Process for the production of high-protein pasta utilizing dried yeast and the resulting product
BACKGROUND OF THE INVENTION 
     This invention relates generally to the incorporation of yeast or a mixture of yeast and soy protein containing material into pasta formulations. More specifically, by the addition of these protein containing materials to pasta formulations, products having high protein levels and improved nutritional value are obtained. Additionally, the protein fortified pasta products have improved taste, texture and cooking properties. 
     In recent years much attention has been directed toward the development of new sources of protein which can be incorporated in foods or food additives suitable for human consumption. Rapid increases in world population have made the continued dependence on traditional sources of protein highly impractical. Moreover, the supply of protein from typical sources of protein, such as animal meat and certain vegetables, is inadequate to provide balanced diets sufficient to satisfy the needs of humans throughout the world. 
     In order to address this mounting problem, the food industry has been making attempts to increase the nutritional quality of pasta products through the addition of proteinaceous materials thereto. In past years, milk and eggs have been used as the proteinaceous material to provide the source of protein in certain types of pasta products. More recently, soy bean flour or soy protein isolates and concentrates have been suggested as the protein source. However, the addition of soy bean proteins to pasta formulations result in the production of pasta products characterized by light brown to a red-brown color and light beany taste. These characteristic features render the pasta product unattractive in terms of appearance as well as taste. The grayish-brown color gives a &#34;dirty&#34; appearance to the pasta product. The use of soy bean proteins suffers from the further disadvantage in that some soluble protein loss occurs when the pasta is cooked in water. Thus the initial high protein level of the dry pasta is significantly reduced. Surprisingly, we have discovered that the addition of yeast to the pasta formulation along with soy bean protein eliminates the disadvantages mentioned above in the use of soy bean protein alone. Thus the addition of yeast facilitates the production of high protein pasta products. Further, we have found that the addition of yeast alone to pasta formulations enables the production of pasta products with desirable nutritional, flavor, texture and cooking qualities. 
     SUMMARY OF THE INVENTION 
     According to this invention, there is provided a process for producing pasta having high protein levels and improved nutritional value. More specifically, we have found that by the addition of yeast alone or a mixture of yeast and soy bean material to pasta products such as macaroni, noodles, vermicelli, and spaghetti, enables the production of pasta formulations with a higher nutritional value, improved taste and cooking properties. We have discovered that the addition of yeast, in a percentage amount of from about 1 to about 16 percent, to pasta formulations on a dry flour weight basis or in conjunction with from about 6.25 to 12% soy flour enables the production of pasta formulations having highly desirable properties. Particularly, we have found that when the percentage amount of yeast, based on the dry weight of the flour present in the pasta formulation is within the range of 3 to 12,  sprayed dried yeast (1) holds the texture of macaroni together; (2) reduces the amount of solubles lost during cooking; and (3) increases lysine, protein and vitamin content of the pasta, thereby achieving a pasta product having better nutritive value. Further, the addition of yeast in the percentage amount mentioned above imparts retort stability to the macaroni which can be used in canned foods. Additionally, yeast imparts freeze-thaw-heat-freeze or cool cycle stability to the macaroni texture. 
     By practicing the process of this invention, therefore, one can prepare a pasta formulation containing yeast alone or a yeast-soy bean mixture having high protein and nutritional value with improved taste, texture and cooking properties. 
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The process of this invention is especially designed to provide a method for improving texture, taste and cooking properties along with protein and nutritional value to mixtures of (1) pasta and yeast or (2) pasta, yeast and plant protein wherein the yeast were grown by known commercial fermentation processes. 
     By way of illustration, yeasts such as those listed in Table I are suitable materials in the practice of this invention. 
     
                       Table I                                                     
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           Suitable Yeasts                                                
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         Candida curvata                                                  
         Candida lipolytica                                               
         Candida pulcherima                                               
         Candida utilis                                                   
         Hansenula anomala                                                
         Oidium lactis                                                    
         Saccharomyces carlsbergensis                                     
         Saccharomyces cerevisiae                                         
         Saccharomyces fragilis                                           
         Trichosporon cutaneum                                            
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     The use of Candida utilis, Saccharomyces cerevisiae, Saccharomyces fragilis, or Saccharomyces carlsbergensis is the preferred yeast material incorporated in the pasta formulations of this invention, because each is considered by the U.S. Food and Drug Administration to be suitable for use in food products. 
     The soy protein containing material which can be employed in accordance with this invention is selected from the group consisting of soy flour, defatted soy flour, soy protein isolates and concentrates, and soy flakes. 
     In general, the process for preparing pasta such as Semolina or blends thereof, comprises mixing flour, and liquid, such as water, to form a pasta dough which is thereafter shaped and dried, wherein the improvement comprises incorporating a protein-containing material selected from the group consisting of (1) yeast and (2) yeast and plant protein mixture, into said pasta dough. The yeast material selected from the abovesaid preferred yeasts, is added in an amount of from about 1 to about 16 percent of the weight of flour used to make the pasta dough. The presence of yeast in the amounts of 1.5, 3.0, 5.0 or 9.0 percent is especially preferred. When the above said soy protein containing material is added to the pasta formulations of this invention, it is present in an amount ranging from 6.25 to 12 percent based on the dry weight of flour used to make the pasta dough. A pasta formulation containing Candida utilis and soy flour in the amount of 6.25 percent each is especially preferred. The pasta formulations of this invention can be shaped in the form of macaroni, spaghetti, vermicelli and noodles. The type of macaroni products derived by rolling, stamping, or cutting procedures, such as the products generally known as &#34;Pasta Bologna&#34; as well as ravioli products are herein contemplated within the scope of this invention. 
     The increase in Torula yeast in the macaroni up to 9% increased the egg yolk color of the dry and cooked macaroni and gave the cooked macaroni a slight meat taste. Moreover, the addition of Torula yeast organoleptically improved the bite of the cooked macaroni on longer cooking and did not interfere with the tomato flavor when in tomato sauce. However, in the presence of cheese sauce, the Torula yeast gave a slight cheddar enhancement and meaty flavor. 
     Additionally, we have found, as shown in Table 3, that the amount of protein loss from cooked macaroni decreases with increased amounts of Torula yeast whereas the amount of nucleic acid in the cook water is increased. 
    
    
     EXAMPLES 
     The following examples are illustrative, without implied limitation, of our invention. 
     Example I 
     A group of macaroni products were prepared by using 1.5%, 3%, 5% and 9% Torula yeast (see Table No. 1). All of these yeast added macaroni products had as good flavor as the non-yeast control. The cooked texture of the yeast added samples was better than the texture of the yeast free control sample. The presence of yeast did not adversely affect the color or the taste when tomato sauce was used in cooking. An egg macaroni color and the egg flavor were generated at increasing levels with increased yeast content. 
     Example II 
     A group of macaroni products were prepared by using soy bean and yeast mixture (see Table No. 2). When 12.5% defatted soy flour is used the color of the new macaroni was gray, and the cooked macaroni was slightly gray, the texture was mushy and the taste was poor. As the soy flour was replaced with incrementally added yeast, both the raw and the cooked macaroni quality improved with the increased amount of yeast in the formulation. The best color, taste, and texture was obtained when 6.25% soy flour and 6.25% yeast were used in the formulation. Presence of yeast eliminated the raw flour taste, and reversed the negative effects of soy flour. 
     
                                           Table 1                                 
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EFFECTS OF VARYING LEVELS OF TORUTEIN                                     
ON THE CHARACTERISTICS OF MACARONI                                        
              Sample                                                      
              Control  98.5% Semolina                                     
                                 97.0% Semolina                           
                                           95% Semolina                   
                                                     91% Semolina         
Property      100% Semolina                                               
                       1.5% Torutein*                                     
                                 3% Torutein                              
                                           5% Torutein                    
                                                     9%                   
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                                                     Torutein             
Dry Color     Light yellow                                                
                       Light yellow                                       
                                 Light yellow,                            
                                           Light yellow,                  
                                                     Light yellow,        
                                 slight egg yolk                          
                                           egg yolk color                 
                                                     egg yolk color       
                                 red                                      
Cooked Color  Cream    Cream     Cream, slight                            
                                           Cream, slight                  
                                                     Cream, slight        
                                 egg yolk red                             
                                           egg yolk red,                  
                                                     egg yolk red,        
                                           opaque    opaque               
Cooked Flavor Cereal   Very slight meaty                                  
                                 Slight meaty                             
                                           Slight meaty                   
                                                     Slight meaty         
Cooked Texture                                                            
 10 minutes   Elastic  Elastic   Elastic   Elastic   Elastic              
 20 minutes   Slightly Slightly  Elastic   Elastic   Elastic              
              elastic  elastic                                            
Hydration                                                                 
gm/water/100 gm macaroni                                                  
 10 minutes   131      142       138       144       145                  
 20 minutes   225      212       221       223       230                  
Color with    Good     Good      Good      Good      Good                 
Tomato Sauce                                                              
Flavor with   Good     Good      Good      Good      Good                 
Tomato Sauce                                                              
Flavor with   Good     Good      Slight meaty                             
                                           Slight meaty                   
                                                     Slight meaty         
Cheese Sauce                     Slight intensify                         
                                           Slight intensify               
                                                     Slight intensify     
                                 cheddar   cheddar   cheddar              
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  *Torutein refers to Amoco Torula dried yeast grown on ethanol, which has
 the trade name Protam-10.                                                
 **The term &#34;slight&#34; indicates a lower intensity than the term &#34;light&#34; whe
 appearing in Tables 1 and 2.                                             
 
    
     
                                           Table 2                                 
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EFFECT OF YEAST-SOY COMBINATIONS ON THE CHARACTERISTICS OF MACARONI       
              Sample                                                      
                                  87.5% Semolina                          
                                            87.5% Semolina                
                                                      87.5% Semolina      
              Control  87.5% Semolina                                     
                                  11.0% Soy Flour                         
                                            9.5% Soy Flour                
                                                     6.25% Soy Flour      
Property      100% Semolina                                               
                       12.5% Soy Flour**                                  
                                  1.5% Torutein*                          
                                            3.0% Torutein                 
                                                     6.25%                
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                                                     Torutein             
Dry Color     Light yellow                                                
                       Dirty, light brown                                 
                                  Dirty, light                            
                                            Yellow light                  
                                                     Egg yolk red,        
                                  brown     brown    slight brown         
Cooked Color  Cream    Dirty, slight                                      
                                  Dirty, slight                           
                                            Dirty, slight                 
                                                     Egg yolk red,        
                       brown      red brown red brown                     
                                                     very slight brown    
Cooked Flavor Cereal   Cereal, slight soy                                 
                                  Cereal, slight                          
                                            Cereal, slight                
                                                     Slight meaty,        
                                  soy       soy      slight cereal        
Cooked Texture                                                            
 10 minutes   Elastic  Mushy      Mushy     Slightly mushy                
                                                     Slightly elastic     
 20 minutes   Slightly Mushy      Mushy     Slightly mushy                
                                                     Slightly elastic     
              elastic                                                     
Hydration                                                                 
gm water/100 gm macaroni                                                  
 10 minutes   131      151        137       140      134                  
 20 minutes   225      203        194       217      219                  
Color with    Good     Dirty      Slight dirty                            
                                            Slight dirty                  
                                                     Good                 
Tomato Sauce                                                              
Flavor with   Good     Good       Good      Good     Good                 
Tomato Sauce                                                              
Flavor with   Good     Grassy, soy                                        
                                  Grassy, soy                             
                                            Grassy,  Slight meaty,        
Cheese Sauce                                slight meaty                  
                                                     enhanced             
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                                                     cheddar              
   *Torutein refers to Amoco Torula dried yeast grown on ethanol, which ha
 the trade name Protam-10.                                                
  **Soy Flour - Central Soya&#39;s defatted soyflour Soyafluff 200W was used. 
 
    
     
                       Table 3                                                     
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EFFECT OF TORUTEIN ADDITION ON THE PROTEIN                                
AND NUCLEIC ACID LOSS OF COOKED MACARONI                                  
            Protein                                                       
            Loss (mg/100 Nucleic Acid Loss                                
Sample      gm macaroni) (mg/100 gm macaroni)                             
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Control, 100%                                                             
            23           0.5                                              
Semolina                                                                  
98.5% Semolina                                                            
            22           8                                                
1.5% Torutein*                                                            
97.0% Semolina                                                            
            15           12                                               
3.0% Torutein                                                             
95.0% Semolina                                                            
             8           14                                               
5.0% Torutein                                                             
87.5% Semolina                                                            
            45           17                                               
6.25% Torutein                                                            
6.25% Soy Flour                                                           
87.5% Semolina                                                            
            68           12                                               
3.0% Torutein                                                             
9.5% Soy Flour                                                            
87.5% Semolina                                                            
            83           11                                               
1.5% Torutein                                                             
11.0% Soy Flour                                                           
87.5% Semolina                                                            
            89           10                                               
12.5% Soy Flour                                                           
______________________________________                                    
 *Torutein refers to Amoco Torula dried yeast grown on ethanol, which has 
 the trade name Protam-10.                                                
 
    
     The improvement of the nutritional quality of the yeast added macaroni is illustrated in Tables 1, 2 and 4. 
     
                       TABLE 4                                                     
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Nutrient Composition of Macaroni - Enriched                               
100 g/Sample                                                              
                              % Change                                    
            Without With 3%   With                                        
            Yeast*  Yeast*    3% Yeast                                    
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Calories kcal 362.8     348.5                                             
Protein g     12.5      13.2      +5.6                                    
Fat g         1.2       1.3       +8.3                                    
Carbohydrate g                                                            
              75.5      71.0      -6.0                                    
Ash g         0.7       0.9       +29.0                                   
Minerals:                                                                 
Calcium mg    27        26        -4                                      
Phosphorus mg 162       214       +32.0                                   
Iron mg       2.9       3.0       +3.0                                    
Sodium mg     2.0       5.0       +150.0                                  
Potassium mg  197       252       +28.0                                   
Vitamins:                                                                 
Choline mg    0         23.4      Y                                       
Thiamine mg   0.88      0.84      -5.0                                    
Riboflavin mg 0.37      0.48      +30.0                                   
Niacin mg     6.0       7.2       +20.0                                   
Vit. B12 μg                                                            
              --        0.000012  Y                                       
Vit. B6 μg --        0.25      Y                                       
Pantothenic Acid mg                                                       
              --        0.28      Y                                       
Folic Acid μg                                                          
              --        0.012     Y                                       
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-- = Data not available.                                                  
Y = Total contribution by yeast                                           
INCREASE IN ESSENTIAL AMINO ACIDS WITH 3% YEAST.                          
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Lysine 7%                                                                 
Threonine 3%                                                              
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 *Protam-10 (Torutein)?                                                   
 
    
     
                       TABLE 5                                                     
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Nutrient Composition of Macaroni - Nonenriched                            
100 g/Sample                                                              
                              % Change                                    
            Without With 3%   With                                        
            Yeast   Yeast*    3% Yeast                                    
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Calories kcal 362.8     348.5                                             
Protein g     12.5      13.2      +5.6                                    
Fat g         1.2       1.3       +8.3                                    
Carbohydrate g                                                            
              75.5      71.0      -6.0                                    
Ash g         0.7       0.9       +29.0                                   
Minerals:                                                                 
Calcium mg    27        26        -4.0                                    
Phosphorus mg 162       214       +32.0                                   
Iron mg       1.3       1.5       +15.0                                   
Sodium mg     2.0       5.0       +150.0                                  
Potassium mg  197       252       +28.0                                   
Vitamins:                                                                 
Choline mg    --        23.4      Y                                       
Thiamine mg   0.09      0.11      +22.0                                   
Riboflavin mg 0.06      0.19      +217.0                                  
Niacin mg     1.7       3.2       +88.0                                   
Vit. B12 μg                                                            
              --        0.000012  Y                                       
Vit. B6 μg --        0.25      Y                                       
Pantothenic Acid mg                                                       
              --        0.28      Y                                       
Folic Acid μg                                                          
              --        0.12      Y                                       
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-- = Data not available                                                   
Y = Total contribution by yeast                                           
INCREASE IN ESSENTIAL AMINO ACIDS WITH 3% YEAST                           
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Lysine 7%                                                                 
Threonine 3%                                                              
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 *Protam-10 (Torutein)                                                    
 
    
     The many advantages in the use of yeast in the preparation of macaroni and other pasta products include lower soluble solids loss, resistance to processing at high temperatures for long periods of time required in the preparation of meat-pasta products, and flavor stability. Yeast imparts elasticity to the pasta and does not impart undesirable color. It has been found that by increasing the concentration of yeast above five (5) percent, of the dried flour weight, contributes an egg color and flavor which is very appealing in the pasta products. Additionally, yeast functions to clarify and remove starch flavor and thereby avoids interfering with the flavor of other products with which it is mixed. 
     The nutritional advantages of the yeast are also significant since most pasta products are now enriched and yeast addition will reduce this requirement.