1

CHANGES OF GLUCOSE CONCENTRATION IN MEDIUM

INOCULATED WITH RAGI TAPAI

Heng Joe Shen and Leo Chin Yin

Department of Chemical Engineering

University of Malaya

50603 Kuala Lumpur

Email: hengjoeshen@gmail.com

Abstract

The main objective to carry out this experiment is to investigate the changes of glucose concentration in

fermentation process. The yeast strain used in this experiment is commercialized ragi tapai UV

spectrophotometer is used to test for the glucose concentration presence. In order to prove the consistency of the

experiment, 2 different packets of ragi tapai are used. The findings suggested that ragi tapai is capable of

hydrolyzing the tapioca flour into simple sugar and eventually convert them to another product.

Keywords: glucose concentration, ragi tapai, UV spectrophotometer and tapioca flour.

1.0 INTRODUCTION

Tapai is a traditional fermented food found in Asia. The main ingredients in the preparation of Tapai are by

fermenting flour with Ragi powder. Ragi is actually a type of plant known as finger millet and mainly found in

Africa and Asia. Scientifically, it is known as Eleusine coracana. It however, contains a lot of microorganism

includes yeast. Generally, yeast cannot hydrolyze complex starch into simple sugar due to diastatic activity.

Ragi Tapai yeast however; possess active amylase systems that are capable of hydrolyzing starch into simple

sugar and eventually into alcohol through anaerobic process.

2

Starch

Gelatinization

Amorphous gel

Liquefaction

Glucose solution

Saccharification

Glucose

Figure 1: Starch structure Figure 2: Hydrolyzation process

2.0 METHODOLOGY

2.1 Apparatus and Materials

Test tubes, test tube rack, pipette, beaker, inoculated shaker and UV spectrophotometer.

Deionized water, tapioca flour, Ragi Tapai yeast, KimWipe paper, tissue paper and standard solution.

3.0 RESULTS

Table 1: Absorbance of standard solution (Set 1)

Glucose concentration

(mg/ml)

Absorbance

1 2 Average Actual (Average – Blank)

Blank 0.010 - 0.010 0.00

0.50 0.114 - 0.114 0.104

1.00 0.242 0.239 0.241 0.231

2.00 0.414 0.416 0.415 0.405

3.00 0.602 0.608 0.605 0.595

4.00 0.812 0.817 0.815 0.805

5.00 - - ERROR -

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Table 2: Absorbance of standard solution (Set 2)

Glucose concentration

(mg/ml)

Absorbance

1 2 Average Actual (Average – Blank)

0.000 0.010 - 0.010 0.00

0.500 0.065 0.063 0.064 0.054

1.000 0.176 0.172 0.174 0.164

2.000 0.440 0.443 0.442 0.432

3.000 0.618 0.618 0.618 0.608

4.000 0.758 0.757 0.758 0.748

5.000 0.929 0.933 0.931 0.921

Graph 1: Graph of Absorbance against glucose concentration

y = 0.1981x + 0.0099 R² = 0.9985

y = 0.1908x - 0.0046 R² = 0.9904

0.000

0.100

0.200

0.300

0.400

0.500

0.600

0.700

0.800

0.900

1.000

0.000 0.500 1.000 1.500 2.000 2.500 3.000 3.500 4.000 4.500 5.000

Sta

nd

ard

ab

sorb

an

ce

Glucose concentration (mg/ml)

Set 1 Set 2

4

Table 2: Changes in glucose concentration

Samples

(hours after

fermentation)

Sample A Sample C

Observed

absorbance

Absorbance

(-blank)

Glucose

concentration

(mg/ml)

Observed

absorbance

Absorbance

(-blank)

Glucose

concentration

(mg/ml)

0 0.478 0.468 2.312 0.615 0.605 3.003

1 0.862 0.852 4.250 0.854 0.844 4.209

2 1.119 1.109 5.547 1.039 1.029 5.143

16 0.890 0.880 4.391 0.686 0.676 3.362

18 0.785 0.775 3.859 0.531 0.521 2.579

20 0.819 0.809 4.033 0.376 0.366 1.797

22 0.764 0.754 3.755 0.245 0.235 1.136

24 0.681 0.671 3.336 0.149 0.139 0.651

40 0.398 0.388 1.908 0.074 0.064 0.273

42 0.340 0.330 1.615 0.071 0.061 0.258

44 0.273 0.263 1.277 0.068 0.058 0.243

46 0.234 0.224 1.080 0.064 0.054 0.223

48 0.179 0.169 0.803 0.066 0.056 0.233

Samples

(hours after

fermentation)

Sample B Sample D

Observed

absorbance

Absorbance

(-blank)

Glucose

concentration

(mg/ml)

Observed

absorbance

Absorbance

(-blank)

Glucose

concentration

(mg/ml)

0 0.699 0.689 3.427 0.455 0.445 2.196

1 0.880 0.870 4.341 0.507 0.497 2.458

2 1.096 1.086 5.431 0.526 0.516 2.554

16 0.889 0.879 4.386 0.024 0.014 0.021

18 0.862 0.852 4.250 0.023 0.013 0.016

20 0.873 0.863 4.305 0.028 0.018 0.041

22 0.743 0.733 3.649 0.021 0.011 0.006

24 0.718 0.708 3.523 0.020 0.010 0.000

40 0.438 0.428 2.110 0.021 0.011 0.006

42 0.406 0.396 1.948 0.033 0.023 0.066

44 0.364 0.354 1.737 0.033 0.023 0.066

46 0.305 0.295 1.439 0.036 0.026 0.081

48 ERROR - - 0.037 0.027 0.086

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Graph 2: Graph of Absorbance against glucose concentration

4.0 DISCUSSION

From graph 1, the absorbance of ultraviolet using UV spectrophotometer increase almost linearly with glucose

concentration in the medium. The gradient of the graph is found to be 0.19815 with y-intercept equals to

0.00991. Thus, we can then convert the absorbance rate obtained in sample set A and set C by using the

equation

From graph 2, although the initial glucose concentration of set C (0.615mg/ml) is higher than set A

(0.478mg/ml), glucose concentration in set C are generally lower than that of set A. The possibility of this trend

is that the amount of yeast presence in set C is higher than that of set A. Thus, lower amount of glucose

concentration presence because it has been fermented by the yeast into another product.

0.000

1.000

2.000

3.000

4.000

5.000

6.000

7.000

8.000

0 5 10 15 20 25 30 35 40 45

Glu

cose

con

cen

trati

on

(m

g/m

l)

Time after fermentation (hours)

Sample A

Sample B

Sample C

Sample D

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3.1 Errors involved in the experiment

In the experiment, there may be several errors that cause experimental results to deviate from theoretical values.

Inaccurate dilution of the sample with deionized water.

The time lag between obtaining the sample to centrifuge and eventually freeze in the -20ºC freezer. The

glucose concentration may have increase or decrease during the time lag.

The glucose concentration between 2 with 16 hours and 24 with 40 hours are purely predicted by using Excel

software. There may be deviations during the period.

5.0 CONCLUSIONS

1. Both starches are hydrolyzed in a similar trend.

2. Different amount of ragi tapai yeast presence in set A and set C.

3. There is a significant difference in heat flux between starch solution heated using hotplate and microwave

respectively.

6.0 REFERENCES

1. Azmi, A., Hasan, M., Mel, M. Ngoh, C. Single-step bioconversion of starch to bioethanol by the coculture of

ragi tapai and Saccharomyces cerevisiae. Deparment of Chemical Engineering, University of Malaya, Kuala

Lumpur & Biotechnology engineering, Kulliyah of Engineering, International Islamic University Malaysia,

Kuala Lumpur.

2. Saelim, K., Dissara, Y. & Kittikun, A.H. Saccharification of cassava starch by Saccharomycopsis fibuligera

YCY1 isolated from Loog-Pang (rice cake starter). Department of Industrial Biotechnology, Faculty of Agro-

Industry & Department of Microbiology, Faculty of Science, Prince of Songkla University, Hat Yai,

Songkhla, 90112 Thailand.

3. Ko, S.D. Tape Fermentation. Agricultural University, Department of Food Science, Wageningen.

Netherlands.

4. Borglum, G.B. Starch Hydrolysis for Ethanol Production. Miles Laboratories, Inc. Industrial Products

Group, Elkhart, Indiana.

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