Toward an Understanding of Physical and Biological Properties of Corn-Based Whole Stillage, Thin Stillage, and Condensed Distillers Solubles and Changes Thereof During Storage

The production of bio-based ethanol has been one of the fastest growing industries in the United States during the past decade. Thus, wider exploration of ethanol coproduct uses is necessary in the ethanol plant. Currently, process steams such as whole stillage, thin stillage, and syrup are processed into distiller dried grains with solubles and fed to livestock. The storability of whole stillage, thin stillage, and syrup influences the economic and energetic balances of fuel ethanol production. However, there are few investigations of the shelf life for these products or how to measure these quantities. The objectives of this research were to test physical and biological properties of whole stillage, thin stillage, and syrup and determine storability and allowable shelf life for these materials as influenced by storage temperature levels. Using standard laboratory methods, several properties were determined, including moisture content, water activity, thermal properties (conductivity, resistivity, volumetric heat capacity, and diffusivity), color, mold development, and CO2 production. Also, the separation processes due to settling were observed over 72 h. The thin stillage and whole stillage had relative high average moisture contents of 92% (w.b.) and 87% (w.b.), respectively, and a mean water activity of 0.99; the high water content marked samples easily susceptible to rapid spoilage. Time had a significant effect (p < 0.05) on properties of coproducts. Both thin stillage and whole stillage samples got mold growth after 5 days incubation at 32°C. Thin stillage had the greatest separation rate in the settling experiment. However, syrup had a relative low average moisture content of 62% and an average water activity of 0.92. No mold growth and settling separation happened in syrup samples. There was no evidence showing that a linear relationship exists between Hunter L*, a* and b*, and mold growth. The Solvita® test showed that high-temperature treatment caused high CO2 production in all samples. The exponential models described the relationship between storage time (from 0 to 5 days at 25 and 35°C) and CO2 concentration for the three coproducts. This study is a first step to explore opportunities for utilizing valuable components from these coproducts. Follow-up study should work on separation processes to concentrate the valuable components of these coproducts. Exploring the potential value of ethanol coproducts could maintain and improve the profitability of the ethanol industry.

Distillery decarbonisation and anaerobic digestion: balancing benefits and drawbacks using a compromise programming approach

The anaerobic digestion (AD) of distillery by-products presents benefits such as greenhouse gas (GHG) emission savings and electricity savings, as well as drawbacks such as reduced animal feed and protein production and the potential import of animal feeds. This work balances these benefits and drawbacks using compromise programming (CP). The best combination of byproducts (from 9,261 scenarios) to use in AD was selected based on criteria chosen by management of a large distillery. The use of all by-products maximises benefits and drawbacks; the contrary also applies. When benefits and drawbacks are equally important, CP recommends using 50% of available draff, 50% of available thick stillage, and 55% of available thin stillage. The best combination when accounting for criteria weights chosen by distillery management is the use of 100% of available draff and 100% of available thick stillage. This could replace 48% of natural gas consumption at the distillery, reduce Scope 1 emissions by 45%, achieve a Scope 3 emissions savings of 22% of current Scope 1 emissions, and reduce electricity consumption in the feeds recovery plant of the distillery by 63%. Protein loss of 9,618 t could require the import of 19.59 kilo-tonne wet weight of material (ktwwt) of distillers grains and 9.15 ktwwt of soybean meal. If different criteria or criteria weights were used, a different result would be recommended. The methodology developed herein can aid in decarbonising the food and beverage industry by allowing decision-makers to balance the benefits and drawbacks of AD while accounting for subjective preferences.

Diverse Profile of Fermentation Byproducts From Thin Stillage

The economy of biorefineries is influenced not only by biofuel production from carbohydrates but also by the production of valuable compounds from largely underutilized industrial residues. Currently, the demand for many chemicals that could be made in a biorefinery, such as succinic acid (SA), medium-chain fatty acids (MCFAs), and lactic acid (LA), is fulfilled using petroleum, palm oil, or pure carbohydrates as raw materials, respectively. Thin stillage (TS), the residual liquid material following distillation of ethanol, is an underutilized coproduct from the starch biofuel industry. This carbon-rich material has the potential for chemical upgrading by microorganisms. Here, we explored the formation of different fermentation products by microbial communities grown on TS using different bioreactor conditions. At the baseline operational condition (6-day retention time, pH 5.5, 35°C), we observed a mixture of MCFAs as the principal fermentation products. Operation of a bioreactor with a 1-day retention time induced an increase in SA production, and a temperature increase to 55°C resulted in the accumulation of lactic and propionic acids. In addition, a reactor operated with a 1-day retention time at 55°C conditions resulted in LA accumulation as the main fermentation product. The prominent members of the microbial community in each reactor were assessed by 16S rRNA gene amplicon sequencing and phylogenetic analysis. Under all operating conditions, members of the Lactobacillaceae family within Firmicutes and the Acetobacteraceae family within Proteobacteria were ubiquitous. Members of the Prevotellaceae family within Bacteroidetes and Lachnospiraceae family within the Clostridiales order of Firmicutes were mostly abundant at 35°C and not abundant in the microbial communities of the TS reactors incubated at 55°C. The ability to adjust bioreactor operating conditions to select for microbial communities with different fermentation product profiles offers new strategies to explore and compare potentially valuable fermentation products from TS and allows industries the flexibility to adapt and switch chemical production based on market prices and demands.

Corn Bioethanol Side Streams: A Potential Sustainable Source of Fat-Soluble Bioactive Molecules for High-Value Applications

This paper reports data from a characterization study conducted on the unsaponifiable lipid fraction of dry-grind corn bioethanol side streams. Phytosterols, squalene, tocopherols, tocotrienols, and carotenoids were quantified by High Performance Liquid Chromatography with Diode-Array Detector (HPLC-DAD) and Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) in different lots of post-fermentation corn oil and thin stillage collected from a bioethanol plant over a time-span of one year. Fat-soluble bioactives were present at high levels in corn oil, with a prevalence of plant sterols over tocols and squalene. Beta-sitosterol and sitostanol accounted altogether for more than 60% of total sterols. The carotenoid profile was that typical of corn, with lutein and zeaxanthin as the prevalent molecules. The unsaponifiable lipid fraction profile of thin stillage was qualitatively similar to that of post-fermentation corn oil but, in quantitative terms, the amounts of valuable biomolecules were much lower because of the very high dilution of this side stream. Results indicate that post-fermentation corn oil is a promising and sustainable source of health-promoting bioactive molecules. The concomitant presence of a variegate complex of bioactive molecules with high antioxidant potentialities and their potential multifaceted market applications as functional ingredients for food, nutraceutical, and cosmeceutical formulations, make the perspective of their recovery a promising strategy to create new bio-based value chains and maximize the sustainability of corn dry-grind bioethanol biorefineries.

Towards a Valorization of Corn Bioethanol Side Streams: Chemical Characterization of Post Fermentation Corn Oil and Thin Stillage

First-generation biofuel biorefineries may be a starting point for the development of new value chains, as their by-products and side streams retain nutrients and valuable molecules that may be recovered and valorized for high-value applications. This study provides a chemical characterization of post-fermentation corn oil and thin stillage, side streams of dry-grind corn bioethanol production, in view of their valorization. An overall long-term study was conducted on the two co-products collected over 1 year from a bioethanol plant. Water content, acid value, sedimentation, mineral composition, and fatty acid profiles were analyzed on post-fermentation corn oil. Results highlighted that its acid value was high (19.72–24.29 mg KOH/g), indicating high levels of free fatty acids, but stable over the year due to standardized operating conditions. The fatty acid profile was that typical of corn oil, with a prevalence of linoleic (54–59% of total fatty acids) over oleic (23–27%) and palmitic (12–17%) acids. Macronutrients, fatty acid, and mineral profiles were investigated in thin stillage. Results revealed the acidic pH (4.05–4.68) and high dilution (90–93% water) of this side stream. The dry mass was composed of fats (19–30%), proteins (8.8–12.8%), ash (8.7–9.5%), and fiber (7.3–9.8%). The concomitant presence of a variegate complex of molecules of nutritional interest in corn bioethanol co-products, with several potential high-value market applications, make the perspective of their recovery a promising strategy to create new cross-sector interconnections according to circular economy principles.