Monica Haros

Starch Hydrolyzing Enzymes for Retarding the Staling of Rice Bread

ABSTRACT Previous attempts have been made to obtain gluten-free bread of acceptable quality for bread specific volume and crumb texture. Rice bread is a good alternative to celiac patients, but it has a very rapid staling during storage. Rice starch is more prone to retrograde during storage than wheat starch, and the special hydrophobic nature of the rice proteins requires specific enzymes to be used in the rice bread process. To retard rice bread staling, two different starch hydrolyzing enzymes (α-amylase of intermediate thermostability and cyclodextrin glycoxyl transferase [CGTase]) have been tested and their effect on fresh bread quality and staling during storage has been evaluated. The addition of α-amylase improved bread specific volume and crumb firmness but very sticky textures were obtained. The addition of CGTase produced even higher specific volume and similar crumb firmness with better texture. Both enzymes decreased the ability of amylopectin to retrograde during storage. The firming kineti...

Effect of freezing and frozen storage on the staling of part-baked bread

The effect of part-baking, freezing, frozen storage, thawing, rebaking on the aging behaviour of bread was evaluated. The amylopectin modification during the process was assessed by differential scanning calorimetry (DSC), while changes in bread quality were followed by crumb hardness measurements. During frozen storage no retrogradation of amylopectin was detected in the part-baked dough. When analysing the aging of the rebaked samples, it was observed that the time of frozen storage produced a progressive increase of the retrogradation temperature range of the amylopectin, and also great energy was required for amylopectin melting at longer storage period, indicating that structural changes of amylopectin were produced during frozen storage. Regarding the quality of the fresh bread resulted after rebaking, crumb hardness increase with the time of frozen storage, and also the hardening rate during aging was dependent on that time. Crumb hardness results of the fresh bread and also DSC studies indicate that some changes are produced during the frozen storage.

Effect of temperature and SO2 on the rates of water absorption of three maize hybrids

Abstract The rates of water absorption of three maizes, dent (PIONEER 3379), semident (ICI RF67) and flint (CARGILL T-42), in plain water and 0.25% SO2 aqueous solution were studied. The steeping temperatures were 45, 55 and 65 °C. The absorption kinetics in plain water and SO2 solution follows a ‘Fickian’ behavior (moisture content of the kernels varies with the square root of time) during the first hours of steeping. The rates of absorption in SO2 solution were slightly higher than in plain water at all temperatures, even though at the onset of steeping, the SO2 seemed to retard the rate of absorption. This increase was relatively higher for flint and semident types than for dent maize. The activation energies for water sorption in SO2 solution were lower than for plain water, this effect being more marked for flint and semident types.

Corn steeping: influence of time and lactic acid on isolation and thermal properties of starch

Abstract A semi-dent corn hybrid was laboratory batch-steeped at 52°C in a sulfur dioxide solution (2500 ppm) and sulfur dioxide solution with lactic acid (2500 ppm SO2+0.5% v/v lactic acid) for various time intervals. Starch was laboratory wet milled and gelatinization characteristics were analyzed by differential scanning calorimeter (DSC). Starch isolated from corn steeped in SO2 solution alone had higher peak temperatures and narrower gelatinization range as the steeping time increased. This demonstrated that the wet milling process anneals corn starch during the isolation procedure. Such an effect was less pronounced when starch was milled from corn steeped with lactic acid. Higher starch yields were obtained from corn steeped in sulfur dioxide solution with lactic acid.

Effect of steeping corn with lactic acid on starch properties.

ABSTRACT Pasting and thermal properties of starch from corn steeped in the presence of lactic acid and at different steeping times (8, 16, 24, 32, and 40 hr) were investigated. Corn kernels were steeped at 52°C with 0.2% (w/v) SO2 and with and without 0.5% (v/v) lactic acid. The isolated starch obtained by corn wet-milling was characterized by determining starch recoveries, retrogradation, and melting transition properties of the lipid-amylose complex by differential scanning calorimetry (DSC), and pasting properties by the Rapid Visco Analyser (RVA). Damaged granules and the starch granule size were determined by using microscopic techniques. Starches from corn steeped in the presence of lactic acid (LAS) were compared with control starch (CS) steeped without lactic acid. Greater starch recoveries were obtained for LAS samples than for CS samples, and practically no damaged starch was present in the former preparations. The presence of lactic acid affected the RVA profiles and steeping time affected the ...

Effect of drying, initial moisture and variety in corn wet milling

A laboratory wet-milling process was used to determine starch yield and starch recovery of dent and flint corn dried under different drying conditions. A comparison with undried samples was performed. For the undried samples the starch recovery was not significantly different between both varieties. It decreased as both initial moisture content of the grains and drying air temperature increased. The reduction in starch recovery as well as the contamination by protein was greater for the flint than for the dent corn. Swelling, solubility and initial gelatinization temperatures of the starch derived from both varieties were affected by the drying conditions.

Effect of Chemical Pretreatments and Lactic Acid on the Rate of Water Absorption and Starch Yield in Corn Wet-Milling

ABSTRACT The relative effectiveness of dehulling, potassium hydroxide dipping (alkali concentrations 0.2, 0.5, and 1.0 %), and ethyl oleate spraying (aqueous emulsion 1%, v/v) to increase the rate of water absorption by dent and flint corn during steeping was compared with untreated corn samples. These pretreatments increased the water absorption rate of both hybrids when compared with the untreated control samples. To evaluate the observed increase, the diffusion coefficients of pretreated and untreated corn samples were estimated. Corn grains steeped in SO2 aqueous solution and variable lactic acid concentrations (0.2, 0.5, and 1.0%, v/v) were performed. Absorption rates for lactic acid concentrations were ≈0.5% higher than those steeped only in SO2 solution. This effect was more marked for dent than for flint corn. Corn samples pretreated with potassium hydroxide had lower starch yields than the control. However, the presence of lactic acid in steepwater increased the starch yield of dent and flint cor...

Influence of corn drying on its quality for the wet-milling process

Abstract Flint and dent corn were forced air-dried at 70–110 °C to a final moisture of about 12.0%. The rates of water absorption of both hybrids in the presence of 0.25% SO2 aqueous solution were evaluated in terms of the diffusion coefficient. Drying temperature affected negatively the rate of absorption of both hybrids. A laboratory wet-milling procedure was developed to evaluate starch recovery of corn samples. For flint corn starch recovery drop from 96.5% (undried) to 82% (dried at 110 °C); for dent corn the drop was from 97.5% to 90%. The starch isolated from air-dried corn contained greater amounts of protein than starch originated from undried corn. The effect was more marked for flint than for dent corn and increased with the drying temperature. Sorptional characteristics of starch were practically unaffected by drying temperature. DSC transition temperatures of starch showed an increasing tendency with drying temperature. For both hybrids the gelatinization enthalpy of starch decreased with the increasing of drying temperature, the effect being more marked for flint than for dent corn.

Effect of steeping time on the starch properties from ground whole corn

Abstract Ground whole corn was steeped for various time intervals (8, 16, 24, 32 and 40 h) in SO 2 solution, at 52 °C. The isolated starch, obtained by corn wet-milling, was characterized determining starch yields and gelatinisation parameters such as onset ( T o ), peak temperature ( T p ), conclusion ( T c ), enthalpy (Δ H ) and peak height index (PHI). Damaged granules and the starch granule size were tested through microscopic techniques. The results obtained were compared with the control sample (whole corn kernels steeped during 40 h at same condition). Greater starch yields were obtained from ground corn than whole kernels, and they increased with longer steeping time, confirming the largest disrupting action of SO 2 in the protein matrix when using ground corn. Starch recovery levels varied from 95.7% to 98.4%, and they were also higher than ones from whole kernels (85.1%). Several differences were detected between the physical properties of the starch samples recoveries from corn ground at different steeping times and those of starch recovered from whole kernels. Great homogeneity in the size distribution of starch granules were reached by using steeping times from 16 to 32 h. Δ H values showed a slight increase with steeping time as well as PHI, in addition, a narrow range of gelatinisation temperature was obtained. Annealing, different size distribution, changes in the damaged granules and protein contents are responsible of the different starch properties.