Arcliaeomerry 27 , 2 (1985), 231-236. Printed in Great Britain

G A S LIQUID CHROMATOGRAPHIC A N A L Y S I S O F F A T T Y ACIDS IN FOOD RESIDUES FROM CERAMICS F O U N D IN T H E

SOUTHWESTERN CAPE, SOUTH AFRICA

M . PATRICK

Dept. of Archaeology, University of Cape Town, South Africa

A . J . d e KONING

Fishing Industry Research Institute, University of Cape Town, South Africa

and A . B . SMITH

Dept. of Archaeology, University of Cape Town, South Africa

I N T R O D U C T I O N

Until comparatively recently the reconstruction of diets in prehistory has been confined to the analysis of faunal and floral remains. Other than pollen analyses, most of the results obtained from various dietary investigations have been derived from a dry analysis of materials. More recently successful identification of animal tissue has been achieved by investigating fatty material buried in soil using gas chromatography techniques (Morgan el al. 1973, 1984).

As part of a long-term project, where an attempt is being made to understand the food procurement strategies of foragers and herders in the Southwestern Cape, researchers in the Department of Archaeology, University of Cape Town have adopted a multidisciplinary approach, and consequently the application of multiple methodologies to the materials recovered from prehistoric sites.

Coastal shell-middens have traditionally been seen as hunter-gatherer sites with mollusc remains representing the food staple in the economy of stone-age people. Recent excavation of later middens suggests that they are indicators of a mixed economy in which food production, in this case cattle and sheep herding, provided the basis of the diet, with shell-fish as a supplement. In virtually all of these sites less than 2000 year old ceramics, which appear with domestic stock in this area, are part of the cultural material.

A R C H A E O L O G I C A L SAMPLE A N D P R O V E N I E N C E

Excavation of an open-air coastal site on the Vredenburg Peninsula at Kasteelberg (17'57'E, 32'49's) in the Southwestern Cape produced quantities of sheep bones, along with other terrestria1 animals: eland, hartebeest, tortoise. The largest faunal component, however, came from marine resources: shellfish, crayfish, seals, cetaceans, marine birds, etc. (Smith 1984). These remains suggest that this was an early pastoralist campsite where the inhabitants made use of coastal resources.

Among the cultural remains associated with the bones and shell were fragments of pottery. Brown flaky consolidated residues were recognised adhering to the inside of 13.7% of the potsherds, A sample of this residue from square A2: 15-20 cn? was analysed.

23 1

232 M. Patrick, A . J. de Kotiing and A. B. Smith

I D E N T I F I C A T I O N 01: O R G A N I C C O M P O U N D S

The residue was collected by simply scraping the sherd with a sharp blade. Samples were stored in sealed glass bottles at room temperature until use.

Since the composition of the residue on the ceramic sherds was an unknown substance elemental analysis was performed routinely on all samples t o determine the organic/inorganic nature of the material. The Heraeus Universal Composition Analyser was used t o determine the values o f carbon (19.50%), hydrogen (2.35%) and nitrogen (1.3070). The nitrogen value was converted by multiplication with a factor of 6.25 to give a protein value of 8.1%. This indicated that the sample was most likely to be of animal or vegetable origin. The Fishing Industry Research Institute was asked t o determine the fatty acid composition by means of gas-liquid chromatography,

[ 'AT E X T R A C T I O N A N D F A T T Y A C I D A N A L Y S I S

The fat extraction method is an adaptation of the Bligh and Dyer (1959) procedure. The sample (100-500mg) was transferred t o a 200ml centrifuge bottle and 20ml of chloroform, 40 ml of methanol plus 1 6 m l of water pipetted into i t . The mixture was then homogenised by inserting the shaft of a high-speed Silverson heavy duty laboratory emulsifier (Model L2R) into i t for three minutes. Another 2 0 m l of chloroform was pipetted in and the mixture was homogenised for a further one minute. An additional 20 in1 of water was added and the mixture was finally homogenised for another minute. The centrifuge bottle was removed, the shaft washed with a small amount of methanol and centrifuged at 3000 rpm for 10 minutes. The clear chloroform layer was carefully pipetted out and the chloroform evaporated on a rotary evaporator.

The fat obtained by extraction and evaporation was refluxed with 5 ml of 0.5 M solution of sodium hydroxide in methanol for about 10 minutes. After saponification 5 ml of a 15% solution of boron triiluoride in methanol was added and the mixture refluxed for two minutes. Hexane ( j m l ) was added through the top of the condenser and the mixture refluxed for another minute. The flask was removed and a sufficient amount of a saturated solution of sodium chloride was added to the flask t o make the hexane solution of the methyl esters rise into the neck of the flask. The methyl esters in the hexane were removed with a Pasteur pipette, dried over anhydrous sodium sulphatz and filtered.

The methyl esters in hexane were injected into a 5710 Hewlett Packard Gas Chromatograph. They were separated on a 44 m glass capillary column with an ID of 0.3 m m having an OV-73 coating and using hydrogen as carrier gas. The temperature was programmed from 140°C- 230°C rising 4°C per minute, while the injection port remained at 250°C. Methyl esters were identified by using suitable authentic fatty acid methyl esters obtained from Sigma Chemical Company and quantification was carried out by a Hewlett Packard 3353 Lab Data System.

R E S U L T S

The overall fatty acid composition of the sample seemed t o indicate that it was of animal rather than plant origin (see table 1). No polyunsaturated fatty acids were detectable, but this is understandable since they would have decomposed under the conditions of shell-midden storage in the archaeological site. Although the fatty acid composition of the archaeological material is presumably different from the starting substance, it might nevertheless be possible

Gas liquid chromatographic analysis of fatty acids in food residues 233

to postulate what this was, as the ratios of certain fatty acids in the archaeological material might not have altered through time. The values obtained from the archaeological sample from Kasteelberg were compared with Hilditch and Williams’ (1 964) tabled fatty acid compositions of natural fats in various plants and animals, including the component acids of the Atlantic Grey Seal (Halichoems gryphus).

The ratio of C16:O (palmitic acid) to C18:O (stearic acid) was used to interpret the archaeological values against the Hilditch and Williams data. Using this ratio it appeared that the value of 2.28 obtained from archaeological sample KBB A2: 15-20 cm compared favourably with the values for the Grey Atlantic Seal whose given values were 3.81 to 1.06. The presence of the fatty acid C24: 1 (nervonic acid) was also indicative of a marine component.

E X P E R I M E N T A L M E T H O D

In order to test our working hypothesis that the archaeological sample may have come from seals, two samples of modern seal tissue from a 1.09 m Cape Fur Seal (Arctocephalus pusillus pusillus), a species represented in the faunal remains from Kasteelberg, were analysed (table 1 : sample 1 and sample 2) (see figure 1: 1st run). These gave C16:O to C18:O ratios of 4.91 and 4.97 respectively. It then became apparent that the ratios of two extremely closely related acids, C18:l w9 (oleic acid) and C18:l w7 (vaccenic acid), were now available. Comparison of this ratio for the two modern seals (5.71 and 6.67) with the KBB sample (5.04) allows us to speculate that the archaeological sample might be from a marine animal, such as seal.

We then tried a control test where we attempted to simulate the residue on the prehistoric potsherds by baking a sample of frozen seal tissue (41 g tissue and 4 g brain tissue) in a modern ceramic pot. To this was added l00ml of tap water. The mixture was heated over a blue flame until boiling - about 20 minutes. Thereafter the mixture was heated over a low flame for one hour, at which time the liquid mixture began to turn to a thick yellow crusty mass. This deposit, still in the ceramic pot, was heated in an oven at 55°C for 72 days. At this time the sample was removed and analysed for fatty acid composition. The ratio for C18:l w9 to C18: 1 w7 obtained was 6.43 (see figure 1 : 2nd run). The sample was then reheated at a temperature of 120°C for 17 days and the analysis for fatty acid composition gave a ratio of 6.11 (see figure 1: 3rd run).

C O N C L U S I O N S

Comparison of the fatty acid composition of the residue in the ceramic pots with that of anchovy and seal seems to indicate that it is of marine origin. At present it is not possible to identify with absolute certainty the marine organism from which the Kasteelberg sample came, but the possibility that it came from a seal is suggested by the ratio of oleic acid to vaccenic acid (5.04 for the deposit, 2.0 for anchovy and 5.71 for modern seal). The ratio does not appear to alter with age, as indicated in the experimental section. Furthermore, the evidence is supported by the number of seal bones (a minimum of 33 individuals) in the excavation, and historical observation from the area around the site in 1653 which noted: ‘Saldanhars (Khoi pastoralists) at a certain point jutting into the sea, where they were killing many seals (of which there were thousands) for food, etc.’ (Thom 1952, Vol. 1 p. 176). The conclusion reached is that meat from a marine animal, possibly seal, was being prepared in the pots, probably by boiling.

134 M. Patrick, A. J. de Koning and A . B. Smith

d l : I z 3

V: L L 3(CM)

F : L L 3 I : L Z 3 (IIM)

5 : It3 5 : 023 ( C M )

t : OL 3 ( E M )

I : O L 3 (VM) 1:023 1 : 0 1 3

2 : 9 1 3 I : ~ I ~ ( L M )

1:813(6M)

o:u13

t:v15 I ' V I 3

o:v13 0 : 5 1 3 0:t13

2 : g " S -

i e w 10 %

2 'f

E P

% U

3

Tab

le

1

Fat

ty

acid

dist

ribu

tion

in

the

fats

of

vari

ous

arch

aeol

ogic

al

and

cont

rol

sam

ples

(Con

tent

of

each

acid

as

a %

of

the

tota

l

fatt

y

acid

s

anal

ysed

j

C14

:O

C15

:O

C16

:O

C16

:l

C16

:3

C16

:4

C18

:O

C18

:lw

9

rati

o

C18

:

lw7

C18

:2

C18

:4

C20

:l

C20

:4w

6 C

20:4

w3

C20

:5w

3 C

21:S

c2

2:

lw

11

C22

:5

C22

:6w

3 C

24:l

U

nide

ntifi

ed

acid

s

2 .o 0.

8 20

.3

0.8

-

-

8.9

13'6

]

5.04

2.7

-

-

6.0

-

-

-

-

6.7

-

-

5.8

32.4

8

- 5.6

6.4

- 0.3

0.3

19

6.4

15.7

17.9

11

- 8.5

7.5

-

-

-

- 1

2 3 5 .O 3.2

3.6

20.3

24.0

6}

2.0

25.7

]

5.71

3

- 4.5

3.6

1 66.6

1.3

1.3

2

- 1 .o

1.1

1

- 7.5

8.6

1

- 0.5

0.3

1

- 0.7

0.7

22

- 3.6

3.1

1

- 0.4

0.3

1

- 1.9

3.1

2

- 3 .I 3.2

13

-

11.1

10.8

1

- 0.3

0.4

-

-

-

Mod

ern

seal

s

Q

3

E:

0

3

E

Fat

t-v

KB

B

Sunf

low

er

Sam

ple

2

Age

d

sam

ple

I

Age

d

sam

ple

2 Q

+

17da

ys@

120a

C

3

% 0'

:

26.2

2.

acid

A2:

15-2

0

Anc

hovy

oil

Sam

ple

I (I

4 M

ay

1

72

days

@

55

C

%

%

%

%

%

%

(19

Sep)

(9

Oct

)

%

a 7.9

0.6 a

6.6

3

0s

Q

3

a -

-

6.5 x

ro

%

4.4 .1" 6.

43

26'9

1 6.

11 2

1

1.7

4.5

3.8

7.7

0.5

23.4

7.

2 -

0.1

5.5

27.0

6.67

4.2

0.6

0.2

10.8

0.

2 0.

2 4.

3 0.

3 0.

6 0.

6 -

6.6

0.5

0.3

-

0.8

3.6

N

w

ul

236 M. Patrick, A . J. de Koning and A . B. Smith

Residue has also been recognised on potsherds excavated from inland sites of the South- western Cape, An analysis of some of this material from De Hangen (18'52'E, 32'5's) (Parkington and Poggenpoel 1971) could only be identified as possibly coming from several terrestrial animals, using the comparative tables in Hilditch and Williams. Again, it would appear that these particular pots were used for cooking meat. Clearly, comparative samples of South African species need t o be run, and a species index compiled before more accurate identifications can be made.

The sample is very small, but here is a potential methodology for expanded work in the future to define even more clearly the diet of early pastoralists and foragers a t the Cape. The uses identified from this analysis d o not preclude the use of the pots for other purposes, e.g. storage of milk, water, or other commodities. Traditional Khoi pastoralists demonstrated their affluence in conspicuous consumption of fat by rubbing it on their bodies (see Schapera and Farrington 1933 pp. 51, 129 . etc.). Among the San fat has mystical power or n/um (Lewis- Williams 1981 p. 51). I t is possible that the cooking of these animals was not just for food, but to render the fat ,

ACK N 0 W L E D G EM E N T S

We are grateful to J . Parkington for permission to use the potsherds from De Hangen and to R. Yates for alerting us to their existence. Thanks also go to Prof. J . P. H . Wessels of the Fishing Industry Research Institute for permitting the analysis to be done. bfrs A . Evans of FIR1 did the gas liquid chromatography analysis and Mr W. R. T . Hemstead of the Microanalytical Section of the Organic Chemistry Dept., University of Cape Town, did the elemental analysis. P. Best of the Sea Fisheries Research Institute kindly supplied the modern seal samples. The Oppenheimer Institute for African Studies funded the analysis, while the excavation at Kasteelbeg was supported by the Human Sciences Research Council.

REF13 R E NCE S

Bligh, t. G . and Dyer, W. J . , 1959. A rapid method of total lipid extraction and purification, Gznad. J. Bioclietn. Phj.siril. 37, 911-917.

Hilditch, T. P. and Williams, P. N., 1964, The vhetnical constittition of natirral fats, 4th ed., London: Chapman and Hall.

Lewis-Williams, J . D., 1981, Believing and seeing, New York: Academic Press. Morgan. E. D., Cornford, C., Pollock, D. R. J . and Isaacson. P., 1973, The transformation of fa t ty material

Morgan. 1:. D., Titus, L.. Small, R. J . and Edwards. C., 1984, Gas chromatographic analysis of fatty material

Parkington, J . E. and Poggenpoel, C., 1971, Excavations at De Hangen, 1968, S. African Archaeol. Bull. 26 ,

Schapera. I . and Farrington. E. , 1933, n i e early Cape Hottentots , Cape Town: Van Riebeeck SOC. No. 14. Smith. 4. B.. 1984. Seasonal exploitation of resources o n the Vredenburg Peninsula after 2000 B.P., Paper

Thorn. H . B., 1952, Thc joitrtialofJart van Rieheeck, 3 vols., Cape Town: BaIkema.

buried in soil, Science and Archaeology 10,9-10 .

from a Thule Midden,Archaeometrjz 26 ( l ) , 43- 48.

3-36.

presorted at Spacial Archaeological Research Ut i i t Workshop, Uniwrsitv of Cape Town.