UP’s part of WP 2

The Whole Gory Story

(but fortunately for all concernedin a very shortened form)

Extraction of sorghum with aqueous ethanol (70%) + sodium hydroxide and sodium metabisulphite yields pure kafirin

Addition of Sodium Hydroxide improves the yield of kafirin, also makes it more soluble, less prone to gelation gives it better film forming properties

No NaOH With NaOH

Method for casting free-standing films with aqueous ethanol

A plasticiser combination of equal parts: Glycerol, Polyethylene glycol 400 and Lactic acid found to be satisfactory for making kafirin films

Brittle film Plasticised film

Glacial Acetic Acid, Lactic Acid and Aqueous Isopropanol identified as alternative food compatible solvents for kafirin

Extraction of sorghum with Glacial Acetic Acid after pre-soaking with Sodium Metabisulphite

gives high yield of pure kafirin

Kafirin can be extracted from both white and red sorghum bran

Free-standing films can be made from kafirin extracted from sorghum bran

Tannic acid (a Hydrolysable Tannin) and Sorghum Tannin (Condensed Tannin) can cross-link with kafirin

% p

olyp

hen

ol b

oun

d

(cat

ech

in e

qu

ival

ents

)

0

300

600

900

1200

1500

1800

2100

0 300 600 900 1200 1500 1800 2100

Sorghum condensed tannins (g catechin equivalents)

0

10

20

30

40

50

60

70

80

90

100

g p

olyp

hen

ol

bou

nd

0

1

2

3

4

5

6

0 5 10 15 20

Modification level (% w/w of protein)

Str

ess

at m

axim

um

for

ce, s

y

(MP

a)

SCT

TA

Kafirin films with modified properties can be made from kafirin cross-linked with tannic acid or with sorghum tannin  Modified films have increased tensile stress and decreased tensile strain and oxygen permeabilityWater barrier properties unaffected

Kafirin films made with different levels of Glycerol, Polyethylene Glycol 400 and lactic acid

 Principal Component Analysis showed that the most effective Plasticisers for

kafirin films are the Associated Moisture, Glycerol (G) and Polyethylene Glycol (PEG)

 Lactic Acid (LA) is an essential component of plasticised kafirin films,

but probably as solvent rather than a plasticiser

-1.0 -0.5 0.0 0.5 1.0

Principal component 1 : 56.06%

-1.0

-0.5

0.0

0.5

1.0

Prin

cip

al c

ompo

nent

2 :

12

.65%

G

Moisture

% Strain

LA

E'(Tg inters)Tg E"peak

Tg intersect

Stress at break

Stress

OP PEGd(Tg inters)

OTrWVP

WVTR

Glucono delta-lactone (GDL) when present with lactic acid was found to have potential as a kafirin film plasticiser

GDL

(% relative to protein wt)

Stress

(N/mm2)

Strain

(%)

0 28.6 2.6

21 15.4 13.8

42 9.7 23.1

Journal papers Emmambux, M.N. and Taylor, J.R.N. 2003. Sorghum kafirin interaction with

various phenolic compounds. J. Sci. Food Agric. 83: 402-407.Da Silva, L.S. and Taylor, J.R.N. 2004. Sorghum bran as a potential source of

kafirin. Cereal Chemistry 81: 322-327.Emmambux, M.N., Iannace, S. and Stading, M. 2004. Cereal biopolymer films,

coatings and other industrial products. Chemical Technology (1): 27-31Taylor, J., Taylor, J.R.N., Dutton, M.F. and De Kock, S. 2004. Identification of

kafirin film casting solvents. Food Chemistry (In press).Emmambux, M.N., Stading, M. and Taylor, J.R.N. 2004. Sorghum kafirin film

property modification with hydrolysable and condensed tannins. Journal of Cereal Science (In press)

Da Silva, L.S. and Taylor, J.R.N. 2004. Physical, mechanical and barrier properties of kafirin films from red and white sorghum milling fractions. Cereal Chemistry (In press)

Gao, C., Taylor, J., Wellner, N., Byaruhanga, Y.B, Parker, M.L., Mills, C. and Belton, P.S. (2004). Effect of preparation conditions on protein secondary structure and biofilm formation of kafirin. Journal of Agricultural and Food Chemistry (In press)

Deliverables D4: Kafirin protein from sorghum bran, Report: Extraction of kafirin from red

and white sorghum milling fractions. L S da Silva, December 2002D5: Screening of food-compatible non-ethanol kafirin extraction methods.

J Taylor, December 2002.D6: Casting of free-standing kafirin films and investigation into film preparation

and film properties using food compatible non ethanol solvents.J Taylor December 2002

D16: Modified kafirin films (cross-linked, plasticised and combined cross-linked and plasticised) J Taylor, August 2004

D17: Sorghum kafirin film property modification with hydrolysable and condensed tannins. M N Emmambux, M Stading and J R N Taylor, August 2004

D21: The physical properties, including biodegradability of modified kafirin protein films. J Taylor, M N Emmambux, H van Eck, Y B Byaruhanga and J R N Taylor, August 2004 (actually part of WP3)

Exhibitions Sorghum Protein Films. Science at the World Summit on Sustainable Development, CSIR, Pretoria, August 2002  Sorghum and Sorghum Protein Biofilms. University of Pretoria Open Day, May 2003. Out of Africa: Sorghum the Sustainable Cereal. Royal Society Summer Science Exhibition, London, July 2003