Effects of Arabinoxylans on Thermal Behavior of Frozen Wheat Doughs as Measured by DSC, DMA, and DEA

ABSTRACT: The effects of water extractable arabinoxylans (WEA) on physical state of frozen wheat dough with added sucrose, NaCl, and their mixture were investigated using DSC, DMA, and DEA. DSC thermograms were obtained for annealed samples, and they showed only an endothermic peak of ice melting. Annealed samples were also analyzed using DMA and DEA with both dynamic heating and isothermal steps. Added sucrose and NaCl decreased the onset temperature of ice melting and it decreased with increasing WEA concentration. Isothermal measurements showed an a-relaxation peaks, taken as the T_g'. Added NaCl had a great depressing effect on the T_g' at low frequencies as measured by DEA.     

EFFECTS OF MOISTURE,SUCROSE, NaCl,AND ARABINOXYLAN ON RELAXATION IN WHEAT DOUGH AS MEASURED BY DMTA

The effects of sucrose, NaCl, and arabinoxylan on the α-relaxation of wheat doughs with different water contents were investigated using Dynamic Mechanical Thermal Analysis (DMTA). DMTA measurements were made at the heating rate of 2°C/min from at least 30°C below the observed onset of the α-relaxation (glass transition) to at least 30°C above the transition. The glass transition temperature, T_g , was taken from the onset temperature of the decrease in storage modulus (G′). The frequencies used were 0.1, 1, and 5 Hz and amplitude was 16 μm. The storage modulus, G′, showed α-relaxation in all doughs with added ingredients. Added ingredients decreased the glass transition temperature of dough. The T_g of doughs with different ingredients decreased with increasing water content of doughs over the whole a_w range used (0.113–0.753). Also, the T_g increased with increasing frequency.     

Dynamic Mechanical Analysis for Glass Transitions in Long Shelf-Life Bread

Dynamic Mechanical Analysis (DMA) showed three thermal transitions in meal, ready-to-eat (MRE) bread, resulting in various degrees of change in the viscoelastic property. The moisture-dependent transition at an extremely low temperature (-90°C to – 50°C) was due to humcctants added, while that at a higher temperature T1 was possibly due to ice melting and the polymer components. T1 increased from ～?10°C at 29% moisture to ～ 150°C as moisture decreased to 2%. This correlated with hardening of the sample. A moisture independent transition at ～ 10-15°C by DMA was identified as a melting process of lipids (shortening). During storage, the magnitude of tan 8 peak decreased but its peak temperature did not change. No evidence of any network could be observed by DMA throughout 3 yr storage.     

Annealing effects on structural changes and thermal shrinkage of poly(lactic acid) draw-textured filaments

To control the thermal shrinkage of poly(lactic acid) draw-textured yarns, the annealing effects on structural changes and thermal shrinkage were investigated. Specifically, annealing temperatures of 100 and 160°C and annealing times of 10–50?min per every 10?min were investigated. Differential scanning calorimetry thermograms revealed that filaments annealed at 100°C produced double melting peaks due to crystal imperfections, while those annealed at 160°C for more than 30?min showed a single melting peak. Moreover, wide angle X-ray scattering revealed that annealing at higher temperatures led to better developed crystal structures. Although, the crystal structure developed by annealing birefringence indicated that average molecular orientation was not greatly affected. Yarns annealed at 160°C showed the least thermal shrinkage of 2%, while those annealed at 100°C decreased from 7.9–5.4% with increasing annealing time.     

Effect of additives on the thermo-mechanical behaviour of dough systems at sub-freezing temperatures

The aim of this study was to examine the effects of different additives, ascorbic acid, α-amylase, protease, hemicellulase, gluten, and gum guar, on thermo-mechanical dough properties at sub-freezing temperatures as measured by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMA). The DSC thermograms showed that dough with a combination of ascorbic acid and hemicellulase had greater amount of water unable to crystallize and a lower co-operativity in ice-melting transition, indicating more polymer–water interactions. DMA studies permitted identification of three peaks, which were related to the ice melting, α-relaxation and β-relaxation. α-transition occurred over a temperature range of ∼40 °C and the ascorbic acid and their combination with hemicellulase, amylase, protease and gum guar increased temperature transition. An increment of the matrix viscosity due to higher number of inter- and intra-molecular interaction caused by oxidation of gluten proteins (ascorbic acid), and the increment of aggregated solid or generated molecules in the unfrozen phase could explain the increment in this transition.     

Extracellular Ice Nucleators from Pantoea Ananas: Effects on Freezing of Model Foods

Parameters of freezing of sucrose solutions and emulsions were evaluated using differential scanning calorimetry (DSC) at cooling rates of 1 to 20°C/min. The differential and cumulative nucleation spectra of extracellular ice nucleators (ECINs) were established using a w/o emulsion technique. Freezing curves were obtained in a cabinet at ?7 and ?12°C. The ECINs increased the ice nucleation temperature and reduced the time of the supercooling stage. Although the time of phase transition increased in the presence of ECINs, the total time of freezing decreased. The ECINs caused lower onset temperatures of freezing as compared to the original cells.     

Influence of Annealing Temperature on Tg′ of Cooked Rice Stick Noodles

T_g′, a glass transition temperature under conditions of maximal freeze concentration, is important to the stability of frozen food. The procedures for using differential scanning calorimetry (DSC) to measure T_g′ have been reported under different experimental conditions. The aims of this study were to investigate the T_g′ of cooked rice stick noodles, and to determine the effect of the annealing temperature on its T_g′ value using DSC. Cooked rice stick noodles in aluminum DSC pans were scanned from ?60°C to 25°C at 5°C/min. to locate the apparent T_g′, which was ?5.3°C in the non-annealed state. When subjected to 4 different annealing temperatures of ?2, ?6, ?8 and ?10°C for 15 minutes, the T_g′ of cooked rice stick noodles was ?5.3, ?4.0, ?4.2, and ?4.9°C, respectively. The value of T_g′ was clearly observed in the annealed sample at ?6°C. The annealing process allowed time for the maximum formation of ice. This study showed that annealing at a temperature slightly below T_g′ gave a higher and more accurate value.     

Determination of Oxygen Solubility in Liquid Foods Using a Dissolved Oxygen Electrode

A rapid method for determining oxygen solubility in foods was introduced. Fructose, glucose, sucrose, orange juice, apple juice, grape juice, grapefruit juice, lemonade, and tomato juice had similar oxygen solubilities at comparable °Brix readings. The equation: In [ppm O₂] = 2.63 ? 0.0179 (°Brix) ? 0.0190 (°C) estimated to within 5% the oxygen solubility of sugar solutions and fruit juices at temperatures between 4°C and 40°C. At likely food concentrations, citric acid, ascorbic acid, and NaCl reduced oxygen solubility by less than 10%. Tests for component interactions were also conducted. There was no measurable synergism or antagonism between fructose, glucose, and sucrose with or without organic acids.     

Differential Scanning Calorimetry Analysis of the Effects of Heat and Pressure on Protein Denaturation in Soy Flour Mixed with Various Types of Plasticizers

The effects of heat and pressure on protein denaturation in soy flour were explored by an experimental design that used pressure (atmospheric to 600 MPa), temperature (room to 90 °C), time (1 to 60 min), and type of aqueous plasticizer (NaCl, sucrose, betaine, and lactobionic acid (LBA)) as factors. When 50% (w/w) soy flour‐water paste was high hydrostatic pressure (HHP)‐treated for 20 min at 25 °C, the treatment at 200 MPa showed a small effect on denaturation of only the 7S soy globulin, but the treatment at 600 MPa showed a significant effect on denaturation of both the 7S and 11S soy globulins. The treatment at 60 °C showed a less‐pronounced effect on denaturation of the 11S globulin, even at 600 MPa, but that at 90 °C showed a similar extent of denaturation of the 11S globulin at 600 MPa to that at 25 °C. Chaotropic 2N NaCl, 50% sucrose‐, 50% betaine‐, or 50% LBA‐water solutions showed protective effects on protein denaturation during HHP treatment at 25 °C. Although LBA enhanced the extent of thermostability of soy protein less than did 2N NaCl, LBA exhibited better stabilization against pressure. The results from DSC analysis demonstrated that thermostable soy proteins were not always barostable.     

Thermal Transitions in Gelatinized Wheat Starch at Different Moisture Contents by Dynamic Mechanical Analysis

Gelatinized starch was analyzed by DMA and the resulting overlapped tan 5 curve was characterized. At high moisture contents (>30% w/w), transitions around ice melting region of tan 5 peak (>50°C wide) showed skewness at the low temperature side. After deconvolution, a symmetrical, sharp, main peak was correlated with the ice melting endotherm but the cause of the lower temperature asymmetrical peak was not identified. At <30% moisture, two deconvoluted Gaussian peaks indicated at least two separate, broadly distributed domains (slightly frequency dependent). Transitions (other than ice melting), if caused by glassy rubbery transitions, were small in tan 5 and broad (50–100°C wide).     

Technological Assessment of Chestnut Flour Doughs Regarding to Doughs from Other Commercial Flours and Formulations

The technological assessment of chestnut flour doughs was studied using Mixolab® apparatus, establishing a comparison with gluten (soft, hard and whole wheat) and gluten-free (rice and yellow corn) flour doughs as well as corn starch pastrymaking and breadmaking formulations. This equipment measures the torque in function of temperature and time, firstly at 30 °C (mixing curve) and secondly the mixing during heating (4 °C/min up to 90 °C) and cooling (4 °C/min up to 50 °C) steps (complete curve). Different hydrations of doughs ranging from 41.4% to 68.5% (flour basis) were necessary to reach the torque of 1.10?±?0.07 Nm. Parameters of mixing such as water absorption, development time, stability and mixing tolerance index were obtained. Parameters of heating and cooling cycle related to weakening of proteins, gelatinization starch, amylase activity and starch retrogradation as well as range of gelatinization temperatures were also determined. Chestnut flour showed suitable parameters in the mixing stage such as arrival time (1.93?±?0.1 min), stability (12.1?±?0.4 min) and departure time (14.0?±?0.3 min). In the heating cycle, chestnut flour exhibited close behaviour to soft wheat flour with cooking stability of 1.12?±?0.01 min and seems to be suitable for pastrymaking products. Finally, in the cooling cycle the behaviour revealed that products of this flour can present problems of staling and crumbs firmness due to high values (2.88 Nm) of C5 parameter.     

Partial replacement of NaCl by KCl in salted mackerel (Scomber japonicus) fillet products: effect on sensory acceptance and lipid oxidation

Mackerel fillets were salted with NaCl and/or KCl to determine the most acceptable level by sensory evaluation. Additionally, the effects of ascorbic acid, vacuum packaging, and cold storages on lipid oxidation were determined for the salted mackerel fillets. Appropriate level of NaCl was ≤2%. Fifty percent replacement of NaCl by KCl reduced NaCl level with minimal impact on sensory quality. The higher the level of ascorbic acid (0–0.5%, weight basis), the higher the antioxidant effect observed with thiobarbituric acid value and peroxide value. There was no significant difference in sourness (α = 0.05) between the salted mackerel samples treated with and without ascorbic acid (0.25%). Vacuum packaging and storage at ?18 °C along with ascorbic acid was most effective in retarding lipid oxidation in the salted mackerel. Vacuum‐packaged sample with ascorbic acid stored at 2 °C was least oxidised, followed by vacuum packaging without ascorbic acid and then ascorbic acid without vacuum.     

Ascorbic Acid Effects on Bovine Muscle Pigments in the Presence of Radiant Energy

Untreated and treated (dipped in ascorbic acid solutions of 0, 0.5, 1.0, or 5.0%) raw psoas major muscle samples were exposed to radiant energy in a model system (500W Hg lamp, 577 nm, 2°± 1°C, 20% 02) with spectral reflectance measured every 30 min. Results varied with reflectance ratios or differences at 572/525, 630-582, 630/582, or 630-614 nm. Differences between 0 and 4 hr exposure indicated that ascorbic acid retarded pigment oxidation. The K/S ratio at 572/525 nm indicated that 5% ascorbic acid solution retarded pigment oxidation and protected muscle color most. Ascorbic acid retarded lipid oxidation (TBA values) in muscle stored at ?26°C from 3–10 wk; a 5% solution gave the least protection of the solutions tested.     

Effect of trehalose on the glass transition and ice crystal growth in ice cream

The effects of trehalose and sucrose on the rate of ice crystal growth in ice cream during accelerated shelf‐life were compared. Experimental and theoretical freezing curves were shown to be in good agreement. Glass transition temperatures (T_g) of maximally freeze concentrated trehalose and sucrose solutions (40% w/w) were found to be ?39.5 °C and ?47 °C respectively. For ice cream mixes, the T_g value increased from ?46.4 °C for the 100% sucrose‐based mix to ?42.0 °C for the 100% trehalose sweetened ice cream. However, no differences in viscosity, nucleation rate or inhibition of ice crystal growth were observed with increasing trehalose concentration in ice cream.     

Destructive Effect of Aspartame on Ascorbic Acid in Cu-catalyzed Solutions

The effect of aspartame on the early stage of ascorbic acid oxidation in solutions was studied by measuring ascorbic acid retention in an open system at 30°C and the oxygen uptake in a closed system at 33°C. Comparisons were also made between aspartame (0.06% and 0.12%) and sucrose (10% and 20%) in Cu-catalyzed and noncatalyzed solutions at 30°C. Copper activity in aspartame solution was measured by using a cupric ion selective electrode. Aspartame increased the rate of ascorbic acid oxidation in all tested solutions. In the presence of copper the oxidation rate of ascorbic acid was significantly higher in aspartame solutions than in sucrose solutions despite the fact that aspartame showed Cu-complex capacity in solution.     

Phase Transitions of Amorphous Sucrose and Frozen Sucrose Solutions

Amorphous sucrose showed typical thermal transitions of amorphous materials. The temperatures of those transitions, glass transition, crystallization and melting, decreased with increasing moisture content. The glass transition temperature of dry amorphous sucrose at 57°C was decreased to -46°C as the sucrose was plasticized with excess water. That value remained constant due to maximal freeze-concentration with 72-73% sucrose in the unfrozen matrix which showed ice melting at -34°C. Concentrated solutions may become supercooled resulting in partial freeze-concentration with resultant lowering of glass transition temperature.     

Glass transition behaviour of fructose

The glass transition temperature and the second transition (the endothermic change between the glass transition and melting temperatures) of fructose were studied. The thermal history strongly affected both transitions of fructose. Storage for 10 days at 22 °C increased the dynamic glass transition temperature from 16 to 25 °C and decreased the second transition of fructose from 110 to 98 °C in the first differential scanning calorimetric (DSC) scan. The amplitude of the second transition increased slightly with storage time and reached 260% of the first transition for vacuum oven dried samples. The effect of thermal history on the glass transition temperature of fructose can be removed by scanning the sample in a DSC to 130 °C. The effects of water content, glucose and sucrose on the two transitions were also investigated.     

The measurement of the glass transition temperature of sucrose and maltose solutions with added NaCl

The effect of added NaCl on the glass transition temperatures of 200 and 300 g kg⁻¹ sucrose and maltose solutions was determined using DSC and capacitance measurements. Negative shifts of around 4 °C were seen upon the addition of 0.1 mol kg⁻¹ NaCl, consistent with the freezing point depression expected for the maximally freeze‐concentrated solutions. Changes in the capacitance were seen which matched both the onset of the devitrification event and the main heat capacity step seen in DSC scans. © 2000 Society of Chemical Industry     

Stability of lutein under various storage conditions

The stability of lutein, a major xanthophyll, was investigated under various storage conditions. Continuous exposure of lutein-containing samples to cold white fluorescent light (4600 lux) at 25 °C resulted in the degradation of lutein at 0.8%-10.7% per day in the samples containing ascorbic acid, ascorbic acid + KOH and H₂O (as control) over a period of 75 days. It was found that ascorbic acid could retard lutein degradation (0.04% - 2.5% per day) at temperatures from ?30 °C to 50 °C under the alkaline condition in darkness. High temperature promoted the degradation of lutein in all the samples. Under the alkaline condition and at low temperature (-12 °C), the stability of pure lutein was similar to that of the lutein extracted from the alga Chlorella protothecoides cultivated heterotrophically.     

The effects of wheat sourdough on glutenin patterns, dough rheology and bread properties

Sourdough was prepared with cellular suspension containing 10⁹ cfu of each strain mL⁻¹ and incubated at 28 °C for 24 h and at 37 °C for 4 h. Two different sourdough levels (20 and 40%) were used in bread dough preparation. The bread doughs were proofed at 30 °C and 85% relative humidity for 60/120/180 min. When glutenin changes that occurred in samples 17, 18, 19, and 20 (40% SD 28) are compared with those that appeared in controls, it is obvious that, the relative intensities of some of the protein bands slightly decreased and a few fainter protein bands appeared (which did not exist in controls). A few fainter protein bands corresponding to the MM ≈ 25 kDa (high-mobility region) and the MM ≈ 66 kDa (low-mobility region) were appeared in the same samples. In the samples prepared with 20% sourdoughs incubated at 28 or 37 °C, the bands were still evident after 180 min of proof. This can be explained that glutenin fractions were not hydrolysed in these applications due to the delay in pH drop. The use of 40% sourdough incubated at 28 °C for 24 h resulted in sticky doughs and breads with lower volume, harder texture, unsatisfactory crumb grain and unpleasant flavour than the rest of the samples. The use of sourdoughs incubated at 37 °C for 4 h caused positive effect on loaf volumes, specific loaf volumes and crumb structure.