Analysis of minor low molecular weight carbohydrates in cocoa beans by chromatographic techniques coupled to mass spectrometry

• Published in: Journal of Chromatography A 2019-01, Vol.1584, p.135-143
• Main Authors: Megías-Pérez, Roberto, Ruiz-Matute, Ana Isabel, Corno, Marcello, Kuhnert, Nikolai
• Format: Article
• Language: English
• Subjects: 1-Kestose; Cocoa bean; Galactinol; GC–MS; HILIC-ESI-TOF MS; Scyllo-inositol
• ISSN: 0021-9673
• DOI: 10.1016/j.chroma.2018.11.033

•scyllo-Inositol and kestoses were found for the first time in cocoa beans by GC–MS.•scyllo-Inositol, 1-kestose and galactinol were selected as target carbohydrates.•HILIC-ESI-TOF MS method was optimized for the analysis of target carbohydrates.•Target LMWC were quantified in cocoa beans from different origin and fermentation status.•Galactinol could be a potential indicator of fermentation status. The low molecular weight carbohydrate (LMWC) profile of cocoa beans has recently been studied using hydrophilic interaction liquid chromatography coupled to electrospray ionization-time of flight mass spectrometry (HILIC-ESI-TOF MS) and HILIC-ESI-tandem mass spectrometry (HILIC-ESI-MSn). However, different LMWC could not be unambiguously identified. Thus, as a first approach in this paper, gas chromatography coupled to mass spectrometry (GC–MS) was used as a complementary analytical technique to characterize LMWC of cocoa beans. Different mono-, di-, tri- and tetrasaccharides, as well as myo-inositol, galactinol and a diglycosil glycerol were detected. scyllo-Inositol, 1-kestose and 6-kestose were identified in unfermented cocoa beans for the first time. Moreover, other minor LMWC were tentatively assigned as fructosyl-fructose, fructosyl-glucose and glucosyl-sucrose. As a second step, in order to evaluate new possible indicators of cocoa bean origin or fermentation status, scyllo-inositol, 1-kestose and galactinol were selected as target compounds and a HILIC-ESI-TOF MS method was optimized for their analysis. The optimized conditions, using an acetonitrile:water gradient with 0.05% ammonium hydroxide at 40 °C showed narrow peaks (wh: 0.3-0.5 min) with good resolution values (Rs: 0.83–2.83). The validated HILIC-ESI-TOF MS method was applied to the analysis of 35 cocoa bean samples from different origins and fermentation status. The content of scyllo-inositol, 1-kestose and galactinol in unfermented beans (n = 21) was in the range of traces-504.9, 36.1–133.5 and traces-1970.4 μg g−1 cocoa DM respectively. In fermented beans (n = 14), the content of scyllo-inositol and 1-kestose was in the range of 15.5–491.9 and traces-115.5 μg g−1 cocoa DM respectively. Galactinol was absent in fermented beans, indicating that it could be a potential indicator of fermentation status. The methodology proposed could be used for quality control of natural products and other food ingredients containing inositols and oligosaccharides.