The disclosure relates to a solid glass matrix of polysaccharide, saccharides and polyols as delivery vehicle for preservation and post gastric administration of a probiotic. The delivery vehicle is capable of releasing the probiotic at their site of action. The present invention further includes methods of making and using the solid glass matrix delivery vehicle of the invention.

Description of the Invention

BACKGROUND OF THE DISCLOSURE

The disclosure relates generally to the field of a delivery vehicle for probiotic bacteria comprising a dry matrix of polysaccharides, saccharides and polyols in a glass form. Methods of making and uses thereof are also provided.

Probiotics are defined as live microbes that beneficially affect the host by modulating mucosal and systemic immunity, as well as improving intestinal function and microbial balance in the intestinal tract. Various nutritional and therapeutic effects have been ascribed to probiotics including: modulating immune response, lowering serum cholesterol concentrations, improving lactose intolerance symptoms, increasing resistance to infectious intestinal diseases, decreasing duration of diarrhea, reducing blood pressure, and helping to prevent colon cancer (Isolauri E et al. 2001, Kailasapathy K and J. 2000, Marteau PR et al. 2001, Perdigon G et al. 2001). In order to exert their beneficial effects on the host, probiotics must remain viable and reach the intestine in large numbers (Favaro-Trindade and Grosso 2002). However, maintaining long term stability of probiotics requires special storage conditions, since viability deteriorates rapidly over a short time period at ambient temperature and humid conditions (Shah 2000). In addition to poor shelf life, a significant loss of viability occurs upon exposure of the probiotics to gastric conditions of low pH and digestive enzymes. Existing preservation methods fail to provide satisfactory viability upon storage and gastric protection, especially if cells are stored at ambient or higher temperature and humidity.

Freeze-drying is often used for preservation and storage of bacteria because of the low temperature exposure during drying. However, it has the undesirable characteristics of significantly reducing viability as well as being time and energy-intensive. Freeze-drying involves placing the cells in solution, freezing the solution, and exposing the frozen solid to a vacuum under conditions wherein it remains solid and the water and any other volatile components are removed by sublimation. Standard freeze drying temperature of -30.degree. C. to -70.degree. C. are below the freezing point of water, but are well above the glass transition (Tg) temperature of the drying solution, which results in the undesirable effect of crystallization of water into ice. Freezing bacterial cultures results in substantial physical damage to the bacterial cell wall and subsequent loss of viability. Therefore, avoiding ice formation during cold storage of proteins, viruses, cells, tissues, and organs is an important problem in cryobiology.

The freezing point of water can be lowered by adding solutes that lower the vapor pressure of water. Freezing point depression is the physical basis on which essentially all currently used antifreeze agents (e.g., glycols, sugars and salts) perform. The disadvantage of freezing point depressors, known as cryoprotectants, is that large quantities of solutes (10% or more) are required to lower the freezing point by even a few degrees Celsius. At sufficiently high concentrations (typically 50% or more), conventional antifreeze agents can prevent ice formation, allowing aqueous solutions to be cooled to temperatures well below 0.degree. C. without freezing. However, cryoprotectants are generally toxic at the high concentrations required to achieve glass formation or vitrification.

Other methods used to prepare dry and stable preparations of probiotics such as desiccation at ambient temperature and spray drying also has drawbacks. Desiccation at low or ambient temperature is slow, requires extra precautions to avoid contamination, and often yields unsatisfactory viability. Spray drying involves short excursions to relatively high processing temperatures and results in viability losses and limited storage times, even when stabilizing excipients are used (Lievense L C, van't Riet K. 1994. Convective drying of bacteria. II. Factors influencing survival. Adv Biochem Eng Biotechnol. 51:71-89).

A viable and stable formulation for intestinal targeting of probiotics has been described by Simmonds et al. (2005). The process requires the granulation of lyophilized bacteria with microcrystalline cellulose stabilizers such as skim milk, salts or short chain sugars and a disintegrant such as starch or alginic acid. The granulated semi dry bacteria are then desiccated at 40-70.degree. C. to reduce the residual moisture level to less than 2 percent. This is followed by coating with an enteric agent and plasticizer. This multi-step process results in large particle size (over 425 micron) and still results in up to 1.5 logs loss of viability. An additional disadvantage of this method is the high content of the enteric coating agents (over 25% of the microsphere weight), which are mostly synthetic and not recognized as food grade materials. An inherent disadvantage of a coating procedure is that the relative proportion of the coating to active agent goes up by a cubic function of the particle, as the particle size gets smaller, making the process less usable for the production of particles of sizes less than 300 micron.

An alternative method of bacterial preservation has been described which uses a foam formation technique while eliminating the formation of ice crystals (Bronshtein et al. 2004, Roser et al. 2004). This method requires high concentrations of sugars (a combination of methylated mono, di and oligo saccharides) in the drying media and a freeze drier that is equipped with a controlled vacuum system and temperature exposure, and the addition of foam forming elements and stabilizers. In spite of some advantages of this method in achieving longer shelf life stability, the foam-preserved bacteria are not protected from gastric excursion. Furthermore this process is difficult and costly to scale up because the foam requires, by definition, large volumes of space under reduced atmospheric pressure (i.e., in a vacuum) for the production of very little mass. In addition, this material is very sensitive to humidity and the product will take up water readily, decreasing the viability of the bacteria.

A composition containing a sugar (trehalose) partly in amorphous glassy phase and partly in crystalline hydrate phase has been proposed by Franks et al (2003). The crystalline hydrate phase serves as an agent to dehydrate the amorphous phase, thereby enhancing the glass transition temperature of the amorphous glassy state. This composition was shown to stabilize single molecules such as proteins or nucleotides. The glass transition temperature of a mixture depends, among other factors, on its chemical composition (sugars, proteins, salts) and the moisture content, with water acting as a plasticiser, depressing the glass temperature. If, at any time, the glass transition temperature (Tg) is exceeded, either by exposure to heat or in consequence of moisture migration into the product, the amorphous glassy state may become liable to irreversible phase separation by crystallization. If crystallization occurs, any residual amorphous phase will then be composed of the other components and the moisture, resulting in a further depression of the glass transition temperature.

A glass is an amorphous solid state that is obtained by controlled desiccation of a solution. The advantage of the glassy phase in achieving long term stability results from the fact that diffusion in glassy (vitrified) materials occurs at extremely low rates (e.g., microns/year). Glassy materials normally appear as homogeneous, transparent, brittle solids, which can be ground or milled into a powder. The optimal benefits of vitrification for long-term storage are observed under conditions where Tg is greater than the storage temperature. The Tg is directly dependent on water activity and temperature, and may be modified by selecting an appropriate combination of solutes (i.e., polysaccharides, sugars, salts and proteins).

Glass formation occurs naturally in some plant and arthropod species that are very desiccation tolerant. A number of mosses and ferns, so-called resurrection plants, can undergo severe desiccation and survive for many years in a quiescent metabolic state only to revive upon the return of water to the environment. In most cases, the adaptation characteristic is to increase internal concentrations of certain saccharides such as trehalose to a level that form glassy states.

Prior to the current disclosure, no one has been able to provide a common and cost effective solution to the separate problems facing the probiotic industry, namely maintaining long shelf life stability (i.e., viability) of bacterial cells at ambient temperatures and high water activities (or high humidity) and providing gastric protection to minimize losses of probiotic viability during the transit through the stomach. The present invention overcomes these problems.

BRIEF SUMMARY OF THE DISCLOSURE

The present invention encompasses compositions and methods of producing microparticles comprising a solid matrix in a glass form suitable for oral delivery. The compositions include a combination of a polysaccharide, a saccharide, a polyol and a probiotic bacteria. These compositions are designed to provide longer shelf life stability at ambient temperature in high water activity environments, and gastric protection of the probiotic. Furthermore, the method of production of this matrix involves processes that result in a minimal loss of probiotic viability.

Accordingly, one aspect of the invention comprises a preservation mixture of carbohydrates including at least one polysaccharide, one saccharide (mono di or oligo saccharide) and one polyol and at least one bacterium to be incorporated in the carbohydrate mixture.

In a preferred aspect, the bacteria in the preservation carbohydrate mixture are probiotic bacteria selected from, but not limited to the group consisting live Lactobacillus, Bifidobacterium, Enterococcus, Propionobacterium, Bacillus, and Streptococcus.

In another aspect of the invention the polysaccharide in the preservation mixture provides gastric protection and control release mechanism that gradually release the microbes at their site of action along the fore and hind gut of the animal or man. Examples of polysaccharides with gastric protection and a controlled release mechanism are hydrocolloid forming polysaccharides selected from the group including, but not limited to starch (including non-digestible starch), pectin, insulin, xanthan gum, alginate, alginic acid, chitosan, carrageenan, carboxymethyl cellulose, methyl cellulose, guar gum, gum arabic, locust bean gum and combinations thereof. Also preferably, the concentration of the polysaccharides in the preservation mixture is less than 10% w/v and more preferably less than 5% w/v of the preservation mixture.

In another aspect of the invention the saccharide/polyol combination in the preservation mixture is formulated so that it does not crystallize during drying and long-term storage at ambient temperature. A suitable glass formulation system includes, but is not limited to, trehalose/glycerol, trehalose/mannitol, trehalose/maltitol, trehalose/isomalt, trehalose/adonitol, trehalose/lactitol and trehalose/sorbitol. Trehalose is a naturally occurring, non-reducing disaccharide, which is associated with the prevention of desiccation damage in certain plants, microbes and animals that can dry out without damage and revive when rehydrated. Trehalose also has been shown to be useful in preventing denaturation of proteins, viruses and foodstuffs during desiccation (Chen et al. 2001, Crowe and Crowe 1992, Liao et al. 2002). Compared to sucrose, the glass transition temperature of trehalose is significantly higher (110.degree. C. vs. only 65.degree. C.) (Crowe et al. 1998). However, trehalose alone is not always sufficient to stabilize bacteria especially at high temperature and humidity. In addition, cell membranes are more permeable to external sugar alcohols than to external trehalose (Krallish I et al. 1997, Linders L J et al. 1997, Qiu L et al. 2000). It is the synergetic effect of trehalose and sugar alcohols that provide better protection and improve cell viability over extended period of storage. Preferably, the concentration of the both saccharide and polyol in the mixture is less than 60% w/v and more preferably less than 40% w/v of the preservation mixture. The ratio between the saccharide and the polyol is preferably about 3:1 trehalose/polyol, although a ratio of 1:3 trehalose/polyol is also similarly effective in the preservation of certain probiotic species.

The present invention also provides methods of drying the mixture in glass form with a minimum loss of viability. It was discovered that vitrifying and efficient drying of the preservation mixture under vacuum was possible without the need of foam formation as described by Bronshtein (2004). Gelling or cross-linking the polysaccharides in the preservation mixture and slicing it to small pieces eliminated the need to foam the mixture in order to dry it under vacuum. It also reduced the formation of a rubbery product which happened often in the foaming process. Preferably, the preservation mixture, including the probiotic, is allowed to gel at low temperature and is then sliced and vacuum dried under conditions suitable for glass formation. More preferably the polysaccharide in the mixture is selected from the group of cross-linkable polysaccharides such as alginate, pectin or chitosan. The mixture is then extruded into Ca.sup.++ bath and the strings or particles collected, rinsed with water, and then soaked in a suitable trehalose/polyol mixture followed by vacuum drying under conditions suitable for glass formation.

The present invention also provides methods of vacuum drying the preservation matrix without foaming or ice formation. The glass formation drying method comprises maintaining the matrix at 40.degree. C., applying an initial vacuum of about 2,500 mTOR for a period of time followed by drying at less than 100 mTOR for another period of time. The initial product temperature is preferably maintained at or about 10-20.degree. C. during the period at partially reduced pressure (2,500 mTOR) and then increased to 40-50.degree. C., as the atmospheric pressure is decreased to less than 100 mTOR. A final drying step at 20.degree. C. under maximum vacuum (ca. 10 mTOR) for additional period of time can also be of benefit for the final water removal. The dry matrix can then be ground or milled and, if necessary, sieved to a desired particulate powder.

DETAILED DESCRIPTION

Fundamental to this invention is a polysaccharide capable of forming a strong gel matrix. This matrix preferably retains the bacteria and the preservation mixture even after being sliced into small pieces or formed into thin threads, strings, or particles. Additionally, the polysaccharide matrix preferably possesses a controlled release mechanism that protects the bacteria in the stomach, but is able to release the bacteria at their site of action along the intestine.

Several polysaccharides exhibit these requirements and are suitable for use as described herein. High amylose starch is a polysaccharide capable of forming firm gel after hydrating the starch granules in boiling water, dispersing the granules with the aid of high shear mixer and then cooling the solution to about 0-10.degree. C. The firmness and strength of the gel depend on the concentration of the starch in the solution, with a maximal workable concentration of up to 10% w/v. The sliced starch gel matrix is also capable of retaining the live bacteria in the preservation mixture, and since it is mostly non-digestible by intestinal or gastric juices, the bacteria are protected from gastric destruction while within the starch matrix. The controlled release mechanism is provided by the fact that high amylose starch is readily digestible by the gut microflora at which time the delivered live bacteria are then released in their intact form.

Pectin is another suitable polysaccharide that performs very similar to high amylose starch. Pectin has an additional advantage since the strength of the pectin gel matrix can be further increased by the addition of divalent cations such as Ca.sup.++ that forms bridges between carboxyl groups of the sugar polymers.

In a preferred embodiment of the present invention, alginate or a combination of alginate and non-digestible starch is used. Alginate can form a firm gel matrix by cross-linking with divalent cations. The alginate containing preservation solution can be hardened into a firm gel matrix by internally cross-linking the alginate polysaccharides with Ca.sup.++ and then slicing the gel into small pieces while the bacteria and the preservation mixture are fully retained within the gel matrix. Another method of cross linking the solution containing alginate and preservation mixture is by extruding thin threads or strings of the solution into Ca.sup.++ bath. The strings harden instantly upon interaction with Ca.sup.++. The thin strings are harvested, rinsed with fresh water and then soaked again in the preservation solution but without the presence of polysaccharides. Another suitable method is to inject the thin threads into Ca.sup.++ bath, which also contains a preservation mixture at equal concentration and proportion of that of the extruded solution. An alternative method of preparation of the matrix is to spray atomize the mixture into a bath containing Ca.sup.++ cations. In such a procedure, small microparticles from 50 to 500 microns are produced. Such particles are harvested, rinsed and soaked in the preservation medium, or the bath itself may contain the preservation mixture as described above for the production of thin threads or strings.

The level of Ca.sup.++ in the bath is constantly monitored and only sufficient amount of cations necessary to cross link the alginate are added at a time. This eliminates the need to rinse excessive Ca.sup.++ from the strings or particles, thereby retaining all the sugar in the matrix, which would otherwise be washed away. In one preferred mode of the present invention, monitoring the Ca.sup.++ cations within a range of 0.25-0.5% w/v in the cross-linking bath is sufficient to harden the extruded alginate solution without any damage to the probiotic bacteria. The gastric protection and controlled release trigger is also fulfilled by the use of alginate polysaccharide. A polymeric matrix containing alginate remains firm in the acidic environment of the stomach, thereby protecting the bacteria, but quickly disintegrates in the higher pH and phosphate-rich environment of the intestine. This results in the release of the probiotic bacteria at their site of action along the intestine.

The purpose of the preservation mixture is to provide protection from temperature and moisture excursions of the final product without undue loss of viability of the probiotic bacteria. An ideal mixture contains a combination of saccharides and sugar alcohols that form an amorphous glassy phase with a glass transition temperature (Tg) well above ambient temperature and water activity of the product. Trehalose alone is not always sufficient to stabilize bacteria, especially at high temperature and humidity. A more suitable mixture was found to be a combination of trehalose and additional sugar alcohol that provides a synergetic effect of better protection and improved cell viability over extended periods of storage. In addition to sugar alcohols and other long chain polyalcohols, other preservation agents include sucrose, lacto sucrose, raffinose, maltodextrose, sepharose and dextran. These compounds may synergistically improve the preservation of certain bacteria species.

The concentration and proportion of different carbohydrates in the preservation mixture depends on several factors, but most particularly on the bacteria species, strain, and drying conditions. The present invention discloses several optimal concentrations and sugar proportions suitable for inclusion in the preservation mixture for a number of probiotic bacteria. Preferably, the carbohydrate concentration should be less than about 50%, as higher concentrations may interfere with effective drying.

The preservation mixture optionally include other additives that contribute to the overall stability of the probiotic bacteria. Suitable additives include proteins, amino acids, diluents, chelating agents, buffers, preservatives, stabilizers, antioxidants, and lubricants. Specific examples of such additives would include, but are not limited to: amino acids, lysine, glycine, L leucine, isoleucine, arginine, cysteine; proteins, human serum proteins, egg albumin, gelatin; buffers, various sodium phosphate buffers, citric/citrate buffers; preservatives, derivatives of hydroxybenzoic acids; antioxidants, vitamin E, ascorbic acid; lubricants, water miscible silicone/silicates; chelating agents, citric acid, EDTA, EGTA.

In a preferred mode of the present invention, the sliced gel or thin threads or strings are dried in such a way that a glass is formed. Several drying methods can be employed, including, but not limited to, air drying at ambient temperature, spray drying, fluidized bed drying, vacuum drying, and freeze drying. As used herein, the glass containing the dried bacteria cells preferably contains a residual moisture content of less than about 5%, and, more preferably, less than about 2%.

Drying is preferably performed under vacuum in a freeze drier at a product temperature above the freezing temperature of water under such conditions. In general, vacuum drying are performed in two stages. The first stage involves moderately reduced pressure (ca. 2500 mTOR) at mild temperatures (20.degree. C.), while the second stage involves lower pressures (i.e., higher vacuum -100 mTOR) at higher temperature (up to about 50.degree. C.). This process can be achieved using a programmable control system for vacuum pressure and product temperature. The vacuum and temperature conditions for the first drying stage are adjusted empirically according the size of the drier, heat transfer capacity, and the product load, but the goal is to keep the product above its freezing temperature while maximizing the water evaporation rate. In one embodiment, the temperature is initially maintained at about 20.degree. C. for about 16 hours, followed by gradually increasing the temperature to about 50.degree. C. for the following 48 hours. These drying conditions allow the formation of glassy state wherein the bacteria are locked in a quiescent state inside the polysaccharide matrix.

In a preferred embodiment, the probiotic bacteria are dried as follows: the initial vacuum pressure is adjusted to about 2500 mTOR, with initial shelf temperature of 40.degree. C. for 12 hours, followed by incrementally reducing the atmospheric pressure (i.e., increasing the vacuum) to less than 100 mTOR at a rate of 125 mTOR/hr. Once the vacuum reaches 100 mTOR, the sample is maintained at 40.degree. C. for an additional 12 hours. Following this protocol, the drying procedure is completed within 48 hours without substantially compromising viability. In accordance with the present invention, the large surface area of the sliced and chopped gel or strings greatly increases evaporation rate without the need to boil or foam the product, thus eliminating inconsistent drying conditions and splattering of the foaming product solution in the vacuum chamber. Additionally, the disclosed composition and method of drying results in a higher loading capacity of product as compared to the foam drying method, that permits only a thin layer of solution to foam and dry efficiently.

An alternative drying procedure for the freshly prepared matrix strings or particles includes a controlled desiccation of the matrix by addition of the hydrogel to a certain volume (preferably 1:10 by weight) of dry powdered saccharide such as trehalose or dry powdered preservation mixture. During this process, the hydrogel is rapidly desiccated at ambient temperature, concentrating the preservation material in the matrix itself. The process is preferably set up in a counter-current fashion where the fully hydrated hydrogel matrix containing the bacteria is added to one end of the process stream and fresh, dry powdered preservation saccharide flows from the opposite direction (FIG. 1 (see Original Patent)). The wetted powdered saccharide material are dried at elevated temperature and reused while the partially desiccated hydrogel then goes on to the second stage of vacuum drying described above. This process significantly reduces the drying time and process costs.

The resultant matrix-bound glass material containing the dried, stabilized probiotic bacteria has a Tg sufficiently high to preserve the bacteria at ambient temperature (up to 30.degree. C.) in a relative humidity of 33%. Generally, the higher the Tg, the higher the allowable storage temperature and humidity. Tg of the dry glassy preservation mixture of the present invention is determined using standard techniques in the art, such as differential scanning calorimetry.

The methods and compositions of the invention facilitate the development of several products, including, but not limited to: live bacterial vaccines in a dry stable form, live bacterial neutraceuticals (probiotics) in a dry stable form, live bacterial starter cultures in a dry stable form, live bacteria in a dry stable form for agricultural, aquaculture, or bioremedial use, and live bacterial cultures in a dry stable form for the biotechnology industry.
 

Claim 1 of 10 Claims

1. A process for producing a glass matrix comprising a probiotic bacteria, the process comprising: a) dispersing under heating conditions at least one polysaccharide in water; b) adding trehalose, a sugar alcohol and a probiotic bacteria to the dispersed polysaccharide to form a slurry, wherein the ratio of trehalose to sugar alcohol is 3:1 to 1:3 and wherein the sugar alcohol is selected from a group consisting of mannitol, glycerol, sorbitol, xylitol, maltitol, lactitol and isomalt; c) contacting the slurry with a bath comprising Ca.sup.++ ions for a sufficient time to allow cross-linking thereby forming a gel matrix d) harvesting the gel matrix and placing the harvested gel matrix in a drier wherein the temperature of the harvested gel matrix is maintained above the freezing temperature of water; e) reducing the pressure during a first drying stage and maintaining the temperature at about 10-20.degree. C. for a first period of time; and f) further reducing the pressure during a second drying stage and increasing the temperature to between about 40-50.degree. C. for a second period of time to produce the glass matrix comprising the probiotic bacteria.

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