Development and optimization of low temperature enzyme-assisted liquefaction for the production of colouring foodstuff from purple pitaya (Hylocereus sp. [Weber] Britton & Rose)

Abstract

An innovative liquefaction process for the production of colouring foodstuff from purple pitaya was developed and optimized. Conducting an enzyme screening, the most suitable enzyme preparation for the liquefaction of pitaya pulp at low temperatures (4–12 °C) was selected allowing extensive viscosity reduction (50%) and high betalain retention (80%). A modified D-optimal design was used for the optimization of significant influence factors. Maximizing a heuristic optimization function composed of regression terms of the responses relative viscosity (R ² = 0.97), betalain retention (R ² = 0.88) and betanin–isobetanin retention (R ² = 0.92), a numeric algorithm was established for process parameter optimization. The total juice yield was increased from 25–39 to 48–60% by implementation of the optimized liquefaction procedure into the pitaya juice production process. Mucilage separation steps were unnecessary and pitaya seeds could simply be separated as a by-product after juice filtration due to the extensive degradation of the mucilaginous matrix. In contrast to previously described mucilage liquefactions, the betalain profile was remarkably changed due to the applied enzymatic treatment resulting in a colour shift (Δh° = −14.7 ± 0.3) to bluish tones, and concentration of the so obtained pitaya juices from 12.3% TSS to 33% TSS and 65% TSS was successful at pilot plant scale.