**6. Applications to foodstuffs**

In a food system, many other ingredients influence the process of gelatinization, pasting, breakdown and retrogradation/setback of starch pastes (BeMiller, 2011). Recent data about starch pastes and gels as governed by their ingredients and the interactions with other hydrocolloids is presented. Furthermore, the role of these interactions in controlling rheology in model food is discussed. Examples given include stability issues of ready to eat white sauces, soups and caramel sauces.

### **6.1. White sauces**

Béchamel sauce or ''white sauce'' is used in a lot of preparations or as a basis for other more complex sauces (Heyman et al., 2010). Sauces often exhibit stability problems during prolonged storage either caused by emulsion instability or by changing polymer interactions (Mandala et al., 2004b; Mc Clemments, 2006).

Non-starch hydrocolloids added in starch paste can alter the continuous phase of the system which contains them. In a complex system like that of a sauce, apart from rheology, they can also alter water holding capacity of the sauces. The effects of partially replacing modified starch by hydrocolloids (guar gum, xanthan gum and carboxymethylcellulose) on the rheological behavior and the physicochemical stability of the sauces is discussed.

Oscillatory spectra of all sauces are very similar to those of starch gels (example model sauce and guar gum at different concentrations, (Fig. 4)). All samples exhibit a dominant elastic behavior since G' is larger than G'' over the studied frequency range.

When different hydrocolloids such as xanthan, guar or CMC gum are added, xanthan gum causes the greatest increase in G' compared to the model system. Guar gum and CMC also shift the G' curve to higher values (Fig.4), but in a less pronounced way than xanthan gum does. White sauces present similarities between their values and those of starch gels alone supporting the hypothesis of a strong influence of both native and modified starches present in the system (Caisawang & Suphantharika 2006). Same conclusions are reached by Mandala et al. (2004b). During preservation at 7°C for 30 days the overall profile of the frequency curves does not change. Slight reductions in both G' and G'' are noticed with the most significant changes to occur the first 2 weeks.

**Figure 4.** Effect of guar addition on oscillatory measurement of béchamel sauces. (From Heyman et al. (2010). Journal of Food Engineering 99, 115-120, with permission).

#### *6.1.1. White sauce and freeze-thaw stability*

226 Viscoelasticity – From Theory to Biological Applications

**6. Applications to foodstuffs** 

white sauces, soups and caramel sauces.

(Mandala et al., 2004b; Mc Clemments, 2006).

most significant changes to occur the first 2 weeks.

**6.1. White sauces** 

pronounced effects on the viscous one.

common observation was the increase in both viscous and elastic character with more

Regarding gelation, it is induced by adding hydrocolloids. Short-term retrogradation is

Gelation acceleration does not mean retrogradation acceleration as well, since a more

 Concerning long-term retrogradation, it is clearly reduced by hydrocolloid addition. Factors that may contribute are the associations of hydrocolloid-amylopectin, the stabilization of water molecules and last but not least the molecular weight of the gum.

In a food system, many other ingredients influence the process of gelatinization, pasting, breakdown and retrogradation/setback of starch pastes (BeMiller, 2011). Recent data about starch pastes and gels as governed by their ingredients and the interactions with other hydrocolloids is presented. Furthermore, the role of these interactions in controlling rheology in model food is discussed. Examples given include stability issues of ready to eat

Béchamel sauce or ''white sauce'' is used in a lot of preparations or as a basis for other more complex sauces (Heyman et al., 2010). Sauces often exhibit stability problems during prolonged storage either caused by emulsion instability or by changing polymer interactions

Non-starch hydrocolloids added in starch paste can alter the continuous phase of the system which contains them. In a complex system like that of a sauce, apart from rheology, they can also alter water holding capacity of the sauces. The effects of partially replacing modified starch by hydrocolloids (guar gum, xanthan gum and carboxymethylcellulose) on the

Oscillatory spectra of all sauces are very similar to those of starch gels (example model sauce and guar gum at different concentrations, (Fig. 4)). All samples exhibit a dominant elastic

When different hydrocolloids such as xanthan, guar or CMC gum are added, xanthan gum causes the greatest increase in G' compared to the model system. Guar gum and CMC also shift the G' curve to higher values (Fig.4), but in a less pronounced way than xanthan gum does. White sauces present similarities between their values and those of starch gels alone supporting the hypothesis of a strong influence of both native and modified starches present in the system (Caisawang & Suphantharika 2006). Same conclusions are reached by Mandala et al. (2004b). During preservation at 7°C for 30 days the overall profile of the frequency curves does not change. Slight reductions in both G' and G'' are noticed with the

rheological behavior and the physicochemical stability of the sauces is discussed.

behavior since G' is larger than G'' over the studied frequency range.

also related to this gelation acceleration, as well as to amylose amount.

viscous character is maintained by hydrocolloid addition in many cases.

Starches combined with different hydrocolloids are used in white sauces and the freeze/thaw stability of the produced samples is investigated. In a typical white sauce, after a freeze/thaw cycle, an increase in the viscoelastic functions is observed as a consequence of extensive starch retrogradation. By adding hydrocolloids this increase is reduced, leading to a less structured system. This can be justified by hydrocolloid interaction with solubilised amylose that reduces amylose - amylose interactions, preventing also structure ordering and hence reducing the extent of retrogradation (Arocas et al., 2009).

#### *6.1.1.1. Ambient conditions' thawing*

Specifically, the viscoelastic properties of fresh and thawed white sauces containing different corn starches (native waxy corn starch (NWS), native corn starch (NS), hydroxypropyl distarch phosphate waxy corn starch (HPS) and pregelatinized acetylated distarch adipate waxy corn starch (AAS)) are compared. Samples are frozen at -18°C and thawed at room temperature until 20°C.

A different behavior is found among the modified and the native starch sauces (Fig. 5).

The fresh modified starch sauces show higher G' and G'' values than the fresh native starch sauces, HPS being the one with the highest capacity and NWS the one with the lowest capacity. A high thickening capacity is ascribed to the fact that modified starches present high starch granule stability in comparison to the native starches and their granules do not break down in the thermal and shear conditions.

Moreover, a temperature increase from 20 to 80°C does not affect the values of G' and G'' either in the fresh or freeze/thaw samples. On the contrary, in native starch sauces a slight decrease in the values of the viscoelastic moduli is observed after 50°C, particularly pronounced after the freeze/thaw cycle. Furthermore, the values of the G', G'' of samples

prepared with native starches after freeze/thaw cycle are much greater than those of the fresh samples due to retrogradation phenomena occurring during the freezing process.

Viscoelastic Properties of Starch and Non-Starch Thickeners in Simple Mixtures or Model Food 229

convection heating and potato starch can be influenced much more than corn starches

The effects of microwave thawing and water bath thawing on white sauces prepared with two different native starches (potato and corn) and a modified waxy maize starch are compared. Starch retrogradation is strongly affected by freezing and thawing. Thus, possible reduction of starch retrogradation upon different thawing methods could be

Furthermore, microwave treated samples are quite similar to the freshly prepared sauces compared to the water bath-thawed ones. In this regard, microwaving could be considered more suitable than the water bath for diminishing the loss of quality associated with the

The differences in the viscoelastic properties of the microwave-and water bath-thawed native starch sauce can be explained because of the shorter heating time required in the microwave, which reduces the time available for the retrogradation occurring from -5 to 20°C. Furthermore, the big local temperature and the differences occurring during microwave heating can lead to an improved localized melting of amylopectin and eventual

**Starch type Treatment G′ (Pa) G\* (Pa) tanδ**

WB 326.0 A 328.0 A 0.114 C MW 265.2 B 267.0 B 0.118 C Fresh 80.4 E 81.9 E 0.189 B

WB 177.6 C 179.8 C 0.158 BC MW 114.7 D 116.7 D 0.183 B Fresh 97.6 DE 101.0 DE 0.265 A

WB 270.7 B 272.5 B 0.118 C MW 264.7 B 267.7 B 0.149 BC Fresh 206.6 C 210.5 C 0.194B

beneficial for the quality characteristics of the final product.

melting of amylose (at temperatures near 100°C).

Corn

Potato

Modified waxy corn

**Table 1.** Influence of starch type and treatment in the rheological parameters G′, G\*

and tan δ. Frequency: 1 Hz. ABCDE Means with the same letter are not significantly different (p < 0.05) according to the Tukey's multiple range test. WB water bath thawed samples, MW microwave thawed samples. (From Arocas et al, 2011, Food Hydrocolloids 25, pp 1554- 1562, with

This can lead to new starch/water interactions and consequent water adsorption. Generally, heating during thawing improves the quality of frozen sauces as amylose bonds formed during retrogradation are broken accompanied with re-absorption of the previously released water. Furthermore, the modified starch resists the heating applied during the

(An et al., 2008).

freezing step (Table 1).

permission).

**Figure 5.** *G*′ and *G*″ as a function of increasing temperature for : a) freshly prepared sauces and b) freeze/thawed sauces. NS sauce (G′:●, G″:○), NWS sauce (G′:♦, G″: ◊), AAS sauce (G′:(▲, G″:∆) and HPS sauce (G′:■, G″:□). Frequency: 1 Hz. γ: 0.001. Heating rate: 1.5 °C/min. (From Arocas et al., 2009, Food Hydrocolloids, 23, pp 901-907, with permission).

Concerning mechanical spectra, all samples behave as soft gels with values of G' higher than values of G''. A weak dependence on frequency is observed, as well as in starchhydrocolloid mixtures. After freeze/thaw, as it was expected, structural changes occur mainly in sauces containing native starches. As a consequence, great values of G' and G' are observed and these samples presented a spongy structure depending also on freezing rate (the lower the freezing rate, the more pronounced the spongy structure). Thus, chemical modification is effective in providing freezing and thermal structure stability.

#### *6.1.1.2. Microwave and water bath thawing*

Differences between conductive heating and MW heating of starch dispersions are found not in the mechanism of gelatinization but on the starch crystallinity, which disappears at a higher rate when samples were heated by microwaves. Furthermore, the attainment of a certain viscosity required longer time in the conduction-heated samples. Microwaving can cause incomplete gelatinization of the starch in comparison to convection heating and potato starch can be influenced much more than corn starches (An et al., 2008).

228 Viscoelasticity – From Theory to Biological Applications

Hydrocolloids, 23, pp 901-907, with permission).

*6.1.1.2. Microwave and water bath thawing* 

prepared with native starches after freeze/thaw cycle are much greater than those of the fresh samples due to retrogradation phenomena occurring during the freezing process.

**Figure 5.** *G*′ and *G*″ as a function of increasing temperature for : a) freshly prepared sauces and b) freeze/thawed sauces. NS sauce (G′:●, G″:○), NWS sauce (G′:♦, G″: ◊), AAS sauce (G′:(▲, G″:∆) and HPS sauce (G′:■, G″:□). Frequency: 1 Hz. γ: 0.001. Heating rate: 1.5 °C/min. (From Arocas et al., 2009, Food

modification is effective in providing freezing and thermal structure stability.

Concerning mechanical spectra, all samples behave as soft gels with values of G' higher than values of G''. A weak dependence on frequency is observed, as well as in starchhydrocolloid mixtures. After freeze/thaw, as it was expected, structural changes occur mainly in sauces containing native starches. As a consequence, great values of G' and G' are observed and these samples presented a spongy structure depending also on freezing rate (the lower the freezing rate, the more pronounced the spongy structure). Thus, chemical

Differences between conductive heating and MW heating of starch dispersions are found not in the mechanism of gelatinization but on the starch crystallinity, which disappears at a higher rate when samples were heated by microwaves. Furthermore, the attainment of a certain viscosity required longer time in the conduction-heated samples. Microwaving can cause incomplete gelatinization of the starch in comparison to The effects of microwave thawing and water bath thawing on white sauces prepared with two different native starches (potato and corn) and a modified waxy maize starch are compared. Starch retrogradation is strongly affected by freezing and thawing. Thus, possible reduction of starch retrogradation upon different thawing methods could be beneficial for the quality characteristics of the final product.

Furthermore, microwave treated samples are quite similar to the freshly prepared sauces compared to the water bath-thawed ones. In this regard, microwaving could be considered more suitable than the water bath for diminishing the loss of quality associated with the freezing step (Table 1).

The differences in the viscoelastic properties of the microwave-and water bath-thawed native starch sauce can be explained because of the shorter heating time required in the microwave, which reduces the time available for the retrogradation occurring from -5 to 20°C. Furthermore, the big local temperature and the differences occurring during microwave heating can lead to an improved localized melting of amylopectin and eventual melting of amylose (at temperatures near 100°C).


**Table 1.** Influence of starch type and treatment in the rheological parameters G′, G\* and tan δ. Frequency: 1 Hz. ABCDE Means with the same letter are not significantly different (p < 0.05) according to the Tukey's multiple range test. WB water bath thawed samples, MW microwave thawed samples. (From Arocas et al, 2011, Food Hydrocolloids 25, pp 1554- 1562, with permission).

This can lead to new starch/water interactions and consequent water adsorption. Generally, heating during thawing improves the quality of frozen sauces as amylose bonds formed during retrogradation are broken accompanied with re-absorption of the previously released water. Furthermore, the modified starch resists the heating applied during the

sauce preparation as well as during the thawing process. Although the modified starch granules swell, little release of the starch components occurs. Thus, the differences between thawing techniques are related to their effect on structure changes related to starch retrogradation (Arocas et al., 2011).

Viscoelastic Properties of Starch and Non-Starch Thickeners in Simple Mixtures or Model Food 231

(a) 5% standard corn starch (P1), gradually replaced with fenugreek at 0.1% (P2), 0.15% (P3), 0.2% (P4), 0.25% (P5),

(b) soup formulations with 5% standard corn starch (S1), gradually replaced with fenugreek at 0.1% (S2), 0.15% (S3), 0.2% (S4), 0.25% (S5) and 0.3% (S6), 0.5% (S7), 0.7% (S8), 0.9% (S9). All measurements were carried out at 25 °C (From Matia-Merino & Ravindran, 2009, Food Hydrocolloids, 23(3), pp 1047-1053, with

**Figure 6.** Storage modulus (*G*′), loss modulus (*G*″), and tan *δ* measured at 1 Hz and 1% strain

rheology can be achieved improving caramel sauces performance.

character much more pronounced than the elastic one.

products with good network structure.

were measured. On the contrary to the assumptions in previous examples, the storage moduli of all sauces are much lower than their loss moduli. Sauces have very weak elastic and very strong plastic properties. This feature is considered disadvantageous, because the sauce can very easily flow down from the surface of the glazed products. An increase in xanthan gum amount results in moduli increase, both before and after storage. Controlled

Sauces and soups containing starch and hydrocolloids behave like weak gel-like

Caramel sauces containing starch and hydrocolloids are fluid-like with viscous

0.3% (P6), 0.5% (P7), 0.7% (P8), 0.9% (P9).

permission).

Concluding:

## **6.2. Chilli sauce**

Chilli sauces investigated presented a dominant elastic behavior compared to the viscous behavior typically observed in suspensions with network-like structure (Gamonpilas et al., 2011). Weak gel-like characteristics are found in chilli sauces containing starch and hydrocolloids, as well as in white sauces mentioned above. The presence of starch/xanthan mixture in the commercial chilli sauces promotes their elastic properties. Furthermore, the sauce with low solid content and without xanthan gum has weak network structure and inferior flow properties. The addition of xanthan gum and/or modified starch can provide a network-like characteristic of the sauce.
