Maillard Reaction May Explain Image Formation

THE SHROUD OF TURIN: AN AMINO-CARBONYL REACTION

(MAILLARD REACTION) MAY EXPLAIN THE IMAGE FORMATION

Raymond N. Rogers* & Anna Arnoldi†

This article originally appeared in Melanoidins vol. 4, Ames J.M. ed., Office for Official

Publications of the European Communities, Luxembourg, 2003, pp.106-113.

*University of California, Los Alamos National Laboratory, 1961 Cumbres Patio, Los

Alamos, NM 87544, USA

†University of Milan, Department of Molecular Agrifood Sciences, via Celoria 2, 20133

Milano, Italy.

Summary.

The Shroud of Turin is a large piece of linen that shows the faint image of a

man on its surface: it has been claimed to be the shroud of Jesus. Here we report evidences that
colour can be produced by reactions between reducing sugars, left on the cloth by the
manufacturing procedure, and amines deriving from the decomposition of a corpse. Treatment of
a cloth prepared according to the ancient technology gave a distribution of colour on the thread
fibres in good agreement with the Shroud features. Such a natural image-production process
would support the hypothesis that the Shroud of Turin had been a real shroud. However, these
observations do not

prove

how the image was formed or the "authenticity" of the Shroud.

INTRODUCTION.

The Shroud of Turin is a large piece of linen that shows the faint image of a man on its

surface (Jumper et al., 1984). It has been claimed to be the shroud of Jesus, making it very
controversial.

In 1978, its custodians allowed the Shroud of Turin Research Project (STURP) to test the

different image-formation hypotheses. The outstanding characteristic of the image on the Shroud
of Turin is the discontinuous distribution of the colour on the surface. STURP members took
many photomicrographs of the surface of the Shroud in 1978 (Pellicori & Evans, 1981). They
reported that the image "consists of a light sepia colour with the darkest coloration on the thread
tops." All image areas are very faint, and most image fibres are gold (Schwalbe & Rogers, 1982).
The colour density seen in any area of the image appeared primarily to be a function of the
number of coloured fibres per unit area rather than a significant difference in colour density,
which was called the "half-tone" effect. A very specific feature is that the colour appeared only
on the surface of individual fibres (Heller and Adler, 1981).

No image fibres were cemented together by any foreign material, which seemed to

eliminate any image-formation hypothesis that was based on the flow of a liquid into the cloth.
The hypothesis of a gaseous diffusion into the cloth would have produced a colour gradient
through its thickness (Schwalbe & Rogers, 1982).

Visible and ultraviolet spectrometry, infrared spectrometry, x-ray fluorescence

spectrometry, and direct microscopic viewing did not detect any known Medieval painting
materials. Later microscopy, microchemistry, pyrolysis-mass-spectrometry, and laser-microprobe

Raman analyses failed to detect foreign materials. Pyrolysis-mass-spectrometry analysis was
sufficiently sensitive to detect ppb levels of polyethylene oligomers that came from sample bags.
Reflectance spectra of image areas, scorched areas, and aged linen were identical (Gilbert and
Gilbert, 1982). In conclusion, all the observational methods applied by STURP failed to detect
any of the historically known painting vehicles, media, or pigments, suggesting that the image
was not a painting in any normal sense (Schwalbe & Rogers, 1982).

Taking into account all these results, it was decided to check the hypothesis that the image

could derive from an amino-carbonyl reaction between sugar residues on the cloth and amino
derivatives produced by the corpse post-mortem reactions. In order to get historically reliable
results, experiments were performed on a linen cloth prepared following exactly the procedure
described by Pliny the Elder (77).

RESULTS

Observations on the cloth.

Every scientific hypothesis for image formation has to take into account and explain a very

important experimental fact: although the surfaces of Shroud image fibres show a characteristic
golden colour, their medullas are clear (Figure  1  above  ), which supports the Heller and Adler
observation that all image colour resides on fibre surfaces (Heller and Adler, 1984). They
reported that: "The absence of products expected from a high-temperature cellulose degradation
[…] suggests that the process that formed the final chemistry took place at lower temperatures
(less than 200ºC), because no pyrolytic compounds were found. The fluorescence  of the scorch
areas, however, demonstrates the presence of high-temperature pyrolytic products in these
areas"(Heller and Adler, 1984).

Several holes were burned in the cloth when the shroud was badly damaged in a fire in

1532. Scorch colours between light lemon yellow and black appear around these holes and the
fibres involved are coloured all of the way through their diameter. Fluorescent products are
observed around the burned areas, confirming high temperature pyrolysis conditions.

Observations of weave density and lignin content of the shroud fibres (Rogers, 2001)

indicate a very mild bleaching technique in agreement with the methods described by Pliny the
Elder (77). The same technology was in use, with some minor differences, until after the last
crusade in 1291 (Hochberg, 1980). Linen was spun by hand on a spindle whorl. When the spindle
was full, the spinner made a hank of thread. Each hank of thread was bleached separately, and
each was a little different. Different parts of the same thread in the shroud's weave show slightly
different colours, like a variegated yarn. The warp thread was protected with starch during the
weaving process, making the cloth stiff. The final cloth was washed in a solution made from

Saponaria officinalis.

Saponaria

produces four glycosidic saponins, and all hydrolyse to produce

sugar chains. (Ya Chirva et al., 1969) The following carbohydrates were identified in those
chains: galactose, glucose, arabinose, xylose, fucose, rhamnose, and glucuronic acid.

The presence of starch, in particular amilose, on the shroud was confirmed by the fact that

during testing for sulfoproteins in blood areas with an iodine-azide reagent (which bubbles
vigorously when sulfur is present), a reddish background was formed. Image colour does not
appear under the bloodstains when they are removed with a proteolytic enzyme. Whatever
process produced the image, colour must have occurred after the blood flowed onto (or was
painted onto) the cloth, and the image-producing process did not destroy the blood (Heller and
Adler, 1981).

Saponaria officinalis,

also called "soapweed," reduces the surface tension of water making

it a good wetting agent. Both hydrophobic and hydrophilic materials on a newly woven cloth are
put into solution or suspension by

Saponaria

. After been washed in a

Saponaria

solution, ancient

clothes were "laid out on bushes to dry" (Donadoni, 1978) Under such conditions, materials that
are in solution or suspension in the wash water will concentrate at the drying surface. We
hypothesize that evaporation / concentration can explain the superficial nature of the image.

The commercial production of linen started during Medieval times: most commercial

bleaching in Europe took place in "bleach fields" in the Low Countries, where completed pieces
of cloth were spread out for bleaching. These medieval linens are homogeneous, whereas the
shroud shows bands of different densities.

Experimental production of image-like colours.

Tests of image-formation hypotheses needed fresh material. However, modern linen is

useless for experimental image-production purposes because it is vigorously bleached and been
coated with sizing compounds and fluorescent fabric brighteners.

Kate Edgerton (deceased, Norwich, CT) grew flax and made some linen, using both starch

and

Saponaria

. Unfortunately, she ironed the samples with a "warm iron" which coloured the

cloth and changed the

Saponaria

glycosides. Edgerton's samples could be bleached to remove

most of the colour by soaking in 3.5% hydrogen peroxide. This treatment did not remove the
natural waxes. That material was used in the reported experiments.

Because Edgerton's linen was scarce, many preliminary tests were performed on pure-

cellulose filter paper. These experiments were done by placing drops of test solutions on a dry
plastic plate and laying a piece of Whatman's #4 filter paper over them. The liquid migrated

through the paper and evaporated at the surface. No colour could be observed in either sunlight or
ultraviolet illumination with

Saponaria

alone or with the model saccharides. The different

samples were treated with ammonia vapour for different times. Light colours developed slowly
on the tops of samples that contained reducing saccharides.

A technical grade dextrin, that reduced Fehling's solution, was used to test crude-starch

reactions. Paper was laid over different numbers of drops of dextrin, and the liquid was allowed
to migrate into circular spots and evaporate. Samples were then laid over drops of

Saponaria

solution, which caused the polysaccharides to move radially, as in a circular paper
chromatogram. Afterwards, these samples were treated with ammonia that produced the
development of a brown colour, which was more intense where the dextrin had been concentrated
by migration at the

Saponaria

-solution front and on the paper's surface.

Very little colour was obtained when the same experiments were repeated with purified

starch or plant gum. It was evident that colour development required both reducing sugars and
amines.

After these successful experiments, a sample of Edgerton's bleached linen was placed on

four drops of dextrin solution on a plastic plate. A round spot was obtained and the water was
allowed to evaporate from the cloth: at this point no colour could be seen on either surface. The
middle of the same sample was placed on four drops of

Saponaria

solution. The wet spot

expanded radially through the cloth. The water was allowed to evaporate, and no colour could be
observed. The sample was then treated for 10 minutes with ammonia vapour: a very light colour
could be observed on the top surface after standing 24 hours at room temperature. To increase the
reaction rate, a sample was treated at 66 ºC for a few minutes (Figure 2 above). In these

conditions the development of colour is very clear and the most intense colour appears in the ring
on top. Some colour appears around the ring on the back surface; however, the centre of the back
is nearly white.

Experimental manipulations of concentrations and one-dimensional migration of solutions,

as in a large cloth, could produce the same front-to-back colour separation as observed on the
shroud.

When observed under a microscope, the fibres on the top-most surface are the most

coloured and the colour is a golden yellow similar to that on the shroud (Figure 3 above).

The coating of brown products is too thin to be resolved with a light microscope, and it is

all on the outside of the fibres. There is no coloration in the medullas: the colour does not scorch
the cellulose. There is essentially no colour on fibres from the middle of the back surface (Figure
4 above).

DISCUSSION

A large number of attempts have been made to reproduce the Shroud image by different

methods, and many "theories" have been proposed (Vignon, 1970). All have failed when
compared with observations and measurements on the Shroud and none of them was able to
explain the experimental fact that only the surfaces of the fibres are coloured .

Studies on contact and material-transfer hypotheses (Pellicori & Evans, 1981) eliminated

hypotheses based solely on vapour-diffusion and/or material-transfer mechanism. Vapours and

liquids penetrate the cloth: materials that will colour the surface will also diffuse into and colour
the inside of the cloth.

Hot irons, statues, etc., must be ruled out, because different colours can be seen as a

function of the depth into the cloth. Colour penetration is different for contact and non-contact
areas, and fibres are coloured through their entire diameter.

Other "theories" and attempts at image production have ranged from pseudoscience to the

lunatic fringe. Many have involved unknown physics, some involving ionising radiation,
postulated at the time of the Biblical resurrection (Antonacci, 2000).

This is certainly the first report of colour development with features very similar to the

Shroud obtained by a natural process on a cloth prepared following the procedure that was in use
about 2000 years ago as it was described by Pliny the Elder. This ancient technology used to
leave residues of reducing sugars on the cloth both deriving from crude starch and

S. officinalis

The amino reactants required to develop colour may derive from a corpse. In fact

decomposing bodies start producing ammonia and amines, e.g., cadaverine (1,5-diaminopentane)
and putrescine (1,4-diaminobutane), fairly quickly, depending on the temperature and humidity.
The ammonia and many of the amines are volatile, and they rapidly undergo Maillard reactions
with any reducing saccharides they contact. It is well known that browning rates depend on pH:
rates peak in the neutral to basic pH range, but rates are still rapid in the 3-7 pH range (Ledl and
Schleicher, 1979)

Human sebaceous secretions are about 28% free fatty acids; therefore, human

skin is normally slightly acid, but the developing amines should neutralize the medium increasing
the reaction rate.

Melanoidins, the brown polymeric materials coming from the Maillard reaction, although

their structures are still rather elusive (Arnoldi et al, 2002), have certainly a highly unsaturated
structure as observed for example by Cammerer and Kroh (1995). This seems in good agreement
with the fact that image fibres could be decolourised with strong reducing agents, indicating the
presence of conjugated double bonds (Heller and Adler).

Such sugar-amine reactions may offer a simple, realistic, natural explanation for the colour

on the shroud.

Several Shroud researchers have wondered why there is no mention of an image on the

"cloths" reportedly found in Jesus' tomb. Assuming historical validity in the accounts, such a
situation could be explained by the delay in the development of the Maillard reactions' colours at
moderate temperatures.

Another important observation is the fact that the image-forming process produced slightly

different colour densities on the different lots of thread (Jumper et al., 1984). The density-density
of the image is not simply a function of the chemical properties of cellulose: it also depends on
the individual properties of the threads. The observed effects must have been caused by different
amounts of impurities that originally coated the surfaces of the threads as a result of slightly
different production conditions.

Slightly different amounts of impurities on the linen threads would cause slightly different

surface energies. Liquids would wet the threads as a function of the difference between the
surface tension of the washing solution and the surface energy of the specific linen thread. This
would explain the "banded" appearance of the Shroud.

The chemistry of the colour does not answer all questions about how the "photographic"

image formed. The image seems to show the body of a man, and it is darkest in areas that should
have been closest to the body's surface.

Vapour diffusion parallel to the cloth's inner surface would follow Graham's Law, and high

Maillard reaction rates would limit the spread of reactive amine vapours. Gaseous reactive
amines can be lost by diffusion through the porous cloth, reducing concentrations and reaction
rates inside the cloth. The surface area of cloth is large, and decomposition amines adsorb
strongly. All of these phenomena would cause a rapid reduction in amine concentrations away
from contact points.

Postmortem body temperatures can reach 41ºC (Irvine, 2001), and steep temperature

gradients would exist across the cloth as a result of the low thermal diffusivity of linen and the
angular dependence of radiant heat flow from a nonmetallic surface (Gubareff et al, 1960). The
temperature gradients will have a large effect on Maillard reaction rates. These combination of
factors could produce a distribution of reaction products with the appearance of the image.

The problem of radiocarbon age determination.

In 1988 Damon et al. (1989) reported result of a radiocarbon age determination as 1260-

1390 with at least 95% confidence. The instruments and methodologies applied were certainly
the best that could be used in the world, however that datation does not reflect the STURP
observation on the linen-production technology and the chemistry of the fibres. A detailed
description of the characteristics of the fibres used for determination has not been reported,
however the sample was cut very near to another sample given in 1973 to Professor Gilbert Raes
of the Ghent Institute of Textile Technology.

Some of the fibres of this latter sample are in the hands of R. Rogers who has observed a

series of very peculiar characteristics that indicate very clearly that this sample is incoherent with
the general features of Shroud. The most important experimental observations are the following
(Rogers and Arnoldi, 2002):

An evident contamination with cotton fibres (easily recognizable from linen at the

microscope), which do not appear in the other parts of Shroud. Cotton was practically unknown
in ancient times and was introduced in use only around 1350.

Linen fibres in the Raes sample show at the microscope only traces of lignin at the

nodes in comparison with the rest of Shroud, indicating a more modern technology for cloth
preparation, which is confirmed by the chemical quantitative determination of lignin.

All Reas threads show coloured encrustations on their surfaces that are lacking on

the rest of Shroud.

All these observations suggest that the sample for the radiocarbon age determination came

from an area, which had been darned, a phenomenon that must not surprise, because the Shroud
may have been restored during his complicate history, especially after it was damaged by a fire in
1532. Therefore the 1988 radiocarbon age determination, which indicated that the Shroud was
Medieval, seems highly unreliable. A second radiocarbon analysis should be very advisable, at
least on the charred materials removed during the June-July 2002 restoration (Ghiberti, 2002).

CONCLUSION.

The chemical analyses performed by the STURP (Schwalbe and Rogers, 1982) are in good

agreement with the Pliny description of ancient cloth technology, as extensively discussed
recently by us (Rogers and Arnoldi, 2002):.

We can now formally propose a completely natural hypothesis for image formation.

Impurities in ancient linen could have been suspended by the surfactant property of a

Saponaria

officinalis

washing solution and they would be concentrated at the cloth surface by evaporation.

Reducing saccharides would react rapidly with the amine decomposition products of a dead body.

This hypothesis is the first one, which can explain the very peculiar distribution of colour

on the Shroud fibres. Such a natural image-production process would support the hypothesis that
the Shroud of Turin had been a real shroud. However, these observations do not

prove

how the

image was formed or the "authenticity" of the shroud.

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