新型酶制剂对面包品质的改良研究

面包是一种经过发酵的烘焙食品。烤制的新鲜面包松软可口、品味宜人,深受大多数消费者的喜爱。然而,随着贮存时间的延长,面包的上述特征发生变化,即老化发生。如何改善或解决面包老化问题是众多食品行业从业者及研究人员关注的焦点。通过选用不同酶制剂,以面包的比容和有效贮藏期内其硬度的变化比较,获得不同酶制剂对面包品质的影响,最后通过正交试验,确定对面包品质改良有显著作用的复配酶制剂用量、组合及配比。     

The Effect of Non‐Gluten Proteins on the Staling of Bread

As part of our studies on the mechanisms of bread staling, starch bread was used as a research tool that enables us to gain insights into the individual contributions that starch and gluten have on staling. Reconstitution experiments have demonstrated that bread of equivalent specific loaf volume stales at the same rate irrespective of protein concentration, or type of protein. However, other properties of bread, such as specific loaf volume, may be altered by specifically changing the protein component in the flour.     

The glutenin fraction of wheat protein: The importance of genetic background on its quantity and quality

The influence of high-molecular-weight glutenin subunits on the properties of the gel-protein fraction of glutenin proteins in wheat was determined on 20 varieties grown in the 1989 UK Recommended List trials. Both the presence of subunit 1 (chromosome 1A) and the 1B/1R rye translocation were shown to influence gel-protein weight and breakdown rate during mixing. The gel-protein tests were correlated with CBP (Chorleywood Bread Process) loaf volume, but they did not add anything to the correlation between Glu-1 score and loaf volume. Both gel-protein tests indicated that phenotypic variation could be almost as large as genotypic variation. Breakdown rate was able to detect the abnormal properties of Pastiche (weak) and Fresco (extra-strong) that were not observed using established quality tests such as the sodium dodecylsulphate sedimentation volume.     

The susceptibility to mould growth of white bread produced by different processes

Summary. Bread produced by the Chorleywood Bread Process (CBP), which is a mechanical development process, had a mean mould-free shelf life which was 14.5-19 hr shorter than that of bread made by a 3-hr bulk fermentation process, following natural inoculation by controlled exposure to a low mould-spore concentration in the air. Assessing mould susceptibility by comparing the time taken for half the exposed surfaces to show some mould growth, four-fifths or more of the deficiency in mould resistance of the GBP bread compared with the bulk-fermented could be made good by adding at the dough-mixing stage a fermented-out brew which had been started with one part of sugar for every twenty-eight parts of flour to be used in the dough.
Correlation of mould resistance with the strengths of fermented-out sugar brews indicated that the favourable effect was due to a fermentation product. Ethanol was found to be the substance responsible, products present in trace amounts evidently not playing any important part in the observed differences in rate of mould growth on CBP bread with and without added brews. the ethanol content of the bread accounted for most but not all of the mould resistance of bulk-fermented bread compared with CBP bread. Equilibrium relative humidity, pH, and propionic acid and moisture contents did not vary enough from one kind of bread to another to affect relative mould-free shelf life appreciably. Evidently, therefore, an unidentified mould inhibitor is present in the bulk-fermented bread.
The commercial significance of the findings is discussed.     

Influence of Tomato Seed Addition on the Quality of Wheat Flour Breads

Tomato seed, an abundant tomato processing waste product, contains high amounts of crude fat and protein. The protein is especially high in lysine, the limiting amino acid of cereal products. Dried, ground tomato seeds were added at 5, 10, 15, and 20% wheat flour replacement levels. The influence of tomato seed addition on amino acid content, loaf volume, and staling rate were studied. A sensory evaluation based on odor only was conducted to identify consumer attitudes towards “tomato seed bread.” The addition of tomato seed at a replacement level of 20% to a bread formula with shortening resulted in no significant change (P < 0.05) in staling rate, but showed an increase in specific loaf volume of 20.4%. No significant differences in specific loaf volume were found between bread with 3% shortening and the 10% tomato seed supplemental bread without shortening. Addition of fat extracted tomato seeds at the 20% level decreased specific loaf volume by 72%. The supplementation of wheat flour bread at the 10% and 20% replacement levels increased lysine by 40.2% and 69.0% respectively.     

Physical properties and water state changes during storage in soy bread with and without almond

Soy bread was formulated to impart different isoflavone profiles by addition of almond: a natural source of β-glucosidase. In this study, the influence of almond powder on loaf quality and storage stability of soy bread was investigated using thermal analysis, texture, loaf volume and air cell imaging techniques. Lipids introduced with the almond fraction, served as mediators to strengthen the interaction between wheat and soy protein, thereby increasing dough extensibility. Loaf quality of the almond soy bread was therefore improved since the collapse of air cells during bread preparation was prevented. This in turn favored better loaf quality. Additionally, water binding strength and changes thereof during storage, probed by thermal analysis, were found to significantly hinder the staling rate during prolonged storage of soy-containing breads.     

Structural changes in the wheat dough and bread with the addition of alpha-amylases

The influence of fungal and bacterial -amylases on the texture and microstructure of dough and bread was investigated. Loaf specific volume, crumb porosity and texture properties were accepted as bread structure and texture characteristics. The microstructure analysis of dough and bread using light and scanning microscopy methods was performed.The changes in loaf specific volume, crumb porosity and texture properties showed different anti-staling activity of the enzymes used. The simultaneous action of enzyme addition and the fermentation process evoked significant changes in the microstructure of dough. The character of these changes depended on the kind of enzyme used. A substantial effect of both amylases on starch behaviour during bread baking and staling was also observed.     

A Rheological Study of Mechanical Dough Development and Long Fermentation Processes for Cream-Cracker Dough Production

In the manufacture of products such as bread and cream-crackers mechanical development and long fermentation processes are used to develop dough. A rheological study of cream-cracker doughs made using both types of process has shown that fermentation weakens, but does not rearrange, intermolecular interactions. The rearrangement of storage proteins into a continuous network of gluten is achieved by the shearing action of mixing, which need only be gentle after a sufficient period of fermentation, but must be intense if prior fermentation is omitted, as in mechanical dough development. In the long fermentation process a dough with the desired characteristics was produced following a minimum of 4 h fermentation time. Dough with similar rheology was produced by mechanical development when additional water was used in the recipe. For mechanically developed cream-cracker doughs there was also an increase in the elasticity of the developed gluten. When the Chorleywood Bread Process was invented it was found that more water and less protein were required to achieve the same dough rheology as in long fermentation processes. It seems that the same relationship between mechanical dough development and long fermentation may apply to other products, such as cream-crackers. These results confirm that the technological experience gained by switching from long fermentation to mechanical dough development processes for bread production could be applied to other products such as cream-crackers. © 1997 SCI     

Staling in Starch Bread: the Effect of Gluten Additions on Specific Loaf Volume and Firming Rate

Hypotheses on the role of gluten in bread staling range from gluten having an anti-firming effect, or no effect on firming, to gluten-starch interactions being essential for bread firming. To test these hypotheses, the firming rate of starch bread made from protein-free synthetic flour was compared with that of starch-gluten breads made from synthetic flours containing 1–15% gluten (Fig. 1). Only loaves of similar specific loaf volume and crumb moisture content were compared to eliminate these parameters as variables that might influence firming rate. The starch breads clearly increased in firmness up to six days, indicating that gluten was not essential to the firming process, starch alone causing bread to firm with time. The starch-10% gluten breads and starch-15% gluten breads had very similar specific loaf volumes, moisture contents and firming rates to that of the starch breads. This indicates that protein possibly has some role in firming, because if only starch has a role in firming then adding gluten would effectively dilute the starch and reduce the rate of firming. We propose that increasing bread firmness results from glucan chains of partially leached amylose and amylo-pectin attached to swollen starch granules forming hydrogen bonds with other starch granules and, to a smaller extent, with gluten fibrils.     

The composition,rheological properties and breadmaking behaviour of stored flours

Flours milled from English (‘weak’), Canadian (‘strong’) and mixed English and Canadian wheats (‘medium’) had different rates of lipolysis (weak>medium>strong) during prolonged storage at ambient temperatures (average about 12°C). Lipolysis was more rapid in the medium flour at 25°C, but was very slow in ‘control’ flours kept at - 20°C in an inert atmosphere. Loss of baking quality in stored flours was assessed using the Chorleywood Bread Process (CBP), a long fermentation process (LFP) and the Activated Dough Development process (ADD). The loaf volume changes varied with the flour type and test method, especially depending on whether or not fat was included in the recipes. In tests with fat, the CBP was the most sensitive to deteriorative changes (strong?medium>weak); with the medium and strong flours, loaf volumes were nearly constant for 24 months before decreasing rapidly. Deterioration became apparent more gradually when using LFP and ADD tests with fat. When fat was omitted, short-term improvement (weak>medium>strong) occurred with all three baking methods, but there was subsequent loss of volume. To account for these changes in baking behaviour, it is suggested that the tests differ in their sensitivity to flour type and variations in dough composition, especially to the level of bakery fat, the level of fatty acids (generally deleterious), and to protein changes which were also detectable by rheological tests on stored flour doughs (flour ‘maturation’; generally beneficial).     

INFLUENCES OF THE PROPORTION OF SOLID FAT IN A SHORTENING ON LOAF VOLUME AND STALING OF BREAD

Fats and oils are an important component of bread. Fats and oils are added to improve the properties of a loaf of bread, such as increasing loaf volume and increasing the time before staling is initiated. The physical form of the added fat can affect the overall dough behavior. The effect of hydrogenated soybean oil concentration in an emulsion used for the baking of bread was studied. It was observed that increasing concentration of hydrogenated soybean oil (solid fat) while keeping total lipid content constant led to increased loaf volume and decreased loaf weight. Also, increasing solid fat content led to a reduction in the rate of staling.     

Effect of HPMC addition on the microstructure, quality and aging of wheat bread

The effect of hydroxypropylmethylcellulose (HPMC) addition on a basic bread formulation is described. The effect of HPMC as bread improver and antistaling agent was analysed in terms of microstructure. Bread quality was assessed by physical parameters (volume, width/height ratio, moisture content and hardness), crumb grain structure (number of air cells, cells area and the ratio between cells area and total area) and sensory evaluation (appearance, aroma, taste and texture). Bread staling was determined by following both the hardness increase and the starch retrogradation during storage. The microstructure was analyzed by cryo scanning electron microscopy (cryo-SEM). The results confirm the ability of the HPMC for improving fresh bread quality and for delaying staling. The presence of HPMC decreased the hardening rate of the bread crumb and also retarded the amylopectin retrogradation. The microstructure analysis revealed the possible interaction between the HPMC and the bread constituents, which could partially explain the antistaling effect of this hydrocolloid.     

Studies on electrical properties of wheat bread as a function of moisture content during storage

Bread undergoes several physicochemical changes during storage that results in a rapid loss of freshness. These changes depend on the moisture content present in the bread product and collectively termed as staling. The present work explains how the electrical properties of bread vary with time and moisture content at its crust and crumb. An instrument based on electrical impedance spectroscopy with multichannel electrodes is developed for the present investigations. Detailed studies have been carried out to understand the influence of changes in moisture profile at bread crust and crumb in terms of electrical properties during the storage of 120 h. A linear relationship is observed between the measured impedance and capacitance and residual moisture content in bread at crust during storage. It is observed that the measured Resistance at bread crumb has a nonlinear mathematical relationship with moisture content present at crumb.     

Effect of Starch Substitution by Buckwheat Flour on Gluten-Free Bread Quality

The buckwheat flour was studied as a potential healthy ingredient for improving the nutritional and technological quality of gluten-free bread. The effect of exchange of gluten-free formulation mass by buckwheat flour in 10, 20, 30 and 40 % was investigated. The increase in loaf specific volume with rising buckwheat flour addition was observed. Compared with the control sample, decrease in whiteness and increase in redness and yellowness of crumb were noticed. The rising amount of buckwheat flour in gluten-free bread formulation caused a decrease in crumb hardness during storage. This was in agreement with the decrease in starch gelatinisation enthalpy with the increasing amount of buckwheat flour in gluten-free formula in comparison with the control sample. Buckwheat flour could be incorporated into gluten-free formula and have a positive influence on bread texture and delaying its staling.     

Potato flour as a functional ingredient in bread: evaluation of bread quality and starch characteristics

Potatoes have been added to bread for improvement of texture and moisture retention. The functional quality and starch digestibility in bread containing 5%, 10% or 15% potato flour were evaluated. Farinograph absorption of wheat and potato flour blends ranged from 59.0% to 77.7%. Bread with potato flour had significantly (P < 0.05) lower bread firmness during storage. There was a significant (P < 0.05) decrease in starch molecular weight as the level of potato flour increased. Inclusion of potato flour in these breads significantly (P < 0.05) increased the level of resistant starch (RS), while significantly (P < 0.05) decreasing the estimated glycemic index (eGI). Bread with no potato flour had 5.2% RS and an eGI of 95, while the bread with 15% potato flour had 11.3% RS and an eGI of 87. Overall, the addition of potato flour may reduce dough strength and loaf volume, but it reduced staling and increased resistant starch content of the bread.     

Use of response surface methodology to investigate the effects of processing conditions on sourdough wheat bread quality

Response surface methodology was used to investigate the influence of three factors, sourdough fermentation time, proof time and amount of yeast addition on the quality of sourdough wheat bread. Each predictor variable was tested at five levels. Sourdough fermentation times were 5, 11, 20, 29 and 35 h, yeast addition rates were 0.05, 0.75, 1.77, 2.80 and 3.50% (flour weight basis) and proof times were 16, 40, 75, 110 and 134 min. The performance of two different starter culture types, a mixed strain starter culture called Böcker Reinzucht–Sauerteig Weizen and a single strain starter culture of Lactobacillus brevis, was compared by separately completing the experimental design for each. Independently non-acidified control bread was prepared. A range of loaf quality parameters was determined including pH, total titratable acidity, loaf height, specific volume, crumb mean cell area and crumb hardness. Overall breads with better specific volume values were achieved with the use of sourdough relative to the control. Results indicated that maximum loaf specific volume was achieved when L. brevis sourdough was used particularly when it was used in conjunction with a high rate of yeast. Given a lower rate of yeast addition however, the mixed strain starter culture yielded better bread.     

Studies on glass transition and starch re-crystallization in wheat bread during staling using electrical impedance spectroscopy

Bread staling is a very complex phenomenon that is not yet completely understood. The present work explains how the electrical impedance spectroscopy technique can be utilized to investigate the effect of staling on the physicochemical properties of wheat bread during storage. An instrument based on electrical impedance spectroscopy technique is developed to study the electrical properties of wheat bread both at its crumb and crust with the help of designed multi-channel ring electrodes. Electrical impedance behavior, mainly capacitance and resistance, of wheat bread at crust and crumb during storage (up to 120 h) is investigated. The variation in capacitance showed the glass transition phenomenon at room temperature in bread crust after 96 h of storage with 18% of moisture in it. The resistance changes at bread crumb showed the starch recrystallization during staling.Industrial relevanceSimultaneous measurement of moisture content, glass transition and starch recrystallization is possible with the designed instrument without disturbing the experimental set-up. Thus, the present work is going to help manufacturers and researchers to understand the bread staling phenomenon at crust and crumb without opting very complex instrumental procedures.     

添加猪油对馒头品质的改善

研究了猪油对酵母发酵性能,馒头品质及馒头老化的影响。实验结果表明,猪油能增加面团的膨发体积,改善馒头体积,色泽和组织结构,并在延缓馒头化方面起到了一定作用。     

嗜热真菌耐热木聚糖酶对面包品质的改善

研究了纯化的耐热木聚糖酶对面包品质及老化的影响，探讨了耐热木聚糖酶影响面包发酵及烘烤过程的作用机理。适量添加木聚糖酶的面包体积显著增加且面包芯的组织结构优良，同时老化变缓：本试验条件下，添加纯酶1．5mg／kg为最适酶添加量，体积增加43％，硬度减小44％，老化速度放缓近一半。     

A Comparative Study of Commercial Modified Celluloses as Bread Making Additives

The effect of commercial modified celluloses: microcrystalline cellulose, carboxymethyl cellulose, and hydroxypropylmethyl cellulose on bread quality attributes and their potential protective effect with respect to bread staling were analyzed. Two levels of gums were assayed (0.5 and 1.5 g/100 g flour). The best performance was obtained with carboxymethyl cellulose and hydroxypropylmethyl cellulose F 4 M at both levels; these gums led to higher specific volumes and a better crumb texture as measured by texture profile analysis. In general, crumbs were softer, more cohesive, and resilient and exhibited lower chewiness values. Other gums like microcrystalline cellulose and hydroxypropylmethyl cellulose F50 did not improve bread quality on the same extent. Mechanical spectra obtained by dynamic mechanical analysis assays indicated a marked change in molecular mobility when carboxymethyl cellulose was present. Bread staling was evaluated by texture profile analysis, moisture loss, and calorimetric assays. Gums did not avoid retrogradation and even exhibited an accelerating effect, probably due to changes in water retention and migration during storage. However, in most cases, final crumb hardness in samples with hydrocolloids was lower than that in the control sample.