Small Amplitude Oscillatory Tests Research Articles

Starch and Amylopectin — Rheological Behavior of Gels

AbstractRheological behavior of starch and amylopectin gels was evaluated by small amplitude oscillatory testing using the storage modulus (G′), loss modulus (G″) and the complex viscosity (n*). It was found for the three starches (normal and waxy corns, and amaranth) that at low frequency the viscous component G″ had a major contribution on the gel structure than the elastic G′ and that the complex viscosity (n*) diminished when the frequency was increased. Amaranth amylopectin showed G″ values higher than those of G′. Corn commercial and waxy corn amylopectins presented a similar behavior in the G′ values. Normal corn amylopectin gave the highest complex viscosity values.

Rheological and Structural Properties of Egg White/Oat Globulin Co‐Gels

ABSTRACTCo‐gels of egg white (EW) and oat globulin (native and deamidated) were prepared by heating mixtures of the two proteins at different ratios. Rheological properties of the co‐gels were assessed by small amplitude oscillatory tests. Storage (G′) and loss (G″) moduli of the co‐gels increased with increases in EW content in the mixtures. At comparable EW/non‐EW ratios, EW formed much stronger co‐gels with deamidated oat globulin (DOG) than with native globulin (OG) or several other non‐EW proteins. Microscopic examination of mixed gels revealed structural differences between EW/OG and EW/DOG co‐gels. The former exhibited a two gel system with OG distributed discontinuously throughout the supporting EW matrix. DOG and EW formed a homogenous gel network, demonstrating compatibility between the two proteins.

SMALL AMPLITUDE OSCILLATORY TESTING (SAOT). APPLICATION TO PECTIN GELATION

The setting characteristics of pectin gels during cooling from 105°C to 25°C and reheating to above 100°C have been determined using a versatile food rheometer capable of small amplitude oscillatory testing. Gel strength development during cooling was linearly correlated to temperature and on reheating the gel softened initially then hardened again as the temperature exceeded about 70°C. The linear parameters (slope, intercept) describing the gel development on cooling were related to pectin concentration up to 0.85% but 1% pectin could not be distinguished from 0.85%. On cooling, 75–85% of the gel strength attainable on standing overnight was developed within 30 min. The quick set up on cooling provides the possibility of developing a rapid test method for determining pectin gel properties.

New rotary rig at RAE and experiments on HIRM

SummaryA rig for measurement of forces and moments due to continuous rate of roll has been commissioned at RAE Bedford. Tests have been made on a High Incidence Research Model (HIRM) in two wind tunnels at M = 0·2, 0·4 and 0·7. At present models can be tested up to 40° angle of attack at rotational speeds up to 350 rpm.Tests on HIRM included an investigation of configuration and Reynolds number effects. Results are compared with similar data from tests with another rolling rig and from small amplitude oscillatory tests.

Protein Structure Development in Relation to Denaturation Temperatures

Small amplitude oscillatory testing (SAOT) has been used to follow the aggregation phenomenon associated with the thermal denaturation of egg albumen, whey protein concentrate (WPC) and Pro-mine D. For egg albumen and WPC, thermal transitions corresponding to the denaturation of the individual protein species in these mixed systems were evident using differential scanning calorimetry (DSC). Rheologically significant structures, however, did not appear until the principal protein components had been denatured. This implies that the gel networks produced upon heating both albumen and WPC do not begin to appear until the ovalbumin and β-lactoglobulin proteins, respectively, have been denatured. Similar trends could not be established for Promine D as there was no evidence of thermal denaturation in the DSC analysis.