Digestible reactive lysine in selected milk-based products

Area of Science:

• Animal Nutrition
• Food Science
• Biochemistry

Background:

• Milk proteins are a significant source of amino acids, particularly lysine.
• Accurate assessment of lysine bioavailability is crucial for formulating balanced animal diets.
• Processing can potentially alter the nutritional value of milk proteins.

Purpose of the Study:

• To determine reactive lysine content and true ileal digestibility in various processed milk products.
• To compare reactive lysine digestibility with conventional total lysine digestibility measurements.
• To assess the impact of processing on lysine availability in milk-based foods.

Main Methods:

• Utilized a validated assay involving O-methylisourea reaction for reactive lysine determination.
• Fed semisynthetic diets with milk products as the sole protein source to growing rats.
• Collected ileal digesta and analyzed for reactive lysine (homoarginine) and endogenous lysine losses.
• Determined true ileal reactive lysine digestibility and compared it with total lysine digestibility.

Main Results:

• True ileal reactive lysine digestibility was consistently high across all tested milk products, exceeding 91%.
• UHT milk showed the highest digestibility (100%), while infant formulas had the lowest (91-93%).
• Conventional total lysine digestibility significantly underestimated reactive lysine digestibility, with differences ranging from 1.3% to 7.1% units.
• Significant discrepancies between digestible total lysine and available lysine were observed in several products.

Conclusions:

• Milk proteins are generally a highly digestible source of lysine.
• Conventional methods for determining lysine digestibility may be inaccurate for some processed milk products.
• Processing, such as in evaporated milk or sports formulas, can lead to lysine modification, impacting its bioavailability.