Low Calorie Salad Dressing Having Smooth, Creamy, Organoleptic Characteristics

This application is related to U.S. patent application Ser. No. 395,800 filed Aug. 18, 1989, now U.S. Pat. No. 5,011,701 which is a continuation-in-part of PCT application No. PCT/US89/01813 filed Apr. 28, 1989, which is a continuation-in-part of U.S. application Ser. No. 292,568 filed Dec. 30, 1988, now abandoned which is a continuation-in-part of U.S. patent application Ser. No. 188,283 filed Apr. 29, 1988, now abandoned and U.S. patent application Ser. No. 177,184 filed Apr. 4, 1988, now U.S. Pat. No. 4,885,179. U.S. patent application Ser. No. 024,507 filed as PCT application US85/01265 on July 1, 1985, which entered national stage in the United States on Mar. 1, 1987, now U.S. Pat. No. 4,762,726, which is a continuation-in-part of U.S. patent application Ser. No. 567,096 filed Dec. 30, 1983, now U.S. Pat. No. 4,563,360, and U.S. patent application Ser. No. 567,277 filed Dec. 30, 1983, now U.S. Pat. No. 4,559,233, and is a continuation-in-part of U.S. application Ser. No. 081,115 filed Aug. 3, 1987, abandoned in favor of continuation-in-part application Ser. No. 307,069 filed Feb. 6, 1989, which is a continuation-in-part of U.S. application Ser. No. 658,618 filed Oct. 9, 1984, now U.S. Pat. No. 4,684,533, which are incorporated by reference herein.

The present invention is directed to low calorie, substantially fat-free viscous dressing food products having exceptional organoleptic mouthfeel characteristics simulating fat containing viscous dressings, such as viscous French dressing and salad dressing food products.

Very significant technical effort has been directed over many years to the development of reduced fat or substantially fat-free food products which possess a smooth and creamy mouthfeel, texture and lubricity accurately simulating the texture and mouthfeel of edible fat containing food products.

Such efforts include the use of various types of undigestible fat-like materials such as sucrose polyesters and polyglycerol polyesters which pass through the digestive system without absorption. Substantial work has also been carried out over an extended period of time with bulking agents such as powdered and microcrystalline cellulose in fat-containing and reduced fat food products. In this regard, for example, U.S. Pat. Nos. 3,067,037, 3,141,875, 3,157,518, 3,251,824, 3,388,119, 3,539,365, 3,573,058, 3,684,523, 3,947,604, 4,199,368 and 4,231,802, 4,346,120, 4,400,406, 4,427,701 and 4,421,778 relate to the preparation, or use of various types of cellulose in various food products. Such cellulose materials have been used or proposed for reduced fat or substantially fat-free food products. However, as the fat content is reduced in food products containing substantial levels of cellulose products such as microcrystalline cellulose, adverse organoleptic effects such as a mouth-coating or astringency sensations, and a lack of a well-rounded organoleptic sensation corresponding to that provided by conventional fat-containing food products such as ice cream, and viscous and pourable dressings, tend to become more pronounced.

High pressure treatment and attrition of microcrystalline cellulose, and the use of gums to prevent reagglomeration of crystalline cellulose particles has been used to prepare "colloidal" grades of microcrystalline cellulose having a high proportion of the cellulose in particles of submicron size. High pressure homogenization of fibrous cellulose pulp, as opposed to microcrystalline cellulose, has also been used to produce a "microfibrillated" fibrous product for food product utilization [e.g., see U.S. Pat. Nos. 4,089,981, 4,143,163, 4,341,807, 4,374,702, 4,481,076, 4,481,077 and 4,659,388].

Microcrystalline cellulose has been used in low and reduced calorie food formulations as both a carbohydrate thickening agent and as a fat replacer, with powdered products of relatively large particle size (e.g., 15-90 micrometer length) utilized for carbohydrate reduction and colloidal grades of submicron size being used to reduce fat. However, as the fat content is reduced in food products containing substantial levels of microcrystalline cellulose, adverse organoleptic effects such as a mouth-coating or astringency sensations, and a lack of a well-rounded organoleptic sensation corresponding to that provided by conventional fat-containing food products, tend to become more pronounced, and accordingly, fully acceptable fat-free food products have not generally been provided. In addition, microcrystalline cellulose may produce an astringent or drying mouthfeel when used as a substantially full-fat replacement, which is deleterious to the acceptability of the product.

It is an object of the present invention to provide methods for the manufacture of novel, nutritious, low calorie, substantially fat-free viscous food dressing compositions which have exceptional, smooth, creamy oil-like textures and well rounded fat mimetic mouthfeel characteristics, as well as desirable stability and functionality characteristics. It is a further object to provide novel, substantially fat-free viscous food dressings and pourable dressings which have such characteristics. These and other objects of the invention will become apparent from the following detailed description and the accompanying drawings.

FIG. 1 is a schematic diagram illustrating a specific embodiment of a multiple pass continuous method of the continuous stirred tank reactor type for manufacture of a microreticulated microcrystalline cellulose aqueous dispersion which may be utilized in the preparation of low-fat or substantially fat-free food products having creamy, organoleptic characteristics;

FIG. 2 is a schematic diagram illustrating a specific embodiment of a discrete, serial multiple pass method for manufacture of microreticulated microcrystalline cellulose aqueous dispersions which may be utilized in the preparation of low-fat or substantially fat-free food products having creamy, organoleptic characteristics;

FIG. 3 is a cross-sectional view of a circular superpressure processing valve of microreticulation apparatus such as illustrated in FIGS. 1 and 2;

FIG. 4 is a graph of the median particle size of three samples of a microcrystalline cellulose slurry as it is being microreticulated in apparatus like that of FIG. 1;

FIG. 5 is a graph of the Brookfield viscosity of a microcrystalline cellulose slurry as a function of the number of volumetric passes through a microreticulation apparatus of the type illustrated in FIG. 1;

FIG. 6 is a graph of the viscosity of and particle size of microcrystalline cellulose as a function of the number of passes of a 7.2 percent solids aqueous dispersion through microreticulator apparatus of the type shown in FIG. 1;

FIG. 7 is a graph of the Brookfield viscosity of a microcrystalline cellulose dispersion as a function of the number of passes through three different microreticulation systems of the type shown in FIG. 1, which are of varying size;

FIG. 8 is a graph of the viscosity of a microcrystalline cellulose dispersion as a function of the number of discrete passes through apparatus of the type shown in FIG. 2;

FIG. 9 is a graphical representation of the viscosity of three different microcrystalline cellulose runs using apparatus of the type shown in FIG. 1;

FIGS. 10A and 10B are scanning electron micrographs of a hydrated microcrystalline cellulose product before microreticulation treatment, at two different magnifications;

FIG. 10C is a scanning electron micrograph of two crystals illustrating a fuzzy surface after 1 pass through the fluidizer;

FIG. 10D is a higher magnification scanning electron micrograph of the crystal surface of the hydrated microcrystalline cellulose illustrating the shape and size of microcrystals which have been dislodged from the larger crystal;

FIGS. 11A and 11B are scanning electron micrographs of the microcrystalline cellulose after 3 passes through microreticulation apparatus of the type illustrated in FIG. 1:

FIGS. 11C and 11D are scanning electron micrographs of the microcrystalline cellulose of FIGS. 10A-B after 7 passes through the microreticulation apparatus showing microcrystals and small crystals aggregated into a microreticulated structure;

FIGS. 12A and 12B are cryo-scanning electron micrographs in low magnification (FIG. 12A) showing the relative size and distribution of microreticulated microcrystalline cellulose particles and in higher magnification (FIG. 12B) illustrating the composition of a single microreticulated aggregate, showing its open nature;

FIG. 13 is a light micrograph via darkfield optics of microreticulated microcrystalline cellulose;

FIG. 14 is a transmission electron micrograph of pourable dressing made with a microreticulated microcrystalline cellulose aqueous dispersion, illustrating "clear" areas (c) devoid of microcrystalline cellulose with indications of spherical aggregations (a) of microcrystalline cellulose; and

FIG. 15 is a schematic diagram depicting a specific embodiment of a continuous method for preparing a viscous dressing utilizing multiple component streams to prepare a viscous substantially fat-free premix in accordance with the invention.

The present invention is directed to a method for preparing a viscous dressing. The dressing may be prepared using batch techniques, however, the method is particularly suitable for a continuous process for preparing viscous dressings. In the method, a gum blend is prepared which includes a gum and a diluent. A spice blend is prepared which includes water, a sweetener, spices and/or flavorings. An aqueous dispersion of a microreticulated microcrystalline cellulose dispersion is prepared. The gum blend, the spice blend and the microreticulated microcrystalline cellulose are then combined to provide a premix. The premix is then blended with a pre-prepared starch base to provide the viscous dressing product of the invention.

After separate preparation of the gum blend, the spice blend, the microreticulated microcrystalline cellulose dispersion and the starch base, the components can be used in a continuous process for preparation of the viscous dressing product.

The present invention is directed to a substantially fat-free, fat-mimetic viscous food dressing such as mayonnaise-like dressings and salad dressings, having organoleptic fat-like characteristics closely simulating such food products which conventionally have relatively high fat content. Such fat-free, fat-mimetic viscous dressings utilize an aqueous microreticulated microcrystalline cellulose dispersion having specific viscosity, particle size, and micro-reticulation characteristics, as well as stability and mouthfeel characteristics, as will be described in more detail.

Generally, the viscous dressings of the invention comprise from about 0.25 to about 4 weight percent of dispersed, porous, particulate, microreticulated microcrystalline cellulose (MMC), from about 0.1% to about 2% of a gum, from about 60 to about 80 weight percent of water, from about 2 to about 20 weight percent carbohydrates including starch, from 0 to about 10 weight percent protein, and less than about 4 weight percent of triglycerides. The microreticulated microcrystalline cellulose is particulate, and has a particle size distribution such that substantially all (i.e., at least about 75 weight percent) of the microreticulated microcrystalline cellulose particles have a maximum dimension of less than about 25 microns. The microreticulated microcrystalline cellulose particles are porous, and in this regard, have a void volume of at least about 25 volume percent, preferably at least about 50 volume percent of the particles. The microreticulated microcrystalline cellulose particles of the high viscosity aqueous dispersions are believed to be an intimately interconnected product of microfragmented microcrystalline cellulose which has reagglomerated under controlled conditions to form stable, porous particles formed of microcrystalline particle fragments which are connected at spaced-apart zones of contract through crystalline bonding forces. The microreticulated particles of the aqueous dispersion desirably have a mean particle size in the range of from about 2 to about 25 microns, and desirably, at least about 50 percent by weight of the microreticulated microcrystalline cellulose particles of the aqueous dispersion have a maximum linear dimension in the range of from about 2 to about 25 microns and preferably in the range of from about 5 to about 20 microns.

It is important that the microreticulated cellulose be prepared from highly crystalline microcrystalline cellulose. Microcrystalline celluloses are conventionally prepared from wood pulp by acid hydrolysis of cellulose fiber which weakens the disordered para-crystalline region. Subsequent shearing releases the insoluble, highly crystalline cellulose bundles. [Thomas, W. R., "Microcrystalline Cellulose (MCC or Cellulose Gel)", Food Hydrocolloids, Vol. III (Ed. M. Glickman), pp. 9-42 (1986), CRC Press, Inc., Boca Raton, Florida; "Avicel Microcrystalline Cellulose--Product Description", Technical Bulletin G-34, FMC Corporation, Food & Pharmaceutical Products Division, Philadelphia (1985)]. Cellulose is a linear polymer of .beta.1-4 linked D-glucose units. Because of the linear nature of cellulose which allows close contact of adjacent chains, as well as an abundance of hydroxyl groups available for hydrogen bonding between chains, cellulose readily forms bundles of molecules which further interact to form fibrils. Although much of the cellulose found in nature is arranged in tightly packed crystalline regions, these are interspersed with less densely packed amorphous areas, called para-crystalline regions. In the typical manufacture of microcrystalline cellulose, acid hydrolysis is utilized to attack the para-crystalline regions, followed by a process of attrition (a high shear treatment), to break out the microcrystalline regions. Because of their highly crystalline nature, the microcrystalline cellulose particles have a strong tendency to recrystallize after being broken apart while in an aqueous dispersion.

In the formation of the microreticulated microcrystalline cellulose materials, it is believed that the generally solid microcrystalline cellulose crystallites are progressively converted to porous microreticulated particles of specific size distribution by a process of controlled microfragmentation and reagglomeration.

Microreticulated microcrystalline cellulose dispersions may be produced by providing an aqueous suspension of a microcrystalline cellulose comprising from about 88 to about 99 percent water and from about 1 to about 12 weight percent microcrystalline cellulose, and preferably from about 5 to about 9 weight percent of microcrystalline cellulose, based on the weight of the aqueous dispersion. The aqueous dispersion should not contain materials such as gums which prevent recrystallization of cellulose fragments. The solid microcrystalline cellulose particles may desirably have a mean particle size in the range of from about 5 to about 40 microns, such as in the range of from 20 to 30 microns. The aqueous microcrystalline cellulose dispersion is repeatedly conducted through a superpressure, high shear zone to fragment the microcrystalline cellulose to crystalline fragments having a maximum dimension of less than about 1 micron, and reagglomerating the submicron crystalline fragments under high shear conditions at a very small turbulence scale, to produce porous microreticulated microcrystalline cellulose particles having the desired particle size distribution. By "superpressure high shear zone" is meant a shear zone operated at a driving pressure drop of at least 12,000 psi which is dissipated viscously to heat. As indicated, the material is repeatedly conducted through the superpressure high shear zone. In this regard, the material should best be conducted at least twice, and preferably at least three times through a high shear zone.

The microcrystalline cellulose should best be conducted through a high shear zone having a shear rate of at least about 5.times.10.sup.6 (e.g., 1.times.10.sup.7) seconds.sup.-1 at a specific turbulent energy dissipation rate of at least about 8.5.times.10.sup.5 ergs per cubic centimeter of the high shear zone. Preferably, all of the microcrystalline cellulose slurry is conducted serially through the superpressure high velocity and shear fragmentation zone, so that all of the material which has passed through one stage of processing is conducted to the next stage of processing. However, processing may also be carried out by recycle in a stirred tank reactor mode, which however is not as efficient. In a flow through system with continuous high shear treatment, the specific energy requirement (the energy dissipation rate per unit throughput of product stream) may desirably be at least about 1.times.10.sup.8 ergs per gram. Preferably, a turbulent energy dissipation rate of at least about 4.times.10.sup.11 ergs per pound of aqueous dispersion is provided per pass through the high shear, high velocity zone. The kinetic and shearing forces are dissipated and converted viscously to heat and fragmentation of the microcrystalline cellulose, and the temperature of the dispersion should rise at least about 30.degree. C. upon conduction through the superpressure microfragmentation zone.

The superpressure high shear zone should best have a shear rate of at least about 1.times.10.sup.7 inverse seconds, with a turbulent energy dissipation rate sufficient to raise the temperature of the suspension at least about 30.degree. C. through viscous dissipation of input energy to heat.

As indicated, microreticulated microcrystalline cellulose dispersions may be prepared by subjecting an aqueous slurry or suspension of the microcrystalline cellulose to intense shear at very high driving pressures to provide the microfragmentation and microporous reagglomeration treatment. Effective results have been achieved by using a CD30 or CD150 homogenizer (A.P.V. Gaulin Corp., Boston, MA) or a Rannie homogenizer (A.P.V. Rannie, Copenhagen) using a knife edge homogenization element within a closely surrounding impact ring at an inlet pressure of at least about 12,000 psig and preferably at least 13,000 psig, to obtain microporously reagglomerated microfragments having a mean particle size in the range of from about 5 microns to about 15 microns in maximum dimension.

Microreticulated microcrystalline cellulose is currently fragmented using homogenizers in either a volumetric or series pass set-up. Using the volumetric pass set-up, as shown in FIG. 1, the microcrystalline cellulose slurry travels in a loop between the superpressure microreticulation device 102, which may be a CD30, CD150 or Rannie homogenization apparatus operated at a high driving pressure (e.g., 13,500 psi) and the hold tank 104. "Pass" times or effective number of passes through the superpressure microfragmentation zone are calculated based on the volume of the batch and the flow rate of the material, with time for one pass being equivalent to the time it takes for the entire volume to be conducted through the superpressure shear zone at the treatment flow rate. Upon completion of a desired number of volumetric passes, the microreticulated material in the tank 104 may be conducted to food product preparation tank 106 where the microreticulated microcrystalline cellulose dispersion may be mixed with xanthan gum to coat and stabilize its microreticulated particles, and may subsequently be blended with selected food components to prepare a low fat or substantially fat-free food product having smooth, creamy fat-like organoleptic characteristics. In the series pass set-up, the material passes through each homogenizer (up to 6) only once. The pass number is equivalent to the number of homogenizers operating.

Illustrated in FIG. 7 is volumetric pass data utilizing three different homogenizers as microfragmentation apparatus 102. The apparatus are of three different sizes, from the Gaulin CD30 shown as #1, the somewhat larger Gaulin CD150 shown as #2, and a production scale Rannie (smallest to largest) shown as #3. The microreticulated cellulose product used was the PH101 product of FMC Corporation, which is substantially pure microcrystalline cellulose. Processing temperatures using this set-up average 70.degree. F. at the homogenizer inlet and 110.degree. F. at the outlet (a plate heat exchanger cools the microcrystalline cellulose material between passes), and a solids level of 6.5-7 weight percent. These homogenizers utilize a knife-edge valve and seat high pressure shear homogenization valve arrangement as shown in cross-section through the axis of rotation of FIG. 3. The aqueous dispersion enters the valve at a pressure P1 of over 13,000 psi, and is forced at high velocity which may exceed 1300 feet per second, through the gap between the knife edge valve 302 and seat 304, which are preferably of extremely hard and wear resistant ceramic. From the data, it is apparent that the smaller homogenizers provide the more efficient fluidization of microreticulated microcrystalline cellulose.

Illustrated in FIG. 4 is a graph of median particle diameter for three separate sample runs in a volumetric recycle pass system of FIG. 1 for microcrystalline cellulose [PH101 microcrystalline cellulose product of FMC Corporation] illustrating the relatively constant particle size of the microreticulated microcrystalline cellulose particles which are formed, with increasing number of effective passes through the superpressure shear zone. However, although the particle size is not reduced in proportion to the number of passes, the viscosity continues to increase.

FIG. 5 is a graph of Brookfield viscosity of a PH101 microcrystalline cellulose slurry as a function of number of volumetric passes measured by Brookfield RVD instrument at 10 rpm using Helipath T-bar B spindle. A similar combined graph illustrates the particle size by line 602, and viscosity by line 604, of an Avicel PH101 microcrystalline cellulose suspension at 7.2 weight percent suspension in water as shown in FIG. 6.

FIG. 9 is a graph of the concentration dependence, at 8 passes through CD150 apparatus in a recirculation system like FIG. 1, of the microreticulated Avicel PH101 microcrystalline cellulose.

The highly fragmented output stream from each of the production scale Rannie homogenizers 602-610 is directed to a subsequent homogenizer without recycle of the material. The output stream from the final homogenizer 612, after passing through heat exchanger 624 may be conducted to a vortexing mixer 640 such as a Breddo mixer, which continuously renews the surface 642 of the microreticulated microcrystalline cellulose 644 therein by means of a shearing, vortexing circulation pattern. A gum blend may be continuously fed by an auger feeder 648 to a vibrating plate to disperse the gum powder in air, for introduction to the surface 642 and consequent formation of a premix as described in detail hereinbelow.

Illustrated in FIG. 8 is a graph depicting the viscosity of microreticulated microcrystalline cellulose dispersions (prepared from Avicel PH101 microcrystalline cellulose at a solids level of about 7 weight percent) as a function of the number of series passes through the production Rannie homogenizers 602-612 of FIG. 2. By comparing FIG. 8 with FIG. 7, curve #3 for the same Rannie homogenizer operated in recyclic continuously stirred tank mode, it will be seen that the series operation without recycle as shown in FIG. 2 is much more efficient than recycle operating as shown in FIG. 1.

Illustrated in FIG. 2 is a series pass embodiment 200 of a processing system for manufacturing microreticulated microcrystalline cellulose. In the embodiment 200, an array of superpressure microfragmentation homogenizers 602, 604, 606, 608, 610 and 612 are connected in series through respective reservoir tanks 614, 616, 618 and 620 and heat exchangers 622, 624.

In operation of the FIG. 2 systems, the processing temperatures increase with each pass in this set up: starting at 60.degree. F. at the inlet to homogenizer 602 and increasing 40.degree. F. with each pass through successive homogenizers 604, 606. Plate heat exchangers 622, 624 after the third and sixth pass cool the microreticulated microcrystalline cellulose dispersion back to 60.degree. F., insuring that the temperature never exceeds 195.degree. (outlet temperature of homogenizers 606, 612) in the illustrated embodiment. Comparing the Rannie data from both processing set-ups, it is apparent that series passes build the microreticulated microcrystalline cellulose viscosity more quickly than the volumetric set-up.

The main mechanism responsible for the breakage of microcrystalline cellulose crystals is high speed shear and direction change. In a production scale machine, the material is processed traveling at a flow rate of approximately 900 gal/hr. After being forced and sheared through a 0.0014 inch gap (FIG. 3) under 13,500 psi pressure P1, the microcrystalline cellulose dispersion reaches velocities of 1,000 ft/sec or more (v2 on diagram of FIG. 3). The microcrystalline cellulose dispersion is forced to abruptly change direction by the surface of the stream impact ring 306 at such high velocity, resulting in the division of microcrystalline cellulose crystals and the generation of crystallite fragments which may recrystallize imperfectly in a reticulated, porous structure, thereby building the microreticulated microcrystalline cellulose viscosity.

Full hydration of the starting material is an important step for obtaining the desired fat-like, microreticulated microcrystalline cellulose functionality. The microcrystalline cellulose may desirably be boiled in aqueous suspension or may be heated during microfragmentation treatment by allowing the temperature to rise through input energy dissipation in the aqueous dispersion.

Viscosity in a solution or suspension of cellulose materials is controlled by many factors. In conventional, solid colloidal microcrystalline cellulose suspensions, viscosity is related to the number and size of solid crystallites in the suspension. Colloidal grades of products comprising such crystallites are typically protected by an anionically charged layer of carboxymethyl cellulose and are thus prevented from aggregation by charge repulsion. As the particle size of colloidal microcrystalline cellulose is reduced by high pressure homogenization, the number of individual crystallites increases, the total exposed surface area increases, and the viscosity increases proportionally. This explanation does not hold true for superpressure high shear fragmentation of microcrystalline cellulose suspensions which do not have a protective colloid to prevent reagglomeration, under appropriate processing condition as described herein. In this case the apparent particle size remains relatively the same, but the viscosity continues to increase with increasing superpressure microfragmentation/ reagglomeration treatment.

In this regard, initially the microcrystalline cellulose material is in the form of very densely-packed solid crystalline cellulose particles, which may have an average particle length of, for example, 20 to 30 .ltoreq.m (longest dimension, e.g., when measured by a particle size analyzer such as a MicroTrac Particle Analyzer), but with many particles as large as 200 .mu.m by light microscopy, and a very low viscosity. After 1 or 2 passes through superpressure high shear homogenizer, there are many isolated crystallites (about 1.times.0.1 .mu.m) but still mostly densely packed solid crystals (about 10 .mu.m in their longest dimension). The viscosity is still low, as shown in FIGS. 5, 6 and 7. This progressive formation of microreticulated microcrystalline particles is illustrated in FIGS. 10-12. In this regard, FIGS. 10A and 10B are scanning electron micrographs of hydrated Avicel PH101 microcrystalline cellulose product starting material before passing it through a volumetric multi-pass superpressure homogenization treatment such as shown in FIG. 1, at two different magnifications. FIGS. 10C and 10D illustrate the surface of two microcrystalline crystals of the FIG. 10A material after one pass, at different magnifications, as shown by the length line marks.

FIGS. 11A and 11B are scanning electron micrographs of the material of FIGS. 10A, 10B after three passes through the microreticulation apparatus of FIG. 1, while FIGS. 11B and 11C illustrate the material after seven volumetric passes through the system of FIG. 1 showing the microfragments aggregated into a microreticulated structure.

FIGS. 12A and 12B are cryoscanning electron micrographs made without chemical fixation or dehydration artifacts, revealing the open nature of the particles. FIG. 13 is a light micrograph of the microreticulated microcrystalline cellulose. FIG. 14 is a transmission electron micrograph of a pourable dressing of the type described hereinafter, with areas of microreticulated cellulose A separated by areas C which are devoid of the material.

As shown in these FIGS., after multiple passes through the superpressure homogenizer at a small turbulence scale, microreticulated aggregates (which appear under microscopy to be like "cotton balls") of crystallites are apparent, with a particle size, for example, of 10 to 15 .mu.m. Very few isolated submicron crystallites or dense crystalline particles can be seen. Embedded within the loose microreticulated "cotton ball" aggregates are bits and pieces of the dense crystalline cellulose particles, which have not yet completely dispersed. The viscosity at this point is high and continues to increase with increasing microfragmentation treatment.

It is believed that the microreticulated cellulose particles are formed by weak interactions between the individual crystallites as they are subjected to the turbulent flow through the homogenizer. The aggregates grow by increasing the number of associated crystallites until they reach an optimum size which may be related to the shear force through the homogenizer. These aggregates trap water by capillary action, thus driving up the viscosity. Submicron crystallites continue to shred off of the dense microcrystalline cellulose particles with each pass, and aggregate imperfectly with other crystallites to form a porous, reticulated network which is bonded with strong crystallization energy at the points of contact, and increase the total number of "cotton ball" aggregates available to absorb water. Eventually the entire continuous phase may be crowded with the aggregated microreticulated microcrystalline cellulose particles, even though the solids content is relatively low, and the viscosity becomes very high.

In a recent study on the coagulation of microcrystalline cellulose dispersions, Evans and Luner observed the behavior of microcrystalline cellulose in a turbulent field under relatively low shear conditions of 600 inverse seconds, in respect to the formation of microcrystalline cellulose flocs with a large, uniform aggregate diameter of about 200 .mu.m [Evans, et al., "Coagulation of Microcrystalline Cellulose Dispersions", J. Colloid Interface Sci., 128, 464-476 ] (1989). Such large flocs would not be suitable for use as a fat-mimetic food component, but were described as resulting from the inherent colloidal instability of microcrystalline cellulose, which tends to aggregate by parallel alignment of the crystallites followed by hydrogen bonding of the cellulose molecules. In the absence of a turbulent field, cellulose crystallites tend to reform into very dense wood-like structures. In a turbulent field, the parallel alignment is prevented by interaction with other crystallites. The final particle size which is achieved by this process is determined by the lower size limit of the turbulent eddies. The aggregates will grow to this size, while larger aggregates will be disrupted. A very narrow particle size distribution would be predicted, and was found experimentally.

It is theorized that the particle size distribution of the microreticulated microcrystalline cellulose becomes relatively narrow during superpressure microfragmentation processing, and the particle size of the microreticulated particles plateaus after multiple passes. In the formation of fat-mimetic microreticulated microcrystalline cellulose, the size of the aggregated microcrystalline cellulose is much smaller than the one reported by Evans and Luner, due to the much higher shear force. The size of the turbulent eddies is believed to be somewhat less than 10 .mu.m, roughly corresponding to the observed particle size distribution.

In any event, in preparing microreticulated microcrystalline cellulose, the microcrystalline cellulose dispersion may be passed through a cell disruptor or other high shear zone, a sufficient number of times to provide a microreticulated microcrystalline cellulose dispersion of desired particle size having a high viscosity. The microreticulated dispersion will desirably have a total solids content of the porous, microreticulated microcrystalline cellulose particles in the range of from about 5 to about 10 percent, and more preferably from about 6 to about 8 percent, by weight, solids basis, based on the total weight of the aqueous dispersion. Superpressure microfragmentation of microcrystalline cellulose dispersions over about 10 weight percent solids content may be difficult. If a low solids content dispersion (e.g., 0.5-1 weight percent) is formed by high pressure shearing, the resulting dispersion may be concentrated by ultrafiltration, thin film evaporation or centrifugation procedures, if desired. After concentration, these microreticulated microcrystalline cellulose dispersions are smooth, creamy, bland, white, and have a fat-like mouthfeel, and after treatment with an astringency reducing agent, can be used as a fat replacer in a variety of food products at very low solids content levels to provide substantially fat-free products. For example, frozen desserts and food dressing products prepared with from about 1 to about 3 weight percent of such microreticulated microcrystalline cellulose on a total solids basis are stable, smooth and creamy.

Microreticulated microcrystalline cellulose as prepared by superpressure microfragmentation under small macroscalar turbulence conditions may have an astringent or drying mouthfeel, which adversely affects food product acceptability. Further in accordance with various additional aspects of the present invention, the fat-mimetic characteristics of food products containing microreticulated microcrystalline cellulose may be enhanced by coating the surface of the microreticulated microcrystalline cellulose particles with an astringency control agent. An effective treatment is post-homogenization gum coating. In this regard, microreticulated microcrystalline cellulose is combined with from about 40 to about 60 weight percent of an ionic or neutral gum, or mixture of gums, based on the total solids weight of the microreticulated microcrystalline cellulose in the aqueous dispersion. A number of anionic or neutral gums may be used including xanthan, carboxymethyl cellulose, carrageenan, alginate, locust bean gum, guar gum and mixtures thereof. The most effective gums are xanthan gum and carrageenan. The aqueous microreticulated microcrystalline cellulose dispersion having 2% to 10% microreticulated microcrystalline cellulose solids content is continuously mixed in a low shear vortex mixer, such as a Hobart mixer or a Breddo mixer, with the gum which has been treated in accordance with the invention to facilitate continuous mixing as described in more detail hereinafter. It is theorized that allowing the gums to hydrate in contact with the complex allows the gums to interact and coat the microreticulated microcrystalline cellulose in a particularly effective manner.

By "xanthan gum" is meant the heteropolysaccharide produced by fermentation of the microorganism of the genus Xanthomonas. A discussion of the physical and chemical properties may be found in Industrial Gums, R. L. Whistler, Ed., Academic Press, N.Y. (1973), p. 473.

Xanthan gum in aqueous solution with an appropriate counterion such as sodium or potassium is highly negatively charged because its side chains are composed of charged glucuronic acid, mannose and its pyruvate derivative. In aqueous solution, the highly charged mutually repelling and relatively bulky side chains, which are regularly disposed along the relatively narrow backbone, are believed to provide hydrated xanthan gum with a relatively linear structure, which is further believed to be an important factor in the provision of the desirable properties and functionality of the preferred microreticulated microcrystalline cellulose dispersions which include xanthan gum, and food products containing such dispersions, as will be further discussed.

Carrageenans are structural polysaccharides of red sea plants such as Chondus crispus and Gigartina stellata. There are several varieties of carrageenans which may be extracted from red sea plants for food use, including kappa, lambda and iota carrageenans. Carrageenans are strongly charged anionic polyelectrolytes of high molecular weight and regular configuration which have anionic sulfate ester groups regularly disposed along a polysaccharide backbone. Lambda carrageenan has a general linear structure having substantially three pendant sulfate groups for each two monosaccharide groups along the polymer backbone.

Kappa carrageenan and iota carrageenan have significantly less ester sulfate than lambda carrageenan, with iota carrageenan having approximately one sulfate group per monosaccharide group, and kappa carrageenan having approximately one sulfate group for each two monosaccharide group along the backbone. A discussion of the physical and chemical properties of lambda carrageenan may be found in Industrial Gums, R. L. Whistler, Ed., Academic Press, N.Y. (1973).

Addition of gum to the aqueous microreticulated microcrystalline cellulose dispersion has several purposes. Coating with gum has the qualities of improving mouthfeel, improving texture, mitigating undesirable flavors and sensations, and improving stability.

Post-homogenization coating of the aggregated microcrystalline cellulose with gums such as xanthan, carrageenan, or carboxymethyl cellulose is believed to stabilize the microreticulated microcrystalline cellulose structures in their interlocked network geometry and particle size distribution, and prevent further agglomeration. The charged layer of gum keeps the aggregates dispersed in food products prepared using the microreticulated cellulose dispersions, while improving their mouthfeel. Micrographic evidence which demonstrates that these "cotton ball" aggregates persist in food products, and appear to function as units of fat substitute functionality. Additional advantages of post-homogenization gum coating include exceptional smoothness, prevention of mouth-drying sensations, and minimization of cardboard or paper-like off-flavors.

The particle size distribution of the predominant proportion of the microreticulated microcrystalline cellulose particles (e.g., 8 to 12 .mu.m) is on the order of the size of emulsified fat droplets in many products. For example, butterfat droplets in milk may average about 4 .mu.m. In viscous dressings, such as mayonnaise or salad dressing, the average droplet size may typically be about 10 .mu.m. The porous microreticulated microcrystalline cellulose aggregates may be able to mimic fat in many products because they form structures which are about the same size as fat droplets. Moreover, they have a resiliency by virtue of their microreticulated structure which prevents the sensation of hard gritty particles, and which produces a high degree of functionality for a relatively small amount of the material. The functionality of the microreticulated microcrystalline cellulose material is believed to result from its ability to mimic the functionality of fat by not only providing viscosity enhancement to a food product, but also by imparting a unique, creamy, fat-like mouthfeeling.

The microreticulated microcrystalline cellulose dispersions have particularly desirable shelf-life, thermal, pH and dispersion stability, and a very high functionality to weight percent of solids ratio together with smooth, creamy texture and mouthfeel characteristics, and a bland taste which is generally compatible with a wide variety of food products.

Having generally described manufacture of microfragmented dispersions, various aspects of producing the viscous dressings will be further described with respect to methods and apparatus schematically illustrated in FIG. 2 and FIG. 15.

The viscous dressings of the present invention may be prepared by batch techniques, however, the components used to prepare the viscous dressings of the present invention are particularly suitable to a continuous method for the manufacture of low oil or oil free viscous dressings, such as mayonnaise type dressings and salad dressings. Accordingly, for purposes of simplicity, various aspects of the invention will be described hereinbelow in respect to a continuous process. As shown in FIG. 15, a premix is prepared from three previously prepared components, these components being a gum blend which is prepared in batch mixing tank 402 and is transferred to holding tank 408, a spice blend which is prepared in batch mixing tank 404 and is transferred to holding tank 410 and a microreticulated microcrystalline cellulose dispersion which is provided from tank 406 or from the heat exchanger 624 shown in FIG. 2.

The gum blend is a mixture of a gum, as previously described in connection with the gums which may be combined with the microreticulated microcrystalline cellulose, and a diluent selected from a dry water soluble component of the dressing or a triglyceride oil which is fluid at ambient temperature. The level of diluent is from about 25% to about 500% by weight based on the weight of the gum. All percentages used herein are by weight unless otherwise indicated.

Due to the high level of gum utilized in the gum blend compared to the level of microreticulated microcrystalline cellulose, i.e., from about 40% to about 60%, based on the weight of the microreticulated microcrystalline cellulose, it has been determined that the diluent is desirable to permit hydration of the gum during the short retention time encountered during continuous mixing of the three component streams to provide the premix.

The spice blend is a mixture of the balance of water required for the viscous dressing and the remaining components required for the dressing. In general, these components include salt, a sweetener, corn syrup solids having a D.E. of from about 15 to about 75, spices, flavors, colors and vitamins.

A gelatinized starch paste is separately prepared in mixing and heating tank 424. The starch paste contains sugar at a level of from about 4% to about 23%, corn syrup solids at a level of 0 to about 8%, vinegar (120 gr equivalent) at a level of from about 3% to about 8%, starch at a level of from about 8% to about 13%, sufficient edible acid to adjust the pH to within the range of from about 2 to about 4 and water at a level of from about 60% to about 70%.

In operation, the three previously prepared components of the premix, i.e., the gum blend, the spice blend and microreticulated microcrystalline cellulose dispersion are continuously transferred by metering pumps 412, 414 and 416, to mixing tank 640 (FIGS. 2 and 15) to provide a premix. The retention time in mixing tank 640 is from about 0.5 minutes to about 5 minutes. As previously described, the diluent for the gum blend can be an edible liquid, triglyceride oil or a dry, water soluble component of the viscous dressing, such as sugar or salt. In the case of the use of a liquid oil, the gum blend is in the form of a slurry of dispersed gum particles and the metering pump 412 can be used to feed the gum blend to mixing tank 640. When the diluent is a dry component, as shown in FIG. 2, the gum blend in powder form is metered onto a suitable powder dispensing device, such as the vibrating plate disperser 650 by an auger type metering device such as a salt and gum feeder 648.

A vibrating plate device 650 such as a flat plate held at a very sight angle to perpendicular which vibrates such that the gum blend powder falls in a dispersed fashion from the end of the plate towards the liquid may be used.

A sifting screen device may also be used as a means of dispersing the gum blend powder in air. The screen mesh may have openings slightly larger than the size of the gum particles may be moved at a speed of 30-120 cycles per minute in a circular motion or back and forth in the horizontal plane. The amplitude of the motion may in general be small, around two inches or less.

The mixing tank 640 should be capable of moving a highly viscous fluid at such a rate so as to create a vortex in the highly viscous fluid and the gum blend, spice blend and microreticulated microcrystalline cellulose dispersion meet the liquid surface at the vortex for maximum effectiveness. Impeller type tanks have been used successfully for this purpose. A recirculation pump 643 in recirculating loop 645 may be used to provide better mixing. A metering pump 426 is adjusted so that the output of the premix from mixing tank 640 matches the sum of the inputs of the gum blend, spice blend and the microreticulated microcrystalline cellulose dispersion.

It is important to add the gum without clumping or aggregation so as to form a well mixed dispersion. The gum, when used with a dry diluent, is desirably added directly, in dry form, to the highly viscous microreticulated microcrystalline cellulose aqueous dispersion under conditions of vortex shear.

The key process steps when the gum is used with a dry diluent are 1) delivery of the gum to a powder metering device without introducing moisture to the gum 2) dispersing the gum powder in air such that it falls towards the vortexing surface of the microreticulated microcrystalline cellulose dispersion, 3) rapid wetting of each gum particle and, 4) thorough mixing of the dispersion. In this way the gum particles are separated from one another and kept that way until they are wetted and dispersed in liquid. At that point there is no danger of clumping. Intimate mixing between the gum and microreticulated microcrystalline cellulose takes place simultaneously with hydration of the gum in the aqueous dispersion.

The oil, to the extent used in the dressing formulation, may be any of the well known edible triglyceride oils derived from oil seeds, for example, corn oil, soybean oil, safflower oil, cottonseed oil, etc., or mixtures thereof. The sweetener used is typically sucrose. However, other sweeteners such as dextrose, fructose, maltose, triose, high DE corn syrup solids and synthetic sweeteners may also be utilized. When the sweetener is sucrose, the sucrose is present in the dressing at a level of from about 8% to bout 15%. When other sweeteners are used, they are added at a level sufficient to provide the same sweetening power as this level of sucrose.

Corn syrups are a particularly desirable component of such fat-free dressing formulations. An important component of the substantially fat-free dressings is a corn syrup component in specific proportions having a dextrose equivalency in the range of from about 15 to about 75, and preferably in the range of from about 20 to about 35. Such corn syrup solids may be provided by acid, enzyme, or acid-enzyme hydrolysis of corn starch. The dextrose equivalent (DE) value may be calculated according to the formula DE =100/(M.sub.n /180.16) where M.sub.n is the number average molecular weight of the corn syrup solids. A substantial proportion of such corn syrup solids may be provided in the viscous dressing products in order to provide maximum benefits. In this regard, the viscous dressing may desirably comprise from about 3 to about 25 weight percent, and preferably in the range of from about 4 to about 21 weight percent of such corn syrup solids based on the total weight of the viscous dressing product.

The corn syrup solids component provides a substantial improvement in the textural organoleptic properties and reduces mouth coating, astringency and related lingering or undesirable aftertastes which could otherwise be present at the level of microreticulated microcrystalline cellulose use employed in the food dressing products.

A starch paste is used as a bodying agent in the viscous dressing to provide desired body or viscosity in accordance with conventional practice. Starch is typically present at a level of from about 2 percent to about 10 percent in the viscous dressing. Any suitable starch containing material may be used, and in this connection, any food starch, whether modified, unmodified or pregelatanized, tapioca flour, potato flour, wheat flour, rye flour, rice flour or mixtures thereof may be used.

The viscous dressing may have an aqueous pH of about 4.1 or lower, preferably in the range of from about 2.75 to about 3.75. Any suitable edible acid or mixture of acid may be used to provide the desired level of acidity in the viscous dressing, with suitable edible acids including lactic acid, citric acid, phosphoric acid, hydrochloric acid, and acetic acid and mixtures thereof. Mixtures of acetic acid and phosphoric acid are particularly preferred acidifying agents. The amount utilized to achieve a desired pH will depend on a variety of factors known in the art including the buffering capacity of protein components of the dressing.

The starch paste and the premix from mixer 640 are blended in bulk mixer 422. Mixer 422 is preferably a moderate shear mixer, such as a pin type mixer. A pin type mixer utilizes a plurality of spaced pins mounted on a vertical shaft which rotate through a plurality of spaced and staggered pins mounted on the wall of a cylindrical container. Prior to introduction of the premix to the bulk mixer 422, the premix is preferably passed through a suitable high shear mixer 420 to add in hydrating the gum. One suitable high shear mixer is a colloid mill.

Having generally described various aspects of the present invention, the invention will now be more particularly described with reference to the following specific Examples. All percentages used herein are by weight and all temperatures are degrees Fahrenheit, unless otherwise indicated.

A microreticulated microcrystalline cellulose product is prepared in aqueous dispersion by pumping 7910 pounds of deionized water with a conductivity of 6.0 micromhos into a mixing tank. 660 pounds of commercially available microcrystalline cellulose (Avicel PH101 product of FMC Corporation) is added to the water through a Tri-blender mixer. The mixture pH is about 6.05 and the conductivity is about 47 micromhos. This mixture separates quickly and must be agitated continuously to keep it suspended. The mixture is transferred to a hold tank and agitated at room temperature for approximately 2 hours. The suspension is then pumped through a high shear Rannie homogenizer system as described in FIG. 1, for 7 volumetric passes, with product samples being taken every pass. The product is cooled through a heat exchanger after each pass. One pass consists of the time calculated at the given flow rate, for all of the material in the hold tank to have passed through the homogenizer. The flow rate is 117.4 lbs/minute as pumped by a positive displacement pump to the homogenizer then through a micro-motion flowmeter to the heat exchanger and back into the same hold tank. The homogenizer inlet pressure is 13,400-13,600 psi. The inlet temperature to the homogenizer is held between 40.degree. and 80.degree. F. The temperature rise through the homogenizer is 40.degree.-50.degree. F. and the cooling from the heat exchanger is 35.degree.-45.degree. F.

The product is sampled each pass as the stream re-entered the hold tank. Samples are tested for particle size, total solids and viscosity (Brookfield). The solids level is measured to be 7.4.+-.0.1% total solids as measured with a microwave solids oven. The particle size after the first pass stays relatively constant in the range of 10-17 microns and the viscosity increases steadily at approximately 2500 cps per pass. Viscosity is measured at 70.degree.-80.degree. F. using a Brookfield viscometer with a B T-bar spindle at 10 rpm. The viscosity is measured from the sample taken at the tank inlet until the viscosity is within 2000 cps of the target 15,000 cps. Bulk samples are then drawn from the hold tank and the viscosity measured. When the bulk sample reaches 14,000.+-.1000 cps, the run is finished. After 7 passes, the sample viscosity is 18,000 cps and the tank sample measured 14,400 cps. The pressure driving the homogenizer is reduced to zero and the product continues to circulate until the tank temperature was less than 50.degree. F. The product is then pumped into drums for storage.

The finished product has a smooth creamy texture with a white appearance and a bland taste. The final solids analysis is 7.7.+-.0.1% and the viscosity is 13,340.+-.1200 cps. The finished product particle size is 12.96.+-.0.68 microns with conductivity of 63 micromhos and pH of 5.92. The water binding capacity is 10.3.+-.3.0% as measured by the amount of water that is released during a centrifuge test. The calculated Herschel-Bulkley rheology parameters were: the consistency coefficient, m, 40-45, the power law index, n, 0.41-0.55 and the yield stress, 450-550 dyne/cm.sup.2. as measured by a Carri-Med controlled stress rheometer with a 1.degree.5- cm cone. at 25.degree. F.

A very low fat viscous dressing of the mayonnaise or salad dressing type was prepared utilizing the microreticulated microcrystalline cellulose of Example 1 as a fat substitute. 3000 pounds of the microreticulated microcrystalline cellulose in the form of an aqueous dispersion having 9.0% solids were transferred to holding tank 406. 2500 pounds of a spice blend was prepared having the following components was prepared by adding the dry ingredients to water in high shear mixing tank 404.

The spice blend was transferred to holding tank 410.

A gum blend Was prepared by combining 378 pounds of xanthan gum, 30.3 pounds of egg white, 5 pounds of sodium caseinate, 20.7 pounds of propylene glycol alginate gum, 42.3 pounds of Viscarin gum, sold commercially by Hercules Division of DuPont Corp., and 1120 pounds of soybean oil in low shear mixer 402. The gum blend was then transferred to holding tank 408.

4000 pounds of a starch base was prepared from the following components:

In preparing the starch base, water was added to a jacketed vessel and the remaining components were added under agitating conditions. The resulting slurry was heated to 190.degree. F. and held at this temperature for a period of one minute to gelatinize the starch. The starch base was cooled to room temperature and transferred to holding tank 424.

In preparing the viscous dressing, the gum blend, the spice blend and microreticulated microcrystalline cellulose dispersion were continuously transferred to vortex mixer 640 at respective rates of 39, 267 and 244 pounds per minute to form a premix. The residence time in mixer 640 was 3 minutes.

The premix was passed through a high shear mixer 420 to further aid in hydrating the gum.

The premix is continuously mixed with the starch base in bulk mixer 422. Bulk mixer 422 mixes the premix and starch base under conditions of moderate shear to avoid breaking down the gelatinized starch. The ratio of premix to starch base is 55:45 parts by weight to continuously provide 1000 pounds per minute of the viscous dressing. The product has a smooth, creamy, organoleptic texture.