Abstract
Sugarcane (Saccharum officinarum L.) is an important perennial grass in the Poaceae family cultivated worldwide due to its economical and medicinal value. In this study, a combined approach using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopy was employed for the large-scale metabolite profiling of sugarcane juice and its by-product molasses. The polyphenols were analysed via UPLC-UV-ESI-MS, whereas the primary metabolites such as sugars and organic and amino acids were profiled using NMR spectroscopy and gas chromatography/mass spectrometry (GC/MS). UPLC/MS was more effective than NMR spectroscopy or GC/MS for determining differences among the metabolite compositions of the products. Under the optimized conditions, UPLC/MS led to the identification of 42 metabolites, including nine flavonoids, nine fatty acids, and two sterols. C/O Flavone glycosides were the main subclass detected, with tricin-7-O-deoxyhexosyl glucuronide being detected in sugarcane and molasses for the first time. Based on GC/MS analysis, disaccharides were the predominant species in the sugarcane juice and molasses, with sucrose accounting for 66% and 59%, respectively, by mass of all identified metabolites. The phenolic profiles of sugarcane and molasses were further investigated in relation to their in vitro antioxidant activities using free radical scavenging assays such as 2,2-Diphenyl-1-picrylhydrazyl free radical-scavenging ability (DPPH), Trolox equivalent antioxidant capacity (TEAC) and ferric reducing antioxidant power (FRAP). In view of its higher total phenolic content (TPC) (196 ± 2.1 mg GAE/100 g extract) compared to that of sugarcane juice (93 ± 2.9 mg GAE/100 g extract), molasses exhibited a substantially higher antioxidant effect. Interestingly, both extracts were also found to inhibit α-glucosidase and α-amylase enzymes, suggesting a possible antihyperglycaemic effect. These findings suggest molasses may be a new source of natural antioxidants for functional foods.
Highlights
Sugarcane juice is well known as a raw material for the production of refined sugar, whereas its wax is a potential substitute for carnauba wax, which is used in cosmetics and pharmaceuticals but is rather expensive
Extracts were subjected to metabolite fingerprinting by nuclear magnetic resonance (NMR) spectroscopy without a purification step, analogous to the procedures used for profiling via gas chromatography (GC)/mass spectrometry (MS) and ultra-high-performance liquid chromatography (UPLC/MS)
UPLC/MS was found to be more effective than NMR and gas chromatography/mass spectrometry (GC/MS) for elucidating the differences in the composition of secondary metabolites as it provides better coverage of different metabolite classes, such as flavonoids and phenolic acids
Summary
Sugarcane juice is well known as a raw material for the production of refined sugar, whereas its wax is a potential substitute for carnauba wax, which is used in cosmetics and pharmaceuticals but is rather expensive. The colour components from sugarcane juice are classified into four major classes: plant pigments, polyphenolic compounds, caramels, and degradation products from the condensation of sugars with amines [1]. The flavonoid content in sugarcane juice (0.6 mg/mL) was found to be comparable to the levels in other food resources, such as orange juice and black tea [10]. Various chromatographic techniques, such as liquid chromatography (LC) coupled to an ultraviolet (UV) diode array [10], LC coupled to an atmospheric pressure chemical ionization tandem mass spectrometry (APCI-MS) system [11], and LC coupled to electrospray ionization mass spectrometry (ESI-MS) [12], have been used to characterize the flavonoids in sugarcane leaves, juice, and bagasse. Several flavone glycosides, including orientin, tricin-7-O-neohesperidoside and tricin-7-O-glucoside, diosmetin-8-C-glycoside, schaftoside, isoschaftoside, vitexin, 4’,5’-dimethyl-luteolin-8-C-glycoside, luteolin 8-C-(rhamnosyl-glucoside), and flavolignan 7-O-glucosides along with their aglycones, have been identified
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