## 1 Introduction  
It has recently been highlighted that food, as well as its main function, i.e., providing essential nutrients that regulate bodily functions, is also expected to prevent, or even cure, diseases. Its health potential results from the presence of bioactive compounds like, e.g., vitamins, phytochemicals, and peptides [1]. The latter ones have attracted the attention of scientists as non-toxic and multi-active molecules [2]. They were proven to act as, i.a., glucose level reductants, blood hypotensors, cholesterol level reductants, anti-oxidants [3, 4], anti-inflammatory, and anti-obesity agents [5]. Reduction of the blood glucose level is related to, i.a., the action of peptides that inhibit dipeptidyl peptidase IV (DPP IV). DPP IV itself (EC 3.4.14.5) is an enzyme involved in the degradation of GLP 1(glucagon-like peptide 1) and GIP (glucose-dependent insulinotropic peptide). These two molecules are released into the gastrointestinal tract and are responsible for glucose homeostasis. The action of DPP IV briefly relies on the cleavage of N-terminal dipeptides from GLP 1 and GIP to produce inactive incretients; hence, it triggers the loss of insulinotropic activity of GLP 1 and GIP. Thus, peptides that inhibit DPP IV action display the anti-diabetic function [6; 7]. DPP IV inhibitors were identified in, e.g., milk and dairy products, rice bran, salmon, tuna, and azuki beans [8]. The hydrolysis of proteins followed by the determination of biological activity of a hydrolysate and the identification and/or synthesis of peptides is the classical procedure of studying bioactive peptides derived from foods. Another research strategy includes an in silico analysis of biopeptides. It involves the application of, i.a., bioinformatic and cheminformatic databases as sources of information about peptide sequences, tools for the molecular docking of peptides to predict the possible mechanism of their action, and the prediction of peptide bioactivity based on its structural nature [9]. The latter is called a QSAR, i.e., the quantitative structure-activity relationship, and, so far, it has been applied in the study of peptides showing a one [9; 10; 11] and dual biological effect [12; 13]. A literature search using the Scopus [14] platform (accession date: October 2023) revealed dozens of records (i.e., 51, including reviews and original papers as well as conference abstracts) dedicated to QSAR of DPP IV inhibitors using \"QSAR and dipeptidyl peptidase 4 and inhibitors\" as a query. Further analysis of these records showed that none of them concerned peptides with such an activity. The articles mostly concerned the QSAR analysis of non-peptide DPP IV inhibitors like, e.g., 4-fluoropyrrolidine-2-carbonitrile and octahydrocyclopenta[b]pyrrole-2-carbonitrile [15], tetralin-sulfonamide derivatives [16], and polyphenols [17]. This literature search via Scopus has shown that there is paucity of literature data related to the QSAR of DPP IV peptide inhibitors, especially those derived from food proteins. The query \"QSAR and dipeptidyl peptidase-IV and inhibition or inhibitors and peptides\" revealed 15 records (as of October 2023), but barely 2 of them were related to the food-originating DPP IV inhibitors. They included an original article concerning the identification of DPP IV inhibitors from camel milk hydrolyses [18] and a review of the efficiency of the QSAR of food-derived bioactive peptides [19]. One of the latest articles concerned the impact of certain structural features on the DPP IV-inhibitory activity of dipeptides. However, the models were based on several attributes describing protein structures (long-chain molecules) which are not applicable to dipeptides (short-chain compounds) [20]. Other articles were related to DPP IV inhibition described by means of programs useful for reporting the DPP IV inhibition of compounds like, e.g., iDPPIV-SCM and StackDPPIV [21; 22].