Freeze dried oven driedbutanol ethanol butanol ethanol

B E

B E

Spray driedethanol

E

ALPHA HELIX

BETA SHEET

0.1 mm mmmm0.1 mm

mmmm

MAINLY HELICAL MAINLY SHEET

Heat treatment during the extraction and drying process appears to cause denaturation and aggregation of kafirin, decreasing solubility.

Kafirin films, where the -helical structure of the “native” protein has been retained, are better quality, smoother and more transparent, than those containing aggregated proteins with a greater -sheet content.

Denatured/aggregated kafirins give less homogeneous films showing phase separation

15251575162516751725

wavenumber (cm-1)

0

0.20.4

0.60.8

1

Abs

orba

nce

αβ

abcde

a = unmodified film, b = 5 %, c =, 10 %, d = 15 %, e = 20 % level of modification

FT-IR spectra of kafirin films with sorghum condensed tannin

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20 25

% TANNIN

FR

AC

TIO

N O

F S

IGN

AL

MOBILE

RIGID

PREDICTED

Tannic acid and sorghum condensed tannins stabilised the kafirin α-helical structure and decreased β-sheet formation

Tannic acid cross-linking decreased the mobility of the kafirin polypeptide chains

1.22

1.24

1.26

1.28

1.3

1.32

1.34

1.36

1.38

1.4

1.42

0 10 20 30 40 50

%glycerol

1650

/163

0 ra

tio

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

GLY/KAF RATIO

MO

BIL

E/I

MM

OB

ILE

RA

TIO

PREDICTED VALUE

RAW DATA

CORRECTED FOR MOBILE PROTEIN

WITH DEUTERATED GLYCEROL

GLYCEROL INCREASES THE ALPHA HELICAL CONTENT OF THE PROTEIN AND CAUSES MOREMOBILE MATERIAL TO APPEAR THAN CAN BEEXPLAINED SIMPLY BY THE AMOUNT OFPLASTICISER ADDED.

Glycerol must also act as solvent

heat

solvent

Hydrophobic interiors unwind slightlyAnd coagulation takes place. Degree of unwinding/ coagulation is determined by the thermal history of the sample

dry

Tannindry

plasticiser

plasticiser

MOSTLY IMMOBILE

MOBILEReverts torandom coil or alpha helix

RIGID CORERemains alpha helical

Highly mobile region

Moreplasticiser

Some absorption of glycerol

Glycerol acts at as a solvent for theunwound region.