Abstract:
A method for making a highly soluble Stevia sweetener is described. The resulting sweetener readily provides solutions with up to or greater than 30% concentration which are stable for more than 24 hours.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a process for the preparation of highly soluble individual or combined sweet glycosides from a  Stevia rebaudiana  Bertoni plant extract, and more particularly for preparation of highly soluble rebaudioside A. 
       DESCRIPTION OF THE RELATED ART 
       [0002]    It is well known that Rebaudioside A exhibits so called polymorphism (Zell et al., 2000). Rebaudioside A amorphous, anhydrous and solvate forms differ significantly from each other in terms of solubility which is one of the main criteria for the commercial viability of a sweetener. In this regard, as shown in Table 1, the hydrate form of Rebaudioside A displays the lowest solubility (Prakash et al., 2008). It was shown that Rebaudioside A may transform from one polymorph form to another at certain conditions (U.S. pat. appl. Ser. No. 11/556,049). 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Properties of Rebaudioside A forms (US Pat. Appl. 11/556,049) 
               
             
          
           
               
                   
                 Polymorph Forms 
               
             
          
           
               
                   
                 Form 1 
                 Form 2 
                   
                 Form 4 
               
               
                   
                 Hydrate 
                 Anhydrous 
                 Form 3 Solvate 
                 Amorphous 
               
               
                   
                   
               
             
          
           
               
                 Rate of 
                 Very low 
                 Intermediate 
                 High (&gt;30% in 
                 High (&gt;35% in 
               
               
                 dissolution 
                 (&lt;0.2% in 60 
                 (&lt;30% in 5 
                 5 minutes) 
                 5 minutes) 
               
               
                 in H 2 O 
                 minutes) 
                 minutes) 
               
               
                 at 25° C. 
               
               
                 Alcohol 
                 &lt;0.5% 
                 &lt;1% 
                 1-3% 
                 &lt;0.05% 
               
               
                 content 
               
               
                 Moisture 
                   &gt;5% 
                 &lt;1% 
                  &lt;3% 
                  6.74% 
               
               
                 content 
               
               
                   
               
             
          
         
       
     
         [0003]    Patent application WO/2010/118218 describes a process of producing highly soluble rebaudioside A by preparing a highly soluble hydrated crystalline form. However the described methodology utilizes low throughput techniques such as evaporative crystallization or hot filtration/centrifugation of slurries which can be hard to accomplish in large industrial scale. 
         [0004]    On the other hand it is known (Prakash et al., 2008) that rebaudioside A amorphous forms prepared by spray drying display high solubility as well. However spray drying of rebaudioside A is a very challenging and low throughput task because generally spray drying requires concentrated feed solutions (about 50% solids content). Rebaudioside A concentrated solutions prepared by simple dissolution are very unstable and tend to crystallize very fast. These concentrated solutions (&gt;10%) prepared by common solubilization methods such as heating under normal conditions crystallize shortly after cooling down to room temperature. Thus spray drying of such solutions requires special equipment capable of maintaining the solution at elevated temperature. 
         [0005]    On the other hand extended exposure of rebaudioside A to high temperature both in solid form and in aqueous solutions results in hydrolytic decomposition of the material (Prakash et al., 2008). 
         [0006]    Therefore a high throughput process of manufacturing highly soluble Rebaudioside A or other steviol glycosides on an industrial scale without needing a sophisticated equipment setup will offer certain advantages compared to other techniques known to art. 
       SUMMARY OF THE INVENTION 
       [0007]    The invention is directed to a method for producing a sweetener comprising the steps of providing a Stevia sweetener powder and solubilizing it in the water under gradient temperature treatment conditions, to produce a highly stable concentrated solution, and spray drying the highly stable concentrated solution to obtain a highly soluble Stevia sweetener powder. 
         [0008]    Hereinafter the term “steviol glycoside(s)” will mean Rebaudioside A, Rebaudioside B, Rebaudioside C, Rebaudioside D, Rebaudioside E, Rebaudioside F, Stevioside, Steviolbioside, Dulcoside A, Rubusoside, or other glycoside of steviol and combinations thereof. 
         [0009]    Hereinafter, unless specified otherwise, the solubility of material is determined in RO (reverse osmosis) water at room temperature. Where the solubility is expressed as “%” it to be understood as number of grams of material soluble in 100 grams of solvent. 
         [0010]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]    A process for the preparation of highly soluble Stevia sweetener, particularly Rebaudioside A, is described herein. 
         [0012]    Crystalline Rebaudioside A has an inherently very low solubility, ranging from about 1%-2%. As described above, Rebaudioside A exhibits polymorphism, resulting in a variety of forms with very different characteristics and handling properties. The hydrate form has very low solubility (less than 0.2%), and is therefore not commercially viable as a sweetener. The solvate form has a solubility typically greater than 30%, but this form has only of scientific interest and cannot be used for food or beverage applications because the level of residual alcohol (1-3%) makes it unfit for use in foods and beverages. The anhydrous form has a solubility reported in literature of a maximum of up to about 30% solubility. The amorphous form has as solubility generally greater than 30%, but for its preparation, the crystalline form has to be dissolved in the water at very high concentrations (approx. 50%) which is not achievable by common solubilization techniques. 
         [0013]    Typical spray drying techniques involve the use of a highly concentrated, and yet stable, starting solution to achieve the highest output possible. As noted above, crystalline Rebaudioside A has a very low solubility, so to create a stable solution (one which will not crystallize at room temperature), the solution has to be very dilute. Spray drying very dilute solutions is not economically efficient as the output of the spray dried powder will be very low. The need exists, therefore, for a process in which a high solubility Rebaudioside A is obtained by a process which does not require significantly diluted Rebaudioside A solution in order for the solution to be stable at room temperature. 
         [0014]    In one embodiment of the present invention, an initial material, comprising sweet glycoside(s) of the  Stevia rebaudiana  Bertoni plant extract, which includes Stevioside, Rebaudioside A, Rebaudioside B, Rebaudioside C, Rebaudioside D, Rebaudioside E, Rebaudioside F, Steviolbioside, Dulcoside A, Rubusoside or other glycoside of steviol and combinations thereof, was combined with water at a ratio of about 1:1 (w/w). 
         [0015]    The obtained mixture was further subjected to a gradient heat treatment which resulted in high stability and high concentration solution. The gradient of about 1° C. per minute was used in heating the mixture. The mixture was heated to the temperature of about 110-140° C., preferably about 118-125° C. and was held at maximum temperature for about 0-120 min, preferably about 50-70 min. 
         [0016]    After the heat treatment the solution was cooled down to room temperature at gradient of about 1° C. per minute. 24-hour incubation of this high stability and high concentration solution did not show any crystallization. 
         [0017]    The solution was spray dried by a laboratory spray drier operating at about 175° C. inlet temperature and about 100° C. outlet temperature. A highly soluble amorphous form of rebaudioside A was obtained with greater than about 30% solubility in water at room temperature. 
         [0018]    The following examples illustrate preferred embodiments of the invention. It will be understood that the invention is not limited to the materials, proportions, conditions and procedures set forth in the examples, which are only illustrative. 
       EXAMPLE 1 
     Preparation of Rebaudioside A Concentrated Solution 
       [0019]    100 g of rebaudioside A containing Stevioside 0.2%, Rebaudioside C 0.3%, Rebaudioside F 0.3%, Rebaudioside A 97.7%, Rebaudioside D 1.0%, and Rebaudioside B 0.3%, all percentages being on a percent dry weight basis, and having water solubility of 0.6% was mixed with 100 g of water and boiled on a laboratory heater until complete dissolution. Upon complete dissolution, the solution was cooled to room temperature to make Solution #1. 
       EXAMPLE 2 
     Preparation of Rebaudioside A Concentrated Solution 
       [0020]    100 g of rebaudioside A containing Stevioside 0.2%, Rebaudioside C 0.3%, Rebaudioside F 0.3%, Rebaudioside A 97.7%, Rebaudioside D 1.0%, Rebaudioside B 0.3%, all percentages being on a percent dry weight basis, and having water solubility of 0.6% was mixed with 100 g of water and incubated in autoclave (AMA 270, Astell Scientific, UK), at 121° C. for 1 hour. Upon completion of incubation period the obtained clear solution was cooled to room temperature to make Solution #2. 
       EXAMPLE 3 
     Preparation of Rebaudioside A Concentrated Solution 
       [0021]    100 g of rebaudioside A containing Stevioside 0.2%, Rebaudioside C 0.3%, Rebaudioside F 0.3%, Rebaudioside A 97.7%, Rebaudioside D 1.0%, Rebaudioside B 0.3%, all percentages being on a percent dry weight basis, and having water solubility of 0.6% was mixed with 100 g of water and incubated in thermostatted oil bath. The temperature was increased at 1° C. per minute to 121° C. The mixture was maintained at 121° C. for 1 hour and then the temperature was decreased to room temperature (25° C.) at 1° C. per minute to make Solution #3. 
       EXAMPLE 4 
     Rebaudioside A Concentrated Solution Stability 
       [0022]    Rebaudioside A Solution #1, Solution #2 and Solution #3 prepared according to EXAMPLE 1, EXAMPLE 2 and EXAMPLE 3, respectively, were assessed in terms of their stability at room temperature (25° C.). The results are summarized in Table 2. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Rebaudioside A concentrated solution stability (50% total solids, 25° C.) 
               
             
          
           
               
                 Time, 
                 Observation 
               
             
          
           
               
                 hrs 
                 Solution #1 
                 Solution #2 
                 Solution #3 
               
               
                   
               
             
          
           
               
                 0.5 
                 Clear solution 
                 Clear solution 
                 Clear solution 
               
               
                 1 
                 Intensive 
                 Cloudy solution, precipitate 
                 Clear solution 
               
               
                   
                 crystallization 
                 on the bottom 
               
               
                 2 
                 Viscous slurry 
                 Intensive crystallization 
                 Clear solution 
               
               
                   
                 of crystals 
               
               
                 4 
                 Solidified 
                 Viscous slurry of crystals 
                 Clear solution 
               
               
                   
                 crystalline 
               
               
                   
                 mixture 
               
               
                 24 
                 Solidified 
                 Solidified crystalline mixture 
                 Clear solution 
               
               
                   
                 crystalline 
               
               
                   
                 mixture 
               
               
                   
               
             
          
         
       
     
         [0023]    It can be seen that the solution prepared by temperature gradient method shows greater stability against crystallization. 
       EXAMPLE 5 
     Preparation of Highly Soluble Rebaudioside A 
       [0024]    Rebaudioside A Solution #1, Solution #2 and Solution #3 prepared according to EXAMPLE 1, EXAMPLE 2 and EXAMPLE 3, respectively, were dried using YC-015 laboratory spray drier (Shanghai Pilotech Instrument &amp; Equipment Co. Ltd., China) operating at 175° C. inlet and 100° C. outlet temperature. Solution #1 and Solution #2 had to be maintained at 80° C. to prevent premature crystallization whereas Solution #3 was maintained at room temperature. The Solution #1 yielded Sample #1, Solution #2 yielded Sample #2 and Solution #3 yielded Sample #3. 
         [0025]    The obtained amorphous powder samples were compared for solubility (Table 3). 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Highly soluble Rebaudioside A 
               
             
          
           
               
                 Solubility, 
                 Observation 
               
             
          
           
               
                 % 
                 Sample #1 
                 Sample #2 
                 Sample #3 
               
               
                   
               
             
          
           
               
                 5 
                 Clear solution 
                 Clear solution 
                 Clear solution 
               
               
                 10 
                 Slightly cloudy 
                 Clear solution 
                 Clear solution 
               
               
                   
                 solution 
               
               
                 20 
                 Cloudy solution 
                 Slightly cloudy 
                 Clear solution 
               
               
                   
                   
                 solution 
               
               
                 30 
                 Undissolved matter 
                 Cloudy solution 
                 Clear solution 
               
               
                   
                 on the bottom 
               
               
                 40 
                 Significant amount of 
                 Significant 
                 Slightly cloudy 
               
               
                   
                 undissolved matter 
                 amount of 
                 solution 
               
               
                   
                   
                 undissolved matter 
               
               
                   
               
             
          
         
       
     
         [0026]    The process of the present invention resulted in a Rebaudioside A polymorph which demonstrated high degree of solubility in water. Although the foregoing embodiments describe the use of Rebaudioside A, it is to be understood that any Stevia-based sweetener may be used and prepared in accordance with this invention, and all Stevia-based sweeteners are contemplated to be within the scope of the present invention. 
         [0027]    Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the application is not intended to be limited to the particular embodiments of the invention described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the invention, the compositions, processes, methods, and steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the invention.