Study On The Degradation Of Phytic Acid In Germinated Soybean And Development Of Low Phytic Acid Content Soy Milk

Phytic acid (PA) was also known as myoinositial-1,2,3,4,5,6-hexakisphosphate, and serves as the main storage of phosphorus in plant seeds. PA can covalently bind with some mineral cations such as calcium, potassium, magnesium, iron and zinc. It can also form complex with protein, thus lowering protein digestibility. Thus, PA is regarded as a kind of anti-nutritional factor. In this present study, PA content in soybean seeds and soybean sprouts was analyzed. Influence of soaking medium and its concentration, soaking time, germination temperature and germination time on PA content in soybean sprouts was investigated. And influence of CaCl2 and citric acid spraying during germination on PA content and main physiological and biochemical index in soybean sprouts was also observed. Meanwhile, germinated soybean were as used as raw material, a low-PA content soy milk product was developed. The research findings were summarized as follows:1. The testing method of PA content was established. Soybean meal sample was mixed with HCl. The mixture was oscillated at 25℃ for 1 h, and standing at 30℃ for 2 h. Then the supernatant was transferred into centrifuge tube and boiled for 5 min and centrifuged at 4000g for 20 min. The supernatant was passed onto DEAE Sepharose FF weak base anion-exchange resin. The column was washed respectively with distilled water and 0.05 mol/L NaCl. Finally the retained PA was eluted with 0.70 mol/L NaCl. The elution was digested for 0.5 h at 400℃ with digestion furnace. The sample PAP (PA phosphorus) was calculated according to P standard curve. PAP was converted to PA via multiplying by 3.548. This method had better precision and accuracy.2. Soybean seeds were soaked by sodium bicarbonate (NaHCO3) solution before germination, influences of soaking concentrations of NaHCO3, soaking time and germination temperature on PA content of soybean sprouts were investigated. The PA content of soybean seeds soaked by 0.05% NaHCO3 decreased by 11.94% compared to CK (distilled water soaking) at ungerminated stage. After 4 d of germination, there was no significant difference between 0.05% NaHCO3 soaking and CK. The optimum germination conditions for minimum PA content were:germination temperature of 33℃, soaking time of 3 h, NaHCO3 concentration of 0.02% and under this optimum condition, the PA content decreased to 7.92 mg/gDW at 4 d of germination, and was the 0.89 time of CK.3. The influence of citric acid, CaCl2 and mixture solution of citric acid and CaCl2 spraying on degradation of PA in soybean sprouts was investigated. Compared with CK (distilled water spraying), the 0.25-1.00 mmol/L of citric acid spraying or 3-9 mmol/L of CaCl2 spraying leaded to more degradation of PA. CaCl2 spraying significantly promoted the degradation of water-soluble protein and increased the content of total calcium and total iron content. Citric acid spraying significantly increased the total zinc content. Mixture solution spraying significantly promoted of phytase activity, decreased PA content and inhibited protease activity, and also significantly promoted the growth of hypocotyl of soybean sprouts. Mixture solution made the 59.04% reduction in soybean sprouts PA at 5 d of germination. At the tested time points of 2 d to 5 d, the higher phytase activity was observed under mixture solution spraying than that under CK. Meanwhile, mixture solution spraying decreased the loss of total calcium, total iron and total zinc compared with CK during sprouting process. Additionally, mixture solution spraying caused the lower molar ratios of PA/Fe, PA/Zn and PA/Ca than CK at all time points -tested during sprouting.4. The soybean sprouts of 1 d were developed into soy milk. Results showed that the basic ingredients of soy milk were as follows:The optimum ratio of sample and solution was 1:6; the optimum stabilizer prescription of PA-lowed soy milk was:0.07% of CMC, 0.02% of xanthan and 0.14% of sodium alginate.12% of condensed milk addition was added for the optimum flavor. No deposition was observed after 7 d storage at room temperature. The soy milk was in accordance with consumer drinking requirements.