Nowadays, plant-based fermented products are attracting a lot of consumer interest due to their probiotic and health-promoting properties. The aim of this study was to evaluate the microbiological quality and antioxidant activity of innovative fermented oat beverages with the addition of extracts and freeze-dried local fruit. In the first step, chokeberry and hawthorn were selected based on their antioxidant and antimicrobial properties. The final study material consisted of oat beverages fermented with the use of the Lactiplantibacillus plantarum DKK 003 strain for 20 h with the addition of 1 and 5% of extracts and freeze-dried fruits. It was found that freeze-dried chokeberry and chokeberry extracts showed a higher content of polyphenolic compounds than freeze-dried hawthorn and hawthorn extracts. After the fermentation process of the innovative beverages, the content of polyphenolic compounds remained the same or there was a slight decrease depending on the additive type. Antioxidant activity significantly decreased after 20 h of fermentation in all enriched oat beverages with no significant differences observed compared to control samples. The obtained fermented beverages were characterised by a high lactic acid bacteria count (above 8 log CFU/mL), a low pH (approximately 4.15), and no microbiological contamination. Oat fermented beverages with fruit additives can be good dietary enrichment products.

Increasing food consumption and waste generation are today’s most difficult economic and environmental challenges. In line with the sustainable production and consumption concept, wasted food, as a source of valuable resources, can be reused to produce new products of higher value than the raw materials from which they were made. This concept was used in this work to design products that are a plant-based alternative to fermented milk drinks, which arouse great interest among consumers due to their health-promoting properties. This study aimed to design potential probiotic beverages from food industry waste, including wheat-rye bread and chokeberry pomace, using lactic acid fermentation with different strains of lactic acid bacteria (LAB) and to evaluate selected quality features of the obtained beverages. In the first stage of the research, the group of LAB strains was tested for their efficiency in bakery waste fermentation, and then the potential probiotic properties of chosen LAB strains (Lactiplantibacillus plantarum A7, Lacticaseibacillus paracasei INV001, Lacticaseibacillus rhamnosus INV002, Lentilactobacillus buchneri P7, Loigolactobacillus coryniformis INV014) were characterized according to FAO/WHO requirements. For the prepared beverages, microbiological quality, antioxidant properties, and the content of polyphenolic compounds were determined. It was found that bakery and chokeberry waste may constitute a good base for obtaining fermented beverages with some beneficial properties, including a high number of potentially probiotic bacteria, reaching 10⁸ CFU/mL, and antioxidant properties, which positively verified their functional properties. The research confirms the high potential of lactic acid fermentation in managing food waste to create innovative, sustainable food products with probiotic properties.