Extraction of soluble fibre food ingredients within integrated biorefineries

Integrated biorefineries, in which several co-products are produced in ways that exploit interaction opportunities for enhancing efficiency and reviving economics, are necessary in order to make bioethanol commercially viable, while offering the opportunity to create new product markets. Arabinoxylans (AX) are potentially a novel class of food ingredients that could be extracted from cereal bran; production of AX involves precipitation with ethanol, hence the extraction could be integrated within bioethanol biorefineries. Having established this as a viable proposition in principle, now greater understanding of the functional properties of arabinoxylans is required, as these properties vary according to feedstock and extraction techniques. In order to investigate functional properties in food systems, significant quantities of AX extracts are necessary. Thus, the objective of the current research is to screen a range of pre-treatments approaches and extraction conditions for the purpose of facilitating the scale-up of AX from two biomass sources, wheat bran and sugarcane bagasse.

AX was extracted at lab-scale from wheat bran (WB) and sugar cane bagasse (SCB) via several extraction methods: alkaline extraction (pH 11.5, 60°C, 4 Hours), alkaline oxidative extraction (pH 11.5, H2O2 2%, 60°C for 4 hours) and enzymatic extraction utilizing three xylanases (β-xylanase, 1,4-β-D-xylanase, and Endo-1,4-β-xylanase) and feruloyl esterase. Several pre-treatment techniques were examined including cellulase treatment for 24 hours, milling and autoclaving. Purification of the extracts was investigated via two methods: firstly, washing the bran (water, 60°C for 20 minutes) prior to the extraction; and secondly, applying amylase and protease during the extraction. The samples were concentrated by ultrafiltration using a 10 kDa membrane, prior to ethanol precipitation, to reduce the ethanol requirement. Crude yields and total protein content were measured for all extracts.

Preliminary results demonstrated that the enzymatic extraction yield was the lowest, ranging between 4.6-9.3% for WB and 7.0-8.2% for SCB, while the alkaline extraction yielded 17.6 and 13.8% for WB and SCB, respectively, and the alkaline oxidative extraction yielded 33.7% for WB and 16.3% for SCB. Autoclaving wasn’t successful in improving the yields, while milling increased the yield from WB and SCB to 39.79% and 18.2%, respectively. Higher yields were obtained by using cellulase pretreatment, reaching 40.12% and 23.8% for WB and SCB, respectively. The protein content in SCB samples was relatively low (0.6-0.8%) and much higher in WB samples (12.7-14.2%). Protease treatment reduced the protein content in the WB extracts to 8.2%. Preliminary monosaccharide analysis utilising HPEAC-PAD was undertaken. Unfortunately, these analyses were not sufficiently reliable, perhaps due to incomplete hydrolysis of samples. Nevertheless, significant progress was made towards understanding the basis for enhancing AX extraction yields from these feedstocks.