Effects of processing on biochemical and rheological properties of wheat gluten proteins

Protein solubility increases during mixing at water absorption suitable for bread doughs. The changes that result from heat treatment may be much greater than the differences normally found among wheat varieties. Sheeting brings about a reduction in the gluten content and increase in gel protein content of doughs. This may be due to increase in temperature during sheeting as a result of work input to the dough resulting in protein denaturation. Drying at higher temperatures causes denaturation of pasta dough protein. In addition, it has been shown that high temperatures contribute to the formation of the protein network. During extrusion processing proteins are denatured and chemical bonds are weakened as result of heat and shear through the extruder.     

A GENERALIZED VISCOSITY MODEL FOR EXTRUSION of PROTEIN DOUGHS1

A theoretical model to predict the apparent viscosity of protein doughs during thermal processing involving heat induced denaturation is presented. the model allows viscosity prediction based on the effects of temperature-time history, strain history, temperature, shear rate and moisture content. Data from several sources have been considered in investingating the performance of the model. the approach facilitates an understanding of the mechanisms associated with protein texturization during extrusion.     

A heat denaturation study of the 11S globulin in soybean seeds

When the 11S globulin, one of the major storage proteins in soybean seeds (Glycine max), was heated at 0·5 ionic strength, the denaturation temperature was biologically estimated to be about 10 degrees higher than that at 0·1 ionic strength. The results also coincided well with those obtained by differential scanning calorimetry. The heat denaturation temperatures of the protein obtained by differential scanning calorimetry were estimated to be 78·1°C and 89·6°C at 0·1 and 0·5 ionic strength respectively. The enthalpies of heat denaturation were 2·0 cal/g and 3·2cal/g at 0·1 and 0·5 ionic strength, respectively. Correlation was not observed between the heat stability at high ionic strength and the content of the ordered secondary structure or a dissociation-association reaction of the protein with change of ionic strength. However, increase of the hydrophobic region at high ionic strength indicated the possibility of stabilisation of the quaternary structure of the 11S globulin by hydrophobic bonding during heat denaturation.     

THE EFFECT OF HEAT AND SHEAR ON THE VISCOELASTIC PROPERTIES OF SOY FLOUR DOUGH

This paper is concerned with the effect of heat and shear on the rheological properties of defatted soy dispersions and doughs of 30 to 60% flour by weight. Capillary and rotary rheometers (Rheometrics Mechanical Spectrometer) were used to heat doughs up to 75° C and shear them simultaneously. In one series of experiments using a modified Instron capillary rheometer the doughs were heated to several different temperatures and then sheared. The linear viscoelastic properties of the dough which were determined by means of a plate-plate rheometer were then compared to the fresh dough and those of a heated but nonsheared dough. In another experiment a cone-and-plate rheometer was used to heat and shear the dough. The linear viscoelastic response of the dough was used to monitor any changes as it was heated and sheared. It was observed that only in the higher moisture dispersions (i.e., moisture contents greater than 50%) were there any signs of an increase in rheological properties which might be associated with “cooking”. It was concluded that cooking of soy flour doughs most likely does not involve the formation of a permanent network formed by covalent chemical bonds. Hence, in extrusion cooking processes involving soy flour doughs, it may not be necessary to treat the rheological properties of the dough as a thermosetting system.     

Optimisation of time/temperature treatment,for heat treated soft wheat flour

Chlorination of wheat flour in the EU countries has been replaced in recent years, to some extent, by heat treated flour which is used to produce high ratio cakes. Heat treated flour allows high ratio recipes to be developed which generate products with longer shelf life, finer texture, moist crumb and sweeter taste. The mechanism by which heat treatment improves the flour is not fully understood, but it is known that during the heat treatment process, protein denaturation and partial gelatinisation of the starch granules occurs, as well as an increase in batter viscosity. Therefore, it is important to optimize the flour heat treatment process, in order to enhance baking quality. Laboratory preparation of heat treated base wheat flour (culinary, soft, low protein) was carried out in a fluidised bed drier using a range of temperatures and times. The gluten was extracted from the final product and its quality was tested, to obtain objective and comparative information on the extent of protein denaturation. The results indicated that heat treatment of flour decreases gluten extensibility and partial gelatinisation of the starch granules occurred. After heat treatment the gluten appeared to retain moisture. The optimum time/temperature for the heat treatment of base flour was 120–130 °C for 30 min with moisture content of ≈12.5%.     

基于红外光谱分析热处理对牛乳蛋白质二级结构的影响

运用傅里叶变换红外光谱技术对乳蛋白及其酰胺Ⅰ带进行解析,进一步用红外解谱法对其二级结构进行表征。以原料乳为对照,研究65℃/30 min(低温长时巴氏杀菌)、80℃/15 s(高温短时巴氏杀菌)、95℃/5 min(酸乳热处理)、137℃/5 s(超高温灭菌)等不同热处理条件对乳中蛋白质二级结构的影响。结果表明,热处理会导致乳蛋白间发生相互作用,乳蛋白原空间结构受到破坏,导致分子内氢键被破坏。不同热处理程度的乳蛋白酰胺Ⅰ带均向低波数方向发生了不同程度的红移,表明乳蛋白变性过程中疏水氨基酸残基暴露形成分子间氢键。同时热处理后乳蛋白各二级结构比例发生明显改变。α-螺旋含量显著降低(P0.05),无规卷曲含量显著升高(P0.05),β-转角及β-折叠含量在加热过程均呈先增加后减少变化趋势,表明热处理程度增强导致部分有序结构向无规卷曲结构转化,蛋白质热变性后会发生热聚集现象,且β-折叠、β-转角结构在热聚集体的形成过程中具有重要作用。     

Influence of drying and hydrothermal treatment of corn on the denaturation of salt-soluble proteins and color parameters

The effect of heat treatments (drying and hydrothermal treatment) on the extractability of salt-soluble protein (SSP) was assessed using Promatest methodology for corn kernels heated between 60 °C and 120 °C. During drying, the evolution of the grain moisture content is fitted using the analytical solution of Fick equation developed by Crank (1979) for spherical material. The decrease of extractible salt-soluble protein during heating is forecasted using a first and a second order ordinary differential equation. It was found that temperature; moisture content and time of processing greatly influence the kinetic denaturation of SSP of corn kernels. The evolution of extractible SSP content of corn kernels during drying at high temperature is more correctly described with second order kinetic than with the first order kinetic reaction. The Hunterlab color parameters of corn also vary during drying. Lightness and color intensity decrease while yellowness, redness, chroma and hue angle increase through drying time. Most of these Hunterlab color parameters are highly correlated with the salt-soluble proteins content and therefore could be used as indicators of excessive heat treatment and denaturation of salt-soluble proteins in corn kernels.     

抗冻剂对冷冻鱼糜蛋白理化和凝胶特性的影响综述

冷冻储藏是一种广泛用于保存鱼糜制品的方法。但是在储藏的过程中会使蛋白质发生冷冻变性,使鱼糜蛋白的空间构象发生变化,导致蛋白理化性质及凝胶特性发生变化,包括盐溶性蛋白含量、Ca2+-ATPase活性以及巯基含量的降低,二硫键含量和表面疏水性增加,凝胶破断力、变形程度以及持水力减小等。加入抗冻剂可在一定程度上抑制蛋白冷冻变性。本文概述了冷冻鱼糜蛋白变性机理,并总结了几种抗冻剂对冷冻鱼糜蛋白理化性质及凝胶特性的影响。     

Effect of Dehydration Methods on the Functionality of Plant Protein Concentrates

The significance of different dehydration methods for rice bran protein and soy protein coagulates on composition and functionality of the resulting protein concentrates was investigated. Minor compositional differences were found between the freeze-, spray- or drum-dried samples. Protein solubility data indicated limited effects of dehydration methods on heat coagulated samples but significant reduction of protein solubility by drum drying was found in the case of soy protein coagulated at room temperature. Water absorption capacity and emulsion properties were significant affected by dehydration methods but no consistent trends could be observed for fat absorption capacity. A significant increase of specific bread loaf volume, relaxation time of doughs and in some cases deformation of protein fortified samples was detected from freeze-dried to drum-dried samples. In general the effects of dehydration methods on protein functionality were more consistent for heat coagulated rice bran protein than for soy protein concentrates processed at ambient temperatures.     

Quality Characterization of Waste Olive Cake During Hot Air Drying: Nutritional Aspects and Antioxidant Activity

Olive cake, a by-product of the olive oil industry, was characterised through a drying process, where the influence of air drying temperature on physicochemical properties and antioxidant activity was investigated. A comparison of fresh and dehydrated olive cake showed that drying led mainly to denaturation of crude protein. Crude fibre content showed a slight increase during drying and may have undergone some alterations in its structure due to Maillard reactions. Fatty acid analysis revealed that olive cake was especially rich in oleic acid and fatty acid composition did not significantly change during drying. Ash content also showed a slight variation but may be considered as practically unchanged. Potassium and sodium were respectively the most and the least abundant minerals found in olive cake. Total phenolic content showed a direct relationship to DPPH radical scavenging activity. Overall antioxidant activity, highest in fresh olive cake, was affected by air drying temperatures being more evident at 90 °C. Vitamin E showed an increasing trend at all drying temperatures. According to this investigation, convective dehydration can lead not only to a dried olive cake that can be used as a material for many processing industries (e.g. food and cosmetic) but also can contribute to minimize the environmental impacts of this agro-industrial waste.     

热处理对牛乳成分的影响以及热敏感指标的变化研究进展

热加工可以有效杀灭生牛乳中的各种致病微生物,但也会对牛乳成分产生影响。随着热处理温度的升高,乳清蛋白变性和凝集、乳糖异构化和降解、美拉德反应等理化反应会依次发生,这些反应中活性成分(例如碱性磷酸酶和乳清蛋白)的减少或反应产物的生成(例如乳果糖和糠氨酸)都可作为热加工强度的标识。本文对牛乳的热加工条件、牛乳在受热情况出现的理化变化以及相应的热敏感成分的变化进行综述。     

Semi-industrial production of a minimally processed infant formula powder using membrane filtration

Infant formula (IF) is submitted to several heat treatments during production, which can lead to denaturation or aggregation of proteins and promote Maillard reaction. The objective of this study was to investigate innovative minimal processing routes for the production of first-age IF powder, thus ensuring microbial safety with minimal level of protein denaturation. Three nutritionally complete IF powders were produced at a semi-industrial scale based on ingredients obtained by fresh bovine milk microfiltration (0.8 and 0.1-µm pore size membranes). Low-temperature vacuum evaporation (50°C) and spray-drying (inlet and outlet temperatures of 160 and 70°C, respectively) were conducted to produce the T? formula with no additional heat treatment. The T+ formula was produced with a moderate heat treatment (75°C for 2 min) applied before spray-drying, whereas the T+++ formula received successive heat treatments (72°C for 30 s on the milk; 90°C for 2–3 s before evaporation; 85°C for 2 min before spray-drying), thus mimicking commercial powdered IF. Protein denaturation and Maillard reaction products were followed throughout the production steps and the physicochemical properties of the powders were characterized. The 3 IF powders presented satisfactory physical properties in terms of a_w, free fat content, glass transition temperature, and solubility index, as well as satisfactory bacteriological quality with a total flora <10³ cfu/g and an absence of pathogens when a high level of bacteriological quality of the ingredients was ensured. Protein denaturation occurred mostly during the heat treatments of T+ and T+++ and was limited during the spray-drying process. The IF powder produced without heat treatment (T-) presented a protein denaturation extent (6 ± 4%) significantly lower than that in T+++ (58 ± 0%), but not significantly different from that in T+ (10 ± 4%). Although T? tended to contain less Maillard reaction products than T+ and T+++, the Maillard reaction products did not significantly discriminate the infant formulas in the frame of this work. The present study demonstrated the feasibility of producing at a semi-industrial scale an infant formula being bacteriologically safe and containing a high content of native proteins. Application of a moderate heat treatment before spray-drying could further guarantee the microbiological quality of the IF powders while maintaining a low protein denaturation extent. This study opens up new avenues for the production of minimally processed IF powders.     

EFFECT OF STORAGE ON NUTRITIVE VALUE OF FOOD1

With few exceptions, nutrient levels and/or their bioavailability are reduced in foods following harvest, slaughter, or collection. Rate of these losses is usually attenuated by reducing temperature of storage. Initial heat processing to the point of enzyme inactivation, or to the point of microbial sterilization, “stabilizes” the food so that it does not “spoil” but at the same time causes a greater initial reduction in certain nutrients, and a more gradual reduction with extended storage. Initial heat processing and mechanical treatments may also release nutrients so that they become more available, but once released, they are also subject to losses unless stored at low temperatures. Ascorbic acid is undoubtedly the most sensitive to loss and changes to a less active form as the result of time and temperature in storage. In many instances changes in ascorbic acid reflect general changes in quality. Thiamine is the other vitamin which is frequently affected adversely by time and temperature of storage. The A vitamins appear to be lost readily in leafy vegetables, but relatively unchanged in other foods. There is little effect on mineral content of foods, but bioavailability, particularly of iron may be influenced during prolonged storage. Substantial losses in carbohydrates may be encountered as a result of respiratory activity in extended storage at relatively high temperatures. Protein content is rarely affected, but protein availability is readily reduced even in low moisture foods unless they are protected from oxygen and stored at low temperatures. These anticipated changes in nutritive value are of particular significance in nutrient labeling, and must be taken into account when preparing nutrient labels.     

The effect of lipoxygenase action on the mechanical development of wheat flour doughs

The mechanical development of dough has been followed by measurement of the relaxation time of dough samples after mixing to various levels of work input. Parallel determinations of free and bound lipid have also been made. When doughs were mixed in air, addition of full-fat, enzyme-active soya bean flour (subsequently referred to as “soya flour”) resulted in an increase in relaxation time, particularly at higher work levels. The magnitude of this improvement increased with increasing work input and was dependent on the rate of work input. Addition of soya flour also enabled a higher level of mechanical work to be introduced before dough breakdown occurred. When doughs were mixed under nitrogen, or when the soya flour was heat denatured, no change in the rheological properties compared with the respective control doughs was found. The release of bound lipid, which occurred during dough development in air in the presence of soya flour, could also be induced by adding purified lipoxygenase to the dough, together with linoleic acid as a substrate. This resulted in rheological changes similar to those observed using soya flour. However addition of enzymically pre-peroxidised lipid to doughs mixed in nitrogen was without effect on relaxation times. These findings suggest that lipid release is linked with structural changes in dough protein and provide further support for a mechanism of coupled oxidation of protein -SH groups by lipoxygenase.     

Concentrated whey protein ingredients: A Fourier transformed infrared spectroscopy investigation of thermally induced denaturation

Thermal denaturation of whey protein solutions was investigated from a structural perspective utilising attenuated total reflectance – Fourier transformed infrared spectroscopy (ATR‐FTIR). Solutions (100 g protein/L, pH 7) of commercial whey protein isolate (WPI) powders and enriched protein fractions of β‐lactoglobulin (β‐lg) and α‐lactalbumin (α‐la) were heat‐treated at temperatures of 50–90 °C. Subsequent analysis by ATR‐FTIR highlighted the structural changes occurring as a direct result of heat treatments. Molecularly, WPI dispersions exhibited pronounced differences in denaturation behaviour depending on their method of manufacture. ATR‐FTIR is an informative tool to discern the structural molecular interactions not apparent through physical analysis of concentrated ingredients.     

Effect of β-Glucan Concentrate on the Water Uptake,Rheological and Textural Properties of Wheat Flour Dough

The effects of the addition of β-glucan concentrate (2.5–10 g/100 g flour) and water (58–70 mL/100 g flour) on the rheological and textural properties of wheat flour doughs were studied. Various empirical (farinograph, extensograph, dough inflation, and dough stickiness) and fundamental rheological tests (oscillatory and creep-recovery) were employed to investigate composite dough structure and an attempt was made to correlate the data obtained from different instrumental measurements. The water absorption increased with the addition of β-glucan concentrate into wheat flour. An increase in mixing time and stability were recorded upon addition of β-glucan concentrate (≤ 5 g/100 g flour), and the extensibility decreased at similar condition. The composite dough exhibited predominating solid-like behavior. The mechanical strength, dough stickiness, the peak dough inflation pressure decreased with increasing water content but those parameters increased with β-glucan concentrate incorporation within the studied concentration range. Creep-recovery tests for 5 g β-glucan concentrate/100 g flour doughs recorded less resistance to deformation with an increase in water level and data were well described by the Burger model. Thermal scanning of doughs revealed that the protein denaturation peak was significantly influenced by water content, and the values were ranged between 110 and 124°C. Significant relationships between empirical and fundamental rheological testing methods were found.     

A kinetic model for whey protein denaturation at different moisture contents and temperatures

The denaturation of whey protein samples that had previously undergone heat-treatment for different times at different temperatures and moisture contents was analysed by differential scanning calorimetry (DSC), using the DSC enthalpy as a measure of residual undenatured protein. Data were fitted to first order irreversible or reversible kinetic expressions, and the resulting rate constants were found to increase with both temperature and moisture content. The whole data set was then fitted as a function of time, temperature and moisture content, with rate constants varying according to either Arrhenius or Williams-Landel-Ferry (WLF) kinetics and with selected fit parameters made empirical functions of moisture content. The best fits were obtained using reversible WLF kinetics, which could be further slightly simplified without loss of accuracy. The model provides a platform for single- and multi-objective drying trajectory optimisation with respect to protein denaturation in dairy products.     

Macromolecular changes associated with the heat treatment of soya isolate

The denaturation temperatures of both the 7S and 11S proteins present in a 70 PDI soya flour and an isolate prepared from it, increased by over 30°C as the water content of the system decreased from 90 to 20%. In dilute dispersions (> 70% water), the precipitate formed on heat treatment was almost totally soluble in 3.0% sodium dodecyl sulphate (SDS), irrespective of the heating temperature (20-120°C). However, in more concentrated systems, heat treatment at 120°C for 1 hr caused increasing amounts of SDS insoluble protein to form as the water content decreased. Such aggregates were also insoluble in beta-mercaptoethanol (ME), but soluble in mixtures of SDS plus ME.
It is suggested that at low concentrations, heat treated soya proteins are primarily aggregated by hydrophobic interactions but that, on decreasing the water content of the system, disulphide bond formation becomes a significant factor in stabilizing the aggregate.     

Role of Whey Components in the Kinetics and Thermodynamics of β-Lactoglobulin Unfolding and Aggregation

The optimisation of dairy unit operations involving heat transfer requires the control of fouling and aggregation phenomena following the denaturation of thermosensitive proteins, in particular β-lactoglobulin (β-lg). This study intends to give a better view of the influence of whey components (whey proteins, lactose, and minerals such as calcium) on β-lg denaturation through a combined kinetic and thermodynamic approach. β-lg denaturation in model solutions of increasing complexity (pure β-lg solution, whey protein solution, and two model wheys differing in mineral content) was characterised at temperatures ranging from 64.5 to 98 °C by following the evolution of soluble β-lg concentration with HPLC. It was demonstrated that whatever the model solution composition, a two-step mechanism (unfolding followed by aggregation) of 1.5-order kinetics could be adopted to describe β-lg denaturation reaction, as the temperature dependence of the denaturation reaction rate was properly fitted by Arrhenius equation. The dependency of kinetic and thermodynamic parameters on solution composition indicated that the presence of whey proteins enhanced β-lg aggregation, whereas lactose showed a small protective effect against β-lg unfolding. Additionally, minerals, especially calcium, tended to stabilise β-lg native state while increasing β-lg aggregation rates. However, at high mineral content, calcium influence could be hindered or even reversed, presumably owing to a lower bioavailability due to complexation with anions such as inorganic phosphates.     

Effects of continuous flow microwave treatment on chemical and microbiological characteristics of milk

Raw cows' and goats' milks were heated by microwave in a continuous flow unit up to temperatures ranging from 73.1 to 96.7°C. The effects of the heat treatments were estimated by measurements of lactose isomerization, protein denaturation, inactivation of alkaline phosphatase and peroxidase and the total bacterial count. Negative phosphatase tests and low bacterial counts, together with low degrees of whey protein denaturation, were achieved under several temperature/time combinations. The results indicate that continuous microwave processing may be an efficient and mild approach for the pasteurization of milk.