Inactivation of Bacillus subtilis and quality assurance in Chinese bayberry (Myrica rubra) juice with ultrasound and mild heat

Combined ultrasound and mild heat (UH) and traditional thermal pasteurization (TP) were employed to inactivate thermoacidophilic B. subtilis suspended in Chinese bayberry juice. Flow cytometry was used to evaluate different action mechanisms of these two treatments. The changes of physicochemical properties, anthocyanin content, and volatile components were also studied to assess the effects on juice quality. Results showed a 5-log reduction was achieved in 36.91 min by TP, 23.06 min by UH55 degrees C (400W), 14.18 min by UH63 degrees C (200w), 9.59 min by UF63 degrees C (400W), and the inactivation date had a high goodness of fit with Weibull model, exhibiting a fast drop in first and a slow decline at last. Compared to the TP, UH treatment was not only able to cause lethal effect by compromising membrane integrity, inactivating esterase activity, but also destroying nucleic acids through the flow cytometry analysis. The pH and soluble solids content of bayberry juice had no significant changes with different treatments, while the light transmittance of UH groups during storage was higher, the color and anthocyanin retention were better than TP treatment. The GC-MS analysis indicated UH treatment can significantly inhibit the decline of key aromatic substances of bayberry juice, including 1-hexanol, (Z)-3-hexenol, (Z)-3-nonenol and dihydro-S-pentyl-2(3H)-furanone.