Methods and Implications for DDGS Production
Published: November 25, 2024
By: Dr.S.Sridhar M.V.Sc., (Animal Nutrition) / Product Manager, OPTIMA POULTRY PVT.LTD., Optima Square,46/2, Dhanalakshmipuram South, Central Studio Road, Singanallur, Coimbatore- 641005, India.
Introduction
Corn processing plays a pivotal role in the bioethanol industry, utilizing both wet and dry methods to extract valuable components from corn. Understanding the strengths and weaknesses of each approach is essential for producers aiming to optimize efficiency and product quality, particularly in the production of Distillers Dried Grains with Solubles (DDGS). In this article, we explore the two processing methods, their implications for DDGS production, and the challenges related to contaminants.
Corn Processing and Starch Preparation by Wet Process
Overview
Wet processing of corn starch for ethanol production is a well-established method, albeit more expensive than dry processing. This approach primarily utilizes starch for fermentation, leading to various valuable co-products.
Key Components of Wet Processing
· Co-products Produced
- Fiber
- Gluten
- Germ
- Oil Extraction
-The germ is removed from the corn kernel, and corn oil is extracted, yielding approximately 34 to 38 kg of oil per ton of corn.
- Remaining By-products
-The leftover germ flour is combined with fiber and corn gluten.
-Gluten can be further processed to create corn gluten meal, a high-protein animal feed.
Importance of Starch
Starch is the primary component in bioethanol production and represents the largest volume fraction in the fermentation process.
Starch Hydrolysis Process
To promote starch hydrolysis, the dough is heated to 105°C, which
· Physically breaks apart the starch granules.
· Opens the crystalline structure, allowing enzymes to act effectively.
Role of Enzymes
Two key enzymes used during hydrolysis are:
· α-Amylase
· Glucoamylase
- The action of these enzymes increases the viscosity of the paste by 20 times, complicating mixing and pumping.
pH Control in Hydrolysis
Cooking starch at temperatures between 30°C and 105°C requires the addition of:
· Lime
· Caustic soda
· Sulfuric acid
- These substances help maintain optimal pH for hydrolysis but increase energy consumption, representing 10-20% of the total bioethanol production cost.
Corn Processing and Starch Preparation by Dry Process
Overview
Industries now predominantly utilize the dry processing method for starch preparation, reducing energy consumption by lowering processing temperatures during starch conversion to glucose.
Key Features of Dry Processing
· Lower Temperature Gelatinization
- Corn starch gelatinization begins at 65°C, promoting efficient conversion to glucose.
- Granular starch is insoluble in water; thus, enzyme degradation occurs in the solid phase.
· Enzyme Activity and pH Control
- Enzymes first adsorb to starch granules, reducing the risk of microbial contamination.
- Lowering the pH enhances glucoamylase activity and inhibits contaminating bacteria growth.
· Cooking and Liquefaction
- The mixture is cooked at 100°C with steam injection, then transferred to retention tanks where the temperature drops to 80-90°C.
- α-Amylase is added, and the pH is adjusted to 6.0 for at least 30 minutes to optimize enzyme activity.
- Liquefaction significantly reduces starch polymer size, creating a dextrinized wort.
· Enzymatic Hydrolysis
- After liquefaction, the wort's pH is adjusted to 4.5, and glucoamylase is added to convert liquefied starch into glucose.
- This enzymatic hydrolysis allows for effective degradation of starch granules.
Fermentation Process
- In fermentation, Saccharomyces cerevisiae yeast transforms glucose into alcohol and carbon dioxide. Starch that is not converted to glucose remains intact.
· Simultaneous Saccharification and Fermentation
- Dry milling plants can minimize glucoamylase requirements by performing simultaneous saccharification and fermentation at 65°C.
· Advantages of Simultaneous Saccharification and Fermentation
- Reduces initial osmotic stress on yeast, avoiding concentrated glucose solutions.
- Can yield up to 8% more ethanol.
- Generally more energy-efficient.
Fermentation and Ethanol Recovery
The wort is cooled to 32°C and transferred to fermenters where yeast and nitrogen sources like ammonium sulfate or urea are added. Fermentation lasts 48-72 hours, achieving a final ethanol concentration of 10-12%. The pH drops below 4.0 due to carbon dioxide production.
· Distillation
- After fermentation, the mixture (must) is centrifuged and distilled to recover ethanol (up to 95% purity).
- The remaining liquid, called vinasse, contains water, oil, protein, and grain components.
By-products and Applications
· Vinasse Processing
- Vinasse undergoes centrifugation to separate wet grains (solids) from fine vinasse, which can then be evaporated to form a concentrated mixture called Wet Distillers Grains with Solubles (WDGS).
- WDGS is high in moisture and suitable for cattle farming but has a limited shelf life (around one week) unless dried.
· DDGS Production
- Industries can dry WDGS to 10-12% moisture content, enhancing transportability and extending shelf life.
· Oil Extraction and Co-products
- Advanced distillation technologies allow for the extraction of corn oil, with oleic acidity ranging from 10-15%.
- This oil, along with the WDGS, generates a co-product known as Distillers Dried Grains with Solubles (DDGS) with reduced oil content.
- DDGS and WDGS are increasingly used in animal feed, supporting the sustainability of the bioethanol industry.
Nutritional Challenges and Contaminants in DDGS
- The variability in DDGS composition is significant due to differing production processes across industries, complicating nutritional matrix applications.
· Contaminant Risks:
- Concerns about contaminants in DDGS, such as mycotoxins and pathogens, can impact animal health and marketability.
- While comprehensive studies on DDGS variability exist, data on how these variations affect nutrient availability—proteins, energy, and amino acids—are limited, hindering effective applications in poultry and swine diets.
Conclusion: Which Method is Best?
· Cost: Wet processing is more expensive due to higher energy consumption and pH control requirements, while dry processing is generally more cost-effective and energy-efficient. Fig: DDGS Fractionation
· Contamination Risks: The dry process reduces the risk of microbial contamination due to lower temperatures and initial enzyme adsorption.
· Acid-Free and Ash-Free Production: The dry process can result in lower ash and acid levels compared to the wet process, enhancing the quality of the resulting DDGS.
· Variability: Both methods show variability in nutrient composition; however, dry processing may have a more consistent quality profile due to fewer steps and controlled environments.
“In conclusion, the choice between wet and dry processing methods depends on operational goals, including cost, product quality, and market demands. Dry processing emerges as a favorable option, particularly in reducing contamination risks and enhancing nutrient stability in DDGS production.”
New advancement Optimization of Dry Grinding with Supercritical Technology:
Integrating dry grinding with supercritical technology can enhance the valorization of corn byproducts like DDGS, extracting valuable components such as oil enriched with carotenoids and phenolic compounds, while also generating protein-rich fractions for high-value feedstock.
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