molecules Article The Annealing of Acetylated Potato Starch with Various Substitution Degrees Tomasz Zi˛eba 1 , Aleksandra Wilczak 2, Justyna Kobry´n 3 , Witold Musiał 3 , Małgorzata Kapelko-Zeberska˙ 1,* , Artur Gryszkin 1 and Marta Meisel 1 1 Department of Food Storage and Technology, Faculty of Biotechnology and Food Science, Wroclaw University of Environmental and Life Sciences, Chełmo´nskiego37, 51-630 Wrocław, Poland; [email protected] (T.Z.); [email protected] (A.G.); [email protected] (M.M.) 2 Department of Physico-Chemistry of Microorganisms, University of Wroclaw, Przybyszewskiego 63-77, 51-148 Wrocław, Poland; [email protected] 3 Department and Chair of Physical Chemistry and Biophysics, Wrocław Medical University, Borowska 211A, 50-556 Wrocław, Poland; [email protected] (J.K.); [email protected] (W.M.) * Correspondence: [email protected]; Tel.: +48-71-320-7765 Abstract: This study aimed to determine the effect of “annealing” acetylated potato starch with a homogenous granule size and various degrees of substitution on the thermal pasting characteristics (DSC), resistance to amylases, rheology of the prepared pastes, swelling power and dynamics of drug release. A fraction of large granules was separated from native starch with the sedimentation method and acetylated with various doses of acetic anhydride (6.5, 13.0 or 26.0 26 cm3/100 g starch). The starch acetates were then annealed at slightly lower temperatures than their pasting temperatures. The annealing process caused an almost twofold increase in the resistance to amylolysis and a threefold increase in the swelling power of the modified starch preparations. The heat of phase Citation: Zi˛eba,T.; Wilczak, A.; transition decreased almost two times and the range of starch pasting temperatures over two times, Kobry´n,J.; Musiał, W.; but the pasting temperature itself increased by ca. 10 ◦C. The 40 g/100 g addition of the modified Kapelko-Zeberska,˙ M.; Gryszkin, A.; starch preparation decreased the rate of drug release from a hydrogel by ca. one-fourth compared to Meisel, M. The Annealing of the control sample. Acetylated Potato Starch with Various Substitution Degrees. Molecules 2021, 26, 2096. https://doi.org/10.3390/ Keywords: annealing; acetylation; starch particle size distribution molecules26072096 Academic Editor: Drago Šubari´c 1. Introduction Received: 11 March 2021 The process of native starch heating in a water suspension having a temperature that Accepted: 5 April 2021 fits within the range of glass transition temperatures and the initial pasting temperatures Published: 6 April 2021 is called annealing. The goal of this thermal modification is to bring starch temperature to such a value that would excite the motility of starch molecules but prevent starch Publisher’s Note: MDPI stays neutral transformation into a paste. It makes the crystalline structure of starch homogeneous, with regard to jurisdictional claims in thereby protecting the structure of granules [1–3]. Annealing causes an increase in pasting published maps and institutional affil- temperatures and, at the same, makes the temperature range narrower. In addition, it has iations. a little effect on process enthalpy. If starch retains its grainy structure after modification, its swelling power decreases with an increase in pasting temperatures [4]. In turn, the viscosity of pastes obtained from annealed starch depends on starch origin. For example, the annealing process was reported to increase the viscosity of pastes made of wheat Copyright: © 2021 by the authors. and potato starches, and to decrease the viscosity of those obtained from lentil and oat Licensee MDPI, Basel, Switzerland. starches [5]. Starch modified using this type of heat treatment has some special applications This article is an open access article in the food industry. Due to its thermal stability and reduced tendency for retrogradation, distributed under the terms and it is used in food preserves and frozen foods [6]. In turn, Hormdok R. and Noomhorm conditions of the Creative Commons A. [7] showed the hydrothermally-modified starch exhibited properties desirable in pasta Attribution (CC BY) license (https:// making. The annealing can also contribute to an increased content of resistant starch, creativecommons.org/licenses/by/ especially when coupled with other modifications [4]. The double-modified starch can also 4.0/). Molecules 2021, 26, 2096. https://doi.org/10.3390/molecules26072096 https://www.mdpi.com/journal/molecules Molecules 2021, 26, x FOR PEER REVIEW 2 of 12 increased content of resistant starch, especially when coupled with other modifications [4]. The double-modified starch can also have some non-food uses. The application of Molecules 2021, 26, 2096 2 of 11 various modified biopolymers may lead to the development of new hydrogel formula- tions to be used in the field of drug delivery [8]. The annealed native starch of various botanical origin has been broadly investigat- haveed and some described non-food [9,10 uses.]. In The turn, application few works of various are available modified regarding biopolymers changes may leadevoked to by theannealing development in the ofearlier new hydrogelchemically formulations-modified starch to be used [11– in13] the. Potato field of starch drug deliveryproves to [8 ].be an The annealed native starch of various botanical origin has been broadly investigated excellent raw material for chemical modifications because, unlike cereal starches, its and described [9,10]. In turn, few works are available regarding changes evoked by granules do not contain other substances, such as protein and fat [14]. In the case of po- annealing in the earlier chemically-modified starch [11–13]. Potato starch proves to be tato starch, small changes in the chemical structure of the polymer cause significant an excellent raw material for chemical modifications because, unlike cereal starches, its granulesmodifications do not in containits properties other substances,[15]. Despite such a high as protein chemical and purity, fat [14 potato]. In the starch case is of not a potatohomogenous starch, smallmaterial. changes Its pasting in the chemicaltemperature structure depends of the on, polymer i.a., the cause size of significant its granules modifications[14], which ranges in its propertiesfrom a few [15 to]. over Despite 100 a µm. high In chemical the case purity, of its potatoannealing, starch th isis notproperty a homogenoustriggers differences material. in Its the pasting transformations temperature of depends granules on, having i.a., the various size of its sizes. granules To minimize [14], whichthe effect ranges of fromthis factor, a few to it overseems 100 reasonableµm. In the caseto use of itsthe annealing, fraction thisof granules property obtained triggers by differencessorting native in the potato transformations starch. of granules having various sizes. To minimize the effect of thisThe factor, aim it of seems this study reasonable was to usedete thermine fraction how of the granules annealing obtained of acetylated by sorting starch native with potatohomogeneous starch. granule size can affect its thermal pasting characteristics (DSC), resistance to amylases,The aim ofrheology this study of wasthe prepared to determine pastes, how swelling the annealing power of and acetylated drug release starch with dynam- homogeneousics. granule size can affect its thermal pasting characteristics (DSC), resistance to amylases, rheology of the prepared pastes, swelling power and drug release dynamics. 2. Results PotatoPotato starch starch granules granules differ differ significantly significantly in size; in theirsize; diameterstheir diameters can range can from range a few from a tofew over to over 100 µ 100m. Granulesµm. Granules of various of various sizes undergo sizes undergo pasting pasting at different at different temperatures temperatures and forand this for reason this reason the raw the material raw material used in used our study in our to producestudy to annealedproduce acetylatedannealed starchacetylated wasstarch firstly was homogenized firstly homogenized in terms ofin granule terms of size. granule Particle size. size Particle distribution size ofdistribution native starch of na- andtive ofstarch native and starch of native with homogenized starch with homogenized fraction size determined fraction size using determined a laser particle using size a laser diffractionparticle size analyzer diffraction (LSD) analyzer is presented (LSD) in is Figure presented1. in Figure 1. Figure 1.1. ParticleParticle sizesize distribution distribution of of native native starch starch (NS) (NS) and and starch starch with with homogenous homogenous fraction fraction size size determined usingusing a a laser laser particle particle size size diffraction diffraction analyzer analyzer (LSD). (LSD). TheThe meanmean granule granule diameter diameter of theof the non-homogenized non-homogenized starch, starch, expressed expressed as the volumet-as the volu- µ ricmetric diameter diameter D[4,3], D[4, reached3], reache 42.3d 42.3m, and µm, that and measured that measured after separating after separating small granules small gran- reached 61.7 µm. In the present study, the acetylation of large starch granules with var- ules reached 61.7 μm. In the present study, the acetylation of large starch granules with ious doses of acetic acid anhydride resulted in the production of starch acetates which various doses of acetic acid anhydride resulted in