Preparation Of Soy Protein Ingredients For Special Populations And Evaluation Of Nutritional Benefits

Intake of soy proteins(SPs) is closely associated with prevention and treatment of several human chronic diseases. The existing research of soy protein isolated(SPI) focuses on improvement of functional performance, but rarely on development of SPs for exclusive use as nutriments. This work starts from the perspectives of nutritional components and functional improvement, and focuses on the interaction between SPs and soy isoflavone(ISO) as well as the preparation of SP-ISO complex. SP ingredients were developed for two special populations closely correlated with ISO contents: SPI as foods for infants and young children, and SPI as foods for menopausal women. The functional effects of SP-ISO compounds on osteoporosis(OP) were explored through animal experiments. The main conclusions are listed below.1. Preparation of low-ISO, low-phytic-acid and low-Mg/Al SP ingredients for exclusive use as milk powder by infants and young children. Low-ISO, low-phytic-acid and low-Mg/Al SP ingredients for exclusive use as milk powder by infants and young children(SPC-JCEU) were prepared as follows: with alcohol-prepared soy protein concentrate(SPC) as raw material, then jet cooking reconstruction and physical disaggregation technique combined with enzyme-assisted membrane enrichment processing technique were used to find out the association between heat treatment conditions and functional performance of high-solubility protein base material as-prepared, and then products were prepared by changing the ultrafiltration conditions in jet cooking and enzymolysis assistance. SPCJCEU contains up to 90% proteins, and has a nitrogen solubility index of 85.4% and a protein yield of 36%. The contents of phytic acid, total ISO, Mg and Al decrease to 5.80 mg/g, 70.0 mg/kg, 0.16 mg/g and 6.6 mg/kg respectively. Heat treatment not only promotes the formation of soluble protein aggregates, but along with the changes of protein molecular weight, it also improves membrane efficiency and eliminates membrane contamination. SPC-JCEU with higher-quality exclusive protein ingredients is potent for use by ISO-intolerant groups or infants and young children.2. Systematic study on SPs-ISO interaction, and improvement of bioavailability in SPs-ISO compounds. SPs-ISO compounds(SPP-ISO) were prepared at 120 ℃ and p H 6.0, and then were compared with the normal-temperature mixture of SPI and SPs-ISO(SPI/ISO). Tests of physiochemical properties show that these nanoparticles are microstructurally spheric and possess high colloid stability: potential-35.4 ± 0.6 m V; polydispersity index(PDI) 0.59-0.60; particle size 280.1 ± 2.6 nm. Infrared spectroscopic analysis, X-ray diffraction analysis(XRD) and fluorescence quenching analysis confirm that SPs and ISO interacted to form compounds under heat treatment, and that heat treatment is favorable for the SPs-ISO combination. The powder of SPP-ISO compounds contains 6.42-6.68 mg/g ISO, which are significantly higher compared with SPI or SPI/ISO. Simulated digestion experiments were conducted by addition of β-glucosaccharase into intestinal environment in vitro. The results confirm that the ISO in the compound ingredients after heat treatment can be well released into the simulated intestinal fluid and converted to aglycon-typed ISO. Pharmacokinetic experiments confirm that the oral bioavailability of soy ISO by rats is the highest. The content, solubility and bioavailability of ISO in the SPP-ISO ingredients were largely improved, indicating the potent application as functional protein ingredients for menopausal women.3. Preparation of ISO-rich SPs fermented soymilk(FSM). The binding of SPs with soy ISO affected the properties of the fermented products. Compared to protein-ISO ingredients directly mixed(SPI/ISO), the ingredients after heat treatment(SPP-ISO) after 48 h of fermentation possess the p H, titratable acidity and total bacterial count as ordinary soymilk. Moreover, morphologic analysis, sodium dodecyl sulfate polyacrylamide gel electrophoresis(SDS-PAGE), amino acid analysis, and rheological properties test reveal thae high digestibility of SPP-ISO. In particular, the soy ISO is highly capable of being converted to aglycon-typed ISO, and the bioavailability of ISO is up to 39.07 ± 1.23%, which is higher compared with the SPI/ISO-based FSM. During simulated digestion in vitro, the DPPH? clearance activity and the oxygen free radicals absorption ability both validate the high antioxidation activity. The SP ingredients containing ISO after heat treatment well reserve the properties of the raw material and can be used as ingredients for functional fermented foods. The ISO-rich SP FSM is potent for application by menopausal women.4. Curative effect of SP-ISO compound ingredients on mouse OP. The administration of the model drugs reduced the bone density and significantly decreased estradiol level in mice. The administration of SPP-ISO ingredients led to the increase of serum estradiol level in mice. Bone histomorphometry(right femur), pathological slices(left femur), and bone biomechanics(left tibia and fourth lumbar) data reveal that SPP-ISO ingredients, compared to soy ISO and SPI, led to sparsity, rupture and wide spacing of bone trabecula due to modest eleviation of retinoic acid level. In other words, SPP-ISO modestly intervened with and prevented the retinoic-acid-induced OP in mice. On the contrary, such effect was not found in the SPC-JCEU ingredients prepared from heat treatment under the same conditions. It is further inferred that the presence of soy ISO is highly correlated with the intervenence or treatment of OP under experimental conditions. The key factors improving the treatment effect include the higher solubility and bioavailability of soy ISO, and the better exertion of estrogen-like effect.5. Curative effect of 7S protein-ISO compound ingredients on mouse OP. Based on the preparation and evaluation of SPP-ISO ingredients, we also prepared higher- dispersity 7S protein-ISO compound ingredients(7S-ISO), and compared the two ingredients. After three months of administration, the mice treated with 7S-ISO recoved better, as indicated by haematin-eosin(HE) staining of uterine tissues and pap smear of cervical exfoliated cells. The serum biochemical indicators, bone histomorphometry(right femur) and bone biomechanics(left femur) data all indicate that OP was well inhibited by the treatment with 7S-ISO. Moreover, the expressions of osteoclast differentiation signaling pathway(OPGRANKL-RANK) genes were tested. Results show that 7S-ISO compound ingredients better activated OPG expression, thereby elleviating the OP symptoms in ovariectomized rats. A part of inhibitory effect indicators of 7S-ISO ingredients are better than SPP-ISO ingredients. It is inferred that the heattreated 7S SPs could more effectively improve the bioavailability and solubility of soy ISO. Thus, more research is needed to explore the working mechanism of this special ingredient and evaluate the functional effects for special populations.