Sustainable use of apple pomace as a new functional ingredient due to its enhanced antioxidant and prebiotic properties

The characteristics of apple pomace (AP) are being thoroughly studied to support the industries from the sector, implementing sustainable circular economy guidelines and, at the same time, providing consumers with health-promoting food products. Although plentiful, AP is still a largely untapped resource, rich in interesting bioactive compounds. In this work, the antioxidant capacity of AP was measured by two in vitro assays: the TBARS assay, which assesses the ability to inhibit the formation of thiobarbituric acid reactive substances in brain cell homogenates, and the ORAC assay, which measures the oxygen radical absorbance capacity. The prebiotic activity was compared with positive controls (glucose, inulin, and fructooligosaccharides (FOSs)). Three Lactobacillus and one Bifidobacterium were used, namely Lactobacillus casei (NCTC 6375), Lactobacillus plantarum (DSM 12028), Lactobacillus acidophilus LA-5 (Probio-Tec, Denmark) and Bifidobacterium animalis spp. lactis Bb12 (Probio-Tec, Denmark). Considering the different reaction mechanisms in the antioxidant activity assays, AP generally demonstrated good antioxidant activity, particularly in the ORAC test (161 µmol TE/g). In terms of the prebiotic activity, AP exhibited optical density values exceeding those of the positive controls for all the tested microorganisms, indicating that microorganisms accepted the sample as food. These results demonstrated that AP could be an effective carbon source for various prebiotic strains, fostering their growth more effectively than well-known prebiotics. This study highlights AP's potential as a functional ingredient in dietary supplements or nutraceuticals. Its antioxidant properties could be harnessed to develop natural food preservatives, providing a healthier alternative to traditional ones while supporting circular economy principles. AP could also be incorporated into formulations to boost gut health.