Co-production of ethanol and protein isolates from the by-product of pulse with Air-Currents Assisted Particle Separation (ACAPS) process
Creators: Widjaja, Elisabeth Kezia
Publisher: name: University of Alberta Library
Year: 2023

<p>Biorefinery approaches aimed at adding value to waste materials to support a sustainable bio-based economy have gained much more attention in the last decades. Bioethanol, as biofuel, stands out as a key product derived from the innovative processes that have been developed using various agricultural feedstocks. In this study, pulse starch concentrate obtained as a by-product of the Air-Currents Assisted Particle Separation (ACAPS) technology was used to produce bioethanol with a reduced environmental footprint, while concurrently generating a co-product in the form of protein-rich fermentation residue.<br>
The conversion of starch-rich pulse materials starts with the hydrolysis of starch into glucose, facilitated by an enzyme cocktail containing α-amylase, glucoamylase, glucanase, and protease. Of all three types of feedstocks, the degree of hydrolysis of field pea, red lentil, and faba bean, was comparable to barley starch concentrate. The maximum conversion was achieved within 24 hours for field pea and red lentil, and within 48 hours for faba bean. The enzyme concentration used for hydrolysis was also studied and showed that lower enzyme concentrations than what was used do not produce the same glucose concentration within the same timeframe. The enzyme combination was also studied and it was found that the combination of α-amylase and glucoamylase only did not produce high glucose concentration, due to the presence of protein and fiber surrounding the starch granules. However, the addition of urea as a hydrogen bond breaker increased the starch conversion.<br>
The starch hydrolysis behavior indicated partial hydrolysis, which was observed by quantifying residual starch after hydrolysis. The high amylose content of 28-32% for all pulse feedstock was one of the causes of partial hydrolysis, but it was also observed that the surface of pulse starch granules was smooth without any pinholes or fissures, decreasing the contact between enzyme and starch. However, with hydrolysis, physical changes in the starch granules were observed as well as subsequent gelatinization behavior which combined appeared to support higher glucose production.<br>
           The final element of the starch conversion was fermentation in the bioreactor following an established Simultaneous Saccharification and Fermentation (SSF) protocol. At the end of fermentation, residual starch was observed, in accordance with the previously observed partial hydrolysis results. Improvement of ethanol conversion efficiency was achieved through enzyme combinations, the addition of urea, as well as supplementation of phosphate or trace minerals. Sodium chloride supplementation was also found to increase the ethanol conversion efficiency, due to its osmotic regulation properties. At the end of fermentation, a protein-rich Distiller’s Dried Grains with Soluble (DDGS) was obtained.<br>
    To summarize, pulses, alternative feedstocks for ethanol production were examined in this study with a promising result. Pulses present different kinetics of amylolysis behavior compared to common feedstock such as corn, barley, and wheat due to the high protein content, but approaches taken were successful in producing both ethanol and protein-rich residue with improved conversion efficiency. It is expected that the hydrolysis and fermentation processes lowered the anti-nutritional content, making it more attractive for both human and animal consumption. As pulses are widely consumed for the protein and dietary fiber benefits, the nitrogen-fixing capabilities as well as the potential for fuel production are additional appeals for crop diversification. Thus, the bioconversion of ACAPS-treated pulse feedstock into bioethanol and protein residue using a biorefinery process can help address the bioeconomy challenges.</p>