Relationship between Proteins, Peptides, and Amino Acids
Proteins: Functional macromolecules formed by one or more polypeptide chains folding into specific three-dimensional structures through helices, sheets, etc.
Polypeptide Chains: Chain-like molecules composed of two or more amino acids linked by peptide bonds.
Amino Acids: The basic building blocks of proteins; more than 20 types exist in nature.
In summary, proteins are composed of polypeptide chains, which in turn are composed of amino acids.
Process of Protein Digestion and Absorption in Animals
Oral Pre-treatment: Food is physically broken down by chewing in the mouth, increasing the surface area for enzymatic digestion. As the mouth lacks digestive enzymes, this step is considered mechanical digestion.
Preliminary Breakdown in the Stomach:
After the fragmented proteins enter the stomach, gastric acid denatures them, exposing peptide bonds. Pepsin then enzymatically breaks down the proteins into large molecular polypeptides, which subsequently enter the small intestine.
Digestion in the Small Intestine: Trypsin and chymotrypsin in the small intestine further break down the polypeptides into small peptides (dipeptides or tripeptides) and amino acids. These are then absorbed into the intestinal cells via the amino acid transport systems or the small peptide transport system.
In animal nutrition, both protein-chelated trace elements and small peptide-chelated trace elements improve the bioavailability of trace elements through chelation, but they differ significantly in their absorption mechanisms, stability, and applicable scenarios. The following provides a comparative analysis from four aspects: absorption mechanism, structural characteristics, application effects, and suitable scenarios
1. Absorption Mechanism:
| Comparison Indicator | Protein-chelated Trace Elements | Small Peptide-chelated Trace Elements |
|---|---|---|
| Definition | Chelates use macromolecular proteins (e.g., hydrolyzed plant protein, whey protein) as carriers. Metal ions (e.g., Fe²⁺, Zn²⁺) form coordinate bonds with the carboxyl (-COOH) and amino (-NH₂) groups of amino acid residues. | Uses small peptides (composed of 2-3 amino acids) as carriers. Metal ions form more stable five or six-membered ring chelates with amino groups, carboxyl groups, and side chain groups. |
| Absorption Route | Require breakdown by proteases (e.g., trypsin) in the intestine into small peptides or amino acids, releasing the chelated metal ions. These ions then enter the bloodstream via passive diffusion or active transport through ion channels (e.g., DMT1, ZIP/ZnT transporters) on intestinal epithelial cells. | Can be absorbed as intact chelates directly through the peptide transporter (PepT1) on intestinal epithelial cells. Inside the cell, metal ions are released by intracellular enzymes. |
| Limitations | If the activity of digestive enzymes is insufficient (e.g., in young animals or under stress), the efficiency of protein breakdown is low. This may lead to premature disruption of the chelate structure, allowing metal ions to be bound by anti-nutritional factors like phytate, reducing utilization. | Bypasses intestinal competitive inhibition (e.g., from phytic acid), and absorption does not rely on digestive enzyme activity. Particularly suitable for young animals with immature digestive systems or sick/weakened animals. |
2. Structural Characteristics and Stability:
| Characteristic | Protein-chelated Trace Elements | Small Peptide-chelated Trace Elements |
|---|---|---|
| Molecular Weight | Large (5,000~20,000 Da) | Small (200~500 Da) |
| Chelate Bond Strength | Multiple coordinate bonds, but complex molecular conformation leads to generally moderate stability. | Simple short peptide conformation allows for the formation of more stable ring structures. |
| Anti-interference Ability | Susceptible to influence by gastric acid and fluctuations in intestinal pH. | Stronger acid and alkali resistance; higher stability in the intestinal environment. |
3. Application Effects:
| Indicator | Protein Chelates | Small Peptide Chelates |
|---|---|---|
| Bioavailability | Dependent on digestive enzyme activity. Effective in healthy adult animals, but efficiency decreases significantly in young or stressed animals. | Due to the direct absorption route and stable structure, trace element bioavailability is 10%~30% higher than that of protein chelates. |
| Functional Extensibility | Relatively weak functionality, primarily serving as trace element carriers. | Small peptides themselves possess functions like immune regulation and antioxidant activity, offering stronger synergistic effects with trace elements (e.g., Selenomethionine peptide provides both selenium supplementation and antioxidant functions). |
4. Suitable Scenarios and Economic Considerations:
| Indicator | Protein-chelated Trace Elements | Small Peptide-chelated Trace Elements |
|---|---|---|
| Suitable Animals | Healthy adult animals (e.g., finishing pigs, laying hens) | Young animals, animals under stress, high-yield aquatic species |
| Cost | Lower (raw materials readily available, simple process) | Higher (high cost of small peptide synthesis and purification) |
| Environmental Impact | Unabsorbed portions may be excreted in feces, potentially polluting the environment. | High utilization rate, lower risk of environmental pollution. |
Summary:
(1) For animals with high trace element requirements and weak digestive capacity (e.g., piglets, chicks, shrimp larvae), or animals requiring rapid correction of deficiencies, small peptide chelates are recommended as the priority choice.
(2) For cost-sensitive groups with normal digestive function (e.g., livestock and poultry in the late finishing stage), protein-chelated trace elements can be selected.
Post time: Nov-14-2025
