Dual-frequency ultrasound for ultrasonic-assisted esterification

Received: 4 March 2019 | Revised: 17 May 2019 | Accepted: 19 May 2019 DOI: 10.1002/fsn3.1115 ORIGINAL RESEARCH Dual‐frequency ultrasound for ultrasonic‐assisted esterification Elahe Abedi1 | Kiana Pourmohammadi1 | Sahar Abbasi2 1 Department of Food Science and Technology, College of Agriculture, Fasa University, Fasa, Iran 2 Department of Food Science and Technology, Sarvestan Azad University, Sarvestan, Iran Correspondence Elahe Abedi and Kiana Pourmohammadi, Department of Food Science and Technology, College of Agriculture, Fasa University, Fasa, Iran. Email: elaheabedi1389@gmail.com; e.abedi@ fasau.ac.ir; Kpourmohammadi@yahoo.com Abstract The optimization of wheat starch esterification (acetylation) with a high degree of substitution was performed through response surface methodology (RSM) via various concentrations of reagents (acetic anhydride), pHs, and temperatures under various ultrasonication frequencies (25, 40, and 25 + 40 kHz). According to RSM methodology, optimized samples were selected by achieving high degrees of substitution at various frequencies, temperatures, and pHs. Solubility, swelling, X-ray, RVA, DSC, freeze–thaw stability, texture, and SEM analysis of the optimized samples were performed at three frequencies. X-ray pattern exhibited a more significant reduction in the crystallinity percentage of esterified starch at frequency 25 + 40 kHz compared with 25 kHz, 40 kHz, and native starch. According to DSC analysis, To, Tp, Tc, and enthalpy of gelatinization (ΔH gel) were lower in AC at frequency 25 + 40 kHz compared with AC at frequency 25 and 40 kHz and N starches. According to morphology analysis, in acetylated starches at 25 and 40 kHz, the surfaces and small granules underwent more damage, whereas in 25 + 40 kHz, large granules were more affected than small granules. Upon acetylation, freeze–thaw stability and textural properties of the starch significantly increased and decreased, respectively. The peak and final viscosity of acetylated starch increased (25 + 40 kHz ˃ 25 kHz ˃ 40 kHz ˃ N starch). KEYWORDS Acetylation, dual-frequency ultrasonic, optimization, wheat starch 1 | I NTRO D U C TI O N the functional groups into the starch molecules, chemically modified starches, such as oxidized, hydroxypropylated, and acetylated Starch is an accessible, thickening, and texturizing stabilizer, and of starches, were employed. When starch is modified, its gelatiniza- paramount importance when it comes to augmenting the overall tion, pasting, and retrogradation characteristics undergo different quality of the products, reducing costs, and facilitating the process- changes (Kaur et al., 2012, 2010; Singh, Kaur, & McCarthy, 2007). ing procedure (Berski et al., 2011; Choi & Kerr, 2003); however, due Acetylated starch (AC) was introduced with CH3CO group which to the high affinity toward retrogradation, its application is restricted caused a cleavage in the hydrogen bonds inside the starch chain and in certain food products (Kaur, Ariffin, Bhat, & Karim, 2012; Kaur, resulted in amphiphilic properties (Hong, Chen, Zeng, & Han, 2016). Sandhu, & Lim, 2010). In frozen foods and desserts containing starch, AC with a low degree of substitution (DS) is used as an emulsifier, resistance to syneresis of water, resistance to freeze and thaw, and coating, and thickening agent, which is stable and resistant to retro- reduction in retrogradation are important issues. In this regard, na- gradation (Chi et al., 2008; Singh, Chawla, & Singh, 2004). Moreover, tive starch was modified to overcome this limitation. By introducing in such kinds of modified starch, solubility, swelling power, viscosity, This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. © 2019 The Authors. Food Science & Nutrition published by Wiley Periodicals, Inc. Food Sci Nutr. 2019;00:1–12. www.foodscience-nutrition.com | 1 2 | ABEDI Et Al. hardness, adhesiveness, cohesiveness, and translucency of the gels an input power of up to 400 W and working frequencies of 25, 40, are increased, while the initial gelatinization temperature is reduced and 25 + 40 kHz) at 45, 60, and 75°C. The time duration of sonica- (González & Perez, 2002). The replacement of the modifier groups tion in each frequency was 5 min (25 kHz: 5 min, 40 kHz: 5 min, and may boost the free movement of the starch chains within the amor- 25 + 40 kHz: 5 min). pH was then maintained at 4.5 with HCl solution phous regions in the granule, owing to the disruptions taking place (1 M) for 5 min. All the experiments were performed in bakers placed at among the inter- and intramolecular hydrogen bonds. The weakened known positions in ultrasonic bath (Pacisa SA) equipped with a temper- internal bond structure in the starch granules, due to the derivatized ature controlling system. The ultrasonic bath with internal dimensions modifier groups, enhances the freeze–thaw stability, reduces the ge- of 300 × 150 × 150 mm3 consisted of a rectangular tank containing latinization temperature, generates high levels of peak viscosity, and four transducers at the bottom. The suspensions were completely leads to starch paste clarity (Han, 2010; Han, Lee, Lim, & Lim, 2005). washed, lyophilized, and milled using a laboratory mill (AlexanderWerk, Ultrasonic treatments can accelerate chemical reaction and increase yields. Under sonication, the surface area of starch gran- Model WEL82), and manually sieved to obtain particle sizes < 40 μm (Wojeicchowski, Siqueira, Lacerda, Schnitzler, & Demiate, 2018). ules increases due to the formation of channels and/or holes on the surface and inside the granules (Huang, Li, & Fu, 2007). Several modifications have been performed upon ultrasonication, includ- 2.3 | Acetyl percentage ing acetylation of dioscorea starch following ultrasound treatment The titrimetric method of Mbougueng, Tenin, Scher, and Tchiégang (Zhang, Zuo, Wu, Wang, & Gao, 2012), octenyl succinate starch (2012) was employed in order to specify the acetyl group percentage (Chen, Huang, Fu, & Luo, 2014), carboxymethyl starch (Gao et al., (AC%) and (DS). AC (5.0 g), 50 ml of distilled water, and 24 ml of 0.45 M 2011; Shi & Hu, 2013), and octenylsuccinates of carboxymethyl NaOH were added in a 240-mL flask and mixed for 30 min at room starch (Čížová, Sroková, Sasinková, Malovíková, & Ebringerová, temperature. The surplus alkali was back-titrated using 0.2 M HCl and 2008). However, there is no information about the acetylation of phenolphthalein as an indicator. The reaction mixture was put to stand starch under various frequencies of ultrasonication. The aim of this for 2 hr, where the alkali was removed from the titrated sample. The study was to optimize the AC wheat starch in various parameters native starch was also used as a blank sample. Initially, the acetyl (%) such as acetic anhydride concentration, pH, and temperature under and DS were calculated according to Equations (1) and (2), respectively: frequencies (25, 40, and 25 + 40 kHz) of bath ultrasound; the optimization was further investigated on the amount of modification ) ( % Acetylation = [ VB − VS × NHCl × 0.043 × 100]∕W (1) (molar substitution) in the modified starch. Based on the minimal reagent consumption, the optimized samples were selected and their physicochemical properties (solubility, water absorption), X-ray diffraction, scanning electron microscopy (SEM), Rapid Visco Analyzer VB and VS are the volumes of the control and modified samples (0.2 M HCl basis), respectively. (RVA), differential scanning calorimetry (DSC), and Texture Profile NHCl is the normality of the consumed acid. Analyzer (TPA) were investigated at three frequencies (25, 40, and W is the weight of the sample. 25 + 40 kHz). The freeze and thaw stability of AC wheat starch was further compared with that made with native wheat starch. 2 | M ATE R I A L S A N D M E TH O DS 2.1 | Materials DS = (162 × Acetyl %)∕[4300 − (42 × Acetyl %)] (2) 2.4 | X‐ray diffraction To obtain a relative humidity of 75%, all starch samples were pri- Native wheat starch was obtained from Fars Glucosin Company, marily placed, for 5 days, in a relative humidity box containing su- Shiraz, Iran. The moisture, fat, ash, and protein of native (N) and AC persaturated NaCl at room temperature. X-ray diffraction pattern wheat starch prepared under ultrasonication were specified along of the samples was determined by use of an X-ray diffractometer with the standard methods of AACC, 2000. Amylose content (%) (Model D8 Advance, Germany) (Li et al., 2014). Utilizing the instru- was calculated by iodine method (Pourmohammadi, Abedi, Hashemi, ment software (EVA, Version 9.0), the degree of starch crystallin- & Torri, 2018). ity was specified through dividing the area under the peaks by the total curve area. 2.2 | Acetylation of wheat starch We added 100 g of starch to 224 ml of distilled water and stirred for 2.5 | Solubility and water absorption 1 hr at 24°C. The pH was set to 6.5, 8, and 9.5 with NaOH solution The method of Li et al. (2014) was used to determine water swell- (1 M), and acetic anhydride (4, 6 and 8%) was slowly added to the sus- ing and solubility of the samples with a slight modification. Native pension at various pHs. Whole acetylation reaction was performed at and modified wheat starches (1 g) and distilled water (30 ml) were 10 min. The suspensions were sonicated at an amplitude of 24% (with added into a centrifuge tube, and, using a vortex mixer set at high | ABEDI Et Al. 3 speed, they were shaken at room temperature for 5 min. Each tube speed of 5 mm/s, time interval of 10 s, and strain deformation of 24%. was incubated in water bath for 30 min at 95°C followed by centrif- The recorded force–time plots were analyzed for the following: hard- ugation for 15 min at 3000 g. The weights of the pellet and dried ness (N), springiness (Length 2/ Length 1), cohesiveness, the ratio of the supernatants (at 120°C for about 2 hr) were further obtained. The areas of the two resistance peaks (A2/A1), and gumminess according to water solubility and swelling values of the native and modified Abedi, Majzoobi, Farahnaky, Pourmohammadi, and Mahmoudi (2018). samples were calculated using Equations (3) and (4), respectively. Water solubility (%) = weight of dissolved solids in supernatant/weight of dry sample solids in the original sample × 100 (3) ( ) ( ( )) Water swelling (%) = weight of sediment × 100 ∕ weight of dry sample solids × 100 − solubility (4) 2.6 | Pasting properties Using the method described by Pourmohammadi et al. (2018), the Data were analyzed three times, and the results were averaged. 2.10 | Freeze–thaw stability pasting properties of the native and modified wheat starches were determined through RVA (Newport Scientific Pty. Ltd) interfaced With slight modifications in the methods described by Lawal with a personal computer. (2010), we determined the syneresis of the starch gels belonging to the native and modified starches during cold and frozen stor- 2.7 | Thermal properties age. A starch suspension (5% dry basis, w/w) was heated at 95°C under constant agitation for 1 hr. 20 g of noodle strands belong- The gelatinization properties of the native and modified wheat ing to N and AC starch was centrifuged at 2000 g for 10 min to starches were analyzed using a DSC instrument (OIT-5000; Sanaf) remove free water. The free water (supernatant) was decanted, equipped with STAR software making using of Pourmohammadi et and the tubes containing starch paste were exposed to freeze and al. (2018) method. The device was calibrated with indium and mer- thaw cycles, followed by centrifugation at 3,500 g for 30 min. The cury, and an empty pan was used as a reference. Native and modi- freezing process was done at −18°C for 24 hr, and the melting fied wheat starches (10 g) were weighed into the standard aluminum process was carried out at 30°C for 4 hr. The two processes were pan. Distilled water (30 ml) was added, and the pans were sealed and repeated for 8 cycles, in each of which the isolated water was equilibrated for 24 hr at room temperature. After that, the starch determined. The weight of water was taken, and the amount of slurry was gelatinized in the DSC instrument, by heating at 6°C/ syneresis was calculated as the percentage of water separated as min, from 10 to 160°C. Following heat treatment, the samples were Equation (5): cooled to 25°C and then removed from the DSC. The changes in enthalpy (ΔH in J/g of dry starch), onset temperature (To), peak tem- Syneresis (%) = Water separated (g) × 100)∕Total weight of sample (g) (5) perature (Tp), and conclusion temperature (Tc) for gelatinization were obtained from the exotherm DSC curves. 2.8 | Microstructure determination The microstructure of the modified starch was specified using SEM (Model Leica Cambridge) by use of the method proposed by Pourmohammadi et al. (2018). 2.11 | Statistical analysis So as to specify the regression coefficients, the Design-Expert (version 6.0.5) methodology (Abedi, Sahari, Barzegar, & Azizi, 2015) and statistical software packages SAS 9.1 (SAS Institute) were made. A Box–Behnken design from the response surface was used to study the effect of three different factors on the acetylation degrees of 2.9 | Textural analysis Textural properties of starch gels were specified using a Texture Profile Analyzer (TA Plus; Stable Micro System). To prepare the paste of gelatinized starch, 10 g of starch was added to 100 ml of distilled water, where the slurry remained in water bath (95°C for 30 min). The hot paste was wheat starch. Factors associated with acetylation were acetic anhydride (4, 6, and 8%), pH (6.5, 8, and 9.5), and temperature (45, 60, and 75°C). The experimental data were fitted in accordance with Equation (6) as a second-order polynomial equation, including the linear and interaction effects of each factor: collected and transferred into a cylindrical plastic container of 10 mm diameter and 10 mm height, and kept at 4°C for 24 hr. The gels were then removed from the container and tested for their textural proper- Y = 𝛽0 + k ∑ i=1 𝛽i Xi + k ∑ i=1 𝛽ii X2i + k−1 k ∑ ∑ 𝛽ij Xi Xj (6) i=1 j=2 i<j ties. Utilizing a cylindrical aluminum plunger with a diameter of 10 mm, where Y is the predicted response, Xi and Xj are independent fac- the gels were packed at a test speed of 2 mm/s, pretest and post-test tors, b0 is the offset term, bi is the ith linear coefficient, bii is the ith 4 | ABEDI Et Al. F I G U R E 1 The effect of acetic anhydride (4, 6, and 8%), pH (6.5, 8, and 9.5), and temperature (45, 60, and 75°C) on the degree of wheat acetylation (A) at frequencies 25 kHz, 40 kHz, and 25 + 40 kHz. Lack of fit: not significant quadratic coefficient, and bij is the ijth interaction coefficient. All the optimized AC wheat starch was acetic anhydride (5%), pH 8.5, analyses were obtained in triplicates and reported as mean values. and temperature 60°C with 1.22%, 1.37%, and 1.02% acetylation for 25 kHz, 25 + 40 kHz, and 40 kHz, respectively. 3 | R E S U LT S A N D D I S CU S S I O N As a result of Equations (7–9), the effect of A (acetic anhydride content) > B (pH) > C (reaction temperature) is on route to 3.1 | Molar substitution of AC wheat starch the maximum acetylation. The negative effect of temperature at dual frequency (25 + 40 kHz) was more than 25 and 40 kHz; Concerning the AC wheat starch at sonication frequencies of 25, 40, and 25 + 40 kHz, optimization was done in order to investigate the effect of acetic anhydride content, pH, temperature, and ultrasonic frequency on the amount of modification or molar substitution of the modified starch (Figure 1). same as 40 kHz. The addition–elimination is the main mechanism for acetylation reaction, in which hydroxyl groups are converted to acetyl. The hydroxyl groups presented different levels of reactivity. The most reactive group was the hydroxyl of Carbon 6, followed by those of Carbons 2 and 3 (Wojeicchowski et al., 2018). Degree of acetylation (%) at frequency 25 kHz = The C = O bond of the acetyl group was substituted in all amor- + 1.48 + 0.37 × A + 0.18 × B + 0.017 × C + 0.17 × A × B + 0.16 × A × C + 0.043 × B × C − 0.26 × A2 − 0.37 × B2 − 0.50 × C2 however, the effect of temperature at 25 kHz frequency was the phous areas and at the outer lamellae of crystalline sections due (7) to the poor ability of acetic anhydride to penetrate granule structures (Singh et al., 2007). Degree of acetylation (%) at frequency 40 kHz = The differences in the DS of modified starch are related to + 1.02 + 0.32 × A + 0.13 × B + 0.13 × C + 0.15 × A × B + 0.15 × A × C + 0.12 × B × C − 0.12 × A2 − 0.29 × B2 − 0.36 × C2 several parameters, such as starch source, amylose-to-amylo(8) amylose and amylopectin, granular size, presence of lipids, and Degree of acetylation (%) at frequency 25 + 40 kHz = reaction medium factors, such as pH, temperature, reaction time, + 1.52 + 0.35 × A + 0.12 × B − 0.14 × C + 0.093 × A × B + 0.080 × A × C + 0.001 × B × C − 0.21 × A2 − 0.33 × B2 − 0.63 × C2 pectin ratio, degree of crystallinity, molecular weight (MW) of (9) mixing uniformity, and reagent content during the modification of the starches (Ayucitra, 2012; González & Perez, 2002; Halal Optimized samples were selected based on minimum reagent et al., 2015; Salcedo Mendoza, Hernández RuyDíaz, & Fernández consumption (acetic anhydride with achieving to maximum modifi- Quintero, 2016; Singh et al., 2007; Sodhi & Singh, 2005; Wang & cation). According to response surface methodology (RSM) analysis, Wang, 2002). | ABEDI Et Al. 5 3.4 | Effect of pH DS increased following the addition of NaOH to the reaction medium, when the pH was set to 6.5, 8, and 9.5. Alkaline pH was able to enhance the DS owing to the disruption in the hydrogen bonds between molecules in amorphous and crystalline regions, and the facilitation of the percolation and penetration of the esterifying groups into the starch granular structure (Halal et al., 2015; Han et al., 2012). Although pH plays a major factor in the DS improvement of acetylation, very high pHs can diminish DS due to the hydrolyzation of acetic anhydride and the inhibition effect of gelatinized layer on the efficient contact between starch and acetic anhydride (Halal et al., 2015; Han et al., 2012). Various botanical starches have been F I G U R E 2 X-ray diffraction of native and acetylated wheat starch at frequencies 25 kHz, 40 kHz, and 25 + 40 kHz acetylated with different degrees of acetylation, such as 0.104%– 0.184% for maize starch (Singh et al., 2004), 0.081 for waxy maize starch (Wang & Wang, 2002), 0.087%–0.118% (Sodhi & Singh, 2005) for rice starch, 0.041%, 0.059, and 0.076 for tapioca starch 3.2 | Effect of ultrasonication (Babic et al., 2007), 1.85, 0.85, and 2.79% for corn starch (Chi et al., Under sonification, DS was increased since the solubility and swelling starch (Mirmoghtadaie, Kadivar, & Shahedi, 2009), and 0.9 and 2.7% of granules were improved as a result of sufficient contact with rea- for barely starch (Bello-Pérez, Agama-Acevedo, Zamudio-Flores, 2008), 0.11 and 0.05 with 6 and 8% acetic acid consumption for oat gents, which enhanced the homogeneity of the reactants. Collapse of Mendez-Montealvo, & Rodriguez-Ambriz, 2010), 0.08%–0.21% for cavitation bubbles upon ultrasonic treatment is capable of mechani- corn starch (Ayucitra, 2012). Potato, oat, wheat, maize, and rice cally damaging and rupturing the starch granules and breaking the starches presented significant differences in their DS when acety- chains of polymers due to high-pressure gradients, high local velocities lated under similar reaction conditions (Mirmoghtadaie et al., 2009; of liquid layers, shearing force, and microstreaming. According to Amini, Singh et al., 2007). Razavi, and Mortazavi (2015) and Zhu (2015), ultrasound creating frac- The high molar substitution acetylation in this study was inter- ture, pore, and crack on glanular surfaces may enhance the surface area preted by reaction medium under ultrasonic process, which affects of starch, facilitate the penetration of esterifying agents (acetyl) into the amylose regions. The extent of modification by ultrasonication the granular structure, and accelerate the chemical reactions. The fre- in the crystallinity of starch granules depends on experimental con- quency of ultrasound is a key factor for enhancing cavitational bubble ditions and the type of starch (Zhu, 2015), and requires the intro- due to certain reasons (Abedi, Sahari, & Hashemi, 2017): (a) Cavitation duction of acetyl group throughout the amylose or amylopectin yield decreases with the increase in frequency, which is attributed to sections. According to Singh et al. (2004), with low amylose content the scattering, attenuation, and shortening of the acoustic cycle at high (low amylose/amylopectin ratio) a very high DS of acetylation can frequencies (Abedi et al., 2017). (b) Instable cavitation at low frequen- be observed. Surface of granule is another major factor affecting cies causes the bubble to collapse very quickly and violently, resulting DS. Furthermore, González and Perez (2002) interpreted that the in more rapid agitation and mass transfer (Abedi et al., 2017). low degree of substitution in rice starch might be due to the lack of enough large inner channels or granular surface pores which can 3.3 | Effect of temperature facilitate the access of acetic anhydride to the interior of the granule. Temperature had a progressive effect on the DS of the modified 3.5 | The crystalline structure starch, which is attributed to the swelling of starch granules, diffusion of the esterifying agents, mobility of reactant molecules for The X-ray diffraction pattern of native and modified acetylated reaction with amorphous regions, destruction of the crystalline re- wheat starches is presented in Figure 2. X-ray diffraction analysis gions of the starch granules, and conversion to amorphous regions estimates the crystalline structure and the amount of crystal exist- (Han et al., 2012). This phenomenon can simplify the acceptability ing in the starch granules. The structure is related to amylopectin of granules in acetic anhydride and propylene glycol percolation. double helix. The results showed that the X-ray pattern of wheat Temperature is an important factor, yet a very high temperature is starch was the same as other cereals (A pattern). The native starch not conducive to the absorption of the esterifying agent (acetyl) by had sharp diffraction peaks at 15°, 17°, 18°, 23° (2θ), indicating the the starch. This is because of the exothermic esterification reaction typical A pattern of cereal starch (Zobel, Young, & Rocca, 1988). of starch (Han et al., 2012; Singh et al., 2007) and the facilitation of Following the esterification process, the degree of crystallinity the gelatinization layer, which inhibits the contact of reagents with was significantly reduced (p < 0.05) from N (36.89 ± 0.62) to AC starch molecules (Han et al., 2012; Singh et al., 2007). at 25 kHz (17.80 ± 0.38), 40 kHz (22.43 ± 0.42), and 25 + 40 kHz 6 | ABEDI Et Al. F I G U R E 3 Solubility and water absorption of native and acetylated wheat starch at frequencies 25 kHz, 40 kHz, and 25 + 40 kHz (13.57 ± 0.41) frequencies of wheat starches. The X-ray diffraction showed that with acetylation, the structures of native starch were 3.6 | Solubility and water absorption destroyed, and new structures of esterified starches were formed. Figure 3 illustrates the water absorption (WA) and solubility of na- Crystalline regions are the main factors preventing the loss of gran- tive and acetylated wheat starch at different temperatures. The ular structure during reaction with reagents, and preserving the in- solubility and WA of N and AC wheat starch at various frequencies tegrity of granular structure (Sha et al., 2012; Singh et al., 2007). differed significantly (p < 0.05) at all measured temperatures. The Moreover, it is to be noted that starch granules in amorphous solubility and water absorption of AC wheat starch at frequencies regions are more susceptible to reagents during the modification 25, 40, and 25 + 40 kHz were 7.37–36.77 and 6.30–23.98, 6.57– process, while crystalline regions remain intact. Acetylation under 34.49, and 5.83–20.94, and 8–40.77 and 7.03–27.60, respectively, ultrasonic conditions created fractures and cracks on granular which is much higher than N wheat starch (2.28–9.03 and 2.28– surfaces, thereby facilitating the penetration of acetic anhydride 12.72 at temperatures ranging between 30 and 90°C, respectively). for reaction with amorphous (granule composed of amylose) and Similar increasing trends in solubility and WA due to acetylation crystalline regions. The amylose content of N (26.30 ± 0.26) was have been reported for potato and corn starches (Singh et al., 2004), reduced to 12.68 ± 0.12, 18.93 ± 0.24, and 9.23 ± 0.36 following waxy and normal maize (Liu, Ramsden, & Corke, 1999), small and acetylation at ultrasound frequencies 25, 40, and 25 + 40 kHz, re- large wheat starch (Van Hung & Morita, 2005a), tapioca (Babic et spectively. This means that amorphous regions reacted with acetic al., 2007), normal and waxy rice starch (Liu et al., 1999), rice starch anhydride, a finding which is in accordance with Diop, Li, Xie, and (González & Perez, 2002; Sodhi & Singh, 2005), barely (Bello-Pérez Shi (2011); Simsek, Ovando‐Martínez, Whitney, and Bello‐Pérez et al., 2010; Halal et al., 2015), sweet potato (Lee & Yoo, 2009), oat (2012); Mbougueng et al. (2012); Wani, Sogi, and Gill (2012). (Mirmoghtadaie et al., 2009), and corn (Diop et al., 2011; Han et al., | ABEDI Et Al. 7 F I G U R E 4 The RVA profiles in native (1) and acetylated wheat starch at frequencies 25 kHz (3), 40 kHz (2), and 25 + 40 kHz (4) 2012). Further reported is the increasing pattern of swelling and 25 + 40 kHz (9,423 ± 112 and 11,174 ± 131). The AC at frequency solubility properties of various starch sources under ultrasonic pro- 25 + 40 kHz (50.9 ± 1.2) had lower pasting temperatures compared cesses (Chan, Bhat, & Karim, 2010; Herceg et al., 2010; Luo et al., with 25 kHz (58.3 ± 1.4), 40 kHz (64.4 ± 1.2), and N (71.6 ± 1.6). 2008; Montalbo‐Lomboy et al., 2010; Režek Jambrak et al., 2010; These findings are in accordance with the results of Li et al. (2014) Sujka & Jamroz, 2013; Zheng et al., 2013). Such increase is probably where the starch with higher amylose content reduced the gelati- due to the destruction, disorganization, and reduction in the crystal- nization temperatures due to less crystalline and more amorphous linity degree of starch granules. regions (Li et al., 2014). These results are in accordance with certain The acetyl group disorganized the starch components upon other research (González & Perez, 2002; Van Hung & Morita, 2005a, acetylation due to the following: (a) disruption of hydrogen bonds b; Liu et al., 1999; Salcedo Mendoza et al., 2016). In these studies, in the starch granules and facilitation of water access to the amor- the modification of starch by acetylation increased the peak viscos- phous region (Babic et al., 2007; González & Perez, 2002; Liu et al., ity due to (a) the decrease in the strength of associative intermo- 1999), (b) repulsion force between starch molecules as well as starch lecular forces in the amorphous regions of the granules, (b) lower chain, (c) partial depolymerization principally in the amylopectin, re- degrees of crystallinity in AC compared with N wheat starches, (c) ducing the average molecular weight (MW) (Bello-Pérez et al., 2010; increase in solubility and swelling power (Figures 3 and 4), (d) the sol- González & Perez, 2002), (d) loss of granule crystallinity based on ubilizing amylose released outside the swollen starch granule (Han, the X-ray diffraction pattern (Bello-Pérez et al., 2010; Van Hung & 2010; Salcedo Mendoza et al., 2016), and (e) improvement in the hy- Morita, 2005a, 2005b; Liu et al., 1999), and (e) reduced interactions drophilic capacity of the reorganized structures (Han, 2010; Salcedo between the starch chains due to the introduction of acetyl groups, Mendoza et al., 2016). On the other hand, compared with the native solubilizing and releasing the amylose to the exterior of the swollen starches, the AC wheat starches presented better stability during starch granule (Salcedo Mendoza et al., 2016). According to Figure 3, heating. Reassociation of amylose molecules occur when leached temperature had a progressing effect on solubility and swelling of out from swollen starch granule, thus providing a higher resistance N and AC starch. The increase in the temperature of the medium to thermal or mechanical forces (Colussi et al., 2015). induces the thermodynamic activity of starch molecules; moreover, a high granular mobility can increase the water penetration in the amorphous regions of starch granules and destroy the crystalline regions as well (Mirmoghtadaie et al., 2009). 3.8 | Thermal behavior Table 1 summarizes the DSC gelatinization parameters including transition temperatures (To, Tp, and Tc) and enthalpy of gelatiniza- 3.7 | The pasting properties tion (ΔH gel) related to N and AC (under sonication at frequencies Figure 4 and Table 1 present the RVA profile of N and AC starch sus- values were lower in AC at frequency 25 + 40 kHz compared with pensions (5%, w/w) at various frequencies (25, 40, and 25 + 40 kHz) AC at frequency 25 and 40 kHz and N starches. Modification in- during heating from 30 to 90°C. The peak viscosity is indicated by duced a major reduction from 56.8 ± 0.8°C for N wheat starch to the maximum swelling of the majority of starch granules and their 48.2 ± 1.04°C, 51.0 ± 0.8°C, and 44.9 ± 1.4 for AC wheat starches subsequent collapse (Van Hung & Morita, 2005a, b). The peak and at frequencies 25, 40, and 25 + 40 kHz, respectively. Among the final viscosity of native starch (3,757 ± 48 and 7,034 ± 34) were found starches, N starch presented the highest ΔHgel value (11.8 ± 0.8 J/g), to be significantly (p < 0.05) lower than AC starches at frequencies followed by AC wheat starches at frequency 25 kHz (6.4 ± 0.8), 25 (7,188 ± 32 and 8,851 ± 31), 40 (5,846 ± 65 and 7,648 ± 66), and 40 kHz (9.5 ± 0.4), and 25 + 40 kHz (5.8 ± 0.8). Singh et al. (2004), 25, 40, and 25 + 40 kHz) wheat starches. It was observed that these 8 | TA B L E 1 ABEDI Et Al. Pasting profile (RVA), thermal (DSC), and textural (TPA) analysis of native (N), acetylated (AC), wheat (dry basis) starches RVA parameters Pasting tem‐ perature (°C) a Thermal parameters Peak viscosity (mPa•s) 3,758±48 d Final viscosity (mPa•s) 7,034±34 d Breakdown vis‐ cosity (mPa•s) 1,214±84 d Setback viscos‐ ity (mPa•s) 3,576±38 T0 (°C) a 56.8 ± 0.8a N wheat starch 71.6 ± 1.6 AC wheat starch (25 kHz) 58.3 ± 1.4c 7,188±32b 8,851±31b 3,102±18b 1663±53d 48.2 ± 1.0 c AC wheat starch (40 kHz) 64.4 ± 1.2b 5,846±65c 7,648±66c 2,492±16c 1802±67b 51.0 ± 0.8b AC wheat starch (25 + 40 kHz) 50.9 ± 1.2d 9,423±112a 11,174±131a 4,011±24a 1753±53c 44.9 ± 1.4d Note: Different letters in each column show significant statistical difference between the values (p < 0.05). Babic et al. (2007), and Lee and Yoo (2009) also reported a statisti- of granules with a slight gelatinization when esterification reactions cally significant (p < 0.05) decrease in the gelatinization tempera- were performed in the presence of catalyst (NaOH solution; Halal ture of corn, potato, tapioca, and sweet potato starches following et al., 2015). According to Hirsch and Kokini (2002), the cross-linked acetylation. The starch gelatinization is controlled by two factors: (a) bonds formed by acetic anhydride mostly occur on the surface of the amylopectin molecular structures such as molar mass, integrity and starch granules. order of crystallites, polydispersity, and amylopectin chain length Modification by ultrasonication influenced the granule morphol- with a degree of polymerization (DP) ranging between 5 and 12, and ogy through forming deep grooves in the central core zone, cracks (b) granule structures including granule size, amylose/amylopectin on the starch granules, and blister-like and doughnut-like shapes, ratio, crystalline zone relationship, and the quality and amount of which is in line with the SEM morphology of Kaur et al. (2004). The amorphous crystallites (Tester & Morrison, 1990). The enthalpy major impact of acetylation on the surface of the granules is due value attributed to the ordered double-helix loss was more than the to the reaction of acetic anhydride with starch granules under ul- crystallinity loss. The difference in enthalpy value between the N trasonic processes. Ultrasonic-induced cracks, pores, and fractures and modified wheat starch showed that the acetylation of wheat on granular surfaces facilitate the penetration of chemical reagents starch with a high substitution degree generated disorganization as into structure granules. According to the results of Bello-Pérez et is shown by X-ray, SEM, and RVA experiments. The reduction in the al. (2010), esterification of starch generated higher granule fusion, gelatinization parameters of acetylated starches was due to the in- which is attributed to the increase in hydrogen bonding due to the in- sertion of acetyl and propyl oxide groups into the starch molecules, sertion of hydrophilic groups into the starch molecules. Accordingly, particularly into the amorphous areas. This further reduced the integrity of the amorphous and crystalline sections of starch granules and disrupted the inter- and intramolecular hydrogen bonds, destabilizing the granular structure (Babic et al., 2007). ΔH indicates an overall measure of crystallinity and loss in the molecular order. The esterifying agents reduce ΔH due to (a) the change in the amylopectin double helices, (b) diminished crystallinity, (c) increase in starch chain flexibility, and (d) reduction in gelatinization temperature (Halal et al., 2015). These findings are consistent with Halal et al. (2015); Bello-Pérez et al. (2010); Mirmoghtadaie et al. (2009); Kaur, Singh, and Singh (2004). 3.9 | The effects of modification on starch morphology The morphological patterns of N and modified starches are shown in Figure 5 where A and B granules of wheat starch can be clearly observed. In AC wheat starches at dual frequency (25 + 40 kHz), the surfaces of all large granules were more damaged after modification, compared with those of the small granules. Meanwhile, at frequency 25 and 40 kHz of wheat starch, small granules were more affected than large granules. Starch granules indicated a partial disintegration F I G U R E 5 Scanning electron microscopy (SEM) of native (a) and acetylated wheat starch at frequencies 25 kHz (b), 40kHz (c), and 25 + 40 kHz (d) | ABEDI Et Al. 9 TPA parameters TP (°C) 62.0 ± 1.4 TC (°C) a 67.4 ± 1.3 ΔH (J/g) a 11.8 ± 0.8 Hardness (g) a 1,420 ± 34 a Cohesiveness 0.93 ± 0.05 a Adhesiveness (g/s) −234 ± 13 a Springiness 1.18 ± 0.09 Gumminess (g) a 1,321 ± 85a 53.4 ± 1.3c 59.4 ± 1.84c 6.4 ± 0.8c 634 ± 28c 0.87 ± 0.05a −312 ± 38c 0.71 ± 0.04c 852 ± 34c 57.6 ± 1.2b 62.1 ± 1.4b 9.5 ± 0.4b 896 ± 48b 0.91 ± 0.03a −281 ± 24b 0.95 ± 0.08b 936 ± 52b 50.8 ± 1.1d 54.6 ± 1.8d 5.8 ± 0.8d 574 ± 31d 0.86 ± 0.09a −327 ± 30 d 0.62 ± 0.07d 616 ± 43d coalescing starch molecules induce the fusion of starch granules and amylopectin molecules (reducing retrogradation). There were no (Bello-Pérez et al., 2010), which is in line with the SEM morphology significant differences (p < 0.05) between N and AC wheat starches in the present study (Figure 5). The SEM results are also consistent as far as cohesiveness is concerned; however, their gumminess was with Van Hung and Morita (2005a, b). reduced. Adhesiveness is the attraction between the gel and an external surface. Adhesiveness of N wheat starch gel was significantly 3.10 | Gel texture (p < 0.05) higher than AC wheat starch gels, which is in line with Liu Table 1 demonstrates the texture profiles of N and AC wheat starches al. (2015). et al. (1999), Choi and Kerr (2003), Babic et al. (2007), and Colussi et under various frequency ultrasounds. The order of the hardness of AC wheat starch was as follows: 25 + 40 kHz < 25 kHz < 40 kHz. Acetylation was able to reduce the hardness of the gels due to (a) the introduction of large and hydrophilic acetyl groups which aided 3.11 | Freeze–thaw stability The purpose of the present research was to stabilize the starch gels ultrasonication via increasing the space between the starch chain from syneresis during freezing and thawing. The tendency to retrogra- molecules and reducing retrogradation, (b) slight depolymerization dation of gels prepared from N and AC wheat starches was calculated by of the starch molecules by the acetic anhydride under sonication determining the syneresis (percentage of water loss) during storage at (although more amylose molecules are reassociated, the depolym- 4°C (Figure 6). During the freezing cycles, the crystal size was enlarged erization can weaken the gel), and (c) acetyl group preventing the with the reduction in their number. In the thawing stage, the ice crys- formation of amylose gel network and the reassociation of amylose tals were converted to water masses easily removed from the polymer FIGURE 6 Freeze and thaw stability profile in N and AC wheat starch 10 | network (syneresis) (Smith & Schwartzberg, 1985). Furthermore, water leakage led to the formation of sponge texture in starch. N starch gels started to retrograde following 24 hr, indicated by the increase in the ABEDI Et Al. C O N FL I C T O F I N T E R E S T The authors declare that they do not have any conflict of interest. percentage of water from 42.64% to 63.47% during storage (8 cycles). Acetylated starch gels prevented the separation of water from E T H I C S S TAT E M E N T starch noodle even after five freeze–thaw treatments, showing a better freeze–thaw stability due to high DS. The percentage of water Human and animal testing is unnecessary in this study. separated from AC starch gels at frequencies 25 kHz, 40 kHz, and 25 + 40 kHz reached 1.10%, 3.36, and 0.39%, respectively, indicating ORCID the lower increment in syneresis compared with the N wheat starch gel, as illustrated in Figure 6. The highest resistance to freeze–thaw cycle(s) Elahe Abedi https://orcid.org/0000-0003-3574-9786 was observed in AC wheat starch at frequency 25 + 40 kHz (lowest % separated water), while the lowest belonged to N wheat starch (highest % separated water). Syneresis in freeze-thawed gels is due to the reassociation of amylose molecules together and with amylopectin chain in starch granules at reduced temperatures which accelerates the exclusion of water from the gel structure. Amylose association takes place at the initial step of storage, while amylopectin association occurs in the following stages. Retrogradation may occur when a gelatinized starch is cooled. The increase in the amount of separated water indicates the lack of freeze–thaw stability. After acetylation, water molecules were absorbed by functional groups and were not able to freeze, thereby reducing syneresis (Han et al., 2012). On the other hand, the introduction of large groups of acetyl into the starch chains reduced the inner and outer bonds. Moreover, the acetyl group is smaller in size, which is effective on water absorption and stability against water exclusion. By inserting the acetyl group, the hydrophilic nature of these reagents resulted in the electrostatic repulsion between the chains, preventing the amylose–amylose and amylose–amylopectin interactions (Kaur et al., 2004; Lawal, 2010). When the amylose molecules carrying acetyl group are mingled with amylopectin, the acetyl group sterically prevents the aggregation of amylopectin, entailing lower retrogradation and reduction in the percentage of water separated during freeze– thaw cycles (Kaur et al., 2004; Lawal, 2010). 4 | CO N C LU S I O N S In order to increase the DS and consumption of minimum reagents, a reaction mixture was carried out under ultrasonic processes. The molar substitution optimizing AC wheat starch was 1.22%, 1.37%, and 1.02% for 25 kHz, 25 + 40 kHz, and 40 kHz, consuming 5% of acetic anhydride. High DS is due to the ultrasonic conditions at dual frequency (25 + 40 kHz) which form fractures, pores, and cracks on the surface of granules, facilitating the penetration of reagents into granule starch. Acetylation ameliorates the solubility, water absorption, resistance to freeze and thaw cycle, and viscosity peak, and reduces the gelatinization temperature. AC K N OW L E D G M E N T S The authors would like to thank Dr. Mohsen Ajdari, University of Fasa, for his technical assistance. REFERENCES AACC (2000). Approved methods of the american association of cereal chemists (10th ed.). St. Paul, MN: The Association. Abedi, E., Majzoobi, M., Farahnaky, A., Pourmohammadi, K., & Mahmoudi, M. R. (2018). Effect of ionic strength (NaCl and CaCl2) on functional, textural and electrophoretic properties of native and acetylated gluten, gliadin and glutenin. International Journal of Biological Macromolecules, 120, 2035–2047. https://doi.org/10.1016/j.ijbio mac.2018.09.155 Abedi, E., Sahari, M. A., Barzegar, M., & Azizi, M. H. (2015). Optimization of soybean oil bleaching by ultrasonic processing and investigate the physico-chemical properties of bleached soybean oil. International Journal of Food Science and Technology, 50, 857–863. Abedi, E., Sahari, M. A., & Hashemi, S. M. B. (2017). Accelerating bleaching of soybean oil by ultrasonic horn and bath under sparge of helium, air, argon and nitrogen gas. Journal of Food Processing and Preservation, 41, 1–7. https://doi.org/10.1111/jfpp.12987 Amini, A. M., Razavi, S. M. A., & Mortazavi, S. A. (2015). Morphological, physicochemical, and viscoelastic properties of sonicated corn starch. Carbohydrate Polymers, 122, 282–292. https://doi.org/10.1016/j. carbpol.2015.01.020 Ayucitra, A. (2012). Preparation and characterisation of acetylated corn starches. International Journal of Chemical Engineering and Applications, 3, 156–159. https://doi.org/10.7763/IJCEA.2012.V3.178 Babic, J., Subaric, D., Ackar, D., Kovacevic, D., Pilizota, V., & Kopjar, M. (2007). Preparation and characterization of acetylated tapioca starches. Deutsche Lebensmittel‐Rundschau, 103, 580–585. Bello-Pérez, L. A., Agama-Acevedo, E., Zamudio-Flores, P. B., MendezMontealvo, G., & Rodriguez-Ambriz, S. L. (2010). Effect of low and high acetylation degree in the morphological, physicochemical and structural characteristics of barley starch. LWT ‐ Food Science and Technology, 43, 1434–1440. https://doi.org/10.1016/j. lwt.2010.04.003 Berski, W., Ptaszek, A., Ptaszek, P., Ziobro, O., Kowalski, G., Grzesik, M., & Achremowicz, B. (2011). Pasting and rheological properties of oat starch and its derivatives. Carbohydrate Polymers, 83, 665–671. https://doi.org/10.1016/j.carbpol.2010.08.036 Chan, H. T., Bhat, R., & Karim, A. A. (2010). Effects of sodium dodecyl sulphate and sonication treatment on physicochemical properties of starch. Food Chemistry, 120, 703–709. https://doi.org/10.1016/j. foodchem.2009.10.066 Chen, H. M., Huang, Q., Fu, X., & Luo, F. X. (2014). Ultrasonic effect on the octenyl succinate starch synthesis and substitution patterns in starch granules. Food Hydrocolloids, 35, 636–643. Chi, H., Xu, K., Wu, X., Chen, Q., Xue, D., Song, C., … Wang, P. (2008). Effect of acetylation on the properties of corn starch. Food Chemistry, 106, 923–928. https://doi.org/10.1016/j.foodchem.2007.07.002 Choi, S. G., & Kerr, W. L. (2003). Effects of chemical modification of wheat starch on molecular mobility as studied by pulsed 1HNMR. ABEDI Et Al. Lebensmittel‐Wissenschaft Und Technologie, 36, 105–112. https://doi. org/10.1016/S0023-6438(02)00200-1 Čížová, A., Sroková, I., Sasinková, V., Malovíková, A., & Ebringerová, A. (2008). Carboxymethyl starch octenylsuccinate: Microwave- and ultrasound-assisted synthesis and properties. Starch/Stärke, 60, 389– 397. https://doi.org/10.1002/star.20080 0221 Colussi, R., Halal, S. L., Zanella Pinto, V., Bartz, J., Carlos Gutkoski, L., da Rosa Zavareze, E., & Dias, A. R. G. (2015). Acetylation of rice starch in an aqueous medium for use in food. LWT ‐ Food Science and Technology, 62, 1076–1082. https://doi.org/10.1016/j. lwt.2015.01.053 Diop, C. I. K., Li, H. L., Xie, B. J., & Shi, J. (2011). Impact of the catalytic activity of iodine on the granule morphology, crystalline structure, thermal properties and water solubility of acetylated corn (Zea mays) starch synthesized under microwave assistance. Industrial Crops and Products Journal, 33, 302–309. https://doi.org/10.1016/j.indcrop.2010.11.018 Gao, W., Lin, X., Lin, X., Ding, J., Huang, X., & Wu, H. (2011). Preparation of nano-sized flake carboxymethyl cassava starch under ultrasonic irradiation. Carbohydrate Polymers, 84(4), 1413–1418. https://doi. org/10.1016/j.carbpol.2011.01.056 González, Z., & Perez, E. (2002). Effect of acetylation on some properties of rice starch. Starch, 54, 148–154. https://doi.org/10.1002/1521379X(20020 4)54:3/4<148:AID-STAR148>3.0.CO;2-N Halal, S. L. M. E., Colussi, R., Pinto, V. Z., Bartz, J., Radunz, M., Carreño, N. L. V., … Zavareze, E. D. R. (2015). Structure, morphology and functionality of acetylated and oxidised barley starches. Food Chemistry, 168, 247–256. https://doi.org/10.1016/j.foodchem.2014.07.046 Han, F., Liu, M., Gong, H., Lü, S., Ni, B., & Zhang, B. (2012). Synthesis, characterization and functional properties of low substituted acetylated corn starch. International Journal of Biological Macromolecules, 50(4), 1026–1034. https://doi.org/10.1016/j.ijbiomac.2012.02.030 Han, J. A. (2010). Pasting properties of hydroxypropylated starches before or after proteinase treatment. Starch, 62, 247–261. https://doi. org/10.1002/star.20090 0204 Han, J., Lee, B., Lim, W. J., & Lim, S. T. (2005). Utilization of hydroxypropylated waxy rice and corn starches in Korean waxy rice cake to retard retrogradation. Cereal Chemistry, 82, 88–92. https://doi. org/10.1094/CC-82-0088 Herceg, I. L., Jambrak, A. R., Šubarić, D., Brnčić, M., Brnčić, S. R., Badanjak, M., … Herceg, Z. (2010). Texture and pasting properties of ultrasonically treated corn starch. Czech Journal of Food Science, 28, 83–93. https://doi.org/10.17221/50/2009-CJFS Hirsch, J. B., & Kokini, J. L. (2002). Understanding the mechanism of cross linking agents (POCl3, STMP, and EPI) through swelling behavior and pasting properties of cross linked waxy maize starches. Cereal Chemistry, 79, 102–107. Hong, J., Chen, R., Zeng, X.-A., & Han, Z. (2016). Effect of pulsed electric fields assisted acetylation on morphological, structural and functional characteristics of potato starch. Food Chemistry, 192, 15–24. https://doi.org/10.1016/j.foodchem.2015.06.058 Huang, Q., Li, L., & Fu, X. (2007). Ultrasound effects on the structure and chemical reactivity of cornstarch granules. Starch, 59, 371–378. https://doi.org/10.1002/star.20070 0614 Kaur, B., Ariffin, F., Bhat, R., & Karim, A. A. (2012). Progress in starch modification in the last decade. Food Hydrocolloids, 26, 398–404. https://doi.org/10.1016/j.foodhyd.2011.02.016 Kaur, L., Singh, N., & Singh, J. (2004). Factors influencing the properties of hydroxypropylated potato starches. Carbohydrate Polymers, 55, 211–223. https://doi.org/10.1016/j.carbpol.2003.09.011 Kaur, M., Sandhu, K. S., & Lim, S.-T. (2010). Microstructure, physicochemical properties and invitro digestibility of starches from different Indian lentil (Lens culinaris) cultivars. Carbohydrate Polymers, 79, 349–355. https://doi.org/10.1016/j.carbpol.2009.08.017 Lawal, O. S. (2010). Hydroxypropylation of pigeon pea (Cajanus cajan) starch: Preparation, functional characterizations and enzymatic | 11 digestibility. Lebensmittel‐ Wissenschaft Und Technologie, Food Science and Technology, 44, 771–777. Lee, H. L., & Yoo, B. (2009). Dynamic rheological and thermal properties of acetylated sweet potato starch. Starch, 61, 407–413. https://doi. org/10.1002/star.20080 0109 Li, W., Cao, F., Fan, J., Ouyang, S., Luo, Q., Zheng, J., & Zheng, G. (2014). Physically modified common buckwheat starch and their physicochemical and structural properties. Food Hydrocolloids, 40, 237–244. https://doi.org/10.1016/j.foodhyd.2014.03.012 Liu, H. J., Ramsden, L., & Corke, H. (1999). Physical properties and enzymatic digestibility of hydroxypropylated ae, wx, and normal maize starches. Carbohydrate Polymers, 40, 175–182. https://doi. org/10.1016/S0144-8617(99)00052-1 Luo, Z., Fu, X., He, X., Luo, F., Gao, Q., & Yu, S. (2008). Effect of ultrasonic treatment on the physicochemical properties of maize starches differing in amylose content. Starch/Stärke, 60, 646–653. https://doi. org/10.1002/star.20080 0014 Mbougueng, P. D., Tenin, D., Scher, J., & Tchiégang, C. (2012). Influence of acetylation on physicochemical, functional and thermal properties of potato and cassava starches. Journal of Food Engineering, 108(2), 320–326. https://doi.org/10.1016/j.jfoodeng.2011.08.006 Mirmoghtadaie, L., Kadivar, M., & Shahedi, M. (2009). Effects of crosslinking and acetylation on oat starch properties. Food Chemistry, 116, 709–713. https://doi.org/10.1016/j.foodchem.2009.03.019 Montalbo-Lomboy, M., Khanal, S. K., van Leeuwen, J. H., Raj Raman, D., Dunn, L. Jr, & Grewell, D. (2010). Ultrasonic pretreatment of corn slurry for saccharification: A comparison of batch and continuous systems. Ultrasonics Sonochemistry, 17, 939–946. https://doi. org/10.1016/j.ultsonch.2010.01.013 Pourmohammadi, K., Abedi, E., Hashemi, S. M. B., & Torri, L. (2018). Effects of sucrose, isomalt and maltodextrin on microstructural, thermal, pasting and textural properties of wheat and cassava starch gel. International Journal of Biological Macromolecules, 120, 1935– 1943. https://doi.org/10.1016/j.ijbiomac.2018.09.172 Režek Jambrak, A., Herceg, Z., Šubarić, D., Babić, J., Brnčić, M., Rimac Brnčić, S., … Gelo, J. (2010). Ultrasound effect on physical properties of corn starch. Carbohydrate Polymers, 79, 91–100. https://doi. org/10.1016/j.carbpol.2009.07.051 Salcedo Mendoza, J., Hernández RuyDíaz, J., & Fernández Quintero, A. (2016). Effect of the acetylation process on native starches of yam (Dioscorea spp.). Revista Facultad Nacional De Agronomía Medellín, 69(2), 7997–8006. https ://doi.org/10.15446/rfna. v69n2.59144 Sha, X. S., Xiang, Z. J., Bin, L., Jing, L., Bin, Z., Jiao, Y. J., & Kun, S. R. (2012). Preparation and physical characteristics of resistant starch (type 4) in acetylated indica rice. Food Chemistry, 134, 149–154. https://doi. org/10.1016/j.foodchem.2012.02.081 Shi, H., & Hu, X. (2013). Preparation and structure characterization of carboxymethyl corn starch under ultrasonic irradiation. Food Chemistry, 90, 24–28. Simsek, S., Ovando‐Martínez, M., Whitney, K., & Bello‐Pérez, L. A. (2012). Effect of acetylation, oxidation and annealing on physicochemical properties of bean starch. Food Chemistry, 134(4), 1796–1803. https://doi.org/10.1016/j.foodchem.2012.03.078 Singh, J., Kaur, L., & McCarthy, O. J. (2007). Factors influencing the physicochemical morphological thermal and rheological properties of some chemically modified starches for food application – A review. Food Hydrocolloids, 21, 1–22. Singh, N., Chawla, D., & Singh, J. (2004). Influence of acetic anhydride on physicochemical, morphological and thermal properties of corn and potato starch. Food Chemistry, 86, 601–608. https://doi. org/10.1016/j.foodchem.2003.10.008 Smith, C. E., & Schwartzberg, H. G. (1985). Ice crystal size changes during ripening in freeze concentration. Biotechnology Progress, 1, 111–120. https://doi.org/10.1002/btpr.5420010208 12 | Sodhi, N. S., & Singh, N. (2005). Characteristics of acetylated starches prepared using starches separated from different rice cultivars. Journal of Food Engineering, 70, 117–127. https://doi.org/10.1016/j. jfoodeng.2004.09.018 Sujka, M., & Jamroz, J. (2013). Ultrasound-treated starch: SEM and TEM imaging, and functional behaviour. Food Hydrocolloids, 31, 413–419. https://doi.org/10.1016/j.foodhyd.2012.11.027 Tester, R. F., & Morrison, W. R. (1990). Swelling and gelatinisation of cereal starches. I. Effects of amylopectin, amylose and lipids. Cereal Chemistry, 67, 551–557. Van Hung, P., & Morita, N. (2005a). Effects of granule sizes on physicochemical properties of cross-linked and acetylated wheat starches. Starch, 57, 413–420. https://doi.org/10.1002/star.20050 0417 Van Hung, P., & Morita, N. (2005b). Physicochemical properties of hydroxypropylated and cross-linked starches from A-type and B-type wheat starch granules. Carbohydrate Polymers, 59(2), 239–246. https://doi.org/10.1016/j.carbpol.2004.09.016 Wang, Y.-J., & Wang, L. (2002). Characterization of acetylated waxy maize starches prepared under catalysis by different alkali and alkalineearth hydroxides. Starch, 54, 24–30. https://doi.org/10.1002/1521379X(200201)54:1<25:AID-STAR25>3.0.CO;2-T Wani, I. A., Sogi, D. S., & Gill, B. S. (2012). Physicochemical properties of acetylated starches from some Indian kidney bean (Phaseolus vulgaris L.) cultivars. International Journal of Food Science & Technology, 47(9), 1993–1999. https://doi.org/10.1111/j.1365-2621.2012.03062.x Wojeicchowski, J. P., Siqueira, G. L. A., Lacerda, L. G., Schnitzler, E., & Demiate, I. M. (2018). Physicochemical, structural and thermal ABEDI Et Al. properties of oxidized, acetylated and dual-modified common bean (Phaseolus vulgaris L.) starch. Food Science and Technology, 38(2), 318– 327. https://doi.org/10.1590/1678-457x.04117 Zhang, L., Zuo, B., Wu, P., Wang, Y., & Gao, W. (2012). Ultrasound effects on the acetylation of dioscorea starch isolated from Dioscorea zingiberensis C.H. Wright. Chemical Engineering and Processing: Process Intensification, 54, 29–36. https://doi.org/10.1016/j. cep.2012.01.005 Zheng, J., Li, Q., Hu, A., Yang, L., Lu, J., Zhang, X., & Lin, Q. (2013). Dualfrequency ultrasound effect on structure and properties of sweet potato starch. Starch/Stärke, 65, 621–627. https://doi.org/10.1002/ star.20120 0197 Zhu, F. (2015). Impact of ultrasound on structure, physicochemical properties, modifications, and applications of starch. Trends in Food Science & Technology, 43(1), 1–17. https://doi.org/10.1016/j.tifs.2014.12.008 Zobel, H. F., Young, S. N., & Rocca, L. A. (1988). Starch gelatinization. An X-ray diffraction study. Cereal Chemistry, 66, 443–446. How to cite this article: Abedi E, Pourmohammadi K, Abbasi S. Dual-frequency ultrasound for ultrasonic-assisted esterification. Food Sci Nutr. 2019;00:1–12. https://doi. org/10.1002/fsn3.1115