Enzymatic Production of High-Protein Amaranth Flour and Carbohydrate Rich Fraction

The basic conditions of an enzymatic process to produce high-protein amaranth flour (HPAF) and carbohydrate rich fraction (CRF) from raw flour were determined. Commercial preparations of α-amylase and glucoamylase were used. Conditions for both enzymes were: 20% (w/v) slurries of gelatinized whole flour and 0.10% (v/w) enzyme; for amylase, pH 6.5, 70°C and 30 min liquefaction time; for glucoamylase, pH 4.5, 60°C and 60 min. The yield of HPAF was 38–39%. HPAF from both enzymes had 26–28% protein, 10–16% fat and 40–52% starch. Protein digestibility (76%) and reactive lysine (6.6–7.1 g/100g protein) of HPAF were comparable to raw flour. CRF had a 17–21 dextrose equivalent.     

Production and Size Distribution of Rice Maitodextrins Hydrolyzed from Milled Rice Flour using Heat-Stable Alpha-Amylase

Maltodextrins were produced from milled rice flour in a single-step process using a heat-stable α-amylase preparation. The starting solids content was 30% (w/w), and processing temperatures and times were varied between 70–97°C and 15–75 min, respectively. Optimum liquefied starch yields, which accounted for virtually all of the starch present, were obtained at temperatures of 80°C and above, but reducing sugars and DE values were highest at 70°C. Low molecular weight saccharide concentrations (DP 1–10) were greatest at 80°C. Because processing at temperatures of 90–97°C resulted in decreased levels of reducing sugars and DP 1–10 concentrations without providing a substantial increase in solubilized starch yields, it was concluded that rice maltodextrins could be most effectively produced at a processing temperature of 80°C.     

Properties and Structure of Amylose-Glyceryl Monostearate Complexes Formed in Solution or on Extrusion of Wheat Flour

Differential scanning calorimetry (DSC), alpha-amylolysis, and gel filtration chromatography (GFC) were used to characterize the lamellar morphology of solution-grown amyloseglyceryl monostearate (GMS) complexes. The complexes grown at 60°C and 90°C had melting temperatures of 100°C and 114°C, respectively. Both enzyme digested complexes had broad overlapping GFC chromatographs; however, the amylose-GMS-90°C complex had chain lengths 25% to 40% larger than the lower temperature complex. Assuming the main GFC peak was representative of the ordered lamellar regions, the complexes grown at 60°C and 90°C had helical chain segments of 104 Å and 145 Å, respectively. The influence of GMS addition on the twin screw extrusion of soft wheat flour was also investigated. Formation of a complex during extrusion, characteristic of the amylose-GMS-90°C polymorph, decreased the starch solubility, water holding capacity, enzyme susceptibility and degree of expansive-puffing of the extrudate.     

Effect of thermal treatment on the proteins of amaranth isolates

The effect of thermal treatment of proteins from Amaranthus hypochondriacus was studied. Two protein isolates were obtained from the defatted flour by water extraction at a pH of 9 (A9 isolate) and 11 (A11 isolate), followed by isoelectric precipitation at a pH of 5. Effect of thermal treatment (70 and 90 °C, during 3, 5, 10, 15 and 30 min) on A9 and A11 dispersions were analyzed by differential scanning calorimetry (DSC), polyacrylamide gel electrophoresis, UV spectrophotometry, superficial hydrophobicity and solubility in water. Thermal treatment induced the aggregate formation of high molecular mass stabilized by disulfide and non‐covalent bond. Thermal treatment at 70 °C produced a 30% denaturation in both, while at 90 °C A9 was more denatured than A11 (75% and 55% of denaturation, respectively). An increase in thermal stability was also detected by DSC in A9 treated at 90 °C. The denaturation process was accompanied at short heating times by an increase in UV absorbance and changes in superficial hydrophobicity. A decrease in water solubility (35–50%, depending on time–temperature conditions) was also observed for the A9 isolates. The results suggest that the A9 isolates, enriched in a globulin protein fraction, are more sensitive to thermal treatment than isolates A11 enriched in glutelin protein fraction. The changes shown by both isolates, indeed, could affect their functional properties and could definitely limit their use in food products. Copyright © 2007 Society of Chemical Industry     

Potato Tuber Dynamic Mechanical Analysis at Temperatures of Starch Gelatinization

Dynamic mechanical analysis (DMA) was applied to potato cortex tissue in temperature scans in range 30–90°C and constant air humidity of 90%. The obtained scans indicate peaks in both storage and loss module of elasticity (SM and LM, respectively) at temperatures higher than 70°C. The peaks follow starch gelatinization processes in tissue detected by DSC at lower temperatures. The peak characteristic temperatures were determined in replicated experiments for seven potato varieties. It was shown that increasing tissue density leads to higher characteristic temperatures. The peak characteristic values (for both SM and LM) were more variable and cultivar role for them was not proved. The role of the observed module peaks in the potato cooking process is discussed.     

Differential Scanning Calorimetry of Rice Starches

DSC thermograms from 5–135°C of eight rice starches, pretreated with sodium dodecyl benzenesulfonate (DoBS) to remove milled rice proteins, gave gelatinization endotherms with characteristic temperature ranges. Good positive correlations were found between gelatinization temperatures measured by DSC and photometry, and between gelatinization enthalpies and gelatinization temperatures. The enthalpy of the amylose-lipid endotherm at 90–97°C was less for two DoBS-prepared rice starches than for the same pronase-treated starches. The endotherm was absent in waxy starch, and its enthalpy followed the level of lipids extracted by cold water-saturated butanol (WSB). It was concluded that DoBS treatment removed and replaced some of the starch lipid. Although this DoBS did not form a complex with amylose that was observable by DSC, the adsorbed DoBS was extracted by hot WSB.     

Thermal Properties of Sorghum Starch

The differential scanning calorimeter (DSC) was used to measure thermal properties of sorghum starch and flour. DSC gelatinization temperatures of 24 nonwaxy sorghum varieties were: T_o (onset temperature): 71.0 ± 1.0°C; T_p (peak temperature): 75.6 ± 0.9°C and T_e (end temperature): 81.1 ± 1.1°C, respectively. The gelatinization energies ranged from 2.51 to 3.96 cal/g. There were no consistent relationships between DSC gelatinization temperatures or gelatinization energies and grain characteristics or physicochemical starch properties. DSC gelatinization temperature for nonwaxy, heterowaxy and waxy sorghum tended to increase as the number of waxy alleles (wx) increased. However, it appeared that at least a difference of two waxy alleles was required before differences in thermal properties of the samples were significant.     

DIFFERENTIAL SCANNING CALORIMETRY OF STARCH12

At high water-to-starch (2:1) ratios a single endotherm was obtained for starch gelatinization. As the water-to-starch ratio was decreased the endotherm area decreased and the peak developed a trailing shoulder. At high water-to-starch ratios birefringence is lost over a temperature range of about 7°C. That narrow range increases to about 30°C at a low water-to-starch ratio. Starch and flour gave essentially the same endotherm initiation temperatures. In low-water systems the second DSC peak is much smaller with starch than with flour. It appears that in a starch system, water migrates during gelatinization. In dough, gluten limits that migration. As the level of sucrose was increased in a dough, the transition temperature increased and the gelatinization temperature range decreased. At the levels found in bread doughs both sugar and salt increase starch gelatinization temperatures.     

Freezing and Thawing Conditions Affect the Gel Stability of Different Varieties of Rice Flour

The freeze‐thaw stabilities of three different rice flour gels (amylose rice flour with 28% amylose, Jasmine rice flour with 18% amylose and waxy rice flour with 5% amylose) were studied by first freezing at –18 °C for 22 h and subsequent thawing in a water bath at 30 °C, 60 °C and 90 °C, or by boiling in a microwave oven. The freeze‐thaw stability was determined for five cycles. Starch gels thawed at higher temperature exhibited a lower syneresis value (percent of water separation) than those thawed at lower temperature. Amylose rice flour gels gave the highest syneresis values (especially at the first cycle). The Jasmine rice flour gels gave a higher syneresis value than the waxy rice flour gel. Except for freezing by storage at –18 °C and thawing at 30 °C, there was no separation of water at any cycle when waxy rice flour gel was thawed at any temperature, irrespectively of the freezing methods used. Cryogenic Quick Freezing (CQF) followed by storage at –18 °C and then thawing (by boiling or by incubation at any other temperatures) gave lower syneresis values than all comparable samples frozen by storage at –18 °C. The order of syneresis values for the three types of rice flour was waxy rice flour < Jasmine rice flour < amylose rice flour. The syneresis values and the appearance of starch gels, which had gone through the freeze‐ thaw process, suggested that the order of freeze‐thaw stability of gels for the three types of rice flour was waxy > Jasmine > amylose rice flour.     

Thermal and dynamic rheological properties of wheat flour fractions

A commercial high gluten flour (HGF) was fractionated into prime starch (PS), tailing starch (TS), and gluten (G). Fractions were examined alone or in various combinations. Dynamic rheological properties of samples were measured in an oscillatory rheometer (strain 0.02; frequency 0.1 Hz) during heating at 1°C/min. Thermal characteristics of samples were determined by differential scanning calorimetry (DSC) at a heating rate of 10°C/min. The loss (G″) and storage (G′) moduli of PS and mixed G/PS, G/TS, and G/PS/TS increased after 60°C, reaching peak values (e.g. 81, 301, 313, and 3000 Pa in G′, respectively) around 75°C after which the moduli decreased. HGF showed a steady increase in G′ from 32 to 2490 Pa as temperature increased from 65 to 90°C, indicating continuous formation of elastic networks. Cooling increased G′ for G/PS/TS, decreased G′ for HGF, and produced no rheological transitions for all samples. TS and G alone did not exhibit appreciable viscoelastic responses to the heating and cooling temperatures. DSC measurements revealed a major endothermic transition in HGF. This transition, with a peak around 60°C, was due to starch gelatinization. The presence of G or TS resulted in reduced melting enthalpies of starch in the PS fraction. Gluten or TS fractions alone or in combination did not exhibit any endothermic transitions.     

Thermal Transitions of Actomyosin and Surimi Prepared from Atlantic Croaker as Studied by Differential Scanning Calorimetry

Differential scanning calorimetry (DSC) was used to investigate thermal transitions of fish mince (surimi) and actomyosin from croaker. Three endothermic peaks were observed in DSC thermograms of surimi. After addition of salt, transition temperatures shifted to lower temperatures. Preheating samples containing 3% salt at various temperatures showed that 40°C heating caused the first peak to disappear, and preheating at temperatures higher than 50°C caused virtual disappearance of all transition peaks. Low temperature storage (4°C) of samples caused no significant change in thermograms of salted or unsalted surimi over a 5-day storage period. Evidence suggests that changes of fish protein during low temperature “setting” are different from those occurring during high temperature “setting.”     

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.     

Rheology of Sol-Gel Thermal Transition in Cowpea Flour and Starch Slurry

A thermal scanning rigidity monitor was used to follow rheological changes during heating of cowpea flour and starch slurries. The gelantinization temperature of cowpea starch was in the range 67–78°C. For cowpea flour, in addition to starch gelatinization, a shallow plateau was observed. The starch gelatinization onset temperature shifted from 67°C for starch to 72C for 25% cowpea flour that contained 12–15% starch. The modulus (G′) of cowpea gels increased with flour concentration according to a power relationship. Rigidity of the cowpea starch and flour gels decreased at temperatures higher than 78 and 87°C, respectively.     

The stability of wheat starch lipids in untreated and chlorine-treated cake flours

Untreated flour and flour treated with chlorine (2.2 g Cl₂ kg_-1) were stored in air at 25°C for 4 months. Starch samples prepared from the original flours were stored in air at 25°C for 4 months. Starch samples were also prepared from the fresh flours (control starches) and from the stored flours. Some of the starches from the stored flours were subsequently held at 70°C for 1 month. Starch lipids were not affected by flour chlorine treatment, or by storage at 25°C. There was slight hydrolysis of starch lysophospholipids at 70°C, but negligible autoxidation of unsaturated fatty acids in the total starch lipids. There was appreciable hydrolysis of non-starch lipids in the untreated stored flour, but no detectable autoxidation of unsaturated fatty acids. Chlorine treatment of flour caused an immediate loss of approximately half of the oleic, linoleic and linolenic acids in all the non-starch lipids which were examined. There was no further change in the fatty acid composition of the non-starch lipids when the treated flour was stored, but lipid hydrolysis was substantially reduced compared with the untreated stored flour.     

The effect of cooking on proteins from acha (Digitaria exilis) and durum wheat

The effect of cooking on proteins from acha and durum wheat was assessed from an analysis of protein extractability, gel electrophoretic profiles, in-vitro protein digestibility (IVPD) and the amino acid compositions of wholemeal flour and residue proteins. Heating wholemeal flour samples at 100–140°C (t = 10–40 min) resulted in 0–30% and 45–55% decreases in acha and durum protein solubility, respectively. In general, high molecular weight (30–70 k Da) protein subunits were more susceptible to heat damage. For both cereals, sodium dodecyl sulphate (SDS; 10 g litre^?1) and/or dithiothrcitol (DTT; 10 mM ) increased protein solubility in unheated and heated samples. The IVPD index was 90–91% and was not significantly altered by cooking (100–120°C, t = 40 min). Cooking at extreme temperatures (140°C, t = 40 min) reduced the IVPD by 8% (P = 0.05). Osborne fractionation resulted in a durum or acha residue level of 7.8% or 55.2%. Treatment with solvent containing propanol, SDS and/or DTT at room temperature followed by SDS-polyacrylamide gel electrophoresis of non-solubilised proteins showed that the glutelin fraction of acha, with the exception of a 65 kDa subunit, was insoluble owing to strong inter-subunit hydrophobic and disulphide interactions. Wholemeal acha flour and residue protein showed a significantly greater level of hydrophobic and sulphur amino acids as well as glutamine which is associated with H-bonding. The possibility that cereal protein solubility is also dependent on protein-carbohydrate links is discussed.     

Emulsifying Capacity and Emulsion Stability of Soy Proteins Compared with Corn Germ Protein Flour

Both emulsifying capacity (EC) and emulsion stability (ES) increased with increasing concentrations from 0.4% to 0.8% of soy flour (SF), soy concentrate (SC), soy isolate (SI) and corn germ protein flour (CGPF) when studied by response surface methodology. EC and ES increased as pH increased from 6 to 8 in all samples. Increasing incubation temperatures of protein solutions from 20–70°C or from 4–20°C did not affect EC or ES, respectively. SF had the highest EC, followd by SI, SC, and CGPF.     

The effects of low mixing temperature on dough rheology and bread properties

In this research, the effects of a low mixing temperature on dough rheology and the quality of bread were investigated. In the experiments, strong flour samples (Type 550), 1.5% salt, 3% of yeast and 1% additive mixture were used and dough samples were mixed at 17 °C (low temperature), 23 °C (control) and 30 °C (high temperature). Five different periods (0, 30, 60, 90 and 120 min) were applied at the bulk fermentation stage. At the final proofing stage, the dough was fermented until it reached a constant height. It was determined that almost every bread from dough samples mixed at 17 °C resulted in not only the highest bread volume and bread weight, but also the best texture, elasticity and crumb structure. The results of dough samples mixed at 23 °C were worse than those of dough samples mixed at 17 °C. The worst results were obtained from dough samples mixed at 30 °C (high temperature). As a result, it may be concluded that the quality of bread from dough samples mixed at low temperature (17 °C) is superior to those from dough samples mixed at the higher temperatures. Besides these findings, it may also be stated that prolonging the period of bulk fermentation in dough samples mixed at 17 °C positively develops baking performances.     

Effect of thermal treatment on the texture and microstructure of abalone muscle (Haliotis discus)

The texture and microstructure of edible abalone meats were studied during heat treatments from 50 to 100°C for 60 min. No increase in extractable soluble collagen content was observed below 80°C, but a 9-fold increase was observed at 100°C. SDS-PAGE showed that extractable myosin heavy chains and paramyosin contents reduced significantly at 80°C, and disappeared completely at 100°C. The shear force increased slowly from 50 to 70°C, but relaxed back to the initial level at 100°C. Rapid reduction of hardness was observed at 50°C, minimum hardness was obtained at 100°C. Springness, cohesiveness, chewiness, and resilience were enhanced to maximum levels at 70, 90, 70, and 90°C, respectively. Optical micrographs and transmission electron microscope showed a significant increase of intermyofibrillar gaps at 90°C and broken fibers at 100°C. Results suggested that 80°C might be a suitable temperature to produce ready-to-eat abalone products.     

Effect of natural fermentation on phytate and polyphenolic content and in-vitro digestibility of starch and protein of pearl millet (Pennisetum typhoideum)

Natural fermentation at 20, 25 and 30°C for 72 h brought about a significant reduction in phytic acid content of pearl millet (Pennisetum typhoideum Rich) flour. The phytate content was almost eliminted in the flour fermented at 30°C. An increase in polyphenol content of fermented flour was noticed, the higher the temperature of fermentation the greater was the increase in polyphenol content of pearl millet. An improvement in starch as well as protein digestibility (in vitro) was noticed at all the temperatures of natural fermentation, the highest being at 30°C.     

Degradation of wood surfaces by water

Weight losses and ultrastructural and chemical changes in pine and lime following exposure to deionised water in the temperature range 60° C–90° C are examined. Similar weight losses of 10% occur in pine and lime strips after 100 days exposure to water at 60 and 70° C but at 80 and 90° C lime shows greater weight losses (30%) than pine (15%). Observations of transverse surfaces exposed to water at 90° C for 50 days revealed separation of the secondary wall from the compound middle lamella region and some separation of individual cells. Chemical analysis of pine and lime wood flour exposed to deionised water at 65° C for 50 days revealed losses of hemicelluloses and lignin with little loss in cellulose. Changes in hemicellulose composition are thought to result primarily from degradation of pectinacious polysaccharides. Losses in lignin and hemicellulose were higher and lower respectively in lime than in pine. Viscometry measurements on cuprammonium dispersions of holocellulose isolated from hot water exposed pine strips indicate that little depolymerisation of cellulose occurs. It is suggested that the chemical and ultrastructural changes noted here accord with the losses in wet tensile strength and toughness of hot water exposed thin wood strips and failure of these particularly in lime by inter-fibre shear.