Firming of starch gels and amylopectin retrogradation as related to dextrin production by α-amylase

 The effect of dextrins produced by α-amylase on the firming and amylopectin retrogradation of wheat starch gels was studied. Different gel samples were prepared and included several ingredients, for example, α-amylase, vital gluten and glucoamylase. Amylopectin retrogradation, gel firming and the dextrin profile were analysed throughout a 5-day storage period. Both processes, i.e. firming and starch retrogradation, increased with time, and were not affected by the incorporation of gluten into the mixture. The well-known effect of α-amylase to retard bread crumb firming was also found to be relevant to starch gels. From the results obtained in this work, it seems that this anti-firming effect is not due to modifications of the starch but to dextrins produced by starch hydrolysis, since the effect did not occur when dextrins were removed by glucoamylase. Received: 30 December 1996     

Thermal properties of doughs formulated with enzymes and starters

 Thermal properties (gelatinization, amylose-lipid complex dissociation and amylopectin retrogradation) of bread samples formulated with two different quality wheat flours, two enzymes (α-amylase/pentosanase, lipase and their mixture), and three microbial sourdough starters were studied with a differential scanning calorimeter. The carbohydrases modified gelatinization temperature and enthalpy, whilst the lipase modified the amylose-lipid complex dissociation. The enthalpy of amylopectin retrogradation was significantly influenced only by the storage of breads. Second-order interactive effects of enzymes with flour or starter were found for gelatinization and/or amylose-lipid complex dissociation parameters. Some interesting relationships were observed between thermal and textural properties of fresh and stored breads. Received: 22 September 1998 / Revised version: 28 October 1998     

Bread quality of frozen dough substituted with modified tapioca starches

Rheological properties of dough and bread quality of frozen dough-bread containing 18.4% of hydroxypropylated (HTS), acetylated (ATS), and phosphorylated cross-linked (PTS) tapioca starch with different degrees of modification and 1.6% of dried powdered gluten were compared to the same amount of native tapioca starch (NTS) or wheat flour-bread. Doughs substituted with native or modified tapioca starches had the same mixing tolerance as 100% wheat flour. The dough was frozen and stored for 1 week at −18°C, and thawed (one freeze-cycle). The amount of freezable water in the dough substituted with native or modified tapioca starches was not significantly different from that of wheat flour. Frozen dough-bread substituted with highly modified HTS (degree of substitution; DS 0.09–0.11) retarded bread staling, while lowly modified HTS (DS 0.06–0.07) or ATS (DS 0.02–0.04), and PTS (0.004–0.020% phosphoryl content) substitution fastened bread staling as compared with frozen dough-bread baked from wheat flour. The breadcrumbs containing HTS and ATS felt tacky, whereas the bread containing PTS was dry feel. HTS and ATS swelled and collapsed easily during heating, while PTS was difficult to swell and disperse as compared with NTS, therefore the gelatinization properties seemed to affect the texture of bread. Breadcrumb containing HTS showed small firmness during storage, and highly modified HTS-h (DS 0.1) was the smallest. This means highly hydroxypropylated tapioca starch significantly retards bread staling. Staling properties and texture of frozen dough-bread with various tapioca starches were the same as conventional bread baked with the same amount of tapioca starches. These results suggest that a one freeze–thaw cycle and a 1-week frozen period do not change characteristics of starch, gelatinization and retrogradation properties as compared with the conventional method, and the highly modified HTS-h is prominent anti-staling food-stuff in frozen dough.     

Effect of different carbohydrases on fresh bread texture and bread staling

The effect of cellulase, xylanase and #-glucanase on the properties of wheat bread and its staling during storage was studied. The presence of the carbohydrases tested led to breads with high specific volume compared to the control. The texture profile analysis was greatly modified in that the firmness of bread crumb was reduced by all the carbohydrases. A kinetic study of the firmness along with the storage by the Avrami equation showed that the presence of carbohydrases produced softer crumbs and also reduced the rate of bread firming, although no great differences were found between enzymes. Since retrogradation of starch is one of most important factors related to bread staling, the modification of the amylopectin retrogradation was measured by scanning calorimetry. Those studies showed that all the carbohydrases decrease the starch retrogradation, and that the xylanases had the greatest effect. The simultaneous analysis of the firming and starch retrogradation results revealed that the anti-staling effect of xylanase might be due to the retardation in the starch retrogradation, while in the case of cellulase and #-glucanase some other mechanism should be implied in their anti-staling action.     

The use of normal and heat-treated barley flour and waxy barley starch as anti-staling agents in laboratory and industrial baking processes

Normal and heat-treated barley, both as flour and waxy starch, were added at a concentration of 3% to a white wheat bread. The effect not only of selected additives, but also of laboratory- and industrial baking processes on stalling was evaluated. Laboratory baked breads with heat-treated barley flour differed from control breads with regard to water content, firmness and amylopectin retrogradation. The influence of water content on firmness increased with storage time. All laboratory baked breads with barley additives, except normal barley flour, were less firm after 7 days of storage as compared to the control although amylopectin retrogradation tended to increase. Improved water absorption, and consequently, increased water content and/or different water binding capacities of the flour/starch could explain these results. Industrial baking caused higher water losses, especially in breads containing additives, thus reducing the effects on amylopectin retrogradation and firmness.     

Impact of the addition of resistant starch from modified pea starch on dough and bread performance

The interest in the use of resistant starch (RS) for the development of new bakery products has significantly increased due to its ascribed physiological effects with proven health benefits. The objective of the present work was to analyse the effects of the wheat flour substitution by modified pea starch with high level of RS (PeaP) on breadmaking performance. The effects of PeaP on wheat dough functionality were evaluated by mixing/overmixing properties, texture profile analysis, viscometric profile and thermal properties. Bread quality was evaluated by physico-chemical parameters, crumb texture profile, digital image analysis, nutritional parameters and sensory evaluation. Flour substitution by PeaP up to 20% allowed keeping mechanical, extensional and viscometric parameters without significant hindering of dough machinability. Overdose of modified pea starch (30%) negatively affects dough mixing and overmixing behaviour. As a functional/prebiotic fibre, PeaP addition up to 10–20% of flour replacement entitles the formulation of wheat bread allowing a significant increase in the RS level (from 0.70 to 5.10%), delay/decrease in amylopectin retrogradation, with acceptable changes in bread quality up to 10–20% of flour replacement.     

The anti-staling effect of pre-gelatinized flour and emulsifier in gluten-free bread

The use of gluten-free products is increasing since an increasing number of people (1–2 %) are suffering from Celiac disease and thereby need a gluten-free diet. Gluten-free bread tends to have shorter shelf life and quality compared with white wheat bread. In this study, 3 % (flour basis) of pre-gelatinized oat and barley flour as well as an emulsifier were added to a gluten-free mix to increase the water content by 1.5–2 %, affect the starch retrogradation and the formation of amylose lipid complex. The staling was followed measuring the firmness (texture analyzer), water content and distribution (nuclear magnetic resonance), amylopectin retrogradation and the formation of amylose–lipid complex (differential scanning calorimetry) in order to see the impact of both macroscopic and molecular changes on firmness. Both gluten-free bread and a white wheat bread were used as control loaves. Largest specific volume was found in the gluten-free control. The firmness varied with both the specific volume and the point of measurement. The amount of retrograded amylopectin increased the firmness, although this effect was dependent on the type of bread, in terms of distribution and availability of the water within the system. The proton relaxation time, which was representing movable water, decreased during storage and revealed that both the amylopectin retrogradation and the lipid complex formation were affecting the rigidity of the amorphous domain and not only the crystalline regions. In contrast to the other recipes, the use of emulsifier caused limited retrogradation and a low correlation between the texture properties and time-dependent events.     

Staling in Starch Breads: The Effect of Antistaling α-Amylase

A novel starch bread that contained no gluten was found to firm at a rate comparable to a normal standard bread made from wheat flour. Treatment of both the starch and the standard bread with Novamyl, an antistaling enzyme mix, inhibited firming. ¹³C CP/MAS NMR studies showed that the decreased firming of the Novamyl-treated starch bread was correlated with decreased starch retrogradation. For the Novamyl-treated bread the increase in retrograded starch over six days following baking was about 11% compared to an increase of over 200% for the untreated bread. These results suggests that starch retrogradation is sufficient to cause bread firming.     

The staling of bread: an X-ray diffraction study

Bread crumb X-ray patterns were analysed by different methods, the objective being to provide more in-depth knowledge of the relationships among starch crystallinity, amylopectin retrogradation and bread firming. Both crumb-firming and amylopectin retrogradation increased with storage time. However, total mass crystallinity grade and relative crystallinity increased only in the first 24 h. The determination of starch crystallinity requires the separation of the crystalline and amorphous intensities, which is sometimes arbitrary, so it would be useful to improve this methodology. Different methods used to determine total crystallinity grade only show the differences existing between fresh and stored bread. B-type crystal structure—corresponding to the amylopectin retrogradation—increased during bread storage, showing a high correlation with bread-firming and storage time. This fact emphasized the above results and suggested that amylopectin retrogradation is an important component to the elucidation of bread staling.     

Phospholipid Hydrolysate and Antistaling Amylase Effects on Retrogradation of Starch in Bread

Effects of phospholipid hydrolysate and antistaling amylase on starch retrogradation in bread and wheat flour were investigated by differential scanning calorimetry (DSC). Phospholipid hydrolysate containing more than 90% lysophospholipid was obtained using phospholipase A₂ and was effective in forming amylose-lipid complexes. Both wheat flour and bread containing phospholipid hydrolysate were retrograded to a lesser degree when stored at room temperature. The retrogradation rate for bread with antistaling amylase was low. We postulated that antistaling amylase broke links in amylose and amylopectin, thereby promoting the formation of amylopectin-lipid complexes. The combined effect of phospholipid hydrolysate and antistaling amylase was greater than their individual effects.     

Starch affecting anti-staling agents and their function in freestanding and pan-baked bread

Anti-staling agents with different mechanisms were added to a normal white wheat bread to investigate the relation between bread staling, amylopectin retrogradation and water-related properties (i.e. water content and distribution between crumb and crust). Bread was baked both as pan-baked and freestanding loaves. The anti-staling agents maltogenic α-amylase, distilled monoglyceride and lipase had a direct influence on starch retrogradation, whereas gluten and waxy wheat flour diluted the amylopectin content or changed the ratio between amylose and amylopectin. The degree of staling was measured as the firmness and springiness, together with two new methods, crumbliness and cutability. In addition, the degrees of amylopectin retrogradation and amylose–lipid complex formation were analyzed by differential scanning calorimetry, and the water content, water loss and water migration were measured. The addition of α-amylase improved most staling parameters, although the changes were not as large as expected. Furthermore, monoglyceride and lipase increased the formation of amylose–lipid complexes, but only lipase gave better results regarding the specific volume and firmness. Increased amylose–lipid complex formation was seen to increase water migration from crumb to crust. Adding 10% waxy wheat flour appeared to lead to a slight overall improvement i.e. lower water migration and better cutability. Adding gluten or 3% waxy wheat flour only improved the specific volume. The method of baking the loaves, i.e. freestanding or pan-baked, had a greater influence than the anti-staling agents, which shows that bread quality is not always improved by starch affecting anti-staling agents without process changes.     

Relative importance of moisture migration and amylopectin retrogradation for pound cake crumb firming

Moisture migration largely impacts cake crumb firmness during storage at ambient temperature. To study the importance of phenomena other than crumb to crust moisture migration and to exclude moisture and temperature gradients during baking, crustless cakes were baked using an electrical resistance oven (ERO). Cake crumb firming was evaluated by texture analysis. First, ERO cakes with properties similar to those baked conventionally were produced. Cake batter moisture content (MC) was adjusted to ensure complete starch gelatinisation in the baking process. In cakes baked conventionally, most of the increase in crumb firmness during storage was caused by moisture migration. Proton nuclear magnetic resonance (¹H NMR) showed that the population containing protons of crystalline starch grew during cake storage. These and differential scanning calorimetry (DSC) data pointed to only limited amylopectin retrogradation. The limited increase in amylopectin retrogradation during cake storage cannot solely account for the significant firming of ERO cakes and, hence, other phenomena are involved in cake firming.     

馒头硬化机理探讨

详细分析了馒头在贮存过程中硬度和支链淀粉结晶的变化规律,研究表明,馒头中支链淀粉结晶、小麦蛋白质与淀粉分子之间的交互作用是影响馒头硬化的主要因子。具体讲,馒头中支链淀粉结晶速率加快或小麦蛋白质和淀粉之间的交互作用加强,会加速馒头的硬化,而改善馒头的比容可以延缓馒头的硬化。     

The bread baking quality of six wheat starches differing in composition and physical properties

Starch was isolated from six types of wheat and separated into large A-granule and small B-granule fractions which exhibited a suitable range of properties. Respective amylose contents were 28.6–31.0% and 25.1–31.5%, lysophospholipids 707–1014mg 100 g^?1, and 1058–1398 mg 100 g^?1, and gelatinisation temperatures (GT) by differential scanning calorimetry (DSC) 58.4–62.7°C and 60.5–64.5°C. The A- and B-granule fractions were remixed in various proportions and reconstituted with freeze-dried gluten and freeze-dried water-solubles from flour to test the effects of changes in the properties of the total starch, A-granule or B-granule fractions, and the effects of various proportions of B-granules on the quality of bread. The specific volumes of the loaves were not affected by starch amylose or lipid content, but were significantly correlated with either the GT of the total starches or their A-granules. The optimum proportion of B-granules was 25–35% by weight, but their GT had no effect on loaf specific volume. Staling changes were quantified from crumb compressibility measurements and the enthalpy of the endotherm for gelatinisation of retrograded amylopectin in stored breadcrumb, measured by DSC. Initial and limiting moduli of crumb firmness were correlated with loaf specific volume and starch GT, but rate and time constants calculated from the Avrami equation were independent. Rate and time constants and limiting enthalpy values calculated from the DSC results were independent of all other measured parameters.     

Influence of damaged starch on cookie and bread-making quality

In this study two wheat and one triticale cultivars were milled in a disc mill to obtain different levels of damaged starch. The effects of the damaged starch content on physicochemical flour tests and cookie and bread-making quality were analyzed. The grain milling conditions in disc mill and grain hardness influenced the amount of damaged starch. The solvent absorption of flours, as measured by Solvent Retention Capacity Profile (SRC) and Alkaline Water Retention Capacity (AWRC), was significantly incremented by the damaged starch content. There was a consistent loss in cookie quality as the damaged starch content increased. In spite of the fact that the proteins were not affected by flour milling, bread quality decreased as the damaged starch content increased.     

海藻酸钠对小麦淀粉性质及馒头品质的影响

采用快速黏度计、差示扫描量热仪、动态流变仪、粉质仪等,研究了海藻酸钠(AG)对小麦淀粉(WS)糊化性质及馒头品质的影响。结果表明,AG显著影响WS性质,明显改善馒头品质。AG增加WS糊化难度,表现为起始糊化温度、峰值糊化温度升高,降低溶解度。促进WS溶胀,表现为提高峰值黏度、膨胀力、终止糊化温度和糊化焓升高。提高淀粉糊的稳定性,表现为衰减值、回生值和老化率降低。AG提高糊化后的WS在外力作用下的稳定性,有利于WS黏弹性凝胶的形成,且形成的凝胶更趋向于固体。AG提高小麦粉的加工品质,使面团吸水率、形成时间、稳定时间增加,跌落值降低。一定质量分数的AG可增大馒头比容、高径比,AG在馒头中的建议用量为小麦粉质量的0.05%~0.15%。     

Techno‐functional properties of wheat flour‐resistant starch mixtures applied to breadmaking

Resistant starch can be used to reduce the availability of carbohydrates in baked products. In this study, the effect of type 4 resistant wheat starch (RS₄) on wheat flour dough and breads was evaluated. Wheat flour was substituted by RS₄ at 10%, 20% and 30% w/w (RS10, RS20 and RS30, respectively). Rheological and thermal behaviours of dough were evaluated. Besides, bread quality, starch digestibility and bread staling were analysed. All substituted dough exhibited viscoelastic behaviour but lower elastic and viscous moduli. Regarding to bread quality, specific volume and crumb texture were negatively affected in samples with RS₄. However, all samples were technologically acceptable. During storage, crumb hardening was observed in breads without and with RS₄ but amylopectin retrogradation was not particularly affected. The in vitro digestibility of bread with RS showed a lower release of reducing sugars and a lower estimated glycaemic index, suggesting a healthier profile for these breads.     

An approach to studying the effect of different bread improvers on the staling of pre-baked frozen bread

The usefulness of different bread improvers (-amylase, sourdough, -carrageenan, hydroxypropylmethylcellulose) in an interrupted baking process was evaluated by using a differential scanning calorimeter as an oven. The thermal transitions of the wheat starch produced during the part-baking process, frozen storage at –18 °C, finish baking and aging of the baked dough at 4 °C were registered. The thermal properties of wheat starch during gelatinisation measured by differential scanning calorimetry were slightly affected by the dough formulation: only the peak temperature and the onset temperature underwent an increase, whereas the gelatinisation enthalpy decreased. The presence of the bread improvers minimised the negative effect of the frozen storage observed in the control sample, which showed an increase in the retrogradation temperature range. Concerning the aging of the baked dough after freezing and re-baking, all the improvers decreased the retrogradation enthalpy of the amylopectin, retarding the staling. Bread improvers can act effectively in the interrupted baking processes with frozen storage of the part-baked breads.     

Effect of frozen storage time on the bread crumb and aging of par-baked bread

The effect of frozen storage time of par-baked bread on the bread crumb and staling of bread obtained after thawing and full baking is described. The moisture content, hardness and retrogradation enthalpy of the amylopectin were determined in the par-baked bread and in the full baked bread after 7, 14, 28 and 42 days of frozen storage at −25 °C. In addition, the effect of frozen storage on the crumb microstructure was analyzed by cryo scanning electron microscopy (Cryo-SEM). The moisture content of both partially and full baked bread decreased with the time of frozen storage. The crumb hardness of the par-baked bread after different periods of frozen storage was kept constant, while that of their full baked counterpart increased with the time of frozen storage. In both types of breads, the enthalpy of amylopectin retrogradation did not vary with the period of frozen storage. The staling, measured as hardness increase and amylopectin retrogradation, increased along the frozen storage. The changes observed on the frozen par-baked bread after thawing were attributed to the damage of bread structures produced by the ice crystallization, and the microstructure study support that conclusion.     

DSC法研究小麦淀粉与面粉糊化和回生特性

利用差示扫描量热仪结合Avrami方程考察了8种不同小麦淀粉与面粉糊化和回生特性,探讨了直链淀粉和蛋白含量对其热力学行为产生的影响,并用SPSS软件计算其相关性。结果表明:对于淀粉与面粉体系,直链淀粉含量与糊化热焓值△H呈较显著的负相关,与Avrami指数n呈弱的负相关,而与速率常数k呈较显著的正相关,与最大回生度DR呈一定的正相关;对于面粉体系,蛋白含量与面粉糊化热焓值△Hf呈一定的负相关,与面粉体系Avrami指数nf和速率常数kf分别呈弱的正相关和较显著的负相关,与面粉体系最大回生度DRf呈弱的正相关。