applied sciences Article Potato Starch Extrusion and Roasting with Apple Distillery Wastewater as a New Method for Resistant Starch Production Tomasz Zi˛ eba 1 , Dominika Soli ´ nska 1 , Artur Gryszkin 1 , Malgorzata Kapelko- ˙ Zeberska 1, * , Bartosz Raszewski 1 , Ður ¯ dica Aˇ ckar 2 , Jurislav Babi´ c 2 , Borislav Miliˇ cevi´ c 2,3 and Antun Jozinovi´ c 2   Citation: Zi˛ eba, T.; Soli´ nska, D.; Gryszkin, A.; Kapelko- ˙ Zeberska, M.; Raszewski, B.; Aˇ ckar, Ð.; Babi´ c, J.; Miliˇ cevi´ c, B.; Jozinovi´ c, A. Potato Starch Extrusion and Roasting with Apple Distillery Wastewater as a New Method for Resistant Starch Production. Appl. Sci. 2021, 11, 9169. https://doi.org/10.3390/app11199169 Academic Editor: Agnieszka Kita Received: 18 September 2021 Accepted: 29 September 2021 Published: 2 October 2021 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). 1 Department of Food Storage and Technology, Wroclaw University of Environmental and Life Sciences, ul. Chelmo ´ nskiego 37, 51-630 Wroclaw, Poland; tomasz.zieba@upwr.edu.pl (T.Z.); dominika.solinska@upwr.edu.pl (D.S.); artur.gryszkin@upwr.edu.pl (A.G.); bartosz.raszewski@upwr.edu.pl (B.R.) 2 Faculty of Food Technology Osijek, Josip Juraj Strossmayer University of Osijek, F. Kuhaˇ ca 18, 31000 Osijek, Croatia; dackar@ptfos.hr (Ð.A.); jbabic@ptfos.hr (J.B.); bmilicevic@ptfos.hr (B.M.); ajozinovic@ptfos.hr (A.J.) 3 Polytechnic in Požega, Vukovarska 17, 34000 Požega, Croatia * Correspondence: malgorzata.kapelko@upwr.edu.pl; Fax: +48-71-320-77-67 Abstract: Potato starch was extruded and roasted with apple distillery wastewater to produce starch esters substituted with malic acid residues. The starch esterification degree was higher at the higher roasting temperatures. Starch modification contributed to its darker color, its increased resistance to the action of amylolytic enzymes, and its decreased solubility and heat of phase transition. The changes in the other starch properties examined depended on the extrusion and roasting temperatures. The process, which was conducted without a chemical agent—in this case, the process of starch extrusion and roasting with apple distillery wastewater—should be deemed a novel method for resistant starch production. Keywords: potato starch; extrusion; roasting; apple distillery wastewater; resistant starch; starch esters 1. Introduction Resistant starch is a starch fraction that is not digested in the human digestive tract. Being a prebiotic, it is a source of carbon to symbiotic bacteria that naturally colonize the large intestine [1]. The proper development of these bacteria increases the synthesis of short chain fatty acids, whose presence prevents the formation of colon cancer. In addition, resistant starch stabilizes the insulin level, while it reduces the blood levels of glucose and triglycerides and also the energy value of foods [2]. Due to its health- promoting properties, there is a need to increase its content in food. This can be achieved by, e.g., its addition to commonly consumed foods, such as bread and pasta. Resistant starch preparations are obtained through various modifications, including: genetic (high- amylose varieties), physical (e.g., annealing at elevated humidity and temperature, freezing, extruding), physicochemical (complexation with lipids), and chemical (e.g., esterification, roasting of starch saturated with iron ions, roasting with glycine) [3,4]. The chemical modifications applied in the food production process are those that involve chemical reactions that require the use of specific chemical substances and occur without a biological agent [5]. The low-substituted modified preparations obtained in this way are used as food additives and are increasingly not accepted by consumers. However, it should be remembered that, during food production processes, the native starch of plant materials enters into contact with other substances and—under favorable conditions—may undergo natural chemical modifications under their influence. These compounds include organic acids that have a carboxyl group that can link with the hydroxyl group of starch. Organic acids are mainly found in fruits, and their contents vary widely and depend, among other things, on the species, variety, and degree of ripeness of the fruit; vegetation conditions; as well as storage time or conditions [6]. Most of the fruits contain mainly malic acid [7,8], Appl. Sci. 2021, 11, 9169. https://doi.org/10.3390/app11199169 https://www.mdpi.com/journal/applsci