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.     

改良剂对冷冻面团品质影响的研究进展

冷冻面团被广泛应用于食品工业中,但冻藏过程中会出现面团性质变劣、发酵能力降低等问题。冷冻面团改良剂是解决这些问题的重要方法。目前常用的改良剂有多糖、乳化剂、蛋白质及其他类等。文章阐述了目前冷冻面团技术应用过程中存在的主要问题及其影响因素,综述了不同改良剂对冷冻面团品质影响的作用机理和应用效果,并展望了改良剂的研究与发展趋势。     

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。     

不同剂量的面条改良剂对面条品质的影响

以三种不同筋力的面粉为主要供试材料,分别添加不同剂量的品质改良剂加工成面条,采用MinoltaCR2400型色彩色差计测定分析面片色泽,用TA.XT.plus型质构仪测定分析干面条的断裂强度和熟面条的拉伸性.结合评分,对面条的综合品质进行分析.结果表明,强筋面粉可以不添加改良剂,中筋面粉添加0.6‰效果要优于添加1‰的效果,而弱筋粉添加1‰的效果更明显.     

Comparison of fourier transform mid infrared spectroscopy and near infrared reflectance spectroscopy with differential scanning calorimetry for the study of the staling of bread

The staling of bread has previously been studied by differential scanning calorimetry and by simple rheological measurements. In this collaborative study, two spectroscopic techniques (Fourier transform mid infrared spectroscopy and near infrared reflectance spectroscopy) have been used in addition to differential scanning calorimetry to follow the progress of bread staling. Using each technique, changes in measured properties were apparent which, when fitted by first order exponential equations, gave calculated rate constants of similar magnitude. It is postulated that each technique gives independent information about the crystallisation process in the amylopectin fraction of the bread crumb.     

Effect of fermentation conditions on bread staling kinetics

The effects of yeast dose, temperature and fermentation time on bread volume, bread density, bread texture (firmness, cohesiveness, resilience, springiness and gumminess) and their change during staling were analysed. Thus, changes in the texture profile (TP) parameters as bread aged were modelled and their initial values and their variation rate were obtained. In white and whole breads, the longer the fermentation time and the higher the yeast dose, the lower the firmness and the firming rate. The fermentation temperature only affected the initial firmness in whole breads. Significant linear correlations were found between bread density and volume (r ² = 0.94 in white bread; r ² = 0.96 in whole bread), between density and the initial firmness (r ² = 0.88 in white bread; r ² = 0.61 in whole bread), and between the first two parameters and the firming rate. Between density and firming rate r ² obtained was 0.72 in white bread and 0.32 in whole bread and between volume and firming rate r ² obtained was 0.58 in white bread and 0.29 in whole bread.     

Effect of storage temperature on starch retrogradation of bread staling

The objective of the present work was to study the effect of bread storage temperature on starch retrogradation, using water activity measurement and X‐ray diffractometry technique to analyse the changes produced in the crumb firmness such as recrystallization. When storing bread with crust, the crust tends to trap moisture from the crumb, resulting in a dehydration of the crumb with faster staling. For storage temperatures of 25 and 4°C, water activity decreases as a function of storage time whereas at −18°C it is maintained at an almost constant level for 23 days. During storage, the starch molecules are reassociated and generate a new crystalline order which has a typical XRD pattern: the B‐type structure. The peak at 17.4° is indicative of this structure and is related to bread aging. As observed with the recrystallization kinetics, at −18°C only crystal growth may occur, whereas at 25 and 4°C there would be not only growth but also formation of new crystals. At 4°C the rate of starch retrogradation is the highest for the studied conditions.     

Influence of inulin on physical characteristics and staling rate of gluten-free bread

Inulin preparations with different degree of polymerization (HSI with a DP < 10, GR − DP ? 10 and HPX − DP > 23) were used for the production of gluten-free bread. It was found that an addition of investigated compounds resulted in an increase of loaf volume and reduction of crumb hardness. However, internal structure of the obtained loaves was less uniform and more open than in control bread. Generally, inulin preparations with lower degree of polymerization had stronger effect on all analyzed parameters than that with higher DP. A decrease in staling was observed (measured as the rate of crumb hardening), which was caused by the presence of inulin. The highest content of retrograded amylopectin was found for crumb with HSI, and the lowest for samples with HPX.     

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.     

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.     

Effect of chitosan on physical and chemical processes during bread baking and staling

The objective of this research was to investigate the effect of chitosan on the interaction of water with bread ingredients and on the rate of staling. The changes in freezable bound water and total water contents in bread crumb were assessed by differential scanning calorimetry from water melting and evaporation endothermic peak areas. It was found that freezable water content and total water content in bread crumb decrease during staling more rapidly in the presence of chitosan. The weak interaction of freezable water with protein and starch polymeric chains in bread crumb becomes stronger, but the interaction of nonfreezable bound water with protein and starch molecules in bread crumb becomes weaker in the course of staling during bread storage. Two stages of bread crumb staling were indicated. Chitosan increases the rate of bread staling during both stages. It was suggested that during bread staling chitosan increases water migration rate from crumb to crust, prevents amylose-lipid complexation, and increases dehydration rate both for starch and gluten.     

Effect of freezing and frozen storage on the staling of part-baked bread

The effect of part-baking, freezing, frozen storage, thawing, rebaking on the aging behaviour of bread was evaluated. The amylopectin modification during the process was assessed by differential scanning calorimetry (DSC), while changes in bread quality were followed by crumb hardness measurements. During frozen storage no retrogradation of amylopectin was detected in the part-baked dough. When analysing the aging of the rebaked samples, it was observed that the time of frozen storage produced a progressive increase of the retrogradation temperature range of the amylopectin, and also great energy was required for amylopectin melting at longer storage period, indicating that structural changes of amylopectin were produced during frozen storage. Regarding the quality of the fresh bread resulted after rebaking, crumb hardness increase with the time of frozen storage, and also the hardening rate during aging was dependent on that time. Crumb hardness results of the fresh bread and also DSC studies indicate that some changes are produced during the frozen storage.     

A Calorimetric Study of the Interaction between Waxy Maize Starch and Lipid

There is considerable debate on the definition and measurement of the amount of amylose in starch and whether hydrophobic ligands can form a complex with amylopectin. One method for amylose determination is through the measurement of amylose‐lipid complexation using differential scanning calorimetry (DSC), with the assumption that amylopectin cannot form such a complex. As the sensitivity and methodologies used for DSC improves, the validity of this assumption needs to be tested once again. For the experimental work, α‐L ‐lysophosphatidylcholine (LPC, 10% of starch dry weight) was used as the complexing agent and waxy maize starch. Optimisation of the DSC included changing the heating rate from 10ºC/min to 40ºC/min, which resulted in a higher sensitivity enabling the recording of an endotherm associated with the dissociation of a starch‐LPC complex. The observation of the endothermic formation of such complex could only be achieved when a microcalorimeter, which analyses a much larger sample than a standard calorimeter (190 mg of dry starch compared to 13 mg) was used. There are two possible interpretations for these observations: Either waxy maize starch contains traces of amylose (~ 0.5‐0.7%) and the DSC is sufficiently sensitive to detect these amounts or the α‐1,6 glucan long branches of waxy maize starch bind linear aliphatic compounds.     

Addition of ice-nucleation active bacteria: Pseudomonas syringae pv. panici on freezing of solid model food

Ice-nucleation active bacteria (INAB), Pseudomonas syringae pv. panici, were cultured at 26 °C in a nutrient broth and harvested at late log phase. The ice-nucleation activity unit per unit volume of the bacterial culture measured by the droplet-freezing assay developed by Vali was 3.29 × 10⁴ INA/mL. A differential scanning calorimetry (DSC) analysis of 77 g/100 g Tylose samples showed that the addition of bacteria had no obvious effect on the glass transition temperature and heat of fusion of the samples. Freezing operations carried out at −20 °C showed that the addition of INAB produced no obvious change in the freezing time. The scanning electronic microscope (SEM) observation of microstructure of the model food indicated that the mean ice crystal size was reduced from 25.7 μm to approximately 15 μm by the addition of INAB.     

Effects of freezing and frozen storage conditions on the rheological properties of different formulations of non-yeasted wheat and gluten-free bread dough

Empirical and fundamental rheological measurements were made on fresh and frozen dough to study the effects of freezing and frozen storage conditions. Frozen dough was stored at two different temperatures, −18 °C and −30 °C, and for 1, 7 and 28 days. Four dough formulations were tested: a standard wheat dough, a fibre-enriched wheat dough, a standard gluten-free dough and a gluten-free dough containing amaranth flour. No yeast was used in any formulation. The wheat dough is more affected by freezing and by the first days of storage whereas the gluten-free dough is more affected by a longer storage time. A storage temperature of −30 °C alters dough rheological properties more than a storage temperature of −18 °C. The addition of dietary fibres to the wheat dough increases its resistance to freezing and frozen storage. The addition of amaranth flour to gluten-free dough also increases its resistance to freezing but decreases its resistance to storage conditions.     

Functionality of different emulsifiers on the performance of breadmaking and wheat bread quality

Emulsifiers are widely used in bakeries as dough strengtheners and crumb softeners, but there is a great diversity of compounds with emulsifier action. The objective of this study was to analyze the influence of emulsifiers with different functionalities on the rheological characteristics of wheat dough, as well as their effect in the final bread parameters, including behavior during aging. All the emulsifiers tested increased dough stability, although the extent of this effect was concentration-dependent. The presence of emulsifier retarded dough proofing; in consequence, longer proofing times would be required when emulsifiers are used. In fact, the positive effects of emulsifiers on bread volume were only observed with long proofing times, and that also became evident when crumb hardness was analyzed. Sodium stearoyl lactylate, sucrose ester, lecithin and enriched lecithin were the emulsifiers with the greatst crumb softening effects at extended proofing times. However, when the objective is a hardening delay during storage, the emulsifiers of choice are monoglyceride and lecithin enriched in lysophospholipids. This study reveals the importance of the proofing period to the functionality of the emulsifiers when used for breadmaking performance.     

Effect of sourdough at different concentrations on quality and shelf life of bread

The objective of this work was to study the effect of sourdough obtained with selected exopolysaccharide (EPS)-producing lactic acid bacteria (LAB) strains on the quality of bread and its shelf life. Two sourdough concentrations were used in order to ascertain the best bread composition. Fresh bread quality was studied by means of microbiological, physical, chemical and mechanical analysis, whereas physical, thermal and mechanical properties were investigated to study the product shelf life. The results showed that dough prepared with 30 g/100 g of sourdough had a negative impact on bread quality properties in the absence of EPS-producing LAB strains, whereas the opposite was observed in the presence of EPS-producing strains: bread samples at 30 g/100 g of sourdough showed higher volume, higher moisture content and better mechanical properties during storage than samples at 20 g/100 g of sourdough. Moreover, 30 g/100 g of sourdough showed a protective effect on bread staling, thus confirming the effect of sourdough concentration and the positive role of EPS on functional properties.     

A contribution to the study of staling of white bread: effect of water and hydrocolloid

Staling of white bread at ambient temperature was studied using differential scanning calorimetry and dynamic mechanical thermal analysis. During storage, sample hydration varied slightly, from 0 to 0.4% per day, depending on packaging conditions. An increase in rigidity was observed, which was attributed both to starch rétrogradation and to changes in the organization of the amorphous part of crumb. The glass transition temperature of crumb was not significantly modified by these structural changes. Hydrocolloids did not affect the overall shape of the viscoelastic behavior of crumb in the temperature range from −40°C to 80°C, and had a limited influence on the kinetics of starch rétrogradation during storage. They decreased significantly the rate of increase in rigidity, compared to control bread. Hydrocolloids were expected to play an important role on the plasticity of the amorphous regions of crumb, either through water retention (as locust bean gum), or by inhibiting gluten-starch interactions (xanthan and alginate). Complexes between the native lipids offlour and amy lose were formed during the first two days of storage. They appeared to reduce the maximum level of starch rétrogradation.