# L-lysine improves pork quality during postmortem aging: insights into meat quality, protein properties, and enzyme activities

## TL;DR

Adding L-lysine during pork aging improves meat quality by enhancing tenderness and protein breakdown through enzyme activation.

## Contribution

Demonstrates how L-lysine enhances pork quality via enzyme activity and protein degradation during postmortem aging.

## Key findings

- L-lysine addition reduced shear force, improving pork tenderness on the third day of aging.
- L-lysine increased myofibrillar fragmentation and actomyosin solubility, indicating structural protein breakdown.
- L-lysine elevated calpain-1, caspase-3, and Ca2+-ATPase activity, promoting protein hydrolysis and meat softening.

## Abstract

This study aimed to investigate the intrinsic relationships between meat quality, protein properties, and enzyme activities of pork longissimus dorsi treated with L-lysine (Lys) during postmortem aging.

The pork samples were collected from 18 twelve-month-old crossbred pigs (120 kg, Duroc×Long White Large×White, longissimus dorsi muscle) in three batches of six samples each. The meat was then immediately placed in a thermal container and transported to the laboratory within 1 hour for subsequent processing at 4°C. After removing fat and connective tissue, the pork was cut into 20 g±1 g meat blocks. Then, the samples were vacuum sealed and left in a freezer (4°C) for 0, 1 and 3 days.

The results showed that Lys addition (0.10%, 0.15%, and 0.20%) improved pork quality (water-holding capacity and tenderness). On the third day of aging, the shear force values reached their lowest levels (p<0.05), measuring 38.21 N, 34.04 N, and 30.94 N for the respective treatment groups. In addition, the postmortem addition of Lys significantly increased the myofibrillar fragmentation index and actomyosin solubility during pork aging (p<0.05), with maximum values of 105.07% and 90.35%, respectively. Meanwhile, microscopic structure and electrophoresis results indicated that Lys treatment disrupted the muscle fiber structure, promoted the degradation of myofibrillar proteins (MPs) and dissociation of actomyosin. Furthermore, with increasing Lys addition, calpain-1 activity, caspase-3 activity, and Ca2+-ATPase activity in the muscle significantly increased (p<0.05), reaching maximum values of 17.46 ng/mL, 55.68 μg/mL, and 2.79 μmol (Pi)/min·mg protein, respectively. The activation of these enzymes promoted the dissociation and hydrolysis of key structural proteins.

Lys improved pork quality by increasing calpain-1, caspase-3, and Ca2+-ATPase activity during the postmortem aging, thereby promoting the degradation of MPs and the dissociation of the actomyosin.