Application of Raman Spectroscopy and Chromatographic Techniques in Determination of Phytochemicals as Potential Biomarker of Cantaloupe Maturity

Abstract

Currently, there is no reliable, non-destructive way to assess maturity of cantaloupes (Cucumis melo L.). Therefore, for our first objective, we assessed carotenoids in cantaloupe rind using Raman spectroscopy, as a biomarker for maturity. Five cantaloupe cultivars were grown and harvested at 13, 26, and 39 days after anthesis in College Station, Texas. To predict maturity, Raman spectra were preprocessed, and a partial least-square discriminant analysis (PLS-DA) model was developed. The PLS-DA model predicted maturity with an 82% to100% accuracy in the cultivars studied. As assessed using HPLC, TC varied from 16.88 μg/g to 54.23 μg/g fresh weight. HPLC- analysis of lutein and β-carotene in cantaloupe rind showed an increased in concentration of carotenoids with maturity. The same trend was observed in the vibrational bands originating from carotenoids in the acquired Raman spectra. It indicates that Raman spectroscopy can be a good candidate for evaluating maturity in cantaloupe with further research.

Second study aimed to quantify the composition of Volatile Organic Compounds (VOCs) and amino acids in the rind of cantaloupe cultivars and determine their changes between two different maturity stages and correlate amino acids with VOCs. Flowers of four cultivars were tagged and harvested at 26, and 39 days after anthesis (DAA) grown in Uvalde, Texas. VOCs were determined using headspace solid phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC–MS) and amino acids using ultra high-performance liquid chromatography (UHPLC). Herein, for the first time, the presence of β-cyclocitral is reported in cantaloupe rind and was considered a biomarker for classification of cultivars along with benzaldehyde, benzyl alcohol, eugenol, and decanoic acid. Compounds such as (E, Z)-3,6-nonadien-1-ol and (E,E)-3,5- octadien-2-one and δ-cadinene were identified as maturity biomarkers in rind samples of cantaloupe cultivars and classified for the separation of the maturity stages. Amino acids are quantified for the first time in cantaloupe rind which are significantly varied during maturity stages. Furthermore, analyzed amino acids such as trans-4-hydroxy proline, GABA, and alanine was moderately to strong correlated to volatiles contributing to aroma and defense system of the fruits. The findings of this study may benefit bioactive isolation-based industries for proper utilization of the rind and reduce industrial waste.