Upcycling apple pomace into a type III sourdough ingredient: effects on nutritional quality, antioxidant activity and bread shelf-life

The sustainable valorization of agro-industrial by-products through bioprocessing represents an attractive strategy for developing functional food ingredients while supporting circular economy approaches. Apple pomace, a by-product of apple juice production, is rich in dietary fiber and bioactive compounds; however, its direct incorporation into bakery products may compromise technological quality. In this study, apple pomace was fermented with Lactiplantibacillus plantarum and converted into a type III sourdough ingredient to evaluate its potential as a functional ingredient in breadmaking. Unfermented apple pomace (AP) and fermented apple pomace sourdough (SDAP) were incorporated into wheat bread formulations at replacement levels of 15% and 20%. Effects on nutritional composition, antioxidant activity, technological properties, and mold-free shelf life were investigated. Breads containing SDAP showed higher moisture retention, lower pH values than the control. Both AP and SDAP contributed to extended mold-free shelf life, while SDAP formulations showed lower fungal surface colonization during the early stages of storage, indicating an additional, although limited, effect associated with fermentation. Apple pomace improved the nutritional value of breads but caused technological limitations associated with fiber-rich ingredients, including reduced specific volume and increased crumb firmness, especially at the highest replacement level. These findings demonstrate that apple pomace, either unfermented or processed into a type III sourdough, can enhance the nutritional value and preservation of bread, with fermentation providing additional benefits in limiting early fungal colonization. Overall, apple pomace represents a promising upcycled ingredient for bakery applications. Further optimization is warranted to improve technological performance while maintaining its nutritional and preservation benefits.