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Effects of Heat Treatment on Composition and Amino Acid Digestibility of Canola Meal Fed to Growing Pigs

25 September 2013

Canola meal subjected to moist heat has reduced amino acid concentrations and lower digestibility of crude protein and all amino acids, according to research form the Hans H. Stein Monogastric Nutrition Laboratory at the University of Illinois.

Canola meal is the second most used plant protein source, after soybean meal, in livestock diets. The production of canola meal involves a step in which the meal is treated with steam for 35 to 50 minutes at temperatures from 95 to 115°C. The application of heat and moisture to feedstuffs results in the Maillard reaction, which reduces the concentration and digestibility of amino acids. Lysine is particularly susceptible to the Maillard reaction, so it is important to determine accurate digestible lysine levels in feedstuffs that may be heat-damaged.

Amino acid analysis that does not account for lysine recovered from acid hydrolysis of Maillard products may overestimate the amount of digestible lysine in a sample. Therefore, methods other than simple lysine analysis must be used when assessing feed that may be heat damaged.

An experiment was conducted to determine the effects of heat damage on the digestibility of crude protein and amino acids in canola meal fed to growing pigs. Another objective of the experiment was to develop regression equations to predict the concentration of standardised ileal digestible (SID) amino acids in canola meal.

Experimental Design

Ten growing pigs with an average initial body weight of 26.5kg were surgically equipped with a T-cannula in the distal ileum and fed one of five diets.

Canola meal from a single source was separated into four batches; the first batch was not autoclaved, and the others were autoclaved at 130°C for 20, 30, or 45 minutes. Four diets that contained each of the four batches of canola meal were formulated.

Canola meal was the only source of crude protein and amino acids in the diets. A nitrogen-free diet was used to determine the endogenous losses of crude protein and amino acids.

Ileal digesta were collected after a five-day adjustment period to the diets, and analysed to determine values for apparent and standardized ileal digestibility of crude protein and amino acids in each batch of canola meal.

Composition of Canola Meal and Amino Acid Digestibility are Affected by Heat

The canola meal underwent a number of changes as it was heated for longer periods. Its color became darker and turned from yellow to brown (Table 1).

Table 1. Chemical composition of canola meal subjected to increasing levels of heat treatment
 Canola meal
 Not autoclavedAutoclaved
Item 20 mins30 mins45 mins
Dry matter % 90.87 89.44 89.78 88.42
Ash % 7.54 7.47 7.66 7.55
Crude protein % 36.79 36.49 36.88 36.90
Acid Detergent Fibre (ADF) % 20.00 23.63 22.73 31.30
Neutral Detergent Fibre (NDF) % 33.36 42.18 41.95 46.88
Lignin % 8.02 10.74 10.96 16.45
ADIN1 % 0.37 0.80 0.88 1.75
AEE1 3.71 3.34 3.79 1.97
Total glucosinolates µmol/g 1.58      
Calcium, % 0.64 0.61 0.65 0.62
Phosphorus, % 1.05 1.03 1.02 0.99
Lysine:crude protein ratio2 5.22 4.30 4.09 3.69
Furosine 0.02 0.03 0.03 0.03
Reactive lysine3 1.90 1.53 1.47 1.33
L*4 52.88 47.19 47.63 45.08
a*4 5.76 6.26 5.97 6.35
b*4 12.56 8.93 8.75 7.44
INDISPENSABLE AA %        
- Arginine 2.22 1.96 1.90 1.74
- Histidine 0.97 0.92 0.90 0.91
- Isoleucine 1.41 1.40 1.32 1,35
- Leucine 2.60 2.55 2.50 2.55
- Lysine 1.92 1.57 1.51 1.36
- Methionine 0.74 0.72 0.71 0.72
- Phenylalanine 1.48 1.45 1.42 1.44
- Threonine 1.62 1.60 1.58 1.61
- Tryptophan 0.49 0.48 0.49 0.49
- Valine 1.81 1.79 1.70 1.72
- All indispensable 15.26 14.44 14.03 13.89
TOTAL AA 32.36 31.15 30.54 30.55
1 ADIN = acid detergent insoluble nitrogen; AEE = acid hydrolysed ether extract.
2 Calculated by expressing the concentration of Lys in each ingredient as a percentage of the concentration of crude protein.
3 Reactive Lys (%) = [Lys (%) – (Furosine (%) ÷ 0.32 × 0.40)].
4 L* = lightness; a* = redness; b* = yellowness.

The concentration of reducing sugars in the meal decreased as time of treatment increased, while the concentration of furosine increased with longer heat treatment. These results indicate that the Maillard reaction is taking place.

Concentrations of acid detergent fibre (ADF), (NDF), lignin, and acid detergent insoluble nitrogen (ADIN) increased as time of heating increased. In part, this is because some products of the Maillard reaction analyse as ADF or lignin.

The analyzed concentrations of some amino acids decreased with increasing heat treatment, with the greatest decreases for lysine and arginine. Because the crude protein concentration did not change significantly, the lysine:crude protein ratio was less in canola meal that was heated for longer periods of time.

The SID of crude protein and all amino acids in canola meal decreased (quadratic, P<0.01) as time of heating increased (Table 2).

Table 2. Standardised ileal digestibility of crude protein and amino acids in canola meal subjected to increasing levels of heat treatment by growing pigs
 Canola meal 
  Autoclaved at
130°C
P-value
ItemNot autoclaved20 mins30 mins45 minsLinearQuadratic
Crude protein % 71.69 62.96 64.78 34.54 <0.01 <0.01
INDISPENSABLE AA %            
- Arginine 84.64 81.02 83.86 66.56 <0.01 <0.01
- Histidine 81.34 78.48 79.55 61.04 <0.01 <0.01
- Isoleucine 75.42 71.61 72.43 50.61 <0.01 <0.01
- Leucine 80.25 76.84 77.07 58.58 <0.01 <0.01
- Lysine 68.17 56.24 57.43 20.81 <0.01 <0.01
- Methionine 85.08 82.15 82.62 68.54 <0.01 <0.01
- Phenylalanine 80.25 77.79 78.40 59.56 <0.01 <0.01
- Threonine 71.48 67.92 68.20 45.24 <0.01 <0.01
- Tryptophan 73.88 71.95 71.45 51.99 <0.01 <0.01
- Valine 74.04 69.44 70.39 46.24 <0.01 <0.01
- MEAN 77.85 73.44 74.44 53.02 <0.01 <0.01
DISPENSABLE AA %            
- Alanine 74.20 66.14 68.36 40.08 <0.01 <0.01
- Aspartic acid 71.37 63.31 64.74 36.02 <0.01 <0.01
- Cysteine 75.59 72.26 71.85 48.27 <0.01 <0.01
- Glutamic acid 83.33 80.94 81.07 63.21 <0.01 <0.01
- Glycine 69.21 58.06 60.42 21.96 <0.01 <0.01
- Serine 74.34 70.52 71.23 49.81 <0.01 <0.01
- MEAN 74.68 68.59 69.61 43.56 <0.01 <0.01

Regression Equations Can Predict Concentration of Digestible Amino Acids

The concentration of SID lysine in canola meal may be predicted from the concentration of reactive lysine (RL) or reducing sugars (RS) using the following equations (all concentrations expressed in %):

  • SID Lys = -1.66 + 1.60 × RL (r2 = 0.83)
  • SID Lys = -1.65 + 0.59 × RS (r2 = 0.97)

The concentration of SID methionine in canola meal may be predicted from the concentration of lignin using the following equation:

  • SID Met = 0.76 + 0.02 × lignin (r2 = 0.93)

The concentrations of SID threonine and tryptophan in canola meal may both be predicted from the concentration of ADF in combination with the concentration of reducing sugars (RS):

  • SID Thr = 3.16 - 0.06 × ADF – 0.15 × RS (r2 = 0.89)
  • SID Trp = 0.99 - 0.018 × ADF – 0.05 × RS (r2 = 0.88)

Key Points

  • When canola meal is treated with moist heat, the concentrations of some amino acids are reduced, particularly lysine and arginine.
  • The digestibility of crude protein and all amino acids in canola meal is reduced as a consequence of heat damage.
  • Regression equations developed in this experiment may be used to predict the concentration of SID amino acids in canola meal using analysed concentrations of reactive lysine, reducing sugars, ADF, and lignin.

This report is based on unpublished data by F.N. Almeida and H.H. Stein.

September 2013

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