Coconut water (CW) is a popular and healthful beverage, and ensuring its quality is crucial for consumer satisfaction. This study aimed to explore the potential of near-infrared spectroscopy (NIRS) and chemometric methods for analyzing CW quality and distinguishing samples based on postharvest storage time, cultivar, and maturity. CW from nuts of Wenye No. 2 and Wenye No. 4 cultivars in China, with varying postharvest storage time and maturities, were subjected to NIRS analysis. Partial least squares regression (PLSR) models were developed to predict reducing sugar and soluble sugar contents, revealing moderate applicability but lacking accuracy, with the residual prediction deviation (RPD) values ranging from 1.54 to 1.83. Models for TSS, pH, and TSS/pH exhibited poor performance with RPD values below 1.4, indicating limited predictability. However, the study achieved a total correct classification rate exceeding 95% through orthogonal partial least squares discriminant analysis (OPLS-DA) models, effectively discriminating CW samples based on postharvest storage time, cultivar, and maturity. These findings highlight the potential of NIRS combined with appropriate chemometric methods as a valuable tool for analyzing CW quality and efficiently distinguishing samples. NIRS and chemometric techniques enhance quality control in coconut water, ensuring consumer satisfaction and product integrity.

Aromatic coconut (Cocos nucifera L.) is valued in the consumer market primarily for its distinctive fragrance, which is largely attributed to the compound 2-acetyl-1-pyrroline (2AP). The accumulation of 2AP has been observed in several crops, such as rice, when exposed to salt stress. In rice, exposure to salt stress influences the activity of enzymes, alters amino acid metabolism, and modulates the expression of genes associated with 2AP formation. Nevertheless, the processes responsible for 2AP biosynthesis in aromatic coconut under salt stress conditions are still not well clarified. In this study, five-month-old aromatic coconut seedlings were subjected to four distinct levels of sodium chloride (NaCl) treatment (0, 100, 200, and 300 mM). This experiment was conducted to investigate the mechanisms involved in salt-induced responses and the biosynthesis of 2AP in aromatic coconut. Although salt stress did not produce any apparent injury in the coconut seedlings, it led to a marked decline in chlorophyll content. Meanwhile, salt stress markedly enhanced the accumulation of betaine and boosted the activities of antioxidant enzymes such as superoxide dismutase and catalase. The aromatic coconut demonstrated a moderate level of salt tolerance. Salt stress also had a significant influence on 2AP biosynthesis. Under salt stress conditions, the 2AP content increased substantially, reaching its highest level with a 93.55% rise compared to the control. Furthermore, the synthesis of 2AP in aromatic coconut under salt stress appears to be primarily regulated through the metabolic pathways of proline and glutamate. Therefore, salt stress enhances 2AP production, with 200 mM NaCl identified as the optimal concentration for its accumulation.

The distinct aroma of the coconut (Cocos nucifera L.) is attributed to the presence of 2-acetyl-1-pyrroline (2AP), although the molecular and genetic pathway associated with its stress tolerance and aroma properties is largely unexplored. The glutamate decarboxylase (GAD) enzyme is involved in the formation of γ-aminobutyric acid (GABA), which is implicated in both adaptation to abiotic stress and 2AP synthesis. In this study, we comprehensively characterized the GAD gene family in coconuts and related Arecaceae species, revealing three highly conserved paralogs that diverged before speciation. It is established that CnGAD2 harbors a typical structure for the glutamate decarboxylase domain with palm-specific long-intron structure and the crucial C-terminal residues required for CaM binding. Notably, CnGAD2 was highly expressed in the middle leaves of aromatic germplasm compared with non-aromatic germplasm. Its expression level was also strongly associated with salt-stress severity and the accumulation of GABA and 2AP. An allele-based haplotype association study revealed a dominant haplotype that has higher levels of 2AP content than other haplotypes. Collectively, these findings suggest that CnGAD2 may function as an important link between salt-stress signaling and aroma biosynthesis. The identified dominant haplotype could therefore serve as a promising genetic resource for improving stress tolerance and flavor quality in coconut, an economically important tropical crop.