Macrocolloids of polyhydroxyalkanoates are used as fat substitutes. Polyhydroxybutyrate is the preferred homopolymer. The polymeric particles can have a particle size of from 0.1-10 microns.

BACKGROUND OF THE INVENTION 
The present invention relates to the use of microparticulated 
polyhydroxyalkanoate compositions (PHA) as cream substitutes and to 
low-fat and no-fat foods products containing PHAs to reduce or eliminate 
fat. Additionally, the present invention relates to a method of reducing 
or eliminating fat/cream in food products by substituting PHAs for all or 
a portion of the fat normally found in the traditional food. 
Poly(hydroxyalkanoates) (PHAs) are well-known polyester compounds produced 
by a variety of microorganisms, such as bacteria and algae. A PHA 
polyester can include the same or different repeating units, depending 
upon the choice of carbon source substrates and fermentation conditions 
employed in the production of the PHA. One particular PHA including the 
same repeating units is poly(3-hydroxybutyric acid), or 
poly(3-hydroxybutyrate), termed PHB, and having the structural formula: 
##STR1## 
wherein x represents an integer of from 500 to about 17,000. 
PHB is a natural storage product of bacteria and algae, and is present as 
discrete granules within the cell cytoplasmic space. However, unlike 
other, biologically-synthesized polymers such as proteins and 
polysaccharides, PHB is thermoplastic having a high degree of 
crystallinity and a well-defined melting point at about 180.degree. C. 
But, PHB is unstable at its melting point and degrades, essentially 
quantitatively, to crotonic acid at a temperature slightly above its 
melting point. Accordingly, practical applications for this natural, 
biodegradable polyester have been limited. Therefore, investigators have 
studied other PHAs, such as the biodegradable copolyester 
poly(hydroxybutyrate-co-valerate), including both of the monomeric units 
3-hydroxybutyrate and 3-hydroxyvalerate, in order to discover a PHA having 
sufficient thermal stability and other suitable chemical and physical 
properties for use in practical applications. 
Generally, a PHA is synthesized by a microorganism. However, some PHA 
compounds have been synthesized chemically, such as by polymerization of 
racemic and optically-active butyrolactone or other suitable monomers. 
Such chemically-synthesized PHA polyesters exhibit a relatively low 
average molecular weight, and the synthesis is not economically viable. In 
general, the following publications provide background information for PHA 
polymers, both in regard to their synthesis and their properties: 
1) E. A. Dawes, et al., Adv. Microb. Physiol., 10, p. 135 (1973); 
2) P. A. Holmes, "Developments in Crystalline Polymers-2", D. C. Basset, 
ed., Elsevier Applied Science, London, Chap. 1, pp. 1-65 (1988); and 
3) P. A. Holmes, Phys. Technol., 16, pp. 32-36 (1985). 
The preparation, extraction and purification, of a PHA by a biosynthetic 
process is known. For example, Richardson in European Patent Application 
Serial No. 046,344, and Lafferty et al. in U.S. Pat. No. 4,786,598, 
disclose the preparation of poly-D-(-)-3-hydroxybutyric acid (PHB) by 
culturing the microorganism Alcaligenes latus or a mutant thereof. Walker 
et al., in U.S. Pat. No. 4,358,583, teach the extraction and purification 
of poly(3-hydroxybutyric acid) from the cells walls of PHB-producing 
microorganisms. Furthermore, the bacterial synthesis of various 
co-poly(hydroxyalkanoates), such as the copolymer of 3-hydroxybutyric acid 
and 3-hydroxypentanoic acid, is described in publications such as: 
Y. Doi, et al., "Production of Copolyesters of 3-Hydroxybutyrate and 
3-Hydroxyvalerate by Alcaligenes eutrophus from Butyric and Pentanoic 
Acids", Appl. Microbiol. Biotechnol., 28, pp. 330-334 (1988); 
Doi, U.S. Pat. No. 4,876,331; 
Holmes, Phys. Technol., 16, pp. 32-36 (1985); 
M. Kunioka, et al., "Crystalline and Thermal Properties of Bacterial 
Copolyesters: Poly(3-Hydroxybutyrate-co-3-hydroxyvalerate) and 
Poly(3-Hydroxybutyrate-co-4-hydroxybutyrate)", Macromolecules, 22, pp. 
694-697 (1989); and 
R. Gross, et al., "Biosynthesis and Characterization of 
Poly(s-Hydroxyalkanoates) Produced by Pseudomonas oleovorans", 
Macromolecules, 22, pp. 1106-1115 (1989). 
The above-listed patents and publications are representative of the state 
of the art relating to PHAs. In general, the homopolymeric and copolymeric 
PHAs described in the above references are attempts to improve the 
physical and chemical properties of the PHA by altering the carbon source 
for the biological synthesis of the PHA, or are attempts to find a 
suitable microorganism to produce a sufficient amount of the desired PHA. 
In general, a poly(hydroxyalkanoate) has the general structural formula 
(I), wherein R is hydrogen or an alkyl group having 1-12 carbon atoms, and 
the term "x" is the number of repeating units usually from about 500 to 
about 17,000. The term "alkyl" when used herein is meant to encompass 
cyclic, branched, saturated and unsaturated alkyl groups. As illustrated 
in general structural formula (I), a PHA is a polyester having a 
hydroxy-terminated end and a carboxy-terminated end. The most widely-known 
and intensively-studied 
##STR2## 
poly(hydroxyalkanoate) is the previously-described, biodegradable PHA 
known as poly(hydroxybutyrate), or PHB, wherein the R substitutent in 
general structural formula (I) is methyl. However, PHAs having an R 
substituent of up to nine carbon atoms have been biosynthesized and 
studied, as have PHAs including 4-hydroxybutyrate [(--CH.sub.2 CH.sub.2 
CH.sub.2 CO.sub.2 --).sub.x ] as a repeating unit. 
In addition, copolymers of general structural formula (II) have been 
biosynthesized by the appropriate choice of carbon substrates. For 
example, the copolymer of general structural formula (II), 
##STR3## 
wherein b and c represent the number of repeating units (wherein b+c 
equals from 500-17,000), R4 is methyl and R5 is ethyl, known as 
poly(hydroxybutyrate-co-valerate) or (P[HBcoHV)), has been biosynthesized 
and studied. In general, the copolyesters of general structural formula 
(II) wherein the substituents R4 and R5 independently, are hydrogen or an 
alkyl or alkenyl group including up to nine carbon atoms are known. 
Alkenyl-branched PHA's are described by K. Fritzsche, in "Production of 
Unsaturated Polyesters by Pseudomonas oleovorans", Int. J. Biol. Macromol 
, Vol. 12, pp. 85-91 (1990). In addition, a terpolymer of structural 
formula (III) has been biosynthesized by the bacterium Rhodospirillum 
rubrum from a carbon source including 3-hydroxybutyric acid, 
3-hydroxypentanoic acid and 4-pentenoic acid. 
##STR4## 
wherein d, e and f represent the number of repeating units and d+e+f 
equals from about 500-17,000. This terpolymer is described by R. Gross et 
al. in the publication, "The Biosynthesis and Characterization of New 
Poly(e-Hydroxyalkanoates)", in Polymer Preprints, 30(1), pp. 492-493 
(1989). 
The biologically-synthesized PHAs exhibit a molecular weight of up to about 
1,500,000 daltons. These high molecular weight, biologically-synthesized 
PHAs can be degraded, or depolymerized, to yield a PHA having a molecular 
weight as low as about 3000 daltons. For example, Trathnigg et al., in 
Angew. Macromol. Chem., 161, p. 1-8 (1988), described the preparation of a 
low molecular weight PHB by a controlled acid hydrolysis of a high 
molecular weight, biologically-synthesized PHB using aqueous formic, 
acetic or butyric acid at an elevated temperature of 
90.degree.-100.degree. C. Similarly, B. Heuttecoeur, et al., in C. R. 
Hebd. Seances Acad. Sci., 274, pp. 2729-2732, (1972), describe the partial 
alkaline degradation of PHB, and S. Akita, et al., in Macromolecules, 9, 
pp. 774-780 (1976), describe the alcoholysis of PHB with methanol and 
p-toluenesulfonic acid. The methods of Trathnigg, et al and Heuttecoeur, 
et al provide a degraded PHB polymer with a carboxylic acid or a 
carboxylate terminal group, whereas the method of Akita provides an ester 
terminal group. Also see S. Coulombe, et al., "High-Pressure Liquid 
Chromatography for Fractionating Oligomers from Degraded 
Poly(s-Hydroxybutyrate)", Macromolecules, 11, pp. 279-280 (i978); and A. 
Ballistreri, et al., "Sequencing Bacterial 
Poly(s-Hydroxybutyrate-co-o-hydroxyvalerate) by Partial Methanolysis, 
High-Performance Liquid Chromatography Fractionation and Fast Atom 
Bombardment Mass Spectrometry Analysis" , Macromolecules, 22, pp. 
2107-2111 (1989). 
H. Morikawa et al. in Can. J. Chem., 59, pp. 2306-2313, (1981) demonstrated 
that thermal degradation of a PHA copolyester yields monomeric, oligomeric 
and polymeric PHAs with olefinic terminal groups. Morikawa et al. 
pyrolyzed PHB to yield crotonic acid and oligomers of PHB having a 
terminal crotonate moiety, as shown in the polyester of structural formula 
(IV) wherein k is from 500 to about 17,000. Therefore, pyrolysis of a PHA 
can provide an 
##STR5## 
oligomer with a reactive vinyl terminal group as a site for further 
chemical modification of the degraded PHA. 
Accordingly, from the above degradation methods, i.e. acidic hydrolysis, 
alkaline hydrolysis, alcoholysis or pyrolysis, a high molecular weight, 
biologically-synthesized PHA can be degraded to a relatively low molecular 
weight PHA that includes one of a variety of reactive terminal 
functionalities, including hydroxyl, free carboxylic acid, carboxylate, 
ester, and olefinic functionalities. These reactive terminal 
functionalities therefore allow the introduction of numerous other types 
of terminal functionalities onto the degraded PHA polyester. 
In the past, interest in PHAs concentrated on their unique biodegradable 
and biocompatible properties, as well as their various physical properties 
that range from thermoplastic to elastomeric. The physical and chemical 
properties inherent to PRAs suggest a variet of applications, such as in 
controlled drug release systems, biomedical devices, specialty packaging 
materials, and numerous agricultural applications. However, while PHAs are 
of general interest because of their biodegradable nature, their actual 
use as a plastic material has been hampered by their thermal instability. 
For example, poly-3-hydroxybutyrate is thermoplastic, but also is 
thermally unstable at temperatures exceeding its melting point of about 
180.degree. C. N. Grassie, et al., in Polym. Degrad. Stabil., 6, pp. 47-61 
(1984), disclose that a substantial molecular weight reduction of PHB 
occurs by heating PHB in the temperature range of 180.degree.-200.degree. 
C. The inherent thermal instability of PHB is partially overcome by 
incorporating a second monomer unit into the polyester. The melting point 
of a PHB can, for instance, be reduced to 75.degree. C., as in (P[HBcoHV)) 
including about 40 mol % 3-hydroxyvalerate, resulting in a polymer that 
is thermally stable up to about 160.degree. C. However, further 
enhancements in the thermal stability of PHAs are necessary for their 
practical use in commercial applications. Also see M. Kunioka, et al., 
Macromolecules, 23, pp. 1933-1936 (1990). 
Accordingly, prior investigators have studied the chemical and biological 
synthesis of PHAs, and the degradation of PHAs, in attempts to provide a 
biodegradable polymer having physical and chemical properties suitable for 
consumer, industrial and agricultural applications. However, the prior 
investigators have studied essentially only homopolymeric and copolymeric 
hydroxyalkanoates. In general, to date, very few known references are 
directed to a compound, or its method of preparation, including a PHA 
polymer functionalized with a moiety other than a poly(hydroxyalkanoate). 
Some investigators, like P. B. Dave et al., in "Survey of Polymer Blends 
Containing Poly(3-Hydroxybutyrate-co-16% Hydroxyvalerate", in Polymer 
Preprints, 31(1), pp. 442-443 (1990), studied the physical compatibility 
of a PHA blended with other commercial polymers. However, these were 
physical blends of a PHA with a second polymer, like a poly(ethylene 
oxide), and did not include a PHA polymer covalently attached to a 
molecule or a polymer other than a PHA. R. I. Hollingsworth et al. in 
Carbohydrate Research, 134, pp. C7-C11 (1984) and R. I. Hollingsworth et 
al. in Journal of Bacteriology, 169(7), pp. 3369-3371 (1987) found 
3-hydroxybutyrate covalently attached as a noncarbohydrate substituent in 
the acidic capsular polysaccharide and extracellular polysaccharide of 
Rhizobium trifolii. However, the 3-hydroxybutyrate substituent was 
monomeric and was substituted biologically, not chemically. M. S. Reeve et 
al., in "The Chemical Degradation of Bacterial Polyesters for Use in the 
Preparation of New Degradable Block Polymers", Polymer Preprints, 31(1 ), 
pp. 437-438 (1990), disclose a polyurethane-type copolymer derived from 
the reaction of 4,4'-diphenylmethane diisocyanate with polyethylene glycol 
and degraded PHB, and disclose a PHB-polystyrene block copolymer derived 
from degraded PHB and a polystyrene prepolymer including a carboxylic acid 
functionality. 
SUMMARY OF THE INVENTION 
Briefly, in accordance with the present invention, polyhyroxyalkanoate 
(PHA) particles display fat-like mouthfeel characteristics when the 
particles have a mean diameter distribution in the range of from about 0.1 
to about 10 microns (.mu.) and are dispersed in an aqueous phase as a 
macrocolloid. The particles are preferably spheroidally shaped, 
substantially non-aggregated and exhibit a substantially smooth 
organoleptic character of an oil-in-water emulsion. The present 
macrocolloid can replace all or a portion of the fat or cream in food 
products such as ice cream, yogurt, salad dressings, mayonnaise, cream, 
cream cheese, other cheeses, sour cream, sauces, icings, whipped toppings, 
frozen confections, milk, coffee whitener and spreads. 
Of particular interest, PHB and P(HBcoHV) are formed into stable 
suspensions of spheroidal particles having a particle size distribution 
effective to impart a substantially smooth organoleptic character of an 
oil-in-water emulsion, i.e., mouthfeel of fat/cream.

DETAILED DESCRIPTION OF THE INVENTION 
In practicing the present invention, PHA particles, are added to 
fat/cream-containing food products to replace all or a portion of the 
fat/cream normally present in the food. The resulting food products have 
the creamy mouthfeel of their fatty counterparts. Preferably the particles 
have a substantially spheroidal shape and a mean diameter particle size 
distribution between about 0.1 and about 10 microns (.mu.). 
Any naturally harvested or synthetically produced PHA which can attain a 
substantially spheroidal or substantially round shape in the 0.1-10 .mu. 
diameter size range is acceptable in practicing the present invention. The 
PHAs are made according to well known procedures described hereinbefore. 
Suitable PHAs include PHB and P(HBcoHV). The PHA can also be a copolymer 
of hydroxybutyrate and a C--C alkanoate. Mixtures of different PHAs can 
also be employed. Preferred PHAs include those harvested naturally as 
granules in bacteria. Synthetically produced PHAs must be substantially 
spheroidal in shape and have a mean particle size diameter of from about 
0.1 to about 10 .mu.. 
Once the PHA macro-colloidal particles are formed they must be 
substantially non-aggregated and remain that way. Aggregate blocking 
agents, for example, pectin, lecithin and xanthan gum, can be added to the 
macrocolloid to stabilize the particles. U.S. Pat. Nos. 4,734,287 and 
4,961,953, which are incorporated herein by reference, disclose protein 
macrocolloids useful as fat substitutes and aggregate blocking agents. 
The particle size distribution of PHAs can be controlled in a number of 
ways, including: (a) dissolving the PHA in a suitable polar organic 
solvent, such as methylene chloride, chloroform, dimethylsulfoxide (DMSO), 
dimethylformamide (DMF , etc., and then forcing the dissolved PHA through 
a spinerette, syringe, small diameter orifice, or other suitable device at 
a high speed (rate) in a continuous or intermittant manner to a 
non-solvent, (one in which the PHA is insoluble in) such as water, 
alcohol, or a non-polar organic solvent, etc., to cause precipitation of 
PHA; (b) dissolving the PHA in a suitable solvent, and then removing the 
solvent either by evaporation under high speed shear conditions, by spray 
drying, stirring or other suitable methods to cause precipitation of PHA 
granules; or (c) dissolving the PHA in a suitable solvent at elevated 
temperatures, and then preparing a PHA gel by reducing the temperature of 
the solution to ambient, and, if appropriate, then treating the thus 
obtained gel particles under high shear conditions in a homogenizer, 
blender, or other suitable device, to obtain the desired particle size. A 
suitable mixing apparatus is described in U.S. Pat. No. 4,828,396 which is 
incorporated herein by reference. 
Generally, the hydrated PHA macrocolloid will have from about 5 to about 50 
weight percent or more solids. When added to food products, the hydrated 
macrocolloid is substituted generally on equal weight basis of the fat 
being removed, i.e., 1 part by weight fat/cream is replaced with 1 part by 
weight of hydrated macrolloid. More or less macrocolloid can be employed 
based on the desired creaminess of the resulting food. 
In preparing the present low-fat and no-fat food products the PHA 
macrocolloid is added to the food in place of all or a portion of the fat 
or cream normally present in this food. The order of addition of the PHA 
is not critical to the practice of the present invention. The PHA 
macrocolloid is blended with the other food ingredients employing standard 
blending techniques well known to one skilled in the art. 
The present PHA macrocolloid can be combined with other fat/cream 
substitutes, such as, for example, microparticulated proteins and 
carbohydrates, sucrose polyesters (olestra), protein/xanthan gum complexes 
and other types of fat sparing agents, i.e., starches, gums, thickeners, 
etc. 
In similar embodiments, the various PHA compositions described herein act 
as a fat/cream substitute in foods. The PHA particles are substantially 
spheroidal in shape and have a particle size distribution effective to 
impart an organoleptic character of an oil-in-water emulsion, i.e., a 
cream. The mean diameter particle size distribution ranges from about 0.1 
to about 10 .mu.. 
Additionally, the PHAs can be used as a carrier for flavors and colors as 
described in copending application Ser. No. 616,510 filed evendate 
herewith entitled POLYHYDROXYALKANOATE FLAVOR DELIVERY SYSTEM which is 
incorporated herein by reference.