Effect of Freezing/Thawing Temperature on the Viscoelastic and Nutritional Qualities of Carrots

This study evaluated and correlated the viscoelastic and nutritional properties of carrots after freezing (–20, –70, and –196^oC) and thawing (4 and 18^oC) treatments. Results showed that all samples exhibited a solid behavior (storage modulus G′ > loss modulus G″) dominating the viscoelastic response. After treatments, G′, G″, hardness, fracturability, springiness, and chewiness of carrots significantly decreased, whereas loss tangent (Tanδ) increased. Compared with other treatments, fast freezing (–196^oC) and thawing (18^oC) better maintained G′, G″, hardness, and fracturability of carrots, and intermediate freezing (–70^oC) better retained springiness, cohesiveness, and chewiness. For nutritional parameters, fast freezing and thawing conditions also contributed to preserving the contents of carotenoids of carrots. Partial least squares regression analysis revealed that β- and α-carotene, lycopene, and soluble sugars were positively correlated with hardness, fracturability, G′, and G″, and negatively with Tanδ in carrots. The variation of viscoelastic parameters could well predict the changes at nutritional levels.     

Viscoelastic behavior of reconstituted Aloe vera hydrogels as a function of concentration and temperature

Viscoelastic properties for reconstituted A. vera hydrogels were evaluated in different ranges of concentration (0.2–1.6%, w/v) and temperature (30–60°C). The storage (G′) and loss (G″) moduli were well described by power function of the frequency (R² > 0.92). The combined effect of concentration and temperature was optimized for reconstituted gel formation, targeting maximum viscoelastic moduli (G₀′ and G′′₀) and minimum slope (n′ and n″) values using response surface methodology. The optimum condition selected was 1.6%, w/v at 30°C having higher gel strength [G′₀ (47.8 Pa.s^n′) and G″₀ (27.4 Pa.s^n′)], as well as minimum slope values [n′ (0.24) and n″ (0.08)]. Further, the effect of initial aging time on the viscoelastic moduli of optimized sample (1.6%, w/v at 30 ± 1°C) was noticed by fitting the intermediate creep ringing data to rheological models. The viscoelastic moduli (G′_J and G′_K) increased with aging time (0–180 min) for optimized A. vera hydrogel, as confirmed by Jeffrey’s and Kelvin-Voigt models. The obtained results suggested that optimized conditions for reconstituted A. vera gel formation could be useful to improve the gel strength which could be useful for various food applications.     

Investigating rennet coagulation properties of recombined highly concentrated micellar casein concentrate and cream for use in cheese making

Highly concentrated micellar casein concentrate (HC-MCC) contains ～18% casein with ～70% of whey proteins removed by microfiltration and diafiltration of skim milk, followed by vacuum evaporation for further concentration. When blended with cream, HC-MCC forms recombined concentrated milk (RCM), which could be used as a starting material in cheese making. Our objective was to investigate the rennet coagulation properties of RCM while varying parameters such as casein level, pH, rennet level, and coagulation temperature. The HC-MCC was mixed with cream using low shear at 50°C for 10 min, followed by cooling to 31, 28, or 25°C and adding rennet, and rheological properties were determined. Rennet coagulation time [RCT, the time at which storage modulus (G′) = loss modulus (G″)] decreased from 8.7 to 7.4 min as casein level increased from 3.2 to 5.7%, without a significant additional difference in RCT at casein levels >5.7%. The initial G″ (G″₀) increased about 10-fold when casein levels were increased from 3.2 to 10.9%, whereas no change in initial G′ (G′₀) was observed. When G′ was measured relative to RCT (i.e., 1, 1.5, or 2 times RCT after RCT was reached, and expressed as G′₁, G′_1.5, and G′₂), log relationship was found between relative G′ and casein level (R² > 0.94). Lowering coagulation temperature from 31 to 25°C increased G″₀ by 6 fold and extended RCT from 7.4 to 9.5 min. After coagulation, relative G′ was initially higher at the lower temperature with G′₁ of 3.6 Pa at 25°C and 2.0 Pa at 31°C, but delayed in further development with G′₂ of 0.8 kPa at 25°C and 1.1 kPa at 31°C. Lowering pH of RCM from 6.6 to 6.2 resulted in reduced RCT from 11.9 to 6.5 min with increased relative G′ after coagulation. When less rennet was used, RCT increased in a linear inverse relationship without changes in relative G′ or G″. The microstructure of RCM coagulum (～11% casein), observed using transmission electron microscopy, confirmed that RCM curd had a rigid protein matrix containing extensively cross-linked protein strands.     

BRAZILIAN HULL-LESS AND MALTING BARLEY GENOTYPES: II. THERMAL AND RHEOLOGICAL PROPERTIES OF STARCH

Thermal and rheological properties of starch isolated from two Brazilian barley experimental lines, malting and hull‐less, are reported. Gelatinization's thermal properties were T_o 53.3 and 58C, T_p 59.4 and 62.7C, and ΔH 6 and 6.8 J/g for the malting and hull‐less starch, respectively. A trend to slightly higher retrogradation rates were obtained for the malting (73.3%) compared with the hull‐less (72.1%) starch, while lower hot‐paste peak and final viscosity were observed in the former (125 and 114 RVU versus 169 and 179 RVU, respectively). Changes in storage (G′) and loss (G″) moduli during heating and cooling showed higher values for the starch from the hull‐less line. During heating, G′was higher than G″and developed at higher temperatures. A trimodal distribution pattern of G″was observed in the starch from the hull‐less barley line. Two G′peaks at 75 and 87.5C were 6.2 and 2.4 times higher, respectively, in the starch from the hull‐less line than that from the malting line.     

Impact of wheat bran addition on the temperature‐induced state transitions in dough during bread‐baking process

Wheat bran‐mediated effects on temperature‐induced state transitions of proofed bread dough were studied as function of its level of replacement (5%–15%) to wheat flour. Proofed dough was subjected to rheological tests at small deformations. During heating of proofed dough from 30 °C to 95 °C, the value of elastic modulus (G′) attained its maximum at a temperature () that represented peak gelatinisation temperature (T_P). Dough with 15% bran depicted significant increase in T_P over other formulations. Bran addition increased glass transition temperature (T_g) of dough and suppressed drop in elastic modulus (G′) at T > T_g. The above events resulted in decreased loaf‐specific volume and increased crumb hardness. The former was caused by retarded bubble expansion during initial stages of baking, explained by reduced uniaxial and biaxial extensibilities of dough. Mean bubble size depicted an inverse relationship with the hardness of breadcrumb.     

Effect of Goat and Cow Milk Ratios on the Physicochemical,Rheological, and Sensory Properties of a Fresh Panela Cheese

Fresh cheeses, Panela type, were manufactured from cow milk and with goat milk incorporation, constituting 4 blends of milks (G10:C90, G20:C80, G30:C70, G40:C60, v/v). The cheeses were analyzed to determine the effect of the different goat milk ratios on the physicochemical, textural, rheological, and sensory properties over 15 d of storage. Significant differences in protein (14.6% to 18.5%), fat (13.0% to 19.4%), and moisture contents (51.7% to 61.3%), pH (6.38 to 6.67), color (L_h > 64.4, a_h > 1.06, b_h > 5.14), textural (σ_f > 14.8 kPa, ε_C: 0.77 to 0.79, elasticity modulus > 13.5 kPa), and rheological parameters (G′ > G′′, G′: 10.6 to 31.9 kPa, G′′: 2.39 to 7.31 kPa, tan δ: 0.21 to 0.24) were detected as a function of the milks ratio, as well as a function of the storage time. The incorporation of goat milk improved the overall quality in the formulation of Panela cheese, enhancing the texture, flavor and aroma, commonly associated with hand‐crafted cheeses when they are used in the proper ratio. Furthermore, the nutritional value of the cheese is increased with the incorporation of goat milk, which can contribute to a better consumer health.     

Impact of arabinoxylan with different molecular weight on the thermo‐mechanical,rheological, water mobility and microstructural characteristics of wheat dough

The aim of this study was to investigate the effects of arabinoxylan with different molecular weight on the wheat dough thermo‐mechanical, rheological, microstructural and water mobility properties. Arabinoxylan was extracted from wheat bran and hydrolysed by endo‐1,4‐β‐xylanase (EC 3.2.1.8 from Trichoderma reesei, 10 000 U g^?1) for 2 min (AX_M) and 10 min (AX_L), respectively. The addition of hydrolysed arabinoxylan AX_L increased the stability time, decreased the setback value of wheat dough and enhanced the values of storage modulus (G′) and loss modulus (G″), while unhydrolysed arabinoxylan (AX_H) reduced these values. Meanwhile, unhydrolysed arabinoxylan increased T₂ relaxation time while hydrolysed arabinoxylan AX_L decreased T₂₁ and T₂₂. Confocal laser scanning microscope (CLSM) results showed that the addition of hydrolysed arabinoxylan AX_L promoted the formation of a more compact and continuous protein network in wheat dough. These results revealed that compared with high molecular weight arabinoxylan, hydrolysed arabinoxylan could improve the rheological properties and processing properties of wheat dough by enhancing the interaction among water molecules, starch and gluten in wheat dough.     

Relationship between physicochemical and rheological properties of starches from Indian wheat lines

Starches from nine Indian wheat lines were evaluated to study the relationships between physicochemical and rheological properties. Large granules (>15 μm) were present in the highest proportion followed by medium (5–15 μm) and small granules (<5 μm). Amylose content ranged between 27.4 and 37.2%. Starch with the highest proportion of large granules (68.9%) showed higher values of G′_peak (576 Pa) and G′_final (432 Pa). Amylose content showed positive relationships with retrogradation, gel firmness, gumminess and adhesiveness while negative with springiness. Cooked starch pastes with the highest amylose content (37.2%) had higher ΔH_ret (0.88 J g^?1), G′_ret (361 Pa), adhesiveness (1.48 Ns), firmness (0.45 N) gumminess (0.22 N) and the lowest springiness (0.88). Amylose–lipid complex (AML) dissociation showed negative relations with swelling power, G′_peak, G′_breakdown and breakdown viscosity (r = ?0.779, ?0.66, ?0.771 & ?0.775, respectively, P < 0.05) while positive relationship with pasting temperature (r = 0.775, P < 0.05).     

Microencapsulation of peppermint oil in an alginate–pectin matrix using a coaxial electrospray system

This study investigated the microencapsulation of peppermint oil in alginate (A)–pectin (P) matrix using an electrospray system where the microcapsules were characterised by determining their compositions and properties. The minimum size (1.58 μm) was obtained with A80P20, while the maximum (3.24 μm) was obtained with A0P100. The zeta potential ranged from ?53.1 to ?21.7 mV with all combinations. The polydispersity index (PDI) tended to increase with the pectin content. There was a gradual increase in microparticles in terms of the loss modulus (G′) and the storage modulus (G″) with increasing frequency. The δ value (loss tangent) increased with the pectin content, indicating more unstable. The encapsulation efficiency increased relative to the alginate content. The maximum encapsulation efficiency (85.15%) was obtained with A80P20. This study showed that an electrospray system can be used to make an alginate–pectin microcapsule containing peppermint oil, which has an adequate composition in terms of rheological properties and encapsulation efficiency.     

Effect of preservatives addition on the shelf-life extensions and quality of flat bread as determined by near-infrared spectroscopy and texture analysis

Many people do not have refrigeration or frozen storage to inhibit mould growth and keep the Arabic bread fresh for more than a few days. Therefore, shelf-life extension is necessary for this type of bread. The present study hypothesised that the addition of preservatives may be done in Arabic flat bread (AFB) to extend shelf-life. Thus, objectives of this study were to evaluate selected preservatives to inhibit mould growth and to employ physical techniques, to monitor bread aging. Three preservatives, fumaric acid (0.2%, F), sodium propionate (0.3%, P), and sodium propionate-fumaric acid mixture (PF) were used. Tensile tests, and near-infrared reflectance spectroscopy (NIRS) were used to monitor bread ageing. The addition of PF in the AFB formula significantly increased the time of tearing at 0 day. For all treatments, the NIRS results showed high R²-values between the actual storage days and NIRS predictions. The NIRS and texture analysis are valuable tools to detect the effect of the preservatives on AFB shelf-life and quality.     

Hydrocolloids and Rheology: Regulation of Visco-elastic Characteristics of Waxy Rice Starch in Mixtures with Galactomannans

Texture and sensory properties of starch solutions or gels, resp., can be influenced by regulating the visco-elastic properties that cannot be adjusted by simply varying the waxy rice starch concentration. Therefore, the hydrocolloid galactomannans guar gum and locust bean gum were used for addition. A total polymer concentration of c = 5% was maintained through all tests, the hydrocolloid fractions varied (c_HK = 0.5%, 1%, 2%). The mixtures were entirely decomposed in an autoclave at 130°C resulting in an almost complete destruction of the granular starch structure. With rheomechanical oscillation measurements in the linear-visco-elastic range the influence of the galactomannans onto viscosity yield and visco-elasticity was determined quantitatively. It was found that the influence on the viscosity is depending on the deformation rate. At low frequencies and with increasing galactomannan fraction the viscosity decreases, while above a critical frequency ω_kr an increase in viscosity could be detected compared to pure starch. The mixtures also displayed an increase in viscous fractions versus elastic fractions compared to pure starch. With increasing galactomannan fraction, the ratio storage modulus/loss modulus is reduced continuously from G′:G″ > 10 (definitely mainly elastic) to G′:G″ = 1 with simultaneously decreasing influence of the frequency. Based on the presented data and knowledge on solution structure of the individual components, a model for describing network structures in mixtures was developed. Changes in viscous-elastic properties are based on a thermodynamic incompatibility between starch and galactomannan fractions. The mixtures contain mixed network structures, with waxy rice starch (permanent network points) and galactomannans (temporary network points) contributing individually and characteristically to the resulting flow behaviour.     

Substitution of wheat starch with non-wheat starches and cross-linked waxy barley starch affects sensory properties and staling of Arabic bread

Substitution of starch from barley, corn, oat, potato, rice or sorghum for prime wheat starch in the formulation of Arabic bread resulted in breads with significantly (P < 0.05) different textural attributes from regular wheat bread except for barley starch. Substitution of waxy barley starch (957 g kg⁻¹ amylopectin) for wheat starch (279 g kg⁻¹ amylopectin) resulted in bread that was not significantly different from regular wheat bread when assessed in the fresh state. However, upon aging, the waxy barley starch-containing bread staled at a significantly (P < 0.05) faster rate than regular wheat bread. Breads made with waxy barley starch cross-linked with 50, 200 or 500 ppm phosphorus oxychloride showed higher enthalpy of melting (ΔH) upon aging and staled faster than the bread formulated with waxy barley starch. These findings suggest that amylopectin retrogradation is one of the determinants of Arabic bread staling and that cross-linking promotes recrystallisation of amylopectin, possibly by keeping the polymer chains in close proximity. The rate of staling in breads formulated with cross-linked waxy barley starch decreased with increasing levels of cross-linking, possibly owing to restrictions in the degree of starch swelling. © 1999 Society of Chemical Industry     

EFFECTS OF ADDED WEIGHTING AGENT AND XANTHAN GUM ON STABILITY AND RHEOLOGICAL PROPERTIES OF BEVERAGE CLOUD EMULSIONS FORMULATED USING MODIFIED STARCH

Stability of beverage emulsion is measured by the rate at which the emulsion creams, flocculates or coalesces, and is generally dependent on rheology of water phase, difference in specific gravities of the two phases and droplet size/distribution of the emulsion. The effects of weighting agents (sucrose acetate isobutyrate and brominated vegetable oil) and xanthan gum on modified starch‐based emulsions were evaluated in this study. Emulsion was formed by addition of 9% coconut oil, in the presence or absence of weighting agents, into the water phase containing modified starch at 10, 12 or 14% without or with the addition of 0.3% xanthan gum. Stabilities of emulsions were evaluated both in the concentrated form used for storage and dilute form used in beverages. The addition of xanthan gum into the water phase decreased the flow behavior index (n) from 0.88 down to 0.31 and increased elastic modulus (G′) over 20 times at elevated frequency (ω = 50 rad/s) and elevated the stability of the emulsion. The xanthan gum‐added emulsion had smaller particle size and demonstrated 14 and 5 times slower phase separation compared to the emulsions without or with the addition of weighting agents, respectively. When the elastic modulus was larger than the viscous modulus (G′ > G″), the emulsions demonstrated greater stability. In dilute beverage solutions, creaming was observed in the absence of xanthan gum.     

Studies on the morphological,thermal and rheological properties of starch separated from some Indian potato cultivars

The starches separated from five different Indian potato cultivars (Kufri Chandermukhi, Kufri Badshah, Kufri Jyoti, Kufri Sindhuri and S1) were investigated for morphological, thermal, rheological, turbidity and water-binding properties. The starch separated from all the five potato cultivars had a granule size ranging between 15–20 μm and 20–45 μm. The shape of starch granules varied from oval to irregular or cuboidal. Starch isolated from cv. Kufri Badshah had largest irregular or cubiodal granules while starch from cv. Kufri Chandermukhi had small and oval granules. The transition temperatures and enthalpy of gelatinization (ΔH_gel) were determined using differential scanning calorimetry (DSC). The enthalpy of retrogradation (ΔH_ret) of gelatinized starch was also determined after 14 days of storage at 4°C using DSC. Kufri Chandermukhi starch showed the lowest ΔH_gel and ΔH_ret while Kufri Badshah starch showed the highest values. ΔH_gel and ΔH_ret values of 12.55 J/g and 6.42J/g, respectively, for Kufri Chandermukhi starch against 13.85 J/g and 8.61 J/g, respectively, for Kufri Bhadshah starch were observed. Rheological properties of starches from different potato cultivars, measured using the Dynamic Rheometer during heating and cooling, also differed significantly. The starch from cv. Kufri Badshah showed the highest peak G′ and G″ and lowest tan δ. The starches having higher peak G′(G′ at gelatinization temperature) showed higher breakdown in G′ and vice versa. The turbidity of gelatinized aqueous starch suspensions from all potato cultivars increased with increase in storage period. Starches with low water binding capacity had higher G′ and G″ and lower tan δ values.     

Comparison of the effect of sugars on the viscoelastic properties of sweet potato starch pastes

Viscoelastic properties of sweet potato starch (SPS) pastes (5% w/w) were studied in the presence of various sugars (sucrose, glucose, fructose, and xylose) at different concentrations (0, 10 and 20%) by small‐deformation oscillatory measurements. Dynamic frequency sweeps at 20 °C indicated that all SPS–sugar mixtures were more elastic than viscous with storage moduli (G′) higher than loss moduli (G′′) at all values of frequency with a frequency dependency. Dynamic moduli (G′ and G′′) values increased with the increase in sugar concentration from 10 to 20%. Changes in the dynamic moduli were more pronounced with xylose in comparison to the control (no sugar) and other sugars. G′ values as a function of ageing time (10 h) at 4 °C continuously increased with time during ageing without a plateau region. In general, G′ values of SPS–sugar mixtures during ageing decreased in the following order: pentose (xylose) > hexose (glucose and fructose) > control > disaccharide (sucrose), indicating that the xylose had the greatest ability in retarding retrogradation of SPS.     

Factors affecting the quality of Arabic bread—additional ingredients

The effect of ascorbic acid and potassium bromate, reducing agents (L -cysteine and sodium metabisulphite), emulsifiers (sodium stearoyl-2-lactylate (SSL) and sucrose fatty acid esters) and a combination of these additives on the quality of Arabic bread has been studied. Statistical analysis indicated that the internal quality parameters of Arabic bread significantly deteriorated with the addition of ascorbic acid and potassium bromate. The addition of reducing agents has the advantage of reducing mixing time and improving dough sheeting quality. SSL (3 g kg^?1) improved the quality of Arabic bread especially after overnight storage. Sucrose ester F-110 had an adverse effect on most aspects of Arabic bread quality.     

Influence of temperature,calcium and sucrose concentration on viscoelastic properties of Prosopis chilensis seed gum and nopal mucilage dispersions

Viscoelastic properties of two nontraditional hydrocolloid dispersions were evaluated. Prosopis chilensis seed gum was evaluated based on temperature (5–80 °C) and added CaCl₂ (0.07%), whereas nopal mucilage was evaluated based on temperature (5–80 °C) and sucrose concentration (0–20%). Viscoelasticity was tested by the small strain oscillatory shear test; storage modulus (G′), loss modulus (G″) and tan δ were reported. Prosopis chilensis and nopal dispersions behaved as weak gels (G’ > G’’) regardless of experimental condition. Raising temperature from 20 to 80 °C significantly increased G’. The gel structure was strengthened by adding CaCl₂ and G’ increased at 40 °C. The sucrose effect depended on concentration and temperature; at low sucrose concentrations, G’ modulus increased regardless of temperature level, but at high concentrations, it decreased at temperatures >40 °C. In conclusion, nopal and Prosopis chilensis dispersions show weak gel structure regardless of experimental condition. G′ increases as temperature increases, and these dispersions could be suitable for food applications requiring heat tolerance.     

Steady and Dynamic Shear Rheology of Fucoidan‐Buckwheat Starch Mixtures

Rheological properties of fucoidan (F) and buckwheat starch (B) mixtures (3% or 6%) at different blending ratios of fucoidans (0, 0.1, 0.2, 0.5 and 1.0%) were investigated in steady and dynamic shear. Steady shear viscosity measurement revealed that aqueous pastes of the BF blends (3%, w/v) had a pseudoplastic and shear‐thinning behavior with flow behavior index (n) values of 0.61–0.68. The substitution of starch with fucoidan polymers significantly lowered the apparent viscosities compared with the pure starch paste and, when mixed with less than 0.5% of fucoidan, the viscosities of the pastes were even lower than those of the starch pastes at the corresponding starch concentrations. According to dynamic viscoelastic measurement performed at 6% total carbohydrate concentration, buckwheat starch mixtures behaved like weak gels and the BF blends containing less than 0.5% fucoidan had considerably lower storage (G') and loss (G') moduli than the starch paste at the corresponding starch concentrations. However, the magnitude of G' increased with fucoidan concentrations over 0.5%, suggesting that a concentration of fucoidans > 0.5% might enhance the formations of three‐dimensional networks and crosslinking of the starch samples, probably because of the mutual exclusion between starch and fucoidan polymers through the phase separation process. This study indicates that it is possible to obtain the BF blends having various rheological properties by changing the concentration of fucoidan polymers.     

Effect of mechanically damaged starch on wheat flour,noodle and steamed bread making quality

Wheat flour was ground in an ultrafine pulveriser to obtain different levels of damaged starch (DS). The effect of DS content on physicochemical properties of flour and quality attributes of Chinese noodles and northern‐style Chinese steamed bread were investigated. Results showed that the degree of starch damage raised from 6.54% to 12.06% as grinding intensity increased from 0 to 130 Hz (P < 0.05). The falling number, sedimentation value, starch pastes' viscosity, dough proofing stability were negatively, while water absorption, pastes thermal stability, the degree of starch pastes and dough level were positively correlated with DS content, respectively (P < 0.05). The increase in DS content from 6.54% to 8.86% did not lead to a deterioration of texture characteristic, which might be attributed to the slight declining in hardness while enhancing in springiness and cohesiveness. The flour with DS content of 6.54–9.66% was suitable for steamed bread making.     

Thermal and Rheological Properties of Dough and Bread as Affected by Various Cross‐linked Cornstarch Substitutions

Various kinds of cross‐linked cornstarches (CLCSs) were used to substitute for wheat flour (5 and 10%), and thermal and rheological properties of dough and bread were examined. The pastes of the substituted flours had lower gelatinization temperatures and higher viscosities than those of the control. The substitution with low‐swelling waxy CLCS (L‐CWCS) had higher paste consistency and lower transition enthalpy than those with high‐ or low‐swelling non‐waxy CLCS (H‐CNCS or L‐CNCS) or the control. The substitutions with L‐CNCS made harder doughs and higher firmness of breadcrumbs during storage than the others. The specific volumes of breads with cross‐linked cornstarch substitutions were slightly smaller than that of the control because of the lack of gluten. The firmness of bread substituted with L‐CWCS was softer than that with H‐ or L‐CNCS. In addition, the breads with H‐CNCS were softer than that with L‐CNCS. The results showed that the compression stress of dough was highly positively correlated with firmness of breads after storage for one and three days (r = 0.876, P < 0.01 and r = 0.809, P < 0.05, respectively). Also, significant positive correlations were detected between the transition enthalpy of dough and firmness of breads after storage for one and three days (r = 0.840, P < 0.05 and r = 0.853, P < 0.05, respectively), whereas no correlation between transition enthalpies of breadcrumbs and firmness of breads was observed.