Aleksandra Katanski

Bioethanol is a renewable, environmentally-friendly biofuel conventionally produced through the alcoholic fermentation of sugary or starch-rich substrates by microorganisms, commonly Yeast Saccharomyces cerevisiae. Intermediates of industrial wheat flour wet milling processing to starch, such as A-starch and B-starch milk, are cost-effective, abundant, and non-seasonal feedstocks for bioethanol production. This study evaluates the bioethanol production from wheat A-starch and B-starch milk and mixtures of these two substrates in different ratios (1:3, 1:1, and 3:1) using two cold hydrolysis procedures at 65 °C: (i) simultaneous liquefaction and saccharification (SLS) followed by fermentation, and (ii) liquefaction by alpha-amylase followed by simultaneous saccharification and fermentation (SSF). The results demonstrated that SSF and SLS are equally efficient procedures for reaching a high ethanol yield of 53 g per 100 g of starch and 93% of starch conversion to ethanol for all investigated substrates. Lower levels of non-starch components in A-starch milk, which typically contribute to volatile by-product formation, allowed clear distillate profiles in terms of and lower content of aldehydes, methanol, and volatile acidity, enhancing ethanol distillate purity compared to B-starch milk. Mixing high-quality A-starch milk with low-cost B-starch milk enables higher ethanol yield, improved distillate quality, and energy savings for efficient industrial-scale applications.

The present work highlights the advances of integrated starch and bioethanol production as an attractive industrial solution for complex wheat exploitation to value-added products focusing on increased profitability. Bioethanol is conventionally produced by dry-milling wheat grain and fermenting sugars obtained by the hydrolysis of starch, while unused nonfermentable kernel compounds remain in stillage as effluents. On the other hand, the wet-milling of wheat flour enables complex wheat processing for the simultaneous production of starch, gluten, and fiber. The intermediates of industrial wheat starch production are A-starch milk, containing mainly large starch granules (diameter > 10 μm), and B-starch milk, containing mainly small starch granules (diameter < 10 μm). The present study investigates different starch hydrolysis procedures using commercial amylase for bioethanol production from A-starch and B-starch milk by batch fermentation using distillers’ yeast Saccharomyces cerevisiae Thermosacc^®. Cold hydrolysis with simultaneous liquefaction and saccharification at 65 °C, a pH of 4.5, and a duration of 60 min was the most efficient and energy-saving pretreatment reaching a high conversion rate of starch to ethanol of 93% for both of the investigated substrates. A process design and cost model of bioethanol production from A-starch and B-starch milk was developed using the SuperPro Designer^® v.11 (Intelligen Inc., Scotch Plains, NJ, USA) software.