#09-119

Complete

Date Full Report Received

11/15/2010

Date Abstract Report Received

11/15/2010

Investigation

Institution:
Primary Investigator:

PART A
The objective of this study is to monitor the changes in lysine concentration and reactivity through the unit operations and processes that are used to make fuel ethanol. The concentrations of lysine and heat related compound, i.e. furosine, will be measured in the corn used as the feedstock, the distiller’s dried grains with solubles (DDGS) that is produced as the final coproduct, and at important intermediate steps in the process in order to identify processes and steps which result in heat damage of lysine during the bioprocess of making DDGS.

Among all the indispensable amino acids in DDGS, lysine is the most variable amino acid and has the lowest digestibility in pig feeding trials. The culprit was suggested to be heat damage that occurs during DDGS production. In this study, we conducted a pilot-plant trial to investigate the effects of corn-to-ethanol unit operation conditions on lysine quality in intermediates and DDGS. We also focused on three operational parameters for DDGS production: fermentation completeness (reducing sugar level), syrup addition rate (ratio of syrup to wet cake), and dryer outlet temperature. In order to better estimate the heat damage to lysine, we tested furosine, a compound produced when lysine is damaged during a heat induced reaction called the Maillard reaction. A total of eighty samples were analyzed and they include corn flour, slurry, mash, fermentation broth, whole stillage, thin stillage, syrup, wet cake, DDG and DDGS. What we learned from this study is summarized in the following:

1. High temperatures, long residence times and high glucose levels are the major factors causing heat damage to lysine during the bioprocess of making DDGS. Among all the unit operations, liquefaction, evaporation and drying are the main processes contributing to the heat damage to lysine.
2. With the lysine level in corn around 0.27% and L/CP (percentage of lysine in crude protein) of corn around 3.0%, the DDGS produced in this study contained lysine levels ranging from 0.52% to 1.1% and L/CP from 1.9% to 3.2%, due to the various extent of heat damage to lysine. The DDGS generated under high temperature and incomplete fermentation had the lowest lysine level and L/CP.
3. Furosine is not a naturally occurring compound in corn, but the furosine levels in DDGS in this study ranged from 0.03% to 0.22% due to the various extent of heat damage to lysine. The high end of the furosine levels in DDGS suggests that heat damage could lead to lysine digestibility as low as 70%.
4. The furosine to lysine ratio of DDGS can be a good indicator for heat damage to lysine. Based on this study, the DDGS with good quality lysine had F/L (percentage of furosine in lysine) lower than 10%, while the DDGS with heat damaged lysine contained F/L as high as 40%.
5. Besides F/L, the L/CP can be a good estimate for lysine quality if the L/CP of the corn (as the feedstock) is known. The lower the L/CP of DDGS compared with that of corn, the more damage to lysine caused by heat.
6. Color of DDGS is not a very good indicator for heat damage to lysine.
It is strongly recommended that the dry grind ethanol plants monitor and control processing parameters during corn to DDGS production. The total sugar level in the drop fermentation broth sample should be lower than 1% to ensure the completeness of fermentation, and the dryer temperature should be kept as low as possible to meet the moisture level requirement and protect lysine quality.
PART B
This objective of this study is to monitor the changes in phytate concentration through the unit operations and processes that are used to make fuel ethanol. The concentrations of phytate and total phosphorus will be measured in the corn used as the feedstock in a pilot-plant trial at NCERC, the distiller’s dried grains with solubles (DDGS) that is produced as the final coproduct, and at important intermediate steps in the process, including liquefaction, fermentation, distillation, and coproduct processing (e.g., the concentrations will be measured in wet cake, thin stillage, and syrup).
Phosphorus (P) is an important nutrient in swine feed. More than 80% of the P in corn is in the form of phytate P which is not bioavailable, but the data on various P forms in DDGS are rare and the P bioavailability of DDGS is not well understood. In this study, we conducted a pilot-plant trial to investigate the effects of corn-to-ethanol unit operation conditions on the conversion of phytate P to inorganic P which is bioavailable in intermediates and DDGS. The operational parameters of the bioprocess we focused on included fermentation completeness (reducing sugar level), syrup addition rate (ratio of syrup to wet cake), and dryer outlet temperature. A total of forty-five samples were analyzed and they included corn flour, slurry, mash, fermentation broth, whole stillage, thin stillage, syrup, wet cake and DDGS. What we learned from this study is summarized in the following:
1. Among all the unit operations of the bioprocess of making DDGS, the fermentation process was the only unit operation which had a strong impact on the conversion of phytate P to inorganic P, with complete fermentation causing stronger conversion of phytate P to inorganic P than incomplete fermentation.
2. While the percentage of phytate P in total P was about 80% in corn as feedstock, that percentage decreased to 40% in DDGS generated from complete fermentation, and to 50% in DDGS generated from incomplete fermentation.
3. The unit operation of centrifuging changed the absolute level of phytate P and total P in wet cake and thin stillage due to mass partition, but the ratio of phytate P to total P stayed close to that of fermentation end product and DDGS.
4. It is confirmed that the yeast strain used for the corn to ethanol production was able to produce phytase to convert phytate P to bioavailable P. The more vital the yeast, the stronger the conversion of phytate P to bioavailable P.
It is highly recommended that dry grind ethanol plants monitor and control fermentation in order to produce more bioavailable P in DDGS. Growing healthy yeast is the key to produce more bioavailable P in DDGS. Including DDGS in swine diets can certainly help to reduce the amount of inorganic phosphate and phytase needed.