Beetroot (2004)
Stephen Nottingham
© Copyright: Stephen Nottingham 2004
|
|
5. Colour
The
tops of cultivated Beta vulgaris are typically dark green in colour
and the roots are white, yellow or red. Root colour is at its most intense
and variable in beetroot (beets, garden beet or table beet). Most beetroot
cultivars have red roots, in shades ranging from deep reddish-purple to
bright vermilion, but some cultivars also have orange, yellow or white roots.
These colour differences are due to different levels of pigments (betalains)
that are characteristic of beetroot. Beetroot red or betanin is used as a
food colouring, while beetroot juice is used as a natural dye for fabrics.
Betaine compounds also contribute to beetroot's importance as a
health-promoting vegetable. This chapter examines the pigments in beetroot
and the uses to which they are put. The condition known as beeturia is also
described, in which betalains are not processed normally by the human
digestive system and therefore colour the urine red.
There are four main classes of plant pigment:
chlorophylls, carotenoids, flavonoids and betalains.
Chlorophylls and carotenoids are insoluble in
water and are found in the organelles of cells. Organelles are the structures
in cells that have a particular function, for example, the nucleus,
chloroplasts and mitochondria. When organelles are coloured by pigment they
are also called chromoplasts. Chlorophylls are blue-green or yellow-green
pigments that are mainly found in the chloroplasts. Chlorophylls are the
primary light-trapping pigments involved in photosynthesis. Their main role
is to absorb light energy and convert it into chemical energy. The
carotenoids also trap light energy and act to prevent the degradation of
chlorophyll molecules in the chloroplasts. Carotenoid pigments occur in red,
orange, yellow and brown colours. The carotenoids produce many of the colours
typical of autumn foliage; floral colours that attract pollinators; and the
characteristic colours of many fruits and vegetables. The carotenoids are
divided into two subgroups: the carotenes and the xanthophylls.
Flavonoids and betalains are water soluble
pigments found in vacuoles, spaces within a cell filled with air, water or
other liquids, and the cytosol, the semi-fluid part of the cell in which the
organelles are suspended. Flavonoids are yellow, orange, red and blue
pigments. They are responsible for many of the intense colours in vegetables,
flowers and fruits. Flavonoid pigments come in a wide range of colours due to
subtle structural variations and differences in concentration.
The betalains are a group of nitrogen-containing
pigments that are yellow, orange, pink, red and purple in colour. Unlike the
other three main classes of plant pigment, betalains have a limited
distribution. Most red colouration in plants is due to carotenoids and
flavonoids. The red colour of most fruit and vegetables, such as
strawberries, grapes and red cabbage, is due to anthocyanins, which are in
the flavonoid class of pigments. Betalains are restricted to plants in the
order Caryophyllales, and the fungal genus Amanita. In addition to Beta
vulgaris (family Chenopodiaceae), betalains have been described from
Cactaceae fruits (prickly pear), Amaranth seeds (Amaranthaceae), Bougainvillaea
bracts (Nyctaginaceae), and flowers or other plant parts within the
Aizoaceae, Basellaceae, Didieraceae, Phytolaccaceae and Portulaceae. Nine of
the eleven families within the order Caryophyllales have plants containing
betalains. The other two families (Caryophyllaceae and Molluginaceae) have
anthocyanins (flavonoids) instead, which probably reflects an early taxonomic
division within this plant order. Red beetroot and prickly pear (Opuntia
ficus-indica) are the only edible sources of betalains.
Betalain pigments were first isolated from the
red roots of Beta vulgaris; the betalain class of pigments are in fact
named after the plant genus Beta. Incidentally, bett is the Celtic
word for red, although the published suggestions that this is how Beta
vulgaris got its name are pure speculation. There are currently over
fifty known betalain pigment molecules, which occur in flowers, fruits,
shoots and roots. The betalains are subdivided into two structural groups:
the red-violet betacyanins and the yellow betaxanthins.
Beetroot contains a complex mixture of betalain
pigments. However, the characteristic purple-red-violet colour of beetroot is
mainly derived from a betacyanin pigment called betanin. Betanin was first
discovered in around 1920, while a crystalline form of betanin dye was
produced in the 1960s. Up to 200 mg of betanin is typically found in one
beetroot. It normally occurs at much higher levels in the roots of red
beetroot than other betacyanin pigments. Like all betacyanins, betanin is
metabolically derived from a molecule called 3,4-dihydroxyphenylalanine
(L-DOPA). Betanin is formed from two L-DOPA molecules. The first undergoes a
change to form betalamic acid. The second L-DOPA molecule is changed to
cyclo-DOPA glucoside (CDG), which condenses with betalamic acid to produce
betanidin. A change in structure, involving the addition of glucose, converts
betanidin to betanin. Other minor biochemical modifications give rise to
other betacyanin pigments.
After betanin, the yellow betaxanthin pigments
vulgaxanthin-I and vulgaxanthin-II are the next most significant in beetroot.
Mario Piattelli and colleagues, working in Naples, first described these
pigments in beetroot in the 1960s. They found at least six betaxanthins in
the cultivar they studied (Piatta d'Egitto), all present in minute
quantities. In total, they listed sixteen different betalains, including
indicaxanthin, isobetanin, neobetanin and prebetanin. The characteristic root
colouration of beetroot cultivars is due to variations in levels of different
betalain pigments, especially the relative concentrations of betanin and the
yellow betaxanthin pigments. Cultivars with deep purple-red roots have a high
ratio of betanin to betaxanthin pigments, while yellow and gold cultivars
such as Burpee's Golden have relatively high levels of betaxanthins and very
little or no red betanin pigment. Cultivars with white roots, including
Albina Vereduna and Blankoma, have extremely low levels of both betacyanin
and betaxanthin pigments.
Distinct light and dark rings are usually visible
when beetroot is cut transversely. This is due to different amounts of
pigment in the vascular system and storage tissue of the root. The vascular
system appears as darker bands due to higher levels of pigment, while the
storage tissue appears as lighter bands. In some deep red cultivars like
Boltardy and Red Ace this colour difference can be quite subtle. The colour
difference is at its most obvious in Chioggia, with its concentric bullseye
pattern of rosy red bands (vascular system) and white bands (storage tissue).
The betalains are distributed mainly towards the
outer parts of the roots of beetroot. However, betalains are not just
confined to the roots, but contribute to the redness observed in leaves,
stalks and flowers.
Foods have been coloured red using beetroot juice
in the home for many years. In the eighteenth century, for example, Mrs.
Raffald used beetroot colouring, in a recipe for pink pancakes, in The
Experienced English Housekeeper (1769). Today, it is used to provide
colour in a wide variety of dishes. The colourful world of beetroot cuisine
is explored in Chapter Seven.
It is not just for its red colour, however, that Beta
vulgaris has been utilized. For many years, extracts of leaf beet and spinach
were used to colour confectionary green. Laura Mason, in her book about the
prehistory of sweets, lists beets among the plants used to colour sweets, up
until the Victorian era in Britain. Beet leaf green was a benign addition
compared to some of the things that were added to colour sweets in former
times, such as dye from quinces cooked in pewter (lead), acid fruits cooked
in untinned copper vessels (copper), and Prussian blue (cyanide). Following a
scandal, when fatalities occurred after lozenges were consumed in 1850, a
major reappraisal of the colourings and ingredients used in foodstuffs was
undertaken. This eventually led to modern food-safety legislation. In the
1860s, however, new synthetic pigments replaced many of the old colourings
(including beet green), and these gave an intensity and consistency of colour
not previously seen in confectionary.
Betalains are important natural colourings within
the food industry. The main source of betalains is beetroot. During
commercial extraction, beet roots are first crushed, and the coloured juice
is collected and concentrated. Betalain pigments are sold to the food
industry either as juice concentrates or powders. Juice is concentrated under
vacuum until it comprises around 60-65% of total solids. Freeze drying
techniques are used to produce a powder, typically containing 0.3-1.0%
pigment.
A higher level of pigment concentration in juice
and powder products can be obtained through fermentation. The fermentable
solids present in beet juice can be removed in a biofermentor, using yeasts
such as Candida utilis and Saccharomyces cerevisiae, to leave a
more concentrated pigment product. Powders obtained after fermentation of
beet juice contain five to seven times more betacyanin than powders obtained
from unfermented beet juice.
Betalain extracts can have a range of colours,
depending on the relative proportion of betacyanin and betaxanthin pigments
present. Colouring products are usually odourless and tasteless, but they can
impart odour and flavour to food. The most important food colouring is pure
betanin or beetroot red, which is used to colour a wide range of processed
food products.
Betalain stability The
stability of betalains dictates their range of food colouring applications.
Betalain extracts need to be treated with care because they are sensitive to
environmental conditions, particularly pH, heat, light, moisture and oxygen.
These environmental factors have interactive effects, and pigments can
quickly discolour under adverse conditions. The red pigment betanin, for
example, degrades on exposure to air, bright light and high temperatures to a
light brown colour. This discolouration is partially reversible, if adverse
conditions are only temporary.
Betalain colouration is unaffected by pH in the
range 3.5 to 7.0 (acid to neutral). Beetroot extracts in most foods will
therefore not discolour as a direct result of pH. The optimum pH for both
betacyanin and betaxanthin pigments occurs in the slightly acidic 5.0-6.0
range. The colour of red beetroot extract changes from red towards blue as pH
increases above 7.0. Root tissue exposed to high or alkaline pH (7.5-8.5)
becomes discoloured. Cut beetroot retains its purple-red colour well in
acidic solutions such as malt vinegar (acetic acid).
The heating of betalains can cause
discolouration. The red pigment betanin, for example, can become light brown
if gradually heated, especially if high temperature is accompanied by an
alkaline pH. High light intensities accelerate pigment discolouration.
The stability of betalains is greatest in food
products with low moisture content. High moisture levels increase pigment
degradation rates. Exposure to oxygen accelerates pigment darkened or
discolouration in food products over time. Betalains react with the oxygen in
the air, but discolouration is partially reversible if oxygen levels are
subsequently lowered.
Despite having lower stability than synthetic
food colourings, betalain pigments are widely used in food products.
Delgado-Vargas et al. (2000) list numerous products containing
betalain food colourings. They note that betalain pigments are particularly
suitable for use in food products with a short shelf-life, that have been
produced with minimum heat treatment, and that are packaged in a dry state
under reduced levels of light, oxygen and humidity.
The tendency for betalain pigments to discolour
under certain environmental conditions has resulted in them being used in the
detection of food oxidation. Betalain formulations can be used as indicators
of oxidation. The colour change from red to brown on oxidation is clearly
visible, and calibrated betalain strips inside food packaging offer an
alternative method to sell-by or use-by dates for avoiding the sale of
spoiled food. A system of this type has been patented in the USA.
Betanin The
main betacyanin in red beetroot is betanin. It is known as beetroot red when
extracted from beetroot and is used in many processed foods, especially in
ice creams and frozen desserts, to give colour without imparting flavour.
Beetroot red is used, for example, to enhance the redness of tomato paste,
strawberry ice cream and yoghurt, oxtail soup, tomato products in pizzas,
sausages, cooked ham, bacon burgers, liquorice, fruit preparations, sauces,
jams, jellies, marzipan, dry powder beverages, sugar confectionary, biscuit
creams, and a range of dessert products. Only a small amount of pigment is
usually required to obtain the required colour in food products (e.g.
0.1-1.5% levels). Betanin is mainly used to impart a deep purplish-red
colour.
In Europe, the framework legislation for food
additives is provided by the Directive on Additives (1989). Additional
Directives cover particular additives, including a 1994 Directive on colours
used in food. Food additives, including colours, are assigned E-numbers. In
Europe, betanin is either listed by name or as E162 on food labels.
Natural food colourings are undergoing a revival
within the food industry. In a review of trends in the use of colouring in
foods, Downham and Collins noted that the use of naturally derived colours
was expanding, due to improvements in stability and public concerns about
synthetic food dyes. The synthetic Red Dye number 2, for instance, has been
prohibited in foodstuffs because of health concerns. Recent health scares
have centred around the presence of the banned synthetic red dyes Sudan 1 and
Para Red in foods. Betalains have no toxic effects in the human body and are
seen as a natural and safe alternative to synthetic red colourings. Natural
pigments such as betalains may therefore become increasingly used in food
products. Methods are being developed to improve the production of betalain
in beets, through plant breeding, and cell tissue culture and biotechnology.
In addition to increasing the quantity and quality of betalains, the ultimate
aim is to improve the stability of betalain molecules in food products.
Plant breeding
Selective breeding is being carried out to produce beetroot cultivars with
increased betanin content. The average red pigment content of beetroot is
around 130 mg per 100 g fresh weight, but new red beetroot cultivars bred for
pigment extraction can yield up to 450-500 mg per 100 g root fresh weight. A
Hungarian study identified the cultivar Rubin as having high levels of
betanin and a good suitability for food colourant production. Seneca Foods
(USA) have selectively bred a beetroot with high pigment content, which
enables pigment concentrations of 1.4% to be achieved. The use of
high-concentration pigments means that smaller amounts can be added to colour
foods, with no taste being imparted.
Tissue culture and biotechnology Betanin
has to date been extracted from harvested roots to produce concentrates and
powders. However, new technologies are now available that could be used to
produce betalains from beet cells in tissue culture. Cell tissue culture
systems could be used to supply the food industry with cheap, continuous,
uniform and high-quality sources of plant pigments, without the environmental
changes that alter pigment qualities in the field. However, bioreactor
systems are expensive to operate. Therefore, pigment yields and downstream
processing methods need to be optimized before betalain production by this
method becomes commercially viable.
Cultures established from Beta vulgaris
callus tissue have been obtained that exhibit a variety of colours, including
yellow, orange, red and purple, depending on the proportion of red
betacyanins and yellow betaxanthins in the cell vacuoles. It has been
possible to obtain cultures that produce specific betalains in comparable or
larger quantities than observed in the tissues of the original plant. Both
red and yellow pigment products are likely to be produced for the food
industry using this method in the coming years, although in commercial terms
betanin will probably be the most important product.
A range of factors influence pigment production
in cell tissue culture, including light, temperature, and the presence of
growth regulators and micronutrients. Studies are ongoing to establish
optimum conditions, in order to create controlled conditions within cell
culture production systems. Light is necessary for the initial synthesis of
betalains, due to the light-sensitivity of certain enzymes involved in the
synthetic pathway. Light induction is therefore vital when beetroot clones
are being raised in cell cultures. Betalain synthesis in the field is
enhanced at lower growing temperatures and this is also likely to be the case
for Beta vulgaris cell tissue culture. Growth media, for optimum
pigment production from beet cells, have been formulated through adjustments
in the levels of minerals and micronutrients present. Levels of betacyanin
production of around 40 mg per litre of media per day have been reported,
which are promising yields in commercial terms.
Betalains are set to become increasingly
important as nutraceutical ingredients (foods marketed in terms of their
health benefits), as they replace synthetic food colourings. The betalains
have a number of health-giving properties. Infusions of betalains from the
bracts of Bougainvillaea mixed with honey, for example, are used to
treat coughs in parts of Mexico. Some antiviral and antimicrobial activity
has been attributed to betalains. This has evolved against viral and
microbial pathogens. Red pigment has been shown to be active, for example,
against Pythium, a pathogenic fungi of beets. This antiviral and
antimicrobial activity could also be beneficial in medicinal terms. The main
focus of interest, however, has recently been on betalain pigments as
antioxidants. The presence of betalains means that beetroot has a stronger antioxidant
activity than most vegetables. Antioxidants in the diet reduce the risk of
cardiovascular disease and cancer. The following chapter looks at the health
benefits of consuming beetroot in more detail.
A downside of preparing beetroot is its ability
to stain both skin and clothing. However, some food writers have blown the
'problem' out of all proportion. They may even have needlessly put some
people off preparing beetroot. Jane Grigson, who was not a fan of beetroot,
for instance, wrote that beetroot "is not an inspiring vegetable, unless
you have a medieval passion for highly coloured food. With all that purple
juice bleeding out at the tiniest opportunity, a cook may reasonably feel
that beetroot has taken over the kitchen and is far too bossy a
vegetable".
Beetroot is relatively easy to prepare, but much
of the effort of preparing it is aimed at preventing the colouring (and
nutrients) escaping prematurely. It is best to cook the roots intact, without
stabbing, slicing or damaging them in any way that promotes bleeding.
Nevertheless, it is not advisable to handle beetroot when wearing your best
clothes. Wearing rubber gloves will prevent staining to the hands. In any
case, betalains are water-soluble pigments and wash off hands and cooking
implements relatively easily.
Removing beetroot stains from clothes is no
harder than removing other vegetable and fruit stains. A rinse in cold water
loosens the stain, while beetroot pigments respond well to biological washing
powders. For persistent stains of this type, non-chlorine bleach has been
recommended. Being red, beetroot juice is more easily noticed on surfaces
than other vegetable juices that have similar staining properties.
A dislike for food that visibly stains has led to
a revival for Golden beetroot, with improved cultivars being produced from
Burpee's Golden. G Marketing of Ely in Cambridgeshire, for instance, have
bred a Golden beetroot that grows successfully in the UK. The beetroot was
launched in October 2004 as a new line in a British supermarket chain
(Waitrose). The product has been marketed as "a beetroot that doesn't
stain".
Beetroot juice has been used as a vegetable dye
since at least the sixteenth century. It was fashionable in Britain during
Victorian times, for instance, where it was used to dye all manner of
foodstuffs, and it was even used as a coloured hair rinse.
There have been repeated attempts to use beetroot
as a natural dye for textiles. Up until 1856, almost all textile dyes were
made from natural sources, such as the leaves, fruits, roots or flowers of
plants, and certain minerals. After 1856, however, things changed when Sir
William Henry Perkin (1838-1907) made mauve, the first synthetic dye, from
aniline obtained from coal tar. Synthetic dyes subsequently replaced natural
dyes in textiles and other industrial applications. However, natural dyes are
making a comeback, in part due to health and environmental concerns about
synthetic dyes, which can be toxic or carcinogen, and are generally
non-biodegradable. Around one-fifth of textile dyes are azo dyes. This type
of dye is particularly harmful and, for instance, is known to trigger
allergies in allergy-sensitive people. In one German study, 30% of children
were found to suffer from some degree of textile-related allergy. Germany has
banned certain synthetic azo dyes due to health and environmental concerns.
Vegetable dyes have therefore grown in popularity
for textile dying, with a growth in the market for natural products and lower
impact dyes. A natural red colour has been hard to achieve, however, with
madder, cochineal, brazilwood and beetroot all failing to meet the required
standard to act as alternatives to synthetic red dyes. The problem with
beetroot dye, in this respect, is that the betanin pigment degrades to give a
brownish or pinkish-cream colour. Moreover, vegetable dyes are water soluble
and have to be fixed, to make the colour fast or permanent, using fixatives
or mordants. The red colour of beetroot cannot be fixed with any of the
mordants traditionally used in textile dying. A method of obtaining a
colour-fast red dye from beetroot would enable it to be exploited as a
natural textile dye.
Some people pass red urine, even after eating a
modest amount of beetroot. This occurs because the pigment betanin passes
straight through their digestive system and is harmlessly excreted in the
urine and stools. This condition is known as beeturia or betacyaninuria.
Betanin and other betalain pigments are usually absorbed by the digestive
system and so do not normally colour the urine so dramatically.
Beeturia produces no ill effects, but it can have
serious consequences if it is misdiagnosed as blood in the urine (haematuria).
An article by Dr. Rees in The Lancet in 1836 relates how a patient on
the verge of being treated for haematuria was re-diagnosed, when the urine by
a mere chance fell to his observation, and "I discovered the red
colouration to proceed from the presence of a vegetable matter. On enquiry,
the patient stated that he had been eating a salad, of which beetroot was an
ingredient". A misdiagnosis of haematuria could initiate unnecessary and
risky treatments. Today, hospitals still get referrals for suspected haematuria,
which turn out to be beeturia.
It has long been know that some individuals
produce pink or red urine after eating beetroot, while others appear immune
to the condition. This observation led scientists in the 1950s to conclude
that beeturia was a genetic trait, that is, an inherited condition that is
passed down through the generations. It is commonly reported that beeturia
occurs in about one person in eight, or in around 10% to 14% of the
population. Zindler and Colovos first reported a figure in this order in
1950. They examined 78 patients and found beeturia in 12.6% of cases. In
1956, Allison and McWhirter found that out of 104 subjects, 10 of them or
9.6% had beeturia. The latter authors postulated that a single recessive gene
controlled the characteristic. However, other scientists, including Penrose
in a letter to the British Medical Journal, were critical of such
studies, which reached conclusions based on insufficient data.
A widely reported figure for beeturia is that it
occurs in 14% of individuals. This derives from a study conducted by Watson
and his co-workers at the Glasgow Royal Infirmary, published in 1963. The
study was initiated after a patient with severe anaphylactic shock was also
found to have gross beeturia. An early theory of beeturia suggested that it
was associated with food allergy. The Glasgow team found that food allergy
was not a factor in causing beeturia. The group, however, did provide a
valuable insight into the condition by looked at beeturia in groups of people
with different clinical conditions. The control group of healthy subjects had
a 13.8% incidence of beeturia, but the clinical group with iron deficiency
had an unusually high incidence of beeturia. Around 80% of the iron-deficient
clinical group had red-coloured urine. Iron-deficiency anaemias in these
patients were caused by several factors, including haemorrhoids, bleeding
peptic ulcers, hernias and poor diet. In further tests, by giving iron to
this iron-deficient group, along with a standard amount of beetroot, the
incidence of beeturia was reduced to around 49%.
The Glasgow study started a shift away from
regarding beeturia as being primarily a genetic condition, toward one that is
environmentally determined. Studies have now demonstrated that environmental
factors are the main determinants of beeturia, with genetic factors at best
only having a small influence by increasing susceptibility to the condition.
Steve Mitchell, from Imperial College in London, evaluated all the available
data on beeturia in 2001 and concluded that, "beeturia is more a
function of an individual's physiological constitution and not a phenomenon
under direct polymorphic genetic control as originally implied".
A range of evidence has helped to topple the
simple genetic model for beeturia. Firstly, people reported to have beeturia
do not have the condition consistently. The excretion of red urine comes and
goes over time, suggesting additional environmental factors. A study from the
1990s demonstrated that individuals who took the same amount of beetroot on a
number of different occasions showed a wide range of variation in the amount
of betanin they excreted in their urine.
Secondly, as studies of healthy individuals have
accumulated, there has been an increasingly wide range of variation in the
proportion of people reported to have beeturia. Studies conducted in Hungary
in the 1960s and 1970s, for instance, reported close to 100% of subjects
excreting red urine after consuming beetroot. Presumably, some undisclosed
environmental factor in this population was causing the high levels of
beeturia.
Thirdly, the use of spectrophotometry in recent
beeturia studies has shown that there is a continuous spread in the degree of
redness in the urine within a population. If the condition were genetically
controlled there would be distinct categories, such a non-excretors and
excretors. The non-excretors in such studies may simply be producing too
little pigment to be visible to the naked eye. The increasing sensitivity of
the scientific equipment used may also explain the higher recorded incidence
of beeturia in studies since the 1960s.
Fourthly, studies with twins have failed to show
any obvious hereditary pattern for beeturia. Fifth and finally, the type of
beetroot used affected the outcome in one beeturia study, with individuals
giving intensely coloured urine after consuming one cultivar, but a normal
urine colour after eating a different one. Betalain pigment content is known
to vary between beetroot cultivars. Steve Mitchell notes that time of
planting and harvest also influence the pigment content of beetroot, while
some pre-packaged brands enhance beetroot colour by adding concentrated
beetroot extract. Furthermore, chemicals such as oxalic acid and ascorbic
acid, which are found in beetroot, can limit the digestive system's ability
to process betalains. All in all, these factors make the wide variation in
the reported incidence of beeturia unsurprising.
Betanin is degraded to a certain extent in the
stomach, by the acids present and through bacterial action, but the pigment
is mainly absorbed in the colon or large intestine. An acceptor substance
usually transports ingested betanin through the intestinal wall; therefore
little is recovered from the urine. In contrast, if betanin is injected into
the bloodstream, bypassing the digestive system, most of it is recovered in
the urine.
In cases of beeturia, the absorption process in
the intestine is disrupted. Iron deficiency appears to be the most effective
disrupter of betanin absorption. The oral administration of iron can
partially rectify the condition. However, there appears to be no simple
correlation between iron levels in the blood and beeturia. If very large
quantities of beetroot are eaten, it should be noted, the pigment will
overload the digestive system's capacity to absorb it and red urine will
almost certainly be excreted.
I thank Jason Avent for comments on this chapter.
Adams, J.P., J.H. von Elbe and C.H. Amundsen
(1976) Production of betacyanine concentrate by fermentation of red beet
juice with Candida utilis, Journal of Food Science, 4: 78-81.
Akita, T., Y. Hina and T. Nishi (2002) New medium
composition for high betacyanin production by a cell suspension culture of
table beet (Beta vulgaris L.), Bioscience, Biotechnology, and
Biochemistry, 66(4): 902-905.
Allison, A.C. and K.G. McWhirter (1956) Two
unifactorial characters for which man is polymorphic, Nature (London),
178: 748-749.
Bauer, J.A. (2001) Study of the metabolic
pathways leading to betanin in Beta vulgaris L. cell cultures by
incorporation of tyrosine and dihydroxyphenylalanine. PhD Thesis, Facultees
Sciences de l'Universitee Lausanne,
Delgado-Vargas, F., A.R. Jimenez and O.
Parades-Lopez (2000) Natural pigments: carotenoids, anthocyanins, and
betalains - characteristics, biosynthesis, processing, and stability, Critical
Reviews in Food Science and Nutrition, 40 (3): 173-289.
Downham, A. and P. Collins (2000) 'Colouring our
foods in the last and next millennium', International Journal of Food
Science and Technology, 35: 2-22.
Forrai, G., G. Bankovi and D. Vaguljfalvi (1982)
Beetinuria: A genetic trait?, Acta Physiol. Acad. Sci. Hung., 59:
265-282.
Forrai, G., D. Vaguljfalvi and P. Bolosky (1968)
Beetinuria in childhood, Acta Paed. Acad. Sci. Hung., 9: 43-51.
Forrai, G., D. Vaguljfalvi, J. Lutter, E. Benedik
and E. Soos (1971) No simple association between betanin excretion and iron
deficiency, Folia Haematol (Liepz), 117: 424-426.
Girod, P.A. and J.P. Zryd (1987) Clonal
variability and light induction of betalain synthesis in red beet cell
cultures, Plant Cell Reports, 6: 27-30.
Hanssen, M. (1984) E for Additives.
London: Thorsons.
Harmer, R.A. (1980) Occurrence, chemistry and
application of betanin, Food Chemistry, 5: 81-90.
Kays, S.J. (1997) Postharvest Physiology of
Perishable Plant Products. Athens, Georgia, USA: Exon Press, pp. 190-201.
Kujala, T.S., J.M. Loponen and K. Pihlaja (2001)
Betalains and phenolics in red beetroot (Beta vulgaris) peel extracts:
Extraction and characterization, Z. Naturforsch., 56c: 343-348.
Kujala, T.S., M.S. Vienola, K.D. Klika, J.M.
Loponen and K. Pihlaja (2002) Betalain and phenolic compositions of four
beetroot (Beta vulgaris) cultivars, European Food Research and
Technology, 214: 505-510.
Leathers, R., C. Davin and J. Zryd (1992)
Betalain producting cell cultures of Beta vulgaris L. red beet, In
Vitro Cell Dev. Biol., 28: 39-45.
Mabry, T.J. and A.S. Dreiding (1968) The
betalaines, Recent Advances in Phytochemistry, 1: 145-160.
Mason, L. (1998) Sugar-plums and Sherbet: The
Prehistory of Sweets. Totnes, UK: Prospect Books.
Mitchell, S.C. (2001) Food idiosyncrasies:
Beetroot and asparagus, Drug Metabolism and Disposition, 29(4):
539-543.
Penrose, L.S. (1957) Two new human genes, British
Medical Journal, 1: 282.
Piattelli, M., L. Minale and G. Prota (1965)
Pigments of Centrospermae III. Betaxanthins from Beta vulgaris L., Phytochemistry,
4: 121-125.
Rees, G.O. (1836) On the analysis of the blood
and urine in health and disease. With directions for the analysis of urinary
calculi, The Lancet, 1: 969-971.
Saldanha, P.H. (1962) On the genetics of betanin
excretion, Journal of Heredity, 53: 296-298.
Saldanha P.H., L.E. Magalhaes and W.A. Horta
(1960) Race differences in the ability to excrete beetroot pigment (betanin),
Nature (London), 187: 806-807.
Sayid, R. (2004) 'The beetroot that doesn't
stain', The Mirror, 3 September, http://www.mirror.co.uk/
Stafford, A. (1991) The manufacture of food
ingredients using plant cell and tissue cultures, Trends in Food Science
Technology, 5(2): 116-122.
Strack, D., T. Vogt and W. Schliemann (2003)
Recent advances in betalain research, Phytochemisty 62: 247-269.
Stintzing, F.C., A. Schieber and R. Carle (2002)
Identification of betalains from yellow beet (Beta vulgaris L.) and
cactus pear (Opuntia ficus-indica (L.) Mill.) by high-performance
liquid chromotography-electrospray ionization mass spectrometry, Journal
of Agricultural and Food Chemistry, 50(8): 2302-2307.
Watson, W.C., R.G. Luke and J.A. Inall (1963)
Beeturia: Its incidence and a clue to its mechanism, British Medical
Journal, 2: 971-973.
Watts, A.R., M.S. Lennard, S.L. Mason, G.T.
Tucker and H.F. Woods (1993) Beeturia and the biological fate of beetroot
pigments, Pharmacogenetics, 3: 302-311.
Zindler, G.A. and G.C. Colovos (1950)
Anthocyaninuria and beet allergy, Annals Allergy, 8: 603-617.
|
|
© Copyright Stephen Nottingham, 2004
sf.nottingham@btinternet.com
No comments:
Post a Comment