Effect of ultrasound and pasteurisation on the structure and visual quality of black elderberry juice

Black elderberry juice is rich in polyphenols but tends to form a visually unappealing, cloudy precipitate, which is unappealing to consumers. This study aimed to evaluate how high-intensity ultrasound combined with lower-temperature pasteurisation affects the particle size distribution, turbidity, centrifugal sedimentation rate, viscosity, and colour of black elderberry juice. Ultrasound alone reduced the particle mean diameter (D₄,₃) values, indicating the deagglomeration of cell clusters and the formation of finer particles, while slightly decreasing centrifugal sedimentation. After ultrasound treatment (UT) and pasteurisation at 60–70 °C, particle size and the centrifugal sedimentation rate increased. Turbidity decreased to approximately 40 NTU, yielding clarified juice with large, dense aggregates that settled.

In contrast, prolonged UT combined with pasteurisation at 60–70 °C significantly reduced D₄,₃ and increased turbidity to 425 NTU, indicating a fine, stable colloidal cloud. Colour analysis showed that UT followed by pasteurisation at 60 °C enhanced redness and chromatic hue. In contrast, prolonged UT and 70 °C temperature pasteurisation produced darker, less vivid red tones, consistent with partial pigment degradation and polymerisation. The results revealed two technological pathways within the same juice matrix: a clarification pathway (ultrasound + pasteurisation) and a cloud stabilisation pathway (extended ultrasound + pasteurisation), offering a tool for developing elderberry juices with the desired visual outcome.