Transcript Document

UP’s part of WP 2
The Whole Gory Story
(but fortunately for all concerned
in 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
100
2100
80
1500
70
g polyphenol
bound
1800
60
1200
50
900
40
600
30
20
300
10
0
0
0
300
600
900
1200
1500
1800
Sorghum condensed tannins (g catechin equivalents)
2100
% polyphenol bound
(catechin equivalents)
90
Kafirin films with modified properties can be made
from kafirin cross-linked with tannic acid
or with sorghum tannin
Stress at maximum force, s y
(MPa)
Modified films have increased tensile stress
and decreased tensile strain and oxygen permeability
Water barrier properties unaffected
6
5
SCT
4
TA
3
2
1
0
0
5
10
15
Modification level (% w/w of protein)
20
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
Stress
Principal component 2 : 12.65%
G
Moisture
0.5
Stress at break
WVTR
WVP
OTr
0.0 d(Tg inters)
OP
Tg intersect
PEG
Tg E"peak
E'(Tg inters)
% Strain
-0.5
LA
-1.0
-1.0
-0.5
0.0
0.5
Principal component 1 : 56.06%
1.0
Glucono delta-lactone (GDL) when present with lactic acid
was found to have potential as a kafirin film plasticiser
GDL
(% relative to
protein wt)
0
Stress
(N/mm2)
Strain
(%)
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): 27-31
Taylor, 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 2002
D5: 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