Hello this is Charmaine Espinosa and in this presentation, we will be sharing some results that we have generated from two experiments where we determined how excess heat can influence ME and AA digestibility in corn.
Corn is shelled or harvested when the moisture content of the kernel is below 30% but to store it safely, the moisture must be reduced to approximately 14-15%. Therefore, drying or further heat treatment is necessary to achieve this moisture requirement. At the moment, the grain industry reduces energy costs during the air-forced drying process of corn by applying temperatures that are greater than 100◦C. And that is where heat treatment can potentially be termed as a necessary evil since excess heat could negatively influence nutrient digestibility in corn.
This negative effect of overheating occurs due to formation of Maillard reaction products. Maillard reaction involves the reaction of reducing sugars with the terminal/Ɛ-amino group of amino acids, and products of the Maillard reaction can render AA in diets and/or feed ingredients unavailable. The initial stage of the Maillard reaction consists of a sugar-amine condensation, and products of this reaction are further rearranged and converted to what we call as Amadori compounds. Formation of these Amadori compounds does not reduce concentration of AA, however we typically observe reduction in AA digestibility in our feed ingredient. On the other hand, formation of melanoidins, which occurs during the final stage of the Maillard reaction results in both reduction of concentration and digestibility of AA in feed ingredients.
Variations in heat processing such as differences in temperatures and duration of heating may also affect the kinetics of the reactions and how does this influence concentration and digestibility of AA and energy in corn. However there is still limited information about how these certain factors influence AA and energy digestibility.
Therefore, we conducted two experiments to test the hypothesis that the degree and duration of heating influence the standardized ileal digestibility of AA, and concentration of metabolizable energy (ME) in corn.
To conduct these two experiments, we used corn that originated from a single source. And this corn was divided into 11 batches that differs in how this single source of corn was heat treated. Four batches of corn were dried at 80ºC for 1.5, 3.0, 24, or 48 h, whereas 7 batches of corn were dried at 130ºC for 1.5, 3.0, 6.0, 9.0, 12, 24, or 48 h.
We then analyzed these sources for AA, and this graph shows the concentration of analyzed Lys in our corn sources in a DM basis. Green bars represents sources that were dried at 80c whereas yellow bars represent sources that were dried at 130c. Here we can observe that when corn is dried at 80c, the duration of heating does not affect the concentration of Lys; however, when corn is dried at 130c, the concentration of Lys decreases as the duration of drying increases.
And when we look at gross energy in these sources, we have observed a slight increase on GE when we look at drying time from 1.5 h to 3 h. But in general, drying temperature and the duration of heating does not appear to influence the concentration of GE. Now, the question is how digestible these corn sources are and how temperature and time of drying affects these digestibility values.
To shed light into this, we conducted the first experiment to determine the digestibility of energy and concentrations of ME in the 11 sources of corn.
A total of 88 pigs with an average initial BW of 20 kg were randomly allotted to the 11 diets in a randomized complete block design with 3 blocks, 11 diets, and 8 replicate pigs per diet. These 11 diets were prepared by having each source of corn in one diet as the only energy containing ingredient.
For this experiment and also for the aa digestibility experiment, we used contrast statements in SAS to determine the linear and quadratic effect of drying time at 80°С, the linear and quadratic effect of drying time at 130°С, and to determine effects of 2 different heat treatment temperature
Now this slide shows the ATTD of GE in 11 sources of corn. Here we can observe that the duration of heating does not appear to influence digestibility of GE regardless of the drying temperature. However, when we determined how digestibility looks like between the two drying temp, the ATTD of GE in corn sources dried at 130cel tended to be greater compared with that of corn sources dried at 80celcius. And this may be a result of increased gelatinization of starch, which results in starch becoming more available for intestinal enzymes.
When we look at the concentration of ME on a DM basis, corn sources dried at 80 celcius quadratically increased as duration of heating increases. However, when corn sources were dried at 130 celcius, the ME tended to decrease as duration of heating increases and this observed reduction is likely a result of reduced absorption of AA due to Maillard reactions and other detrimental effects of high temperatures
Now the second experiment that we conducted for this project determines how drying temperature and the duration of heating influence digestibility of AA in corn sources 
And in this experiment, we used 24 pigs with an initial BW of 22.8 kg and these pigs were randomly allotted to the 12 diets. These 12 diets consisted of 11 diets that were prepared by having each source of corn in one diet as the only source of CP and AA in these diets. We also prepared a N free diet to determined basal endogenous loss of AA for us to be able to calculate for SID of AA in corn.
This slide shows the SID of Lys in corn sources. And at 80oC, the duration of heating does not affect Lys digestibility; however, the SID of Lys in corn sources dried at 130oC was reduced as duration of heating increases. This is likely a result of the observed decrease in the concentrations Lys and these results indicate that corn dried at 130°C resulted in damage of AA due to Maillard reactions, in which Lys is the most reactive AA due to the presence of an ε-amino group on the molecule that can react directly with reducing sugar under heating conditions. Due to the huge negative impact of excess heat in Lys digestibility, corn sources dried at 130oC also had reduced digestibility of Lys when compared with corn sources dried at 80oC, which is 71% for 80oC and 62.7% for 130 oC.
When we look at Met digestibility, it appears that duration of heating does not influence Met digestibility in corn sources dried at 80 oC; however, a linear reduction was observed for corn sources that were dried at 130 oC as duration of heating increases. But when we compare the two drying temperatures, no difference was observed. 
Similar results were observed for the Thr where duration of heating does not impact digestibility when the heating temperature was at 80 oC. On the other hand, Thr digestibility was linearly reduced as drying time increases and corn sources dried at 130 oC. And the same as Met no difference was observed when compared corn sources dried at 80 oC and corn sources dried at 130 oC.
Overall, in terms of comparing the two temperatures, we have observed that corn sources dried at 130oC  had less concentration and had reduced digestibility of Lys compared with corn sources dried at 80 oC. However, digestibility of other AA were not different between the two drying temperatures, which demonstrates the Lys is the most susceptible AA to Maillard reactions. ME, on the hand, is greater in corn sources dried at 130 oC compared with that of corn sources dried at 80 oC. 
We have demonstrated that when corn is dried at 80 oC, increased drying time does not influence concentration AA on a DM basis.  Increased drying time does not also influence digestibility of AA indicating that corn sources dried at 80 oC were not heat damaged regardless of the duration of heating. The concentration of ME on the other hand increased by increased drying time.
When corn is dried at 130 oC, we have observed that increased dryng time resulted in a reduction of both concentration and digestibility of Lys. Increased drying time also reduced the concentration of ME in corn sources dried art 130 oC, and this just tells us the negative consequences of overheating our feed ingredients not only in AA but with energy as well. Therefore, if heat damaged corn is included in diets for pigs, it is necessary that extra energy and extra AA are included in the diets to avoid negative impact of heat damage on growth performance of pigs.
Thank you for listening and for your interest in this presentation and if you would like to know more about nutrition, you can visit our website at nutrition.ansci.illinois.edu.