Bread staling assessment of enzyme-supplemented pan breads by dynamic and static deformation measurements

Dynamic mechanical analysis and thermal mechanical analysis techniques were used in order to evaluate the effect of amylolytic-, non-amylolytic- and gluten-cross-linking enzymes on the viscoelastic properties of fresh and stored pan breads. The relationships between dynamic and static compression measurements in bread staling characterization and the correlations between sensory firmness and thermomechanical properties were also investigated. Rheological changes in bread associated with recipe and storage time were successfully detected via dynamic thermomechanical analysis (DTMA) in the compression mode. Relationships between the dynamic (DTMA) and static (texture analysis) methods were found. All the bread quality indicators measured by static methods were negatively correlated with the viscoelastic dynamic parameters.     

Methodological developments in bread staling assessment: application to enzyme-supplemented brown pan bread

In this study, texture profile analysis (TPA) at 40 and 80% compression and a newly proposed penetration test were used to evaluate the effects of amylolytic and non-amylolytic enzymes on the textural properties of fresh and stored brown pan breads. The correlations between instrumental parameters and sensory attribute results obtained by a trained panel of assessors were also investigated. Comparison of the results obtained through TPA at the two compression rates was very useful, as the 40% compression TPA hardly reflected the changes that took place in the enzyme-supplemented bread samples over a storage time of 20 days. The penetration curve profiles provided very valuable information, which complemented the TPA for the purposes of assessing bread ageing and the effect of adding enzymes.     

Significance of microbial transglutaminase on the sensory, mechanical and crumb grain pattern of enzyme supplemented fresh pan breads

The impact of microbial transglutaminase (TGM) on the sensory, mechanical and crumb grain pattern of fresh pan breads has been investigated in white and wholemeal flour sponge dough samples supplemented with amylolytic-(NMYL) and non-amylolytic (PTP) enzymes. Assessment of bread performance has been carried out by physico-chemical measurements, texture profile analysis, sensory evaluation, digital image analysis and multivariate data handling. Improving effects of TGM addition were prominent when added to low extraction rate flours (increased cohesiveness by 11%, volume, aroma intensity by 31%, typical taste and crumb to cell ratio by 25% and decreased cell number by 17%). For white and whole flours, NMYL addition to TGM breads led to 16% softer breads. For the pool of enzyme supplemented samples tested, it was observed that the higher the specific volume of breads, the lower the acidification power, the better the mechanical behaviour with high cohesiveness and low hardness values and the higher the sensory scores for visual and textural attributes.     

Impact of microbial transglutaminase on the viscoelastic profile of formulated bread doughs

The effects of microbial transglutaminase (TGM) on the viscoelastic profile of wheat flour doughs when added singly and in combination with hydrocolloids—hydroxypropylmethylcellulose (HPMC) and a high ester pectin (GENU pectin type BIG, or BIG)—, amylolytic (-amylase) and non amylolytic enzymes (xylanase) and an emulsifier [diacetyl tartaric acid ester of mono-diglycerides (DATEM)] have been investigated by applying response surface analysis to a Draper-Lin small composite design of formulated dough samples. In spite of the major effects on mixing, textural, extensional and viscometric parameters, which were provided by hydrocolloid/surfactant combinations, incorporation of TGM into dough formulas improved some viscoelastic properties. TGM, when added to DATEM and/or HPMC-containing doughs, induced synergistic effects on mixing parameters, resulting in increased water absorption, development time and stability. Highly cohesive doughs with improved water holding capacity and gluten strength during mixing and fermentation, and suitable pasting behaviour during cooking were achieved using TGM/BIG/DATEM mixtures, mainly associated with suitable interactions of the pairs TGM/DATEM and DATEM/BIG.     

Probing thermal behaviour of microbial transglutaminase with fluorescence and in silico methods

BACKGROUND: Knowledge of transglutaminase behaviour at thermal treatment allows efficient applications in food processing. The heat‐induced conformational changes of microbial transglutaminase were studied by fluorescence spectroscopy and a molecular modelling approach. RESULTS: The experimental results indicate the unfolding of transglutaminase in a single‐phase reaction, at temperatures over 60 °C. The incidence of conformational changes is also supported by the increase of both intrinsic and 1‐anilino‐8‐naphthalene sulfonate fluorescence intensity with temperature. Changes in the secondary and tertiary structure of transglutaminase were outlined after running molecular dynamics simulations at temperatures ranging from 25 °C to 80 °C. CONCLUSION: The motif's particularities varied with the temperature, suggesting structural rearrangements of the protein, mainly in helices. The largest deviation from the structure equilibrated at 25 °C was observed at 80 °C. © 2012 Society of Chemical Industry     

Impact of microbial transglutaminase on gelling properties of Indian mackerel fish protein isolates

Impacts of microbial transglutaminase (MTGase) (0–0.6 units/g sample) on gel properties of Indian mackerel unwashed mince, surimi and protein isolates with and without prewashing were studied. Generally, lower myoglobin and lipid contents were found in protein isolate with and without prewashing, compared to those of unwashed mince and surimi (P < 0.05). Protein isolate had the decreased Ca²⁺-ATPase and protein solubility, indicating protein denaturation. When MTGase was incorporated, breaking force and deformation of all gels markedly increased, especially as MTGase levels increased (P < 0.05). At the same MTGase level, gel from protein isolate with prewashing exhibited the highest breaking force and deformation (P < 0.05). The addition of MTGase could lower the expressible moisture content of most gels. No change in whiteness of gel was observed with the addition of MTGase (P > 0.05), but gel from protein isolate gels had decreased whiteness as MTGase at high level was added. The microstructure of protein isolate gels without prewashing showed a similar network to unwashed mince gels, whilst a similar network was observed between surimi gel and gel from protein isolate with prewashing. Nevertheless, a larger void was noticeable in gels from protein isolates. All gels incorporated with MTGase (0.6 units/g) showed a slightly denser network than those without MTGase. Thus, gel with improved properties could be obtained from protein isolate from Indian mackerel with added MTGase.     

Effect of microbial transglutaminase on spaghetti quality

ABSTRACT:  To examine the potential application of microbial transglutaminase (MTG) on semolina dough properties and quality of raw and cooked spaghetti, the effects of various MTG addition levels on the solubility of proteins, SDS-PAGE pattern of semolina dough proteins, and textural and structural properties of raw and cooked spaghetti were investigated using semolina from a high-protein good variety (MACS 1967) and a low-protein poor variety (PDW 274) durum wheat. To increase the concentration of lysyl residues and possibly enhance the extent of cross-linking of protein matrix by MTG, a commercial soy protein isolate (SPI) was added at a level of 3% (w/w) in combination with MTG, and its effect on semolina dough properties and spaghetti quality was investigated. The addition of MTG significantly decreased the solubility of semolina dough proteins. SDS-PAGE results showed that with increasing levels of MTG, a progressive decrease in the intensity of the bands corresponding to molecular weight of around 66 kDa was observed. Protein cross-linking reaction catalyzed by MTG resulted in changes in dough properties, dry spaghetti quality, cooking quality characteristics, and microstructure of cooked spaghetti. However, the quality improvements were more evident in spaghetti from the poor variety PDW 274 than from the good variety MACS 1967. The results also showed the ability of MTG in the formation of heterologous polymers between SPI and durum wheat proteins to improve the quality of spaghetti samples.     

Effect of damaged starch levels on flour-thermal behaviour and bread staling

The effect of the amount of damaged starch in two different flours (wheat and triticale) on the bread quality and its behaviour during storage has been analysed. Two wheat and one triticale flour cultivars were milled in a disc mill to obtain different levels of damaged starch. Differential Scanning Calorimetry (DSC) and Rapid Visco Analyser (RVA) were used to characterize the flour properties and TA-XT2 textural analyses were made on breadcrumb. The effect of the damaged starch content on the bread firming, the amylopectin retrogradation and starch-pasting properties were studied in order to establish any relationship between damaged starch and bread staling. DSC analysis showed that the damaged starch content changed the thermal behaviour of flour–water mixtures: the higher the levels of damaged starch the lower the starch-gelatinization enthalpy and the higher the melting enthalpy of amylose–lipid complexes. The amount of amylopectin retrogradation and breadcrumb firming increased with the damaged starch content at the beginning of storage time; however, differences were decreasing at final storage time. The flour viscosity during pasting decreased as their damaged starch content increased.     

微生物谷氨酰胺转胺酶对牛乳改性作用的研究进展

微生物谷氨酰胺转胺酶（MTG）是一种催化酰基转移反应的酶。综述了MTG对牛乳蛋白和乳脂肪球的改性机理及其对牛乳热稳定性、凝胶性、乳化性等方面的影响。为其在乳品工业的应用提供了理论依据。     

Impact of cooling rates on the staling behavior of cooked rice during storage

The impact of cooling rates (0.40, 1.11, 1.42, 1.64, 2.47 and 3.36 °C/min) on starch retrogradation and textural properties of cooked rice was evaluated. The relationship between cooling rates and different properties were determined using Pearson correlation. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by differential scanning calorimetry, and textural properties were determined by a Texture Analyser. This study showed that the ΔH_r value and hardness value had a negative correlation with cooling rate during storage, −0.963  r  −0.716, P < 0.01; −0.826  r  −0.706, P < 0.05, respectively. However, a positive correlation was found between adhesiveness and cooling rate (0.237  r  0.882, P < 0.05). These results indicated that the cooked rice chilled with slower cooling rate retrograded faster than chilled with rapid cooling rate. Therefore, high quality cooked rice can be produced by rapid cooling process.     

微生物转谷氨酰胺酶对鱼糜制品凝胶性能的影响

比较了微生物转谷氨酰胺酶(MTG)对五种海鱼鱼糜制品凝胶性能的影响。研究结果表明,鱼糜中加入MTG使鱼糜制品凝胶强度有不同程度的提高,特别是对本身凝胶性能不佳的梅鱼和黄姑鱼,凝胶强度分别提高了529%和489%。在加入MTG的同时,淀粉和大豆蛋白的添加对鱼糜制品的凝胶性能也有不同程度的影响,最佳添加量分别是:MTG20～100U/100g鱼糜(因鱼糜品种不同而有所差异),10%的淀粉,5%的大豆蛋白。对添加MTG的鱼糜热凝胶条件研究表明,采用50℃,30min/80℃,30min的两段式加热,鱼糜制品的凝胶效果最好。     

转谷氨酰胺酶对豆腐凝胶性能的影响

研究了在豆腐制作过程中传统的化学凝固剂对豆腐品质影响的基础上,利用微生物转谷氨酰胺酶(MTG)对豆腐的品质进行改良。研究结果表明,添加适量的MTG可以明显提高豆腐的凝胶强度,有效的改善豆腐的成型性和品质。得出对于浓度为10%～15%的豆浆,石膏用量为1%、内酯用量为0.33%时,MTG的最佳浓度为0.1～0.2u/mL、作用温度为50℃、作用时间为20～40min。     

微生物谷氨酰胺转氨酶的来源与生物工程技术研究进展

微生物谷氨酰胺转氨酶（MTGase）是一种通过异肽键来催化蛋白质或多肽链之间的酰基发生转移反应的重要酶制剂,在食品、生物医药、化妆品、纺织等领域有着广泛的应用前景。该文综述了MTGase的国内外研究现状,MTGase基因、MTGase工程菌株的构建和表达,以及MTGase的分子改造技术研究进展,并对生物工程技术应用于MTGase的产品生产进行了展望,为高效和低成本MTGase的产品开发及应用提供新的思路和方法。     

Effect of baking conditions and storage with crust on the moisture profile,local textural properties and staling kinetics of pan bread

To investigate the impact of baking conditions on staling kinetics and mechanical properties, pan breads were baked at 180 °C/34 min and 220 °C/28.6 min using a ventilated oven and metallic moulds. After baking, bread slices were stored with and without crust at 15 °C in hermetic boxes for 9 days. This investigation provides a textural and physical analysis by examining the Young's modulus, crumb density and crust/crumb ratio during storage. In order to understand the relationship between firmness and moisture content, a moisture profile and a Young's modulus profile were determined during the storage of bread. To fit the staling, a first order model was used. It was found that the kinetics were faster for samples baked with a fast heating rate than for those baked with a slow heating rate. Moreover, the staling rate of bread stored with crust was faster than for bread without crust and the outer crust area staled more rapidly than the centre of the bread slice. These results suggest that the firming of the crumb is related to moisture distribution between the crumb and crust and to the impact of local baking conditions on local firmness.     

面包老化抑制因素的研究

在西方国家，面包是餐桌上的主食，面包的质量与人们的健康和幸福息息相关。随着经济水平的提高，面包已经悄悄走进了我们的生活。但是，老化的面包口感差，易掉屑且香味丧失，不为广大消费者所接受。我们需要研究面包老化的机理，并从理论上寻找抑制面包老化的方法，提高面包的质量。本文综述了近年来国内外对面包老化的研究结果，从水分、淀粉结晶、添加剂、淀粉酶、贮存和温度几方面论述了抑制面包老化的方法。并对抑制面包老化，全面提高面包质量的研究趋势进行了展望。     

Effects of red rice flour addition on the rheological,textural, sensory and bioactive properties of wheat flour-based pan breads

Red rice, rich in fibre and phenolic contents, is one of the underutilised grains. Therefore, the present study developed the wheat/red rice flour (RRF) composites followed by its utilisation in pan breads. It led to an increase in ash and fibre contents of resultant flour combinations, but gluten network became weaker. The values for water absorption were unaffected with RRF replacements ≤15% of wheat flour. Moreover, the proximate estimates of RRF added breads demonstrated increased moisture and fibre contents. Substituted bread combinations were harder with increased gumminess and springiness values; however, cohesion decreased. The per cent change in cohesion and hardness of individual breads upon storage was lesser in composites compared to control suggesting decline in staling phenomenon. Nutritional assessment of both RRF containing flour and breads showed higher total phenolic content and DPPH radical scavenging activity compared to their respective controls. Composite breads also demonstrated reduced glycaemic index suggesting its importance for diabetic patients.     

Incorporation of microbial transglutaminase into non-fat yogurt production

This study investigated the physical, chemical and sensory characteristics of non-fat yogurts treated with microbial transglutaminase (MTGase) at varying concentrations from 0 to 0.5 g L⁻¹. Also, the effect of enzyme inactivation prior to fermentation on the selected properties of the yogurts was studied. Acid development rate was reduced with increasing MTGase doses. Cross-linking of milk proteins by MTGase had a growth-slowing effect on yogurt starter bacteria, which was more pronounced at higher concentrations. Physical properties of the yogurts were improved by MTGase throughout 21-day storage; on the contrary, the production of acetaldehyde was slowed down by increasing MTGase concentrations during the same period. Principal component analysis (PCA) and hierarchial cluster analysis (HCA) clearly differentiated the samples with added MTGase at lower (⩽0.3 g L⁻¹) and higher (0.4–0.5 g L⁻¹) concentrations regarding the physical and sensory properties. The physical and sensory properties of non-fat set yogurt could be improved by incorporating MTGase up to a level of 0.3 g L⁻¹.     

微生物转谷氨酰胺酶催化乳清蛋白聚合研究

采用SDS－PAGE分析，研究了不同条件下微生物转谷氨酰胺酶（MTGase）催化乳清蛋白（WPI）聚合。结果显示，MTGase可催化乳清蛋白的β－乳球蛋白（β-LG）和α－乳清蛋白（α－LA）聚合，形成低聚物或生物聚合物，其中β-LG更易受MTGase的催化，当TGase酶浓度一定时（0.5U/mL),TGase催化WPI聚合的最佳底物质量分数范围为2％－4％，对WPI进行加热预处理，同时添加还原剂，可明显提高MTGase对WPI的催化活性，MTGase催化WIP的最适PH值范围为6．5－7．5，当WPI经预热处理（85℃，15min），同时添加20mmol/L的DTT，TGase催化WPI聚合12h，可使质量分数为92％的β-LG和质量分数为75％的α－LA聚合。     

微生物谷氨酰胺转胺酶对乳清蛋白的改性

介绍了该酶的来源、性质及催化反应机理。由于乳清蛋白应用于食品加工中时，其理化功能尚不突出，所以通过谷氨酰胺转胺酶对乳清蛋白的改性，可以加强乳清蛋白的功能性质，从而合理利用资源，开发新产品，扩大其在食品中的应用。