# Enzymatic hydrolysis of starch from the anthocyanin extraction residue (AER-starch) with ultrasound pretreatment: A techno-economic assessment

## TL;DR

This paper studies how to efficiently convert starch from purple yam waste into glucose syrup using ultrasound and enzymes, and evaluates the cost-effectiveness of the process.

## Contribution

The study introduces a novel ultrasound-assisted enzymatic hydrolysis method for converting anthocyanin extraction residue starch into glucose syrup.

## Key findings

- Ultrasound pretreatment improved enzymatic hydrolysis of AER-starch, achieving starch conversion above 90%.
- The cost of manufacturing glucose syrup dropped significantly with higher AER-starch concentrations.
- Economic feasibility is achieved when AER-starch costs under $1.20/kg and glucose syrup sells for at least $3.50/kg.

## Abstract

Purple yam (Dioscorea alata) is a tropical tuber crop that is a source of anthocyanins and starch. Starch can be isolated from the large quantity of extraction residues and become a raw material for hydrolyzate production. Ultrasound pretreatment was evaluated in consecutive enzymatic hydrolysis (UCEH) and simultaneous enzymatic hydrolysis (USEH) of starch from anthocyanin extraction residue (AER-starch). A techno-economic assessment was performed. Ultrasound pretreatment showed a positive influence on CEH and SEH. The hydrolysis degree (HD) was higher in CEH (72.87 ± 3.01%) than in SEH (28.10 ± 1.32%). CEH performed better than SEH, primarily due to the thermal instability of the enzymes. Enzymatic hydrolysis solubilized almost all AER-starch. Starch conversion (SC) above 90% was achieved for all CEH experiments using AER-starch concentrations ranging from 10 to 50 g L-1. The cost of manufacturing (COM) for glucose syrup using AER concentrations of 10 and 350 g L-1 was US$61.25 kg−1 and US$2.90 kg−1, respectively, when the purchasing cost for AER-starch was US$1.50 kg−1. The CRM was the major component of the COM (above 50%) when AER-starch concentrations were higher than 100 g L-1, AER-starch being the primary raw material contributing to the COM. The production of the glucose syrup was economically feasible when the AER-starch purchasing price was under US$1.20 kg-1 and the selling price was at least US$3.50 kg-1.