Microstructure, fundamental rheology and baking characteristics of batters and breads from different gluten-free flours treated with a microbial transglutaminase

Gluten is a fundamental component for the overall quality and structure of breads. The replacement of the gluten network in the development of gluten-free cereal products is a challenging task for the cereal technologist. The functionality of proteins from gluten-free flours could be modified in order to improve their baking characteristics by promoting protein networks. Transglutaminase (TGase) has been successfully used in food systems to promote protein cross-linking. In this study, TGase was investigated for network forming potential on flours from six different gluten-free cereals (brown rice, buckwheat, corn, oat, sorghum and teff) used in breadmaking. TGase was added at 0, 1 or 10 U/g of proteins present in the recipe. The effect of TGase on batters and breads was evaluated by fundamental rheological tests, Texture Profile Analysis and standard baking tests. Three-dimensional elaborations of Confocal Laser Scanning Microscopy (CLSM) images were performed on both batters and breads to evaluate the influence of TGase on microstructure. Fundamental rheological tests showed a significant increase in the pseudoplastic behaviour of buckwheat and brown rice batters when 10 U of TGase were used. The resulting buckwheat and brown rice breads showed improved baking characteristics as well as overall macroscopic appearance. Three-dimensional CLSM image elaborations confirmed the formation of protein complexes by TGase action. On the other side, TGase showed negative effects on corn flour as its application was detrimental for the elastic properties of the batters. Nevertheless, the resulting breads showed significant improvements in terms of increased specific volume and decreased crumb hardness and chewiness. Under the conditions of this study, no effects of TGase could be observed on breads from oat, sorghum or teff. Overall, the results of this study show that TGase can be successfully applied to gluten-free flours to improve their breadmaking potentials by promoting network formation. However, the protein source is a key element determining the impact of the enzyme.     

Preliminary Notes on Equine Tissue Transglutaminase Serology and A Case of Equine Gluten-Sensitive Enteropathy and Dermatitis in an 11-Year-Old Dutch Warmblood Horse

It has been suggested that gluten may play a role in equine inflammatory small bowel disease (ISBD). Previous work showed an association between equine gluten-sensitive enteropathy and IgA antibodies to tissue transglutaminase (TGA) in serum. The purpose of this study is to investigate the prevalence of IgA antibodies to TGA in a group of healthy non–gluten-free sport ponies and to present a case of tentative gluten-sensitive enteropathy and dermatitis in a horse. Blood samples were obtained from 40 healthy jumping ponies. The ponies comprised 12 mares, 8 stallions, and 20 geldings with an average age of 9.0 ± 3.8 years (±SD; range 3–19 years). Sera were tested for IgA antibodies against human recombinant TGA. Significance (P < .05) of the correlation between TGA titer and age in these ponies was assessed using Pearson test (two tailed). In addition, to further illustrate tentative equine gluten-sensitive enteropathy and dermatitis, the clinical course in an 11-year-old Dutch Warmblood sport horse gelding has been described. The average TGA titer was 21.4 ± 13.6 AU/mL (range 2–65 AU/mL). There was a significant (P = .013) correlation (r = 0.389) between age and TGA titer in ponies. One of the 40 ponies (2.5%) showed an elevated TGA titer. An elevated TGA titer decreased after a gluten-free ration for 3 months in an 11-year-old Warmblood gelding with a tentative diagnosis of ISBD associated with full remission of the generalized skin reaction. To our best knowledge, this is the first study assessing TGA antibodies in sera from healthy non–gluten-free ponies and showing a correlation with age. The presented case could be the first one of a horse with a tentative diagnosis of gluten-sensitive enteropathy combined with dermatitis. Given the reported findings, this study warrants further investigations into gluten-sensitive enteropathy and dermatitis in individual horses affected with ISBD.     

谷氨酰胺转氨酶对不同脂肪含量Cheddar干酪品质的影响

本研究在添加凝乳酶的同时,添加谷氨酰胺转氨酶（TG）（1．0U／g蛋白）,测定不同脂肪含量Cheddar干酪的得率和组分回收率,并监测成熟90d中干酪理化、功能指标的变化以及蛋白水解情况,分析TG对不同脂肪含量Cheddar干酪品质的改善作用．．结果表明,添加TG的全脂干酪的得率、蛋白和脂肪回收率与对照组相比差别不大,添加TG的减脂干酪的得率、蛋白和脂肪回收率比对照组分别增加2．1％、1．9％和13G,（P〈0．05）,添加TG的低脂干酪的得率、蛋白和脂肪回收率比对照组分别增加2．2％、7％和12％（P〈0,05）、干酪成熟前期（1～15d）,添加TG酶的减脂、低脂干酪的硬度显著低于对照组（P〈0．05）,而全脂干酪变化不明显？随着成熟期的延长,TG酶对酪蛋白的交联作用抑制了蛋白的水解,导致干酪硬度增大。     

Facilitation of α-polylysine in TGase-mediated crosslinking modification for gluten and its effect on properties of gluten films

In this study, α-polylysine was used to enhance the cross-linking effect of TGase on gluten and its effects on properties of gluten films were investigated. The amount of free ammonia released from the cross-linking reaction of gluten induced by TGase at the presence of α-polylysine obviously increased, and more polymers with higher molecular weight were formed from the SDS-PAGE results, which indicated that the TGase-mediated cross-linking reaction ability of gluten was strengthened with the incorporation of α-polylysine. The tensile strength of the films from gluten modified with TGase (20 units/g wheat gluten) and 2% α-polylysine (g/g gluten) for 3 h increased from 4.02 ± 0.09 MPa to 5.28 ± 0.14 MPa, which was more effective than that treated with TGase alone (in which the tensile strength of the films was 4.49 ± 0.10 MPa). The TGase treatment with α-polylysine of gluten improved the water stability of the films much more than that treated with TGase alone. A rougher surface and a more compact cross-section structure were observed by SEM for the films from TGase-α-polylysine treated gluten. The contact angles between the gluten films surface and a water droplet increased because of TGase-mediated cross-linking modification.     

Role of enzymes in improving the functionality of proteins in non-wheat dough systems

Gluten free systems lack the viscoelastic network required to resist gas production and expansion during baking. Enzymatic treatments of the GF flours have been proposed initially for creating protein aggregates that mimic gluten functionality but then also for modifying proteins changing their functionality in GF systems. To better exploit the technological function and the potentials of enzymatic processing for improving GF bread quality, it is important to understand the key elements that define the microstructure and baking functionality of GF batters as compared to wheat dough. In this review, some keys are pointed out to explain the different mechanisms that are available for understanding the action of enzymes to effectively design GF viscoelastic matrixes. Focus will be on protein modifying enzymes, because they play a decisive role in the formation of the fine network responsible for improving the expansion of rice batters.     

谷氨酰胺转胺酶和大豆粉在荞麦面包加工中的应用

以添加谷氨酰胺转胺酶及脱脂大豆粉来改善面团的加工品质和荞麦面包的食用品质为目的,利用单因素试验和正交试验,研究了荞麦粉与小麦粉的比例、谷氨酰胺转胺酶用量、大豆粉用量、酵母粉用量、加水量等因素对产品品质的影响规律,并对各因素的水平进行了优化。通过谷氨酰胺转胺酶和大豆粉的共同作用,荞麦面团和荞麦面包的品质得到了显著提高。在1 kg混合粉(其中荞麦粉300 g,小麦粉690 g,大豆粉10 g)中加入0.5 g谷氨酰胺转胺酶、25 g酵母粉1、5 g食盐6、0 g糖、650 mL水。结果表明,在所选最优条件下,采用国标面包生产工艺就可以生产出高质量、高荞麦粉含量(300 g/kg)的荞麦大豆营养强化面包。     

Rheological properties and baking performance of rye dough as affected by transglutaminase

Since protein aggregation and formation of a continuous protein matrix in rye dough is very limited, an enzyme-induced protein aggregation method to improve the baking properties was investigated. The effects of microbial transglutaminase (TG) on the properties of rye dough were studied by rheological tests, confocal laser scanning microscopy (CSLM), standard-scale baking tests and crumb texture profile analysis. Addition of TG in the range of 0-4000 Ukg⁻¹ rye flour modified the rheological properties of rye flour dough, resulting in a progressive increase of the complex shear modulus (|G∗|) and in a decrease of the loss factor (tan δ) due to protein cross-linking or aggregation. CLSM image analysis illustrated a TG-induced increase of the size of rye protein complexes. Standard baking tests showed positive effects on loaf volume and crumb texture of rye bread with TG applied up to 500 Ukg⁻¹ rye flour. Higher levels of TG (500 U ≤ TG ≤ 4000 U) had detrimental effects on loaf volume. Increasing TG concentration resulted in an increase of crumb springiness and hardness. In conclusion, the results of this work demonstrated that TG can be used to improve the bread making performance of rye dough by creating a continuous protein network.     

Shelf-Life Extension of Fish Fillets by Spraying with Microbial Transglutaminase

The effect of spraying microbial transglutaminase (MTGase) at various levels (1, 4, 7, and 10 units/gram) on the quality of mackerel (Scomber scombrus) fillets was investigated during refrigerated storage. The results of pH and the total volatile base nitrogen (TVB-N) revealed that 7 µ/g MTGase treatment met the best results regarding fish quality. The oxidation was hindered by increasing MTGase concentration, and the lowest totox value was recorded in the fillets treated with 10 µ MTGase. The progress in the total free amino acids was suppressed with the addition of MTGase, and the most effective concentration was found to be 7 µ/g MTGase treatment. Moreover, this concentration was the most promising in inhibition of the total mesophilic aerobic bacteria, the total psychrophilic aerobic bacteria, coliform, and yeast-mold. Panelists preferred the samples treated with 7 µ/g MTGase in terms of odor, texture, and appearance. The addition of MTGase straightened the fish muscle and helped preserve its initial texture. It is important to use the proper concentration of MTGase instead of high concentrations.     

剪切力对链霉菌谷氨酰胺转胺酶发酵的影响

考察了以摇瓶发酵过程中添加玻珠为剪切力,对链霉菌(Streptomyces sp.)HS-1发酵生产谷氨酰胺转胺酶的影响,在10 L发酵罐上不同搅拌转速对产酶的影响。结果显示,摇瓶发酵中,在种子阶段添加玻珠,提高剪切力不能促进产酶;在发酵阶段,加入4颗玻珠时,酶活相对最高,比对照增加20%;36 h时添加玻珠,与对照相比,酶活提高12%,菌体浓度增加40%,且氨基氮消耗明显。10 L发酵罐中,适宜的搅拌转速为250 r/min,36 h调整转速至250r/min,酶活比维持90 r/min提高21%。因此剪切力对谷氨酰胺转胺酶发酵有明显影响。     

茂原链霉菌DSM 40847全基因组测序及序列分析

茂原链霉菌（Streptomyces mobaraensis）是一种高GC含量的革兰氏阳性放线菌,它广泛用于生产转谷氨酰胺酶、博来霉素、莫能霉素等。目前,还没有相关研究报道茂原链霉菌的全基因组序列,这限制了基于功能基因挖掘和利用的定向育种以及分子遗传研究。本研究首次通过高通量测序技术对茂原链霉菌DSM40847进行全基因组测序,使用Velvet软件进行拼接得到266 contigs,整个基因组大小约7.5 Mb,GC含量为73.2%,序列已提交至美国国立生物技术信息中心（NCBI）的GenBank数据库。通过对基因组序列进行分析,成功鉴定转谷氨酰胺酶酶原激活相关蛋白基因,同时对该菌株的次级代谢产物合成基因簇进行了预测,相关研究结果将为茂原链霉菌的功能基因组学研究提供基础数据。