Correlation between the degree of ultrasound-induced cell disintegration and the extraction efficiency of intracellular compounds from purple sweet potato

Ultrasound (US) is an effective intensified extraction technology for natural plant resources, but detailed microscale investigations into US-induced plant cell disintegration are lacking. This study explored the correlation between US-induced (P = 0-800 W, t = 0-40 min) cell disintegration degree and the extraction efficiency of intracellular components from purple sweet potato, also discussing extraction selectivity and visualizing the cell micro-disintegration process. Cell disintegration degree was estimated via electrical conductivity (cell permeabilization index, Z_i) and fractal dimension analysis of damaged cells (cell wall disintegration index, Z_d). Extraction efficiency was evaluated by using the extraction indexes of carbohydrate (Z_c), protein (Z_p), and total phenolic compound (Z_TPC). Results indicated that US markedly enhanced cell permeabilization and intracellular components release. For example, at the highest intensity (800 W, 40 min), the enhancement in carbohydrate, protein and TPC contents were approximately 2 to 7 folds, compared to untreated sample (0 W, 40 min). Extraction efficiencies depended on the applied P and t, with the extractability order was carbohydrate > protein > TPC at each power. Different non-linear correlations between Z_d with Z_i, Z_p, Z_c, and Z_TPC, reflecting the differences in the release behaviors of these water-soluble components after US treatment. Additionally, US favored carbohydrate extraction over protein, but stronger US intensity resulted in lower extraction selectivity. The visual microscale model showed that increasing P elevated cell surface acoustic pressure, cell stress and volume strain. Cell micro-disintegration process would initiate at the side and end faces, then gradually spread to the edges.