高压二氧化碳对桃果胶甲基酯酶活性的钝化效果与动力学研究

采用高压二氧化碳技术(High Pressure Carbon Dioxide,HPCD)处理桃果胶甲基酯酶(Pectin Methylesterase,PME)粗酶液,分析了HPCD对粗酶液中PME的钝化效果及动力学,进一步比较了粗酶液和桃汁两种体系中PME对HPCD的敏感性。HPCD对粗酶液中PME具有较好的钝化效果,处理温度和压力的共同作用导致了PME活性降低,钝化动力学遵从一级动力学模型。随着处理压力和温度的提高,钝化速率逐渐增大,而指数递减时间则逐渐减小;在最优的处理条件(22MPa、55℃)下,HPCD钝酶的钝化速率和指数递减时间分别为0.408 8min-1和5.63min。温度为55℃时HPCD钝酶的压力敏感指数为16.40MPa,活化体积为-383.00cm3/mol;压强为15MPa时HPCD钝酶的温度敏感指数为13.30℃,活化能为1 845.86kJ/mol。比较HPCD对桃汁和粗酶液中PME的钝化效果,发现HPCD处理16min后(15MPa、55℃),桃汁中PME残存酶活在80%左右,而粗酶液中PME活性已完全钝化,表明桃汁体系中存在保护PME活性的因素,有关机制需要进一步研究。     

超高压引发胰蛋白构象变化与酶活性间的关系

采用超高压技术处理胰蛋白酶,改变其空间结构,研究酶空间结构变化与酶活力之间的关系。采用傅立叶红外光谱(FTIR)检测超高压处理后胰蛋白酶的二级结构变化;采用荧光光谱检测处理后胰蛋白酶的三级结构;酶活力的检测采用福林酚法。结果显示,与未处理的相比,在37 ℃,不同压力(100～600 MPa)条件处理20 min,对胰蛋白酶活力影响显著(p＜0.05)。其中,300 MPa处理,胰蛋白酶活力达到最大,较未处理的酶活提高了0.386倍。FTIR检测分析显示,300 MPa处理的胰蛋白酶,α-螺旋与β-转角的峰面积比值达到最大(2.749);内源性荧光光谱检测结果显示,当激发波长为295 nm,其荧光强度达到最高值(1 353);激发波长为280 nm,其荧光强度达到最高(4 262);外源性荧光光谱结果显示,当激发波长为228 nm,疏水氨基酸残基的荧光强度达到最高(2 022); 上述荧光强度的变化较0.1 MPa处理的胰蛋白酶均有显著差异(p＜0.05)。结论：超高压处理影响胰蛋白酶的空间结构及酶活性。其中,胰蛋白酶活性与α-螺旋和β-转角的峰面积的比值、色氨酸等疏水氨基酸及酪氨酸残基暴露程度有关。     

超高压处理对多酚氧化酶活性的影响

 研究了超高压中温协同处理对砀山梨汁中多酚氧化酶活性的影响,实验压力为0.1~500 MPa,温度为20~60 ℃。此外,考察了不同pH值（3~7）和保压时间（2~34 min）超高压处理对酶活性的影响。实验结果分析表明：在处理温度为50 ℃、保压时间为10 min和梨汁pH值为5的条件下,200~300 MPa处理梨汁时多酚氧化酶被激活,活性表现最高;500 MPa时酶的活性下降到75.3%。协同温度为30 ℃处理梨汁时,酶的活性反而增大;30 ℃以后,酶活性随温度升高而迅速降低;有效协同高压处理的温度为40 ℃。随着保压时间的延长,梨汁中过氧化物酶的活性减小;18 min以前下降速度较快些,之后下降速度变缓。pH在5~6之间,酶的残留活性最大;pH值为6时,梨汁中多酚氧化酶最为耐压。     

高压对米曲霉理化性质影响及诱变的研究

 在100~400 MPa压力、保压20 min的条件下处理酱油酿造菌种——米曲霉,研究高压对米曲霉存活率、形态特征、生理性质、蛋白酶、淀粉酶活性等的影响,并诱变筛选优良菌株。结果表明：高压对米曲霉的存活率、形态特征有明显的影响;压力对蛋白酶及淀粉酶活性的影响也有特异的规律,即在一定压力范围内（0.1~200 MPa）蛋白酶的活性随着压力的增加而减小,但随着压力的进一步升高（200~400 MPa）蛋白酶的活性又逐渐增强,在300 MPa时超过对照组,400 MPa时蛋白酶的活性达到最高值;淀粉酶在0.1~100 MPa时活性下降,在200 MPa时其平均的糊化和糖化活性最强、活力最高,当压力升高活性又开始降低,400 MPa时几乎又回到对照值。另外,高压处理后获得一株理想的变异菌株HP300a：生长速度快、孢子数量多、蛋白酶活力高,且不易被杂菌污染。其成曲的几项主要指标均优于对照株,酿出酱油的几项主要指标也明显优于对照株。为利用高压诱变筛选米曲霉优良菌种、提高酿造酱油产品的产量及质量提供了理论依据,并发现了高压处理米曲霉引起其蛋白酶及淀粉酶活性改变的特殊规律。     

超高压处理对海参自溶酶活性影响的研究

 海参的超高压处理与传统的处理方法相比有许多优越性,具有十分广阔的应用前景。研究了超高压处理过程中压力（0.1~550 MPa）、保压时间（0~30 min）、温度（24~62 ℃）及保压方式对海参自溶酶活性的影响。在室温、保压20 min的条件下,200 MPa左右较低压力下酶活性降低,相对残存活性为88.25%;250 MPa较高压力下自溶酶被激活,酶活性为106.77%;550 MPa高压下酶活性最低为29.81%。自溶酶活性随保压时间和温度的增加先上升后下降;保压方式对自溶酶活性的影响不大。同时利用误差反向传播神经网络（Back Propagation Neural Network,BP人工神经网络）,模拟了超高压钝酶效果,与实验结果比较,平均相对误差为0.9%,可以获得较好的预测结果。研究结果表明,在一定的压力、保压时间和温度下,酶被激活,其活性上升;而在一定的压力、保压时间和温度下,酶被钝化,活性降低。对优化海参超高压钝酶工艺具有一定的参考价值。     

超高压处理对荔枝果肉中两种酶和可溶性蛋白的影响

 为了研究超高压处理对荔枝果肉中过氧化物酶（POD）、果胶甲基酯酶（PME）及可溶性蛋白含量的影响,将荔枝（“淮枝”品种）果肉在100~400 MPa压力、10 ℃温度条件下处理30 min,采用分光光度法测定果肉中POD、PME的活性,用天然凝胶电泳法以及活性染色法测定POD、PME同工酶的变化,用SDS凝胶电泳法测定果肉中可溶性蛋白含量。结果表明：100~200 MPa超高压处理使荔枝果肉中POD活性上升且出现新的同工酶,300~400 MPa超高压处理则使其活性降低且新出现的同工酶消失;100 MPa压力处理使荔枝果肉中PME活性上升且出现新的同工酶,200~400 MPa超高压处理则使其活性降低且新出现的同工酶消失;100 MPa超高压处理使荔枝果肉中可溶性蛋白含量有所增加,而在200~400 MPa压力处理下其含量持续下降。     

高压处理对酪蛋白酶解产物抗氧化活性的影响

研究了高压处理条件和处理对象对胰蛋白酶水解酪蛋白特性及产物抗氧化活性的影响。以水解度、DPPH自由基、超氧阴离子自由基、羟基自由基和还原力为测定指标,研究了高压处理胰蛋白酶、酪蛋白、酪蛋白+胰蛋白酶后的酶解特性和产物的抗氧化活性。结果表明:在水解度方面,高压对酪蛋白的处理效果比胰蛋白酶好,在200MPa的压力下保压20min时,酪蛋白的水解度提高了31.14%,但是高压对酪蛋白+胰蛋白酶的处理效果不佳;经100MPa保压15min或50MPa保压5min处理后胰蛋白酶的酶解产物对DPPH自由基和超氧阴离子自由基有较强的清除能力,而经150MPa保压10min处理的酪蛋白以及经150MPa保压15min处理的酪蛋白+胰蛋白酶的酶解产物在羟基自由基的清除能力和还原力方面表现更好,并且酶解产物的抗氧化活性与水解程度不成正相关。     

动态瞬时高压作用对膳食纤维酶解速度的影响

 对纤维素酶对动态瞬时高压处理后膳食纤维的酶解速度进行了研究。豆渣膳食纤维（Dietary Fiber,DF）经微射流均质机的瞬时高压作用（Instantaneous High Pressure,IHP）,在不同的压力以及同一压力的不同作用次数下产生不同粒径和密度,它们对应的酶解速度是不同的。纤维素酶水解膳食纤维产生纤维二糖和葡萄糖等还原糖,通过测定水解后还原糖的含量判断不同粒径和密度的膳食纤维的酶解速度。结果表明,在40～90 MPa的压力范围内随压力的增大物料粒径呈显著下降,物料密度随之增大,酶解速度增大,在90 MPa的均质压力下物料粒径达到最小,为202.4 nm;当压力继续增大时,物料因膨化作用,物料粒径呈增大趋势,但其密度开始减小,酶解速度继续增大,在140 MPa的均质压力下物料密度达到最小,为1.027 g/mL,此时酶解后还原糖含量最高,酶解速度最快。压力超过140 MPa后,由于超微颗粒间的团聚,物料的密度和粒径均增大,酶解速度减小。在90 MPa和140 MPa下对分别对物料进行多次的瞬时高压处理,发现随处理次数的增多物料粒径增大,体系密度先减小后增大,酶解速度减小。     

高压处理对辣根过氧化物酶活性及构象的影响

 高压处理对果蔬过氧化物酶活性的钝化程度会影响果蔬的感官品质和贮藏期,有必要研究高压条件下过氧化物酶的结构变化与其活性的关系。采用圆二色谱法和荧光光谱法,研究了室温下,100、300、500 MPa压力分别处理15 min对辣根过氧化物酶二级、三级结构及活性的影响。结果表明：高压处理对辣根过氧化物酶（HRP）有钝化作用,随着处理压力的增加,HRP的活性依次下降2.36%、5.69%、10.36%,HRP较耐压;HRP的α-螺旋、β-折叠和无规卷曲含量的升幅均小于4%,β-转角含量显著下降,且下降程度均达到11%;高压处理后的HRP在234 nm激发光谱和308 nm发射光谱特征峰的荧光强度下降,下降程度依次为18.28%、5.46%和4.04%,且100 MPa压力下处理的HRP荧光强度下降的程度最大。说明高压处理对HRP有钝化作用,且与其二级和三级结构的变化有关。     

高压处理种子对西瓜生长发育的影响

以8个汴梁西瓜品种(京引21、花皮88、圳板、郭牟、金玫黑、金小兰、日本瓜和蜜玫绿)为实验材料,采用样本率的显著性检验t、检验及单因素方差分析方法,研究了26~28 MPa的高氮气压及50~150 MPa的高静水压处理种子对西瓜出苗率、叶绿素含量、过氧化物酶活性、单瓜重、含糖量等生长特性的影响。结果表明:高压处理会显著(P0.05)或极显著(P0.01)地降低西瓜的出苗率和幼苗期叶片的类胡萝卜素含量,提高幼苗期叶片的叶绿素a含量和过氧化物酶的活性。高压处理种子对于含糖量和单瓜重这两个农艺性状的影响,品种间存在较大差异。其中,在50~150 MPa高压下处理种子20 min主要影响日本瓜(P0.001)和金小兰(P0.092)的单瓜重以及郭牟的含糖量(P0.064)。     

Enrichment of free amino acid content and reduction of astringent taste compounds in soybean by high hydrostatic pressure

ABSTRACT

We investigated the effect of high hydrostatic pressure (HHP) on the distribution of free amino acids and isoflavones in soybean immediately after pressure treatment (100–600?MPa, 10–60?min). HHP-treatment at 200 and 300?MPa resulted in high accumulation of free amino acids. Additionally, Gly, Val, and Pro levels increased even after HHP of 400?MPa. The application of HHP-treatment to soybean decreased sources of an astringent taste such as genistein-, daizein-, and glycitein-type molecules under all pressure conditions over 200?MPa. High accumulation of free amino acids with specific pressure–time conditions would be caused by the acceleration of proteolysis and specific amino acid metabolism. We concluded that HHP alone with no subsequent storage enabled the enrichment of specific amino acids such as GABA, Glu, Lys, and Pro in soybean. Soybean with enrichment of these amino acids and improved taste should be an innovative component of functional foods.     

Effect of high hydrostatic pressure and reducing sodium chloride and phosphate on physicochemical properties of beef gels

ABSTRACT

The effect of high hydrostatic pressure (HHP) treatment (100–200?MPa, 10?min, 20°C) combined with sodium chloride and sodium phosphate on the physicochemical properties of beef gels was investigated. The water content, cooking losses, color, protein composition by SDS-PAGE analysis and texture parameters of beef gels were determined. The beef gels treated with high pressure at 150?MPa showed a synergistic effect in the increased water content and the decreased cooking losses compared with the unpressurized gels. The L*, a* and b* color values of beef gels were slightly decreased under HHP treatment at 100–200?MPa. In the SDS-PAGE analysis, the staining intensity of the α-actinin protein band was decreased in pressurized samples. The cohesiveness, adhesiveness, gel strength and modulus of elasticity were improved after HHP treatment. Application of high pressure treatment (150–200?MPa) before heat treatment would be beneficial for the manufacturing of low salt and/or low phosphate meat products for a healthy diet.     

High Pressure Effect on Meat and Lupin Protein Digestibility

High pressure treatment is a mild treatment concerning the nutritional characteristics: for instance vitamins content is very few affected by high-pressure treatment. But the impact of high-pressure on protein digestibility remains poorly understood. This work presents effect of high-pressure treatment on in vitro digestibility of meat and lupin proteins. Two high-pressure conditions (200 and 500 MPa 10 min.) and a heat treatment of 95 °C, 30 min were studied. In vitro digestibility was evaluated with a pepsin reaction. Results show than for both type of proteins, samples pressurised at 500 MPa were the most hydrolysed. Meat proteins were less hydrolysed than control either after heat or 200 MPa treatment. Lupin proteins where more hydrolysed than control after heat or 200 MPa treatment. Thus we revealed that high-pressure treatment presents an effect on the in vitro digestibility of proteins, opening a new perspective of investigations.     

High-pressure effects on cooking loss and histological structure of beef muscle

In this study, we investigate the effects of high pressures (up to 600 MPa) applied at room temperature for 10 min on beef cooking loss and structure. The data on cooking loss, pH and protein solubility, as well as the electron microscopy, illustrate the changes in cooking loss and structure with high pressure processing (HPP). There is a significant reduction in cooking loss of beef with HPP. When the beef sample is imposed upon by 300 or 400 MPa, the cooking loss reduction is about 12%. Further, the pH of beef is dramatically increased as the pressure increases, and the pH increases by about 5% when imposed upon by 500 MPa. When a high pressure was applied at room temperature, the structure of the beef tissue apparently changed. Muscle fiber fragments gradually became slender and sarcomeres became lengthened. Our data indicated that high-pressure treatment on beef leads to stretching of the muscle fiber and an increase in the water-holding capacity.     

动态高压微射流技术对木瓜蛋白酶活性的影响(英文)

研究了动态高压微射流技术对木瓜蛋白酶活性的影响,并以荧光光谱为检测手段对木瓜蛋白酶的分子构象进行表征。结果显示,动态高压微射流处理(120~180 MPa)后,木瓜蛋白酶酶活降低。经180 MPa处理1次,木瓜蛋白酶相对酶活降至90.04%。随着处理压力的增加,木瓜蛋白酶分子、酪氨酸残基、色氨酸残基的荧光发射峰位置分别从对照组的334、285、277.5 nm红移至140 MPa处理组的335.5、285.5、278.5 nm,然后回移至180 MPa处理组的334、285、278 nm。在0~4℃放置24 h后,酶活进一步降低,木瓜蛋白酶和酪氨酸残基的荧光强度出现波动(降低、上升然后再降低),表明动态高压微射流处理(120~180 MPa)改变木瓜蛋白酶分子构象的效果较为明显,形成的新构象稳定性低。     

Comparison of microbiological loads and physicochemical properties of raw milk treated with single-/multiple-cycle high hydrostatic pressure and ultraviolet-C light

The effects of ultraviolet-C radiation (UV-C, 11.8?W/m²), single-cycle and multiple-cycle high hydrostatic pressure (HHP at 200, 400 or 600?MPa) on microbial load and physicochemical quality of raw milk were evaluated. Reductions of aerobic plate count (APC) and coliform count (CC) by HHP were more than 99.9% and 98.7%, respectively. Inactivation efficiency of microorganisms increased with pressure level. At the same pressure level, two-cycle treatments caused lower APC, but did not show CC differences compared with single-cycle treatments. Reductions of APC and CC by UV-C were somewhere between 200?MPa and 400/600?MPa. Both HHP and UV-C significantly decreased lightness and increased pH, but did not change soluble solids content and thiobarbituric acid-reactive substances’ values. Two 2.5?min cycles of HHP at 600?MPa caused minimum APC and CC, and maximum conductivity. Compared with HHP, UV-C markedly increased protein oxidation and reduced darkening.