<p>Lettuce is a highly perishable leafy vegetable, and its postharvest preservation remains a challenge, particularly due to differences between hydroponic and soil cultivation systems. This study aimed to evaluate the combined effects of protocatechuic acid (PCA) and modified atmosphere packaging (MAP) on lettuce. It also compared the postharvest responses of hydroponic and soil-cultivated lettuce. Optimal storage conditions were determined as 4&#xa0;°C under MAP (87% N₂, 10% CO₂, 3% O₂). PCA demonstrated strong in vitro antimicrobial activity against common spoilage bacteria and showed effective scavenging activity against DPPH and ·OH radicals. During storage, PCA-MAP treatment significantly delayed chlorophyll degradation, reduced malondialdehyde accumulation, suppressed microbial growth, and maintained higher moisture and total soluble solids contents in both intact and fresh-cut lettuce. Comparative analysis showed that hydroponic lettuce had higher initial moisture and pH, whereas soil-cultivated lettuce exhibited better retention of chlorophyll and antioxidant capacity under the same treatment. The most effective treatment extended shelf life to 14 days for hydroponic lettuce and 15 days for soil-cultivated lettuce. The combination of PCA and MAP effectively enhances postharvest quality and extends shelf life in both hydroponic and soil-cultivated lettuce, offering a potential preservation strategy for leafy vegetables.&#xa0;</p> Graphical Abstract <p></p>