Abstract:

A process route based on ultrasonic treatment and double-enzyme (cellulase and acidic protease) hydrolysis was designed for the preparation of a nutrient solution with purple sweet potato Fushu 13 as the raw material. To maximize the comprehensive preservation rate of nutrients, which was designated following analytic hierarchy process (AHP) and weighted average methods, orthogonal array design and Box-Behnken experimental design combined with response surface methodology were employed to optimize key process parameters for ultrasonic treatment and double-enzyme hydrolysis, respectively. The optimal ultrasonic treatment parameters were found as follows: ultrasonic power 65 W; extraction temperature 50 ℃; length of extraction time 25 min; and solid/liquid ratio 1:70. The optimal conditions for the enzymatic hydrolysis of the centrifugal precipitate of purple sweet potato after ultrasonic treatment were as follows: acidic protease amount 1.5%; cellulase amount 1.5%; pH 4.3; hydrolysis temperature 48 ℃; hydrolysis duration 65 min; and solid/liquid ratio (g/mL) 1:16. The resultant hydrolysate was centrifugated and the supernntant was then harvested and pooled with the centrifugal supernatant of purple sweet potato after ultrasonic treatment. Finally, a purple sweet potato based nutrient solution was obtained. Its comprehensive preservation rate of nutrients was measured to be 82.26%, namely 82.26% of the main nutrients in fresh purple sweet potato are preserved.

Key words: purple sweet potato, nutrient solution, ultrasonic treatment coupled with enzymatic hydrolysis