大豆蛋白热变性程度对速溶豆腐花粉凝胶成型的影响

针对速溶豆腐花粉的制备工艺中需要对大豆进行热处理,热处理过程中大豆蛋白的热变性程度对豆腐花粉凝结的凝胶强度与凝结所需的时间具有显著影响,而现在速溶豆腐花粉的工业生产中还没有对豆浆热处理程度较为合适的标准。该文以大豆、大豆分离蛋白(soybean protein isolate,SPI)、大豆球蛋白(glycinin,11S)、β-伴大豆球蛋白(beta-conglycinin,7S)为原料,研究大豆蛋白热变性程度对速溶豆腐花粉凝胶成型的影响。研究表明11S比7S更难发生完全变性,SPI中的7S和11S比单独存在的7S、11S更难发生完全变性。传统制备方式、前热处理后喷雾干燥或冷冻干燥制备方式、先喷雾干燥或冷冻干燥后热处理制备方式对豆腐花凝结成型影响不同,其中传统方式制备的豆腐花凝胶效果最好,先干燥后热处理制备的豆粉凝胶效果比前热处理后干燥的豆粉好,引起豆腐花凝胶强度差异的主要原因是大豆蛋白中7S和11S热变性程度不同。制备同一凝胶强度的豆腐花,热处理温度越低,所需的热处理时间越长;制备高凝胶强度的豆腐花比制备低凝胶强度的豆腐花所能进行的热处理温度与时间范围小。大豆蛋白的7S处于完全变性而11S处于未完全变性的状态时,适合制备速溶豆腐花粉的大豆蛋白变性程度应控制热处理温度与时间范围为80℃时热处理20~65 min,85℃时热处理15~50 min,90℃时热处理10~35 min,95℃时热处理5~20 min。该研究结果为调控速溶豆腐花粉的凝胶特性提供理论依据。     

高场强超声-加热联用增强大豆分离蛋白冷凝胶凝胶特性

为探究高场强超声技术对大豆分离蛋白葡萄糖酸内酯冷凝胶性的影响,该研究将高场强超声技术与加热处理联用,对大豆蛋白进行预处理后形成冷凝胶。采用质构仪、圆二色谱、荧光色谱、扫描电镜、电泳、粒度仪等多种表征手段,比较了2种高场强超声-加热联用工艺对大豆分离蛋白冷凝胶凝胶性的影响,并推测其作用机理。研究发现:与传统加热预处理相比,2种高场强超声-加热联用预处理都能够显著(P0.05)增强大豆分离蛋白冷凝胶的持水性和凝胶强度。工艺一(20 k Hz,400 W下先超声0、2、4、10 min后加热20 min)制备的冷凝胶的凝胶强度与持水性随超声时间的增加逐步增加(凝胶强度由(5.83±0.31)g增加到(46.37±1.15)g;持水性由42.04%±1.59%增加到81.74%±6.22%),而工艺二(先加热20 min后超声0、2、4、10 min)制备的冷凝胶的凝胶强度与持水性在较短超声时间内(4 min内)迅速增加(凝胶强度由(5.83±0.31)g增加到(37.57±2.57)g;持水性由42.03%±1.85%增加到79.31%±3.00%)。与工艺一相比,工艺二能够在较短超声时间内增强大豆分离蛋白冷凝胶性的机理可能在于:工艺二的处理方式,大豆蛋白经过热处理后充分展开、变性,使超声作用能在较短的时间内对大豆分离蛋白的二级结构和三级结构明显改变,暴露更多疏水基团,增加疏水环境和表面疏水性,增强蛋白在溶液中的溶解性,并增强大豆蛋白分子间的静电相互作用,从而形成致密、均一的微观凝胶结构,增加凝胶的持水性和凝胶强度。研究结果可为高场强超声-加热联用技术在大豆加工领域中的应用提供参考。     

不同淀粉对带鱼鱼糜凝胶品质的影响

为确定改善带鱼鱼糜凝胶品质的最佳淀粉种类及其添加量,以凝胶强度、质构分析(TPA)值、白度、持水性和凝胶溶解度为指标,探究5种淀粉(小麦淀粉、马铃薯淀粉、木薯淀粉、交联淀粉和羟丙基淀粉)在不同添加量(0、5%、10%、15%和20%)下对带鱼鱼糜凝胶品质的影响。结果表明,不同种类淀粉以及添加量均对带鱼鱼糜凝胶品质有显著影响。当添加量超过15%后,淀粉的添加对带鱼鱼糜凝胶弹性和持水性影响不显著。5种淀粉中,木薯淀粉对带鱼鱼糜凝胶品质的改善效果最好,在鱼糜中添加15%木薯淀粉时,鱼糜凝胶强度、硬度、粘聚性、弹性、咀嚼性、白度值、失水率和凝胶溶解度分别为886.176 g·cm、4 879.56g、0.67、0.87、2 888.86、60.07、5.84%、49.47%。因此,添加15%的木薯淀粉能有效改善带鱼鱼糜凝胶品质。本试验结果为高品质鱼糜制品生产提供了科学依据。     

适量卵磷脂改善低酯苹果果胶凝胶流变性

为了进一步了解卵磷脂在果胶凝胶中的作用,该文考察卵磷脂对果胶凝胶流变性的影响,以低酯苹果果胶为原料,在钙离子浓度为12 mmol/L条件下,加入质量分数0.2%~1.2%的卵磷脂,考察凝胶过程中储能模量(G′)与损耗模量(G″)变化。通过凝胶结构形成速度(structure developing rate,SDR)流变学分析方法探讨在果胶凝胶过程中卵磷脂对凝胶体系的影响,结果显示:卵磷脂的添加对果胶钙凝胶的形成速度(SDR)和储能模量(G′)有影响,在整个温度变化范围内,卵磷脂添加量小于0.4%时对SDR曲线和G′曲线的影响不明显;卵磷脂添加量为0.4%时SDR曲线和G′曲线明显上升,显示出较快的凝胶速度和较强的凝胶强度;当卵磷脂添加量大于0.4%时,SDR曲线和G′曲线下降。凝胶形成动力学研究显示,加入0.4%的卵磷脂,使果胶的凝胶过程在高温区和低温区的差别更大,活化能差别也较大(P0.05):高温区活化能为290.6 k J/mol,低温区活化能为67.1 k J/mol。电镜扫描显示添加0.4%卵磷脂的果胶钙凝胶结构更为均匀紧密。研究结果为卵磷脂/果胶体系的应用提供理论参考数据。     

淀粉对竹荚鱼鱼糜流变性质和凝胶特性的影响

为探讨改善竹荚鱼鱼糜凝胶品质的最佳淀粉种类和添加量,利用流变仪、质构仪、扫描电镜等方法研究了不同来源的原淀粉及其添加量对竹荚鱼鱼糜流变性质和凝胶特性的影响。动态流变性质的结果表明,在加热过程中,竹荚鱼鱼糜的弹性模量G' 经历了2个阶段的变化,首先在20～57℃时G' 逐渐降低;然后在57～80℃由于凝胶网络的形成,使G' 增加。添加淀粉显著影响竹荚鱼鱼糜的G'。添加淀粉能够提高竹荚鱼鱼糜的凝胶强度。添加木薯淀粉、小麦淀粉对改善竹荚鱼鱼糜凝胶品质的效果最好,其添加量为4%,竹荚鱼鱼糜凝胶的凝胶强度分别提高了158%和155%。添加淀粉能提高竹荚鱼鱼糜凝胶的持水性。在相同的添加量时,木薯淀粉和小麦淀粉对提高竹荚鱼鱼糜凝胶的持水性的效果最好。添加淀粉能显著提高竹荚鱼鱼糜凝胶的白度,但淀粉的种类和添加量对鱼糜凝胶色泽的影响不显著。     

不同亲水胶体对带鱼鱼糜凝胶品质的影响

为确定合适的亲水胶体种类及其添加量,以带鱼鱼糜为原料,通过测定凝胶强度、质构(硬度、粘聚性、弹性和咀嚼性)、白度、持水性和凝胶溶解度等指标,分析瓜尔胶、魔芋胶和沙蒿胶3种亲水胶体对带鱼鱼糜凝胶品质的影响。结果表明,瓜尔胶、魔芋胶和沙蒿胶均能提高带鱼鱼糜凝胶强度,但相同添加量下魔芋胶的改善效果最好,而瓜尔胶对鱼糜凝胶强度的影响不显著。魔芋胶能显著改进带鱼鱼糜凝胶的质构特性;瓜尔胶添加量为2.0%时鱼糜凝胶硬度、弹性、咀嚼性、粘聚性比对照组低;沙蒿胶对鱼糜凝胶的粘聚性影响显著,当添加量为1.5%或2.0%时,带鱼鱼糜凝胶的咀嚼性、硬度增加,弹性下降。瓜尔胶、魔芋胶和沙蒿胶均能提高带鱼鱼糜持水性,降低鱼糜凝胶白度和溶解度,但对鱼糜凝胶色泽的影响不显著。扫描电镜结果显示,1.5%魔芋胶处理组形成的鱼糜凝胶表面规则有序、网络结构致密均一。综合比较,添加1.5%魔芋胶能有效改善带鱼鱼糜的凝胶品质。本研究结果为提高带鱼鱼糜制品品质及生产研发提供了一定的理论依据。     

高静压与к-卡拉胶对低脂猪肉凝胶保水和质构的影响

高静压处理与添加水溶性多糖是改善肉制品质构、保水性等品质的重要手段。本研究侧重调查100～300 MPa压力、0～1.0% к-卡拉胶添加水平对猪肉糜凝胶保水、质构的影响。试验结果表明，添加0.5%的к-卡拉胶可显著降低猪肉凝胶的蒸煮损失，提高总持水性及凝胶硬度(P＜0.05)；200 MPa以上的高静压不仅可以显著降低肉糜的蒸煮损失，而且也能够显著提高凝胶的硬度、黏结性与咀嚼性(P＜0.05)；但100～300 MPa的高静压对1.0%卡拉胶水平的凝胶弹性影响不明显(P＞0.05)。此外，对于肉制品保水性的评价，应注意选择合适的评价方法，尤其是蒸煮损失差异较大的肉制品样本，评价方法选择的合理性将直接影响评价的结果。     

不同贮藏期大豆蛋白对千页豆腐品质的影响

为了研究不同贮藏期大豆分离蛋白（soy protein isolate,SPI）对千页豆腐品质的影响,该文首先研究了贮藏期对大豆分离蛋白结构的影响,进而探讨贮藏期对大豆蛋白制备千页豆腐的品质的影响。对不同贮藏期的大豆蛋白分别采用了凝胶质构特性、感官评价、羰基含量、大豆蛋白亚基以及巯基的测定,并采用拉曼光谱对大豆蛋白二级结构、二硫键构型以及侧链结构进行了分析,同时采用扫描电镜观察千页豆腐的微结构。结果表明：随着贮藏期的延长,千页豆腐的感官评价变差,由88分降低至44分;其凝胶网络结构逐渐疏松;大豆蛋白羰基含量逐渐上升;巯基含量逐渐下降;二级结构含量改变;凝胶硬度呈下降趋势,硬度值低于234 g时,将无法达到千页豆腐的质量要求。这表明在贮藏期内SPI发生了氧化,导致大豆蛋白质结构发生改变,使其凝胶性质下降。     

没食子酸对海鳗肌原纤维蛋白氧化及凝胶特性的影响

为研究没食子酸(GA)对海鳗肌原纤维蛋白(MP)氧化抑制作用和凝胶特性的影响,采用羟自由基氧化体系及不同质量分数GA对海鳗MP进行处理,考察不同浓度GA对海鳗MP氧化抑制作用,采用扫描电镜技术结合凝胶特性分析GA对MP的交联作用。结果表明,氧化使海鳗MP羰基含量、表面疏水性显著上升(P<0.05),总巯基含量、凝胶持水性显著降低(P<0.05)。不同浓度GA对MP氧化均有抑制作用,质量分数分别为0.10%、0.15%的GA抑制效果最佳,且凝胶持水性显著增强(P<0.05)。圆二色谱结果表明,质量分数分别为0.10%、0.15%的GA可使MP的α-螺旋、β-折叠含量有所增加。扫描电镜结果显示,添加质量分数为0.15%的GA后形成的MP凝胶结构更加致密、光滑。综上,质量分数为0.15%的GA能有效抑制海鳗MP氧化,并改善MP凝胶持水性和微观结构。本研究为GA在水产品加工及贮藏过程中的应用提供了理论依据和数据支撑。     

饲料原料粉体流动特性预测模型

为了研究不同贮藏期大豆分离蛋白（soy protein isolate,SPI）对千页豆腐品质的影响,该文首先研究了贮藏期对大豆分离蛋白结构的影响,进而探讨贮藏期对大豆蛋白制备千页豆腐的品质的影响。对不同贮藏期的大豆蛋白分别采用了凝胶质构特性、感官评价、羰基含量、大豆蛋白亚基以及巯基的测定,并采用拉曼光谱对大豆蛋白二级结构、二硫键构型以及侧链结构进行了分析,同时采用扫描电镜观察千页豆腐的微结构。结果表明：随着贮藏期的延长,千页豆腐的感官评价变差,由88分降低至44分;其凝胶网络结构逐渐疏松;大豆蛋白羰基含量逐渐上升;巯基含量逐渐下降;二级结构含量改变;凝胶硬度呈下降趋势,硬度值低于234 g时,将无法达到千页豆腐的质量要求。这表明在贮藏期内SPI发生了氧化,导致大豆蛋白质结构发生改变,使其凝胶性质下降。     

不同热处理大豆分离蛋白凝胶冻藏特性

为探究冻藏过程中不同加热温度处理大豆分离蛋白(soybean isolate protein,SPI)凝胶特性变化及评估不同热处理对SPI凝胶冻藏特性的影响。该文以65、90和135℃3个不同温度处理所得SPI为研究对象(分别记为65SPI、90SPI和USPI),采用离心法、质构分析法、可溶蛋白含量测定和电泳等方法对其冻藏过程中的凝胶持水性、凝胶硬度、凝胶弹性、可溶蛋白含量及亚基组成和凝胶作用力进行了分析研究。结果表明:随冻藏时间延长,不同温度处理SPI凝胶持水性、凝胶弹性和凝胶可溶蛋白含量呈下降趋势,而凝胶硬度呈增大趋势。凝胶持水性、弹性的下降和凝胶硬度的升高标志着凝胶品质的劣变。不同温度处理对SPI凝胶的冻前凝胶特性和冻藏特性有较大影响,65和90℃的温度处理降低了冻前SPI凝胶的持水性,增强了冻前SPI凝胶硬度,有更多的β和B亚基参与了凝胶形成,冻藏前后的亚基组成没有变化;超高温瞬时加热(ultra high temperature,UHT)处理则降低了冻前SPI凝胶硬度,冻藏过程中可溶蛋白含量大幅下降且可溶蛋白中β和B亚基含量下降。3种温度处理SPI的凝胶劣变程度均高于未处理SPI。加热处理会造成SPI发生部分或完全变性,变性后疏水基团的暴露会加快蛋白凝胶形成过程中聚集速率,进而增大粗糙凝胶结构形成的几率,而粗糙凝胶网络在冻藏过程中其劣变程度更甚于未加热SPI。由此可知,加热处理尽管在一定程度上增大了凝胶硬度,但会加速其凝胶品质冻藏劣变。     

Gas chromatographic determination of glucono-delta-lactone in foods

A method is described for the gas chromatographic (GC) determination of glucono-delta-lactone in foods. A sample was homogenized with 60-70 degrees C water and filtered. The filtrate was buffered with NH4OH-NH4Cl pH 10 solution, and was passed through a QAE-Sephadex A25 column. The column was washed with water and glucono-delta-lactone was eluted with 0.1N HCl. An aliquot of the eluate was evaporated to dryness and derivatized with pyridine, N,O-bis(trimethylsilyl)trifluoroacetamide, and trimethylchlorosilane at room temperature. GC separation of glucono-delta-lactone as the TMS derivative was performed on a 2% OV-17 column at 180 degrees C. Recoveries from bread, jelly, soybean curd, and other foods fortified with 0.1% glucono-delta-lactone ranged from 92 to 106%, with standard deviations from 2.2 to 9.8%. The detection limit was approximately 0.025%.     

Effects of heat treatment and dehydration on properties of cauliflower fiber

The effects of heat treatment and dehydration on fiber structure and hydration properties, using cauliflower floret/curd and stem tissues, have been investigated. No major changes in fiber composition resulted from sample treatments, but the degree of esterification of pectic polysaccharides, approximately 60% in fresh cauliflower, decreased by approximately 12% in samples heated at temperatures >40 degrees C. Enzymic activity was considered to be responsible, through pectin methyl esterase activity. De-esterification was temperature and moisture sensitive. Hydration properties were also affected by processing conditions. The solubility of nonstarch polysaccharides in fresh, freeze-dried, and 40 degrees C dried samples was approximately 6% but increased to 12% in boiled samples and decreased in samples dried at 75 degrees C. Similar behavior occurred for swelling and water retention capacity (WRC), with swelling and WRC highest for boiled samples and lowest for samples dried at 75 degrees C. Hence, a decrease in de-esterification was not directly responsible for changes in hydration properties. The results demonstrate the importance of processing history on functional properties and on the preparation of fiber-rich ingredients for successful incorporation into foods.     

鲜牛奶与豆浆的氨基酸营养比较

用氨基酸自动分析仪分析了鲜牛奶和5%豆浆的蛋白质氨基酸组成及含量。必需氨基酸(含胱氨酸和酪氨酸)占氨基酸总量牛奶为45.47%,豆浆为37.93%;必需氨基酸指数(EAAI)牛奶为89.72,豆浆为74.92;赖氨酸含量牛奶为479mg/gN,豆浆为351mg/gN;第一限制氨基酸均为蛋氨酸+胱氨酸,其含量鲜牛奶为208mg/gN,豆浆为190mg/gN;氨基酸分(AAS)和化学分(CS),鲜牛奶为0.95和0.54,豆浆为0.86和0.49。     

Stabilization of caseinate-covered oil droplets during acidification with high methoxyl pectin

Polysaccharides are widely used in the food industry to modify the stability of protein-based drinks. However, an in depth knowledge of the interactions occurring in the system is still lacking. In this study, the interactions between sodium caseinate and high methoxyl pectin under acidification conditions were studied nondestructively and without dilution using transmission diffusing wave spectroscopy. Oil-in-water emulsions were prepared with 10% soybean oil and 0.5% sodium caseinate. Various concentrations of pectin (ranging from 0 to 0.2%) were added, and the emulsions were acidified with glucono-delta-lactone. With acidification, a "sol-gel" transition occurred and emulsions containing pectin were more stable at lower pH than those without pectin. Furthermore, the sol-gel transition of the mixtures was more sudden for control emulsions without pectin. While in control samples the final solidlike emulsion after gelation tended to be more inhomogeneous and more dissimilar to the starting emulsion, emulsions with pectin in solution gelled later under acidification. With a sufficient amount of pectin, the emulsions showed no aggregation and the destabilization pH varied depending on the amount of pectin present in the emulsions. At intermediate pH values (pH > 5.5), the emulsions displayed a decrease in particle size, more pronounced in samples containing pectin. The results collected using light scattering in concentrated systems, 10% (v/v) in our case, suggested that pectin stabilizes the emulsion oil droplets forming a network of oil droplets loosely connected by strands of pectin.     

间伐对黄龙山辽东栎林下枯落物持水性的影响

[目的]对黄龙山林区辽东栎林抚育间伐与对照设置试验样地,研究其林下枯落物持水效应特征,为该地区森林抚育提供理论依据。[方法]采用重度(间伐35%)、中度(间伐25%)、轻度(间伐15%)抚育间伐,通过典型取样法、烘干法、浸泡法等开展研究。[结果]枯落物总储量大小依次表现为:CK(23.500±0.780)轻度(22.950±1.012)中度(22.708±0.365)重度(20.725±1.041),只有CK与重度有显著性;枯落物总持水量大小依次表现为:轻度(9.37)CK(8.29)中度(7.61)重度(6.39),轻度间伐下枯落物总有效拦蓄量最大;枯落物持水量与浸泡时间呈对数函数变化,R2均在0.93以上,具有显著相关性;枯落物吸水速率与浸泡时间呈幂函数变化,R2均在0.99以上,具有显著相关性。[结论]综合比较不同间伐强度下枯落物持水性,轻度间伐下枯落物持水性较好,可为黄土高原地区森林抚育提供理论依据。     

Purification and glycosylation analysis of an acidic pectin methylesterase in jelly fig (Ficus awkeotsang) achenes

An acidic pectin methylesterase (PME) is responsible for the gelation of water extract from jelly fig (Ficus awkeotasang) achenes. A new, fast and efficient, method has been developed to purify this acidic PME. The method includes preparing jelly curd by traditional hand washing, extracting proteins from the curd, and separating PME by anion-exchanger. The purified PME exists as a monomer of 38 kDa determined by gel filtration, and exerts enzymatic activity over a broad pH range, particularly in acidic environments where most known PME enzymes from various species are inactivated. Chemical staining and enzymatic cleavage suggest that the jelly fig PME is an N-linked glycoprotein. Fluorophore-assisted carbohydrate electrophoresis reveals that the polysaccharide of this glycoprotein putatively consists of 22 hexoses including 16 mannose, 4 N-acetylglucosamine, and 2 galactose residues.     

用低场核磁共振研究盐溶液漂洗对带鱼鱼糜凝胶品质的影响

为了比较单一成分盐溶液(质量分数为0.30%Na Cl、0.06%Ca Cl2或0.50%柠檬酸钠)和复合盐溶液(0.15%Na Cl、0.04%Ca Cl2、0.35%柠檬酸钠)漂洗对带鱼鱼糜凝胶水分分布及其凝胶特性的影响,该文运用低场核磁技术测定鱼糜凝胶的水分弛豫时间和水分质子密度,并结合鱼糜凝胶含水率、持水性、凝胶强度及其电镜扫描图,对盐溶液漂洗效果进行探究。鱼肉经单一成分0.30%Na Cl、0.06%Ca Cl2或0.50%柠檬酸钠溶液漂洗,柠檬酸钠组鱼糜凝胶中的氢质子束缚力最大,水分难以迁移,自由水的相对含量最低;与单一成分漂洗相比,经过复合盐溶液漂洗后,鱼糜凝胶水分迁移力相对较低,自由水含量较少,而水分质子密度较高,水分分布均匀;盐溶液漂洗后鱼糜凝胶的持水性、含水率、凝胶强度、凝胶显微结构与鱼糜凝胶中的水分分布相关,利用复合盐溶液漂洗带鱼鱼肉,能更好地改善带鱼鱼糜凝胶品质。研究结果为改善鱼肉漂洗工艺、提高鱼糜品质提供参考。     

Temperature-independent pectin gel method for aerobic plate count in dairy and nondairy food products: collaborative study

Ten laboratories participated in a collaborative study to compare the pectin-based plate count (PC) Redigel method with the aerobic plate count and standard plate count agar-based standard methods for the estimation of total bacterial counts in 9 different nondairy food and dairy food products. The foods were cream, homogenized milk, raw milk, cheese, raw chicken, raw oysters, frozen broccoli, flour, and spices. Each laboratory analyzed 6 samples (3 sample pairs) of each food group. Counts obtained by the pectin-based plate count and agar-based plate count methods differed significantly (P less than 0.05) only for homogenized milk, where the pectin gel method resulted in higher counts. The actual counts were higher in the pectin gel method in 8 of the 9 food groups. The log means for pectin gel and agar-based media, respectively, for the 9 food groups were: cream 8.106 and 7.844; homogenized milk 8.642 and 8.231; raw milk 8.711 and 8.423; chicken 7.654 and 7.645; oysters 7.201 and 7.180; broccoli 7.102 and 6.798; cheese 8.045 and 8.055; flour 4.112 and 3.988; spice 5.379 and 5.314. The repeatability standard deviations favored the pectin gel method in 6 of the 9 foods tested. The reproducibility standard deviations favored the pectin gel method in 7 of the 9 foods tested. These results strongly support the suitability of the pectin gel method as an alternative to agar-based plate count and other methods for total bacterial counts in nondairy and dairy food products. The pectin gel method has been adopted official first action.