Combined effect of blanching and sonication on quality parameters of bottle gourd (Lagenaria siceraria) juice

• Bottle gourd (Lagenaria siceraria) juice (BGJ) turned brown without blanching.
• Sonication time, amplitude and frequency affected quality of BGJ.
• Combination of blanching and sonication had beneficial effect on quality of BGJ.
• Microstructural study revealed beneficial effect on physical stability and microbial quality of BGJ.

This study evaluated the combined effect of blanching and sonication treatment on selected quality parameters of bottle gourd juice (BGJ). Bottle gourd cubes were blanched and juice was extracted. Effect of frequency (20–50 kHz), amplitude (50–90%) and time (10–30 min) was also studied on quality parameters like titratable acidity (TA), pH, total soluble solids (TSS), physical stability (PS), ascorbic acid (AA), total phenolics (TP), total carotenoids (TC), browning index (BI), total plate count (TPC) and yeast & mold count (Y&M) of BGJ to derive the level of these parameters. Combined effect of blanching followed by sonication (BFS) showed significant (P ⩽ 0.05) change in all quality parameters except TA. Highest percentage of TSS (5.9 °B), PS (2%), AA (18.99 mg/100 g), TP (1010 mg/100 g) and TC (5.8 mg/100 g) was observed at 70% amplitude, 50 kHz frequency and 20 min. Results suggested 70% amplitude, 50 kHz frequency and 20 min as best treatment conditions for processing of BGJ. Microstructure examination, transmission electron microscopy (TEM) and laser diffraction analysis of BGJ showed significant change in particle size and distribution. Moreover, TEM of blanched and sonicated samples of BGJ also showed significant (P ⩽ 0.05) change in microbial profile.