Phytochemical Profiling (Phenolics and Carotenoids) and Antioxidant Potential of Apple, Plum, Carrot, and Beetroot Juice Pomaces: Towards Sustainable Food Ingredients

Apple (Malus domestica Borkh. cv. Jonathan), beetroot (Beta vulgaris L.), carrot (Daucus carota L.), and plum (Prunus domestica L.) pomaces are among the major by-products generated by the juice processing industry in Europe, particularly in producing countries such as Poland, Germany, Spain, and Romania. Conventionally discarded or utilized as animal feed or bioenergy pellet production, these matrices hold potential as high-value functional food ingredients. Supporting circular bioeconomy goals, this study evaluated the potential of industrial pomaces generated during continuous juice pressing as high-value functional food ingredients following their conversion into powders by air-drying and milling. The pomace powders were characterized for proximate composition, color, individual phenolics and carotenoids, and in vitro antioxidant capacities. Carrot pomace presented a high content of carotenoids (84.37 ± 0.08 µg/g dw) and ash (7.78 ± 0.41% dw), providing natural orange-yellow coloration and contributing to the mineral content. Beetroot pomace recorded the highest dietary fiber (17.20 ± 0.55% dw), as well as betalains, ideal as a natural red colorant and emulsion stabilizer. Plum pomace demonstrated the strongest overall antioxidant capacity, driven by tentatively identified 3-caffeoylquinic acid (712.36 ± 0.31 μg/g dw), flavonols, and anthocyanins (264.16 ± 0.5 μg/g dw). Apple pomace provided a carbohydrate-rich matrix (77.71 ± 0.65% dw) featuring positively identified chlorogenic acid (463.16 ± 0.35 μg/g dw) and tentatively identified dihydrochalcones. These findings support the targeted valorization of these pomaces as functional food ingredients within a circular bioeconomy framework.