Short-chain fructooligosaccharides (scFOS) are nutraceuticals with numerous applications in the food and pharmaceutical industries. The production of scFOS using immobilized biocatalysts offers some functional and technical advantages over free enzyme counterparts. To investigate the economic potential of the immobilized enzyme system relative to the free enzyme system, a techno-economic comparison was conducted on three methods of scFOS production (powder and syrup forms) at a capacity of 2000 t per annum (tpa) by enzymatic synthesis from sucrose: the free enzyme (FE), calcium alginate immobilized enzyme (CAIE), and amberlite IRA 900 immobilized enzyme (AIE) systems. These processes were simulated in Aspen Plus to obtain the mass and energy balances and to estimate the operating and capital costs, followed by economic evaluation and sensitivity analysis. Profitability analysis showed that all three systems are economically viable as their associated minimum selling prices (MSP) were well below the scFOS market price of 5 $ kg −1 . However, the FE system was the most profitable with the lowest MSP of 2.61 $ kg −1 because the savings on cost as a result of enzyme immobilization could not offset the additional costs associated with immobilization. Sensitivity analysis demonstrated that total operating cost, fixed capital investment, and internal rate of return (% IRR) have the greatest effects on the MSP. Furthermore, the syrup form of scFOS production leads to 29% less MSP, compared to powder form. In addition, the studied plant capacities of 5000 and 1000 tpa showed 10% and 16% reductions on MSP respectively.

BACKGROUND Brewers spent grains (BSG) represents ≤85% of a brewery's solid waste and common disposal to landfill is increasingly more difficult. Yet BSG is a food‐grade by‐product with potential economic valorization that can significantly improve resource efficiency and reduction in carbon emissions. This study investigated valorization of BSG through the application of novel high solids hydrothermal processing technology in a small‐scale biorefinery, annexed to a brewery. It focused on three scenarios for the production of: (A) the sugar replacement xylitol; (B) prebiotic xylo‐oligosaccharide (XOS); and (C) co‐production of xylitol and XOS. Economic assessment was conducted by comparing the capital and operating expenditure from process simulations created in Aspen Plus®. The process models developed were supplemented with experimental data to improve accuracy. RESULTS Internal rate of return (IRR) values obtained were greater than the hurdle rate of 9.7% for all scenarios when considering a conservative market price for xylitol and XOS as US$4500 t–1, yet dedicated production of XOS was economically more favourable with a minimum required selling price (MRSP) of US$2509 t–1 compared to US$4153 t–1 for xylitol. Additionally, the scenario for co‐production of xylitol and XOS achieved the lowest MRSP of US$2182 t–1. By‐products significantly contributed to 32.7%, 14.2% and 27.5% of the revenue generated in scenarios A, B and C, respectively. CONCLUSION These results provide a good platform from which to develop the cost‐effective commercial production of XOS and xylitol from BSG. © 2021 Society of Chemical Industry

The immobilization of β-fructofuranosidase for short-chain fructooligosaccharide (scFOS) synthesis holds the potential for a more efficient use of the biocatalyst. However, the choice of carrier and immobilization technique is a key to achieving that efficiency. In this study, calcium alginate (CA), Amberlite IRA 900 (AI900) and Dowex Marathon MSA (DMM) were tested as supports for immobilizing a novel engineered β-fructofuranosidase from Aspergillus japonicus for scFOS synthesis. Several immobilization parameters were estimated to ascertain the effectiveness of the carriers in immobilizing the enzyme. The performance of the immobilized biocatalysts are compared in terms of the yield of scFOS produced and reusability. The selection of carriers and reagents was motivated by the need to ensure safety of application in the production of food-grade products. The CA and AI900 both recorded impressive immobilization yields of 82 and 62%, respectively, while the DMM recorded 47%. Enzyme immobilizations on CA, AI900 and DMM showed activity recoveries of 23, 27, and 17%, respectively. The CA, AI900 immobilized and the free enzymes recorded their highest scFOS yields of 59, 53, and 61%, respectively. The AI900 immobilized enzyme produced a consistent scFOS yield and composition for 12 batch cycles but for the CA immobilized enzyme, only 6 batch cycles gave a consistent scFOS yield. In its first record of application in scFOS production, the AI900 anion exchange resin exhibited potential as an adequate carrier for industrial application with possible savings on cost of immobilization and reduced technical difficulty. K E Y W O R D S adsorption, entrapment, fructooligosaccharides, frustosyltransferase, immobilization, ion exchange

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