual fruit juice, such as guava juice, follows Hill
kinetics as opposed to the traditional Michaelis-Menten behavior, due to
allosteric interactions that are prevalent among the macromolecules present in
the fruit juice [6]. For successful exploitation of the advantages associated
with actual fruit juice depectinization, large scale operation is necessary.
But feasible commercial production and scale-up are possible only by optimizing
reactor design.  If a chemical reaction exhibits non-linear kinetics, it may
lead to multiple steady state solutions [7]. Existence of multiple steady
states would result in a significant deviation from the desired product composition.
Thus, a reactor needs to function under the prescribed operating conditions
that would result in a unique steady state.

In
the present study, a scheme is developed to ensure a unique steady state in
case of enzymatic depectinization of actual guava juice in a continuous stirred
tank reactor, employing the principles of contraction mapping. It is found that
as the desired conversion of the reactant increases, there is widening of the
zone of unique steady state. However, the zone undergoes shrinkage with enzyme
concentration. In order to study the effects of initial substrate and enzyme
concentration, conversion profiles are generated as a function of residence
time of the reactor. In addition, critical residence time to ensure steady
state is also calculated, so that reactor designing can be optimized without affecting
the desired end product specification. The scheme proposed in the current work
is generic in nature, and can be conveniently extended in order to incorporate other
reaction mechanisms.

References:

[1]
Prasanna, V., Prabha, T.N., Tharanathan, R.N., 2007. Fruit Ripening
Phenomena–An Overview. Crit. Rev. Food Sci. Nutr. 47, 1–19.

[2]
Alvarez, S., Alvarez, R., Riera, F.., Coca, J., 1998. Influence of
depectinization on apple juice ultrafiltration. Colloids Surfaces A
Physicochem. Eng. Asp. 138, 377–382.

[3]
Demir, N., Acar, J., Sarıoğlu, K., Mutlu, M., 2001. The use of
commercial pectinase in fruit juice industry. Part 3: Immobilized pectinase for
mash treatment. J. Food Eng. 47, 275–280.

[4]
Bélafi-Bakó, K., Eszterle, M., Kiss, K., Nemestóthy, N., Gubicza, L., 2007.
Hydrolysis of pectin by Aspergillus niger polygalacturonase in a membrane
bioreactor. J. Food Eng. 78, 438–442.

[5]
Kiss, K., Cserjesi, P., Nemestóthy, N., Gubicza, L., Bélafi-Bakó, K., 2008.
Kinetic study on hydrolysis of various pectins by Aspergillus niger
polygalacturonase. Hungarian J. Ind. Chem. 36, 55–58.

[6]
Ninga, K.A., Sengupta, S., Jain, A., Desobgo, Z.S.C., Nso, E.J., De, S., 2018.
Kinetics of enzymatic hydrolysis of pectinaceous matter in guava juice. J. Food
Eng. 221, 158–166.

[7]
Doraiswamy, L.K., Uner, D., 2013. Chemical Reaction Engineering: Beyond the Fundamentals.
CRC Press, Boca Raton.