Heat Inactivation of Trypsin Inhibitors in Soymilk at Ultra-High Temperatures

Soymilk samples at pH 7.5, 6.5 and 2 were subjected to heat treatment at 93°C and indirect ultra-high temperature. When heated at 93°C, 121°C and 132°C, trypsin inhibitor activity (TIA) in soymilk was more heat-labile at high pH than at lower pH. However, the effect of pH on rate of thermal inactivation was less pronounced when the holding temperature was increased to 143°C and 154°C. The point on a curve relating holding temperature and holding time, indicating inactivation of 90% of the TIA in soymilk at pH 6.5 in the range 93–154°C, coincided with the thermal-death-time curve of the organism putrefactive anacrobe 3679 at about 125°C.     

α-Galactosidase and proteolytic activities of selected probiotic and dairy cultures in fermented soymilk

The metabolic activities of Lactobacillus acidophilus (LAFTI^® L10 and La4962) Bifidobacterium (lactis LAFTI^® B94 and longum Bl536), Lactobacillus casei (LAFTI^® L26 and Lc279), Lactobacillus delbrueckii ssp. bulgaricus Lb1466 and Streptococuss thermophilus St1342 were assessed in soymilk. Strains were initially analyzed for α-galactosidase activity and organic acid production in MRS broth at 37 °C. Consequently, soymilk was fermented with each strain and cell growth, production of organic acid, metabolism of oligosaccharides and proteolytic and ACE-inhibitory activities were assessed during 48 h of incubation at 42 °C. All strains exhibited variable α-galactosidase activity, with Bifidobacterium lactis B94 showing the highest activity. The oligosaccharide metabolism depended on α-galactosidase activity. B. lactis B94, S. thermophilus St1342 and L. acidophilus La4962 reduced raffinose substantially by 77.4%, 64.5% and 55.9%, respectively. All strains reached the desired therapeutic level of 10⁸ cfu/ml in soymilk after 48 h at 42 °C. The hydrolysis of protein in soymilk likely depended on strain (P < 0.0001) and time (P < 0.0001). The strains also released bioactive peptides with ACE-inhibitory activities between 17% and 43%.     

Rapid Method for Determining Optimum Coagulant Concentration in Tofu Manufacture

Four methods of determining optimum coagulation levels in tofu manufacture were compared. Full-fat soyflakes were used to produce 5% solids soymilk. Each soymilk batch was coagulated with calcium sulfate dihydrate (0.000–0.0450 N). Electrical conductance of the coagulating batches was recorded at 72°C and 21°C. Coagulated batches were pressed to make tofu and whey volume, pH, transmittance (400 nm) and tofu composition were measured. Whey transmittance and conductance correlated with coagulant concentration (r=0.87). Tofu yield, conductivity, and absorbance data were also related. Measuring the conductance of the coagulating soymilk was faster than obtaining pH and spectrophotometric values. Conductivity and transmittance could be used to optimize tofu coagulation.     

Effect of Continuous Flow High-Pressure Throttling on Rheological and Ultrastructural Properties of Soymilk

ABSTRACT:  Soymilk processing uses a filtration or centrifugation step to remove coarse solids in the comminuted soy. The objective was to utilize the whole beans and determine the effect of continuous flow high pressure throttling (CFHPT) process in reducing particle size and narrowing down the particle size distribution. The rheological and ultrastructural properties of such soymilk were also determined. Whole dehulled soybeans and deionized water were ground in a food processor before comminution in a Megatron (process M) or a Fitzmill (process F) or a Stonemill (process S). The comminuted slurry was homogenized at pressures of 69, 103, 138, 207, and 276 MPa using a CFHPT system, heated to 80 °C in a tubular heat exchanger prior to depressurization, and held at elevated temperatures of 97, 106, 114, 131, and 148 °C, respectively, for each applied pressure after throttling. To avoid flashing, back pressure was applied after the holding tube and soymilk was cooled immediately. Process M produced soymilk with smallest particle size and the highest apparent viscosity. All soymilk samples showed non-Newtonian pseudoplastic flow behavior. Ultrastructural images showed a clear protein network with very small fat globules entrapped in the protein matrix. Particles were uniformly distributed when the highest pressure treatment was applied for process M, which was considered as the best process.     

水杨酸检测豆浆中还原糖方法的改进

本课题对还原糖的常用分析方法进行了比较和改进,旨在选择准确度高、重复性好的分析方法测定豆浆中的还原糖,从而对美拉德反应与腐竹褐变因子之间的关系进行研究。研究结果表明,3,5-二硝基水杨酸比色法（DNS法）为检测豆浆还原糖的最佳方法;对此法进行了应用条件的改进,即按豆浆：乙酸锌：亚铁氰化钾=10：1：2的体积比对豆浆样品进行预处理,可使检测的准确度提高18％以上;用此法处理后的豆浆样品在498nm波长处有最大吸收峰测定,且检测准确度提高2％以上。     

乳酸菌培养物的生长特性及其对豆奶质构和风味的影响

研究了Lactobacillus casei (LC), Lactobacillus helveticus (LH) and Lactobacillus rahmnosus (Lactobacillus casei subsp. rahmnosus 6013) (LR)生长特性及其对大豆奶酪风味的影响.研究表明,经过6 h的发酵,LC、LH和LR的菌落数分别增长至8.74、7.69和8.69 log (CFU/mL);37 ℃时,分别接种LC、LH、LR和添加有Glucono-δ-内酯(GDL)的大豆牛奶都明显出现可滴定酸度增加、pH减少的现象.这三种乳酸菌都能够利用大豆糖源.经质构分析发现,菌种可引起大豆牛奶质构发生变化,其凝乳的能力可与GDL媲美.菌种通过产酶、产酸而水解大豆蛋白,从而导致质构变化形成凝乳.这些菌种可释放18种游离氨基酸(FAA),其中包括可作为奶酪风味物质前体化合物的天门冬氨酸、异亮氨酸、亮氨酸、蛋氨酸、苯丙氨酸和缬氨酸.这些菌种均能利用大豆脂肪酸(FA),而在大豆凝乳中出现某些FA消失的现象表明所选的菌种还能分别完全消耗特定的FA.可见,这三种乳酸菌在大豆牛奶中可引起质感及风味前体物的变化,正是生产大豆奶酪所必需的效果,故选择它们作为制备大豆奶酪的适用菌种.     

豆浆灌根对土壤生物化学性状及烤烟质量的影响

近年来,烤烟豆浆（传统豆浆和酵解豆粕）灌根技术成为河南三门峡烟区的一项常规农艺措施。为揭示豆浆灌根对烟叶质量的影响及相关原因,采用盆栽和大田试验,分析了豆浆灌根对烤烟质量、烟株农艺性状、根系生长和土壤生物化学（酶活性、活性有机碳和土壤蛋白）指标的影响。结果表明,与对照相比,豆浆灌根对烤烟物理特性、化学成分、外观质量和感官品质等方面均有提升作用;豆浆灌根提高了中部叶长度和上部叶宽度,根表面积、根体积和根干重增加;豆浆灌根后土壤酶活性变化不大,土壤活性有机碳含量在灌根初期上升明显,土壤蛋白含量在灌根后较长时间内保持较高水平。因此,豆浆灌根后土壤蛋白和活性有机碳含量上升可能是烤烟根系干物质积累增加和烟叶品质提升的主要原因之一。     

基于电导率快速测定豆类细胞破壁率方法的研究

为了建立一种通过电导率,能够快速准确检测豆类细胞破壁率的方法。通过测定不同处理程度的四种豆子的蛋白含量、电导率,考察了四种豆子水溶性蛋白释放量与电导率之间的关系。研究了豆浆用量、外渗时间、测定温度对破壁率的影响。利用建立的评价方法,分别测定了四种常见豆子在破壁料理机豆浆程序下的破壁率。结果表明:四种豆子破壁过程中水溶性蛋白的释放量与电导率相关性较高(R2≥0.8995),豆浆用量和外渗时间对于破壁率的测定结果影响不显著(p0.05),测定温度对于破壁率的影响非常显著(p0.01),测定温度在25℃左右时破壁率的测定结果较为稳定。四种豆子在新型破壁料理机豆浆程序下的破壁率达到90%左右。结论,利用电导率快速评价豆类细胞破壁率的方法,具有一定的可行性。