谷氨酰胺转氨酶添加量对酸羊乳凝胶特性的影响

采用不同添加量(1、2、3 u/g蛋白)谷氨酰胺转氨酶(transglutaminase,TG)在40℃下处理羊乳2 h后制备酸羊乳,研究TG添加量对酸羊乳凝乳时间,凝乳时及后发酵24 h时的酸度、持水性、质构特性和微观结构的影响。结果表明,TG处理羊乳后制备的酸羊乳其凝乳时间随着TG浓度的增大逐渐缩短,但TG浓度对酸羊乳凝乳时和后发酵24 h的酸度无明显影响(p0.05);TG处理可显著提高酸羊乳的持水性(p0.05),尤其是TG浓度为2~3 u/g蛋白时效果更加明显;质构分析表明,随着TG浓度的增大,酸羊乳凝乳时和后发酵24 h的硬度和黏性显著增加。TG处理酸羊乳凝乳时的内聚性无明显影响(p0.05),但对后发酵24 h时的内聚性影响显著(p0.05)。然而TG处理对酸羊乳弹性影响不大(p0.05);通过对酸羊乳的微观结构观察发现,用TG添加量为2~3 u/g蛋白处理羊乳制备的酸羊乳中蛋白质形成更加致密的网络结构,有利于酸乳凝胶的形成。     

酶制剂对Mozzarella水牛奶酪品质影响

比较了小牛皱胃酶、风味酶及菠萝蛋白酶对Mozzarella(莫兹瑞拉)水牛奶干酪的加工性状、质构及感官品质的影响.结果显示,用0.025 g/L风味酶添加到水牛奶中所制备干酪的产率、凝乳时间、凝乳性状、质构特征、感官品质均与小牛皱胃酶制备干酪的性状接近,说明风味酶可替代小牛皱胃酶用于Mozzarella水牛奶干酪的加工.     

Camembert干酪凝乳过程中微观结构与流变特性的变化

利用流变仪和激光共聚焦扫描显微镜追踪和观察牛乳凝乳的形成过程,通过研究经不同条件处理的Camembert干酪在凝乳时的流变特性和微观结构的变化,来探讨TG酶和CaCl2对干酪品质的影响机制.随着TG酶添加量的增大,凝块聚集交联在一起,凝乳聚集胶团更小,并形成较致密的网络结构;而添加CaCl2引入Ca2+,可显著缩短凝乳时间,提高凝乳凝胶强度.     

谷氨酰胺转氨酶对燕麦熟面条质构及蒸煮特性的影响

以燕麦全粉与小麦粉比例为3:7的混合粉为原料制作面条,研究了4种商品谷氨酰胺转氨酶(TG-M、TG-B、东圣TG和绿维康TG)对燕麦面条质构和蒸煮特性的影响。结果表明:除了TG-B酶,其他3种TG酶均可以显著增加熟面条的硬度;4种TG酶对燕麦熟面条弹性的影响并不显著,但均可以显著增强熟面条的拉断力和拉伸距离。东圣TG酶对面条黏聚性和回复性的改善作用强于其他酶制剂,但对面条吸水率的贡献最小。除了TG-B酶,其他3种TG酶在添加量超过0.2%时均可以降低面条的蒸煮损失。     

谷氨酰胺转氨酶对鸭胸肉糜凝胶性能的影响

以鸭胸肉糜为研究对象,探讨不同谷氨酰胺转氨酶（transglutaminase,TG）添加量（0（T1）、2（T2）、4（T3）、6（T4）、8 g（T5））对肉糜保水性、色差、质构和水分分布状态的影响。结果表明：添加TG酶显著提高鸭胸肉糜的亮度值（L*）、蒸煮得率和质构参数（P＜0.05）,降低红度值（a*）和黄度值（b*）;鸭胸肉糜的L*、蒸煮得率和质构特性随着TG酶添加量的增加而显著提高（P＜0.05）,但T4和T5组差异不显著（P＞0.05）;鸭胸肉糜的T21和T22起始弛豫时间随着TG酶添加量的增加显著缩短（P＜0.05）,T21的峰面积比例显著增加,T22的峰面积比例显著降低（P＜0.05）,表明水分的流动性降低,但T4和T5组差异不显著（P＞0.05）。综上所述,711.6 g鸭胸肉糜中添加6 g TG酶时保水性和质构最佳。     

热处理与均质压力对扣碗酪凝乳质构的影响

热处理与均质是牛奶处理的必须工艺,这两个因素对凝乳形成、蛋白变性等方面都有影响,这些因素也影响到扣碗酪的凝乳质构性质。本文应用物性测定的方法,对热和均质扣碗酪的凝乳质构中的硬度、粘着性和凝聚性的影响进行了分析,发现牛奶的均质压力与热处理温度之间对扣碗酪的凝乳质构性质没有交互作用,选择低温热处理以及低均质压力能够得到比较好的凝乳质构。硬度和粘着性对整体饱满度的影响比较大,相关系数分别达到0.679和0.743。凝聚性对扣碗酪的整体饱满度影响不大。     

酶凝干酪素生产过程中酶凝工艺的优化

研究了凝乳酶添加量、凝乳温度和凝乳时间对酶凝干酪素酶凝工艺的影响,通过对凝乳过程的感官评价,最终确定了酶凝干酪素的最佳酶凝工艺参数。结果表明:凝乳温度和凝乳时间对酶凝干酪素酶凝状态有显著影响,确定最优工艺条件为:凝乳酶添加量的体积分数为0.078%,凝乳温度为32℃,凝乳时间28 min。此条件下生产的酶凝干酪素与市售酶凝干酪素理化指标接近。     

大豆豆酪凝乳参数优化及质构的比较

以大豆为试验原料,凝乳时间、凝乳状态及乳清OD值为参考指标,对大豆豆酪生产中的凝乳工艺参数进行优化,以期获得应用不同凝固剂(木瓜蛋白酶和菠萝蛋白酶)生产的大豆豆酪质构特性(硬度和黏附性)的差异。通过正交试验,对凝乳最佳温度、凝固剂最佳添加量、Ca Cl2的最佳添加量进行研究和探讨,进而对采用最优工艺参数生产的2类豆酪质构特性进行差异比较。结果表明:大豆豆酪凝乳的最佳工艺参数是凝乳温度为59℃、木瓜蛋白酶添加量为0.25%(活力为600 U/mg)、Ca Cl2添加量为0.08%;凝乳温度为55℃、菠萝蛋白酶添加量为0.50%(活力为300 U/mg)、Ca Cl2 0.08%。采用木瓜蛋白酶生产的大豆豆酪硬度比用菠萝蛋白酶生产的大123 g,用菠萝蛋白酶生产的大豆豆酪黏附性比用木瓜蛋白酶生产的大7 g·s。2类豆酪在凝乳工艺参数方面的差异,表现在凝乳温度及酶添加量不同,在质构特性方面的差异,表现在硬度和黏附性的不同。     

谷氨酰胺转氨酶浓度对巴氏杀菌酸羊奶品质的影响

采用不同浓度(2、4、6、8 u/g蛋白)谷氨酰胺转氨酶(transglutaminase, TG)处理羊奶后制备酸羊奶,研究TG酶对巴氏杀菌酸羊奶品质的影响。结果表明,TG酶处理可显著降低巴氏杀菌后酸羊奶的酸度(P0.05),但不同TG酶浓度对其酸度影响不显著(P0.05);TG酶浓度对酸羊奶的黏度和持水性有显著影响(P0.05),当TG酶浓度小于4 u/g时,随着TG酶浓度的增大,酸羊奶的黏度和持水力显著增大(P0.05),当TG酶浓度大于4 u/g时,酸羊奶的黏度变化不大(P0.05),但持水性有所降低,且TG酶对酸羊奶中风味物质乙醛和双乙酰具有抑制作用;质构分析表明,TG酶处理可显著提高酸羊奶的胶黏性(P0.05),降低其内聚力(P0.05),但对酸羊奶的弹性影响不大(P0.05);综合感官分析表明,经4 u/gTG酶处理的巴氏杀菌酸羊奶品质最好。     

TG酶和漆酶对双歧杆菌益生菌酸奶品质的影响

为了比较谷氨酰胺转氨酶(TG酶)和漆酶的添加对双歧杆菌益生菌酸奶感官、蛋白质交联及组织质构变化的影响,测定和分析了两种酶交联益生菌酸奶的游离氨基变化率、感官、质构、表观黏度、蛋白条带及微观结构,并添加阿魏酸改善漆酶酸奶的品质。结果表明:当TG酶用量增加时,TG酶交联酸奶的游离氨基变化率、感官得分和硬度显著增大(p<0.05),胶黏性、粘聚性及表观黏度先增大后减小(p<0.05),内聚性变化不显著(p>0.05),TG酶最佳用量为1.8 U/g;随着漆酶用量的增加,漆酶酸奶游离氨基变化率、感官得分、硬度、内聚性、胶黏性、粘聚性及表观黏度均先增大后减小(p<0.05),漆酶最佳用量为0.3 U/g;添加4.5 mmol/L的阿魏酸明显改善了漆酶交联酸奶的感官、质构及表观黏度;所有待测酸奶中均缺少β-lg条带,TG酶交联酸奶的κ-CN和β-CN条带消失,聚集成了新的蛋白质,而漆酶交联酸奶和阿魏酸+漆酶酸奶与对照及TG酶酸奶相比,分子量在14 kDa的蛋白条带明显变宽;经两种酶交联的酸奶,三维网络结构变得致密,TG酶交联酸奶的胶粒分布更均匀,网络结构更致密,且在漆酶交联酸奶中添加了阿魏酸后,相较于漆酶交联酸奶,蛋白胶束聚集的更紧密,从而得出,不同类型酶对牛奶乳蛋白质交联的催化作用不同,但均可改善酸奶的感官及食用品质。     

Changes in composition and functional properties of proteins and their contributions to Nham characteristics

Changes in composition and functional properties of proteins during fermentation of Nham, a Thai-fermented sausage, were studied. An alkaline-soluble fraction constituted a major protein component of Nham. The amount of each protein fraction in Nham varied, depending on the fermentation time. As fermentation proceeded, the progressive decrease in sarcoplasmic and myofibrillar protein fractions was accompanied by an increase in the alkaline-soluble fraction and non-protein constituents (P<0.05). Slow pH lowering to pH 4.6 during fermentation as a result of bacterial growth and accumulation of lactic acid affected the molecular conformation of the muscle proteins and resulted in changes in protein functional properties. The acid produced resulted in changes in solubility, water-binding capacity, textural properties, and color characteristics. Proteolysis of Nham proteins occurred during fermentation, resulting in increases in TCA-soluble peptides and free α-amino acids, which may contribute to the taste and aroma of Nham.     

Type of starter culture influences on structural and sensorial properties of low protein fermented gels

Organoleptic properties of skimmed milk fermented gels are progressively demanding to produce optimal quality yogurts. Chr‐Hansen trademark registered cultures were used to produce low‐protein (3.4%) gels to assess the ability to redesign the sensorial and textural properties with the choice of starter culture. Resulting gels were assessed for sensorial, textural, rheological, and microstructural properties and compared with a commercial control (4.5% protein). Mouth thickness, syneresis, firmness, elasticity, and consistency values were lower for polysaccharides‐producing cultures. Such cultures contributed to the higher creaminess and tended to give higher ropiness. Observed differences among microstructures of the gel were minute. Microstructural and rheological data corresponded and reflected the instrumental and sensory interpretations. Strong correlations were observed between sensory and instrumental data. Nonprobiotics cultures resulted in promising overall gel properties compared with probiotic cultures according to the principal component analysis. Yet probiotic cultures resulted in lower syneresis than nonprobiotic cultures. Thus, the choice of bacterial culture modifies the sensorial and textural properties of fermented gel with strong correlations, as a result of altered gel network formation with the production of polysaccharides. Inferior textural and sensorial quality aspects, particularly at low protein levels, have negative impact on consumer demand of low protein yogurts. Thus, we attempted to gain required gel textural and sensorial properties with a choice of starter culture with a low protein level. Resulting gel properties at lowered protein content with different starter cultures are not fully known. The present study compares the effect of probiotic and nonprobiotic starter cultures on gel properties, as gel texture and sensory properties are of great interest and thus not willing to be compromised. In addition, we examined the overall texture profile of studied cultures and correlate with sensory properties. Therefore, reducing protein level in milk and achieving required gel properties with the choice of appropriate starter culture is of great commercial interest as a cost‐cutting strategy to produce low‐cost optimum quality yogurt.     

Large Deformation Properties of Gels and Model Comminuted Meat Products Containing Lupin Protein

ABSTRACT: The fracture properties of Lupin seed protein isolate (LSPI) gels prepared by heat-treatment of protein dispersions have been studied at large deformations, by a uniaxial compression test. Fracture parameter values depended both on the method used for isolate preparation and the presence of sodium chloride. The results are explained in terms of LSPI composition and protein solubility. Incorporation of lupin isolate to a model comminuted meat-product system, resulted in a significant increase in fracture stress value while textural parameter values of the heated system such as hardness, fracturability, gumminess, and chewiness were also affected.     

Production of set yoghurt analogue through replacement of milk fat with canola and sesame oil

The aim of this study was to determine the effect of fat level and composition on chemical, textural, microbial and sensory properties of set yoghurt analogue. The best fat level for production of yoghurt analogue was found to be 2% (w/v). Studies on the effect of fat composition (canola‐to‐sesame oil ratios of 2.0/0, 1.3/0.7, 0.7/1.3, 2.0/0) indicated the superior performance of pure sesame oil. Increasing the canola‐to‐sesame oil ratio generally resulted in an inferior product. Replacement of milk fat by vegetable oils yielded yoghurts with a lower saturated fatty acid content and less firmness.     

Micronization Effects on Composition and Properties of Tofu

The effect of infra-red heating (micronization) was investigated on the composition and textural, biochemical and nutritional properties of soymilk and tofu. The yield, protein content and textural properties of tofu made from micronized beans using the common procedures (70°C as coagulating temperature and CaSO₄2H ₂O as coagulating agent) were lower than those of tofu from unprocessed beans; tofu prepared from micronized beans and coagulated at 90°C using a mixture of citric acid (0.01M) and calcium sulfate (0.03M) showed improved characteristics. The microstructure of tofu prepared from micronized beans lacked the regularity of the honeycomb-like structure shown by tofu from unprocessed beans. The heat treatment by micronization had little effect on the protein components of soymilk and tofu as determined by polyacrylamide disc gel electrophoresis.     

Ultrasonic assessment of textural changes in vacuum packaged sliced Iberian ham induced by high pressure treatment or cold storage

Ultrasonic measurements were used to characterize the effect of high pressure treatment (HPT) (600 MPa/6 min) or cold storage (6 °C/120 days) on the textural properties of vacuum packaged dry-cured ham. The ultrasonic velocity, textural properties and fat content were determined in the ham packages. The ultrasonic velocity was related to the ham hardness, which depends on the sample composition. HPT induced molecular alterations which resulted in an average increase in the hardness of lean tissue of 0.2 N and one of 0.3 N in that of fatty tissue. These textural changes give rise to a velocity increase (8 m/s for lean and 17 m/s for fatty tissue). The cold storage of the Iberian ham also led to an increase in hardness (average 1.10 N) and ultrasonic velocity (average 70 m/s). Therefore, the non-destructive ultrasonic technique could be a reliable method with which to assess the textural changes induced by HPT or cold storage on packaged dry-cured ham.     

Salinity alters the protein composition of rice endosperm and the physicochemical properties of rice flour

BACKGROUND: Salinity is one of the major threats to production of rice and other agricultural crops worldwide. Although numerous studies have shown that salinity can severely reduce rice yield, little is known about its impact on the chemical composition, processing and sensory characteristics of rice. The objective of the current study was to investigate the effect of salinity on the pasting and textural properties of rice flour as well as on the protein content and composition of rice endosperm. RESULTS: Rice grown under saline conditions had significantly lower yields but substantially higher protein content. The increase in protein content was mainly attributed to increases in the amount of glutelin, with lesser contributions from albumin. Salinity also altered the relative proportions of the individual peptides within the glutelin fraction. Flours obtained from rice grown under saline conditions showed significantly higher pasting temperatures, but lower peak and breakdown viscosities. Rice gels prepared from the flour showed significantly higher hardness and adhesiveness values, compared to the freshwater controls. CONCLUSION: Salinity can significantly affect the pasting and textural characteristics of rice flour. Although some of the effects could be attributed to changes in protein content of the rice flour, especially the increased glutelin level, the impact of salinity on the physicochemical properties of rice is rather complex and may involve the interrelated effects of other rice components such as starch and lipids. Copyright © 2011 Society of Chemical Industry     

从质构学角度研究肌原纤维蛋白凝胶形成的作用力

通过研究有关试剂对肌原纤维蛋白(MP)凝胶质构特性的影响,探讨了维持凝胶形成的作用力。结果表明:改变pH和离子强度影响了静电相互作用,从而改变了肌源纤维蛋白(MP)凝胶的质构特性;添加二硫苏糖醇(DTT)、N-乙基顺丁烯二酰亚胺(NEM)、溴酸钾能影响二硫键的形成,但MP凝胶质构特性变化不明显,说明二硫键对MP凝胶形成的影响不大;添加微量的十二烷基硫酸钠(SDS)可明显影响凝胶的硬度和弹性,说明疏水相互作用在MP凝胶形成中具有显著作用;添加尿素和盐酸胍能明显降低MP凝胶的硬度和弹性,说明氢键对MP凝胶的形成也具有重要的影响。     

米饭物性与食味形成机理研究进展

随着生活水平的提高,人们越来越重视大米食味品质。大米的蒸煮是影响米饭物性等食味品质的重要环节。较为全面地阐述了大米加水、浸泡、蒸煮、焖制和冷却与静置等工艺条件对米饭物性的影响,并讨论了米饭物性与大米直链淀粉、蛋白质、脂类含量的关系,指出食味形成机理是大米淀粉结构、蛋白质与脂类相互结合的分子构象共同作用的结果。     

Xanthan Enhances Water Binding and Gel Formation of Transglutaminase-Treated Porcine Myofibrillar Proteins

ABSTRACT: In this study, the effect of xanthan on dynamic rheological properties, textural profile, and water binding of transglutaminase (TG)-treated myofibrillar protein (MP) gels was investigated. In experiment 1, MP suspensions (40 mg/mL protein, 0.6 M NaCl) at pH 6.45 with or without 0.05% xanthan were treated with 0%, 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% TG; in experiment 2, MP suspensions (40 mg/mL protein, 0.6 M NaCl) at pHs 6.13, 6.30, 6.45, 6.69 with or without 0.05% xanthan were treated with 0.3% TG. Treated samples were analyzed with differential scanning calorimetry for thermal stability and oscillatory rheometry and Instron penetration tests for gelation properties. The TG treatments lowered the transition temperature (T_m) of MP by as much as 6 °C (P < 0.05) but increased apparent enthalpy of denaturation. However, there was no detectable thermal stability difference between MP samples with or without xanthan. The shear storage modulus (G′) of MP gels increased markedly upon treatments with ≥0.3% TG, and the presence of xanthan further enhanced the gel strength (P < 0.05). The addition of 0.05% xanthan decreased cooking loss of TG-treated MP gels by 17% to 23% when compared with gels without xanthan at all pH levels evaluated (6.13 to 6.67). Thus, the combination of TG and xanthan offered a feasible means to promote cross-linking and gelation of MP while reducing cooking losses.