Stain-inhibiting agent for dyes with affinity for protonatable nitrogen, compositions containing same and uses thereof

The staining effect (particularly with respect to the staining of polyamides) of a colorant such as a dye used in foods and beverages is inhibited by a compound of the formula ##STR1## wherein: Z.sup.1, Z.sup.2, and Z.sup.3 are the same or different and are each a bridging radical or a direct bond, PA1 Ar.sup.1, Ar.sup.2, and Ar.sup.3 are the same or different and are aromatic or bicyclic radicals; PA1 Q is a fused, partially aromatic bicyclic radical, PA1 or Q is a carbohydrate residue having a non-repeating structure, in which case m is 1, or Q is a carbohydrate having repeating saccharide units, in which case Q along with its substituents is repeated m times, where m is the number of said repeating saccharide units, but PA1 when Q is not a carbohydrate residue, m is 1; PA1 R.sup.1, R.sup.2, and R.sup.3 are H or polyhydroxybenzoyl, PA1 R.sup.4, R.sup.5 and R.sup.6 are H or the residue of an esterified alcohol, PA1 x, y, and z are from 2 to 3, PA1 a, b, and c are from 0 to 1, PA1 n is from 0 to 1, except that when Q is an oligo- or polysaccharide having terminal saccharide units, n, in the terminal saccharide units, is from 0 to 2, and PA1 when n is zero, --Z.sup.1 --Q.sub.m --Z.sup.2 -- is optionally a direct bond. Examples of these stain-inhibiting compounds include tannic acid, green tea extract, epicatechin gallate, and the reaction product of gallic acid and a carbohydrate.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to the art of inhibiting the staining action certain 
dyes by means of a stain-inhibiting agent. An aspect of this invention 
relates to artificially colored compositions (particularly ingestible 
compositions) in which the artificial colorant is an ingestible dye having 
an affinity for protonatable N-atoms, which artificially colored 
compositions further contain the stain-inhibiting agent. Still another 
aspect of this invention relates to a method for formulating food products 
or for forming a barrier against the staining of protonatable 
nitrogen-containing polymers such as polyamides (e.g. nylon, silk, wool, 
etc.) and other polymeric materials, particularly household materials, 
which contain protonatable nitrogen atoms. 
2. Description of the Prior Art 
Materials colored with insufficiently-fixed dyes that "run" or "bleed" or 
create stains are a familiar problem. 
In the case of a single instance of staining of a garment or carpet or 
other fibrous material, the problem may appear to be small in economic 
terms, but the cumulative impact on marketing, particularly in the food 
industry, can be enormous. The consumer acceptance of several types of 
foods (particularly soft drinks or other types of drinks, baked goods, 
candies, cake mixes, gelatins, puddings, and other highly processed foods) 
can be adversely affected by dye migration or staining. For example, if a 
highly processed food product containing a dye approved for human 
consumption (in the U.S., these are generally the F, D & C dyes) packaged 
with a material containing a polyamide, and the dye migrates to and stains 
the polyamide, the internal appearance of the food package can be too 
aesthetically displeasing to be sold, even though the packaged product is 
perfectly safe to eat. This problem is sometimes referred to as "color 
bleed". 
Consumer acceptance of artificially colored food products can also be 
adversely affected by stubborn stains produced by inadvertent spills on 
materials commonly found in homes, e.g. melamine-formaldehyde sheets on 
counter tops, polyamide fibers (particularly in wool or nylon carpets, 
clothes, including silk clothes, drapes, and other woven and nonwoven 
materials), etc. Soft drinks are especially likely to stain clothes, 
counter tops, drapes, and carpets, even though these drinks may contain 
only parts per million of the non-toxic dye. 
Various stain-blocking agents have been investigated in terms of their 
ability to block or inhibit the staining action of the ingestible, 
non-toxic dyestuffs used in highly processed foods. Some of these agents 
are referred to as "resist agents" and can be anionic due to the presence 
of carboxylate (--COO.sup.-) and/or sulfonate (--SO.sub.3.sup.-) groups. 
Typically, these agents are polymers of acrylic acid or, more typically, 
sulfonated aromatic compounds. See, for example, U.S. Pat. Nos. 4,780,099 
(Greschler et al), issued Oct. 25, 1988, and 5,096,726 (Keown et al), 
issued Mar. 17, 1992. Treatment of synthetic polyamides with sulfonated 
aromatic compounds after dyeing of the polyamide is described in U.S. Pat. 
No. 3,790,344 (Frickenhaus et al), issued Feb. 5, 1974. 
One study done by Cook et al in 1977, reported in Textile Res. Journ. 47, 
244-249 (1977) suggests that compounds having a plurality of phenol or 
naphthol rings can serve as stain blockers. 
One commercially available sulfonated aromatic compound ("MESITOL NBS", 
available from Mobay Chemical Co.) known to have stain-resistant 
properties is chemically defined as a sulfonic acid-substituted 
phenol-formaldehyde condensate and is a complex mixture of monomeric and 
polymeric materials which can be separated into a number of fractions 
varying widely in molecular weight. One group of fractions amounting to 67 
weight-% of the mixture appears to be made up of insoluble, relatively 
high molecular weight polymeric material. Monomers and substituted 
monomers account for about 20 weight-%. There also appear to be one or 
more relatively low molecular weight polymeric fractions (the molecular 
weight appears to be roughly in the range of about 600 to 700) which 
apparently account for only about 10% of the total weight of this complex 
mixture. 
Although the sulfonic acid-substituted phenol-formaldehyde condensate 
"resist agents" can be low in toxicity, they are typically synthetic 
compounds not having any close analogs in nature. Obtaining government 
approval for their use in foods involves the same quantum of proof of 
safety as would be required for any artificial food additive. 
Accordingly, although some of these synthetic sulfonated aromatic compounds 
are used in stain-resisting agents applied directly to fibrous materials 
such as carpets, they are not presently used in foods. 
Moreover, a very recent study suggests that only the low molecular weight 
polymeric fraction of the complex sulfonated phenol-formaldehyde 
condensate mixtures (which fraction is typically only about 10% by weight 
of the total mixture) provides a high level of stain-resist activity. The 
monomeric material and the insoluble polymeric fractions appear to have 
only slight stain-resist activity. This study therefore suggests further 
that the efficacy of such stain-resist agents, in terms of activity per 
mole of agent, could be improved significantly. 
The mechanism by which "resist agents" or "stainblockers" or 
stain-inhibiting agents prevent staining is not fully understood, partly 
because the staining action of non-toxic dyestuffs has been studied in 
depth only rarely. According to the study carried out by C. C. Cook et al, 
Textile Research Journal, 47:244 (1977), the stain-inhibiting agent 
creates an electric barrier effect with respect to the anionic 
substituents of typical dyestuffs. The effect of pH on the effectiveness 
of stain-inhibition treatments of nylon is disclosed in U.S. Pat. No. 
4,780,099. P. W. Harris et al, in Textile Chemist & Colorist, 21:25-30 
(1989) have proposed that sulfonated aromatic compounds create a ring 
dyeing effect which hinders diffusion of a stain-causing dye by increasing 
the tortuosity of the diffusant. Since the add-on level of the sulfonated 
aromatic compound is not sufficient to block all the free amine end groups 
throughout the cross section of a polyamide fiber, Harris et al attribute 
stain inhibition to a double layer repulsion of the dye anions by the 
residual anionic charges of the surface-deposited stainblocker. Other 
studies include those of Kamath et al, who have demonstrated the use of 
microspectrophotometry to measure absorbance (see their study of ozone 
fading of disperse dyes in nylon in Textile Research Journal, 53:391 
1983!) and have very recently measured the stain resistance and the 
stainblocker content of stainblocker-treated nylon carpet fibers with the 
aid of microspectrophotometry. Y. K. Kamath et al, "Mechanisms of 
Stainblocker Function in Nylon Carpet Yarns", reported in the proceedings 
of the 1992 AATCC International Conference & Exhibition, pages 230 to 233 
(Oct. 6, 1992); see also the abstract of Session 12, Oct. 6, 1992, 1:30 
p.m., proceedings, Volume 24, No. 9, page 34. 
Kamath et al (in the AATCC proceedings reference cited above) have 
attempted to clarify the mechanism for stain-inhibition activity (toward 
incoming dyes) by attributing some of the activity--in addition to 
activity attributed to the "double layer repulsion" effect proposed by 
Harris et al--to a "diffusion barrier" which inhibits entry and absorption 
or diffusion into the nylon fiber of beth nonionic and anionic molecules. 
The diffusion barrier is described as a cross-linked barrier membrane 
formed by the ionomeric polymer with the polyamide near the surface of the 
polyamide fiber. The findings reported in this reference also provide 
further confirmation for the efficacy of the lower molecular weight 
fractions of the stainblocker. 
An electric or ionic barrier effect, even if not the exclusive mechanism, 
is probably of considerable importance. Another stain-inhibition mechanism 
study, reported in Chapter 4 ("Interactions of Food, Drug and Cosmetic 
Dyes with Nylon and Other Polyamides") by L. L. Oehrl et al, ACS Symposium 
No. 473, Food and Packaging Interactions II, S. J. Risch et al, Editors, 
American Chemical Society, 1991, pages 37 to 52, concludes that the 
staining action of water-soluble dyestuffs containing sulfonate groups 
(--SO.sub.3.sup.-) or other anionic solubilizing groups is largely an 
acid-base reaction which results in the formation of ionic bonding. 
Anionic solubilizing groups such as the --SO.sub.3.sup.- of F, D & C dyes 
can, of course, exist in either the salt form (e.g. --SO.sub.3 Na) or the 
sulfonic acid (--SO.sub.3 H) form, but in acid media, one would expect the 
sulfonic acid form to predominate. The stainable substrate (material which 
becomes stained) can contain one or more nitrogen-containing sites capable 
of accepting a proton. For example, the stainable substrate can comprise a 
polymer having such protonable sites in side chains, repeating units, or 
end groups, as in the case of the primary amine terminus of a polyamide or 
polypeptide, a pendent amine group attached to an amino acid unit or a 
melamine ring, or some other non-terminal group with a primary, secondary, 
or tertiary nitrogen atom with a moderately or strongly nucleophilic 
unbonded electron pair (including the --NH-- of a polyimide) or one or 
more combinations of these protonatable nitrogen sites. Perhaps the most 
common of these protonatable nitrogen sites is the primary amino group 
(--NH.sub.2). Because the colored (stain-causing) material which comes 
into contact with the stainable substrate typically has a Ph less than 7 
and typically contains some sulfonic acid groups, transfer of a proton 
from an --SO.sub.3 H group to an N-atom should be possible. Upon 
protonation of that N-atom, a cation is formed, and the cation can form an 
ionic bond with a sulfonate group of the water-soluble dyestuff. When the 
protonation is a direct transfer of the proton of a sulfonic acid group on 
the dyestuff molecule to a protonatable nitrogen of the stainable 
substrate, the staining action can be viewed as an acid-base reaction. 
This theory of staining protonatable N-containing materials is supported by 
evidence showing that staining or dye uptake by the stainable substrate is 
maximized at a pH below about 4. However, dye uptake does not always keep 
getting worse as the pH decreases and may level off or even diminish 
slightly at a pH below about 1 or 2. Oehrl et al account for the decrease 
in dye uptake at very low pH values by suggesting that, at these low pH 
values, each dyestuff molecule becomes more efficient in protonating 
nitrogen atoms, hence fewer dyestuff molecules are taken up by the 
substrate. The maximum number of dyestuff molecules taken up by the 
stainable substrate appears to be reached somewhere within the pH range of 
about 2 to about 4, which happens to encompass the pK.sub.a values of 
acids commonly used in foods, e.g. citric acid (pK.sub.a =3.13). 
Oehrl et al explain how dye uptake by the stainable substrate can be 
reliably measured in experiments conducted in a manner analogous to dye 
bath treatments; the stainable substrate is immersed for some specified 
period of time (e.g. one hour) in a bath containing the dyestuff, and, 
after removal of the substrate, the amount of dye remaining in the bath 
can be measured; in extreme cases &gt;60%--sometimes even &gt;80%--of the 
dyestuff is taken up by the stainable substrate; far less than this amount 
of uptake will produce a visible stain. 
Mildly alkaline agents are not very suitable as stain-inhibiting agents for 
a variety of reasons. For example, some colored materials simply cannot b 
a marketed unless their pH is less than 7; a typical pH range for such 
colored materials is about 2 to about 4, which is exactly in the most 
dangerous pH range from the standpoint of staining with typical F, D & C 
dyes. 
Given the likelihood of at least a partial role for the ionic or acid-base 
theory of staining protonatable N-containing polymeric materials, it 
should follow that a layer of a colorless compound having a plurality of 
its own anionic groups could provide a barrier to staining by taking up 
the dye in preference to the N-containing polymeric material or perhaps by 
repelling the dye. Of course, surface phenomena must be taken into 
account, because the person skilled in the art is typically dealing with 
dye migration or accidental spills, not the complete immersion of a 
stainable substrate in a dyebath for a prolonged period of time. The 
greater the surface-wettability of the stainable substrate, the greater 
the stain. 
Whether or not these theories are valid, there is still a need for 
stain-inhibiting agents suitable for addition to foods which have very 
close analogs among natural materials or are themselves extracts or 
components of natural materials, so that, in use, a high level of safety 
in edible products (particularly human-edible products) will be more 
likely. 
SUMMARY OF THE INVENTION 
It has now been discovered that a class of polyhydroxy (including 
dihydroxy) aromatic ring-containing compounds (which can, if desired, be 
free of sulfonic acid or sulfonate groups) is surprisingly effective in 
inhibiting the stain-producing action of dyes and colored materials, at 
least in those situations in which the stainable substrate (material 
exposed to staining) contains a polymeric material having protonatable 
nitrogen sites. This class of polyhydroxyaromatic compounds can be found 
in extracts obtained from certain naturally occurring materials, and, for 
purposes of the present invention, these naturally-occurring materials are 
a preferred source of the compounds. 
The above-mentioned class of polyhydroxaromatic compounds useful in this 
invention can be represented by formula I: 
##STR2## 
wherein: Z.sup.1, Z.sup.2, and Z.sup.3 are the same or different and are 
each a bridging radical (e.g. --O--CO--) or a direct bend, 
Ar.sup.1, Ar.sup.2, and Ar.sup.3 are the same or different and are each a 
monocyclic aromatic radical or a bicyclic-radical comprising an aromatic 
ring fused to a six-member cyclooxaaliphatic ring (e.g. a bicyclic radical 
such as a benzodihydropyranyl group); 
Q is a fused aromatic ring-containing bicyclic radical (e.g. a 
benzotropolone structure, a benzocylohexenone structure, a 
benzodihydropyranyl structure, or a similar benzocyclooxaaliphatic or 
benzocyclohexenone or benzocycloheptenone structure, all of which can be 
substituted or unsubstituted), 
or Q is a carbohydrate residue which has either a non-repeating structure 
(e.g. the residue of a monosaccharide) or a repeating structure (e.g. the 
residue of an oligo- or polysaccharide having m units); and when Q is a 
carbohydrate residue and said carbohydrate residue is an oligo- or 
polysaccharide residue, Q along with its substituents is repeated m times, 
where m is from 2 up to the number of repeating saccharide units in the 
oligo- or polysaccharide, but when Q is not a carbohydrate residue, m is 
1; 
R.sup.1, R.sup.2, and R.sup.3 are the same or different and are each 
hydrogen or a polyhydroxybenzoyl radical such as 3,5-dihydroxybenzoyl or 
3,4,5-trihydroxybenzoyl (galloyl), 
R.sup.4, R.sup.5, and R.sup.6 are the same or different and are each H or 
the residue of an esterified alcohol, 
x, y, and z are the same or different and are each a number from 2 to 3, 
a, b, and c are the same or different and are each a number from 0 to 1, 
n is a number from 0 to 1, except that when Q is an oligo- or 
polysaccharide having terminal saccharide units, n, in the terminal 
saccharide units, is from 0 to 2, and 
when n is zero, --Z.sup.1 --Q.sub.m --Z.sup.2 -- is optionally a direct 
bond; however, if --Z.sup.1 --Q.sub.m --Z.sup.2 -- is a direct bond, it is 
particularly preferred that the compound of formula (I) not be synthetic 
but be obtained from natural sources (e.g. by extraction, isolation, and 
purification). Presently, the only case in which synthetic compounds can 
perform as well as naturally occurring compounds are those in which Q is a 
carbohydrate residue. 
In one aspect of this invention, a compound of formula I is included in a 
colored composition wherein the colorant is a dye reactive with the a 
protonatable nitrogen of a polymeric material containing a protonatable 
nitrogen site, e.g. an amine group pendent from, or at the terminus of, a 
polymeric series of repeating units. A preferred embodiment of such a 
colored composition is a food product, particularly a food product having 
a pH less than 7 (1 wt. % in water, 23.degree. C.). 
Compounds of formula I can be made by total synthesis or partial synthesis 
from known starting materials (e.g. by esterifying a known polyol or 
carbohydrate with a polyhydroxybenzoic acid such as gallic acid). It is 
ordinarily preferred however that compounds of formula I be obtained by 
extraction from plant matter such as leafy materials, fruits, trees (e.g. 
tree bark), shrubs, or flowering plants. 
A further aspect of this invention relates to methods for formulating 
artificially colored food products in which a compound of formula I is 
included as a stain-inhibiting agent. 
Another aspect of this invention relates to treatment of a stainable 
substrate with a compound of formula I before or simultaneously with the 
exposure of the stainable substrate to a dye reactive with the a 
protonatable nitrogen of a polymeric material containing a protonatable 
nitrogen site. 
DETAILED DESCRIPTION 
Because the aromatic ring-containing compounds useful in this invention can 
be free of --SO.sub.3 radicals, it would appear that they inhibit staining 
through a different mechanism as compared to prior art sulfonated 
phenol-containing stainblocking agents. Moreover, although this invention 
is not bound by any theory, the single phenolic hydroxyl group found on 
each aromatic ring of a typical phenol-aldehyde condensate is believed to 
be insufficient by itself to provide any stain-inhibiting effects, but the 
plurality of phenolic hydroxyl groups on each aromatic monocyclic or 
partially aromatic fused bicyclic structure of the class of compounds 
useful in this invention is believed to be involved in stain inhibition, 
perhaps through a relatively weak type of association with protonatable 
nitrogen or with NH which bears some resemblance to hydrogen bonding. 
Again, this invention is not bound by any theory, but it is believed that 
this relatively weak association is strengthened when the 
polyhydroxyaromatic compound has a molecular weight above about 200, 
preferably above 300. Low molecular weight polyhydroxyaromatic (including 
dihydroxaromatic) compounds such as pyrogallol and resorcinol do not 
appear to exhibit stain-inhibiting activity, and it is theorized 
that--particularly in the presence of liquid water--any association 
between these low molecular weight compounds and protonatable nitrogen- or 
NH-containing groups on the stainable substrate is very short-lived or 
easily overcome. Thus, polyhydroxyaromatic compounds useful in this 
invention typically have molecular weights in excess of 200, more 
typically &gt;300, and their molecular weights can extend well into the 
thousands for oligo- and polysaccharides naturally or synthetically 
esterified with polyhydroxybenzoic acid residues (e.g. gallic acid 
residues). 
In the case of polyhydroxbenzoic acid esters of high molecular weight 
.alpha.- and .beta.-glycosides such as cellulose or starch, where the 
number of repeating glycoside units can reach about 4000, molecular 
weights up to 500,000 or even a million are a theoretical possibility, but 
no advantage appears to be gained by using such enormous polymeric 
molecules as stain-inhibiting agents. Moreover, these large molecules may 
fail to reach the protonatable nitrogen sites on the stainable substrate 
before stains begin to form. Accordingly, oligosaccharides with about 2 to 
10 repeating saccharide units or partially hydrolyzed glycosides having 
less than 1500 repeating glycoside units are preferred over unmodified 
cellulose or starch as polyols to be esterified with polyhydroxaromatic 
compounds. 
Preferred Stain-Inhibiting Agents 
Stain-inhibiting agents useful in this invention typically contain 
compounds of the formula 
##STR3## 
wherein: x' is a number from 2 to 3; 
t is 0 or 1, and when t=0, there is a direct bond from Q to Ar.sup.4 ; 
Ar.sup.4 is a monocyclic aromatic radical or a bicyclic group in which one 
of the rings is a benzene ring and the other ring, to which the benzene 
ring is fused, is a partially unsaturated cycloaliphatic or 
cyclooxaaliphatic ring; thus, when Ar.sup.4 is bicyclic it is typically a 
benzodihydropyranyl structure; 
Q is the residue of a carbohydrate having m repeating saccharide units; m 
being at least 1, or m=1 and Q is a fused aromatic ring-containing 
bicyclic radical (e.g. a benzotropolone structure, a benzocylohexenone 
structure, a benzodihydropyranyl structure, or a similar 
benzocyclooxaaliphatic or benzocyclohexenone or benzocycloheptenone 
structure); and 
n' is a number from 2 to 3, unless Q is the residue of a carbohydrate 
having a plurality of repeating saccharide units; in which case, when Q is 
a terminal saccharide unit, n' is a number from 2 to 4. 
The tropolone ring is peculiar to certain naturally occurring materials; it 
is a C.sub.7 (cycloheptatrienolone) ring with sufficient aromaticity 
(resonance stabilization) to be characterized as "aromatic". Thus, when Q 
is a bicyclic structure comprising a benzene ring fused to a tropolone 
ring, Q in this case can be a benzotropolone (benzocycloheptenone) such as 
3,4,6-trihydroxy-5H-benzocyclohepten-5-one. 
In one preferred embodiment of formula II, Ar.sup.4 is a substituted 
benzene ring, Q is the residue of a mono-, oligo-, or polysaccharide 
having m units, t=1, and n' is typically 2 or 3, more typically 2, in the 
intermediate saccharide units of a saccharide chain, and n' is typically 3 
or 4 (usually 3) in the terminal units. The residues of an 
"oligosaccharide" can be residues of disaccharides such as sucrose, 
lactose, and the like. Typical polysaccharide residues include starch, 
partially hydrolyzed starch, naturally-occurring gums, and other 
carbohydrate residues having up to about 1500 repeating saccharide units. 
(Polysaccharides having up to 4000 units can of course be esterified with 
gallic acid, but as pointed out previously, there appears to be no 
advantage to such enormous molecules in the context of this invention.) 
The preferred monosaccharide or saccharide unit of the oligo- or 
polysaccharide is a hexose such as glucose or fructose. 
Thus, when Q of formula II is the residue of a monosaccharide or an oligo- 
or polysaccharide having m units, the compounds of formula II are 
tannin-like substances such as tannic acid or a substance that bears a 
strong resemblance to tannic acid and other naturally-occurring compounds 
containing residues of ketohexose-like or aldohexose-like polyols in which 
the OH groups of the polyol (aldohexose or ketohexose) are esterified with 
a trihydoxybenzoic acid such as gallic acid (3,4,5-trihydroxybenzoic 
acid). Although the galloyl structure is not required in every compound or 
stain-inhibiting agent found useful in this invention, the galloyl 
structure is believed to be important because it contributes to the 
overall stain-inhibiting structure several adjacent or nearly adjacent 
phenolic hydroxyl groups and a substantial molecular mass increment. Not 
only do these overall stain-inhibiting structures have a molecular weight 
well in excess of 300, they also have, typically, nine phenolic hydroxyls 
per molecule or per repeating unit. 
Tannins can be extracted from the bark of trees (e.g. oak trees) and from 
various fruits and leafy materials such as tea leaves or brewed tea. Some 
varieties of tea also contain materials which are detrimental to the 
objectives of this invention (e.g. compounds which produce stains), but 
such materials can be separated out with thin-layer chromotography. Brewed 
green tea is particularly preferred. 
Tannic acid is a preferred stain-inhibiting agent of this invention, and 
the so-called hydrolyzable tannins are particularly preferred. 
Commercially-available tannic acid obtained from natural sources (usual 
empirical formula given as C.sub.76 H.sub.52 O.sub.46) contains about 10% 
water and is water soluble. It may be a trisaccharide ester. It is a 
yellowish white to light brown, amorphous powder and is virtually 
non-toxic even in rather large doses (LD.sub.50, oral, in mice=6.0 g/kg). 
Tannic acid behaves like a strong organic acid, showing an inflection 
point at a pH of about 4.5 when titrated with NaOH. 
Another preferred type of stain-inhibiting agent contains a compound of the 
formula III 
##STR4## 
where t is 0 or 1, and when t=0, there is a direct bond from Q to 
Ar.sup.4, 
x' is a number from 2 to 3, 
a' is 0 or 1, and where a'=1, R is H or the residue of an esterified 
alcohol, 
Ar.sup.4 is as defined previously, 
Q is either a direct bond, in which case the radical 
##STR5## 
is dimerized, or Q is a bicyclic structure comprising a benzene ring fused 
to a partially unsaturated cycloaliphatic ring, e.g. a benzotropolone or 
benzocyclohexenone structure. 
Compounds of this type include the granatins, epigallocatechin gallate, 
epicatechin gallate, theaflavin, and the like. Granatin A can also be 
called .beta.-1,6 (s) hexhydroxydiphenoyl-D-glucose, hexahydroxydiphenic 
acid. Granatin B can also be called .beta.-1,0 galloyl 
(R)-hexahydroxydiphenic acid, linked 3,6, dehydrohexahydroxydiphenic acid 
linked 2,4. 
Particularly preferred natural sources of stain inhibitors of formula I 
(which formula is intended to encompass formulas II and III) include tea, 
strawberries, pomegranates, crabapples, stripe alder trees, forsythia, and 
oak trees. 
Compounds of formula II in which Q is a carbohydrate such as a sugar can be 
obtained either by extraction from natural substances or by synthesis from 
the carbohydrate+gallic acid, in the presence of an acid catalyst 
typically used in Fischer esterification, e.g. a mineral acid such as 
sulfuric acid. The stain-inhibiting activity of these esterified 
carbohydrates is, however, lower than that of tannic acid obtained from 
natural sources such as tree bark. 
The preferred carbohydrates are monosaccharides with a C.sub.6 -skeleton, 
e.g. glucose, mannose, fructose, galactose, and the like. For stain 
inhibition, optical isomerism appears to be relatively unimportant, hence 
D- and L-forms, racemic mixtures, etc. all appear to be useful in this 
invention. Tetroses and pentoses are less preferred, as are carbohydrate 
derivatives such as sorbitol and mannitol. 
Esterification of a sugar with gallic acid is carried out by mixing these 
two starting materials together and adding 5 weight-% H.sub.2 SO.sub.4 in 
excess, then boiling the reaction mixture until the equilibrium position 
is reached. The gallate ester is then extracted from the reaction medium 
with a simple ester such as ethyl acetate. 
A similar procedure can be used to esterify 
3,4-dihydro-2H-1-benzopyran-3,5,7-triol with gallic acid. 
The following compounds, which can be extracted from naturally-occurring 
plant matter, are particularly preferred for use as stain-inhibition 
agents in compositions and methods of this invention. 
______________________________________ 
Compound Name or Type Formula No. 
______________________________________ 
Corilagin (typical tannic acid component) 
I 
Catechin, 2-(3,4-dihydroxyphenyl)-3,4-dihydro- 
IIa 
2H-1-benzopyran-3,5,7-triol 
Epigallocatechingallate esters 
IIb 
Epigallocatechin gallate IIc 
Epicatechin gallate IId 
Theaflavin, 1,8-bis(3,4-dihydro-3,5,7-trihydroxy- 
III 
2H-1-benzopyran-2-yl)-3,4,6-trihydroxy-5H- 
benzocyclohepten-5-one 
Typical granitins IV 
______________________________________ 
##STR6## 
##STR7## 
##STR8## 
##STR9## 
Optimum stain inhibition appears to be obtained with trihydroxybenzoates o 
oligosaccharides (e.g. oligosaccharide gallates) having repeating hexose 
units and molecular weights in -the range of about 600 to about 2200. 
Concentrates containing very high levels of such compounds are preferably 
isolated from tea (e.g. brewed tea) by means of thin layer chromotography. 
Trihydroxybenzoyl triesters of hexose monosaccharides (empirical formula 
C.sub.27 H.sub.24 O.sub.18) are less effective in this invention as 
compared to the natural tannic acid-like compounds separated from tea. 
These natural compounds are believed to be essentially gallic acid esters 
of di-, tri-, and/or tetrasaccharides; the chemistry of these 
naturally-occurring substances is complex and oftentimes cannot be 
represented accurately by a single compound. Moreover, polyhydroxybenzoic 
acids are, in effect, bifunctional from a polymerization standpoint (like 
hydroxycarboxylic acids) and can form polyesters having two or more 
repeating ester units. 
Preferred Colored Products Containing Stain-Inhibiting Agents 
As indicated previously, highly processed foods artificially colored with 
dyes approved for food, drug, and cosmetic use are examples of preferred 
products to which the stain-inhibiting agents can be added. The preferred 
colorants are dyes generally considered safe for ingestion by humans, 
including F, D & C dyes such as Brilliant Blue (F D & C Blue No. 1), 
Indigo Disulfoacid (F D & C Blue No. 2), Fast Green FDF (F D & C Green No. 
3), Erythrosine (F D & C Red No. 3), Ponceau SX (F D & C Red No. 4) Allura 
Red (F D & C Red No. 40) , Sunset Yellow (F D & C Yellow No. 6), 
Tartrazine (F D & C Yellow No. 5), Orange B, and similar soluble dyes 
containing anionic groups. 
At first glance, many of these dyes appear to have very little in common 
from a molecular structure standpoint. There are at least two F, D & C 
dyes which are triarylmethanes (Blue 1 and Green 3), one indigoid (Blue 
2), one xanthene (Red 3), three monoazos (Red 4, Red 40, Yellow 6), at 
least one pyrozolone (Yellow 5, which also has a monoazo group). Certain 
dyes which still carry an "F D & C" designation as a kind of shorthand 
identification have been "delisted" and are no longer considered safe for 
ingestion by humans, e.g. Orange I and Orange II. The delisted dyes are of 
course less preferred. The preferred dyes are generally artificially 
synthesized from starting materials obtained from non-edible sources such 
as petrochemicals, coal derivatives, and the like. These dyes, being 
synthetic rather than natural, are separate ingredients which do not occur 
in foods except as additives. 
Despite fundamental differences in structure, all of these dyes have at 
least one anionic group substituted on a benzene or naphthalene ring 
structure, typically for the purpose of improving water solubility. The 
anionic group is generally the sulfonate radical (--SO.sub.3.sup.-), which 
can either be in salt form (e.g. --SO.sub.3 Na or an internal salt form) 
or acid form (--SO.sub.3 H); most typically, the commercial form of the 
dye contains at least one sodium sulfonate group substituted on a benzene 
or naphthalene ring structure. The sulfonated benzene can be fused to a 
ring of the dye structure but is more typically an independent ring 
directly attached to an azo group or indirectly linked to a triarylmethane 
structure or whatever the dye moiety happens to be. 
Although this invention is not bound by any theory, it is presently 
believed that the sulfonate or sulfonic acid auxochrome attached to the 
aromatic ring is the moiety common to all these dyes which probably plays 
a major role in the proposed acid-base or ionic-bonding mechanism of stain 
formation. Thus, all of these dyes could be represented by the general 
formulas 
DYE-Ar--SO.sub.3.sup.- or, in the case of the fused aromatic ring, 
DYE(Ar--SO.sub.3.sup.-) where Ar is aromatic, typically a benzene ring, but 
Ar can also be a naphthalene group. 
Although these dyes, being water soluble, can be easily washed off some 
substrates, they may adhere stubbornly to polyamides, polyimides, 
melamine-formaldehyde resins, polypeptides with free (e.g. terminal) 
primary or secondary amino groups, and similar polymeric materials, 
probably for the reasons outlined above (i.e. the acid-base or 
ionic-bonding stain formation mechanism). Therefore, according to one 
concept of this invention, the stain-inhibiting agent somehow interferes 
with interactions between sulfonate or sulfonic acid groups and protonated 
or protonatable nitrogen sites on these polymeric materials. In the case 
of ionic bonding, the stain inhibitor should protect an already-protonated 
nitrogen; in the case of the acid-base mechanism, the stain inhibitor 
would have to inhibit the transfer of a proton from --SO.sub.3 H to the 
unbonded electron pair on the nitrogen atom. 
The amount of ingestible dye needed to provide deep shades of blue, yellow, 
green, red, purple, orange, etc. is relatively small compared to the 
weight of the complete food product, e.g. &lt;1000 parts-per-million, by 
weight (ppm), of a fully constituted food product (including any diluents) 
or &lt;5 wt.-% of a concentrated food product. Amounts less than 100 ppm, 
e.g. 1 to 50 ppm are conventionally used in fully constituted, highly 
processed food products (in the case of concentrates and powdered products 
prior to diluton, the ppm level is 1 to 3 orders of magnitude larger. 
Other artificial and synthetic additives include ingestible carboxylic 
acids (e.g. citric acid), sweetners, preservatives (butylated 
hyroxyaromatic compounds, sorbates, etc.), anti-caking agents (sulfates, 
phosphates, etc.), artificial flavors, synthetic vitamins and minerals, 
and the like. Other ingredients include malto-dextrin, sugars and other 
carbohydrates, natural flavors, and the like. The presence of these 
additives (or of sucrose or other sugars) appears to have no adverse 
effect upon the stain-inhibiting activity of the stain inhibitors used in 
this invention. 
Particularly preferred colored food products of this invention are powdered 
materials which can become drinks when blended with water, e.g. powdered 
imitation fruit juices, punches, etc., including powdered orange juices 
such as TANG.RTM. and powdered sweet drinks such as KOOL-AID.RTM.. Some of 
these powders contain citric acid or some similar ingestible organic acid 
which can provide an aqueous solution with a pH of from 2 to 4 when 
present in the solution at a concentration ranging from 0.001 to about 
0.1N, more typically 0.01N to about 0.1N. The amount of stain-inhibiting 
agent added to the colored food product is generally in the range of about 
1 to about 2000 ppm, based on the weight of the fully constituted food 
product. Up to 8000 ppm of the stain inhibitor can be used, but no 
substantial improvement in stain inhibition is observed with &gt;2000 ppm, 
and very substantial stain inhibition is achieved with as little as 8 to 
50 ppm. From the standpoint of cost effectiveness, about 50 to about 500 
ppm of stain inhibitor are preferred, and some of the stain inhibitors of 
this invention lack water solubility (and probably become aqueous 
dispersions) at levels beyond the 50-500 ppm range. When small amounts of 
anionic or nonionic detergent are added along with the stain inhibitor, 
practical effective levels of stain inhibitor can be lowered to as little 
as 10 ppm. The preferred anionic detergents contain sulfonate groups, as 
in the case of the sulfosuccinate diester detergents. 
Particularly preferred food products besides powdered drinks include 
carbonated beverages, gelatins, puddings, and candies. 
When a preferred food product is formulated according to this invention; 
a. a food ingredient is colored with a color-imparting amount of a 
water-soluble dyestuff having sulfonate radicals (e.g., an F, D & C dye), 
and 
b. the potential staining action of the thus-colored food product is 
inhibited, with respect to a material having protonatable N-containing 
sites, e.g. a polyamide, by adding to the food product a stain-inhibiting 
agent comprising a plant matter extract containing a compound of formula 
I. As explained above, it is theorized that the stain-inhibiting agent 
forms a barrier against the staining of materials such as polyamides by 
becoming associated with a protonatable nitrogen atom in a linear 
polyamide chain or at an --NH.sub.2 terminus of such a chain, the 
association with the protonatable nitrogen atom of the amine group 
involving a plurality of phenolic hydroxyl groups present in the 
stain-inhibiting agent. 
Inhibition or Prevention of Staining 
When nylon (e.g. nylon 6 or nylon 66) is first treated with a 1% by weight 
solution of a stain inhibitor of this invention and then dyed with F, D & 
C Red 40, the protective effect is comparable to a sulfonated 
phenol-aldehyde condensate such as MESITOL NBS (trademark). Further tests 
demonstrate the presence of a chemical bond of some sort between the stain 
inhibitors of this invention and linear aliphatic polyamides (e.g. of the 
nylon 6 or nylon 66 type). Indeed, the stain inhibitors useful in this 
invention are generally most effective in protecting this type of 
polyamide, and also the linear aromatic polyamides, but at least some 
protection of almost any protonatable nitrogen-containing polymer can be 
obtained, the polymers (besides linear aliphatic and aromatic polyamides) 
of greatest interest being protein-like or polypeptide materials (wool, 
etc.) and melamine-aldehyde condensates. 
As used in this specification, the term "polyamide" is intended to include 
linear polyamides (derived from lactams or from the interaction of 
difunctional acid halides or difunctional carboxylic acids with 
difunctional amines or from amino acids), polymers of amino acids 
(including proteins), and crosslinked or crosslinkable polyamides derived 
from the interaction of carboxylic acids (or acid halides) and amines 
having a functionality &gt;2. Because of the ready availability of 
caprolactam, pyrrolidone, adipic acid, hexamethylene diamine, sebacic 
acid, amine-substituted higher aliphatic carboxylic acids, phenylene 
diamine and its analogs, and terephthalic and isophthalic acid, the 
conventional nylons and aromatic polyamides (especially amine-terminated 
nylons) are of particular interest from the standpoint of stain inhibition 
or prevention. 
Stain-inhibiting agents useful in this invention are less effective in 
re-solubilizing stains than they are in preventing the stain in the first 
place. Accordingly, to protect a polymeric material containing 
protonatable nitrogen sites, stain-inhibiting a amount of the 
stain-inhibiting agent is generally applied to the polymeric material 
before or simultaneously with the dye rather than after the dye. 
The following Examples illustrate the principle and practice of this 
invention without limiting its scope.

EXAMPLE 1 
Tannic Acid As Stain-Inhibiting Agent 
To investigate the stain-inhibiting properties of tannic acid, three 
solutions were prepared from the commercial product cherry KOOL-AID.RTM., 
a powdered mixture containing citric acid, maltodextrin (from corn), 
calcium phosphate (anti-caking agent), flavoring agents, vitamins, 
minerals, butylated hydroxyanisole, and F, D & C dyes. Each solution was 
prepared by mixing 1 gram of the KOOL-AID.RTM. powder with enough water to 
make 450 to 500 cm.sup.3 of solution. 
Solution 1A: prepared as set forth above, no sugar added. 
Solution 1B: Solution 1A+50 parts per million (ppm) tannic acid (certified, 
Fisher Scientific Co.). 
Solution 1C: Solution 1A+200 ppm tannic acid (same tannic acid as in 
Solution 1B, hereafter "TA"). 
After the solutions were prepared, four 1 in.sup.2 (6.45 cm.sup.2) samples 
(Carpet Samples 1A, 1B, 1C, and Control) were cut from twisted, heat-set 
66 nylon carpet, mock-acid dyed, and four 1-gram samples of 66 nylon skein 
(Test Fabrics, Middlesex, N.J.) were obtained (Yarn Samples 1A, 1B, 1C, 
and Control). Carpet Samples 1A, 1B, and 1C were soaked in 50 ml. of 
Solutions 1A, 1B, and 1C, respectively, for 1 minute, and allowed to dry 
for 24 hours. The Carpet Control Sample was not exposed to any of the 
solutions. The same procedure was followed with Yarn Samples 1A, 1B, 1C, 
and Control. (The carpet and skeins had been scoured in 0.1% non-ionic 
detergent to remove surface grease and finish.) 
All samples were rinsed thoroughly in distilled water, and allowed to dry. 
The amount of staining on each sample was evaluated by comparison with the 
AATCC Staining Scale (AATCC Test Method, 175-1991), and by the CIE L, a, b 
values obtained from the Minolta Chromameter. 
The results are set forth in Table 1. 
TABLE 1 
______________________________________ 
AATCC Staining 
Sample (ppm TA) Scale Rating L, a, b 
______________________________________ 
Carpet Control 10 85, -1, 2 
Carpet Sample 1A (no TA) 
2 67, 34, 12 
Carpet Sample 1B (50) 
6 78, 9, 3 
Carpet Sample 1C (200) 
10 83, 0.8, 2 
Yarn Control 10 92, -0.8, 2 
Yarn Sample 1A (no TA) 
1 69, 41, 15 
Yarn Sample 1B (50) 
7 81, 12, 4 
Yarn Sample 1C (200) 
9 83, 8, 4 
______________________________________ 
EXAMPLE 2 
Green Tea Extract as Stain-Inhibiting Agent 
The procedure in this Example was similar to that of Example 1. 
1. Fifty grams of Chinese green tea leaves were extracted twice with 80/20 
(v/v) acetone/water at room temperature for 30 minutes and filtered. The 
extract was vacuum dried for 30 minutes at 50.degree. C., extracted with 
chloroform to decolorize, and vacuum dried at 50.degree. C. 
2. The staining solution, Solution 2A, was made up from 0.025 grams of F, 
D, & C Red 40 dye in 1 liter of distilled water, with ca. 3.2 grams of 
citric acid added to pH2.8; then 100 ppm of the decolorized green tea leaf 
extract was added to the staining solution to obtain Solution 2B. 
3. Sample 2A (one gram of the 66 nylon skein as in Example 1) was immersed 
in the staining solution, Solution 2A, for one minute. A second yarn 
sample, Sample 2B, was immersed in staining/stain-inhibitor solution, 
Solution B, also for one minute. Both samples were then dried for 24 
hours. 
4. After rinsing and drying the yarn samples, stains were measured by the 
AATCC Staining Scale and by the Chromameter, as in Example 1. The AATCC 
and L, a, b data are set forth in Table 2. 
TABLE 2 
______________________________________ 
Sample (ppm extract) 
AATCC L, a, b 
______________________________________ 
2A (no extract) 
2 62, 26, 9 
2B (100) 9 82, 2, 1.9 
______________________________________ 
EXAMPLE 3 
Epicatechin Gallate As Stain-Inhibiting Agent 
The procedure in this Example was the same as that of Example 2. 
1. Approximately one gram of the green tea leaf extract was extracted three 
times with 100 ml. ethyl acetate, and concentrated to about 50 ml., by 
vacuum at 50.degree. C. Five ml. of the concentrate was applied as a band 
on a Prep TLC plate (Analtech Silica, 70 m, 20 mm.times.20 mm) and dried 
at room temperature. The plate was eluted with 1:1 (v/v) ethyl 
acetate/chloroform as solvent. The epicatechin gallate (ECG) was 
identified by a comparison with standard obtained from C. T. Ho, Rutgers 
University. The ECG band was scraped off plate, extracted with ethyl 
acetate and freeze dried. 
2. The staining solution was the same as that of Example 2 but is referred 
to herein as Solution 3A. Thus, Solution 3B was prepared by adding 100 ppm 
of the ECG to Solution 3A. 
3. Yarn Samples 3A and 3B were prepared from one gram each of the 66 nylon 
yarn, stained with Solutions 3A and 3B and dried in the same manner as in 
Example 2. 
4. The stains were measured, and the AATCC and L, a, b data are set forth 
in Table 3. 
TABLE 3 
______________________________________ 
Sample (ppm ECG) 
AATCC L, a, b 
______________________________________ 
3A (no ECG) 2 63, 28, 10 
3B (100) 7 81, 4, 2 
______________________________________ 
EXAMPLE 4 
Gallic Acid+Fructose As Stain-Inhibiting Agent 
The procedure was the same as that of Examples 2 and 3. 
1. One gram each of Gallic Acid (certified, Fisher Scientific Co,) and 
Fructose (D. Sigma Chemical) were added to 50 ml of 5% H.sub.2 SO.sub.4, 
and boiled for about 10 minutes. The resultant product was extracted with 
ethyl acetate. 
2. This product was added to the staining solution of Examples 3 and 4 
(hereafter Solution 4A) at the 0.1% concentration to obtain Solution 4B. 
3. Yarn Samples 4A and 4B were prepared from of the 66 nylon yarn, stained 
with Solutions 4A and 4B and dried in the same manner as in Examples 2 and 
3. 
4. The stains were measured, and the AATCC and L, a, b data are set forth 
in Table 4. 
TABLE 4 
______________________________________ 
Sample (TA/fructose) 
AATCC L, a, b 
______________________________________ 
4A (none) 1 67, 39, 14 
4B (0.1%) 8 84, 8, 12 
______________________________________