Canadian Grain Commission
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Using ultrasound to characterize fresh yellow alkaline noodles

Discussion about the results of the experiment

This study shows that ultrasound is capable of:

  • Characterizing the rheological behaviour of noodles from a non-empirical (objective) perspective
  • Responding to a parameter of technological interest. Example: Maximum compress stress relates to noodle firmness (Bellido et al., 2006) and it is well correlated with sensory scores on the force required to compress a noodle between the molars (Oh et al., 1983).

Flour characteristics

Table 1 shows the chemical and physical characteristics of the flour used to make the noodle specimens.

  • Both flours had equivalent protein contents and gluten indices.
  • Ash content of the amber durum flour is higher than that of the hard white spring flour. Higher ash content is typical when yellow pigment-rich durum wheat is milled into flour.
  • Durum flour had significantly greater Farinograph water absorption capacity because of the starch damage caused by milling the harder durum wheat into flour. Rapid Visco Analyzer tests also showed this higher starch damage because durum flour resulted in a paste with reduced peak viscosity and final viscosity.
  • Excessive starch damage is undesirable in noodles made from bread wheat flour (Hatcher, Edwards and Dexter, 2008a). . However, high starch damage in durum flour has less of an effect on noodles made from it (Hatcher, Edwards and Dexter, 2008a).
Table 1. Proximate analyses of the experimental wheat (CWHWS and CWAD) flours used for the production of fresh yellow alkaline noodles.
Analysis CWHWS CWAD LSD b
a Combustion nitrogen analysis
b Least significant difference (p=0.05)
c Breakdown=(Peak Viscosity – Hot Peak Viscosity);
Setback=(Cool Paste Viscosity – Hot Peak Viscosity);
Stability ratio = [(Final Viscosity – Trough)/Trough];
Setback ratio = [(Peak Viscosity – Trough)/Peak Viscosity].
Analytical      
    Protein content (CNA a), % 13.2 13.1 -
    Gluten index, % 95.8 93.6 -
    Ash Content, % 0.41 0.62 -
    Moisture (w.b.), % 14.9 14.2 -
Farinogram      
    Absorption, % 62.4 76.4 -
    Dough Development Time, min 10.0 4.3 -
    Stability, min 14.8 5.8 -
RVA Pasting and Swellling Parameters c      
    Peak Viscosity, Pa s 3.117 2.203 0.051
    Trough, Pa s 1.725 1.324 0.031
    Breakdown, Pa s 1.391 0.879 0.061
    Final viscosity, Pa s 3.130 2.712 0.032
    Setback, Pa s 1.306 1.388 0.042
    Stability ratio 0.81 0.40 0.02
    Setback ratio 0.45 1.05 0.05

Ultrasonic properties

It is possible to use ultrasonic velocity measurements to investigate and quantify the effects various ingredients have on the physical properties of yellow alkaline noodles (Figure 3A). The researchers found that the velocity of the ultrasound wave increased significantly in either type of noodle after either the SK2 or SKT treatments relative to a control treatment.

Figure 3A

A - Ultrasonic velocity, see text for details.

Ultrasonic velocity (A) and attenuation (B) obtained from fresh YAN noodles formulated with CWHWS or CWAD wheat flour and with different combinations of ingredients. SK1= 1% NaCl + 1% kansui, SK2= 3% NaCl + 1% kansui and SKT=1% NaCl + 1% kansui + 2% transglutaminase.

Figure 3B

B - Attenuation, see text for details.

Because ultrasonic velocity is greater in stiffer materials, ultrasonic velocity appeared to be sensitive to the stiffening effects of sodium chloride (Bloksma and Bushuk, 1988) and transglutaminase (Autio et al., 2005; Steffolani et al., 2008) on dough rheology. However, the ultrasonic data showed that ultrasonic velocity measurements could not discriminate differences in the properties of noodles made from 2 different classes of wheat. This is consistent with findings from earlier ultrasonic studies on bread dough (Kidmose, Pedersen and Nielsen, 2001).

The researchers decided that the ultrasonic technique yields velocity measurements free from artifacts. They determined ultrasonic velocity from the inverse slope of the best-fit line passing through the plotted data (Figure 2A). The excellent fit of the straight line (R² = 0.997) shows that the effects on transit times due to stacking the noodle specimens were too small to be detected by the researchers’ experiments.

Figure 2A

A - Pulse time of flight, see text for details.

Pulse time of flight (A) and ultrasonic signal amplitude (B) as a function of sample thickness for fresh YAN doughs made from two wheat classes and various ingredients (fwb), as illustrated here for CWAD dough formulated with SKT treatment (1% NaCl + 1% kansui and 2% transglutaminase). Error bars denote SD (n=3). See text for details.

Figure 2B

B - Ultrasonic signal amplitude, see text for details.

Attenuation coefficient

The researchers found that ultrasonic attenuation in fresh noodles was smaller in noodles that had been prepared with additional salt (SK2) and transglutaminase (SKT) (Figure 2B). The attenuation data shows that the dough samples became stiffer after salt was added, just as the ultrasonic velocity data showed. The dough samples also became stiffer after transglutaminase was added as shown in the ultrasonic velocity data.

Mechanical properties obtained from ultrasonic measurements

Table 2 shows the mechanical properties for the experimental yellow alkaline noodles derived from the density and ultrasonic measurements at a frequency of 40 kHz. Results show that:

  • Ultrasound was sensitive to changes in the mechanical properties of yellow alkaline noodles caused by adding either:
    • More sodium chloride (SK2 versus SK1)
    • Tansglutaminase enzyme (SKT versus SK1).
  • Noodles made with SK2 and SKT had a significantly higher (p<0.05) higher mechanical modulus than noodles made with SK1.

When transglutaminase enzyme was used in the noodles, the elastic component of the longitudinal modulus was sensitive to the stiffening effects of salt and the transglutaminase enzyme. M’ values increased by nearly 30%.

Ultrasound analysis of viscoelastic behaviour of noodle showed that when compared to the standard formula (SK1), dough made from SK2 or SKT and hard white spring wheat flour resulted in noodles with more elastic-like behaviour (as measured by a lower M”/M’ ratio) (Table 2). This effect was not seen in noodles made with durum wheat flour.

The researchers proposed in an earlier study (Bellido and Hatcher, 2009b) that because a relatively smaller fraction of disulfide bonds participate in cross-linking the network protein structure of proteins in amber durum, the rheological properties of noodles made from durum wheat flour would be less susceptible to the cleavage of the disulphide bonds caused by L-cysteine. Similarly, one interpretation of the observed differences in the M”/M’ ratio for durum wheat and hard white spring wheat noodles (Table 2) is that transglutaminase did not bring about as much of a change in the viscoelasticity of durum wheat noodles because durum wheat has a lower fraction of gluten proteins with a high molecular weight(hence a lower number of intermolecular disulfide bonds in its protein newtwork) than hard white spring wheat.

Table 2. Density, storage modulus (M’), loss modulus (M”) and ratio M”/M’ for fresh YAN made from two classes of Canadian wheat (CWHWS and CWAD) flour and different combinations of salts and/or an enzyme. SK1= 1% NaCl + 1% kansui, SK2= 3% NaCl + 1% kansui and SKT=1% NaCl + 1% kansui + 2% transglutaminase.
Treatment Density
(kg/m3) 1
M’ (MPa) 1,2 M” (MPa) 1,2 M”/M’ 1,2
1 Values within the same column with different letters are significantly different at p<0.05.
2 Values derived from triplicate measurements of ultrasonic velocity and attenuation.
CWHWS        
    SK1 1262 ± 23 b 231 ± 95 b 286 ± 23 ab 1.24 ± 0.05 a
    SK2 1265 ± 14 b 300 ± 26 a 285 ± 15 ab 0.96 ± 0.12 c
    SKT 1303 ± 18 a 296 ± 48 a 326 ± 61 a 1.10 ± 0.07 b
CWAD        
    SK1 1277 ± 8 ab 245 ± 21 b 251 ± 28 b 1.02 ± 0.03 bc
    SK2 1260 ± 20 b 301 ± 13 a 291 ± 79 ab 0.97 ± 0.03 bc
    SKT 1281 ± 2 ab 317 ± 21 a 307 ± 29 ab 0.97 ± 0.01 bc
LSD 0.05 28 47 57 0.14

Stress relaxation testing

Canadian Grain Commission researchers used 3 parameters to characterize the stress relaxation behaviour of YAN:

  • Maximum compress stress (σmax)
  • Overall rate of relaxation (1/S*)
  • Residual stress (P*)

Stress relaxation testing showed that SK2 and SKT treatments produced firmer noodle doughs than the SKI treatment (Table 3). This result is similar to the rheological information obtained from the ultrasonic experiments (Table 2).

Table 3. Maximum compression stress (σmax), overall rate of relaxation (1/S*) and residual stress (P*) obtained from stress relaxation testing of fresh YAN made from two classes of Canadian wheat flour and different combinations of ingredients. SK1= 1% NaCl + 1% kansui, SK2= 3% NaCl + 1% kansui and SKT=1% NaCl + 1% kansui+ 2% transglutaminase.
Treatment σmax (kPa) 1 1/S* 1,2 P* 1,2
1 Values within the same column with different letters are significantly different at p<0.05.
2 Values derived from triplicate measurements.
CWHWS      
    SK1 18.9 ± 0.3 c 1.37 ± 0.01 a 0.68 ± 0.01 b
    SK2 21.8 ± 1.5 ab 1.42 ± 0.05 a 0.65 ± 0.01 c
    SKT 22.4 ± 0.4 a 1.42 ± 0.03 a 0.66 ± 0.01 bc
CWAD      
    SK1 20.2 ± 0.4 bc 1.24 ± 0.03 b 0.77 ± 0.02 a
    SK2 21.3 ± 1.8 ab 1.21 ± 0.01 b 0.79 ± 0.01 a
    SKT 21.4 ± 1.4 ab 1.22 ± 0.02 b 0.78 ± 0.01 a
LSD 0.05 2.1 0.05 0.02

Stress relaxation testing showed that durum wheat flour yielded noodles with stronger elastic-like behaviour (greater overall rate of relaxation and residual stress) than hard white spring wheat flour. The greater elastic-like mechanical behaviour of durum wheat noodles compared to hard white spring wheat noodles was also captured by the ultrasonic parameter measuring viscoelastic behaviour (M’/M’; Table 2). However, statistical analysis for the pooled data showed that the correlation between these parameters (overall rate of relaxation, residual stress, M”/M’) were not strong enough to be statistically significant (Table 4).

Table 4. Correlation Coefficients (R) and Probability Values 1 (p) between Stress Relaxation and Ultrasonic Rheological Parameters.
  Maximum Stress 1/S* P*
1 ns denotes not significant at 5% of probability.
Velocity (v) 0.529 -0.034 0.025
0.024 ns ns
Attenuation (α) -0.537 0.246 -0.291
0.022 ns ns
Density (ρ) 0.201 0.259 -0.169
ns ns ns
M’ 0.566 -0.078 0.098
0.014 ns ns
M” 0.304 0.180 -0.226
ns ns ns
M”/M’ -0.410 0.316 -0.382
0.091 ns ns
M 0.485 0.059 -0.070
0.485 0.059 ns