Citation: Derkach, S.R.; Voron’ko, N.G.; Kuchina, Y.A. Intermolecular Interactions in the Formation of Polysaccharide-Gelatin Complexes: A Spectroscopic Study. Polymers 2022, 14, 2777. https://doi.org/10.3390/ polym14142777 Academic Editor: Sergiu Coseri Received: 9 June 2022 Accepted: 5 July 2022 Published: 7 July 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 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/). polymers Review Intermolecular Interactions in the Formation of Polysaccharide-Gelatin Complexes: A Spectroscopic Study Svetlana R. Derkach * , Nikolay G. Voron’ko and Yulia A. Kuchina Department of Chemistry, Murmansk State Technical University, Murmansk 183010, Russia; voronkong@mstu.edu.ru (N.G.V.); kuchinayua@mstu.edu.ru (Y.A.K.) * Correspondence: derkachsr@mstu.edu.ru Abstract: Gelatin, due to its gelling and stabilizing properties, is one of the widely used biopolymers in biotechnology, medicine, pharmaceuticals, and the food industry. One way to modify the char- acteristics of gelatin is molecular modification by forming non-covalent polyelectrolyte complexes with polysaccharides based on the self-organization of supramolecular structures. This review sum- marizes recent advances in the study of various types and the role of intermolecular interactions in the formation of polysaccharide-gelatin complexes, and conformational changes in gelatin, with the main focus on data obtained by spectroscopic methods: UV, FT-IR, and 1 H NMR spectroscopy. In the discussion, the main focus is on the complexing polysaccharides of marine origin-sodium alginate, κ-carrageenan, and chitosan. The prospects for creating polysaccharide-gelatin complexes with desired physicochemical properties are outlined. Keywords: gelatin; polysaccharide; polyelectrolyte complexes; UV spectroscopy; FT-IR spectroscopy; 1 H NMR spectroscopy 1. Introduction The protein-polysaccharide polyelectrolyte complexes that are formed during biopoly- mer interaction are considered to be the basis for the creation of new materials in biotechnol- ogy, medicine, pharmaceuticals, the food industry, and other industries related to human health and nutrition [1–3]. The creation of materials is based on the self-organization principles of the complexes in the bulk of the aqueous phase [4]. The combined use of proteins and polysaccharides in the composition of the complexes contributes to the mutual enhancement of their physicochemical properties: their stabilizing ability and resistance to changes in external factors (pH, the presence of salts, changes in temperature) [5]. Nowadays, proteins and polysaccharides are widely used in the food industry [3,6] to encapsulate bioactive ingredients in functional food products [7,8]. These biomacro- molecules as well as their complexes are used for protection and as delivery systems for bioactive food additives that can control their release and regulate their bioavailability [9,10]. Gelatin, a degradation product of the fibrillar protein collagen, is one of the biopoly- mers that is widely used in the food industry [11–13]. Gelatin has a unique thermoreversible gelation ability, which is accompanied by the macromolecule undergoing a conforma- tional transition: coil↔collagen-like helix [14,15]. This property, along with the ability to interact with polysaccharides, is widely used to create various food systems based on polysaccharide-gelatin complexes that have the desired physicochemical properties [16,17]. Recently, new information on the structure and properties of various polysaccharide-gelatin systems (hydrogels [18–21] and composites [16], colloidal particles [22], emulsions [23–26], films [27], etc.) has come to light, expanding their range of applications in food technologies and products. The interactions that take place between gelatin and polysaccharides play an important role in the development of new food systems. It is known that intermolecular interactions Polymers 2022, 14, 2777. https://doi.org/10.3390/polym14142777 https://www.mdpi.com/journal/polymers