Development of a 13 C NMR spectroscopic method for the determination of sucrose, fructose, and glucose in pumpkin (Cucurbita maxima)

A simple, cost-effective, and environmentally friendly (13) C NMR method was developed and validated for the determination of sucrose, fructose, and glucose in aqueous extracts of the flesh, peel, and seed parts of pumpkin. The (13) C NMR method was validated to determine individual sugars using chemical shifts at d 103.58, 98.07, and 96.45 ppm for sucrose, fructose, and glucose, respectively. The results showed a linear range, 1.08 to 83.3 g/L; R-2, of 0.999 to 1.00; LOD, 0.06 to 0.29 g/L; LOQ, 0.21 to 0.97 g/L; RSD, 0.63 to 0.96%; and %recovery, 97.8 to 101.8%. Accordingly, the developed method can easily be applied for the quantitative determination of individual sugars in pumpkin flesh, peel, and seeds. The content of sucrose in the flesh, peel, and seed samples varied from 0.79 to 1.07%, 0.37-0.46%, and 0.14-0.18%, respectively. The amount of fructose was found to be 0.32-0.40% in pumpkin flesh and 0.08-0.18% in pumpkin peel. The pumpkin flesh and peel contained 0.14-0.20% and 0.06-0.08% glucose, respectively. Sucrose was found in higher amounts in all the samples. Fructose and glucose were not detected in the seed parts of pumpkin. Compared to sucrose and glucose, fructose content showed a better correlation between the flesh and peel parts of the pumpkin.