a culture of candida utilis yeast cells ( atcc - 9256 ) was grown on an ethanol substrate under oxygen - limiting growth conditions . the whole cells were harvested and concentrated into a 10 - 14 weight percent ( dry weight ) aqueous slurry or cream . the aqueous slurry was heated to a temperature of 90 ° c . for about 5 minutes to remove materials which would give the product poor color and flavor characteristics . the slurry was centrifuged to separate the aqueous extract from the cells , which were reslurried into a 10 weight percent suspension with a dilute alkaline solution of 0 . 03n sodium hydroxide having a ph of 9 . 5 . the alkaline slurry was heated to a temperature of about 90 ° c . for about 10 minutes to extract primarily nucleotidic materials . the slurry was centrifuged to separate the alkaline extract from the cells . the separated cells were then reslurried in a 0 . 15n sodium hydroxide solution at a temperature of about 95 ° c . for about 30 minutes to extract the proteinaceous materials . thereafter , the slurry was neutralized to lower the viscosity and the undigested cell residue was separated from the supernatant by centrifugation . the supernatant containing the extracted proteins was acidified to a ph of 4 . 2 to precipitate the isoelectrically precipitable proteins , which were separated from the mother liquor solution or whey by centrifugation . the mother liquor solution was then neutralized to about ph 7 . 0 and spray - dried to yield a yeast whippable protein . also , the precipitated portion of the proteins was neutralized , dissolved in water , and spray - dried to yield a yeast protein isolate . product samples based on 1 kg . starting material ( dry weight ) were prepared with and without dialysis to show the effect of nacl . the composition of the two primary products are summarized in table i . table i______________________________________product compositionproduct dialysis ash , % n , % protein , %* ______________________________________yeast protein isolate - 2 . 4 14 . 0 87 . 5yeast protein isolate + 2 . 6 14 . 2 88 . 7yeast whippable protein - 24 . 8 ** 5 . 2 32 . 8yeast whippable protein + 3 . 2 5 . 7 35 . 6______________________________________ *( n × 6 . 25 ) ** mainly nacl the product samples were further tested for their functional properties . these results are summarized in tables ii , iii , iv , and v . table ii______________________________________foaming and emulsifying properties emulsifying foaming foam capacity ,** dia - ability , stability , ml . oil / g . product lysis ml . * ml . * sample______________________________________yeast protein isolate - 265 208 300yeast protein isolate + 130 50 330yeast whippable protein - 265 180 172yeast whippable protein + 260 30 160______________________________________ * testing procedure on &# 34 ; foaming ability &# 34 ; and &# 34 ; foam stability &# 34 ;: a 1 per cen aqueous solution of the test sample is agitated at 1000 rpm in a virtis 4 mixer for 60 seconds at 32 ° f . the mixture is placed in a measurin cylinder and the measurement of volume in ml . is the &# 34 ; foaming ability .&# 34 ; the foam is allowed to settle for 30 minutes , and the volume of foam remaining at that time , in ml ., is the &# 34 ; foam ** testing procedure on &# 34 ; emulsifying capacity &# 34 ;: a one g . sample of test material is mixed in a waring blender with 50 ml . of a 0 . 9 per cent nacl solution . 50 ml . of vegetable oil is added to the contents of the blender and mixed for ten seconds . a stream of oil is continuously added to the mixture at a rate of 20 ml ./ minute , with the blender mixing , until the emulsion breaks . the amount of oil added when the emulsion breaks is the &# 34 ; emulsifying capacity . table iii______________________________________thermogelability * di - diameter , height , sample alysis cm . cm . observations______________________________________yeast protein - 7 . 0 3 . 6 cake , isolate crystalline mild flavor , brown coloryeast protein + 7 . 0 4 . 1 cake , isolate crystalline , soft , mild flavor , cream color . yeast whippable - 12 . 8 0 . 9 crystalline , protein brittle , tan color . yeast whippable + 13 . 2 0 . 8 crystalline , protein crunchy . promosy 100 - 7 . 7 2 . 5 soft , crystal - line , tough , cream color . sodium caseinate - 9 . 0 2 . 5 crystalline , tough , holes , cream color . * testing procedure : mix the following ingredients ( given in weight per cent ) into a ball and bake at 350 ° f . for 45 minutes : protein sample 10 . 00salt 0 . 75sugar 30 . 00flour 30 . 00water 25 . 25______________________________________ table iv______________________________________whippability in frappe system * product dialysis whippability color______________________________________soy isolate - yes whiteegg white - yes whiteyeast protein - yes dark tanisolate ( low volume ) yeast protein + yes slightly tanisolate ( low volume ) yeast whippable - yes whiteproteinyeast whippable + yes whiteproteincontrol - no slightly tan______________________________________ * testing procedure : heat corn syrup to 245 ° f . and add it to a slurry of invert sugar , water , and the protein sample . beat in a hobert mixer with whip for five minutes . observe if foam is produced . the proportions of the ingredients are as follows ( expressed as weight percent ): corn syrup 47 . 3 invent sugar 47 . 3 water 3 . 6 protein sample 1 . 8 table v______________________________________per cent solubiity in acid ph * ph yeast protein isolate yeast whippable protein______________________________________4 . 0 0 1003 . 8 19 . 8 1003 . 6 81 . 1 1003 . 3 100 100______________________________________ * one per cent of a protein sample in water was adjusted to the desired ph and dispersed for thirty minutes at room temperature . the suspension or solution was centrifuged for twenty minutes at 18 , 000 rpm . the concentration of nitrogen in the supernatant was determined and the percentage of soluble nitrogen calculated . the results of these tests indicate that the yeast protein isolate appears to be responsible for the good emulsification characteristics and has about twice the emulsion capacity of soy isolate . in addition , the yeast protein isolate has thermogelability comparable to that of sodium caseinate . this property may be improved to some extent by mixing the yeast protein isolate with an amount of yeast whippable protein . in addition , the yeast whippable protein product is an excellent whippable protein material having a performance comparable to that of egg white . the functional performance of the yeast whippable protein product is not impaired by the high content of nacl formed from neutralization . furthermore , some hydrolyzed proteinaceous components were apparently lost through dialysis as indicated by the composition data in table i . hence , desalting is not necessary . thus , the products produced by this process have the ability to replace the high - cost functional protein ingredients such as soy isolate , sodium caseinate , and egg white . also , the yeast whippable protein is soluble at all acid ph values and the yeast protein isolate can be completely dissolved at ph 3 . 3 . these properties demonstrate their potential for use in making acidic protein beverages . it will be obvious to those skilled in the art that many variations from the preferred embodiment chosen for purposes of illustration can be made without departing from the scope of this invention .
functional yeast protein products with good thermogelability , emulsification capacity , foaming ability , solubility , and whippability are prepared by an alkali extraction of whole yeast cells preceded by a hot water extraction and / or a dilute alkaline extraction . these products are good substitutes for either casein , sodium caseinate , or egg white , and can also be used in making stabilized acidic protein beverages .