Impact of endogenous constituents from different flour milling streams on dough rheology and semi-sweet biscuit making potential by partial substitution of a commercial soft wheat flour

A flour fractionation-reconstitution procedure was used to study the substitution of a commercial soft wheat flour with gluten, water extractables, prime starch and starch tailing fractions isolated from patent and clear flour streams on dough rheology and semi-sweet biscuit characteristics. Substitution of soft wheat flour with increasing levels of the native patent and clear flour streams raised the dough consistency, hardness and elastic properties as well as the biscuit textural attributes (density, hardness). The dough stickiness of the base flour was also reduced and the biscuits were free of cracks. Gluten isolated from the patent flour had a greater impact on dough consistency, hardness and elastic properties than gluten obtained from the clear flour, likely due to the superior protein quality of the former. Additionally, with increasing gluten levels in the fortified flour there were moderate increases in biscuit density, hardness, and lower crunchiness. The addition of starch tailings produced the largest impact on consistency and hardness of the dough. This fraction also exerted a pronounced effect on biscuit density and hardness, while it lowered crunchiness, presumably due to its higher pentosan content. Overall, the dough rheological properties and biscuit characteristics were controlled by the amount-nature of the fractions added; i.e., besides gluten (amount and quality), other constituents such as pentosans and the overall composition of the flour blends can largely affect the quality of the semi-sweet biscuits.     

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.     

DSC、EM、NMR及 X-射线衍射在淀粉研究中的应用

介绍了差示扫描量热法(Dsc)、电子显微镜(EM)、核磁共振(NMR)及X-射线衍射(X-ray diffraction)等现代分析技术的基本原理及其在淀粉研究中的应用。     

Retrogradation properties of high amylose rice flour and rice starch by physical modification

A new physical modification applied to prevent the retrogradation of rice flour and rice starch was investigated. This study examined the retrogradation properties of treated rice flour or rice starch paste by three stirring or heating-stirring, or without. The results proved that the retrogradations of rice flour and rice starch were both not substantially affected by three stirring modifications. However, three heating-stirring treatments had a marked effect on retarding the retrogradation of rice flour, but did not affect that of isolated rice starch. In the differential scanning calorimetry (DSC) analysis, modified rice flour by three heating-stirring exhibited the lowest retrogradation enthalpy (3.04 J/g dry matter) as compared to the control RF (5.93 J/g dry matter) and by three stirring (5.08 J/g dry matter). Meantime, it had almost the least recrystallization of retrogradation by X-ray diffraction (XRD). It was also found through scanning electron microscopy (SEM) that the granule structure of this modified rice flour had a more honeycomb-like structure and the lowest crystallinity as compared to the others.     

Effects of pulsed electric fields (PEF) treatment on physicochemical properties of potato starch

Potato starch–water suspensions (8.0%, w/w) were subjected to pulsed electric fields (PEF) treatment at 30 kV·cm^− 1, 40 kV·cm^− 1 and 50 kV·cm^− 1, respectively. The physicochemical properties of PEF-treated potato starch samples were investigated using scanning electron microscopy (SEM), laser scattering technique, X-ray diffractometry (XRD), differential scanning calorimetry (DSC), and the Brabender rheological method, with native potato starch as reference. It has been concluded from SEM analysis that dissociation and damage of PEF-treated potato starch granules appeared. Some granules aggregated with each other and showed gel-like structures. It was revealed from particle size analysis that there was an obvious increase of the granule size after PEF treatment. This has been attributed to the aggregation among granules. It was also demonstrated from other analysis that relative crystallinity, gelatinization temperatures, gelatinization enthalpy, peak viscosity as well as breakdown viscosity of modified samples all decreased with increasing electric field strength.

Industrial relevance

In this study, the effect of PEF treatment (up to 50 kV·cm^− 1) on physicochemical properties of potato starch has been investigated. The results from SEM images showed that dissociation, denaturation and damage of potato starch granules had been induced by the PEF treatments. Some of granule fragments showed gel-like structures, and congregated with each other or with other starch granules. Laser scattering measurements of particle size revealed that an obvious increase of granule size under electric field strength of 50 kV·cm^− 1, which was attributed to the aggregation of the starch granules. The X-ray diffraction pattern showed an obvious loss of crystalline structure after the PEF treatment at 50 kV·cm^− 1, which induced a trend of transformation from crystal to non-crystal in potato starch granules. DSC analysis showed a decrease in gelatinization temperatures (T_o and T_p) and gelatinization enthalpy (ΔH_gel) with increasing electric field strength. Brabender rheological method has been used to show that the peak viscosity and breakdown viscosity decrease with increasing electric field strength of PEF treatment. All the results reveal that the PEF treatment can lead to an intragranular molecular rearrangement of potato starch granules, which induces changes of various physicochemical properties of the treated starch thus may endow it some new characteristics and functions. This phenomena may warrant further more detailed study.     

Influence of the polarity of the water phase on the mesomorphic behaviour and the α-gel stability of a commercial distilled monoglyceride

The lyotropic mesomorphic behaviour of a commercial distilled monoglyceride based on fully hydrogenated palmstearin at a concentration of 25% was studied as a function of temperature. Differential scanning calorimetry and wide angle X-ray diffraction were used to determine the Krafft temperature. Polarized light microscopy and small angle X-ray scattering were used to analyze the lamellar dispersion to an inverted bicontinuous cubic phase transition. The addition of a polar solvent, namely ethanol, propylene glycol and glycerol shifted the lamellar dispersion region to lower temperatures. The composition of the water phase also played an important role in the stability of the α-gel that was obtained by cooling the lamellar dispersion. In fact, the stability of this metastable phase as expressed by the coagel-index determined by differential scanning calorimetry was negatively influenced by decreasing the water phase polarity.     

A Tentative Explanation for the Substantial Rise of the Gelatinization Temperature of Starch by Adding Salt and Hydroxide

The effects of three saline solutions, LiCl, NaCl, and KCl, on the gelatinization temperature of starch-salt systems were studied. The same but systems with the addition of NaOH were also studied. A rise of gelatinization temperature of all starch-salt-water systems studied was observed. The gelatinization range (ΔTgr) of starch-salt-water systems, was not affected by the nature of the cation; instead it was affected by its concentration; the rise of the gelatinization temperature (ΔTgel) and gelatinization enthalpy (ΔH) were not affected by the nature and concentration of the cation. The rise of the gelatinization temperature (ΔTgel) of starch-salt-NaOH-water systems was significantly affected by the nature and concentration of the cation, and by the concentration of NaOH. Li⁺ was responsible for a smaller rise of gelatinization temperature and K⁺ for a greater rise of gelatinization temperature. Increases in the gelatinization temperature of up to 48.0°C were measured. These results may indicate that the rise in gelatinization temperature of starch-salt-NaOH-water systems could be explained based on the assumption that starch behaves as a weak ion exchanger governed by the Donnan potential.     

Physicochemical characterization and stability of inulin gels

The ability of three commercial inulins (Raftilose ^®P95, Frutafit IQ^®, and Frutafit TEX^®) with different chemical composition (oligo-polysaccharides profile) to form gels (at 25 and 50 °C) was evaluated. Raftilose^®P95 (rich in mono-disaccharides) did not form gels, Frutafit IQ^® (mainly oligosaccharides) gelatinized in the 30–60% w/w concentration range and Frutafit TEX^® (mainly long-chain saccharides) in the 20–40% w/w range. Textural and thermal properties of the gels were studied and their stability was evaluated during storage at 4 °C. Frutafit TEX^® gels (both fresh and during storage) were harder, more adhesive, and less cohesive than Frutafit IQ^® gels (40% w/w). At 40% w/w, Frutafit TEX^® gels had a significantly higher amount of freezable water than Frutafit IQ^®, and the DSC thermogram line shapes indicated that ice melting was more uniform and occurred at higher temperatures in Frutafit TEX^® than in the Frutafit IQ^® gels. Ice melting profile was not significantly affected by both gelification temperature and storage time. Frutafit IQ^® gels were more stable than Frutafit TEX^® gels during storage.     

Effect of amylose content and rice type on dynamic viscoelasticity of a composite rice starch gel

Amylose content is an important indicator to determine the utility of raw milled rice. Indica type rice with high amylose content is usually used for manufacturing rice noodles, while Japonica rice may be mixed partially to adjust the noodle texture. The effect of amylose and rice type on dynamic viscoelasticity of rice starch gel was investigated using a model starch composite in this study. The information will be helpful to control and obtain the required noodle texture by combination of different rice types. The results show that nonwaxy Indica and waxy Japonica rice starches in a composite mixture were incompatible and demonstrated their individual gelatinization behavior during heating. High amylose starch showed higher moduli and lower loss tangent values, as well as higher retrogradation rate. The starch gel made from Japonica rice starch showed a slow retrogradation rate even containing a similar amount of amylose to Indica starch. The storage modulus of the gel made from higher amylose rice was shown to be more independent of frequency. Not only amylose content but also chain length distribution in amylopectin affected the dynamic viscoelasticity of rice gel. Japonica rice starch, with fewer super-long chains in amylopectin, retrograded slower after gelatinization than Indica rice, thus the paste is too sticky for production of rice noodles.     

中链甘油三酯微胶囊的理化性质表征

从理化性质和感官指标上对实验制得的中链甘油三酯微胶囊产品进行评价。结果显示:制得的中链甘油三酯微胶囊产品,其气味纯正、无异味;颜色洁白;平均粒径为244.20 nm;颗粒均匀、呈圆球状,对芯材保护效果较好;水分含量为2.65%,溶解度为97.60%。差示扫描量热分析结果表明,中链甘油三酯微胶囊在温度低于90℃的加工中能够稳定存在。红外光谱分析证实,中链甘油三酯受微胶囊化的影响不大,能基本保留原有结构。     

豆渣膳食纤维对酥性饼干特性的影响

将豆渣中酶法提取的可溶性膳食纤维(豆渣SDF)、不溶性膳食纤维(豆渣IDF)以及商业菊粉,分别添加到酥性饼干中,研究其对饼干的物理化学特性和感官品质的影响。结果表明:添加豆渣IDF的饼干持水性和硬度较高,添加豆渣SDF和菊粉的饼干松密度值和过氧化值较低,且两者的松密度值没有较大差异,而添加豆渣IDF的饼干与之相反,添加4%豆渣SDF的饼干感官评定结果最优,且总膳食纤维、水分和脂肪含量较空白高,而蛋白质和灰分含量没有明显变化。     

Rheological,thermal and microstructural properties of whey protein isolate‐modified cassava starch mixed gels at different pH values

The objective of this study was to investigate the rheological, thermal and microstructural properties of whey protein isolate (WPI)‐hydroxypropylated cassava starch (HPCS) gels and WPI‐cross‐linked cassava starch (CLCS) gels at different pH values (5.75, 7.00 and 9.00). The rheological results showed that the WPI‐modified starch gels had greater storage modulus (G?) values than the WPI‐native cassava starch gels at pH 5.75 and 7.00. Differential scanning calorimetry curves suggested that the phase transition order of the WPI and modified starch changed as the pH increased. Scanning electron microscopy images showed that the addition of HPCS and CLCS contributed to the formation of a compact microstructure at pH 5.75 and 7.00. A comprehensive analysis showed that the gelling properties of the WPI‐modified starch were affected by the difference between the WPI denaturation temperature and modified starch gelatinisation temperature and by the granular properties of the modified starch during gelatinisation. These results may contribute to the application of WPI‐modified starch mixtures in food preparation.     

Effect of wheat germ addition on the microbiological quality,in vitro protein digestibility,and gelatinization behavior of macaroni

Macaroni was produced from semolina blended with 15% raw and microwaved wheat germ. Samples were stored at room temperature and monitored over one year of storage in terms of their sensory attributes, microbial count, in vitro protein digestibility, and gelatinization phenomena. Small but significant differences between the sensory attributes of the blended samples and those of control macaroni samples were found using the triangle test, and these differences didnt change significantly after a year of storage. Supplementing semolina with raw and microwaved wheat germ resulted in macaroni that gave similar results to control macaroni in terms of in vitro protein digestibility. Differential scanning calorimetry (DSC) was used to study the extent of gelatinization of the starch in the macaroni samples. Two endothermic transitions were observed. Significant changes in the gelatinization of the semolina and macaroni were observed after the addition of raw and microwaved wheat germ. Control macaroni had higher onset (T_o1) and peak (T_p1) temperatures, as well as a narrower gelatinization range (T₁), and a lower gelatinization enthalpy (H₁) than the control semolina. Addition of raw and microwaved wheat germ to the macaroni increased T_o1, but lowered the T₁ and H₁ values of the macaroni significantly. The nature of the second endothermic DSC peak indicated an increase in the amylose-lipid complexation (H₂) in the macaroni after enrichment with raw and microwaved wheat germ.     

Starch properties of various potato (Solanum tuberosum L) Cultivars susceptible and resistant to low-temperature sweetening

Properties of starch granules isolated from different varieties and selections of potato (which vary in their degree of chill sweetening) were examined. Differential scanning calorimetry (DSC) showed an increase in resistance to gelatinisation of isolated starch granules which correlated (r = 0.911) with higher chip scores following storage at 4°C and 12°C. Varying water level content during DSC studies resulted in significantly lower water content required to produce two endotherms for starch isolated from varieties resistant to chill sweetening. These data strongly suggest that starch granule composition might be a factor differentiating the low temperature sweetening sensitive from resistant cultivars, and may provide a screening method for predicting chip colour of potatoes out of storage.     

Physicochemical properties of flour recovered from broken rice noodles during production

Flour recovered from broken rice noodles was evaluated by microscopy, X‐ray diffractometry, differential scanning calorimetry, in vitro starch digestibility, pasting and gel texture analyses. Rice noodle making processes destroyed the granular and crystalline structures of rice flour (RF), but the process‐induced recrystallised amylopectin and amylose‐lipid complexes were observed. Higher level of resistant starch in broken rice noodle flour (BRNF) was due to the retrograded amylose, which formed during noodle making. The absence of pasting temperature and low pasting viscosity of BRNF were distinct from those of RF, whereas gel textures of both flours were similar. BRNF‐added rice noodles showed lower hardness, but the other cooking and texture qualities were close to the one without BRNF. Up to 17% of BRNF could be incorporated into composite rice noodle making. This study thus provided an approach to the management and utilisation of food processing wastes.     

Effect of water and guar gum content on thermal properties of chestnut flour and its starch

Thermal properties of chestnut flour and chestnut starch at several water content (40, 50, 60 and 95%, flour basis, f.b.) as well as the influence of guar gum (0.5, 1.0, 1.5 and 2.0%, f.b.) on both raw materials at fixed water content (50%, f.b.) were determined by differential scanning calorimetry (DSC). Thermal properties of guar gum–water systems at several guar content (0.5, 1.0, 1.5 and 2.0%, w/w) were also obtained by DSC. Results indicated that the water content and the presence of guar gum had a significant impact on the thermal properties of chestnut flour and its starch. For each endothermic curve, the values of onset (T_o), peaks (T_p1, T_p2) and final (T₁) temperatures decreased linearly with increasing water content. Experimental data were successfully (R² > 0.997) described following the Flory equation. A reverse trend was observed in the enthalpy values. Thermal properties of chestnut flour and chestnut starch were suppressed by the presence of guar gum even at the lowest concentrations employed (0.5%, f.b.). The guar gum addition to the assayed systems promoted a starch gelatinization delay and the enthalpy values showed a threshold content above 1.0% of guar gum. Analyses of aqueous guar gum mixtures showed that the existence of a second transition in chestnut starch systems can be successfully explained by means of hydrocolloid–starch interactions, whereas in the flour other interactions should be taken into account.     

The in vitro protein digestibility,microbiological quality and gelatinization behaviour of macaroni as affected by cowpea flour addition

Cowpeas were germinated, fermented, cooked, ground to flour and added to standard durum wheat semolina at 20% (w/w) level for macaroni production. Macaroni samples were analysed for in vitro protein digestibility, microbial count (total bacteria, mould and yeast) and gelatinization behaviour over a 6-month storage period at room temperature (<25 °C). Starch gelatinization behaviour of the samples was analysed using differential scanning calorimetry. Supplementing semolina with cowpea flour did not have a significant affect on in vitro protein digestibilities or aerobic plate counts of macaroni samples (p < 0.05). There was a small but significant increase in mold and yeast counts after 6 months of storage in cowpea treated samples. Two endothermic peaks were observed with significant differences in ΔH values of control and cowpea treated macaroni samples. The transition peak (T_p) temperatures were in the range of 66.9–67.9 and 86.9–100.4 °C for the first and second peaks, respectively. The transition enthalpies (ΔH) were in the range 2.41–4.21 and 1.71–3.86 J/g for the first and second peaks, respectively.     

Identifying key structural indicators of mechanical strength in networks of fat crystals

The mechanical properties of edible fats can be influenced by a series of factors, including the amount of solids, the polymorphism of the solid-state, as well as the microstructure of networks of polycrystalline particles created upon crystallization. This work demonstrates that for binary mixtures of the high-melting fraction of milk fat (HMF) with cocoa butter as well as for mixtures of HMF with the middle-melting fraction of milk fat, changes in the storage shear modulus (G′) are mostly controlled by the solid fat content (SFC), and the material’s microstructure. The SFC, in turn is a function of the phase behavior of the mixtures in the solid state. Experimental techniques used in the characterization of the different levels of structure are presented in this work. A model developed to explain mechanical properties of these materials taking into account all levels of structure is proposed. The polymorphism of the solid state did not seem to influence the mechanical properties of the fats, indicative of this material being structured as a network of weakly-attractive polycrystalline particles. Moreover, the mass fractal dimension of the network was closely related to the polymorphism of the solid state.     

Effects of sugar, protein and water content on wheat starch gelatinization due to microwave heating

 Understanding the interactions between sugar, starch, protein and water, which are the main components of a baked product, will advance the development of high quality, microwaveable products. This paper presents a mathematical model describing the quantitative relationships between water, sugar and protein on the gelatinization of wheat starch following 20 s of microwave heat as determined by differential scanning calorimetry. Addition of sugar decreased the degree of gelatinization of starch due to microwave heating significantly. Water and protein were not found to be as significant as sugar in delaying gelatinization. The effects of sugar and protein on the gelatinization of starch were pronounced in water-limited systems. The model could be used to describe systems containing 33–67% water, 0–33% sucrose and 0–5.8% protein, with a coefficient of determination of 0.91. Received: 29 June 1998