**5.1. Hydrocolloids influence in starch pastes**

Starch pastes have typical biopolymer gel behavior. In typical biopolymer gel behavior greater G' values than G'' along the frequency sweep are observed, however in starch pastes both moduli are frequency dependent. Hydrocolloids modify the dynamic spectra of starch, although different trends can be observed.

First assumption: Hydrocolloids lead to weaker structures with less gel-like character.

With their addition, starch network shifts from an elastic-like to a more viscous-like one (Rosell et al., 2011). Starch-hydrocolloid systems can be considered as biphasic systems. When starch granules are swollen, the hydrocolloid is located entirely in the continuous phase. The concentration of hydrocolloid will then increase as the volume of the phase accessible to the hydrocolloid is reduced. This fact changes the viscoelasticity of the starch. Thus, cellulose derivatives and carrageenans can lead to less solid-like pastes than the control paste (Techawipharat et al., 2008). This assumption depends on starch type as well. In waxy starches, due to an absence of amylose, short-term retrogradation does not occur and therefore, the addition of hydrocolloids could not alter the viscoelastic characteristics of these starch pastes.

Second assumption: Hydrocolloids addition leads to associations with starches resulting in increased G', G'' values.

Several hydrocolloids can promote associations with starches and as a result, when they are added in starch pastes, an increase in G', G'' is often observed, see examples: Mandala et al.(2004a); Achayuthakan & Suphantharika, (2008); Wang et al., (2008). In such systems the question is which ingredient predominates in the overall rheology, starch or hydrocolloid. In wheat starch-hydrocolloid systems, it is the hydrocolloid that predominates in the whole system, according to the shift factors found.

(a) In water of xanthan 0.1 wt% (□, ■) and 0.5 wt% (○, ●), starch 2 wt%/xanthan 0.5 wt% (∆, ▲), amylose 0.3 wt%/xanthan 0.1 wt% (◊, ♦), amylose 0.3 wt%/xanthan 0.5 wt% ( ,▼). (b) In 0.1 M NaCl of xanthan 0.1 wt% (□, ■), 0.5 wt% (○, ●) and 0.8% (◊, ♦), starch 2 wt%/xanthan 0.5 wt% (∆, ▲), amylose 0.3 wt%/xanthan 0.5 wt%,( ,▼). (From Mandala et al, 2004a. Carbohydrate Polymers 58, pp 285–292, with permission).

**Figure 2.** Superimposed shifted spectra.

222 Viscoelasticity – From Theory to Biological Applications

lower tendency to retro gradate.

linking than other kinds of starches (Kaur et al., 2004).

in this section, enhancing the knowledge about such systems.

**5. Interactions with other hydrocolloids** 

**5.1. Hydrocolloids influence in starch pastes** 

although different trends can be observed.

these starch pastes.

increased G', G'' values.

al., 2007b).

and cross-linked starches from different sources increase to a maximum and then drop during heating following the same general rheological pattern as native starches (Singh et

The temperature of maximum G' drops significantly on acetylation or hydroxypropylation, while it increases after cross- linking (Kaur et al., 2004, 2006; Singh et al., 2004). Acetylated corn and potato starches showed greater values of G' and G'' under heating but lower compared to their native starch gels upon cooling of heated starch gels, confirming their

Strengthening bonding between starch chains by cross-linking will increase resistance of the granules towards swelling resulting in lower G' values in a high degree of cross-linking. Cross-link concentration and location could lead to different rheology. Botanical source also influences cross-linking and potato starches show a higher susceptibility towards cross-

According to an excellent review of BeMiller (2011) twenty-one different native starches in combination with thirty two different hydrocolloids have been investigated in different studies. Thus there is an increased interest in starch-hydrocolloid systems as well as a significant amount of scientific work in this area. New research works are mainly presented

Starch pastes have typical biopolymer gel behavior. In typical biopolymer gel behavior greater G' values than G'' along the frequency sweep are observed, however in starch pastes both moduli are frequency dependent. Hydrocolloids modify the dynamic spectra of starch,

With their addition, starch network shifts from an elastic-like to a more viscous-like one (Rosell et al., 2011). Starch-hydrocolloid systems can be considered as biphasic systems. When starch granules are swollen, the hydrocolloid is located entirely in the continuous phase. The concentration of hydrocolloid will then increase as the volume of the phase accessible to the hydrocolloid is reduced. This fact changes the viscoelasticity of the starch. Thus, cellulose derivatives and carrageenans can lead to less solid-like pastes than the control paste (Techawipharat et al., 2008). This assumption depends on starch type as well. In waxy starches, due to an absence of amylose, short-term retrogradation does not occur and therefore, the addition of hydrocolloids could not alter the viscoelastic characteristics of

Second assumption: Hydrocolloids addition leads to associations with starches resulting in

First assumption: Hydrocolloids lead to weaker structures with less gel-like character.

Furthermore, except G', G'' values, tanδ may be important in interpretations of the behavior of starch-hydrocolloids interactions. Thus, although some hydrocolloids promote an increase in G', G'' by their addition, in fact they lead to a less solid-like system (higher tanδ values) as described above. On the contrary, in some cases, hydrocolloid addition may lead

to a more solid-like system as noticed in systems of maize starch with flaxseed gum (Wang et al., 2008).

Viscoelastic Properties of Starch and Non-Starch Thickeners in Simple Mixtures or Model Food 225

**Figure 3.** Changes in storage modulus (G') during aging at 4°C for 10h. Close symbol rice starch. Open symbols rice starch-xanthan gum mixtures (XG:0.2-0.8%). (From Kim & Yoo, 2006, Journal of Food

Gelation and retrogradation can be also influenced by the molecular size of the hydrocolloid in a starch-gum mixture. Thus, the molecular mass and size of guar gum influences gelatinization and retrogradation behaviour of corn starch according to Funami et al. (2005a, 2005b). Viscosity and viscoelastic properties can be measured. Molecular interactions between guar gum and amylose are responsible for an earlier onset of viscosity increase for the composite system of starch-guar gum, whereas molecular interactions between guar gum and amylopectin are responsible for the increase in peak viscosity of the composite system. Moreover, the addition of guar gum accelerates the gelation of starch, in particular when the amylose fraction increases. Concerning the control of retrogradation by adding guar gum, storage modulus (G') for starch systems increases rapidly at very early stage of storage at 4°C. Short-term retardation of retrogradation is also suggested, because the gelled fraction in the system is reduced with the addition of guar gum (loss targent increase). This happens due to the decrease in the amount of amylose leached out of the starch granules during gelatinization. There is a critical Mw up to which the amount of leached amylose can be influenced, which is 15.0x105 g/mol. The effect of guar gum on the inhibition of short-term retrogradation becomes less Mw-dependent at above this Mw value. On the other hand, the

higher the Mw of guar gum, the easier the guar interacts with amylopectin.

G' becomes less-frequency dependent with decreasing Mw of guar gum. These results suggest that the interactions between guar gum and amylose should hardly contribute to forming a gelled or ordered structure (Funami, 2005). Furthermore, the ability of guar gum to inhibit long-term retrogradation is enhanced markedly when the Mw of the guar is over 30.0x105 g/ml. Thus, above this molecular weight guar gum can act easily on either amylose

 Hydrocolloid addition may decrease or increase the gel-like character of starch pastes depending on hydrocolloid and starch type as well as on gum concentration. The most

Engineering 75, pp. 120-128, with permission).

or amylopectin to retard starch crystallization.

Concluding:

In this research work, the variation of the G' with frequency for the maize starch alone and the flaxseed gum-maize starch mixtures with different flaxseed gum concentrations was not significant. This suggests that both the maize starch and its mixture with flaxseed gum have a typical biopolymer gel network, but flaxseed gum helps the formation of stronger gels. Concerning temperature effects, at a temperature range of 25-75°C, flaxseed gum addition shows more significant temperature dependence compared to that of maize starch alone. An increase in temperature results in a decrease in G' of the mixture, indicating that the addition of flaxseed gum affects the thermal stability of the mixture (Wang et al., 2008).

## **5.2. Influence of hydrocolloids during storage**

Gelation and short- or long-term retrogradation of starch can be influenced by hydrocolloids. The addition of a hydrocolloid can accelerate gelation and reduce retrogradation (Kim & Yoo, 2006, Lee et al., 2002; Mandala & Palogou, 2003; Fumami et al., 2005, 2008) but this depends on many parameters, some of which are discussed extensively in the following text.

Concerning gelation, starch-hydrocolloid mixtures may display weak gel-like behavior (Funami et al., 2008; Kim & Yoo, 2006; Lee at al., 2002). According to time-dependent curves of the mixtures of rice starch-xanthan gum, G' values increase rapidly during the first few hours at low temperature aging (5°C) and remained steady afterwards. Gelation could be considerably shortened by the presence of xanthan gum. Increasing xanthan gum concentration increased G' values during aging, indicating that the elastic character of xanthan gum influences the reinforcement of the overall gel properties during aging. A rapid increase and subsequent plateau of G' can be shown by xanthan gum addition (Fig. 3). This is due to the rapid aggregation of amylose chains at the early stage and the slow aggregation of amylopectin chains at the late stage respectively (Kim & Yoo, 2006).

First-order kinetics for structure development of starch-xanthan mixtures during aging (recrystallization) and further retarding during longer storage can be developed. The rate of G' increase (structure development) due to the retrogradation of rice starch during cold storage is apparently affected by the presence of xanthan gum and greatly dependent on the xanthan gum concentration. The same was observed for wheat starch-xanthan mixtures aging (Mandala & Palogou, 2003).

In the long-term retrogradation of different hydrocolloid-starch mixtures (Funami et al., 2008; Kim & Yoo, 2006; Lee at al., 2002) molecular associations between the gum and the amylopectin fraction inhibit the formation of crystalline structures during storage. As another factor to inhibit long-term retrogradation, gums can stabilize water molecules, therefore they can act as water binder effectively depriving amylose or amylopectin of usable water for crystallization as described in the case of corn starch fenugreek gum mixtures (Funami et al., 2008).

**Figure 3.** Changes in storage modulus (G') during aging at 4°C for 10h. Close symbol rice starch. Open symbols rice starch-xanthan gum mixtures (XG:0.2-0.8%). (From Kim & Yoo, 2006, Journal of Food Engineering 75, pp. 120-128, with permission).

Gelation and retrogradation can be also influenced by the molecular size of the hydrocolloid in a starch-gum mixture. Thus, the molecular mass and size of guar gum influences gelatinization and retrogradation behaviour of corn starch according to Funami et al. (2005a, 2005b). Viscosity and viscoelastic properties can be measured. Molecular interactions between guar gum and amylose are responsible for an earlier onset of viscosity increase for the composite system of starch-guar gum, whereas molecular interactions between guar gum and amylopectin are responsible for the increase in peak viscosity of the composite system. Moreover, the addition of guar gum accelerates the gelation of starch, in particular when the amylose fraction increases. Concerning the control of retrogradation by adding guar gum, storage modulus (G') for starch systems increases rapidly at very early stage of storage at 4°C.

Short-term retardation of retrogradation is also suggested, because the gelled fraction in the system is reduced with the addition of guar gum (loss targent increase). This happens due to the decrease in the amount of amylose leached out of the starch granules during gelatinization. There is a critical Mw up to which the amount of leached amylose can be influenced, which is 15.0x105 g/mol. The effect of guar gum on the inhibition of short-term retrogradation becomes less Mw-dependent at above this Mw value. On the other hand, the higher the Mw of guar gum, the easier the guar interacts with amylopectin.

G' becomes less-frequency dependent with decreasing Mw of guar gum. These results suggest that the interactions between guar gum and amylose should hardly contribute to forming a gelled or ordered structure (Funami, 2005). Furthermore, the ability of guar gum to inhibit long-term retrogradation is enhanced markedly when the Mw of the guar is over 30.0x105 g/ml. Thus, above this molecular weight guar gum can act easily on either amylose or amylopectin to retard starch crystallization.

Concluding:

224 Viscoelasticity – From Theory to Biological Applications

**5.2. Influence of hydrocolloids during storage** 

et al., 2008).

in the following text.

aging (Mandala & Palogou, 2003).

mixtures (Funami et al., 2008).

to a more solid-like system as noticed in systems of maize starch with flaxseed gum (Wang

In this research work, the variation of the G' with frequency for the maize starch alone and the flaxseed gum-maize starch mixtures with different flaxseed gum concentrations was not significant. This suggests that both the maize starch and its mixture with flaxseed gum have a typical biopolymer gel network, but flaxseed gum helps the formation of stronger gels. Concerning temperature effects, at a temperature range of 25-75°C, flaxseed gum addition shows more significant temperature dependence compared to that of maize starch alone. An increase in temperature results in a decrease in G' of the mixture, indicating that the addition of flaxseed gum affects the thermal stability of the mixture (Wang et al., 2008).

Gelation and short- or long-term retrogradation of starch can be influenced by hydrocolloids. The addition of a hydrocolloid can accelerate gelation and reduce retrogradation (Kim & Yoo, 2006, Lee et al., 2002; Mandala & Palogou, 2003; Fumami et al., 2005, 2008) but this depends on many parameters, some of which are discussed extensively

Concerning gelation, starch-hydrocolloid mixtures may display weak gel-like behavior (Funami et al., 2008; Kim & Yoo, 2006; Lee at al., 2002). According to time-dependent curves of the mixtures of rice starch-xanthan gum, G' values increase rapidly during the first few hours at low temperature aging (5°C) and remained steady afterwards. Gelation could be considerably shortened by the presence of xanthan gum. Increasing xanthan gum concentration increased G' values during aging, indicating that the elastic character of xanthan gum influences the reinforcement of the overall gel properties during aging. A rapid increase and subsequent plateau of G' can be shown by xanthan gum addition (Fig. 3). This is due to the rapid aggregation of amylose chains at the early stage and the slow

aggregation of amylopectin chains at the late stage respectively (Kim & Yoo, 2006).

First-order kinetics for structure development of starch-xanthan mixtures during aging (recrystallization) and further retarding during longer storage can be developed. The rate of G' increase (structure development) due to the retrogradation of rice starch during cold storage is apparently affected by the presence of xanthan gum and greatly dependent on the xanthan gum concentration. The same was observed for wheat starch-xanthan mixtures

In the long-term retrogradation of different hydrocolloid-starch mixtures (Funami et al., 2008; Kim & Yoo, 2006; Lee at al., 2002) molecular associations between the gum and the amylopectin fraction inhibit the formation of crystalline structures during storage. As another factor to inhibit long-term retrogradation, gums can stabilize water molecules, therefore they can act as water binder effectively depriving amylose or amylopectin of usable water for crystallization as described in the case of corn starch fenugreek gum

 Hydrocolloid addition may decrease or increase the gel-like character of starch pastes depending on hydrocolloid and starch type as well as on gum concentration. The most common observation was the increase in both viscous and elastic character with more pronounced effects on the viscous one.

Viscoelastic Properties of Starch and Non-Starch Thickeners in Simple Mixtures or Model Food 227

**Figure 4.** Effect of guar addition on oscillatory measurement of béchamel sauces. (From Heyman et al.

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

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

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

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

(2010). Journal of Food Engineering 99, 115-120, with permission).

hence reducing the extent of retrogradation (Arocas et al., 2009).

*6.1.1. White sauce and freeze-thaw stability* 

*6.1.1.1. Ambient conditions' thawing* 

thawed at room temperature until 20°C.

break down in the thermal and shear conditions.

