Changes in anthocyanins and colour of black mulberry (Morus nigra) juice during clarification and pasteurization

Abstract

The effects of enzymatic treatment, clarification with bentonite, gelatin and kieselsol, and pasteurization on the anthocyanins (ACNs) and colour of black mulberry juice (BMJ) were studied. Enzymatic treatment caused significant reductions in ACN content (10%), A(max) (53%), colour density (67%) and polymeric colour (67%). The most stable ACN to enzymatic treatment was cyanidin-3-glucoside (cy-3-glu), while the least stable one was pelargonidin-3-glucoside (pg-3-glu). Bentonite showed the copigmentation effect due to Al3+ and Mg2+ in its octahedral sheet structure and enhanced colour density (91%) of BMJ. Similarly, gelatin and kieselsol also caused a high A(max) and a colour density despite a reduction in ACN content. Results revealed that enzymatic degradation of pectin and removal of phenolics by gelatin-kieselsol led to a reduction in the colour density of BMJ after pasteurization. Therefore, bentonite is recommended to produce BMJ with high colour density, while enzymatic treatment and clarification with gelatin and kieselsol are not recommended due to a reduction in ACN content.