Combined impact of Bacillus stearothermophilus maltogenic alpha-amylase and surfactants on starch pasting and gelation properties

Food Chemistry 139 (2013) 1113–1120

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Combined impact of Bacillus stearothermophilus maltogenic alpha-amylase and surfactants on starch pasting and gelation properties Bénédicte Van Steertegem ⇑, Bram Pareyt, Kristof Brijs, Jan A. Delcour Laboratory of Food Chemistry and Biochemistry and Leuven Food Science and Nutrition Research Centre (LFoRCe), KU Leuven, Kasteelpark Arenberg 20, B-3001 Leuven, Belgium

a r t i c l e

i n f o

Article history: Received 9 November 2012 Received in revised form 8 January 2013 Accepted 11 January 2013 Available online 8 February 2013 Keywords: Maltogenic alpha-amylase Surfactants Sodium stearoyl lactylate Monoacylglycerols Starch pasting Starch gel

a b s t r a c t In baking applications involving starch gelatinisation, surfactants such as sodium stearoyl lactylate (SSL) and monoacylglycerols (MAG) and Bacillus stearothermophilus maltogenic alpha-amylase (BStA) can be used jointly. We here showed that SSL but not MAG delays wheat starch hydrolysis by BStA. The effects were explained in terms of different degrees of adsorption of the surfactants on the starch granule surface, retarded and/or decreased water uptake and delayed availability of gelatinised starch for hydrolysis by BStA. Additional experiments with waxy maize starch led to the conclusion that SSL impacts swelling power and carbohydrate leaching more by covering the starch granule surface than by forming amylose–lipid complexes. SSL postponed starch hydrolysis by BStA, but this did not influence subsequent starch gelation. Finally, when adding SSL or MAG on top of BStA to starch suspensions, the effect of the surfactants on gel strength predominated over that of BStA. Ó 2013 Elsevier Ltd. All rights reserved.

1. Introduction Starch is the main structure and texture determining component in many cereal-based products. When starch granules are heated in the presence of water, they absorb the water and swell. Below the gelatinisation temperature, this process is reversible while at or above this temperature, irreversible changes result in loss of crystallinity and disruption of the starch granules (Atwell, Hood, Lineback, Varriano-Marston, & Zobel, 1988; Delcour et al., 2010). Gelatinisation implies starch swelling and pasting. Both starch gelatinisation and pasting impact the properties of starch based products. Surfactants as well as amylases affect starch pasting (Leman, Goesaert, Vandeputte, Lagrain, & Delcour, 2005; Mira, Persson, & Villwock, 2007), gelation and retrogradation and, hence, impact the quality of starch based products (Delcour et al., 2010; Eliasson & Wahlgren, 2000; Kulp & Ponte, 1981). Surfactants contain both a hydrophilic and a hydrophobic substructure. Their amphiphilic nature allows them to position themselves at the interface between two phases (gas, liquid, air) where they decrease the interfacial tension (Belitz, Grosch, &

Abbreviations: SSL, sodium stearoyl lactylate; MAG, monoacylglycerols; AM–L, amylose–lipid; PV, peak viscosity; PT, peak time; CPV, cold paste viscosity; BStA, Bacillus stearothermophilus alpha-amylase; RVA, Rapid Visco Analyser; dm, dry matter; HPV, hot paste viscosity; SP, swelling power; CPC, close packing concentration; DSC, differential scanning calorimetry; CL, carbohydrate leaching. ⇑ Corresponding author. Tel.: +32 (0) 16321634; fax: +32 (0) 16321997. E-mail address: [email protected] (B. Van Steertegem). 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.01.064

Schieberle, 2009). In bread making, surfactants are generally referred to as emulsifiers. They can be divided into dough strengtheners [e.g. sodium stearoyl lactylate (SSL)] and crumb softeners [e.g. monoacylglycerols (MAG)] (Belitz et al., 2009; Stampfli, Nersten, & Molteberg, 1996). Dough strengtheners associate with gluten proteins during mixing, and allow them increasingly to interact, hence yielding stronger dough (De Stefanis, Ponte, Chung, & Ruzza, 1977; Pareyt, Finnie, Putseys, & Delcour, 2011), whereas crumb softeners preferably interact with gelatinised starch and form amylose–lipid (AM–L) inclusion complexes (Pareyt et al., 2011; Stampfli et al., 1996). However, some dough strengtheners (including SSL) can also form AM–L complexes (Krog, 1971). As outlined above, when starch granules are heated in water, gelatinisation and pasting occur. These irreversible changes can be visualised in a Rapid Visco Analyser (RVA) viscogram which displays the viscosity as a function of temperature and time. Such viscogram shows a viscosity peak at a temperature referred to as peak temperature. Due to starch granule swelling and release of amylose into the medium, the relative viscosity of the system increases. However, from a given moment onward, the relative viscosity of the starch system decreases markedly. This is to a large extent caused by shear-induced destruction of the swollen granules (Delcour & Hoseney, 2010). Both MAG and SSL increase the starch pasting temperature (Krog, 1973; Kulp & Ponte, 1981). Eliasson (1985) hypothesised that when AM–L complexes are formed on the starch granule surface, the latter would become

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more lipophilic and that an insoluble film may be formed which could then retard water uptake by the granules and, hence, delay their swelling. Furthermore, Krog (1973) noticed an increased peak viscosity (PV) when adding 0.5% SSL (on starch basis) to an 11.1% wheat starch suspension in a Visco Amylograph. In contrast, Azizi and Rao (2005) demonstrated that addition of the same level of SSL to a 10.0% wheat starch suspension in an RVA system decreases PV and increases cold paste viscosity (CPV). It follows from the above that the effect of SSL on PV is not completely understood. Finally, both distilled MAG and SSL can form AM–L complexes (Krog, 1971). More energy is required to dissociate them in the case of MAG, indicating that more stable AM–L complexes are formed (Ghiasi, Varriano-Marston, & Hoseney, 1982b). It is assumed that SSL and MAG primarily and more easily complex amylose than amylopectin (Gudmundsson & Eliasson, 1990; Kulp & Ponte, 1981; Stauffer, 1996) due to the limited size of the outer branches of the latter. Alpha-amylases hydrolyse alpha-1,4 linkages in starch, thereby rapidly decreasing the size of large starch molecules and reducing the viscosity of starch suspensions (Delcour & Hoseney, 2010). A special type is maltogenic Bacillus stearothermophilus alpha-amylase (BStA). It almost exclusively releases alpha-maltose (Christophersen, Otzen, Norman, Christensen, & Schafer, 1998; Outtrup & Norman, 1984) and preferentially hydrolyses the exterior chains of amylopectin. BStA works mainly according to exo-action, but also displays limited endo-action. The latter becomes more pronounced at higher temperatures (Bijttebier, Goesaert, & Delcour, 2010; Christophersen et al., 1998; Derde, Gomand, Courtin, & Delcour, 2012). This amylase has no impact on initial starch swelling, but slightly reduces PV (Leman, Bijttebier, Goesaert, Vandeputte, & Delcour, 2006; Leman, Goesaert, & Delcour, 2009). In bread making, BStA is a most effective crumb anti-firming amylase (Goesaert, Slade, Levine, & Delcour, 2009b). Starch gel formation upon cooling of heated starch suspensions has primarily been attributed to gelation of amylose in the continuous phase. Double helices are formed between amylose molecules solubilised during gelatinisation, and a continuous network develops. After some hours, the double helices form stable crystalline structures (Delcour & Hoseney, 2010). The length and concentration of the complexing ligands, together with the starch amylose/amylopectin ratio and the system’s water content, determine the impact of amylose-complexing ligands on starch gel formation (Mitchell & Zillmann, 1951). While it has been suggested that formation of AM–L complexes induces starch gelation as the insoluble AM–L complexes form an intergranular network by physical aggregation (Conde-Petit & Escher, 1992), it may also very well be that AM–L complexes, rather than inducing gelation, merely contribute to it. Furthermore, it has been suggested that formation or presence of AM–L complexes interferes with re-crystallisation of amylopectin. When AM–L complexes are formed, amylose cannot co-crystallise with amylopectin to the same extent as without added surfactants (Gudmundsson & Eliasson, 1990). In addition, when assuming that the outer branches of amylopectin would complex with lipids, this would prevent the formation of a three-dimensional crystalline network (Eliasson & Wahlgren, 2000). Several authors (Goesaert, Leman, Bijttebier, & Delcour, 2009a; Würsch & Gumy, 1994) mentioned that removing outer branches of amylopectin molecules by amylolytic hydrolysis prevents formation of a three-dimensional crystalline network during storage. Both surfactants and anti-firming enzymes (Kulp & Ponte, 1981) are frequently added together in recipes of wheat based systems, such as those of bread, waffles or cakes. Although the separate effects of surfactants and amylases on starch pasting and retrogradation have been well documented, there is no clear view

on their effects when added together. Therefore, we set out to study the impact of surfactants and BStA on starch pasting, swelling and gelation, and how these components affect changes in the starch behaviour when added together. In some of our experimental work, we not only used regular starch, but also waxy starch (in principle, containing no amylose). This was done to study whether the effects of surfactants and BStA were mainly on amylose or on amylopectin. 2. Materials and methods 2.1. Materials Wheat starch (moisture content: 12.2%) and waxy maize starch (moisture content: 11.3%) were from Syral (Aalst, Belgium). Moisture content was determined according to AACC Method 44-15.02. (AACC, 1999). SSL and distilled MAG were from Palsgaard (Juelsminde, Denmark). BStA (supplied as NovamylÒ) was from Novozymes (Bagsvaerd, Denmark). 2.2. Methods 2.2.1. Rapid visco-analysis Rapid viscosity analysis was carried out with an RVA (Model RVA-4D; Newport Scientific, Sydney, Australia). Wheat starch suspensions [8.0%, 10.0% and 12.0% dry matter (dm) w/v, total weight 25.0 g], and waxy maize starch suspensions (12.0% dm w/v, total weight 25.0 g) were analysed. Surfactants (SSL or MAG) were added as such (1.0% on starch dm basis), while 1.0 mg NovamylÒ (100 ppm on starch dm basis) was suspended in 72 mL deionised water. Surfactants and/or NovamylÒ were added at the start of each RVA run. The samples were subjected to a linear temperature increase from 50 to 95 °C at 4 °C/min (stirring speed 160 rpm). A holding step (5 min at 95 °C), a cooling step with a linear temperature decrease from 95 to 50 °C (4 °C/min) and a final isothermal step at 50 °C (9 min) were included. RVA parameters were PV, peak time (PT, i.e. the time at which the maximum viscosity is reached), hot paste viscosity (HPV, i.e. the minimum viscosity value after the PV) and CPV (i.e. the viscosity at the end of the RVA run). All viscosity readings were expressed in mPa.s. RVA analyses were also performed with addition of 5.0% surfactants and 500 ppm NovamylÒ (on starch dm basis). However, when adding 5.0% surfactants, the end viscosity could not be measured properly, while addition of 500 ppm NovamylÒ yielded only very low peak viscosities. Although profiles of samples with 5.0% surfactants and 500 NovamylÒ added were not shown, the samples were, besides the ones with 1.0% surfactants and 100 ppm NovamylÒ added, also used for determining the levels of reducing sugars during RVA analyses (see below). Furthermore, it is worth mentioning that 100 and 500 ppm NovamylÒ (on starch dm basis) corresponded to 1.7 and 8.4 enzyme units/g starch dm, respectively, determined according to Derde et al. (2012). One enzyme unit is the amount of enzyme releasing 1.0 lmole maltose equivalents per mL from 1.0% soluble starch per min at pH 6.0 and 35 °C (Derde et al., 2012). In bread making, surfactants are commonly used at a level of 0.3–1.0% (Pareyt et al., 2011), while a BStA dosage up to 9.0 enzyme units/g starch has been mentioned (Leman et al., 2006). Hence, concentrations used in this study are in that range. 2.2.2. Determination of levels of reducing sugars during RVA analyses Levels of reducing sugars of starch suspensions obtained during RVA analyses were determined. For 12.0% dm wheat starch suspensions, RVA runs (total run time 37 min) were also stopped at 5, 10 min, PT (which varied), 18 min (= time at HPV), and

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22 min. For waxy maize starch suspensions, runs were also stopped at 5 min, PT (= 7 min), and 22 min. At these specific times, the starch suspensions were collected and immediately frozen with liquid nitrogen, freeze-dried and ground during 5 s with a laboratory mill (IKA, Staufen, Germany). An aliquot (10.0 mg) of the samples was suspended in 5.0 mL deionised water and placed in a water bath (100 °C) for 10 min. This pre-heating step was done to inactivate the enzyme, but had no impact on the level of reducing sugars. After cooling for 10 min, a sediment was formed, and the supernatant was used to determine colorimetrically the level of reducing sugars according to Waffenschmidt and Jaenicke (1987). Reducing sugar levels were expressed as lmole maltose/g sample. Analyses were performed in triplicate and standard deviations did not exceed 5.0%.

with an Instron 3342 (Norwood, MA, USA) as the maximum force required for a cylindrical probe (75 mm diameter) to compress the starch gels by 12.5% at a constant test speed of 50 mm/min. Before measurements, the gels were removed from the glass cylinders. They were free-standing. As already mentioned by Yang, Liu, Ashton, Gorczyca, and Kasapis (2013) and Pons and Fiszman (1996), forces registered from a probe diameter smaller than the sample diameter are often derived from puncture and shear. Therefore, here, a probe with a larger diameter was chosen. For each cooling time, 4 gels were measured and gel firmness standard deviations did not exceed 6.0%.

2.2.3. Determination of swelling power, carbohydrate leaching and close packing concentration Swelling power (SP) of control wheat or waxy maize starch samples, and samples to which 500 ppm NovamylÒ and/or 5.0% SSL or MAG (on starch dm basis) had been added, were determined according to Eerlingen, Jacobs, Block, and Delcour (1997) with slight modifications. Basically, starch suspensions (100.0 mg starch in 9.0 mL deionised water or in 9.0 mL of a NovamylÒ suspension containing 44 lg NovamylÒ, i.e. corresponding to 500 ppm NovamylÒ on starch dm basis) were heated (30 min at 95 °C in a water bath) with intermittent shaking. After cooling (5 min), the samples were centrifuged (30 min, 4000g). The sediments were weighed and carbohydrate leached (CL), i.e. the carbohydrate in the supernatant expressed as a percentage of the starch dm, was determined according to Dubois, Gilles, Hamilton, Rebers, and Smith (1956). Samples were analysed in triplicate. Close packing concentration (CPC) and SP were calculated as follows (Dubois et al., 1956; Eerlingen et al., 1997):

3.1. Combined impact of surfactants and maltogenic amylase on starch pasting

CPC ð%Þ ¼

Dry matter starch weight  100 Sediment weight

  g Sediment weight  100 SP ¼ g Dry matter starch weight  ð100  %CLÞ 2.2.4. Differential scanning calorimetry (DSC) measurements DSC was performed with a Q2000 DSC (TA Instruments, New Castle, DE, USA). Wheat and waxy starch slurries (12.0% dm, with 1.0% SSL or MAG added alone or in combination with 100 ppm NovamylÒ, all on starch dm basis) at the end of the RVA run were cooled for 15 min (6 °C) and then accurately weighed (10.0–15.0 mg) into aluminium pans (Perkin-Elmer, Waltham, MA, USA). The pans were sealed hermetically and equilibrated at 0 °C before heating from 0 to 120 °C at 4 °C/min (together with an empty reference pan). Before analysis, the system was calibrated with indium. The temperatures and enthalpies corresponding to AM–L complex melting were evaluated from the thermograms using Universal Analysis software (TA Instruments). Samples were analysed in duplicate and enthalpies expressed in Joules per gram dm sample. 2.2.5. Preparation and textural analysis of starch gels A Brabender Visco Amylograph (Duisburg, Germany) was used to produce wheat starch gels (12.0% dm w/v, total weight 450.0 g) with BStA and/or SSL or MAG added in equal levels as in the RVA experiments. The same temperature-time profile was applied as in the RVA experiments. At the end of the Visco Amylograph run, 12 gels were poured in glass cylinders (30 mm height and 35 mm diameter) and stored in a cooling chamber (6 °C). Firmness of gels cooled for 2, 6 and 22 hours was measured

3. Results and discussion

Fig. 1 shows RVA profiles of wheat starch suspensions (8.0%, 10.0% and 12.0% dm) with SSL and/or BStA added. At all starch concentrations, adding BStA together with SSL postponed the initial viscosity increase compared to those of control samples, whereas the effect on PV and CPC varied with starch concentration. Addition of BStA alone decreased both PV and CPV to extents which depended on the starch dm level (Fig. 1). In general, the lower the starch concentration, the higher the decrease in PV and CPV. Leman et al. (2005) related this to the structural properties of the starch paste and its amylose molecules being insufficient to form an effective network during cooling when the starch concentration is closer to its CPC (i.e. 6.4% for control wheat starch samples). However, it may also be that the concentration itself is insufficient to maintain the supramolecular structure. Addition of SSL alone to wheat starch suspensions increased the pasting temperature. Comparison of RVA profiles of starch suspensions with BStA and SSL added separately with those of starch suspensions with both additives added together has shown that both enzyme and surfactant impacted the viscosity profile, demonstrating that BStA lowered PV and CPV, while SSL postponed viscosity increase (Fig. 1). Furthermore, the effect of SSL, when added either alone or in combination with BStA, on pasting temperature, PV and CPV strongly depended on the starch concentration. The increase in pasting temperature was higher when adding the components to more concentrated (12.0% dm) rather than to less concentrated suspensions (8.0% dm). Additionally, the addition of SSL alone or in combination with BStA increased PV and CPV to a larger extent for starch slurries with 8.0% dm than for starch slurries with 10.0% dm, while at 12.0% dm it decreased both parameters compared to the respective control samples with or without BStA (Fig. 1). Furthermore, for all starch dm concentrations tested, addition of SSL alone or in combination with BStA induced a viscosity increase upon cooling at ca. 70 °C. This viscosity increase presumably originated from complexation of SSL with amylose. In this context, it is relevant that Conde-Petit and Escher (1995) suggested that starch gelation is induced by physical aggregation of insoluble AM–L complexes forming an intergranular network (Conde-Petit & Escher, 1995), or that AM–L complexes, rather than inducing gelation, merely contribute to it. In the present case, the PV and CPV increases were most pronounced in RVA profiles at 8.0% dm starch concentration (Fig. 1A). Presumably, while addition of SSL would also increase PV (and CPV) in a more concentrated system, in such system, the starch would experience higher shear during pasting and cooling. Clearly, both BStA and SSL impact RVA profiles. However, it appears that SSL (at least partly) hindered or delayed starch hydrolysis by BStA since, at all dm levels tested, the % PV decrease was lower when BStA was combined with SSL (8.0% dm: 38.7%,

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B

A

C

Fig. 1. RVA pasting profiles of wheat starch suspensions (A: 8.0% dm, B: 10.0% dm and C: 12.0% dm): control ( ), with 1.0% SSL ( ), 100 ppm NovamylÒ ( and 1.0% SSL + 100 ppm NovamylÒ ( ) added (on starch dm basis). NovamylÒ was the source of BStA. The temperature profile is also shown ( ).

10.0% dm: 30.5%, and 12.0% dm: 18.0%, respectively) than when BStA was added alone (8.0% dm: 56.8%; 10.0% dm: 41.0%; 12.0% dm: 20.8%, respectively) (Fig. 1). Monitoring the levels of reducing sugars during RVA analyses revealed that adding BStA to 12.0% dm wheat starch suspension released ca. 30 lmole maltose/g starch sample during the first 10 min of the RVA analysis, with the level thereafter remaining rather constant (Fig. 2A) possibly due to product inhibition or enzyme saturation. Adding BStA together with SSL yielded lower levels of reducing sugars after 5 and 10 min during RVA analysis than when BStA was added alone, which shows that SSL delayed the release of maltose by BStA. It is of note that, at the end of the RVA run, approximately the same level of reducing sugars had been released than when BStA was added alone (Fig. 2A) showing that SSL delays but does not prevent the hydrolytic action of the enzyme. Increasing the levels of NovamylÒ and SSL (500 ppm and 5.0% on starch dm basis, respectively), thereby maintaining their relative ratios, yielded similar trends (results not shown). Probably, addition of SSL retards water uptake, and delays starch swelling. The gelatinised starch hence becomes available for hydrolysis by BStA at a later moment, i.e. at a higher temperature. Different results were obtained when MAG rather than SSL were added together with BStA. The % PV decrease in the RVA profile was similar to that when the enzyme was added alone (Fig. 3). In addition, starch hydrolysis, as deduced from the increase in the level of reducing sugars, was not postponed when combining MAG and BStA (Fig. 2A). The different mechanisms whereby SSL and MAG exert their effects may be related to the former being negatively charged and the latter being nonionic. Most likely, starch granule surface characteristics differ in another way following addition of either SSL or MAG, which then differently affects the granule’s enzyme accessibility. To study whether the effect of surfactants and BStA was mainly on amylose rather than on amylopectin, waxy starch (containing no amylose, which was confirmed by DSC data showing no peaks corresponding to AM–L complex melting) was also used. BStA

)

and SSL or MAG were added to 12.0% dm waxy maize starch suspensions and the mixtures were subjected to the same RVA temperature profile as the above wheat starch suspensions (Fig. 4). The more rapid and extensive swelling of waxy starch granules compared to that of regular starch granules is usually attributed to a more loosely bound starch granule internal structure due to the absence of amylose (Grant et al., 2001; Mira et al., 2007; Tester & Morrison, 1990). Adding BStA to waxy maize suspensions did not alter PV and lowered CPV. Addition of SSL or MAG, alone or in combination with BStA, did not affect greatly the RVA curve of the control waxy maize sample (Fig. 4). Mira et al. (2007), working with waxy wheat starch, reported that nonionic surfactants have only a minor effect on pasting, while ionic surfactants lower pasting temperature. However, in our study, SSL or MAG addition to waxy starch hardly impacted the time at which viscosity increased (Fig. 4). One must also take into account that waxy maize starch has a lower PV than waxy wheat starch, and that the temperature at which both reach PV is similar (Graybosch, 1998). When BStA was added to wheat starch suspensions, reducing sugar levels increased only during the first 10 min of RVA analysis (Fig. 2A). Remarkably, when adding BStA to waxy maize starch suspensions, the levels of reducing sugars continuously increased (Fig. 2B) indicating that BStA continued to hydrolyse amylopectin. During the first 5 min of the RVA analysis, reducing sugar levels increased more rapidly upon addition of BStA to wheat starch than when adding it to waxy maize starch. However, towards the end of the RVA run, reducing sugars were released more easily and to a larger extent in the case of waxy starch. In contrast to the effects observed with wheat starch, combined addition of SSL or MAG with BStA to waxy starch, had little impact on starch hydrolysis by BStA. The increase in levels of reducing sugars during RVA analyses, when adding either of the surfactants and the amylase, was comparable to that of adding BStA alone (Fig. 2B). In this experimental set up, SSL and MAG did not impact BStA activity when adding them to waxy maize starch.

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A

B

Fig. 2. Levels of reducing sugars (expressed as lmole maltose/g) of RVA wheat (A) and waxy maize (B) starch suspensions (12.0% dm): control ( ), with 1.0% SSL ( ), 1.0% MAG ( ), 100 ppm NovamylÒ ( ), 1.0% SSL + 100 ppm NovamylÒ ( ) and 1.0% MAG + 100 ppm NovamylÒ ( ) added (on starch dm basis). NovamylÒ was the source of BStA. RVA-runs were stopped and samples were taken at 5, 10 min, peak time, 18, 22 and 37 min for wheat starch suspensions and at 5, 7, 20 and 37 min for waxy maize starch suspensions.

Fig. 3. RVA pasting profiles of wheat starch suspension (12.0% dm): control ( ), with 1.0% MAG ( ), 100 ppm NovamylÒ ( ) and 1.0% MAG + 100 ppm NovamylÒ ( ) added (on starch dm basis). NovamylÒ was the source of BStA. The temperature profile is also shown ( ).

3.2. Combined impact of surfactants and maltogenic amylase on starch swelling and carbohydrate leaching To increase our understanding of how surfactants and maltogenic amylase affect (regular and waxy) starch swelling behaviour during pasting, CPC, SP and CL were determined. Although BStA addition decreased PV in RVA profiles of wheat starch (Fig. 1), granules had higher SP and CPC than those in control samples due to starch hydrolysis and concomitant release

of maltose and other carbohydrate material, and thus increased CL (Table 1). Adding SSL, alone or in combination with BStA, decreased CPC and logically increased SP. Surprisingly, no such effect was observed upon MAG addition. When combining BStA with MAG, mostly the effect of the former was observed, indicating that MAG hardly impacted CPC and SP. Similar effects were found when these surfactants and BStA were added to waxy maize starch (Table 1). In line with the present results, Ghiasi, Hoseney, and Varriano-Marston (1982a) found that SP of wheat starch at 95 °C increased upon addition of SSL. However, they also noticed a decrease in SP when MAG were added (Ghiasi et al., 1982a). Clearly, SSL and MAG have similar effects on viscosity changes, but the mechanism by which they impact starch swelling differs. SSL probably adsorbs on the starch granule surface, thereby increasing its SP. One can assume that MAG do not cover the starch granule surface to the same extent as SSL, and therefore have less impact on CPC and SP. Furthermore, SP increased largely upon addition of SSL to waxy starch providing further evidence for our view that the mechanism whereby this surfactant operates is by adsorbing on the starch granule surface. Thus, covering the starch granule surface and delaying water uptake must be the most important factor determining SP upon addition of SSL, both for regular and waxy starches. However, although we assume that AM–L complexes do not impact the extent of starch granule swelling, their formation is presumably still responsible for delaying granule swelling. The AM–L melting enthalpy increased with 3.3 and 3.8 J/g when SSL and MAG were added, respectively. Since MAG were superior to SSL at AM–L complex formation and

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B

A

Fig. 4. RVA pasting profiles of waxy maize starch suspensions (12.0% dm level). (A) control ( ), with 1.0% SSL ( ), 100 ppm NovamylÒ ( ) and 1.0% SSL + 100 ppm NovamylÒ ( ) added (on starch dm basis). (B) control ( ), with 1.0% MAG ( ), 100 ppm NovamylÒ ( ) and 1.0% MAG + 100 ppm Ò Ò Novamyl ( ) added (on starch dm basis). Novamyl was the source of BStA. The temperature profile is also shown ( ).

Table 1 Close packing concentration (CPC) (%), swelling power (SP) (g/g) and carbohydrate leaching (CL) (%) of control wheat and waxy maize starch, and with 5.0% SSL, 5.0% MAG, 500 ppm NovamylÒ, 5.0% SSL + 500 ppm NovamylÒ and 5.0% MAG + 500 ppm NovamylÒ added (on starch dm basis). NovamylÒ was the source of BStA. CPC (%)

SP (g/g)

CL (%)

Wheat starch Control 5.0% SSL 5.0% MAG 500 ppm NovamylÒ 5.0% SSL + 500 ppm NovamylÒ 5.0% MAG + 500 ppm NovamylÒ

6.4 4.3 6.2 7.7 5.4 7.8

(±0.1) (±0.1) (±0.1) (±0.2) (±0.1) (±0.0)

23.9 33.1 23.4 25.4 31.2 23.9

31.8 29.9 30.4 48.7 40.7 46.4

(±0.2) (±0.1) (±0.7) (±1.1) (±1.5) (±1.9)

Waxy maize starch Control 5.0% SSL 5.0% MAG 500 ppm NovamylÒ 5.0% SSL + 500 ppm NovamylÒ 5.0% MAG + 500 ppm NovamylÒ

2.3 0.9 2.4 2.9 1.0 3.0

(±0.0) (±0.0) (±0.1) (±0.0) (±0.0) (±0.0)

50.4 (±0.6) 124.8 (±3.4) 47.1 (±2.1) 61.9 (±0.1) 129.8 (±4.3) 53.5 (±1.1)

15.4 13.5 15.2 43.0 22.0 40.4

(±0.8) (±0.1) (±1.3) (±1.3) (±1.5) (±3.4)

(±1.7) (±0.8) (±0.6) (±1.0) (±0.2) (±0.8)

since MAG slightly delayed the time at which viscosity increased to a greater degree than SSL (Figs. 1C and 3), the impact of AM–L complex formation on delaying granule swelling probably predominated over that of retarding water uptake by adsorbing on the granule surface and making it more lipophilic. In contrast,

A

Mira et al. (2007) suggested that the effect of surfactants on the onset of pasting of wheat starch can be related to the dissociation of AM–L complexes. However, it seems more logical that the formation of AM–L complexes rather than their dissociation can impact onset of pasting. Furthermore, besides its impact on the onset of pasting, it is likely that formation of AM–L complexes also affects the end viscosity. The increase in both AM–L melting enthalpy, determined at the end of the RVA run (i.e. 2.9 J/g) and end viscosity (Fig. 1) of samples with SSL combined with BStA, was less pronounced than those of samples with SSL alone. Furthermore, when MAG were combined with BStA, the end viscosity (Fig. 3) and increase in AM–L melting enthalpy (i.e. 3.8 J/g) were both equal to those of samples with addition of only the surfactant. In addition, CL decreased slightly upon adding either of the surfactants to wheat starch (Table 1). Also Eliasson (1985) noticed that, in the presence of SSL, the amount of amylose leached from the granules decreases. Since surfactants such as SSL and MAG complex amylose (Gudmundsson & Eliasson, 1990; Stauffer, 1996), the observed decrease in CL is presumably due to formation of AM–L complexes. Formation of such complexes inside the granules prevents amylose from leaching out (Becker, Hill, & Mitchell, 2001; Eliasson, 1985). However, adding SSL or MAG to waxy maize starch resulted in a slight decrease of or no impact on CL, respectively (Table 1). Presumably, covering the starch gran-

B

Fig. 5. Firmness of wheat starch gels. (A) at 12.0% dm: control ( ), with 1.0% SSL ( ), 1.0% MAG ( ), 100 ppm NovamylÒ ( ), 1.0% SSL + 100 ppm NovamylÒ ( ) and 1.0% MAG + 100 ppm NovamylÒ ( ) added (on starch dm basis). (B) at 8.0% dm: control ( ) and with 1.0% SSL ( ). NovamylÒ was the source of BStA.

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ule surface with SSL (partly) hindered amylose leaching out, while MAG have shown no such effect. 3.3. Combined impact of surfactants and maltogenic amylase on gelation and starch gel strength The impact of surfactants, alone or in combination with BStA, on starch gel strength was also investigated. Starch gels (12.0% dm) produced with BStA addition had higher initial firmness than control gels (Fig. 5). This is probably due to more efficient gelation and a logical consequence of the increased CPV during cooling at the end of RVA analyses. Earlier, Hug-Iten, Escher, and Conde-Petit (2003) found that maltogenic amylase promotes the aggregation of amylose in the bread making process. Starch gels with surfactants added and cooled for 2, 6 and 22 hours, at both 8.0% and 12.0% dm starch concentration, were softer than control gels (Fig. 5). Such results have earlier been described by Osman and Dix (1960), who found that gels with added surfactants are in general weaker than control gels. Surprisingly, the higher viscosity increase during cooling of the RVA sample at 8.0% dm concentration upon addition of SSL did not result in increased gel firmness. Indeed, after 2 hours cooling a weaker gel was obtained. The decreased gel firmness at both starch concentrations for SSL and MAG is probably due to formation of AM–L complexes. When such complexes are formed, less amylose is available for gelation. Addition of MAG reduced gel firmness slightly more than SSL addition (Fig. 5). In the former case, as mentioned previously when discussing DSC results, more AM–L complexes were formed than in the latter. Remarkably, adding BStA in combination with either SSL or MAG yielded softer gels (Fig. 5), indicating that the effect of the surfactants predominated and that, after complex formation, BStA could no longer hydrolyse the starch. As the CPV of samples with both surfactants and BStA was lower than that of control samples (12.0% dm), the cooled samples also had a decreased initial firmness. Postponing starch hydrolysis by BStA upon addition of SSL did not influence gelation of cooled gels since no large difference in gel firmness was observed when adding SSL or MAG combined with BStA. 4. Conclusions When adding BStA together with SSL to wheat starch suspensions, both influenced the viscosity profile, the extent of which varied with the starch dm level. It appeared that SSL (at least partly) hinders or delays starch hydrolysis by BStA, whereas MAG show no such effect. Probably, SSL covered the starch granule surface, thereby (i) retarding water uptake, and making gelatinised starch available at a later moment for hydrolysis by BStA, (ii) stabilising the granules against disruption and increasing SP, and (iii) hindering CL (i.e. amylose leaching). Based on this, it was hypothesised that the observed effects can be explained in terms of differences in the extent to which the surfactants cover the starch granule surface, with MAG doing so to a lesser extent than SSL. Data obtained using wheat and waxy maize starches have shown that SSL exerts its effect on SP and CL. This can be more easily explained when assuming that SSL covers the starch granule surface than that it would form AM–L complexes. Furthermore, since both SSL and MAG had a similar starch granule swelling delaying effect on RVA viscosity profiles, this could probably not only be attributed to surfactants covering starch granule surfaces, but was presumably also affected by formation of AM–L complexes. Finally, it has been demonstrated that postponing starch hydrolysis by BStA upon addition of SSL did not influence starch forming a cooled and set gel structure, and that adding BStA with either SSL or MAG yielded softer gels, indicating that the

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effect of surfactants predominated. It is important to stress that surfactants can impact the action of BStA in cereal systems in which starch is gelatinised. The impact on starch hydrolysis is (partly) determined by the type of surfactant and more specifically by the extent of the interaction of the surfactant with the starch granule surface. Further research is needed to fully elaborate on the specific interactions taking place on a molecular level. FTIR measurements (Cremer & Kaletunc, 2003; Joshi et al., 2013; Miao, Zhang, Mu, & Jiang, 2010) can probably be useful in this context. Acknowledgements The authors are grateful to Kim Melotte for technical assistance and to Liesbeth Derde, Geertrui Bosmans and Sara Gomand for fruitful discussions. We thank the Agentschap voor Innovatie door Wetenschap en Technologie in Vlaanderen (IWT, Brussels, Belgium) for financial support. Bram Pareyt and Kristof Brijs acknowledge the Research Fund – Flanders (FWO – Vlaanderen, Brussels, Belgium) and the Industrial Research Fund (KU Leuven, Leuven, Belgium), for their positions as postdoctoral research fellows, respectively. This research is also part of the Methusalem programme ‘‘Food for the Future’’ (2007–2014) at the KU Leuven. Jan A. Delcour is W.K. Kellogg Chair in Cereal Science and Nutrition at the KU Leuven. References AACC (1999). Approved methods of analysis, 11th ed. Method 44-15.02. Moisture  Air-oven methods. Approved November 3, 1999. AACC International, St. Paul, MN, USA. http://dx.doi.org/10.1094/AACCIntMethod-44-15.02. Atwell, W. A., Hood, L. F., Lineback, D. R., Varriano-Marston, E., & Zobel, H. F. (1988). The terminology and methodology associated with basic starch phenomena. Cereal Foods World, 33, 306–311. Azizi, M. H., & Rao, G. V. (2005). Effect of surfactant in pasting characteristics of various starches. Food Hydrocolloids, 19, 739–743. Becker, A., Hill, S. E., & Mitchell, J. R. (2001). Relevance of amylose–lipid complexes to the behaviour of thermally processed starches. Starch, 53, 121–130. Belitz, H. D., Grosch, W., & Schieberle, P. (2009). Food Chemistry, 4th revised and extended ed. Berlin, Germany: Springer-Verlag. Bijttebier, A., Goesaert, H., & Delcour, J. A. (2010). Hydrolysis of amylopectin by amylolytic enzymes: structural analysis of the residual amylopectin population. Carbohydrate Research, 345, 235–242. Christophersen, C., Otzen, D. E., Norman, B. E., Christensen, S., & Schafer, T. (1998). Enzymatic characterisation of Novamyl (R), a thermostable alpha-amylase. Starch, 50, 39–45. Conde-Petit, B., & Escher, F. (1992). Gelation of low concentration starch systems induced by starch emulsifier complexation. Food Hydrocolloids, 6, 223–229. Conde-Petit, B., & Escher, F. (1995). Complexation induced changes of rheological properties of starch systems at different moisture levels. Journal of rheology, 39, 1497–1518. Cremer, D. R., & Kaletunc, G. (2003). Fourier transform infrared microspectroscopic study of the chemical microstructure of corn and oat flour-based extrudates. Carbohydrate Polymers, 52, 53–65. De Stefanis, V., Ponte, J. G., Chung, F. H., & Ruzza, N. A. (1977). Binding of crumb softeners and dough strengtheners during breadmaking. Cereal Chemistry, 54, 13–24. Delcour, J. A., Bruneel, C., Derde, L. J., Gomand, S. V., Pareyt, B., Putseys, J. A., et al. (2010). Fate of starch in food processing: From raw materials to final food products. Annual Review of Food Science and Technology, 1, 87–111. Delcour, J. A., & Hoseney, R. C. (2010). Principles of cereal science and technology (3rd ed.). MN, USA: AACC International, St. Paul. Derde, L. J., Gomand, S. V., Courtin, C. M., & Delcour, J. A. (2012). Characterisation of three starch degrading enzymes: Thermostable beta-amylase, maltotetraogenic and maltogenic alpha-amylases. Food Chemistry, 135, 713–721. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A., & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Analytical Chemistry, 28, 350–356. Eerlingen, R. C., Jacobs, H., Block, K., & Delcour, J. A. (1997). Effects of hydrothermal treatments on the rheological properties of potato starch. Carbohydrate Research, 297, 347–356. Eliasson, A. C. (1985). Starch gelatinization in the presence of emulsifiers – A morphological study of wheat starch. Starch, 37, 411–415. Eliasson, A. C., & Wahlgren, M. (2000). Starch–lipid interactions and their relevance in food products. In A. C. Eliasson (Ed.), Starch in food, structure, function and applications (pp. 441–460). Cambridge, England: CRC Press, Woodhead Publishing. Ghiasi, K., Hoseney, R. C., & Varriano-Marston, E. (1982a). Gelatinization of wheat starch. I. Excess-water systems. Cereal Chemistry, 59, 81–85.

1120

B. Van Steertegem et al. / Food Chemistry 139 (2013) 1113–1120

Ghiasi, K., Varriano-Marston, E., & Hoseney, R. C. (1982b). Gelatinization of wheat starch. II. Starch-surfactant interaction. Cereal Chemistry, 59, 86–88. Goesaert, H., Leman, P., Bijttebier, A., & Delcour, J. A. (2009a). Antifirming effects of starch degrading enzymes in bread crumb. Journal of Agricultural and Food Chemistry, 57, 2346–2355. Goesaert, H., Slade, L., Levine, H., & Delcour, J. A. (2009b). Amylases and bread firming: An integrated review. Journal of Cereal Science, 50, 345–352. Grant, L. A., Vignaux, N., Doehlert, D. C., McMullen, M. S., Elias, E. M., & Kianian, S. (2001). Starch characteristics of waxy and nonwaxy tetraploid (Triticum turgidum L. var. durum) wheats. Cereal Chemistry, 78, 590–595. Graybosch, R. A. (1998). Waxy wheats: Origin, properties, and prospects. Trends in Food Science and Technology, 9, 135–142. Gudmundsson, M., & Eliasson, A. C. (1990). Retrogradation of amylopectin and the effects of amylose and added surfactants/emulsifiers. Carbohydrate Polymers, 13, 295–315. Hug-Iten, S., Escher, F., & Conde-Petit, B. (2003). Staling of bread: Role of amylose and amylopectin and influence of starch-degrading enzymes. Cereal Chemistry, 80, 654–661. Joshi, M., Aldred, P., McKnight, S., Panozzo, J. F., Kasapis, S., Adhikari, R., & Adhikari, B. (2013). Physicochemical and functional characteristics of lentil starch. Carbohydrate Polymers, 92, 1484–1496. Krog, N. (1971). Amylose complexing effect of food grade emulsifiers. Starch, 23, 206–209. Krog, N. (1973). Influence of food emulsifiers on pasting temperature and viscosity of various starches. Starch, 25, 22–27. Kulp, K., & Ponte, J. G. (1981). Staling of white pan bread: Fundamental causes. Critical Reviews in Food Science and Nutrition, 15, 1–48. Leman, P., Bijttebier, A., Goesaert, H., Vandeputte, G. E., & Delcour, J. A. (2006). Influence of amylases on the rheological and molecular properties of partially damaged wheat starch. Journal of the Science of Food and Agriculture, 86, 1662–1669. Leman, P., Goesaert, H., & Delcour, J. A. (2009). Residual amylopectin structures of amylase-treated wheat starch slurries reflect amylase mode of action. Food Hydrocolloids, 23, 153–164.

Leman, P., Goesaert, H., Vandeputte, G. E., Lagrain, B., & Delcour, J. A. (2005). Maltogenic amylase has a non-typical impact on the molecular and rheological properties of starch. Carbohydrate Polymers, 62, 205–213. Miao, M., Zhang, T., Mu, W., & Jiang, B. (2010). Effect of controlled gelatinization in excess water on digestibility of waxy maize starch. Food Chemistry, 119, 41–48. Mira, I., Persson, K., & Villwock, V. K. (2007). On the effect of surface active agents and their structure on the temperature-induced changes of normal and waxy wheat starch in aqueous suspension. Part I. Pasting and calorimetric studies. Carbohydrate Polymers, 68, 665–678. Mitchell, W. A., & Zillmann, E. (1951). The effect of fatty acids on starch and flour viscosity. Transactions American Association of Cereal Chemists, 9, 64–79. Osman, E. M., & Dix, M. R. (1960). Effects of fats and nonionic surface-active agents on starch pastes. Cereal Chemistry, 37, 464–475. Outtrup, H., & Norman, B. E. (1984). Properties and application of a thermostable maltogenic amylase produced by a strain of Bacillus modified by recombinantDNA techniques. Starch, 36, 405–411. Pareyt, B., Finnie, S. M., Putseys, J. A., & Delcour, J. A. (2011). Lipids in bread making: Sources, interactions, and impact on bread quality. Journal of Cereal Science, 54, 266–279. Pons, M., & Fiszman, S. M. (1996). Instrumental texture profile analysis with particular reference to gelled systems. Journal of Texture Studies, 27, 597–624. Stampfli, L., Nersten, B., & Molteberg, E. L. (1996). Effects of emulsifiers on farinograph and extensograph measurements. Food Chemistry, 57, 523–530. Stauffer, C. E. (1996). Properties of emulsifiers. In C. E. Stauffer (Ed.), Fats and Oils (pp. 29–45). MN, USA: Eagon Press, AACC International, St. Paul. Tester, R. F., & Morrison, W. R. (1990). Swelling and gelatinization of cereal starches. I. Effects of amylopectin, amylose, and lipids. Cereal Chemistry, 67, 551–557. Waffenschmidt, S., & Jaenicke, L. (1987). Assay of reducing sugars in the nanomole range with 2,20 -bicinchoninate. Analytical Biochemistry, 165, 337–340. Würsch, P., & Gumy, D. (1994). Inhibition of amylopectin retrogradation by partial beta-amylolysis. Carbohydrate Research, 256, 129–137. Yang, N., Liu, Y., Ashton, J., Gorczyca, E., & Kasapis, S. (2013). Phase behaviour and in vitro hydrolysis of wheat starch in mixture with whey protein. Food Chemistry, 137, 76–82.