Measurement of dynamic rheology during ageing of gelatine–sugar composites

The effect of sugars (sucrose, glucose and xylose) at different concentrations (0, 10, 20, 30, 40 and 50%) on the dynamic rheological properties of gelatine (2% w/w) was investigated during ageing. Storage moduli (G′), when measured at 5 °C, decreased with increasing concentration of added sugar. Xylose was found to induce the greatest reduction in the values of G′. G′ values, measured as a function of ageing time (10 h) at 5 °C, increased rapidly at the initial stage and then reached a pseudoplateau region after long ageing times. Increasing the sugar concentration resulted in a decrease in the pseudoplateau values. The rate constant (K) for structure development of gelatine during ageing was described by apparent first‐order kinetics. G′ and K values in gelatine–sugar composites increased in the following order: xylose < glucose < sucrose. The magnitudes of G′ at the end of ageing were much greater than those of G′′, showing a small dependence (slope = 0.005–0.088) on frequency (ω).     

Rheology of Rice Starch‐Sucrose Composites

The effect of sucrose at different concentrations (0, 10, 20 and 30%) on rheological properties of rice starch pastes (5% w/w) was investigated in steady and dynamic shear. The steady shear properties of rice starch‐sucrose composites were determined from rheological parameters for power law and Casson flow models. At 25°C all the starch‐sucrose composites exhibited a shear‐thinning flow behavior (n=0.25–0.44). The presence of sucrose resulted in the decrease in consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc). Dynamic frequency sweeps at 25°C indicated that starch‐sucrose composites exhibited weak gel‐like behavior with storage moduli (G′) higher than loss moduli (G′′). G′ and G′′ values decreased with the increase in sucrose concentration. The dynamic (η*) and steady‐shear (η_a) viscosities at various sucrose concentrations did not follow the Cox‐Merz superposition rule. G′ values as a function of aging time (10 h) at 4°C showed a pseudoplateau region at long aging times. In general, the values of G′ and G′′ in rice starch‐sucrose composites were reduced in the presence of sucrose and depended on sucrose concentration.     

Rheology of Mixed Systems of Sweet Potato Starch and Galactomannans

The effect of galactomannans (guar gum and locust bean gum) at different concentrations (0, 0.2, 0.4 and 0.6%, w/w) on rheological properties of sweet potato starch (SPS) was studied. The flow behaviors of SPS‐galactomannan mixtures were determined from the rheological parameters of power law and Casson models. The SPS‐galactomannan mixtures had high shear‐thinning fluid characteristics (n = 0.30‐0.36) exhibiting yield stress at 25°C. The presence of galactomannans resulted in the increase in consistency index (K), apparent viscosity (η_a,100) and Casson yield stress (σ_oc). In the temperature range of 25‐70°C, the mixtures followed the Arrhenius temperature relationship. Dynamic rheological tests at 25°C indicated that the SPS‐galactomannan mixtures had weak gel‐like behavior with storage moduli (G′) higher than loss moduli (G") over most of the frequency range (0.63‐62.8 rad/s) with frequency dependency. The magnitudes of dynamic moduli (G′, G" and η*) of the SPS‐galactomannan mixtures were higher than those of the control (0% gum), and increased with an increase in gum concentration. The tan δ (ratio of G"/G′) values (0.41‐0.46) of SPS‐guar gum mixtures were much lower than those (0.50‐0.63) of SPS‐locust bean gum mixtures, indicating that there was a more pronounced effect of guar gum on the elastic properties of SPS.     

The effect of γ-irradiation on the non-enzymatic browning reaction in the aqueous model solutions

Aqueous solutions of sugars (xylose, arabinose, fructose, glucose or sucrose), alone or in the presence of amino acid (lysine), were γ-irradiated at 0, 5, 10, 20 and 30 kGy at room temperature. Also evaluated were differences between irradiation and heat treatment. Absorbances at 420 nm, of the irradiated sugar–amino acid solutions, were increased although no browning was observed in the irradiated sugar or amino acid alone. The degree of browning of the irradiated sugar–amino acid solution increased with increasing irradiation dose and was dependent on the type of sugar. The non-reducing sugar, sucrose, did not react with lysine by heating for 4 h at 80 °C; however, the irradiated sucrose–lysine solution showed the non-enzymatic browning reaction and it had a higher reactivity than other sugars. For the sugar–lysine solution irradiated at 30 kGy, browning was in the following order of intensity: sucrose > fructose > arabinose > xylose > glucose. Furfural compounds (5-hydroxymethylfurfural and 2-furaldehyde) were not detected in any irradiated samples.     

Steady and Dynamic Shear Rheology of Rice Starch‐Galactomannan Mixtures

Rheological properties of rice starch‐galactomannan mixtures (5%, w/w) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) of guar gum and locust bean gum (LBG) were investigated in steady and dynamic shear. Rice starch‐galactomannan mixtures showed high shear‐thinning flow behaviors with high Casson yield stress. Consistency index (K), apparent viscosity (η_a,100) and yield stress (σ_oc) increased with the increase in gum concentration. Over the temperature range of 20–65°C, the effect of temperature on apparent viscosity (η_a,100) was described by the Arrhenius equation. The activation energy values (E_a = 4.82–9.48 kJ/mol) of rice starch‐galactomannan mixtures (0.2–0.8% gum concentration) were much lower than that (E_a = 12.8 kJ/mol) of rice starch dispersion with no added gum. E_a values of rice starch‐LBG mixtures were lower in comparison to rice starch‐guar gum mixtures. Storage (G′) and loss (G′′) moduli of rice starch‐galactomannan mixtures increased with the increase in frequency (ω), while complex viscosity (η*) decreased. The magnitudes of G′ and G′′ increased with the increase in gum concentration. Dynamic rheological data of ln (G′, G′′) versus ln frequency (ω) of rice starch‐galactomannan mixtures have positive slopes with G′ greater than G′′ over most of the frequency range, indicating that their dynamic rheological behavior seems to be a weak gel‐like behavior.     

Pectin–sucrose–Ca2+ interactions: effects on rheological properties

The effects of varying concentrations of pectin (4.5–6.5%, w/w), sucrose (40–60%, w/w) and calcium (20–60 mg/g pectin) on the viscoelastic properties of pectin dispersions at pH 3.0 were investigated. Pectin samples used were extracted from pomelo fruit peels (Citrus grandis) grown in Malaysia. The dynamic rheological parameters (G′, G″, δ and η*) of pectin–sucrose–calcium dispersion were determined at 1.5% strain from 90–20°C at a cooling rate of 3°C min⁻¹. Plots of G′ and G″ against frequency (rad s⁻¹) showed G″>G′ throughout the frequency range with no occurrence of crossover for most of the pectin dispersions. In addition both storage (G′) and loss (G″) moduli of the dispersions increase on cooling. Increasing pectin, sucrose and calcium concentrations increased G′ and G″ with pectin having the greatest effect. Interactions amongst the three factors were also studied. At lower pectin concentrations, addition of Ca²⁺ increased G′ at all temperatures. This effect was also observed at higher pectin concentrations at 20°C but not at 90°C. The opposite effect was observed with the addition of sucrose, i.e. addition of sucrose at a higher pectin concentration increased G′ whereas at a lower pectin concentration no effect was observed. Interaction between calcium and sucrose gave rise to an increase in G′ when Ca²⁺ was added at high sucrose concentrations, but a decrease in G′ was evident at low sucrose concentrations. Dispersions of pectin alone or in combination with sucrose exhibited a more liquid-like behaviour with G″>G′. However, in the presence of Ca²⁺, mechanical spectra of G′>G″ were obtained.     

Steady and dynamic shear rheology of sweet potato starch–xanthan gum mixtures

The effect of xanthan gum at different concentrations (0.2–0.6% w/w) on the rheological properties of sweet potato starch (SPS) pastes was evaluated under steady and dynamic shear conditions. The presence of xanthan resulted in an increase in the consistency index and vane yield stress of SPS. The effect of temperature on the apparent viscosity of SPS–xanthan mixtures is well described by the Arrhenius equation. Dynamic moduli (G′, G″, and η^*) values of the mixtures increased with an increase in xanthan concentration while the tan δ values decreased. The addition of xanthan appeared to contribute to the elastic properties of the weak network of the SPS pastes. The structure development rate constant (k) of gelation during ageing was strongly influenced by the presence of xanthan. This suggests that the phase separation process caused by the incompatibility phenomena between the amylose component in starch and xanthan can increase the elastic characteristics of the SPS–xanthan mixtures.     

Studies on the free sugars,water-soluble gums and hemicelluloses from barley grains and malts

The free sugars, water-soluble gums, and hemicelluloses have been isolated from four barley grain samples [Hordeum vulgare (L.)], and from their commercial malts. Arabinose, xylose, galactose, glucose, fructose, maltose and sucrose occur as free sugars in the grains and the proportions of these sugars increase on malting. Mannose also occurs as a free sugar in the malts. The water-soluble gums contain arabinose, xylose, lesser amounts of mannose and galactose, and varying amounts of glucose. The aqueous-ethanol supernatants from the hot-water extracts are glucans of low molecular weight. The hemicellulose A polymers contain arabinose, xylose, mannose and glucose. Wide variations in the mannose and glucose contents were observed in these polysaccharides. The hemicellulose B polymers are arabinoxylans, containing lesser amounts of galactose and glucose. The aqueous-ethanol supernatants from the hemicellulose B precipitations contain arabinose, xylose, mannose, galactose and glucose. These polysaccharides differ markedly from those present in the aqueous-ethanol supernatants of the hot-water extracts. All polysaccharides are modified to varying degrees during malting.     

Dynamic Rheological and Thermal Properties of Acetylated Sweet Potato Starch

Dynamic rheological and thermal properties of acetylated sweet potato starch (SPS) pastes (5%, w/w) were evaluated as a function of the degree of substitution (DS). The transition temperatures (T_o, T_p and T_c) and enthalpy of gelatinization (ΔH) of acetylated SPS, which were determined using differential scanning calorimetry, were lower than those of native starch, and significantly decreased with an increase in DS. Magnitudes of storage modulus (G′), loss modulus (G′′) and complex viscosity (η*) of acetylated SPS pastes were determined using a small‐deformation oscillatory rheometer. Dynamic moduli (G′, G′′ and η*) values of acetylated SPS pastes except for 0.123 DS were higher than those of native starch, and they also decreased with an increase in DS. The tan δ (ratio of G′′/G′) values (0.37–0.39) of acetylated SPS samples were lower than that (0.44) of native starch and no significant differences were found among acetylated SPS samples, indicating that the elastic properties of SPS pastes were affected by acetylation but did not depend on DS. The G′ values of acetylated SPS during aging at 4°C for 10 h were much lower than those of native starch, showing that the addition of acetyl groups produced a pronounced effect on the retrogradation properties of SPS.     

Dynamic Rheology of Rice Starch‐Galactomannan Mixtures in the Aging Process

The effect of galactomananns (guar gum and locust bean gum) at different concentrations (0, 0.2, 0.4, 0.6 and 0.8%, w/w) on the dynamic rheological properties of aqueous rice starch dispersions (5%, w/w) was investigated by small‐deformation oscillatory measurements during aging. Magnitudes of storage (G′) and loss (G′′) moduli measured at 4°C before aging increased with the increase in gum concentration in the range of 0.2–0.8%. G′ and G′′ values of rice starch‐locust bean gum (LBG) mixtures, in general, were higher than those of rice starch‐guar gum mixtures. G′ values of rice starch‐guar gum mixtures as a function of aging time (10 h) at 4°C increased rapidly at initial stage and then reached a plateau region at long aging times. However, G′ values of rice starch‐LBG mixtures increased steadily without showing a plateau region. Increasing the guar gum concentration resulted in an increase in plateau values. The rate constant (K) for structure development during aging was described by first‐order kinetics. K values in rice starch‐guar gum mixtures increased with the increase in guar gum concentration. G′ values of rice starch‐galactomannan mixtures after aging were greater than those before aging.     

THE EFFECT OF CARBOHYDRATE ADJUNCTS ON BREWER'S WORT FERMENTATION BY SACCHAROMYCES UVARUM (CARLSBERGENSIS)*

The use of carbohydrate adjuncts such as sucrose, fructose and glucose in brewer's wort significantly modifies the initial wort sugar spectrum and also the pattern of sugar uptake during fermentation by a strain of Saccharomyces uvarum (carlsbergensis). Under these conditions, the concentration of glucose and fructose in the wort was observed to increase when compared to worts in which corn starch was employed as an adjunct and glucose was taken up at a faster rate than fructose. The increase in glucose concentration in the wort also resulted in severe repression of maltose and maltotriose utilization with significant levels of these sugars remaining in the beer produced.     

Glass Transition Study in Model Food Systems Prepared with Mixtures of Fructose,Glucose, and Sucrose

Abstract: The glass transition temperature of model food systems prepared with several glucose/fructose/sucrose mass fractions was studied using differential scanning calorimetry (DSC). A distance‐based experimental design for mixtures of 3 components was used to establish the proportion of sugars of the model systems. Thus, 32 compositions including individual sugars and sugar mixtures, both binary and ternary were prepared and analyzed. Thermograms showing the complete process of heating–cooling–reheating were used to determine the precise glass transition temperature during cooling () or reheating () in amorphous sugars. The Scheffe cubic model was applied to experimental results to determine the influence of sugar composition on the glass transition temperature (P < 0.05). The final model proved to be appropriate (R² > 0.97, CV < 9%, model significance <0.0001) to predict the T_g values of any dry mixture of amorphous fructose, glucose, and sucrose. Practical Application: The experimental values of T_g and the mathematical model proposed in this work may be of great use for making available T_g data that involves the mixture of more than 2 sugars and thus could be used as a tool for predicting the storage stability and quality of dehydrated products such as fruit powders.     

Adsorption kinetics of BSA at air–sugar solution interfaces as affected by sugar type and concentration

The influence of glucose, sucrose and fructose at concentrations ranging from 0 to 40 wt.% on the adsorption kinetics of bovine serum albumin (BSA) at air–aqueous solution interfaces at 20 °C was measured using drop shape analysis. The rate of adsorption of proteins decreased in the presence of sugars. The diffusion coefficient of BSA in 40 wt.% sucrose solutions, calculated from the initial period of protein adsorption, was two orders of magnitude lower than the diffusion coefficient of BSA dissolved in pure water. The decrease of the diffusion coefficient with sugar concentration (δD_eff/δc_sugar) was appreciably higher at low sugar concentrations (<10 wt.%). Diffusion coefficients in the presence of sucrose were smaller than in the presence of glucose or fructose. Results were attributed to an increase in solution viscosity, preferential interactions of sugars with protein surfaces and an increased hydrophilicity of protein surfaces due to preferential hydration.     

Rheological Properties of Honey from Burkina Faso: Loss Modulus and Complex Viscosity Modeling

This study evaluated the rheological behavior of Burkina Faso honey and the use of exponential and polynomial models to predict the influence of chemical composition and temperature on the viscoelastic parameters: complex viscosity (η*) and loss modulus (G’’). Samples were first characterized by evaluating: water activity, 5-hydroxy methyl furfural, sugars (fructose, glucose, and sucrose), electrical conductivity, moisture, and color. Dynamic rheological properties were obtained at different temperatures (5, 10, 15, 20, 25, 30, and 40°C). All the honeys displayed Newtonian behavior. Complex viscosity and loss modulus can be predicted based on the chemical composition and temperature using polynomial models (R² > 98.00%).     

The composition of maturing Omani dates

The composition of two varieties of Omani dates, fard and khalas, was determined as maturity progressed. Free sugars and dietary fibre content were examined in detail. High-performance liquid chromatography (HPLC) of the extracts showed that at the early green stage (Arabic kimri), dates contained small amounts of glucose and fructose. At the intermediate yellow (khalal) and red (rutab) stages, large amounts (500–565 g kg⁻¹ dry weight) of sucrose had accumulated, but no additional glucose or fructose was detected. At the final mature (tamar) stage, all sucrose was converted to glucose and fructose (>800 g kg⁻¹ dry weight). Dietary fibre, determined as non-starch polysaccharides (NSPs) by gas chromatography (GC), decreased from 250 g kg⁻¹ (kimri) to 50 g kg⁻¹ (tamar) on a dry weight basis. The principal monomers of NSPs were glucose, galactose, xylose, mannose, arabinose and rhamnose. On a dry weight basis, pectin, protein and ash contents decreased as the dates matured. On a fresh weight basis, changes in NSPs, pectin, protein and ash could be attributed to loss of moisture and the accumulation of sucrose initially, or of invert sugar later as maturation progressed. © 1999 Society of Chemical Industry     

The physico-chemical properties of commercial canola protein isolate-guar gum gels

Biopolymer mixtures impart desirable texture to foods. Dynamic rheology was used to characterize canola protein isolate (CPI)‐guar gum gels. The effects of pH, salt, guar gum and protein concentrations on the gelling ability of CPI were evaluated. Factorial and response surface optimization models were used to identify the optimum conditions (20%, w/v CPI; pH 10; 1.5%, w/v guar gum; 0.05 m NaCl) that would simultaneously maximize G′ (≥28 000 Pa) and minimize tan δ (<0.17) values of CPI‐guar gum gels. Although pH > 8 is unconventional in food systems, strong and elastic CPI‐guar gum gels (G′ =56 440 Pa; tan δ = 0.18) were produced at pH 10, whereas gels prepared at pH 6 were less elastic (G′ = 2726 Pa; tan δ = 0.2). Under the optimum conditions, CPI alone formed a stronger gel (G′ = 64 575 Pa; tan δ = 0.15) than CPI‐guar gum mixture, suggesting that guar gum interfered with protein gelation.     

Influence of freezing process on free sugars content of papaya and banana fruits

Changes in individual sugar content (fructose, glucose and sucrose) during freezing and frozen storage have been evaluated by HPLC on papaya (Carica papaya grupo Solo var Sunrise), fruits proceedings from female and hermaphrodite flowers, and banana (Musa cavendishii var enana). Effects of thermal treatments, such as blanching and microwaving, prior to freezing banana fruit were examined. Both an increase in total sugar levels of papaya samples during freezing and a decrease in sucrose, by invertase, were found followed by an increase in fructose and glucose. A slight decrease in total sugars of banana samples during freezing and storage has been observed, with no significant differences between the pretreatments applied. © 1998 SCI.     

Sugar and Soluble Solids Changes in Refrigerated Sweet Corn (Zea mays L)

Three sweet corn (Zea mays L) genotypes, one cultivar each, were tested for sugar and soluble solids changes at 6°C for 5 days. Genotypes and cultivars were sugary (su), ‘Silver Queen’; sugary enhanced (se), ‘Incredible’ and super sweet (sh 2), ‘How Sweet It Is.’ Fructose, glucose, sucrose, maltose, total sugars and °Brix were measured. Sucrose predominated. Generally, °Brix, fructose, glucose and sucrose decreased and maltose increased, sh 2 had lowest °Brix and highest sucrose and total sugars, and su had highest °Brix and lowest sucrose and total sugars, su consisted of 3.8% total sugars (DWB); se, 7.2% and sh 2, 10.9%. Overall correlation coefficient between °Brix and total sugars was ?0.99.     

不同品种烤烟成熟期糖代谢酶活性及基因的表达分析

为了探究不同品种烤烟成熟期糖代谢的变化规律,明确烟叶品质形成的分子作用机理。以烤烟品种秦烟96、豫烟6号和K326为试验材料,测定分析了烤烟成熟期水溶性糖组分（葡萄糖、果糖、麦芽糖、蔗糖、还原糖和可溶性总糖）含量、糖代谢关键酶活性及基因表达的变化。结果表明,3个品种烤烟水溶性糖组份含量变化趋势基本一致,各水溶性糖（蔗糖除外）含量呈先升高后降低的变化趋势,烟叶成熟时其含量达到峰值;蔗糖含量呈双峰波动,烟叶成熟时蔗糖含量较低。烟叶打顶至适熟阶段,SPS和AI酶活性对烟叶中水溶性糖的积累贡献最大,NtINV对烟叶糖代谢起主要调控作用;当烟叶由适熟至过熟时,AI酶活性主要参与烟叶糖代谢活动,而SS和SPS则对蔗糖积累起重要作用,NtSS和NtSPS对烟叶糖代谢起主要调控作用。同一生态环境和栽培条件下,豫烟6号内含物质充实,具有较高的水溶性糖分含量,SPS和AI酶活性的差异可能是造成烟叶糖组分及含量不同的重要原因。     

Influence of Sugars on Heat Inactivation, Injury and Repair of Saccharomyces cerevisiae

The type of sugar in the heating and recovery media affected the rate of inactivation and repair capability of a Chablis strain of Saccharomyces cerevisiae. The rate of heat inactivation decreased with decreasing a_w in glucose and fructose but not in sucrose solutions. At any a_w the order of susceptibility to inactivation of yeast cells was consistently: fructose, glucose, and sucrose. In fructose, a major proportion of the survivors exhibited sublethal injury. When suspended in solutions containing the various sugars after heating and incubated for up to 18 hr prior to plating, the type of sugar in the solution influenced the ability of cells to repair injury.