乳清蛋白的体外模拟消化过程及热处理的影响

探讨了乳清蛋白体外胃蛋白酶和胰蛋白酶的消化过程,以及热处理对该消化过程的影响。SDS-PAGE分析结果表明,胃蛋白酶和胰蛋白酶对乳清蛋白的体外消化作用的影响不明显。干热处理(75℃和100℃,1h)几乎不影响乳清蛋白的体外胰蛋白酶消化过程,而在同样条件下,湿热处理能显著提高胰蛋白酶对乳清蛋白的消化作用。乳清蛋白分别经75℃和100℃湿热处理30min后,再由胰蛋白酶消化8h,其氮释放率分别达到82.1%和91.3%,而未湿热处理的氮释放率仅为66.7%,表明不同热处理方式对乳清蛋白的体外消化过程产生不同的影响。湿热处理能有效地提高乳清蛋白的消化速率,且湿热处理温度越高,乳清蛋白的体外消化速率越快。     

不同烹饪方式及体外模拟消化环境对鲟鱼蛋白质氧化及消化性的影响

研究水煮、汽蒸、微波、烤箱烤制、油炸5?种烹饪方式对鲟鱼肉的脂肪和蛋白质氧化的影响,熟肉在模拟消化过程中后续氧化情况及这些氧化反应与蛋白质消化性的相互关系。结果表明,不同烹饪方式均导致鱼肉的脂质与蛋白质氧化,其中烤制与油炸的样品氧化程度最显著,这些氧化反应会在模拟胃肠道消化过程中进一步加深,尤其在模拟肠消化阶段变化更为强烈。在烹饪与消化过程中,脂质与蛋白质的相互氧化作用也非常明显。此外,不同烹饪方式引起的蛋白质氧化显著影响蛋白质在模拟消化过程中的水解程度。在胃消化阶段,烤制与油炸样品中大分子蛋白氧化聚集形成致密结构,降低了蛋白质消化性;小肠消化后,由于部分小分子肽类（＜14?kDa）无法被彻底水解,各类熟制样品的游离氨基值均低于原料肉。?     

Dialysis Cell for the In Vitro Measurement of Protein Digestibility

A dialysis cell was devised to study in vitro digestion of proteins. The inner reaction vessel (surrounded by a tubular membrane with molecular weight cutoff of 1000) was fixed into a cylindrical outer compartment where buffer circulation was provided. The dimensions of compartments, membranes and buffer flow rate were determined with labelled amino acids in order to ensure the most efficient diffusion pattern. For the digestion assay, casein was first hydrolyzed with pepsin (pH 1.9) for 30 min. The mixture was then made alkaline (pH 7.5) and poured into the dialysis tube with pancreatin. Nitrogenous material collected with the sodium phosphate buffer was analyzed without further fractionation for the direct measurement of hydrolysis kinetic or of protein digestibility.     

In Vitro Digestibility of Thermally Processed Diafiltered Whey as Influenced by Water Activity

Diafiltered whey protein concentrates of varying water activity were heated at 121°C for 83.3 min (5000 s). Nitrogen and amino acid digestibilities were determined by the digestion cell technique. Whey nitrogen digestibility significantly decreased only at a water activity of .97. Although this heat treatment did not affect the amino acid profile of the protein, the relative digestibility of most amino acids was slightly increased at a water activity of .3 but relative digestibility decreased at a water activity of .5 and .97. At a water activity of .7, digestibility slightly increased for aspartic acid, threonine, glutamic acid, proline, cysteine, isoleucine, histidine, and arginine and decreased or remained unchanged for the other amino acids. At a water activity of .97, the relative digestibility of aspartic acid, threonine, serine, glutamic acid, glycine isoleucine, leucine, and phenylalanine, significantly decreased. Water activity plays a role in the structural organization of heated whey, which in turn affects the enzymatic liberation of amino acids.     

不同热处理对牛奶乳清蛋白消化的影响

反复加热喷雾干燥所得的脱盐乳清粉是目前市售的婴儿配方奶粉中主要的配料,为了了解蛋白质在反复加热后的变性情况以及对消化率的影响,采用高效液相色谱法测定不同热处理的乳清蛋白中α-乳白蛋白和β-乳球蛋白的变性率,然后通过胃蛋白酶—胰蛋白酶两步法测定了不同变性乳清蛋白的体外消化率。结果表明加热对乳清蛋白变性率是正相关,加热温度越高,时间越长,乳清蛋白变性率越大,消化率也越低。脱盐乳清粉的消化率仅为65.25%,不利于婴儿的消化吸收。     

Effect of Shredding Alfalfa Stems on Fiber Digestion Determined by In Vitro Procedures and Scanning Electron Microscopy

Alfalfa stems were shredded using a rotary macerator, were ammoniated, or were left untreated (control). Shredding increased extent of NDF digestion over ammoniation and control at all times from 12 to 72 h of in vitro incubation. Shredding also increased rate of disappearance of potentially digestible NDF (.032 h⁻¹ for control, .045 h⁻¹ for ammoniated, and .089 h⁻¹ for shredded). Ammoniation increased extent of NDF digestion after 36 h. Computed time required for 95% digestion of potentially digestible NDF was 94 h for control, 66 h for ammoniated and 34 h for shredded stems. Scanning electron microscopy revealed that the most prominent effect of shredding was separation of lignified and unlignified cells. Shredding split stems into a number of fragments and damaged the external cuticular waxy layer and structural integrity. Ammoniation caused cracks in lignified vascular tissue. During in vitro incubations, shredded and ammoniated cell walls were heavily colonized by bacteria by 6 h. After 24 and 48 h, large masses of bacteria were still attached to the surface of pith and lignified vascular cell walls of shredded and ammoniated stems but not control stems. Lignified vascular tissue of control stems was not degraded and structural integrity was maintained.     

Processed Protein Foods Characterized by In Vitro Digestion Rates

In vitro tryptic digestion assays and determination of relative digestion rates of food proteins described previously were used to evaluate changes in the rate of digestion following processing technologies. If pH drop measurements are used, a simple mode for the determination of relative digestion rates is suggested based on the comparison with a single reference of the same protein source. The effect of processing technologies could be tested in vitro. Significant increase in the velocity of digestion was found on microwave treatment of lentil and raw soy bean as well as on acid treatment of commercial defatted soy meals. Increase in the in vitro digestion rates was reflected in decreased feed consumption per weight gain in pig feeding experiments.     

Effect of Myoinositol Phosphate Esters on In Vitro and In Vivo Digestion of Protein

Effects of phytate and its hydrolysis products (myo-inositol phophate esters) on protein digestion were investigated by in vitro and in vivo procedures. Tri-, tetra-, penta-, and hexa-phosphate ester fractions, isolated from phytate hydrolysates, inhibited pepsin digestion of casein and bovine serum albumin in vitro. The inhibition ranged from 0% for the mono- and diphosphate esters to 9–14% with the hexa-phosphate ester (phytate). The phosphate ester fractions did not significantly affect trypsin digestion of the proteins. In the in vivo study, rats were fed phytate and hydrolysates thereof (mixtures of the esters above) at levels of 1–3.5% of the diet. Under the conditions of this study, neither phytate nor its hydrolysates significantly affected protein utilization or weight gain in rats.     

热处理对生鲜乳及复原乳蛋白质体外消化特性的影响

通过体外模拟消化的方法对不同热处理的牛乳样品进行检测,研究热处理对鲜牛乳及复原乳营养价值的影响。通过聚丙烯酰氨凝胶电泳、尺寸排阻高效液相色谱、扫描电镜及质谱分析等多种方法进行检测。结果表明:经过胃液消化后,牛乳中的部分蛋白被消化,其中酪蛋白消化最为明显,鲜牛乳中酪蛋白在胃液中的消化水平高于其他热处理样品;而经过肠液消化后,牛乳中蛋白消化完全,生成游离氨基酸及小肽。乳中蛋白质经消化主要生成分子质量低于1 500 Da的肽段,易于人体消化吸收。通过扫描电镜可以看出,热处理程度越大,乳蛋白变性,发生聚集现象,粒径增大,其中加热复原乳的粒径较其他乳制品大;通过质谱检测及高效液相色谱分析,热处理程度越大,蛋白质美拉德反应程度升高。     

Effect of Domestic Processing and Cooking on In Vitro Protein Digestibility of Moth Bean

Protein digestibility (in vitro) of dry seeds of moth bean cultivars varied significantly from 58.69 to 62.06%. The protein digestibility improved significantly when the seeds were given different domestic processing and cooking treatments including soaking, sprouting, ordinary cooking and pressure cooking. Pressure cooking of the seeds presoaked in plain water or mixed mineral salt solution had the most pronounced effect.     

花青素对大豆蛋白体外胃消化结构的影响

利用胃蛋白酶对大豆分离蛋白-花青素复合物进行体外模拟消化,研究消化过程中花青素对蛋白水解度、结构、亚基组成及分子质量分布等指标的影响。结果表明：大豆分离蛋白在30?min内消化较明显,蛋白对照组最终水解度高达48.5%,花青素的添加一定程度抑制了蛋白消化。花青素抑制11S球蛋白消化,促进7S球蛋白主要致敏原α-亚基降解,因而推测花青素添加有降低大豆蛋白食用致敏性的效果。排阻色谱分析表明,体外消化将大分子蛋白水解为小分子肽,花青素的添加抑制了小分子肽的形成,最终产物分子质量分布主要集中在3～100?kDa。圆二色谱图显示,花青素改变了大豆蛋白构象,α-螺旋含量降低,β-折叠及无规则卷曲含量增加,β-转角变化无明显规律。荧光光谱分析表明,花青素添加使蛋白及消化产物λmax发生红移,并对蛋白产生了荧光猝灭作用。本研究明晰了蛋白与花青素同食过程中大豆蛋白的解离机制,并为食品生产加工领域制备易消化、高吸收、低致敏的优质蛋白产品及营养膳食搭配方式提供理论指导。     

Degradation of Crude Protein in Forages Determined by In Vitro and In Situ Procedures

Objectives were to determine in selected forages fiber and protein fractions, in vitro and in situ CP degradability, and to compare in vitro methods of estimating rumen CP degradability with the in situ bag technique. Forages analyzed (five samples per treatment except alfalfa hays, which had four) included alfalfa as baled hay, alfalfa ensiled in conventional upright silos, alfalfa ensiled in oxygen-limiting silos, ammonia-treated corn silage, untreated corn silage, and orchardgrass hay. Untreated corn silages had the greatest protease insoluble CP at 48 h, indicating protein in corn silage is not degraded well by protease enzyme. In situ CP degradability was greater than 80% for all ensiled forages. Ensiled forages had the greatest estimated A fraction (rapidly degraded in the rumen), alfalfa hays had the greatest B fraction (intermediate rate of degradation), and orchardgrass hays had the greatest C fraction (not degraded in rumen).High correlations between in situ degradability and some in vitro measurements suggest laboratory techniques of estimating CP degradability of forages are possible. For silages, buffer-soluble CP had the greatest correlation (.58) with in situ degradability; for hays, NDIN had the greatest correlation (−.83).     

In Vitro Digestibility of Phytate-Reduced and Phenolics-Reduced Soy Protein Isolates

The effect of removal of phytate and phenolic compounds upon the in vitro digestibility of soy protein isolates by trypsin and pronase enzymes at pH 8.0 and by pepsin at pH 2.0 was studied by pH stat and dialysis equilibrium methods, respectively. Phenolics-reduced (PRSPI) and phytate and phenolics-reduced (PPRSPI) soy protein isolates were both slightly more digestible than control (CSPI). 11S soy-protein with 0.07% phytate was slightly more digestible than 7S soy protein with 1.41% phytate. Kinetic studies indicated that differences in in vitro digestibility of soy protein isolates was probably due to accumulation of end products rather than stearic hindrance at enzyme-substrate reaction sites.     

双螺杆挤压对大豆蛋白体外消化率的影响

采用双螺杆挤压技术,研究了挤压工艺参数对大豆蛋白体外消化率的影响,并采用二次通用旋转组合设计,建立了大豆蛋白体外消化率与物料含水量、挤压温度、喂料速度、螺杆转速的二次回归方程,并利用该方程探讨了各因子对消化率的影响.结果表明,各因子对大豆蛋白体外消化率的影响顺序为:挤压温度>物料含水量>螺杆转速>喂料速度,物料含水量与挤压温度交互作用显著.利用统计优选法寻优,确定了大豆蛋白消化率的最佳挤压工艺条件:物料含水量35%,挤压温度155℃,喂料速度0.4 kg·min-1,螺杆转速150r·min-1,大豆蛋白体外消化率最高值为95.83%.     

大蒜素与乳清分离蛋白结合物的体外模拟消化特性

大蒜素,即二烯丙基硫代亚磺酸酯,具有广谱抑菌、抑制肿瘤及抗氧化性等生理活性。大蒜素极不稳定,易降解成各种有机硫化合物,使其活性大大降低。研究显示,大蒜素与乳清分离蛋白形成的二硫键结合物可显著增强大蒜素的稳定性。本文在此基础上对大蒜素提取液及二硫键结合物的体外模拟消化特性进行研究,结果表明,大蒜素与乳清分离蛋白的结合物经模拟胃肠消化后,其含硫化合物组成成分与大蒜素提取液的消化产物相同,说明大蒜素与蛋白结合后不会影响大蒜素活性成分的释放。3-乙烯基-1, 2-二硫环己-4-烯主要在模拟胃消化阶段释放,而二烯丙基二硫醚主要在模拟肠消化过程中释放。与大蒜素结合不会影响乳清分离蛋白在模拟胃肠消化时的水解度。与蛋白相比,结合物消化产物的小分子质量组分含量增加,说明结合物比蛋白更易被吸收利用。     

Enzyme Diafiltration Technique for In Vitro Determination of Protein Digestibility and Availability of Amino Acids of Legumes

In vitro protein digestibility determined by peptic hydrolysis in a diafiltration reactor gave values comparable to the published in vivo digestibility data in 16 samples from both animal and plant sources. The in vitro technique is easier to perform and the reproducibility is greater than that reported for in vivo rat assays. A high performance liquid chromatographic method was modified to determine the amino acids in the pepsin hydrolysates. The amino acid content of nine samples were compared to the FAO-WHO (1973) reference protein standard and the geometric mean of the essential amino acid content were compared with values for Protein Efficiency Ratio (PER), Net Protein Utilization (NPU), and Biological Value (BV). The geometric mean was most closely related to the NPU value with a correlation coefficient of 0.96.     

Effect of Extrusion Cooking on in Vitro Protein Digestibility of Sorghum

Extrusion variables including moisture (15 and 2.5%), temperature (50°, 125° and 200°C) and screw speed (50, 125 and 200 rpm) of two low tannin sorghum varieties extruded with 0, 2 and 4% calcium hydroxide were studied. Protein digestibility was determined by in vitro pepsin assay. Extrusion improved digestibility from 45.9 to 74.6% and 43.9 to 68.2% for the two varieties, respectively. Temperature was the key extrusion variable that influenced digestibility. Screw speed and moisture did not have significant effects. Alteration of pH before extrusion further improved digestibility.     

高温热处理对大豆蛋白消化利用效果的影响

为明确高温热处理杀菌工序中蛋白质热变性程度对大豆蛋白营养有效性的影响,本研究通过体外模拟婴儿消化,分析高温热处理对大豆蛋白消化利用效果的影响。结果表明：与100 ℃相比,高温热处理（超过120 ℃、20 min）后的大豆蛋白易生成更多更低分子质量的酶解产物;与此同时,这种高温热处理也导致体系内的氨基酸大量被破坏,尤其是胱氨酸损失较多（约48%）;因此严重破坏了大豆蛋白氨基酸合理的模式,降低了大豆蛋白本身的营养有效性。     

Kinetic Compensation Effect in the Heat Denaturation of Whey Protein

The kinetic compensation effect in the heat denaturation of whey proteins was demonstrated using two different kinetic compensation relationships, i.e. Enthalpy (ΔH≠/Entropy (ΔS≠) compensation and Frequency Factor (In ko)/Activation Energy (E_a) compensation. Isokinetic temperatures determined by these methods were 84.0 and 87.8°C, respectively. These values were higher than those associated with thermal death of microorganisms caused by heat denaturation of proteins; however, they were in the experimental temperature range, correlating well the dependent relationship between kinetic parameters.