Exogenous tryptophan and taurine enhance phenolic metabolism and antioxidant defenses in walnut kernels

Amino acids are key signaling molecules in plant stress responses. Fresh walnuts are rich in nutrients but face significant nutrient loss, enzymatic browning, and a decline in antioxidant capacity during postharvest storage. This study evaluated exogenous tryptophan and taurine in quality maintenance of fresh intact walnut (Juglans regia L. cv. 'Niangqing'), focusing on antioxidant capacity and phenolic compounds accumulation. Exogenous tryptophan and taurine were applied individually or in combination, effectively maintaining walnut appearance, delaying browning, and extending the shelf life. The combined TRP + TAU treatment achieved a remarkable 59.2% reduction in malondialdehyde content and increased total phenolic content by 117.4% compared to the control. Mechanistically, tryptophan upregulated key genes in the phenylpropanoid pathway (jrePAL, jre4CL, jreCHI), while taurine enhanced the AsA-GSH cycle (jreAPX, jreGR) and preserved cellular membrane integrity. These results offer new perspectives on the innovative application of amino acid treatments to extend the postharvest storage life of fresh walnuts.