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, per cent polymeric color, total and individual anthocyanin contents, antioxidant capacity and in vitro bioaccessibility in processing samples. Jam processing led to a significant reduction in total phenolics (88%), total flavonoids (89%), anthocyanins (97%), and antioxidant capacity (88-93%). Individual anthocyanin contents, determined using HPLC analysis, also showed a significant decrease (≈ 99% loss). In contrast, per cent recovery of bioaccessible total phenolics, anthocyanins and antioxidant capacity (ABTS assay) increased after jam processing (16%, 12%, and 37%, respectively).
Black mulberry jam processing:
The basic steps include selection of frozen black mulberries (12 °Brix), adding glucose-fructose syrup (approximately 2 times the amount of fruit, 68 °Brix) and water, cooking (performed at 550 mmHg and 78 °C until the dry matter content reaches 71 ºBrix), adjusting the pH through the addition of citric acid and apple pectin, seed removal and finally pasteurization at 95 °C for 25 minutes. During cooking, the seeds collect at the top of the jam mixture and these are subsequently removed. This study reports the effects of the entire industrial-scale processing of black mulberry fruit into jam on the phenolic composition of the end product. 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 antioxidant loss and improve final product quality.
Reference:
Tomas, M., Toydemir, G., Boyacioglu, D., Hall, R.D., Beekwilder, J. and Capanoglu, E., 2017. Processing black mulberry into jam: Effects on antioxidant potential and in vitro bioaccessibility. Journal of the Science of Food and Agriculture, 97(10), pp.3106-3113.
