The classification of natural gums. III. Acacia senegal and related species (gum arabic)

Food Hydrocolloids Yol.7 no.3 pp.255-280. 1993

The classification of natural gums. III. Acacia senegal and related species (gum arabic) P.Jurasek, M.Kosikt and G.O.Phillips' Slovak Technical University, Faculty of Chemical Technology, Bratislava, Slovakia and 1 Newtech Innovation Centre, Deeside, Clwyd, UK

t Deceased Abstract. Chemometric methods have been used to characterise and evaluate commercial gum arabic in relation to authenticated Acacia senegal specimens and gums from the Combretum series. Principal component (PCA) and discriminant component analysis (DCA) were undertaken using firstly parameters mainly associated with the carbohydrate moiety: specific optical rotation, viscosity, %N, and sugar compositions, galactose, arabinose, rhamnose, equivalent weight, glucuronic acid and 4-methylglucuronic acid. Secondly, the compositions of the 18 amino acids were utilised, and subsequently the 27 features were combined. Of the 54 samples investigated, it is evident that the commercial gum arabic and authenticated Acacia senegal mainly fall into a discrete cluster. The outliers are few and can be explained. The Acacia gums can readily be distinguished from the Combretum gums. The samples are drawn from various countries: Sudan, Niger, Nigeria, Uganda, Oman, Mauritania, Mali, Senegal, Ethiopia, Kenya and Uganda. No significant difference is found in the gum from the main producing countries. Local variants from Oman and Kenya do not conform to the specification. Using PCA with amino acid compositions, the family of gums from Uganda can be distinguished. The gums are drawn from periods ranging from 1903 to the present, and no significant change has taken place in the gum over this period. Neither climate nor nature of the soil introduces any particular difference. When all 27 parameters are used, it can be demonstrated that the amino acids are dominant in establishing the distinctive character of Acacia senegal. Using loading-loading plots, the major distinctive features can be selected. As a result a characterisation is now possible using only four features: rotation, viscosity, lysine and hydroxyproline compositions. Based only on the two features (specific optical rotation and % N) proposed by the Joint Expert Committee for Food Additives (JECFA), no correlation is possible. It is proposed that such a chemometric classification could be used to set the specification for commercial gum arabic and provide the basis for a practical quality control system for producers and users.

Introduction

Our previous publications (1-4) have drawn attention to the task of setting a rigorous specification for commercial gum arabic. This natural polysaccharide gum remains an important food additive, used as an emulsifier, stabiliser, flavour encapsulator and texture controller. It is also important as an export commodity for the developing countries of the Sahelian regions of Africa where it originates: Sudan, Nigeria, Ethiopia, Senegal and Chad, with lesser amounts from Ghana and Zimbabwe. There are various .regulatory definitions of commercial gum arabic (1), and the particular current designation by the Joint Expert Committee for Food Additives (JECFA) of FAa is the 'dried exudation of Acacia senegal (L.) Willd. or related species of Acacia fam. Leguminosae' (5). There are > 1000 species and sub-species of the Acacia tree throughout the world which exude gum. It is important, therefore, that those Acacia species which are admitted under the JECFA definition should be identifiable, and that systems are available for establishing that a particular gum exudate conforms to 255

P.Jurasek, M.Kosik and G.O.Phillips

the detailed specification set by JECFA and other legislative bodies, albeit that these do not always precisely conform one with another. It is reasonable to ask what such specifications need to achieve. The toxicological evidence (6) obtained using a standard commercial gum arabic sample has enabled the status 'Average Daily Intake (ADI) not specified' to be granted to this product. Specifications should thus be sufficiently rigorous to establish that the gum arabic used in food products conforms with this test article. They should also ensure that it is possible to detect whether there is any adulteration by non-approved Acacia gums or other species of similar arabinogalactan proteins, such as Combretum and Albizia, which are difficult to distinguish chemically from gum arabic. For this group of closely related polysaccharides there is no single analytical technique which specifically provides an unequivocal identification of one particular gum compared with another. All regulatory definitions recognise that Acacia senegal is the main component of gum arabic, but equally all recognised that other 'related' gums may also be present. JECFA (7) suggested that if the word 'closely' (related species) and setting specific optical rotation (-26 to - 34°) and nitrogen (0.27-0.39%) limits were added, then these along with the basic criteria already in the specification would enable gum arabic to be unequivocally identified. However, representations particularly from producer countries persuaded Codex Alimentarius at its meeting in March 1991 at The Hague to refer the proposals back to JECFA for further assessment. The subject is, therefore, open for discussion and investigation, and further recommendations about how JECFA's commendable objectives might be achieved without the limitations which have now become evident in their 1990 recommendations. It is now becoming increasingly clear that the proposed limits do not achieve the objectives for which they were advanced (1-3,8). If rigorously applied they would result in certain authentic Acacia senegal gums, which do not conform to the specification, being declared illegal, and would certainly exclude blends of Acacia senegal with other 'closely related' species which now are used in commercial practice to enhance specific functional qualities. A practicable specification for gum arabic must overcome the well known variability of this product which arises from variations in geography, climatological or soil differences and as a result of the extensive hybridizations/ adaptions in the Acacia trees themselves. Anderson (9) has repeatedly drawn attention to this variability. Our objective is to develop a system which can encompass this variability but eliminate adulteration by unacceptable arabinogalactan protein (AGP) gums, or gums from other Acacia species which have not been approved for food use within the current definitions used. The basis of our approach is to appraise the analytical data relating to these gums using chernornetrics, Each of these parameters represents coordinates in n-dimensional space. Using principal and discriminant component projection (10-14) it is possible to define the various categories of gum. The various species can be represented graphically as groupings or 'clusters' of points relating to distinctive species or sub-species. Gums from the Vulgares series, for example, fall into a compact and well 256

Classification of natural gums III.

identified cluster. The Gummiferae series falls within a greatly extended cluster, in keeping with its wider taxonomic origin and development (1). The Combretum and Albizia gums can be distinguished individually and are distinct and separate from the Acacia gums. Initially (1) we utilised mainly nine analytical parameters relating to the carbohydrate moiety of the gums: specific optical rotation, viscosity, %N, equivalent weight, and the sugar compositions, glucuronic acid, 4-methylglucuronic acid, galactose, arabinose and rhamnose. Thereafter we extended the study to utilise the 18 amino acids (2,3,4) relating to the protein moiety of the gums. This allowed us to distinguish the Vulgares series, in which Acacia senegal is an important member, from the group of Acacia gums, mainly from Australia, belonging to the Phyllodinous Acacia species. We also extended our study to gums exuded by some Leucaena species. These all have negative specific optical rotation of about -30°, similar to Acacia senegal and have remarkably similar sugar and amino acid composition. These gums have been proposed as a replacement for gum arabic. The chemometric method also enables these gums to be distinguished as separate and distinct from those species which yield gum arabic (2). This paper now directs attention to the gum arabic product itself, comparing authenticated Acacia senegal specimens with commercial products supplied by reputable manufacturers, importers or from source suppliers from a number of producer countries. There has also been a suggestion that the product has changed its character somewhat over the years, and this aspect is also scrutinised by including gum arabic samples from the year 1904 onwards. We first use the nine mainly carbohydrate parameters, then the 18 amino acids, and finally combine these to give 27 features associated with each gum sample. Our method allows us to select those parameters which give the distinctive characteristics to particular gums, and as a result we have been able to reduce our chemometric analysis to using four of the most influential parameters only, but still enabling us to retain the characteristics identified using all 27 parameters. This result could provide a practical basis for drawing up a specification for commercial gum arabic. Materials and methods Data

Table I lists all the gum samples utilised in the present investigation. Those which might conform to the specification of gum arabic are either authenticated specimens of Acacia senegal or representative commercial samples supplied by well known sources. Here we are pleased to acknowledge the extensive analytical measurements undertaken by Dr Douglas Anderson and his research group, without which this analysis would be impossible. In order that reference can be made to the origin and characteristics of the samples we have, whenever possible, retained the designation given in the original papers. The term gum arabic is used for commercial samples and AcaSen or A.senegal for authenticated specimens, with the country of origin 257

P.Jurasek, M.Kosik and G.O.Phillip s Ta ble J. Phvsical and che mical paramet ers for a ra nge of African Acacia gums and from various Combretu'; species No'

•

1 2 3 4 5

6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22

23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44

45 46 47 48 49 SO 51 52 53 54

No'

Spec ies

b 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

25 26 27 28 29 30 31

32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65

l

Feature

....

·3 1

A..IIT .,bt3UIU

".fluhi

r

A .R ~tz ii

VuJpres

AJMIli/ertJ

·32

~

A..JfWllifera

"-...... 415 ,,-.. . .., 417 ,,-.. . ..,419 "-.. . ..x4l14 Gum Arabic

T A..... ,.~.l

IN• ..-Ia) ~

C.sokotk1U~

C..DI• ..s.. . C.Duu,wriciflorwm CA.iculat"'" CJOftx u. icatWft C.fr omii SI 52 53

T CombreU1m ~

T Commercial Gum Arabk (Sudan) ~

Commercial Gum Arabk

N7

IN.....Ia)

U4 U5 U6

T

~

r Commercial Gum Arabk (Up nda) ~

U7 AcaSenl AaSen2 AaSen3 AcaSen4 AcaSen5

T A .JIIIl~al

~

eomm..6 eomm..7 Comm"'.S Comm..9 CommaalO Commaal1 Commaa12 AcaSenNillC1 a AcaSenNi er b AcaSen Nillet c AaSen 13Sudan AcaSen9S i.en a AeaSen7U ..ndl AcaSen9Ken va C.lCi. , iavu

-31 -30 0 -32 -29 -31 . 31 -31 -29 ·28 · 30

·32

N2 N3 N4 N5 N6

U3

·25

-32

NI

N8 N9 U1 U2

·36 .45 · 57 -30 -30 ·31 · 31 · 30 ·21 ·27 ·36 -2 1 - 2

54 55 56 57 S8 59 S10 Sl1 512 5 13

(aID

r Commercial Gum Arabk ~

-27 · 30 -28 -29

·32 -32 -32 ·29 · 29 -32

·30 -32 ·26 -34 -34 -32

-30 -33 -29 -25 .40

·32 · 29 -31 -33 -32

-32 ·29

-32

t

-34 -34

AJ'IIq41

·30

~

-30 · 31

-32 ·43

Viscos ity

N

Gal.

An .

Rh.

(mV2)

(%)

1%)

(%)

1%)

8.0 13.0 21.0 2 1.0 23.5 16.0 16.0 17.0 19.9 17.0

1.08 0.58 0.89 1.30 1.45 03 4 0.34 0.33 0.33 0.30

39 39 46 44 43 44 44 46 40 45

17

12

25

14 9 9 9 14 14 13 16 14

72.0 87.0 62.0 46 .0 53.0 64.0 16.0 17.0 19.0 0.0 19.0 14.0 14.0 16.0 15.0 17.0 17 .0 14.0 20.0 18.0 15.0 19.0 22.0 20.0 17.0 19.0 18.0 16.0 15.0 14.5 12.0 13.7 16.5 15.0 19.0 13.4 18.0 14.0 19.0 14.0 20.0 19.0 17.0 19.0 17.0 17.0 18.0 19.6 19.4 15.5 16.0 18.0 15.0 26.0 35.0

0.13 0.14 0.17 0.45 0.16 0.18 0.38 0.34 0.36 0.38 0.32 0.36 0.36 0.31 0.38 0.36 0.27 0.32 0.32 0.36 0.34 0.47 0 .37 039 0.31 0.32 0.31 0.29 027 027 028 028 0.27 0.27 0.28 0 .29 0.38 0.23 0.24 0.14 0.58 0.28 0.46 0.35 0.32 0.32 0.39 0.28 0.37 0.27 0.34 034 02 7 0.70 0.35

26 42

25 12 45 21 37 33 32 45 48 50 46 45 48 43 42 50 47 36 SO 40 36 51 52 51 51 45 48 48 44 52 46 44 45 44 SO 46 53 41 46 46 45 43 46 44 46 44 42 45 44 47 47

54 30

22

25 27 25 25 24 28 24 26 15 24 25 29

31 27 20 29

2' 29 34 34 29 23 23 20 23 23 22 30 17 21 32 23 29 24 19 21 22 18 22 22 24 28

27

24 24

27 24 27

25 25 23 27 27 2"6 27 21 22 21 22 26 27

25 25 23

25 16 41

12 14 15 16 11 11 12 16 16 13 15 14 13 16 14 9 14 11 12 11 9 12 15 13 11 11 9 14 14 12 13 11 13 10 14 13 10 10 16 14

IS 12 15 15 14 14 12 12 8 15

Iiquiv . weiaht

GIlL

4-Me

acid

1%\

875 918 755 822 843 1050 1050 1040 1085 1020 1040 1110 570 530 1280 740 1020 980 980 1200 950 1160

11.7 16.4 17.0 16.5 10.7 16.0 16.0 15.8 16.0 15.0

8.4 2.8 6.0 4.9 10.2

11.5 5.5 16.0 12.0 6.0 2.5 16.0 16.5 17.0 15.0 16.0 14.0 16.0 14.5 14.0 17.5 13.0 19.0 14.0 16.5 16.5 15.5 17.5 16.5 15.0 17.0 17.5 17.0 16.0 16.0 16.0 14.0 15.0 14.0 18.0 14.5 12.5 14.5 12.5 18.0 13.0 17.0 16.5 19.0 17.0 18.0 17.0 14.0 15.0 15.0 16 .0 16.5 16.0 21.0 8.0

1.5 1.5 1.0 5.0 0.1 2.5 1.0 1.5 1.0 15.0 2.0 1.0 2.0 1.5 2.0 2.5 1.0 1.0 2.0 1.5 1..5 1..5 1.5 1.5 1.0 1.0

990 1120 1130 880 1300 875 1090 970 970 1060 920

980 1090

960 930

960 1030 1060 1030 1200

1070 1180 930 1100 1260 1090 1260

960 1270 970 1000 870

990 860 890 1200 1130 1110 1050 980 1070

800 1244

a ' Numbe ring of objects used for Figures 2, 3. b*Numbe ring of obj ects used for Figure 1. For references see foo tnote to Table II.

258

1.5 \. 5 1.4 1.5 2.0

1.5 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.5

1.5 1.5

1.5 0.0 1.0 1.0 1.5 1.0 \.0 2.0 3.0 1.0 1.0 1.0 1.5 1.5 1.0 1.0 1.0

Classification of natural gums III.

Table II. O rigin of A cacia and Ca mbr etum samples detailed in T abl e I (column b) ObiectNo. 1-5

6-9

to 11-16

Descriniion Vulgares Series

Acacia senegal (Nigeria) (authenticated)

Gum Arabic Combretum

Reference/Designation

I.

Aerubescens

2. 3. 4. 5. 6. 7. 8. 9. 10.

A.jl~ckii

II.

sokodens splendens pinpuriciflorum apiculatum

Quala en Nahal Goz el Ganzara

14. 15. 16. 17. 18. 19. 20. 21. 22. 23.

GozAshgar

24.

Gum Arabic (Sudan)

Asenegal ]

A.senegal.9 A.senegal14 Gum Arabic

12.

13.

17-29

A.goetzii Amellifera (Namibia) Amellifera (Sudan) A.senegal5

longispicatum fromii

(51) (S2) (S3) (54) (55) (56) (57)

supplied by UK Overseas Development Authority reference collection 1939 Rowntrees from 20 ton consignment Collected by (4th picking) ") Mr.M.P.Vidall-Hall (2nd

1904 1905 1935 1960 1960 1962

(Sudan)

30-38

Bomu Province Nigeria

25. 26. 27. 28. 29. 30. 31. 32. 33.

34. 35. 36. 37. 38. 39-45

Uganda (commercial)

39. 40. 41. 42. 43.

44. 46-50

A.senegal (authenticated)

(58) A.G.5elf-eI-Din 1970 (59) European supplier 1971 (510) Rowntrees (used for toxicol. eval.) 1977 (511) American User 1986 (512) European User 1988 (513) Euronean Importer 1988/89 cron (N1) UK Overseas Authority 1905 . .. (N2) .. 1931 . .. .. (N3) 1933 . " (N4) " 1938 (N5) UK User 1958 (N6) UK 1959 (N7» Importer 1960 (N8) Rowntrees 1961 (N9) (Tropical Product's Institute) 1967 (UK Overseas Authoritv) (VI) Collected (U2) in Uganda (U3) Kararnoja (U4) Region (U5)

~~~

45. AcaSen1 From many samples in Sudan Quala en NaJ 46. (Kassalla Prov.) Umm Ruaba & Gos el Ganzara (Kordofan Prov.)

47. 48. 49.

SO.

5enegal2 Prof.J,Vassal Mali 3 Mauritania 4 Oman 5 (R.M.Lawton)

259

PcJurasek, M.Kosik and G.O.Phillips

References for source samples and specimens in Tables I and II: 1,2,4,6 3 6,7

8 9 10-16 17-38 39-45 46-57 58-65

Anderson et al. (1979) Phytochem., 18, 609-610. Anderson tal. (1987) Food Hydrocoll., 1,327-331. Anderson et al. (1990) Food Addit. Contam., 7, 303-321. Anderson et al. (1988) Food Hydrocoll., 2, 477-490 Anderson et al. (1968) Carbohyd. Res., 6, 97-103. Anderson et al. (1990) Food Addit. Contam., 7, 205-209. Anderson et al. (1990) Food Addit. Contam., 7,303-321. Anderson et al. (1991) Food Hydrocoll., 5, 297-306. Anderson et al. (1983) Int. Tree Crops J., 2, 245-256. Andersonetal. (1991) Biochim. Syst. Ecol., 19,447-452.

attached where available. The difficulty in presenting such a mass of data coherently will be evident. We have, therefore, included in Table II additional information about the samples and the source of the analytical data. In other tables the short designation is retained for easy reference. In Table I also there are two sets of numbering for the samples, since not all were utilised in each chemometric evaluation. Greater emphasis is given to the scrutiny of gum arabic (A. senegal and related species) in the more detailed investigations. The particular section and legends to the Figures draw attention to the relevant numbering which is then applicable. Table III deals with the amino acid composition, and the same designations have been used for identical gums for which the other nine features are given in Table I. In the amino acid tables, Al represents (%N), A2 (alanine), A3 (arganine), A4 (aspartic acid), AS (cystine), A6 (glutamic acid), A7 (glycine), A8 (histidine), A9 (hydroxyproline), AlO (isoleucine), All (leucine), A12 (lysine), A13 (methionine), A14 (phenyl alanine), AlS (proline), A16 (serine), A17 (threonine), A18 (tyrosine), A19 (valine). Methods

The chemometric methods employed (10-14) have been previously described (1,2). Principal component and discriminant component projection have been used to set out the data shown in the tables in graphical form. Each point in the figures corresponds to one gum sample. The distance and positions of the points with respect to each other are determined by the similarities between the samples. When the species form a 'cluster' this enables us to identify related species or members of a sub-genus. We have used as coordinates in n-dimensional space the analytical parameters which have been used to characterise arabino-galactan protein gums. These are of two types: 1. Nine physical and chemical parameters relating mainly to the carbohydrate moiety: [alD' viscosity, NOlo, equivalent weight, compositions of glucuronic acid, 4.0-methyl glucuronic acid, galactose, arabinose and rhamnose (Table I).

2. The parameters which relate specifically to the proteinaceous components: 260

Classification of natural gums III.

%N and the composition of the 18 amino acids: alanine, arganine, aspartic acid, cystine, glutanic acid, histidine, hydroxyproline, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tyrosine, valine (Table III). Initially we utilised the nine parameters shown in Table I, thereafter the 18 amino acid compositions in Table III. This information enables us to combine the data and use 27 parameters (Table IV). From these indications we subsequently reduce the number of features in order to establish the minimum number we can use and still provide the characterisation information which can be elucidated using all 27 parameters.

Results and discussion The information shown in Figure 1 utilises the data shown in Table I for all the 65 samples listed. Figure 1 is the PCA plot using information in the plane spanned by PC1 and PC3. This plot includes various Acacia gums from the Vulgares series, Combretum gums, in addition to A.senegal/gum arabic. Figure 2, on the other hand, is the PCA plot (using PCl/PC2) utilising the same data shown in Table I, but selecting only those features which relate to Asenegal/ Gum Arabic. Figure 1 again demonstrates the clear distinction which can be demonstrated between a non-Acacia gum (Combretum series) and the Acacias. A.senegal, the principal component of commercial gum arabic, is a member of Series Vulgares Benth.: subgen Aculeiferum Vas. Most regulatory definitions (1,2) would recognise the broad definition of gum arabic as 'the dried exudate from stems and branches of Acacia senegal (L.) Willd. or other related species (fam. Leguminosae). The gum exudates from the series (Vulgares) would certainly constitute a 'related species'. However, they do not all sit within or very closely to the gum arabic cluster. The gums A.erubescens (no. 1 in Table I), Afleckii (no. 2, not shown clearly because it overlaps Asenegal) Aigoetzii (no. 3) and A.mellifera (nos 4 and 5) also belong to the Vulgares series, and apart from one A.mellifera sample from Sudan (no. 5), fall either close or within the gum arabic cluster. A sample of Amellifera from Namibia (no. 4) borders on the cluster, but the remainder fall very near to the cluster with A.erubescens almost coincidental with authenticated Asenegal. The gum arabic cluster can be scrutinised in more detail by reference to Figure 2A. The corresponding denodrogram (Figure 2B) further demonstrates the coherence of the cluster, since the height is an indication of the similarity of the species. The computer zoom enables the cluster in Figure 2C to be expanded to show the interrelationships more clearly. The outliers are no. 9 (in the second numbering in Table I) which is a commercial gum arabic sample (S4) dating from 1939 and supplied by the UK Overseas Development Authority. Its anomalous behaviour is attributable to the absence of data for [a]D and viscosity, included here to demonstrate the need for a full set of data for classification. The other outliers are nos 53 and 54. The latter is a Combretum not an Acacia, which fully explains its position, and the former (no. 53) a sample from Marsabit, Kenya. 261

...c 'tI

IV

Rj Table III. Th e amino acid compos itions of the protein aceo us moieties (re sidues pe r 1000 residu es) of various Africa n Acacia gums and vario us Co mbretum species No. I 2 3

•

5 6 7 8 9 10 11 12 13

Seeeiee A...,1 A...,2 A...,3 A.... A...,5 A...,6 Alen 7

A, enS A.en9

AIeriIO Aleh l l A. en12

Gum. rabic

14 IS

C .f O.l:lld u Lft

16 17 18 19

C .pUtpw icijlorum Ca pi.clJotlUJl

C..rDI, ,,"IU

21 22 23

C10ftRuDicatum C.fromii 51 r 52 53 54

2'

S~

25

56 Gum

26

51 Arabk: 58 Sud... 59 SI O ~ 511 SI2 SI3 NI N2 t Nl

20

21 28

29 30 31 32 33 3' 15 36 37

3B 39 .0 41

Commercial

Nf Commercial N5 Gum N6 Arabk: N7 N_1a N8 N9 ~

AI' 0.21 0.29 0.33 0./4 0.11 0.22 0.36 0.40 0.33 0.40 0.24 0.31 0.35 0.13 0.1' 0.11 0.'5 0.16 0.18 0.28 0.3' 0.36 0.38 0.32 0.36 0.36 0.31 0.38 ll.36

0.21 0.32 032 0.36 0.3' 0.'7 0.37 0.39 0.31 0.32 0.31 0.28

A2

21 34 26 42 32 28 23 24 26 24 26 28 31 13 82 16 55 110

97 24 29

23 29 26 31

29 25 31 28

24 30

23 22 19 21 19 26 26 26 30 21

A3 8 0 3 6 5 6 5 5 3 5 6 15 1 15

A4 50

5' 23 30 51 .6 11 16 I. 13 12 12 10 13 1 21 10 II 12 12 12 11 13 12 II 12 15

104 112

10

58 .1

.lJ 59

,.,

44 44 .1

44 46 91 60

80

89 96 31 .9

88 69 89

11 63

69 72 13

41 .9

69 71

43 34 13 42 10 78 72 65 67

A$ 0 0 0 0 0 0 0 0 0 0 0 3 I 0 89 50 66 0 0 10 12 0 0 0 0 I I I 3 0 0 0 0 0 0 0 0 2 0 1 0

A6 30 31 29 27 34 35 24 26 21 24 28 36 36 19 .6 66

64 61 69 28 .0 3. 46 39 .2 52 55 .9 .2 31 36 63 32 23 37 29 37 51 69 57 .3

A1 '9 '9 46 23 .7 38 39 37 40 40 '9 53 .9 135 103 101 86 179 123 .1 61 49 40 41 48 5' .8 53 59 .8 41 51 .2 '9 56 39

53 52 53 53 .9

A8 36 .1 .3 29 76 35 '5 .1 .6 .6 31 52 81 18 16 19 21 31 19 51 .1 .8 2' .1 42 40 44 ,1 59 .6 .0 53 31 .2 51 .6 51 52 .8 49 55

A9 32' 2.1 3.1 37l 299 303 358 355 3.8 3.1 355

256 21' 0 0 7)

1. 0 0 318 230 320 331 311 296 118 335 290 2 10 362

304 269 '30 441 280 394 28. 297 251 287 306

AIO 12 12 II 12 I' 15 II II 12 II 12 II

14 33 21 3. 6 37 50 II 16 10 11 13 13 12 10 1 13 II 15 10 8 15 II 17 I. II 16 15 9

All 71 69 13 •5 70 68 63 66 68 61 15 10 15 .1 3. 51 '9 52 68 63 16 69 52 69 51 61 65 65 19

12 61

13 56 60 74 60 76 74 69 78 73

A12

25 2. 20 3\ 21 22 32 19 18 23 20

21 26 31

28 46 54 41 36 22 26 23 21 26 26

22 28 26 26 24 24 31 19 15 26 16 31 26 29 30 2'

A13 I I 1 I I I 0 0 0 1 I 2 0 12 26 8 8 0 16 I 0 0

• • 3

3 I 0 6 0 0 3 3 0 0 0 0 2 I 2 I

AI. 2' 21 22 II 26 25 21 21 21 20 23 30 29 29 3' 36 73 55 29 36 41 28 29 33 21 33 35 11 38 21 31 38 2. 20 32 23 43 J2 39 36 35

AI5 81 138 7.

84 10 83

94 86 81 89 81 64

11 115 162 55 139 50 11 50 63 67 61 55 66 65 48 68 78 51 90 .9 58 56 62 69 56 .9 59 .3 .2

A I6 13' 135 139 13• 139 153 131 139 139 1. 3 115 I" 137 82 71 93 18 53 66 115 134 129 II I 126 132 124 12' 144 152 121 122 138 107 115 133 121 129 1.0 133 12' 153

AI1

A18

n

10

72 81

12 9 20 8 8 9 8 8 10 8 13 II 30 20 36 37 5. 60 13 13 19 29 10 16 9 13 9 18 16 II 12 20 13 2D 16 II 13 12 12 8

60

81 83 10

11 75 15 82 72

11 44 55 66 5. 56 139 60 69 61 56 66 85 63 66 69 86

6S 63 11

55 57

12 63 66 72 75

64 79

A I9 39 '5 36 53 21 .0 32 33 3' 32 33 35

43 51 53 51 5. 56 54 35 39 31 46 .0 40 38 11 24 35 31 '6 33 30 23 35 27 41 32 36 39 25

;:l ~

r

3:

~ ~

~

50C'l

9'tI §

-6. ~

42 43 44 45

46 47 48

VI t U2 Commercial V3 Gum U4 Arabic US IUnada U6 U7

~

0.27 0.27 0.28 0.28 0.27 0.27 0.28

37 45 31 39

19 10 14 11 15

67 49 76 56 70

46

13

72

41

13

63

28

5 0 0 0 12 16 10

62 41 61 46 58 55 53

54

40 57 47 57 58 51

41 51 38 51 39 34 40

179 266 216 257 232 253 240

18 10 16 12 17 17 15

72 65 67 70 69 63 66

42 56 38 30 44 42 54

2 0 2 2 1 2 I

44 40 53 45 48 54 49

64 70 65 82 65 49

64

113 144 109 135 105

99

71 80 65 74 62 55

110

64

16 17 27 15 20 23 25

48 33 49 36 47 49 41

"The parameters are designed: Al (%N), A2 (alanine), A3 (arganine), A4 (aspartic acid), A5 (cystine), A6 (glutamic acid), A7 (glycine), A8 (histidine), A9 (hydroxyproline), AID (Isoleucine), All (leucine), A12 (lysine), Al3 (methionine), A14 (phenyl alanine), A15 (proline), A16 (serine), Al7 (threonine), A18 (tyrosine), A19 (valine). References for sources of samples and specimens in Table III: 1-11 (A.sen) Anderson et ai. (1985), Food Add. Contam., 2, 159-164.

A.sen

No. I 2

3 4 5 6 7

8 9 10 11 12

Origin Mauritania Mali Senegal Oman Kordofan, Sudan Kordofan, Sudan Quala en Nahal, Sudan Goz el Ganzara, Sudan Goz el Ganzara, Sudan (sandy soil) Umm Ruaba, Eastern Kordofan (sandy soil) Ethiopia Sudan

12 (A.sen) Phillips et ai. (1993) J. Agric. Food Chem., 41, 71-77. 12 As 1-11 which gives average value for seven commercial samples. 14-48 As Tables I and II. N 0\ !Jj

rJ

5' ~

5

'~"' g e ...,

.;:-=. e.

~

3

.... '" ....

:-'

"CI

N 0-

L. c

+:.

tlCI>

r'" Table IV. Physical and che mical parameters for a ra nge of Africa n Acacia gums and from vario us Co mbretum series No.

I 2 3 4 5 6 7 8 9 10

II 12 13 14 15 16 17 18 19 20 21 22 23 24 25

26 27 28 29 3D 31 32 33 34 35 36

Species

...

Feature

Gum Arabic C ,30 UJtUfU C

C.srncNUfU

C.DUtDW'ieillorwm C,IJpic ~ 'wm

c. ltwt,upi.calwm C/romii 51 52 S3 54 S5

Combrttum

• t

56

Commercial

57 S8 59 5 10 5 11 51 2 S13 NI N2 N3 N4 N5 N6 N7 N8 N9 UI U2 U3 U4 U5 U6 U1

Gum Arabk Sudan

•

I'

2

3

4

-3D -21 -27 -36 -25 -21 - 2 -32 -31 -3D 0 -32 -29 -31

17.0 72.0 87.0 62.0 46.0 53.0 64.0 16.0 17.0 19.0 0.0 19.0 14.0 14.0 16.0 15.0 17.0 17.0 14.0 20.0 18.0 15.0 19.0 22.0 20-0 11.0 19.0 18.0 16.0 15.0 14.5 12.0 13.1 16.S 15.0 19.0

o.so

45 26 42 25 12 45 21 37 33 32 45 48 50 46 45 48 43 42 50 47 36 50 40 36 51 52 51 51 45 48 48 44

-31 -3 1 -29 -28 -3D -32 -27 -3D -28

-29 Commercial Gum Arabk NiRerlli

-32 -32 -32 -29

•

-29

Coa lllludal

-32 -3D -32

Gum Arabic (\Jnnda

•

-26

-34 -34 -32

0.13 0.14 0.17 0.45 0 .16 0.18 0.38 0.34 0.36 0.38 0.32 0.36 0.36 0.31 0.38 0.36 0.27 0.32 0.32 0.36 0.34 0.47 0.37 0.39 0.3 1 0.32 0.31 0.29 0.27 0.27 0.28 0.28 0.27 0.27 0.28

52 46 44 45

5 24

26 15 24 25 29 28 29 34 34 29 23 23 20 23 23 22 3D 17 21 32 23 29 24 19 21 22 18 22 22 24 28 24 24 21 24

6

7

8

9

10

II

14 31 27 20

1020 1040

15.0 11.5 5.5 16.0 12.0 6.0 2.5 16.0 16.5 17.0 15.0 16.0 14.0 16.0 14.5 14.0 17.5 13.0 19.0 14.0 16.5 16.5 15.5 11.5 16.5 15.0 17.0 11.5 11.0 16.0 16.0 16.0 14.0 15.0 14.0 18.0

2.0 1.5 1.5 1.0 5.0 0.1 2.5 1.0 1.5 1.0 15.0 2.0

31 73 82 76 55 110 97 24

24

7 75 54 23 3D 51 46 17 16 14 13 12 12 10 13 7 21 10

3D

II

23

29 12

27 14 15 16 11

II 12 16 16 13 15 14 13 16 14 9 14

lllo 570 530 12 80 740 1020 980 980 1200 950 1160

990 1120 1130 880 1300 875 1090 970 970 1060

II

920

12

980 1090

II 9 12 15 13

II II 9 14 14 12

960 930

960 1030 1060 1030 1200 1070 1180 930

29

23 29 26

r.o

31

2.0 1.5 2.0 2.5 1.0 1.0 2.0

29

1.5 1.5 1.5 1.5 1.5 1.0

i.o 1.5 1.0 1.0 1.0 1.0

i .o 1.0 1.0 1.0

25 31

28

12 60

SO 104 112 89

96 31 49 88 69 89 77 63 69

72 73 47 49 69 71 45

22 19

12 12 12

27

II

73

19

13

26 26 26

12

42 10 18

3D 21 37 28 45 31 39

46 41

II 12 15 10 19 10 14 11 IS 13 13

34

72

6S 67 67 49 16 56 70

72 63

13

14

15

16

17

1 0 89 50

36 79 46 66 64 61 69 28 40 34 46 39 42 52 55 49 42 31 36 63 32 23 37 29 37 51 69 51 43 62 41 61 46 S8

49 135 103 101 86 179 123 47 61 49 40 47 48 51 48 53 59 48 47 51 42 49 56 39 53 52 53 53 49 54 40 57 47 57 58 51

81 18 16 19 21 31 19 51 47 48 24 47 42 40 44 47 59 46 40 53 37 42 51

274 0 0 73 74 0 0 378 230 320 331 3 11 296 318 335 290 210 362 304 269 430 447 280 394 284 297 251 287 306 119

66 0 0 10 12 0 0 0 0 I 1 I 3 0 0 0 0 0 0 0 0 2 0 1 0 5 0 0 0 12 16 10

55 53

46 51 52 48 49

55 41 51 38 51 39 34 40

266 216 2S1 232 253 240

" T he param eters are designated as follows: 1- 9 as in Table I; IO- 27, the amino acids as in Table III .

3:

18

19

20

21

22

23

24

14 33 21 34 6 37 50

26 37 28 46 54 41 36 22

0 12

16 10 17 13 13 12 10 7 13

75 47 34 57 49 52 68 63 76 69 52 69 57 61 65 65 79

77 175 162 55 139 50 71 50 63 67 63 55 66 65 48

II

72

15 10 8 15 11 11 14 11 16 15 9 18 10 16 12 11 11 15

61 73 56 60 14 60 16 74 69 78 13

24 24 31 19 15 26 16 31

29 29 34 36 73 55 29 36 41 28 29 33 27 33 35 37 38 27 31 38 24 20 32 23 43 12 39 36 35 44 40 S3 4S 48 54 49

137 82 71 93 78 53 66 115 134 129 111 126 132 124 124 144 152 127 122 138 107 115 133 121 129 140 133 124 153 113 144 109 135 IDS

II

72 65 61 10 69 63 66

26 23 21 26 26 22 28

26 26

26 29 3D 24 42 56 38 3D 44 42 54

26 8 8 0 16 I 0 0 4 3 4 3 1 0 6 0 0 3 3 0 0 0 0 2 I 2 I 2 0 2 2 I 2 I

68 78 57 90 49 58 56 62 69 56 49 59 43 42 64 70 6S 82 65 49 64

99 110

25 77 44 55 66

S4 56 139 60 69 67 56 66 85 63 66 69 86 65 63 71 55 57

72 63 66

72 75 64 79 71 80

6S 74 62 55 64

26

27

11 3D 20 36 37 54

45 51 53 51 54

60

54 35 39 31 46 40 40 38 17 24 35 31 46 33 3D 23 35 21 41 32 36 39 25 48 33 49 36 41 49 41

13 13 19 29 10 16 9 13 9 18 16 11 12 20 13 20 16 11 13 12 12 8 16 11 21 IS 20 23 25

56

~

Q

CI>

.,~ "0o c

:"

S

-s' CI>

Classification of natural gums III.

FIGURE 1.

•

FIGURE IA.

27

15

It 14

12 28 13

- - - - i•.,PC1

Fig. I. Prin cip al component analysis of da ta groups (65 objects) sho wn in Table I , with more det ail abo ut the gum sa mples given in Table II . Features: the nine mainl y carbo hydrate par amet er s (Ta ble I). Axes : first and th ird principal components. with 49.7 and 34.3% o f tot al variance . D , Comb retum : /::;. . commer cial gum arabi c and A isenegal ; +. gum ara bic (U ganda) ; _ , Vulgares ser ies add itiona l to A .senegal. (A) Species marked by numbers corresponding to T able I (column b).

265

P.Jurasek, M.Kosik and G.O.Phillips FIGURE 2A.

o

53

o

o

54

o

9

o ~

PC1

FIGURE2B.

Fig. 2. (A) Principal component analysis of data groups relating only to gum arabic/A. senegal (54 objects) shown in Table I. Features: the nine mainly carbohydrate parameters. Axes: first and second principal components, with 27 and 31% variance. (B) Dendrogram relating to (A), with the objects numbered as in Table I (column a). (C) Computer zoom to identify objects in (A). The numbers refer to the 54 objects listed in Table I (column a). (D) Loading-loading plot for (A).

266

Classification of natural gums III.

FIGURE2C.

43 17 39 22

44 1'5' 274~1

1~2

48

8

4

6

7

19 40

47

49

~~224

3 ~

21

46

52

20

29

30 13 14

33

3~5 37

11

31

38

46 ----t~~PC1 FIGURE 20 .

2 8

3 4

------~-------------T---------------------

C\l

oa..

5

r~~ 7

9

- - -....~~PC1

267

P.Jurasek, M.Kosik and G.O.Phillips

The nuclear magnetic resonance spectrum of this sample (15) showed extensive differences from the other A.senegal samples studied from Sudan and Niger. The differences were attributed by Anderson (15) to either climatological or soil differences or possibly more extensive hybridizations/adaptations in the A. senegal trees themselves. In any event, it has previously been shown to be anomalous, and the chemometric analysis demonstrates its difference from commercial gum arabic and the authenticated A.senegal samples which form a remarkably discrete cluster. The loading-loading plot corresponding to Figure 2A is shown in Figure 20, which indicates those features which confer maximum distinctiveness to the gum arabic grouping. Apart from number three (%N), all the other eight features exert a distinctive influence, but since the objects are themselves so similar, this must be anticipated. The features which distinguish A.senegal from other gums need to be further evaluated. Discriminant component analysis is the most effective for separating groups and indicating differences. For the 54 objects in Table I, the DCA plot is shown in Figure 3 (by arbitrarily comparing authentic A.senegal with commercial samples of gum arabic with a single Combretum sample added for reference). No groupings are evident, confirming once again the coherence of the commercial gum arabic/A.senegal samples investigated. This is the pattern based FIGURE3

o o ~

DC1

Fig. 3. Discriminant component analysis utilising two categories of objects in Table I (authentic A.senegal (36 samples) and commercial gum arabic (17 samples) with one Combretum sample for reference. Axes: first and second components, with variance 10 and 5%. D, A.senegal (authentic); 6.. commercial gum arabic; ... , Combretum.

268

Classification or natural gums III. FIGURE 4A.

A

0

+

----4~.PC1 FIGURE 4B

15 17

Fig. 4. (A) Princi pal component analysis of dat a gro ups (48 obj ects) shown in Tabl e III. Features: the composition of 18 amino acids in the gums and % N . Axes: first and second prin cipal component with 50 and 11% varia nce. R . Combretum ; D , A isenegal; 6, gum arabic (Suda n) ; +. gum arabic (Nige ria); - . gum ara bic (Uga nda) . (B) Species mar ked by numbers correspondingto Table III.

269

P.Jurasek, M.Kosik and G.O.Phillips

FIGURE SA.

t,+

tl+

o

o

+

I!J

+0

o o

----I.~PC1 FIGURESB.

17

18 16

23

C')

o0-

14

r

4

15 19

----I.~PC1

270

~ +

Classification of natural gums III.

Fig. 5. (A) Principal component analysis of the data groups (48 objects) shown in Table III . Features: the composition of the 18 amino acids and 'Yo N. Axes: first and third principal comp onents with 50 and 11'Yo variance . IX , Combretum ; D , A isenegal ; 6. , gum arabic (Suda n); + , gum arab ic (Nigeria) ; - , gum arabic (Kenya) . (B) Specie s marked by numbers corresponding to Table 111. (C) As (B) with computer zoom to differentiate species for main cluster.

on the mainly nine carbohydrate features. Again the Combretum sample falls outside the gum arabic cluster. We consider now the characterisation based on the 18 amino acid features (Table III) . Figures 4 and 5 show the PCA plots using PCIIPC2 and PCIIPC3 respectively. Again the Combretum gums are quite distinct from the A.senegall gum arabic cluster. No.4 is a sample from Oman, and is a local variant of Acacia senegal, for which we have previously noted its non-conformance (2). In addition no . 23 remains apart from the main clusters on both PCIIPC2 (Figure 4) and PCIIPC3 (Figure 5) plots. Previously we noted the anomalous behaviour of no. 9 in Figure 2A, which is the same sample (S4). From a practical standpoint it would require further investigation before its full acceptance as a commercial gum arabic. A most interesting observation, based on the amino acid evaluations in Figures 4 and 5, is the separate grouping of the commercial gum arabic samples originating from Uganda (nos 42-48) . This is quite evident, particularly from Figures 5C where the scale has been expanded. They form a family close to but distinct from , other gum arabic samples. These were collected in the Karamaja Region of Uganda (16). According to their properties all would qualify for commercial useage based on the JECFA proposed new specifications. However, 271

P.Jurasek, M.Kosik and G.O.Phillips

they have lower methoxyl, rhamnose and hydroxyproline contents than typical Sudanese commercial samples. They also show different NMR spectra and emulsification capacity. Yet is it clear from our results that it is the amino acids which confer the major difference between the Uganda and Sudanese gums. Scrutiny of the PCA plots based on carbohydrate composition (Figures 1 and 2), shows that on this basis the Ugandan gums show no significant difference from the other gums within the cluster. The Ugandan gums are nos 28-34 in Figure 2C. Here is where the chemometric method demonstrates its superiority over visual scrutiny of the analytical data, despite its extreme value in collecting the data (17). Next we consider all nine carbohydrate-based features together with the 18 amino acids, making 27 features in all in relation to the overall characterisation. Which characteristics exert the overall dominant influence and are there any significant anomalies compared to the analysis based on carbohydrate and amino acids individually? The combined data are shown in Table IV, using the same designations as in the previous tables. Figure 6 is the PCA plot (using PClIPC3) for the 36 objects in Table IV, using the 27 parameters identified therein. Again the amino acid composition of the Ugandan gums (nos 30-36) is dominant, and they form a discrete family along the main gum arabic cluster. Three gums from Nigeria (nos 21, 22 and 24) group together. These are among the oldest dated of the samples studied, with no. 21 originating in 1905, nos 22 and 24 in 1933. Again no. 11 (previously shown as 54) is anomalous, and well outside the acceptable limits. Otherwise there is excellent coherence and all the gums fall into an extremely compact grouping. On this basis also the Combretum gums form a better grouping than in the previous analysis based on carbohydrate and amino acid contents only. Certain conclusions can now be drawn from the chemometric analysis of the 54 gum arabic samples studied: 1. On the basis of the mainly carbohydrate nine parameters, no distinction can be drawn between authenticated A.senegal from Nigeria, Niger, Sudan and Uganda (Figures 1,2 and 3). Similarly, on the basis of the 18 amino acids, authenticated A.senegal from Mauritania, Mali, Senegal, Sudan and Ethiopia fall within the broad cluster (Figures 4 and 5).

2. Using amino acid composition the gum arabic from Uganda can be distinguished (Figures 4 and 5). Such a difference is not apparent using only the nine mainly carbohydrate features (Figure 2e). 3. There is general coherence in the commercial gum arabic samples drawn from Sudan and Nigeria. A mean of eight commercial samples (designated gum arabic in Table I) fall centrally into the clusters based on carbohydrate (Figure 2) and amino acid (Figures 4 and 5). As much variation exists within the cluster between the authenticated A.senegal samples as exists between A.senegal specimens and the various commercial gum arabic samples. 4. The pattern established using mainly the nine carbohydrate features and 18 amino acid features is maintained when they are combined (Figure 6). The 272

Classification of natural gums III.

FIGURE6A.

-,

-: +

4

+

l!lI

l!lI

+ + (")

o

+

a..

i'--------=--::-_ l!lI

----i.~PC1

6

FIGURE 6B.

3il6

4

35

~1

28

?3325 1

7

9

1~ 2629

~16

J§2r8 2

100

5

24 22

(")

o

a..

21

l'

11

----i.~PC1

Fig. 6. (A) Principal component analysis of the data groups (36 objects) shown in Table IV. Features: all 27 features included, to combine those used in Figures 1 and 3. Axes: first and third principal components with 46 and 9% variance . • , gum arabic mean of 8 commercial samples; iii, Combretum; '"I, A.senegal; +, gum arabic (Nigeria); 6., gum arabic (Sudan); - gum arabic (Uganda). (B) Species marked by numbers corresponding to Table IV.

273

P.Jurasek, M.Kosik and G.O.Phillips

dominant nature of the amino acid composition in enabling a distinction to be drawn between the Ugandan gum arabic and the remainder may also extend to certain Nigerian gum arabic originating from the years 1905 and 1933. 5. However, there is no evidence for a significant change in the properties of gum arabic from 1903 until the present time (Figures 1 and 2). 6. Climate and soil (sandy or clay) have no significant influence on the properties of the gum (samples 7, 9, 10, Table III). 7. Gums believed to be A.senegal, or a local variant thereof, from Kenya and Oman do not conform to the coherence shown by the remainder of the gums examined. Our final task was to investigate whether the number of features could be reduced, but still provide the essential information obtained from using all 27 features. Figure 7 shows the loading-loading plot for Figure 6, and the features marked which exert maximum influence in establishing the distinctive character of gum arabic. Highly correlating features are close together in the plot. Features located near the origin in such a plot have only minimal influence on the data structure. There is a predominance of amino acids, confirming their dominant effect in discriminating between one specimen and another. On the basis of Figure 7 and chemical experience, the following nine features were selected from Table IV: viscosity, specific optical rotation 4-methyl glucuronic acid, alanine, hydroxyproline, leucine, lysine, methionine and serine. FIGURE 7.

22 14

25

~f~

4

: ~ ···········································t·······z

16

26

12

8

5


13 6

3

® 23

CD

~ Fig. 7. Loading-loading plot corresponding to Figure 6.

274

@

.

Classification of natural gums III.

FIGURES.

I8l I8l

M

o

0-

r~__ ----I.~PC1

11

FIGURESA.

Fig. 8. Principal component analysis of the data groups (36 objects) shown in Table IV. Features: the nine most discriminant features identified in Figure 7: specific optical rotation, viscosity, 4-methyl glucuronic acid, alanine, hydroxyproline, leucine, lysine, methionine and serine. Axes: first and third principal components, with variance 59 and 11%. 1llI, Combretum; ., gum arabic mean of 8 commercial samples; +, gum arabic (Nigeria); 6, gum arabic (Sudan); -, gum arabic (Uganda). (A) Species marked by numbers corresponding to Table IV.

275

P.Jurasek, M.Kosik and G.O.Phillips

The numbering of the objects remains as in Table IV. Figure 8 shows the PCA plot using PCl/PC3. The results are most encouraging, yielding the same pattern as before, including the separate cluster for the Ugandan gums. It is significant that there is better correlation of the Combretum gums (apart from C.splendens). Sample no. 11 (54) as previously was anomalous. From the loadingloading plot corresponding to Figure 8 the most discriminant features would appear to be: viscosity, hydroxyproline, 4-methylglucuronic acid and lysine (Figure 9). The process of selection was continued, from the PCA plot using PCl/PC2 when a difference of discriminating features was observed. Taking the results together, we identified the following four features which exerted maximum influence: rotation (1), viscosity (2), lysine (3) and hydroxyproline (4). The PCA plot for the 36 objects in Table IV is shown in Figure 10 for PCl/PC2 and in Figure 11 for PCl/PC3. The information is equally good and valid as for Figure 6 (using 27 features) and Figure 8 (using eight features). Equally satisfactory is the loading-loading plot (Figure 12) corresponding to Figure 10. The separation of the four features indicates that they all exert an almost equal contribution towards the correlation. All the major characteristics observed previously are evident from Figures 10 and 11. The Ugandan grouping is clear, the Nigerian gums (1905, 1933) remain peripheral, the Combretum gums are distinguished and the same no. 11 outliers are shown. Even more satisfactory is the close grouping of gum arabic/A. senegal. FIGURE 9.

3

5 8

....................g

;

.

t

6

7

Fig. 9. Loading-loading plot corresponding to Figure 8. 1, specific optical rotation; 2, viscosity; 3,4methylglucuronic acid; 4, alanine; 5, hydroxyproline; 6, leucine; 7, lysine; 8, methionine; 9, serine.

276

Classification of natural gums III.

FIGURE 10A.

+

C\l

o

a..

IL...----I!I_ - - - - ' ----I~~PC1 FIGURE 108.

4

5

3

32

6

2.

2

C\l

o

I' a..

'--

11 ...J

- - - - l.. ~PC1 Fig. 10. (A) Principal component analysis of the data groups (36 objects) shown in Table IV.

Features: specific optical rotation, viscosity, lysine, hydroxyproline. Axes: first and second principal components with S6 and 27% variance. ~, Combretum; ., gum arabic mean of eight commercial samples; t:" gum arabic (Sudan); +, gum arabic (Nigeria); -, gum arabic (Uganda). (B) Species marked by numbers corresponding to Table IV.

277

Pi.lurasek, M.Kosik and G.O.Phillips

FIGURE 11A.

Fig. 11. (A) Details as in Figure 10, but using first and third principal components with variance 56 and 15%. (B) Species marked by numbers corresponding to Table IV.

278

Classification of natural gums III.

FIGURE 12.

4

································3········ 2

Fig. 12. Loading-loading plot corresponding to Figure 10. 1, specific optical rotation; 2, viscosity; 3, lysine; 4, hydroxyproline.

+

FIGURE 13.

+

Fig. 13. (A) Feature-feature plot of various African Acacia gums and from Albizia and Combretum species. Features: specific rotation and %N. 0, Vulgares series; /'::" Gummiferae series; +, Albizia; -, Combretum.

279

P.Jurasek, M.Kosik and G.O.Phillips

To exa mine the validity of using just two features [al v and % N as recommended by JECFA , a feature-feature plot was undertaken . The result is shown in Figure 13. No gro uping occurs and it is not possible to distinguish the vari ou s categories. A similar result was obtained by using all permutations of the four features used to con struct Figures 10 and 11. In summary, therefor e , it can be confidently predicted th at if a commercial gum ara bic sample falls within the cluster in Figures 10 and 11, th en the y fulfil all the legislative criteria for accepta bility . Four ana lytical paramet ers onl y are needed to provide a compl et e specification; two mea surements are inadequate. The gum arabic cluster which is defined by all 27 par am et ers, and subsequently con structed onl y by using four analytical features: rotation , viscosity, lysine and hydroxyproline composition (Figure 11) adequately defines commercial gum ara bic. It takes into account historical , geographical , soil, climatic variations, in addition to conforming to the regulat ory requirement of including only 'A cacia senegal and related species '. On this basis it is possible to set up a practical quality control system which could be used by producer countries and commercial users to monitor adherence to the defined spec ification. References I. Jur asek ,P. , Kosik,M. and Phillips,G.O . (1993) Food Hydrocoll. , 7, 73- 85. 2. J urasek .P,; Kosik,M. and Phillips,G .O. (1993) Food Hydrocoll. , 7,1 57- 174. 3. Phillips,G .O. and Williams,P.A . (1993) In Nishina ri, K. (ed .) , Proceedings International Conference on Food Hydrocolloids, Tsuk uba , Jap an , Elsevier, in press. 4. J urasek.P, ; Kosik ,M. , Phillips,G .O . and Varmuza,K. (1993) Foods Food Ingred. , J. San-Ei (Japan) . 5. JE CFA- FAO (1986) Food and Nutrition Paper, Rom e , No. 34. 6. WHO (Ge neva) , ( 1982) Technical Report Series, No . 683, 28. 7. JE CFA-FAO (1990) Food and Nutrition Paper, No . 49. 8. Osman ,M.E ., Williams,P.A. , Menzies,A. R . and Phillips,G .O. (1993) J. Ag ric. Food Chem . , 41, 71-77. 9. Anderson,D .M.W . and McDougall,F.J . (1985) Phytochem . , 24,1237-1 240. 10. Varmuza ,K. and Lohn inger ,N. (1990) In Hadzi, Zup an ,J. (eds), PCs for Chemists, Elsevier , p. 43. II . Wold,S. (1989) In Brant ,J. and Ugi,I. K. (eds) , Compute r Application in Chemical Research and Education . Hutting-Verlag, Heidelberg, p. 101 -1 20. 12. Var muza, K. (1991) EXCERPT: Chemo metrics Software for Exploratory Data A nalysis of Spectra. Technical Uni versity, Vienna , ACM . 13. Fra ncs,M.A., Seeber ,R., Sferlazzo ,G . and Lea rdi, R. (1990) A nalitica Chimica A cta, 233, 143147. 14. Florina ,M., Leardi,R. , Armanino .C., Lant eri ,S., Conti.P, and Princi.S, (1988) PARVUS, an Extendable Package of Programs fo r Data Exploration , Classification and Correlation , Elsevier , Amsterdam . 15. And erson,D.M.W., MiIlar ,J.R .A . and Weiping.W. (1991) Biochim , Syst. £Col., 19,447-462. 16. And erson ,D .M.W. and Weiping,W. ( 1991) Food Hydrocoll., 5, 297-305 . 17. Anderson ,D .M.W. , Brown ,D .D .M. , Morrison. W. A . and Weiping,W. (1990) Food Addit. Contam. , 7, 303-321.

280