EVALUATION OF QUALITY OF FRESH SOYA-BEAN OIL AVAILABLE IN BANGLADESH

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Methods
Titrimetric method is used for the determination of peroxide, iodine, and acid value of the samples. 

For the determination of peroxide value following steps are followed:

1. 5 gm. of sample was taken in a 250 ml glass stoppered conical flask then 30 ml of a mixture of 30 volumes of glacial acetic acid and 20 volumes of chloroform was added and shaken until the sample was dissolved.

2. Then 0.5 ml of saturated potassium iodide solution was added and shaken for exactly 1 minute and then we added 30 ml of water.

3. Then titration was done slowly, and shaken continuously with 0.01M sodium thiosulphate VS until the yellow color almost disappeared.

4. Also 5 ml of 1% starch solution was added and continued the titration, shaking vigorously, until the blue color just disappeared.

5. The operation was repeated without the substance being examined and this served blank.  The titration in blank determination should not exceed 0.1 ml of the sodium thiosulphate solution.

For the determination of acid value following steps is followed:

  1. 10 gm. Of the sample being examined was taken and dissolved it in 50 ml of a mixture of  volumes of ethanol (96%) and ether that has been neutralized with 0.1M potassium hydroxide  VS  Using 0.5 ml of dilute phenolphthalein solution as indicator.
  2. Then the standardization of KOH solution (0.1M) was done with 0.1M of potassium hydrogen phthalate.
  3. Titration was done with 0.1M potassium hydroxide VS shaking constantly, until a pink color that persisted at least for 15 to 30 seconds.

For the determination of iodine value following steps is followed:
1. 0.1 gm of sample was delivered to a 300 ml conical flask with ground in stopper.  Then 20 ml carbon tetrachloride was added and sealed and dissolved in an ultrasonic washing machine.
2. Further 25 ml Hanus solution was added and sealed.   Shake for a minute.
3. Then it was sealed and leaved it in a dark room (about 20oC) for 30 minutes.
4. 10 ml of 15% potassium iodide and 100 ml water were added and sealed.  And shake for 30 seconds.
5. Titration of it with 0.1ml/L sodium thiosulphate was done to obtain iodine value.
6. Likewise blank test was performed to obtain blank level.

RESULTS
From the table-2, In the month of October, physical observation namely color, clarity, odor, sedimentation and chemical analysis namely peroxide, iodine, acid value of different sample was complies with the specification. But in S-6, iodine value was higher (165.30) than the normal range. In the second months study physical observation of the different samples slightly change from the previous months but it may be considered as complies with the BSTI specification. In the month of November, physical characteristics of all samples was complies with the standard and chemical analysis of peroxide, acid, iodine value of S-1, S-2, S-3, & S-4 was complies according to specification but only iodine value of S-5 (145.65) and S-6 (168.78) was out of specification. In the month of December, only iodine value of S-4 (144.04), S-5 (147.06) and S-6 (170.66) was out of specification.

Table – 2:  Peroxide value, Acid value, Iodine value of different samples.


Peroxide value

Acid value

Iodine value

Sample no.

Oct.

Nov.

Dec.

Oct.

Nov.

Dec.

Oct.

Nov.

Dec.

S-1

0.002

0.004

0.007

0.00729

0.0084

0.0095

121.23

124.35

126.8

S-2

0.039

0.043

0.047

0.00822

0.00895

0.00981

125.96

127.85

129.51

S-3

0.036

0.04

0.045

0.00804

0.00901

0.00985

125.34

126.65

128.63

S-4

0.042

0.046

0.05

0.00862

0.00897

0.01021

139.53

142.6

144.04

S-5

0.096

0.105

0.112

0.00127

0.00139

0.00147

141.78

145.65

147.06

S-6

0.095

0.106

0.109

0.08500

0.0961

0.0978

165.30

168.78

170.66

DISCUSSION
Peroxide value indicates the presence of miff of oxygen per kg of anhydrous oil.  Higher peroxide value also indicates the rancidity of oil and the presence of higher amount of free radicals at the same time.  Actually peroxide value increases due to the auto-oxidation.  Free radical reactions are chain reaction and are ubiquitous in living beings.  As radicals are highly reactive they are capable of randomly damaging all components of the body.  These are involved in the development of chronic disease like cancer, atherosclerosis, and emphysema. According to BP specification the normal limit of peroxide is 5.0. In S-5, October, November, and December result was 0.0096, 0.105, and 0.112 respectively. In the month of November and December the result was high value compared to the month of October due to environment exposure, various contaminations occur in storage. In S-6 has also higher value compared to previous samples but contain it within the limit.

Acid value is the measurement of the presence of free fatty acids in the sample which are normally formed due to hydrolysis of the lipid.  The acid value of oil is used as a measure of quality.  The acid value of the oil must not be  too high, as this denotes an excessively high  content  of free fatty acids [FFA], FFA can be determined from the acid value.  High FFA, affect the yield of the biodiesel.  This is in accordance with literature.  The acid value of the vegetable oil should be less than one for a base [KOH] catalyzed Trans-esterification process.  The causes of high acid value may be due to improper processing or distillation, presence of micro-organisms, improper storage, exposed to light etc.  Temperature has a very important effect on the increases in acid value. It appeared from the table-3, that all the six collected samples had the acid value within the BSTI specification [Max. 0.6].Fats and Oils with higher acid value can result in gastric acidity, gastric discomfort, maldigestion and these also lose the consumer’s acceptability due to odd color and odor. The acid value of all the samples was within the specifications in different months.

The iodine value [IV] is a measurement of the unsaturation of fats and oils.  High iodine value indicates high unsaturation of fats and oils [Knothe, 2002, Kyriakidis and Katsiloulis, 2000].  Among the six fresh soybean oil [Table-11] only five were found to comply with the BSTI specification [120-143] and the rest had the higher value.  So, the degree of the sample was high and could be considered as substandard to respect of iodine value. Sample number 5 was the higher value in November (145.65) and December (147.06) and sample number 6 (S-6) has more value (October-165.30), (November-168.78), (December-170.66) than the other samples. So, we consider it as a substandard sample.

CONCLUSION
The manufacturing technology of Soyabean Oil is sample and so many brands are available in the market.  But some immoral manufactures and salesman intentionally mix up various adulterants which are found to be quite by cheap.  The consumers which have to take this spurious product are the most loser and these may be life threatening because adulterants may also be toxic product.

The Government of the Peoples’ Republic of Bangladesh on 25th July, 1985 had published.  The Bangladesh Standard and Testing Institute Ordinance 1985 to provide for the establishment of an institution, for standardization, quality control, grading and marking of consumer goods.  In the Bangladesh Standard and Testing Institute Ordinance, 1985, it is mentioned that whoever use improper standard mark manufactures and sale any substandard consumer product shall be punished with imprisonment for a term which may extend six month or with fine which may extend to 15,000.00 taka or with both as well as whoever contravenes any of the provision of this ordinance shall be punishable with fine which may extend to five thousand taka.  Unfortunately the people of Bangladesh do not see the application of this law while substandard brand are there in the market.

Unintentionally, the soyabean oils may be substandard due to improper processing, storage, and lack of maintaining good quality control practice.  From the analytical results, it is seen that the analytical result of few brand are very near to the standard value if they do maintain quality control properly they would definitely confirm Bangladesh Standard and Testing Institution (BSTI) Standard. 

Thus, to ensure quality of fresh soyabean oil, many BSTI branch should be set up in different region of Bangladesh and analysis should be continued.  Introducing sample method to detect adulterant may play an important role.

REFERENCES
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18.    British Pharmacopea, 1988, vol. -2, London Her Majesty’s stationery office. P.:128-130.
19.    Wiley & Son J. Bailey’s Industrial Oil Fats Products, vol.:1, 4th edition, 1979.
20.    Williams K.A. – Oils Fats and Fatty Foods, 3rd edition, p.:302-304.
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