Abstract:
Protein obtained by coagulating soymilk with microbially produced protease within a pH range not causing acid coagulation and at a temperature higher than the optimum operation temperature of the protease provides food material of desirable flavor and high processability.

Description:
This application is a continuation of application Ser. No. 032,462 filed Mar. 31, 1987 now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention concerns a process for producing food material from soymilk. 
     More specifically, this invention relates to a process for producing food material of high processability. 
     BACKGROUND OF THE INVENTION 
     Soybean protein has generally been used more and more as protein material for ice creams, yoghurts, cheeses and dressings. It has aso been utilized for other foodstuffs, for example, pastes, daily dishes, cakes, breads, noodles and various kinds of dairy products, and soybean protein has become an extremely useful 
     food material. 
     However, in the case of using soybean protein as food material, it has to provide favorable feeling upon eating and high processability. 
     As processes for producing soybean protein there have been various methods such as acid coagulation method, calcium coagulation method, enzyme method, heating method, alcohol coagulation method, etc. and food materials have been produced from bean proteins by respective methods. 
     However, those food materials obtained by the conventional method involve various problems such as acid taste, salty taste, bitter taste, gritty feeling due to intense coagulation, and poor processability. In addition, there is also a problem for the production process that the steps are complicated such as requirement for acid precipitation, neutralization and washing for isolated soybean protein or pre-heating treatment of soymilk in view of the protease of plant origin. 
     SUMMARY OF THE INVENTION 
     The present inventors have made an earnest study for obtaining coagulated milk-like protein food material having enriched flavor and smooth feeling upon eating and have succeeding in preparing coagulated protein products with no astringent taste, peculiar taste, bitterness or the like and having desirable curd flavor in an extremely convenient method by coagulating soymilk with microbially produced protease at a temperature higher than the optimum operation temperature of the protease. 
     This invention provides a process for producing food material, which comprises subjecting soymilk to a protease treatment within a pH range not causing acid coagulation and at a temperature higher than the optimum operation temperature. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The temperature higher than the optimum operation temperature in this invention is, suitably, higher than 2° C., preferably, higher than 3° C. and, more preferably, higher than 4° C. of the optimum operation temperature. 
     As the starting material in this invention soymilk prepared from soybean, non-fat soybean, concentrated soybean protein and separated soybean protein can be used and, further, any of soymilk such as commercially available soymilk incorporated with sub-raw material such as oils may also be used. One example for the process of producing soymilk will be shown. Dried soybean was at first swollen with water, an aqueous 0.1% sodium hydrogen carbonate solution was then added after draining, the beans then were ground into a liquid which was filtered and the filtrate was taken as a soymilk containing about 4% protein. 
     Generally, since soybean protein coagulates within a pH range from 3.4 to 5.8 and intensely coagulates within a pH range for 4 to 5, it is required in this invention to exclude pH dependent coagulation. Preferably, pH is adjusted to higher than 5.9. 
     Further, since the soybean protein is coagulated with calcium to cause precipitation, in the case of adding calcium in this invention, calcium is present within such a range of concentration as causing no substantial calcium coagulation thereby accelerating protease coagulation. 
     The protein solution of soybean causes intense coagulative precipitation if the calcium concentration (as calcium salt) is higher than 20 mM. Although slight precipitation occurs also at a concentration of higher than 10 mM, since it does not lead to substantial coagulation, the concentration range causing no substantial calcium coagulation is, preferably, between 15 mM and 0.1 mM as the calcium salt. 
     Although the presence of calcium in soymilk is not an essential condition to this invention, since the amount of calcium varies slightly depending on the production method of soymilk and reduction temperature of protease, etc. it is necessary to determine such a concentration range as not causing no substantial calcium coagulation for each of the conditions. 
     In this invention, the soymilk is subjected to a protease treatment at a temperature higher than the optimum protease operation temperature. 
     The temperature higher than the optimum protease operation temperature is higher than by 2° C., preferably, 3° C., and, more preferably, 4° C., but if protease is added to soymilk, the coagulation start time tends to become earlier as the temperature is higher, as well as the condition of the resultant curd is also improved to cause less astringent taste, peculiar taste and bitterness. 
     The protease of microorganism origin may be any of alkaline protease (subtilis, Aspergillus, soya protease, etc.), neutral protease (thermolysin, pronase, etc.), acidic protease (Endothia, Mucur protease, etc. ). 
     Protease may be added in any desired amount so long as it causes the protease coagulation, but it is sufficient to add, preferably, from 0.0002 to 0.2% of an enzyme preparation. 
     Since the optimum operation temperature is different depending on each protease, it is necessary to confirm each of the optimum operation temperatures and determine the milk coagulation temperature. 
     The coagulation reaction can be conducted by increasing the temperature for the soymilk to an appropriate temperature higher by 2°-30° C. than the optimum operation temperature for each of the proteases and adding each of them in an adequate amount. It may be or may not be agitated. The time required for the protein coagulation varies largely also depending on the kind of protease, but coagulation starts after several seconds to about 20 minutes when coagulated under stirring and the protein is completely coagulated by about 10-50 minutes. The coagulation is promoted under the presence of calcium. 
     The thus obtained coagulated protein can be separated through centrifugal separator, filter or the like and then dried by using various kinds of drying means. 
     The thus obtained protein drying products can, preferably, be gelled by merely swelling them again in water, which are suitable as food material. 
     The food material obtained according to the present invention may be used for ice creams, yoghurts, cheeses and dressings made from vegetable protein. It is also suitable as additives to paste-like products, daily dishes, cakes, breads and various kinds of dairy products, noodles, etc. 
     Test examples and examples according to this invention will be shown below. Test Example 
     Soymilk (protein 4.0%, pH 6.1) was used each by 100 ml, and warmed to a reaction temperature (°C.) shown in Table 1 respectively. Each protease in Table 1 was added at an enzyme concentration (ppm) shown in Table 1. The coagulation start time was respectively detected by K. Arima, etc. (Agric. Biol. Chem, 31, 540, 1967) and the soymilk was left for 30 minutes after the starting of coagulation and filtered by using filter cloth in the midway to determine the condition and flavor of curds respectively thereby obtaining a result as shown in Table 1. 
     
                                           TABLE 1__________________________________________________________________________Used enzyme                    Reaction condition                 Optimum temper-                          Enzyme      Test results                 ature for                          concen-                               Reaction                                      Coagulation    Manu-        protein decom-                          tration                               temper-                                      start time                                             Condition                                                    Flavor ofName of enzyme    facturer          Origin position (°C.)                          (ppm)                               ature (°C.)                                      (min) (sec)                                             curd   curd__________________________________________________________________________P-5380   Sigma Bacillus             60     1&#39; 55&#34; good   astringent          Subtilis                 60° C.                          20   65     1&#39; 28&#34; &#34;      good                               70     1&#39; 20&#34; &#34;      &#34;Protine  Daiwa &#34;                    55     3&#39; 49&#34; good   peculiarPC10F    Kasei        50˜55                          200  60     2&#39; 35&#34; &#34;      good                               65     1&#39; 20&#34; &#34;      &#34;Neutralase    Nobo  &#34;                    60     3&#39; 05&#34; good   good0.5L     Industry     45˜55                          200  65     2&#39; 17&#34; &#34;      &#34;                               70     2&#39; 00&#34; &#34;      &#34;Alkalase &#34;     Batillus             60     7&#39; 10&#34; slightly                                                    good0.6L           licheniformis                 60       200  65     3&#39; 46&#34; good   &#34;                               70     3&#39; 40&#34; &#34;      &#34;Zeoplase Nagase &amp;          Bacillus             60     3&#39; 45&#34; good   bittersp4      Company,          Subtilis                 50˜60                          1000 65     3&#39; 40&#34; &#34;      &#34;    Ltd,                       70     2&#39; 02&#34; &#34;      goodP-5147   Sigma Streptomyces         55     9&#39; 02&#34; slightly                                                    good          griseus                 50˜60                          20   60     6&#39; 53&#34; good   &#34;                               65     5&#39; 40&#34; &#34;      &#34;Tasinase Kyowa Ray fungus           50     4&#39; 06&#34; good   slightly    Hakko                                           astringentN-11-100 Kogyo        50       500  60     2&#39; 33&#34; &#34;      good    C., Ltd.                   65     1&#39; 48&#34; &#34;      &#34;Protease Amano Aspergillus          55     1&#39; 39&#34; good   slightly    Seiyaku          oryzae                                    astringent[Amano]               50       500  60     1&#39; 33&#34; &#34;      slightly                                                    bitter                               65     1&#39; 09&#34; &#34;      goodPantidase    Yakult Honsha          &#34;                    55     3&#39; 53&#34; good   goodNP-2     Co., Ltd.    45˜50                          500  60     2&#39; 02&#34; &#34;      slightly                                                    bitter                               65     2&#39; 26&#34; &#34;      goodProtease Amano Aspergillus          55     1&#39; 47&#34; good   slightly    Seiyaku          meleus                                    bitter[Amano]               45       500  60     1&#39; 27&#34; &#34;      slightly                                                    astringent                               65     50&#34;    &#34;      goodFromase  Rapidase          Mucur michei                 55       2000 60     8&#39; 15&#34; slightly                                                    good                               65     6&#39; 50&#34; good   &#34;__________________________________________________________________________ 
    
     EXAMPLE 1 l 
     A dissolved solution of a protease formulation (Protine PC10F : manufactured by Daiwa Kasei Co.) was added to 1 kg of soymilk warmed to 60° C. (protein 4.0%, pH 6.1) to 200 ppm concentration in the soymilk, stirred slowly for 2 minutes, left then for 30 minutes and centrifuged (2700 rpm) to obtain a coagulated protein product of 80% water content. 
     EXAMPLE 2 
     An aqueous 10% calcium chloride solution was added to 1 kg of soymilk warmed to 65° C. (protein 4.2%, pH 7.14) to 0.02% concentration in the soymilk and, further, 0.01 % of an alkaline protease formulation (Alkalase 0.6L, manufactured by Nobo Industry Co.) followed by agitation. Then, they were left at 65° C. for 15 minutes and then centrifugated (2700 rpm) to obtain a coagulated protein product of 80% water content.