Takenobu Ogawa

Effect of Salts on the Water Sorption Kinetics of Dried Pasta

The water sorption kinetics of dried pasta were measured in the 20-90 °C range in 1.83 mol/L of NaCl and at 80 °C in 1.83 mol/L of LiCl, KCl, NaBr and NaI solutions in order to elucidate the role of salt in the kinetics. At the temperatures higher than 70.8 °C, the change in the enthalpy of sorption, ΔH, in the 1.83 mol/L NaCl solution was 33.1 kJ/mol, which was greater than the ΔH value in water, and the activation energy for the sorption, E, in the salt solution was 25.6 kJ/mol, which was slightly lower than the E value in water. The Hofmeister series of ions was an index for their effect on the equilibrium amount of the sorbed solution of pasta. The apparent diffusion coefficient of water into pasta was not correlated with the crystal radius of the salts, but was with the Stokes radius of the hydrated ions. Equations were formulated to predict the amount of sorbed solution under any condition of temperature and NaCl concentration.

Properties and water sorption characteristics of spaghetti prepared using various dies.

Spaghetti was prepared using dies made of different materials. The surface was observed using digital and optical microscopes, and was rougher for the spaghettis prepared using the Teflon, polypropylene, polycarbonate, aluminum, and bronze dies in this order. The extrusion velocity when passing through the die was faster, the bulk density was higher, and the rupture strength was greater for the spaghetti having the smoother surface. The die material did not affect the gelatinization temperature. The water sorption curves in boiling water containing 0.5% (w/v) sodium chloride were also observed. The curves were expressed by an equation of the hyperbolic type except for the early stage of sorption in order to estimate the equilibrium amount of water sorbed based on the bone-dry sample. The momentarily-sorbed amount of water, which is a hypothetical quantity to characterize the initial water intake, was estimated by fitting the experimental points within 60 s. The amount was higher for the spaghetti having the rougher surface.

Effects of relaxation of gluten network on rehydration kinetics of pasta

The aim of this study was to investigate the effects of the relaxation of the gluten network on pasta rehydration kinetics. The moisture content of pasta, under conditions where the effects of the diffusion of water on the moisture content were negligible, was estimated by extrapolating the average moisture content of pasta of various diameters to 0 mm. The moisture content of imaginary, infinitely thin pasta did not reach equilibrium even after 1 h of rehydration. The rehydration of pasta made of only gluten was also measured. The rate constants estimated by the Long and Richman equation for both the pasta indicated that the rehydration kinetics of infinitely thin pasta were similar to those of gluten pasta. These results suggest that the swelling of starch by fast gelatinization was restricted by the honeycomb structural network of gluten and the relaxation of the gluten network controlled pasta rehydration kinetics. Graphical Abstract The moisture content of infinitely thin pasta was estimated by extrapolating the average moisture content of pasta of various diameters to 0 mm.

Destabilization of mayonnaise induced by lipid crystallization upon freezing

The thermal and rheological history of mayonnaise during freezing and its dispersion stability after the freeze-thaw process were investigated. Mayonnaise was cooled to freeze and stored at −20 to −40 °C while monitoring the temperature; penetration tests were conducted on the mayonnaise, which was sampled at selected times during isothermal storage at −20 °C. Significant increases in the temperature and stress values due to water-phase crystallization and subsequent oil-phase crystallization were observed. The water phase crystallized during the cooling step in all the tested mayonnaise samples. The oil phases of the prepared mayonnaise (with rapeseed oil) and commercial mayonnaise crystallized during isothermal storage after 6 and 4 h, respectively, at −20 °C. The dispersion stability was evaluated from the separation ratio, which was defined as the weight ratio of separated oil after centrifuging to the total amount of oil in the commercial mayonnaise. The separation ratio rapidly increased after 4 h of freezing. This result suggests that crystallization of the oil phase is strongly related to the dispersion stability of mayonnaise. Graphical abstract Temperature changes during storage at −20 °C and separation ratio, X, after the freeze-thaw process of commercially available mayonnaise.

Moisture distribution and texture of spaghetti rehydrated under different conditions

Dried spaghetti was rehydrated to its optimal cooking state, known as al dente, at 60, 80, and 100 °C, in distilled water or 0.1, 1.0, and 2.0 mol/L sodium chloride solutions. Then, the moisture distributions and stress–strain curves were examined to identify the major factors governing the texture of rehydrated spaghetti. The difference in moisture content between the inner and peripheral regions of rehydrated spaghetti and its breaking stress were greater at higher rehydration temperatures; however, rehydration temperature did not affect breaking strain. The sodium chloride concentration of the immersion solution did not affect moisture distribution or breaking stress, while breaking strain was decreased by rehydration at higher sodium chloride concentrations. The results obtained in this study suggest that moisture distribution within spaghetti and its material properties govern its breaking stress and strain, respectively. Graphical abstract Moisture distribution of spaghetti rehydrated to the al dente state at 60, 80, and 100 °C.

Effects of Vegetable Oil Type and Lipophilic Emulsifiers on the Induction Period of Fat Crystallization

The induction period of crystallization, which is defined as the time required for oil to start to crystallize, is useful indicator of the freeze-thaw stability of food emulsions such as mayonnaise. We investigated the induction period of vegetable oils with low melting points, such as rapeseed and soybean oils, which are commonly employed for mayonnaise production. The induction period was measured by monitoring the temperature of a specimen during storage at low temperature. The induction period depended on the type of oil and lipophilic emulsifier, emulsifier concentration, and storage temperature. The effect of the oil type on the induction period depended on the composition of the oil. Differential scanning calorimetry (DSC) analyses of the lipophilic emulsifiers suggested that the melting trend of the emulsifier is strongly related to the induction period.

Effects of drying conditions on moisture distribution in rehydrated spaghetti.

Moisture distributions in spaghettis prepared at a maximum temperature of 50, 70, or 85 °C, designated as LT-, HT-, or VHT-spaghetti, respectively, and cooked to the average moisture content of 1.71 ± 0.01 kg-H2O/kg-d.m., were measured. The moisture contents near the surface and at the center of the LT-spaghetti were lower and higher, respectively, than those of HT- and VHT-spaghetti.

Dilatometric Measurement of the Partial Molar Volume of Water Sorbed to Durum Wheat Flour

Moisture sorption isotherms were measured at 25 °C for untreated, dry-heated and pre-gelatinized durum wheat flour samples. The isotherms could be expressed by the Guggenheim-Anderson-de Boer equation. The amount of water sorbed to the untreated flour was highest for low water activity, with water sorbed to the pre-gelatinized and dry-heated flour samples following. The dry-heated and pregelatinized flour samples exhibited the same dependence of the moisture content on the partial molar volume of water at 25 °C as the untreated flour. The partial molar volume of water was ca. 9 cm3/mol at a moisture content of 0.03 kg-H2O/kg-d.m. The volume increased with increasing moisture content, and reached a constant value of ca. 17.5 cm3/mol at a moisture content of 0.2 kg-H2O/kg-d.m. or higher.

Estimation of the Gelatinization Temperature of Noodles from Water Sorption Curves under Temperature-Programmed Heating Conditions

A novel method in which the water sorption curve is observed under linearly temperature-raising conditions was proposed to estimate the gelatinization temperature of starch-containing foods, it was applied in an estimation of the gelatinization temperatures of dried noodles. The gelatinization temperatures of two kinds of spaghetti, dried at high and low temperature, were 52.3 and 53.1 °C, and those of udon, kishimen, juwari-soba, hachiwari-soba, so-called common soba, Malony(®), and kuzukiri were 57.0, 57.8, 61.1, 59.6, 57.4, 48.4, and 49.1 °C. The gelatinization temperatures estimated by the method were between the onset and peak temperatures obtained by differential scanning calorimetric measurement.

Moisture Distributions and Properties of Pasta Prepared or Cooked Under Different Conditions

A method using an image processing technique was developed to measure the moisture profile in pasta during its rehydration process. The method has the higher spatial resolution and can measure the lower moisture content than currently used methods. A very unique profile was recognized. Possible reasons for the profile will be discussed. The moisture distributions within pastas prepared at different temperatures were measured by the method, and the water sorption kinetics and texture of the pasta were also measured. The pasta prepared at higher temperature exhibited better textural properties. The effects of cooking temperature or salt concentration in cooking water on the kinetics and properties were also examined for the pastas prepared under different temperature-programmed conditions.