(652g) Kinetics of Self-Buffering Hydrolysis of Pectin in Batch Reactor

Kinetic
study for a self-buffering hydrolysis of pectin in batch reactor

Heman
P. Asher, Raul Rivas-Cantu, Patrick L. Mills

Processing of citrus
waste generates large amount of wastes. 
From 2008-2011, the USA
generated almost 10.5 million tons of Citrus Processing Waste (CPW) from
processing of grapefruits and oranges. The CPW is dried and then used as a low
cost feed for livestock. Due to low nutritional values of feedstock and high
energy consumption during drying, this operation is not economical and is used
as a remedial process for waste disposal. The unused CPW is sent to landfills,
which incurs environmental hazards and high economical costs. Grapefruit
Processing Waste (GPW) is the primary source of CPW in Texas.
GPW can be used as a renewable source of pectin-rich biomass, which on
hydrolysis gives Galacturonic Acid (GA) and other value added products for
biorefinery applications. GA on catalytic reduction may produce hexoses
(glucose, galactose), which can be used to produce bio-ethanol.

The objective of this
work was to obtain kinetic parameters for self-buffered enzymatic hydrolysis of
pectin in a batch reactor to determine the reaction kinetics with an emphasis
on its conversion into galacturonic acid (GA). Lab scale experiments were
performed in bottom- baffled Erlenmeyer flasks submerged in water bath shaker
at pH 4.8, temperature 45 °C and 175 rpm.

The first step was to evaluate
the experimental results of total hydrolysis of various concentrations of pectin
solutions in 75 mM sodium acetate (NaOAc) buffer solution and in a
self-buffering solution of sodium galacturonate (NaGA) produced during
enzymatic hydrolysis and formed due to addition of sodium hydroxide (NaOH) to
raise the initial pH to 4.8. Experiments for determination of kinetic
parameters were performed for three different enzyme loadings for 0.5 wt%
pectin solutions monitored at periodic time intervals for 5 hours. Commercially
available enzyme complexes, such as Pectinex^R Ultra-SPL and
Accelerase^R XY, were used as biocatalyst. The initial results showed
that the self-buffering system behaved similar to externally buffered system.
Subsequently, the kinetic parameters for a self-buffered system were determined
based on experimental data using the Michaelis-Menten model.  Additional experiments at pH 6.0 are being
evaluated for improving enzymatic activity and to increase the reaction yield.
The determined kinetic parameters are shown in table 1. Fig. 1 shows the
behavior of GA concentration with time during the enzymatic hydrolysis of
pectin and Fig. 2 shows the normalized M-M plot for enzymatic hydrolysis.

These and other
results, including the utility of the kinetic modeling for reaction scale-up by
a volume factor of more than 150, will also be discussed

Table 1 ? Determined
kinetic parameters for various enzyme loading