# Optimization of Solid Lipid Microcapsule Matrix for Enhanced Release and Bioavailability of L-Lysine in Swine

## TL;DR

This study shows that encapsulating L-lysine in optimized solid lipid microcapsules improves its absorption and bioavailability in pigs.

## Contribution

A novel SLM formulation with optimized lipid matrix and emulsifier concentration is shown to enhance L-lysine delivery in swine.

## Key findings

- SLMs with hydrogenated triglycerides showed 94–95% gastric retention compared to 48% with free fatty acids.
- Adding 1% emulsifier increased intestinal release of L-Lys from 74% to 90%.
- Encapsulated L-Lys had a delayed plasma peak and higher total plasma levels over 24 hours compared to free L-Lys.

## Abstract

This study explored the use of solid lipid microcapsules (SLMs) to enhance the effectiveness of L-lysine (L-Lys) supplementation in swine nutrition. The SLMs were formulated with different lipid matrices and varying levels of an emulsifier to improve the L-Lys SLMs’ retention in the stomach and control their release in the intestine. Results from both in vitro and in vivo experiments showed that optimizing the lipid composition and emulsifier concentration significantly improved L-Lys delivery during the digestion phase and delayed its availability in plasma. Encapsulated L-Lys showed markedly higher relative bioavailability than the free form, highlighting the importance of SLM matrix optimization to improve L-Lys supplementation in swine.

L-lysine (L-Lys) is the first-limiting amino acid in swine nutrition, but free-form supplements exhibit poor intestinal absorption, reducing their bioavailability. This study aimed to enhance the gastric retention, controlled intestinal release, and systemic availability of L-Lys by optimizing solid lipid microcapsules (SLMs). SLMs were formulated using hydrogenated triglycerides (C16:0 or C18:1), free fatty acids, and varying emulsifier concentrations. Gastric retention and intestinal release were evaluated in vitro under simulated gastrointestinal conditions (a pepsin buffer at pH 5.0 for 2 h, followed by a pancreatin buffer at pH 6.5 for up to 8 h at 39 °C). SLMs with hydrogenated triglycerides showed significantly higher gastric retention (94–95%) than those with free fatty acids (48%). Specifically, C16:0 triglyceride-based SLMs achieved 74% intestinal release, which was enhanced to 90% with 1% emulsifier. This refined formulation was subsequently evaluated in vivo using weaned pigs (three groups; n = 4) fed a basal cornmeal diet. The treatments included a single oral administration of saline solution (placebo), free L-Lys (0.17 g/kg BW), or L-Lys SLMs (0.38 g/kg BW, equally providing L-Lys at 0.17 g/kg BW). The SLMs delayed the L-Lys plasma peak (T. max. 3–4 h vs. 1 h) and significantly increased the total L-Lys amount in the plasma over 24 h, demonstrating the enhanced relative bioavailability of encapsulated L-Lys.