###### Abstract  
Apple pomace has been proposed as a quality enhancer for gluten-free bread, but its composition and physicochemical features differ significantly depending on the apple cultivar. The objective of this article was to characterize apple pomace powder (APP) from certain varieties from the Basque Country and to study the feasibility of adding it to gluten-free bread, focusing on physicochemical and nutritional aspects. APP was obtained by washing, drying and grinding, and it was added at 0, 5, 6 and 8%, together with other ingredients, such as gluten-free flours, corn starch and whey protein. APP had a reddish-grey coloration (L* 56.49 \(\pm\) 1.39, a* 11.07 \(\pm\) 0.47, b* 27.69 \(\pm\) 1.76), pH 4.19 \(\pm\) 0.15 and Aw 0.235 \(\pm\) 0.084. Pomace powder was used successfully in higher amounts than experiences reported before. Key physiochemical parameters such as specific volume (\(\geq\)2.5 cm\({}^{3}\)/g) and cohesiveness or resilience values (0.538 and 0.378, respectively) suggested good acceptability for gluten-free breads with 8% APP. Additionally, breads were a source of antioxidant potential (437.66 \(\pm\) 38.95 uM DPPH/g APP), fiber (80.13 \(\pm\) 6.07 g/100 g) and micronutrients such as Cu, Mg, Mn and Fe. In conclusion, local apple varieties are a good source of raw material for gluten-free bread manufacture, which offers a solution for environmental pollution and may contribute to boosting the circular economy. apple pomace powder; sustainability; upcycling; gluten-free bread; quality; nutritional value +
Footnote †: journal: _Sciences_  
0000-0001-990  
brings significant management costs [4; 5]. It is composed of substances of nutritional interest, namely fiber and antioxidants [6]. The enrichment of foodstuffs with AP can affect aspects such as specific volume and nutritional value and, therefore, there are plenty of positive experiences adding AP as a value-added ingredient in general food products [4; 7; 8]. AP could also help to improve texture in gluten-free (GF) products: it has been reported that it helps to structure the food matrix due to its high water absorption and swelling capacity; thus, it could be a suitable alternative to gluten. However, studies addressing AP addition in GF products are still scarce [9]. The GF market has grown rapidly in recent years, and it is expected to continue doing so in the following years [9; 10]. These products are not only intended for populations with specific medical needs but also for those who follow a GF diet (GFD) as a health regime. Currently, there are numerous research lines working in this area, where the main objective is to obtain nutritionally appropriate and sensorily attractive products, as close as possible to their gluten-containing homologues [11]. Researchers studying the current GF market in different countries have shown that the nutritional quality of GF products is lower than their gluten-containing homologues [12; 13]. [PERSON] et al. [12] stated that Italian patients suffering celiac disease consume a high quantity of simple carbohydrates and fats, and that the celiac diet is frequently poor in fiber, protein and micronutrients; for instance, iron, calcium and selenium deficiencies are common in the celiac population. Similar results were recently obtained in a broader review performed in our research group about possible nutritional imbalances in adult celiac patients [14]. Moreover, there is still a lot of work ahead because of the technological difficulty caused by a lack of gluten. GF bread formulations have several texture deficiencies and some other quality defects associated with color and taste [15]. Indeed, lack of product variety and increased costs make it a challenge to maintain adherence to the GFD [16]. Achieving an acceptable product usually implies a complex list of ingredients including various refined flours and starches, additional fat and sugar and imbalanced energy [9]. Consequently, concern about the unsatisfactory nutritional quality of GFPs is increasing in recent decades [12; 13; 17].