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Analyzing sulfur amino acids in selected feedstuffs using least-squares nonlinear regression
Shane M Rutherfurd1, Audrey Schneuwly, Paul J Moughan
1Institute of Food, Nutrition and Human Health and Riddet Centre, Massey University, Palmerston North, New Zealand. S.M.Rutherfurd@massey.ac.nz
Journal of Agricultural and Food Chemistry
|August 25, 2007
Summary
Accurate quantification of sulfur amino acids in feedstuffs is crucial. While acid hydrolysis is suitable for methionine, it is not ideal for cysteine quantitation in complex feed matrices.
Area of Science:
- Animal Nutrition
- Analytical Chemistry
- Biochemistry
Background:
- Accurate determination of sulfur amino acids (methionine and cysteine) is essential for evaluating feedstuff nutritional value.
- Traditional acid hydrolysis methods can lead to degradation of these amino acids, affecting quantitation accuracy.
- Optimization of hydrolysis conditions is necessary for reliable analysis in complex matrices.
Purpose of the Study:
- To evaluate the suitability of acid hydrolysis for quantifying methionine and cysteine in various feedstuffs.
- To compare the accuracy of direct measurement versus oxidized forms (methionine sulfone and cysteic acid) for sulfur amino acid content.
- To determine hydrolysis and degradation rates of sulfur amino acids under optimized conditions.
Main Methods:
- Five feedstuffs were subjected to performic acid oxidation.
- Both oxidized and unoxidized samples underwent multiple acid hydrolysis cycles (0-144 hours) in sealed, degassed tubes.
- Sulfur amino acid content (methionine, cysteine, methionine sulfone, cysteic acid) was measured at each time point.
- Least-squares nonlinear regression analysis was employed to predict amino acid content and hydrolysis/loss rates.
Main Results:
- Methionine content estimates correlated well with methionine sulfone measurements across most feedstuffs.
- Cysteine content estimates showed poor agreement with cysteic acid measurements.
- Degradation (loss) rates during acid hydrolysis were low for methionine, methionine sulfone, and cysteic acid.
- Acid hydrolysis in evacuated sealed tubes for 24 hours without prior oxidation proved suitable for methionine but not cysteine.
Conclusions:
- Optimized acid hydrolysis conditions (24 hours, evacuated sealed tube) are effective for methionine quantitation in complex feedstuffs.
- This method is not sufficiently accurate for cysteine determination in the same matrices due to poor recovery and agreement with oxidized forms.
- Further method development is required for reliable cysteine analysis in feedstuffs.
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