Clarification of Tomato Juice with Polygalacturonase Obtained from Tomato Fruits Infected by Aspergillus niger
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Two varieties of tomato fruits commonly available in Nigerian markets are the
Rom a VF and Ibadan local varieties of tomato fruits. The Roma VF fruits are oval
in shape. It is a common type of cultivar in the Northern region of Nigeria and it is
not susceptible to cracking. The Ibadan local variety of tomato fruits is a local
variety commonly found on farmers fields in South-western region of Nigeria.
They are highly susceptible to cracking. The Ibadan local variety was employed for
this research. There are lots of benefits derived from the consumption of
tomato fruits. The fruits can be made into tomato juice clarified with pectinases.
Polygalacturonase is one of the pectinases used commercially in the clarification
of fruit juice from different fruits. This study examined the production of
polygalacturonase during the deterioration oftomato fruits by Aspergillus niger and
the role of the purified polygalacturonase in the clarification of tomato juice.
Tomato fruits of the Ibadan local variety were inoculated with mycelia discs
containing spores of a 96-h-old culture of Aspergillus niger served as the inoculum.
The organism from the stock culture was subcultured onto potato dextrose agar
plates. The extraction of polygalacturonase after 10 days of incubation at 27°C was
carried out by homogenizing the fruits with liquid extractant using the MSE
homogenizer after the deteriorated fruits had been chilled for 30 min inside a
freezer. Control fruits were similarly treated except that sterile potato dextrose agar
served as the inoculum. The effect of different temperature of incubation and
different volume of enzyme on the tomato juice from the tomato fruits was
investigated. Extracts from the inoculated fruits exhibited appreciable
polygalacturonase activity. The juice with polygalacturonase was visually clearer
and more voluminous than the juice treated with water for all parameters studied.
The highest volume of juice was obtained after an incubation period of 30 min for
the tomato fruits. The increase in juice yield can be attributed to the hydrolysis of
pectin which releases the sap inside the cells of the pulp. The occurrence of
polygalacturonase in tomato tissues infected by A. niger coupled with the trace
amount in the non-infected tissues suggests that the enzyme is of fungal origin. The
role ofthe polygalacturonase in the clarification process was established. This study
will be very useful for industrial tomato juice production.
Keywords
QR Microbiology