Bacterial Nanocellulose‐Based Composite Biocatalysts for Starch‐to‐Bioethanol Valorization under Simultaneous Saccharification and Fermentation

Composite biocatalysts (CB) consisting of amylases and Saccharomyces cerevisiae immobilized separately on bacterial nanocellulose (BNC) are used for the process of simultaneous saccharification and fermentation (SSF) of starch (5%, w/v) for bioethanol production. Parameters such as: i) addition of phosphates and/or divalent metal‐ions salts during the co‐immobilization process of the amylases, ii) required co‐immobilization time, iii) fermentation temperature and initial pH of starch, and iv) CB as single or double freeze‐dried are studied. The utilization of double freeze‐dried CB exhibits fermentation efficiency 89.9% and ethanol yield 0.51 g ethanol g−1 starch while the single freeze‐dried CB 81.1% and 0.46 g ethanol g−1 starch, respectively. In the case of double freeze‐dried CB, the fermentation efficiency decreases by only 27.1% in two‐recycling batches, while in the single freeze‐dried one decreases by 51.3%. The application of double freeze‐dried CB can be used for: i) the eco‐friendly biosynthesis of value‐added bioproducts; ii) the promising option for fuel‐grade bioethanol through starchy wastes or foodstuff starchy residues treatment, and iii) the implementation of industrialization. Finally, to simulate an industrial process of one‐step SSF of starch by applying a CB model, a technoeconomic analysis is evaluated, where using BNCs makes the bioprocess cost‐effective and environmentally favorable, simultaneously. Successful immobilization of Saccharomyces cerevisiae and amylases on bacterial nanocellulose is proved by high ethanol production from simultaneous saccharification and fermentation (SSF) of starch. Metal ions (Mg2+, Ca2+, and Mn2+) binding in amylases, except Zn2+, improves substantially the ethanol yield and fermentation efficiency in SSF of starch making the process valuable for agro‐industrial residue valorization.