Processing black mulberry into jam: effects on antioxidant potential and in vitro bioaccessibility.

BACKGROUND Black mulberries (Morus nigra) were processed into jam on an industrialized scale, including the major steps of: selection of frozen black mulberries, adding glucose-fructose syrup and water, cooking, adding citric acid and apple pectin, removing seeds, and pasteurization. Qualitative and quantitative determinations of antioxidants in black mulberry samples were performed using spectrophotometric methods, as well as HPLC- and LC-QTOF-MS-based measurements. These analyses included the determination of total polyphenolic content, percent polymeric color, total and individual anthocyanin contents, antioxidant capacity, and in vitro bioaccessibility in processing samples. RESULTS Jam processing led to a significant reduction in total phenolics (88%), total flavonoids (89%), anthocyanins (97%), and antioxidant capacity (88-93%) (p < 0.05). Individual anthocyanin contents, determined using HPLC analysis, also showed a significant decrease (≈ 99% loss). In contrast, percent recovery of bioaccessible total phenolics, anthocyanins, and antioxidant capacity (ABTS assay) increased after jam processing (16%, 12%, and 37%, respectively). CONCLUSION Fruit processing resulted in losses of polyphenols, anthocyanins, and antioxidant capacity of black mulberry jam. Optimization of food processing could help to protect the phenolic compounds in fruits which might be helpful for the food industry to minimize the antioxidant loss and improve the final product quality.