Improvement Of The Okara Quality And Development Of The Okara Beverage Product Based On Fermentation

Okara is the soybean residue that remains after the manufacture of soymilk or soybean curd with rich nutritional value and good hygienical function.Due to its fibrous mouthfeel,low content soluble dietary fiber(SDF)and beany off-odour,it is often under-utilized.In view of this,this research screened two strains with the function of improving soluble dietary fiber content and removing beany flavor in okara respectively.By inoculating this two strains into okara and optimizing of the fermentation process parameters,a kind of improved okara obtained.Then the improved okara was used to prepare okara beverage with high soluble dietary fiber,no beany flavor.The main conclusions of this paper are as bellows:(1)First,combine the congo red dye method and the cellulase activity,a strain named G-19 with high cellulase-producing activity was selected from the Meidouzha samples and identified as Bacillus subtilis by morphology and 16 S r DNA.The circle ratio reached6.20±0.22 and the cellulase activity reached 25.26±0.28 U/m L of this strain.At the same time,the optimal fermentation conditions of G-19 were determined through single factor and response surface optimization experiments.When the inoculum amount was 6.4%,the fermentation temperature was 38.5 ?,and the fermentation time was 51 h,the average content of SDF in the fermented okara could reach 25.15%,while that of unfermented is only5.2%.Scanning electron microscopy(SEM),fourier infrared spectroscopy(FTIR)and X-ray diffraction(XRD)results showed that G-19 can affect the microstructure of okara SDF including reduce the size and the hydrogen bonds between cellulose molecules,however,the carbohydrate structure and type I crystal structure characteristics of SDF were not changed.(2)Through headspace solid phase extraction(HS-SPME)combined with gas chro matography-mass spectrometry(GC-MS),gas chromatography-sniffing instrument(GCO)and aroma vitality value(OAV),eight beany flavor compounds in okara were identi fied,they are hexanal,hexanol,nonanal,(E)-2-hexenal,2-pentylfuran,1-octene-3-ol,(E)-2-octenal,(E)-2-heptenal.The aroma of okara samples which were fermented by yeast st rains selected from Yunnan milk fans were analyzed by the sensory evaluation method and HS-SPME-GC-MS.Sensory evaluation results show that the okara samples ferme nted by RS-13 are fruity,no beany flavor,and the overall acceptance is the best.Wh en the RS-13 inoculum(v/w)in the okara is 6%,the fermentation temperature is 30?,and the fermentation time is 5 days,the effect of improving the beany flavor is the best.That is the total amount of beany flavor compounds in the okara sample aft er fermentation is only 1/40 of that in the unfermented sample,and the content and t ypes of aromatic ester compounds were the largest,the compounds which can bring o ut off-flavor were the least.R-13 was identified as Pichia fermentans by morphology and 26 S r DNA.(3)The improved okara were prepared by fistly inoculating G-19 and then inoculating RS-13.Using the improved okara as the main raw material,adding citric acid,stabilizers,and white sugar as the main auxiliary materials,the optimal formula and processing parameters were determined through single factor: the addition of okara was 8%,citric acid was 0.12%,white sugar was 6%,high acyl gellan gum was 0.015% and xanthan gum was 0.015%respectively.The quality detection and stability storage experiment of the okara beverage product prepared with the best formula showed that the sensory score of the okara beverage product is 94.3±0.17(percentage system),with no beany flavor,and each milliliter of okara beverage contains 2.0±0.02 g soluble dietary fiber.The experiment of storage stability showed that the sensory quality of okara beverage remained stable after being stored at 37? for 10 days,and the microbiological test results met the national beverage safety standards.