Dynamic rheology of wheat flour dough. I. Non‐linear viscoelastic behaviour

Controlled stress rheometry was used to investigate the effects of starch and gluten fractions on the non‐linearity of wheat flour dough. Flour–water dough showed non‐linear viscoelastic behaviour over all stress values in a cyclic stress sweep. The amplitude‐dependent behaviour of the starch and amplitude‐independent nature of the gluten revealed that starch is responsible for the non‐linearity of the flour–water dough system. Adding starch to gluten caused a substantial narrowing of its linear viscoelastic range. © 2002 Society of Chemical Industry     

苹果酵素复合型羊乳的制备及抗氧化活性研究

苹果酵素具有良好的抗氧化活性,为了增加发酵羊乳的抗氧化活性,作者采用苹果酵素与复合发酵剂发酵羊乳,并研究其理化指标及抗氧化活性。依据发酵羊乳的理化指标和感官评价指标,确定苹果酵素添加质量分数、发酵剂类型和发酵剂添加质量分数:苹果酵素添加质量分数4%,B发酵剂添加质量分数为1%时,发酵羊乳蛋白质含量为3.85 g/hg,脂肪含量为3.72 g/hg,非脂乳固体含量为9.28 g/hg,对DPPH自由基清除能力为95.17%,且发酵羊乳凝固状态好,具有发酵羊乳特有的滋味、气味及苹果口味,酸度、甜度合适,为发酵羊乳制品的研究与开发提供理论基础。     

Compositional and functional properties of buttermilk: a comparison between sweet, sour, and whey buttermilk

Buttermilk is a dairy ingredient widely used in the food industry because of its emulsifying capacity and its positive impact on flavor. Commercial buttermilk is sweet buttermilk, a by-product from churning sweet cream into butter. However, other sources of buttermilk exist, including cultured and whey buttermilk obtained from churning of cultured cream and whey cream, respectively. The compositional and functional properties (protein solubility, viscosity, emulsifying and foaming properties) of sweet, sour, and whey buttermilk were determined at different pH levels and compared with those of skim milk and whey. Composition of sweet and cultured buttermilk was similar to skim milk, and composition of whey buttermilk was similar to whey, with the exception of fat content, which was higher in buttermilk than in skim milk or whey (6 to 20% vs. 0.3 to 0.4%). Functional properties of whey buttermilk were independent of pH, whereas sweet and cultured buttermilk exhibited lower protein solubility and emulsifying properties as well as a higher viscosity at low pH (pH ≤ 5). Sweet, sour, and whey buttermilks showed higher emulsifying properties and lower foaming capacity than milk and whey because of the presence of milk fat globule membrane components. Furthermore, among the various buttermilks, whey buttermilk was the one showing the highest emulsifying properties and the lowest foaming capacity. This could be due to a higher ratio of phospholipids to protein in whey buttermilk compared with cultured or sweet buttermilk. Whey buttermilk appears to be a promising and unique ingredient in the formulation of low pH foods.     

Rheological properties of ice cream mixes and frozen ice creams containing fat and fat replacers

Ice cream mixes and frozen ice creams at milk fat levels of 12%, 8%, 6%, 6% plus a protein-based fat replacer, and 6% plus a carbohydrate-based fat replacer were evaluated for viscoelastic properties by dynamic testing with sinusoidal oscillatory tests at various frequencies. The storage modulus (G'), loss modulus (G"), and tan delta (G"/G') were calculated for all the treatments to determine changes in the viscous and elastic properties of the mixes and frozen ice creams due to fat content. In ice cream mixes, G' and G" exhibited a strong frequency dependence. The G" was higher than G' throughout the frequency range (1 to 8 Hz) examined, without any crossover, except for the 12% mix. Elastic properties of the ice cream mixes decreased as fat content decreased. Tan delta values indicated that fat replacers did not enhance the elastic properties of the ice cream mixes. In all frozen ice creams, G' and G" again showed a frequency dependence throughout the range tested (0.5 to 10 Hz). The amount of fat in ice creams and the degree of fat destabilization affected the elasticity in the frozen product. Even though the ice creams did not have significant elastic properties, when compared as a group the samples with higher fat content had higher elastic properties. The addition of protein-based and carbohydrate-based fat replacers did not enhance the elastic properties of the ice creams but did increase the viscous properties.     

Growth and production of enterotoxin A by Staphylococcus aureus in cream

Behavior of Staphylococcus aureus strains 100-A, 196-E, 254, 473, 505, and 521 in sweet (18 to 80% milk fat) and neutralized sour cream was studied. Cream was inoculated to contain approximately 10(3) to 10(4) S. aureus/ml, depending on milk fat content, and was incubated at 4, 22, or 37 degrees C. Determinations were made of aerobic plate count, S. aureus count, and pH. When growth in cream exceeded 10(7) S. aureus/ml, enterotoxin analysis was done. Sweet and neutralized sour cream supported growth of all strains of S. aureus tested. Strains 100-A, 196-E, 473, 505, and 521 grew sufficiently to produce enterotoxin in sweet cream of 18 or 32% milk fat held at 37 degrees C for 18 h or at 22 degrees C for 52 h. Populations of strains 100-A, 196-E, 505, and 521 exceeded 10(6) cells/ml in sweet cream of 36% milk fat held for 18 h at 37 degrees C. Strains 100-A and 521 grew to more than 10(6) cells/ml in sweet cream of 40% milk fat held for 18 h at 37 degrees C. No strain of S. aureus grew to levels associated with detectable enterotoxin production at 4 degrees C within 14 d in any cream. Incubation temperature, milk fat content of cream, and variation among strains influenced the ability of S. aureus to grow and produce enterotoxin.     

Photosensitized oxidation of cholesterol and altered oxysterol levels in sour cream: Effects of addition of cucumber pickles

The aim of this research was to examine whether sour cream (18% fat) is an exogenous source of oxysterols and whether it is possible to improve its antioxidative properties and to modulate cholesterol transformation by adding cucumber. To determine whether cucumber modifies the properties of sour cream, fresh cucumber or cucumber pickle (pH 3.3; 1.5% lactic acid) was added in an amount of 20%. The sour cream samples were then stored under light (450 lx, 590 cd, 120 lm) for 3 wk. After storage, the addition of the cucumber pickle increased total mesophilic aerobic bacteria from 7.5 to 9.3 log cfu/g and increased the l-lactic acid content from 6.1 to 9.7 g/L. The total conjugated linoleic acid content in sour cream with cucumber pickle also increased to 4.5 mg/g fat after storage, whereas the cholesterol content decreased to 3.44 g/kg fat. Importantly, with the addition of cucumber pickle, the total content of cholesterol oxidization products (COP) did not change after storage (1.7 mg/kg fat). By contrast, the total COP content in the control sour cream sample increased from 1.7 to 7.3 mg/kg fat over 3 wk of storage. The dominant COP before and after storage was 7β-hydroxycholesterol. Thus, despite exposure to light, adding cucumber pickle to sour cream modulates cholesterol transformation and effectively inhibits the formation of oxysterols.     

The effect of inulin as a fat replacer on the quality of low‐fat ice cream

The influence of different levels of inulin as fat replacer on the quality of ice cream was investigated. Inulin was added at 2, 4 and 6% to replace milk fat and the experimental ice creams were compared to a control with 10% milk fat. The chemical composition, overrun, water activity, viscosity, melting rate, hardness and colour value were determined. Sensory properties of the ice cream samples were evaluated during storage. The overall acceptability of ice creams prepared with 2 and 4% substitution were similar to the control.     

Dynamic rheological properties and bread‐making qualities of wheat gluten: effects of urea and dithiothreitol

Controlled stress rheometry differentiated glutens from the cultivars under study into ‘extra‐strong’, strong and weak on the basis of their elastic and viscous moduli measured in the linear domain. The mechanical spectra of different glutens revealed no qualitative differences, but exhibited large quantitative differences in the magnitude of the dynamic measurements, ie elastic modulus, G′, viscous modulus, G″, and loss tangent, tanδ. Both covalent and non‐covalent interactions appeared to contribute to these differences. However, disulfide cross‐links proved to be especially important determinants of differences in the elastic characteristics of the glutens. The present study indicated that dynamic rheological parameters of glutens were related to their bread‐making performance, as evidenced by the significant correlations between the dynamic moduli of the glutens and loaf volume. Copyright © 2004 Society of Chemical Industry     

Effects of polymerized goat milk whey protein on physicochemical properties and microstructure of recombined goat milk yogurt

Goat milk whey protein concentrates were manufactured by microfiltration (MF) and ultrafiltration (UF). When MF retentate blended with cream, which could be used as a starting material in yogurt making. The objective of this study was to prepare goat milk whey protein concentrates by membrane separation technology and to investigate the effects of polymerized goat milk whey protein (PGWP) on the physicochemical properties and microstructure of recombined goat milk yogurt. A 3-stage MF study was conducted to separate whey protein from casein in skim milk with 0.1-µm ceramic membrane. The MF permeate was ultrafiltered using a 10 kDa cut-off membrane to 10-fold, followed by 3 step diafiltration. The ultrafiltration-diafiltration-treated whey was electrodialyzed to remove 85% of salt, and to obtain goat milk whey protein concentrates with 80.99% protein content (wt/wt, dry basis). Recombined goat milk yogurt was prepared by mixing cream and MF retentate, and PGWP was used as main thickening agent. Compared with the recombined goat milk yogurt without PGWP, the yogurt with 0.50% PGWP had desirable viscosity and low level of syneresis. There was no significant difference in chemical composition and pH between the recombined goat milk yogurt with PGWP and control (without PGWP). Viscosity of all the yogurt samples decreased during the study. There was a slight but not significant decrease in pH during storage. Bifidobacterium and Lactobacillus acidophilus in yogurt samples remained above 10⁶ cfu/g during 8-wk storage. Scanning electron microscopy of the recombined goat milk yogurt with PGWP displayed a compact protein network. Results indicated that PGWP prepared directly from raw milk may be a novel protein-based thickening agent for authentic goat milk yogurt making.     

Coagulation of buffaloe's milk and resultant Domiati cheese characteristics as affected by salting and replacement with sour cream butter milk

The action of rennet on buffaloe's milk replaced by 5, 10 or 15% of sour cream butter milk salted by either 6 or 10% before renneting or after the rennet action was studied as the non protein nitrogen (NPN) content. Buffaloe's milk without replacement of butter milk was taken as a control. Results revealed that addition of salt to milk before renneting inhibited the rennet action and consequently increased the coagulation time. The inhibition increased with the increase in the salting percent. In contrast, replacement of buffaloe's milk by sour cream butter milk enhanced the rennet action and shortened the coagulation time compared with the control. This effect was increased proportionally by the increase in sour cream butter milk. Enhanced protein breakdown, slightly higher accumulation of free fatty acids and good quality were observed in Domiati cheese treated with sour cream butter milk compared with the control. This effect was pronounced in case of 15% sour cream butter milk.     

Omega‐3 fatty acid‐fortified butter: Preparation and characterisation of textural,sensory, thermal and physico‐chemical properties

The influence of adding flaxseed oil (2.9–5.1%) and flaxseed–whey protein concentrate (WPC) emulsion (4.8–8.6%) to cream as an omega‐3 fatty acid source was evaluated on the thermal, sensory and physico‐chemical properties of the developed butter. Pulsed nuclear magnetic resonance analysis revealed lower saturated fat content in the fortified butter than control butter. Differential scanning calorimetry exotherms and endotherms also corroborated these findings. Fortified butter prepared with 6.8% flaxseed oil–WPC emulsion had 3.7 times more alpha‐linolenic acid content than control and provided nearly 25% of the recommended dietary allowance in one serving. The developed butter exhibited improved spreadability.     

Dynamic rheology of renneted milk gels containing fat globules stabilized with different surfactants

Anhydrous milk fat was emulsified with alpha s1-CN (casein), alpha s2-CN, beta-CN, kappa-CN, alpha-lactalbumin, beta-lactoglobulin, Tween 80, or phosphatidylcholine to produce a 30% fat cream in a 0.1 M imidazole pH 7 buffer. The creams were mixed with skim milk to yield a fat content of 3.4% and the viscoelastic properties of the recombined milks clotted with chymosin were measured. Recombined milk containing globules coated with the more amphipathic and phosphorylated alpha s2-CN and beta-CN clotted faster but gel firmness increased more slowly and weaker gels were formed. Gel firmness increased more rapidly for milks containing globules coated with of alpha s1-CN and kappa-CN that possess more uniformly distributed hydrophobic domains.     

A tribological analysis of cream cheeses manufactured with different fat content

Fat globules interspersed in the protein network have a major role in cream cheese texture that greatly impacts on its consumer acceptability. This study investigated the effects of fat content on the lubrication, rheological, and structural characteristics of cream cheeses manufactured with 0.5, 5.5 or 11.6% (w/w) fat content. All three cheese samples showed viscoelastic, non-Newtonian and shear thinning behaviour. The fat contents were shown to affect tribological behaviour and their high-speed regimes correlated well with the bulk rheology (viscosity). The low-fat content was associated with higher friction, firmer texture and reduced spreadability of the cream cheese, due to fewer fat globules being interspersed in the protein matrix, which was confirmed from confocal images.     

The effect of adding enzyme‐modified cheese on sensory and texture properties of low‐ and high‐fat cream cheeses

The influence of enzyme‐modified cheese (EMC) and fat content on sensory and texture properties of cream cheese was investigated. Enzyme‐modified cheese and fat content were set at three levels each, and organoleptic and texture properties for all experimental cheeses were then determined. Data were analysed using response surface methodology. Both design parameters had significant influence on sensory and texture properties. The EMC did not alter hardness significantly, whereas the higher fat formula had the higher hardness. The results indicated that the optimum level of EMC was less than 1% for high‐fat cream cheeses and at least 5% for low‐fat cream cheeses.     

Science and technology of cultured cream products: A review

Cultured cream, produced by fermentation, has several culinary uses requiring different properties, and this may necessitate using different production technologies. Products with reduced fat content are increasingly popular, but compromised sensory properties are not desired. Here, the technology for the production of cultured cream and the influence of various parameters on its properties are reviewed; the effect of homogenisation on cream of varying fat content and the subsequent fermentation of this cream is given special focus. The structure of low fat (10–15%) cultured cream is dominated by a milk protein acid gel; high fat (≥30%) cultured cream is dominated by a gel structure consisting of coagulated protein-covered fat globules. Cultured cream with approximately 20% fat has neither a dense protein acid gel nor a high density of coagulated protein-covered fat globules. Quality challenges presented by the latter products may be mitigated by addition of milk protein.     

Acid and rennet gelation properties of sheep,goat, and cow milks: Effects of processing and seasonal variation

Gelation is an important functional property of milk that enables the manufacture of various dairy products. This study investigated the acid (with glucono-δ-lactone) and rennet gelation properties of differently processed sheep, goat, and cow milks using small-amplitude oscillatory rheological tests. The impacts of ruminant species, milk processing (homogenization and heat treatments), seasonality, and their interactions were studied. Acid gelation properties were improved (higher gelation pH, shorter gelation time, and higher storage modulus (G′) by intense heat treatment (95°C for 5 min) to comparable extents for sheep and cow milks, both better than those for goat milk. Goat milk produced weak acid gels with low G′ (<100 Pa) despite improvements induced by heat treatments. Seasonality had a marked impact on the acid gelation properties of sheep milk. The acid gels of late-season sheep milk had a lower gelation pH, no maximum in tan δ following gel formation, and 70% lower G′ values than those from other seasons. We propose the potential key role of a critical acid gelation pH that induces structural rearrangements in determining the viscoelastic properties of the final gels. For rennet-induced gelation, compared with cow milk, the processing treatments of the goat and sheep milks had much smaller impacts on their gelation properties. Intense heat treatment (95°C for 5 min) prolonged the rennet gelation time of homogenized cow milk by 8.6 min (74% increase) and reduced the G′ of the rennet gels by 81 Pa (85% decrease). For sheep and goat milks, the same treatment altered the rennet gelation time by only less than 3 min and the G′ of the rennet gels by less than 14 Pa. This difference may have been caused by the different physicochemical properties of the milks, such as differences in their colloidal stability, proportion of serum-phase caseins, and ionic calcium concentration. The seasonal variations in the gelation properties (both acid and rennet induced) of goat milk could be explained by the minor variation in its protein and fat contents. This study provides new perspectives and understandings of milk gelation by demonstrating the interactive effects among ruminant species, processing, and seasonality.     

Physical,textural, and rheological properties of whipped cream affected by milk fat globule membrane protein

This work aims at improving the textural and whipping properties of whipped cream by the addition of milk fat globule membrane protein. The determination of particle size distribution and average diameter of whipped cream showed that the small particle size was shifted to a larger range after milk fat globule membrane protein was added. The average particle size (d_3,2) of whipped cream reached a maximum value of 5.05 µm at 1% milk fat globule membrane protein, while slowly decreased with increasing milk fat globule membrane protein levels from 2% to 5%. In addition, the partial coalescence of fat increased with the increase of milk fat globule membrane protein levels, and the correlation between the whipping time and the overrun of whipped cream was positive. The addition of milk fat globule membrane protein also altered the rheological behaviour of whipped cream, resulting in the increase of modulus G′ and the loss modulus G″. The results also indicated that higher milk fat globule membrane protein level decreased the serum loss of whipped cream while improved its stability. While milk fat globule membrane protein levels had no significant effect on viscosity, its increasing levels effectively improved the hardness, consistency, and viscosity of whipped cream.     

Dynamic rheology of wheat flour dough. II. Assessment of dough strength and bread‐making quality

Controlled stress rheometry revealed that differences in wheat flour dough strengths could be observed by means of dynamic rheological measurements in the region of higher stress amplitude (ie >100 Pa). At lower stress amplitude (τ_o) the values of elastic modulus G′ for weak doughs were higher than those for strong doughs, but they decreased substantially beyond 100 Pa stress amplitude (τ_o), such that the G′ values for strong doughs crossed over the G′ values for weak doughs. Beyond a critical value of stress amplitude (ie 100 Pa), true differences in dough strengths could be seen on the basis of their elastic characteristics, because at large deformations protein–protein interactions played a more dominant role in the rheological behaviour of flour doughs. Dynamic rheological analysis demonstrated a very weak inverse relationship (R² = 0.16) between the G′ values of flour doughs and loaf volume data for 12 wheat cultivars of diverse bread‐making performance. However, the G′ values of glutens showed significant positive relationships with bread‐making performance, explaining 73% of the variation in loaf volume. © 2002 Society of Chemical Industry