WE CLAIM:
1.A bioreactor for preparing a low-calorie sugar composition, the bioreactor comprising:
a pre-treatment reactor (R-801) for treatment of biomass to obtain cellulose and xylose;
a first column (C-801) connected to the pre-treatment reactor (R-801) via tank (T-802) for receiving the cellulose from the pre-treatment reactor (R-801) and configured to treat the cellulose to obtain a mixture of glucose and cellobiose;
a second column (C-701) connected to the first column (C-801) via tank (T-701) for receiving the glucose from the first column (C-801) and configured to treat the glucose to obtain a mixture of glucose and fructose;
a third column (C-702) connected to the second column (C-701) via tank (T-702) for receiving the fructose from the second column (C701) and configured to treat the fructose to obtain a mixture comprising fructose and psicose;
a fourth column (C-703) connected to the third column (C-702) via tank (T-703) for receiving the psicose from the third column (C702) and configured to treat the psicose to obtain a mixture comprising psicose and allose;
a fifth column (C-301) connected to the pre-treatment reactor (R-801) via tank (T-301) for receiving the xylose and configured to treat the xylose to obtain a mixture comprising xylose and xylulose;
a sixth column (C-401) connected to the first column (C-801) via tank (T-401) for receiving the cellobiose from the first column (C-801) and configured treat the cellobiose to obtain a mixture of cellobiose and glucose, wherein the second column (C-701) is connected to the sixth column (C-401) via tank (T-701) to receive glucose from the sixth column (C-401);
a seventh column (C-601) configured to receive sucrose, glucose and fructose in the form of juices and configured to treat the juices to obtain a mixture of glucose and fructose, wherein the second column (C-701) is connected to the seventh column (C-601) to receive glucose from the seventh column (C-601);

an eighth column (C-901) configured to receive a mixture of sucrose, glucose and fructose in the form of juices and configured to treat the juices to obtain a mixture comprising sucrose and isomaltulose;
a ninth column (C-902) configured to receive sucrose, glucose and fructose in the form of juices and configured to treat the juices to obtain a mixture comprising sucrose and trehaluose; and
a product collection tank (T-1003) connected to and configured to receive output from the fourth column (C-703), the fifth column (C-301), the eighth column (C-901) and the ninth column (C-902).
The bioreactor as claimed in claim 1, wherein a first downstream separation unit (DSP 801) is provided between the first column (C-801) and the second column (C-701), the first downstream separation unit (DSP 801) configured to control the flow from the first column (C-801) towards the first column (C-801), second column (C-701) or the sixth column (C-401) based on the composition of mixture of glucose and cellobiose.
The bioreactor as claimed in claim 1, wherein a second downstream separation unit (DSP 701) is provided between the second column (C-701) and the third column (C-702), the second downstream separation unit (DSP 701) configured to allow flow from the second column (C-701) towards the second column (C-701) or the third column (C-702) based on the composition of mixture of glucose and fructose received from the second column (C-701).
The bioreactor as claimed in claim 1, wherein a third downstream separation unit (DSP 702) is provided between the third column (C-702) and the fourth column (C-703), the third downstream separation unit (DSP 702) configured to allow flow from the third column (C-702) towards the third column (C-702) or the fourth column (C-703) based on the composition of mixture of psicose and fructose received from the third column (C-702).

5. The bioreactor as claimed in claim 1, wherein a fourth downstream separation unit (DSP 703) is provided between the fourth column (C-703) and the product collection tank (T-1003), the fourth downstream separation unit (DSP 703) configured to allow flow from the fourth column (C-703) towards the fourth column (C-703) or the product collection tank based on the composition of mixture of psicose and allose received from the fourth column (C-703).
6. The bioreactor as claimed in claim 1, wherein a fifth downstream separation unit (DSP 301) is provided between the fifth column (C-301) and the product collection tank (T-1003), the fifth downstream separation unit (DSP 301) configured to allow flow from the fifth column (C-301) towards the fifth column (C-301) or the product collection tank (T1003) based on the composition of mixture of xylose and xylulose received from the fifth column (C-301).
7. The bioreactor as claimed in claim 1, wherein a sixth downstream separation unit (DSP 401) is provided between the sixth column (C-401) and the second column (C-701), the sixth downstream separation unit (DSP 401) configured to allow flow from the sixth column (C-401) towards the sixth column (C-401) or the second column (C-701) based on the composition of mixture of glucose and cellobiose received from the sixth column (C-401).
8. The bioreactor as claimed in claim 1, wherein a seventh downstream separation
unit (DSP 601) is provided between the seventh column (C-601) and the second
column (C-701), the seventh downstream separation unit (DSP 601) configured to
allow flow from the seventh column (C-701) towards the seventh column (C-701)
or the second column (C-701) based on the composition of mixture of glucose and
fructose received from the seventh column (C-601).
9. The bioreactor as claimed in claim 1, wherein an eighth downstream separation
unit (DSP 901) is provided between the eighth column (C901) and the product
collection tank (T-1003), the eighth downstream separation unit (DSP 901)

configured to allow flow from the eighth column (C-901) towards the eighth column (C-901) or the product collection tank (T-1003) based on the composition of mixture of sucrose and isomaltulose received from the eighth column (C-901).
10. The bioreactor as claimed in claim 1, wherein a ninth downstream separation unit (DSP 902) is provided between the ninth column (C-902) and the product collection tank (T-1003), the ninth downstream separation unit (DSP 902) configured to allow flow from the ninth column (C-902) towards the ninth column (C-902) or the product collection tank (T-1003) based on the composition of mixture of sucrose and trehaluose received from the ninth column (C-902).
11. The bioreactor as claimed in claim 1, wherein each of the first column to the ninth column are operable individually or in combination and the reaction of sugar substrate in each column is optionally repeated one or more times to get desired low-calorie sugar composition.
12. A process for preparing a low-calorie sugar composition comprising:

a) feeding a sugar source to the bioreactor as claimed in claim 1;
b) processing the sugar source to get a sugar substrate;
c) reacting the sugar substrate with a suitable enzyme immobilized on a suitable matrix in a column under pre-determined reaction conditions to obtain a corresponding sugar product; and
d) feeding the sugar product obtained from one column to another pre-determined column and withdrawing the desired low-calorie sugar composition from final product collection tank;
wherein the reaction of sugar substrate in each column is optionally repeated one or more times to get desired ratio of low-calorie sugar composition.
13. The process as claimed in claim 12, wherein the enzyme is selected from a group
comprising xylose isomerase, D-tagatose-3-epimerase, rhamnose isomerase,

isomaltulose synthase, sucrose isomerase, glucose isomerase, invertase and β-glucosidase.
14. The process as claimed in claim 12, wherein the low-calorie sugar composition comprises: rare sugar, natural sugar and optionally at least one prebiotic component.
15. The process as claimed in claim 14, wherein,
rare sugar is selected from a group comprising isomaltulose, trehalulose
and D-psicose;
natural sugar is selected from a group comprising glucose, fructose,
sucrose and xylose; and
prebiotic component is monomeric or dimeric.
16. The process as claimed in claim 15, wherein the monomeric prebiotic component is xylulose.
17. The process as claimed in claim 15, wherein the dimeric prebiotic component is cellobiose.