2009 Proceedings of the Cornell Nutrition Conference For Feed ...

Estimating Thermal Damage in Feeds: The Furosine Procedure
Furosine analysis has been used for over 40 years as an indicator of thermal
damage in foods (Erbersdobler and Somoza, 2007). ε-N-deoxyfructosyl-L-lysine is the
major Amadori compound formed during the early Maillard reaction (Figure 2). Upon
acid hydrolysis, ε-N-deoxyfructosyl-L-lysine is released in a constant ratio of 50% lysine,
30% furosine, 20% pyridosine, and 10% other compounds (Mauron, 1990). Therefore,
the amount of furosine measured after acid hydrolysis can be used to calculate %
blocked lysine according to the following equation (Mauron, 1990):
% blocked lysine = (3.1 furosine x 100)
[total lysine + (1.86*furosine)]
The acid hydrolysis procedure used in furosine analysis is identical to that used in AA
analysis of feeds. Therefore, the furosine assay is attractive because furosine and AA
content of feeds can all be determined with one procedure. Pahm et al. (2008) used the
furosine procedure to estimate blocked Lys content of 33 DDGS samples, and the
average blocked Lys content of the samples was 16% with a coefficient of variation of
7%. Pahm et al. (2008) also reported that blocked Lys was correlated with standardized
ileal Lys digestibility in swine (R 2 = 0.66). Boucher et al. (2009b) determined the
furosine content of 16 rumen undegraded residue (RUR) samples: 3 samples of
soybean meal (SBM), 3 samples of expeller SBM (SoyPlus ® ), 5 samples of DDGS, and
5 samples of fish meal (FM). One of the SBM, SoyPlus, and DDGS samples were
heated additionally in the laboratory oven to intentionally depress digestibility of RUP-
Lys. Of the 16 samples analyzed, only 9 samples contained furosine, and only the 4
unheated DDGS samples contained appreciable amounts of furosine (Table 1). Blocked
RUP-Lys was calculated from the furosine and Lys concentrations of the RUR
according to the above equation. The same 16 RUR samples were previously fed to
cecectomized roosters to determine digestibility of RUP-Lys in vivo. Results of the
experiment indicated that blocked RUP-Lys determined via the furosine method was
negatively correlated with standardized RUP-Lys digestibility (R 2 = 0.94; Y = 88.43–
0.89X; P < 0.001, n = 9).
Estimating Thermal Damage in Feeds: The Homoarginine Procedure
Homoarginine is an amino acid that is not found in nature. Homoarginine is formed
by the reaction of the epsilon-amino group of Lys (the NH3 group on the side chain) with
O-methylisourea. If the epsilon-amino group of Lys is bound to another compound, such
as a reducing sugar, then homoarginine does not form. Determining the amount of
homoarginine and Lys after the reaction with O-methylisourea allows for the
determination of the reactive Lys content of a feed, or the amount of Lys in which the
epsilon-amino group is not bound to another compound.
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