Quantification of free sugars, fructan, pungency and sweetness indices in onion populations by FT‐MIR spectroscopy

• Published in: Journal of the science of food and agriculture Vol. 98; no. 14; pp. 5525 - 5533
• Main Authors: Clark, Christopher J, Shaw, Martin L, Wright, Kathryn M, McCallum, John A
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.11.2018; John Wiley and Sons, Limited
• Subjects: Allium cepa; composition; Fourier analysis; Fourier‐transform infrared; Fructose; fructo‐oligosaccharide; Glucose; Infrared spectra; multivariate analysis; Onions; Organic chemistry; Phenotyping; Plant breeding; Populations; Pungent principles; Pyruvic acid; Regression analysis; Solids; Spectroscopy; Spectrum analysis; Standard error; Sucrose; Sugar; Sweetness; sweetness index; Weight; Allium cepa; Fourier-transform infrared; fructo-oligosaccharide; sweetness index; composition; multivariate analysis
• ISSN: 0022-5142; 1097-0010
• DOI: 10.1002/jsfa.9099

Background To facilitate faster phenotyping of onions (Allium cepa L.), Fourier‐transform mid infrared (FT‐MIR) spectroscopy with partial least squares (PLS) regression modelling was evaluated for the determination of pungency (pyruvate), sweetness (free sugars) and fructan in juice samples (n = 605) expressed from bulbs from breeding populations. Results Fourier‐transform infrared (FTIR) spectra (range 1700–900 cm−1) were obtained from droplets (30 μL) of unprocessed juice. Goodness‐of‐fit (r2) and prediction errors (standard error of cross validation) for optimal PLS models were: soluble solids (0.997, 0.1 °Brix), pyruvate [0.825, 0.8 μmol g−1 fresh weight (FW)], fructan (0.98, 1.9 mg g−1 FW), glucose (0.941, 1.1 mg g−1 FW), fructose (0.967, 1.0 mg g−1 FW) and sucrose (0.919, 1.7 mg g−1 FW). FTIR models for industry sweetness indices based on glucose or sucrose equivalents were also developed. Because of its very low concentration (0.8–12 μmol g−1 FW) relative to other compounds, pyruvate was the weakest model developed. Fructan could be determined spectroscopically without the need for enzymatic digestion. Conclusions All of the chemometric models developed are acceptable for screening purposes. Those for soluble solids, fructan and fructose are also suitable for routine analysis. FT‐MIR can therefore be utilised for the simultaneous determination of pungency, sweetness and fructan in this crop. © 2018 Society of Chemical Industry