大豆蛋白的体外模拟消化过程及热处理的影响

本研究探讨了天然大豆分离蛋白(SPI)的体外胃蛋白酶消化过程,以及热处理对该消化过程的影响。SDS-PAGE分析表明,天然SPI的大豆球蛋白最易为胃蛋白酶所消化,而β-伴大豆球蛋白则较难。β-伴大豆球蛋白的不同亚基对胃蛋白酶消化的敏感程度也有所不同,其中α-亚基最为敏感。TCA-NSI法分析显示,在一定蛋白浓度下,随酶/底物之比的增加,天然SPI受胃蛋白酶的作用释放氮的过程呈现出较为典型的酶浓度依赖性。另外,不同热处理对SPI的体外消化过程产生不同的影响。一定的干热处理(80℃,30～60min)几乎不影响SPI的体外胃蛋白酶消化过程,而同样条件下的湿热处理则显著提高胃蛋白酶及胰蛋白酶对SPI的消化效果。这结果意味着SPI的体外消化效果取决于其变性程度,热变性程度越高,其消化效果越好。     

加工工艺对荞麦蛋白热性质和体外模拟消化过程的影响

本实验研究了加工工艺对荞麦蛋白(BWP)的热性质和体外模拟消化过程的影响。荞麦蛋白有两个变性温度,在80℃和102℃附近,分别对应8S和13S球蛋白的变性。脂肪的存在对荞麦蛋白的变性温度影响不大,但会降低其热焓。在模拟的胃蛋白酶消化过程中,BWP的氮释放量较大豆分离蛋白(SPI)先高后低;而在胰蛋白酶消化过程中,BWP的氮释放量较SPI高。这与其蛋白组成以及SPI中存在活性较高的胰蛋白酶抑制剂有关。荞麦蛋白的球蛋白(13S和8S)易被降解(胃蛋白酶消化阶段),而2S清蛋白的降解主要集中在胰蛋白酶消化阶段。经脱脂处理、超声协助提取的荞麦蛋白(DFU-BWP)和搅拌提取的荞麦蛋白(FM-BWP)的氮释放量在整个胃蛋白酶消化过程中类似,均明显高于超声提取的荞麦蛋白(FU-BWP)(p<0.05),说明胃蛋白酶对BWP的降解过程与其脂肪含量以及加工工艺有关。     

热处理对小米蛋白体外消化率的影响

为探究不同热处理方式的小米蛋白质的消化情况,采用胃蛋白酶-胰蛋白酶体外模拟消化法测定蒸制、煮制、挤压处理并经淀粉酶解的小米蛋白消化率。对从小米生粉中提取的醇溶蛋白蒸制、煮制的蛋白消化率进行测定,结果表明,经120 min的胃蛋白酶和胰蛋白酶处理,蒸制、煮制和挤压处理的小米的体外蛋白消化率分别较未处理小米降低了31.00%,17.15%和11.02%。蒸煮的醇溶蛋白消化率也分别降低了35.57%和28.63%。蒸煮对小麦蛋白的消化率有不利影响,挤压处理优于蒸煮处理。蒸煮处理降低小麦蛋白体外消化率可能与醇溶蛋白消化率的降低有关。     

加热处理对大豆乳清中胰蛋白酶抑制剂活性以及大豆乳清蛋白体外消化率的影响

采用胃蛋白酶-胰蛋白酶两步体外消化法测定了加热对大豆乳清蛋白的体外消化率的影响。与没有经过加热的对照蛋白相比,适当的加热处理可以提高蛋白的体外消化率,80℃,10min处理的体外消化率达到最高。加热对抑制剂的破坏是正相关,加热处理的程度越高,胰蛋白酶抑制剂活性降低的百分比就越大。1000℃,50min处理以及120℃,8min处理可以将其活性降低到90％以下,达到充分消除豆制品中抗营养因子的目的。     

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。     

热处理对丙二醛氧化米糠蛋白体外胃蛋白酶消化性质的影响

采用不同浓度的丙二醛氧化米糠蛋白,通过95℃水浴热处理氧化米糠蛋白,研究热处理对丙二醛氧化米糠蛋白体外胃蛋白酶消化性以及消化产物抗氧化性的影响。结果表明:随着丙二醛浓度的增加,米糠蛋白羰基和二硫键含量增加,游离巯基含量下降,证实丙二醛致米糠蛋白氧化。随着丙二醛浓度增加,米糠蛋白体外胃蛋白酶消化率、初始消化速率和消化产物中分子质量分布在500～1 500 u的活性肽含量均逐渐下降。同时,米糠体外胃蛋白酶消化产物ABTS~+·,DPPH·,·OH和O_2~-·清除能力、金属螯合能力以及还原能力持续下降。热处理可提高米糠蛋白的体外胃蛋白酶消化率、初始消化速率以及消化产物中活性肽含量和抗氧化性。结论:丙二醛氧化可降低米糠蛋白的消化性以及消化产物的抗氧化性,适当的加热处理可在一定程度上增强米糠蛋白的消化性以及消化产物的抗氧化性。     

双酶水解乳清蛋白ACE抑制肽的制备工艺优化

以乳清蛋白为原料,采用胃蛋白酶和胰蛋白酶双酶先后水解乳清蛋白,通过单因素试验和正交试验优化胃蛋白酶和胰蛋白酶水解乳清蛋白制备血管紧张素转换酶(ACE)抑制肽的工艺,将水解物以3 kDa超滤膜过滤,研究表明,胃蛋白酶水解乳清蛋白最佳酶解工艺条件为水解温度37℃、底物质量浓度6 g/100 mL、酶与底物比3 728 U/g,此时乳清蛋白ACE抑制率为86%;胰蛋白酶水解乳清蛋白最佳酶解条件为温度55℃、底物质量浓度6 g/100 mL、酶与底物比3 480 U/g,此时ACE抑制率为72%。利用超滤离心管获得分子量小于3 kDa的乳清蛋白ACE抑制率96%。     

乌鸡低聚肽的制备及其稳定性研究

以乌鸡为原料,利用两步酶解法制备乌鸡低聚肽,以分子量分布为指标,研究了热处理、pH和体外胃肠道模拟消化对乌鸡低聚肽稳定性的影响。结果表明,乌鸡低聚肽分别于20、40、60、80、100℃下水浴2 h后,各个分子量区间的比例变化不超过2%;pH值分别为2、4、6、8、10,37℃水浴2 h后,各个分子量区间的比例变化不超过2%;分别经过胃蛋白酶单独消化、胰蛋白酶单独消化、先胃蛋白酶消化再胰蛋白酶消化,各个分子量区间的比例变化不超过4%。这表明乌鸡低聚肽具有较好的热稳定性、pH稳定性以及消化稳定性,为其在食品工业中的应用提供了一定的理论依据。     

热处理对过氧自由基氧化米糠蛋白体外胰蛋白酶消化性质及消化产物抗氧化性的影响

选用不同浓度的2,2’-盐酸脒基丙烷(2,2’-azobis (2-amidinopropane) dihydrochloride,AAPH)在有氧条件下热降解生成的过氧自由基氧化米糠蛋白,再通过95℃水浴处理氧化米糠蛋白,研究热处理对过氧自由基氧化米糠蛋白体外胰蛋白酶消化性质及消化产物抗氧化性的影响。结果表明:随着AAPH浓度的增加,过氧自由基氧化米糠蛋白体外胰蛋白酶消化率、初始消化速率、消化产物分子质量分布在500～1 500 u的肽含量、消化产物清除ABTS~+·、·OH、O~-_2·能力和还原能力均先上升后下降,消化产物清除DPPH·能力和金属螯合能力先不变后下降;而热处理后,氧化米糠蛋白体外胰蛋白酶消化产物金属螯合能力先上升后下降,ABTS~+·清除能力和还原能力先不变后下降。同未热处理相比,热处理显著提高了相同氧化程度下米糠蛋白体外胰蛋白酶消化率、初始消化速率以及消化产物抗氧化性。表明过氧自由基氧化会改变米糠蛋白体外胰蛋白酶的消化性质,而热处理可以改善相同氧化程度下米糠蛋白体外胰蛋白酶的消化率和消化产物的抗氧化性。     

物理处理对黄粉虫蛋白理化及消化性质的影响

以碱溶酸沉法提取黄粉虫蛋白（Tenebrio molitor Larvae Protein Isolates,TPI）,探究了热处理和动态高压微射流处理对其理化、功能和体外消化性质的影响。研究结果表明：天然TPI主要由疏水相互作用、氢键及二硫键稳定高级结构。热处理和微射流处理均可诱导TPI聚集体的形成,且这种聚集可能是以疏水性聚集为主。热处理TPI的溶解性略有降低,可能是由于热处理导致蛋白内部疏水基团暴露,削弱了TPI与水分子间的相互作用;高压微射流的机械作用增强了蛋白与水分子间的相互作用,显著提升了TPI的溶解性,且与处理压力呈正相关。中性条件下,50 MPa和100 MPa微射流处理TPI的溶解度由24.05%分别提升至50.08%和64.81%。热处理改善了TPI的乳化活性和泡沫性质,但降低了其乳化稳定性;微射流处理增强了TPI的泡沫稳定性,但对其乳化性能和起泡性均无显著影响。两种物理处理均提升了TPI的体外消化抗性,其中,90 ℃和120 ℃热处理TPI的氮释放量由39.53%分别降至35.58%和33.90%,微射流处理TPI在17 ku附近的亚基无法在体外消化过程中被完全水解。     

Effect of Heat Treatments on In Vitro Digestibility of Delactosed Whey Protein as Determined by the Digestion Cell Technique

Diafiltered whey protein concentrates (WPC) were heated, in liquid form, under various conditions of time and temperature. Protein and amino acid digestibilities were determined by in vitro pepsin and pan-creatin digestion with continuous dialysis. Whey nitrogen digestibility decreased (P < 0.05) after heating at 121°C for 5000 sec. Heating WPC for 5000 set at temperatures below 121°C increased the digestibility of all amino acids except alanine and lysine at 75°C, and methionine and lysine at 100°C. In general, the longer was the heating period at 100°C or 121°C the lower was the amino acid digestibility. These results emphasized the importance of structural modifications brought about by heat treatments on protein digestibility.     

玉米低聚肽硒螯合物的理化性质及稳定性

以玉米低聚肽和亚硒酸钠为原料制备玉米低聚肽硒螯合物,对其水分、酸溶蛋白、总氮(粗蛋白)、分子量分布进行了考察,然后以螯合态的硒含量和分子量分布为指标,研究了螯合物对温度、pH、消化方式的稳定性,结果表明:玉米低聚肽硒螯合物的螯合率为54.25%±0.24%,得率为53.02%±0.17%,水分含量为7.46%±0.07%,酸溶蛋白含量为16.38%±0.03%,总氮含量为21.17%±0.35%,分子量低于1000 u的比例为85.1512%。在25~100℃环境下,分子量低于1000 u的比例变化不超过7%,硒含量最低不小于70%;在pH=2~12的环境下,分子量低于1000 u的比例变化最高不超过16%,硒含量最低仍在75%以上;在经过胃蛋白酶、胰蛋白酶和两种酶的消化后,分子量低于1000 u的比例分别增加5%、7%和8%,硒含量最低仍在70%以上。这说明玉米低聚肽硒螯合物具有一定的热稳定性、酸碱稳定性和消化稳定性。     

Peptic and tryptic hydrolysis of native and heated whey protein to reduce its antigenicity

This study examined the effects of enzymes on the production and antigenicity of native and heated whey protein concentrate (WPC) hydrolysates. Native and heated (10 min at 100°C) WPC (2% protein solution) were incubated at 50°C for 30, 60, 90, and 120 min with 0.1, 0.5, and 1% pepsin and then with 0.1, 0.5, and 1% trypsin on a protein-equivalent basis. A greater degree of hydrolysis was achieved and greater nonprotein nitrogen concentrations were obtained in heated WPC than in native WPC at all incubation times. Hydrolysis of WPC was increased with an increasing level of enzymes and higher incubation times. The highest hydrolysis (25.23%) was observed in heated WPC incubated with 1% pepsin and then with 1% trypsin for 120 min. High molecular weight bands, such as BSA, were completely eliminated from sodium dodecyl sulfate-PAGE of both native and heated WPC hydrolysates produced with pepsin for the 30-min incubation. The α-lactalbumin in native WPC was slightly degraded when incubated with 0.1% pepsin and then with 0.1% trypsin; however, it was almost completely hydrolyzed within 60 min of incubation with 0.5% pepsin and then with 0.5% trypsin. Incubation of native WPC with 1% pepsin and then with 1% trypsin for 30 min completely removed the BSA and α-lactalbumin. The β-lactoglobulin in native WPC was not affected by the pepsin and trypsin treatments. The β-lactoglobulin in heated WPC was partially hydrolyzed by the 0.1 and 0.5% pepsin and trypsin treatments and was completely degraded by the 1% pepsin and trypsin treatment. Antigenicity reversibly mimicked the hydrolysis of WPC and the removal of β-lactoglobulin from hydrolysates. Antigenicity in heated and native WPC was reduced with an increasing level of enzymes. A low antigenic response was observed in heated WPC compared with native WPC. The lowest antigenicity was observed when heated WPC was incubated with 1% pepsin and then with 1% trypsin. These results suggested that incubation of heated WPC with 1% pepsin and then with 1% trypsin was the most effective for producing low-antigenic hydrolysates by WPC hydrolysis and obtaining low molecular weight small peptides. Further research is warranted to identify the low molecular weight small peptides in the WPC hydrolysates produced by pepsin and trypsin, which may enhance the use of whey.     

INFLUENCE OF TRANSGLUTAMINASE-INDUCED CROSS-LINKING ON IN VITRO DIGESTIBILITY OF SOY PROTEIN ISOLATE

The influence of covalent cross‐linking by microbial transglutaminase (MTGase) on the sequential in vitro pepsin and trypsin digestion process and the digestibility of soy protein isolate (SPI), was investigated by sodium dodecylsulfate‐polyacrylamide gel electrophoresis (SDS‐PAGE) and nitrogen release analyses. Various subunits of β‐conglycinin and acidic subunits of glycinin were cross‐linked by MTGase to form high molecular weight (MW) biopolymers, while basic subunits of glycinin were unaffected. SDS‐PAGE analysis indicated that the cross‐linking mainly affected in vitro pepsin digestion pattern of various subunits of β‐conglycinin, while the trypsin digestion pattern of native SPI was nearly unaffected. Nitrogen release analysis showed that the in vitro pepsin or/and trypsin digestibility of native SPI (at the end of pepsin or trypsin ingestion) was significantly decreased (P ≤ 0.01) by the MTGase treatment (for more than 2 h). The cross‐linking by MTGase also significantly decreased the in vitro digestibility of preheated SPI. These results suggest that the cross‐linking by means of transglutaminase may negatively affect the nutritional properties of food proteins.     

湿热处理对牛奶蛋白复合纤维纱线结构和性能的影响

由于牛奶蛋白复合纤维染整加工中经常伴随着湿热加工,因此,着重研究了湿热处理对牛奶蛋白复合纤维结构和性能的影响.结果表明,湿热处理对牛奶蛋白复合纤维的收缩率、强力、白度及表面形态影响显著,对牛奶蛋白复合纤维结构及结晶形态影响很小.随着湿热处理温度的升高,牛奶蛋白复合纤维织物的顶破强力稳步提高,而白度出现下降;当湿热处理温度大于100℃时,收缩率的增幅明显变大,且手感变硬;特别当湿热处理温度超过130℃时,纤维的表面已经几乎没有平整的地方.因此,牛奶蛋白复合纤维宜采用90、100℃为其最高湿热加工温度.     

糖基化大豆蛋白体外消化产物的生物活性研究

为了分析体外消化作用及超滤处理对糖基化大豆蛋白抗氧化活性及抑菌活性的影响,分别利用胃蛋白酶及胰蛋白酶酶解糖基化大豆蛋白,在一定的条件下水解度分别达到了4.9%和6.4%,此时可溶性蛋白质含量分别为13.6、15.0 mg/m L;再经过超滤处理得到相对分子质量低于5 000的组分,两种超滤组分的可溶性蛋白质含量分别为9.65、10.65 mg/m L。糖基化大豆蛋白体外消化产物的抑菌活性没有发生显著变化,但是抗氧化活性下降;进一步的超滤处理能够获得具有较高生物活性的组分:胃蛋白酶消化产物超滤组分的亚铁离子螯合率提高了约1倍;胰蛋白酶消化产物超滤组分的还原力及羟基自由基清除率显著提高;同时,胃蛋白酶消化产物超滤组分对大肠杆菌具有抑制活性,而胰蛋白酶消化产物超滤组分则具有较强的抑制作用。结果表明,结合体外消化作用及超滤处理能够显著改善糖基化大豆蛋白的生物活性。     

苦瓜皂苷与乳清蛋白水解物协同对二肽基肽酶-IV的抑制活性

为评价动植物源天然产物的二肽基肽酶-IV（dipeptidyl peptidase-IV,DPP-IV）抑制活性,以苦瓜皂苷（momordica saponins,MS）、乳清蛋白胃蛋白酶水解物（whey protein pepsin hydrolysates,WPPHs）、乳清蛋白胰蛋白酶水解物（whey protein trypsin hydrolysates,WPTHs）为原料,采用单因素试验和响应面分析优化水解条件,再将MS与WPPHs、WPTH进行复配,结合模拟体外消化,探究DPP-IV抑制活性。结果表明,MS、WPPHs及WPTHs具有DPP-IV抑制活性,最佳水解条件为：当酶添加量4%、pH 2.7酶解2 h时,WPPHs的DPP-IV抑制率最高为15.43%;当酶添加量4%、pH 7.6酶解4 h时,WPTHs的DPP-IV抑制率最高为14.62%。苦瓜皂苷与乳清蛋白水解物具有协同对二肽基肽酶-IV抑制活性作用,当MS与WPPHs、WPTHs的复配体积比均为1:1时,显著高于两者单独累加（p<0.05）。经胃消化后,WPPHs的DPP-IV抑制率降低2.02%,MS和WPTHs的DPP-IV抑制率升高0.99%、7.01%;经肠道消化后,WPPHs的DPP-IV抑制率升高2.23%,而MS和WPTHs的DPP-IV抑制率降低4.12%、2.70%。研究结果可为天然动植物源产物协同对二肽基肽酶-IV抑制活性提供了基础性数据,为降血糖功能性产品的开发提供新的方向。     

Preparation of angiotensin-I-converting enzyme inhibitory hydrolysates from unsupplemented caprine whey fermentation by various cheese microflora

Unsupplemented caprine whey was fermented by 25 cheese microflora in order to produce peptides from α-lactalbumin (α-la) and/or β-lactoglobulin (β-lg) hydrolysis. Fourteen hydrolysates enriched in peptides mainly released from α-la were obtained. Angiotensin-I-converting enzyme (ACE) inhibitory activity of each hydrolysate was investigated. Six of them had high ACE inhibitory activities ranging from 31% to 56%. The highest ACE inhibitory activity was obtained after whey fermentation by the microflora from 18 months ripened Comté cheese. The microflora was identified as a co-culture of Candida parapsilosis and Lactobacillus paracasei. Hydrolysate activity remained stable after pepsin, trypsin and chymotrypsin treatments simulating an in vitro gastrointestinal digestion. This hydrolysate was further fractionated by RP-HPLC. The peptide exhibiting the highest ACE inhibitory activity was characterised as WLAHK (α-la f(104–108): Trp–Leu–Ala–His–Lys). WLAHK was resistant toward pepsin and trypsin treatments but was digested by chymotrypsin.