Previous PageNext Page

Comparison of pressed and extracted rapeseed oils characteristics

Krzysztof Krygier1, Teresa Płatek2

1 Agricultural University, 03-849 Warsaw, Grochowska 272, Poland, tzy ktznoiks@sggw.waw.pl
2
Meat and Fat Research Institute, 04-190 Warsaw, Jubilerska 4, Poland, dt@ipmt.waw.pl

Abstract

Characteristics of pressed, extracted, water degummed and crude oils obtained in industrial conditions in 14 production cycles are presented. In each fresh oil sample contents of: free fatty acids (FFA), phospholipids (as phosphorus), tocopherols, sterols, colours, iron, copper, as well as induction time, peroxide value, anisidine value and UV absorbance were determined. Data are reported as the mean, SD and coefficient of variation. One Way Anova and Correlation procedures were used for statistical analysis. Obtained results indicated that:

- method of oil obtaining affected significantly contents of phosphorus, sterols and oxidative stability,

- degumming process caused very vivid decrease in phospholipids content, that influenced oxidative stability decrease by ca 35%,

- the following order characterized oxidative stability of examined oils:

extracted > pressed ≥ crude ≥ water degummed.

KEYWORDS: rapeseed oil, raw material for refinery

Introduction

Rape is the only industrial oil plant in Poland. Nowadays doubly-improved varietes of rape, i.e. so-called double-zero make up almost 100% of national area of cultivation of this plant. Industrial processing of rapeseed for edible purposes includes oil obtaining from seeds by pressing, followed by solvent extraction of the remainder and then its refining to bottle and/or for further processing. The aim of this work was to characterize raw oils for refining processes, i. e. pressed, extracted, water degummed and crude oils with respect to content of minor substances, oxidative stability and degree of oxidation.

Experimental

Materials and methods

The materials for this study were oils obtained from doubly improved winter rape seeds in two Polish oil mills fitted with typical equipment for oil extracting. The investigation concerned 14 production cycles of pressing, extraction and water degumming. Parameters of each type of oils obtaining were as follows:

Pressing of oil from seeds: flaking of preheated seeds, cooking at temperature 90C, pressing in expeller at pressure of 12 MPa, filtration in Niagara filter.

Extraction of oil from presscake: by using of hexan in horizontal Lurgi′s extractor at temperature 55C, filtration of miscella in Knecht′s filter, desolventizing of oil in 3-step apparatus in the following conditions:

I - 7580C, atmospheric pressure,

II - 9095C, 800 hPa,

III - 110115C, 400 hPa.

Miscella outgoing from I apparatus contains 50%, from II - 90% and from III - 99,8% of oil.

Water degumming of extracted oil: addition of water - about 2% (m/m), temperature - 60C, agglomeration time - 2 h, gum separation in disc type centrifuge, drying of oil at 90C.

Crude oil is a mixture of pressed and water degummed oils in natural proportion 3:1.

Oil samples were taken for examination directly after each process from the following points of production line:

- pressed oils - after filtration in Niagara filter,

- extracted oils - after distilling apparatus,

- water degummed oils - after drier,

- crude oils - from crude oil tank.

In each oil sample the following parameters were determined:

- FFA content - according to ISO 660:1983,

- phospholipids as phosphorus content - according to Polish Standard PN-88/A-86930,

- tocopherol content - HPLC method according to ISO/DIS 9936,

- sterol content - GLC method according to ISO 6799:1991,

- total colour - spectrofotometric method according to Polish Standard BN-86/8050-30,

- iron and copper contents - atomic absorption method according to ISO 8294:1994,

- fatty acid composition - GLC method according to ISO 5508:1990,

- peroxide value - according to ISO 3960:1977,

- anisidine value - according to ISO 6885:1988,

- conjugated dienes and trienes - measuring of UV absorbance according to ISO 3656:1989.

- oxidative stability - Rancimat method, at temperature 120C, air flow 20l/h, sample mass

2,5 g.

Computer program Statgraphics 6.1 was used for statistical analysis. Procedures of One Way Anova - LSD test (α=0,05) and Correlation Analysis were applied.

Results

Comparison of pressed and extracted oils.

Characteristics of pressed and extracted oils are presented in tables 1 and 2. Statistical analysis of quality parameters′ mean values comparison indicated significant differences between these oils (P<0,05) for the following indicators:

• phosphorus content,

• sterol content,

• oxidative stability.

Statistically higher contents of phospholipids and sterols in extracted oils are connected with their more effective obtaining by using extraction in comparison with pressing. Higher concentration of these components that are considered to have antioxidant effect or that aid activity of natural antioxidants, is connected with higher oxidative stability of extracted oil than pressed one. Indicators describing rate of oxidation of pressed and extracted oils did not differ significantly.

Comparison of extracted and water degummed oils.

Water degumming is the first pretreatment refining process, that is carried out in oil mill. Phospholipids shoud be removed from oils in the highest extend, despite their positive antioxidant effect. Acting as a strong emulsifiers, these compounds magnify refining losses, demand usage of more auxiliary materials, make soapstock spitting more difficult, create sediments that are hardly removed and lower efficiency of refining apparatus. Besides, staying in oils, these compounds (precisely products of their transformation) worsen oil flavour, create undesirable brown colour, lower oxidative stability. In addition they act as catalyst poisons in hydrogenation process.

Table 1. Characteristic of pressed oils

No

Oil quality parameters

x

SD

CV

1.

FFA content, %

1,484

0,281

18,9

2.

Phosphorus content, mg/kg

186,4

32,7

17,6

3.

Total colour

A1cm1:10 at λ=460 nm

A1cm1:1 at λ=666 nm

1532,6

0,9917

0,5409

72,6

0,0702

0,0375

4,7

7,1

8,3

4.

Iron content, mg/kg

3,55

1,97

55,5

5.

Copper content, mg/kg

0,364

0,121

33,4

6.

Tocopherol content, mg/kg

748,9

93,2

12,4

7.

Sterol content, mg/kg

8367,9

862,8

10,3

8.

Oxidative stability, induction time, h

8,063

0,706

8,8

9.

Peroxide value, miliequivalents of active oxygen/kg

3,188

0,491

15,4

10.

Anisidine value

2,051

0,386

18,8

11.

Totox value

8,427

0,9851

11,7

12.

UV absorbance:

A1cm1% at λ=233 nm

A1cm1% at λ=268 nm

1,7069

0,2656

0,1309

0,0256

7,7

9,6

x - mean SD - standard deviation CV - coefficient of variation

Table 2. Characteristic of extracted oils

No

Oil quality parameters

x

SD

CV

1.

FFA content, %

1,744

0,314

18,0

2.

Phosphorus content, mg/kg

482,1

74,9

15,5

3.

Total colour

A1cm1:10 at λ=460 nm

A1cm1:1 at λ=666 nm

1536,5

0,9931

0,5419

158,5

0,1170

0,0775

10,3

11,8

12,9

4.

Iron content, mg/kg

4,68

2,15

46,1

5.

Copper content, mg/kg

0,464

0,108

23,3

6.

Tocopherol content, mg/kg

793,6

107,9

13,6

7.

Sterol content, mg/kg

9639,4

902,9

9,4

8.

Oxidative stability, induction time, h

10,516

1,981

18,8

9.

Peroxide value, miliequivalents of active oxygen/kg

3,496

0,846

24,2

10.

Anisidine value

2,450

0,431

17,6

11.

Totox value

9,441

1,542

16,3

12.

UV absorbance:

A1cm1% at λ=233 nm

A1cm1% at λ=268 nm

1,7668

0,2862

0,1316

0,0224

7,4

7,6

x - mean SD - standard deviation CV - coefficient of variation

Statistically significant differences are detected for the following indicators of extracted and water degummed oils:

• phosphorus content - lowering by 63% - 77%

• oxidative stability - shortening of induction period by 35%.

Decrease of oxidative stability after water degumming is usually connected with removing of big quantity of phospholipids, especially phosphatidylethanolamine (Prior 1991, Dimic 1994, Gordon 1994).

Crude oil is an outgoing product from oil mill department. Quality indicators of this oil result from the fact that it states a mixture of pressed and extracted oils. In all examined
batches quality indicators of crude oil, describing a contents of minor substances and impurities, are consistent with Polish standard (PN-87/A-86906). These oils are the materials for refinery.

Summary.

Table 3 states the summary of obtained data. Statistically significant differences between mean values of quality indicators of 4 types of oils are marked.

Table 3. Comparison of pressed (1), extracted (2), water degummed (3) and crude oils(4)

characteristics

No.

Oil quality parameters

Kind of oil

   

1

2

3

4

1.

FFA content, %

1,48 a

1,74 b

1,60 ab

1,56 ab

2.

Phosphorus content, mg/kg

186 a

482 b

138 c

157 ac

3.

Total colour
A1cm1:10 at λ=460 nm
A1cm1:1 at λ=666 nm

1533 a
0,992 a
0,541 a

1536 a
0,993 a
0,542 a

1430 a
0,975 a
0,485 a

1480 a
0,958 a
0,522 a

4.

Iron content, mg/kg

3,5 a

4,7 a

4,5 a

3,6 a

5.

Copper content, mg/kg

0,43 a

0,52 a

0,48 a

0,50 a

6.

Tocopherol content, mg/kg

749 a

794 a

760 a

754 a

7.

Sterol content, mg/kg

8368 a

9639 b

9336 b

8763 ab

8.

Oxidative stability, induction time, h

8,06 a

10,52 b

6,86 c

7,64 ac

9.

Peroxide value, miliequivalents of active oxygen/kg


3,19 a


3,50 a


3,67 a


3,33 a

10.

Anisidine value

2,05 a

2,45 a

2,12 a

2,22 a

11.

Totox value

8,43 a

9,44 a

9,47 a

8,89 a

12.

UV absorbance:
A1cm1% at λ=233 nm
A1cm1% at λ=268 nm


1,707 a
0,266 a


1,767 a
0,286 a


1,759 a
0,269 a


1,742 a
0,268 a

Values in rows with the same letter are not significantly different at α=0,05

Correlation analysis between quality parameters of examined oils showed among others, that induction time was correlated (P<0,05) with absorbance at a wavelenght=666 nm, (R=- 0,6298) as well as with peroxide value (R=- 0,8042) and UV absorbance (R=-7407).

CONCLUSIONS

- Method of oil obtaining (pressing, extraction) affected significantly values of the following quality indicators:

• phosphorus content (about 2,5 times more in extracted oil),

• sterol content (about 15% more in extracted oil),

• oxidative stability (about 30% higher in extracted).

- Degumming process caused very vivid decrease in phospholipids content, that probably influenced oxidative stability decrease by ca 33%.

- Oxidative stability of examined oils was as follows:

* extracted

- 100%

* pressed

- 77%

* crude

- 73%

* water degummed

- 65%.

- Oxidative stability of examined oils was negatively correlated with absorbance at
a wavelenght=666 nm, peroxide value and UV absorbance.

References

1. Dimic E., Karlovic D., Turkolov J.: 1994. Pretreatment efficiency for physical refining of sunflower oil. J. Am. Oil Chem. Soc. 71, 1357-1361

2. Gordon M. H., Mursi E., Rossell J.B.: 1994. Assessment of thin thin-film oxidation with ultraviolet irradiation for predicting the oxidative stability of edible oils. J. Am. Oil Chem. Soc. 71, 1309-1313

3. Prior E.M., Vadke V. S. , Sosulski F.W.:1991. Effect of heat reatment on canola press oils. I: Non-trigliceride components. J. Am. Oil Chem. Soc. 68, 410-406

4. Prior E.M., Vadke V. S., Sosulski F.W.:1991. Effect of heat treatment on canola press oils. II: Oxidative stability. J. Am. Oil Chem. Soc. 68, 407-411.

Previous PageTop Of PageNext Page