Analytical and Bioanalytical Chemistry

Electronic Supplementary Material

Pressurised hot water extraction in continuous flow mode for

thermolabile compounds: extraction of polyphenols in red onions

Jiayin Liu, Margareta Sandahl, Per J. R. Sjöberg, Charlotta Turner

Fig. S1. A schematic diagram of the CFE system (A): and static batch reactor (B): (a) solvent bottle; (b) heating plate; (c) LC pump; (d) thermal meter; (e) preheating coil; (f) extraction cell (100 mm × 15 mm i.d., 5 mL internal volume); (g) GC oven; (h) nitrogen gas; (i) collection tube; (j) cooling bath; (k) valve; (l) metal filter; (m) stirring; (n) high-pressure vessel

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Fig. S2. A typical HPLC-DAD chromatogram of red onion extract at (a) 290 nm, (b) 350 nm and (c) 520 nm. Numbering of the peaks refers to their identification as shown in Table S1

Fig. S3. MS spectrum of quercetin-3,4'-diglucoside extracted from red onion

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Table S1. Identification of phenolic compounds using HPLC-DAD-MS data

Peaka tR (min)a Max (nm)a MS/MS Compound identificationb

1 5.7 295 N.A. Unknown2 8.8 284 279/247/226 Unknown3 14.2 190 N.A. 2,4,6-trihydroxybenzaldehyde4 17.9 279 291/188/146 Unknown5 23.1 265 N.A. Unknown6 28.3 360 N.A. Unknown7 30.1 349 N.A. Unknown8 33.3 515 449/287 (pos) Cyanidin-3-glucoside9 37.2 516 611/287 (pos) Cyanidin-3-laminaribioside10 38.5 253 N.A. Unknown11 39.8 519 N.A. Anthocyanin12 43.7 265 625/463/301 Quercetin-3,4’-diglucosides13 46.5 265 N.A. Unknown14 49.1 517 535/287 (pos) Cyanidin-3-(6”-malonoylglucoside)

15 52.2 519 697/287(pos) Cyanidin-3-(6”-malonoyl-laminaribioside)

16 53.5 256 463/301 (neg) Quercetin-3-glucoside17 54.8 525 465/303 (pos) Delphinidin-3-glucoside

18 56.2 520 577/287 (pos) Cyanidin-3-(malonoyl)(acetoyl)-glucoside

19 60.2 364 463/301 (neg) Quercetin-4’-glucoside20 63.6 364 301/175 (neg) Quercetin21 65.9 376 446/356/301 Flavonoid

aPeak numbers and retention times (tR) refer to the HPLC chromatogram in Fig. 1.bIdentification was accomplished by comparison with reference standards where available and by MS spectra correlation with previous literature.N.A. Not available.

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Calculation of theoretical yield

The theoretical yield of the target polyphenols was modelled using the data (Table 1)

from the static batch extraction experiment (section 2.4). In order to increase the

accuracy of the numerical calculations, the sparsely sampled experimental data points

(n=12) were replaced by a larger number of values (n=120) obtained with a suitable

fitting function. A two-term exponential a·ebt+c·edt was found to give good fits for the

extraction data. The degradation rate constant was determined from the last three

point of the experiment by first-order degradation kinetics. With a numerical

integration procedure it was then possible to calculate the concentration

corresponding to the total amount of extracted material during the extraction. Detailed

procedures can be found at Petersson et al. [1].

Table S2. Pressurised hot water extraction profiles of red onion polyphenols expressed as mg L-1

n Time (min)

C3G C3L C3MG C3ML QDG

1 10 13.25 3.87 42.41 14.10 9.902 20 19.75 6.52 50.53 18.25 12.243 30 19.14 6.20 42.12 15.72 10.194 40 17.20 6.04 33.21 12.65 8.075 50 14.43 4.98 23.70 9.33 5.916 60 11.72 4.11 17.68 7.05 4.317 70 9.43 3.37 12.69 5.08 3.138 80 7.54 2.76 9.32 3.75 2.359 90 6.10 2.22 6.94 2.66 1.7910 100 4.93 1.82 5.14 1.95 1.4611 110 4.54 1.63 3.93 1.51 1.1712 120 3.95 1.49 3.60 1.37 1.07

C3G: cyanidin-3-glucoside; C3L: cyanidin-3-laminaribioside; C3MG: cyanidin-3-(6''-malonoylglucoside); C3ML: cyanidin-3-(6''-malonoyl-laminaribioside)

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Table S3. Extraction yields (mg g-1) of red onion polyphenols obtained by different extraction methods and theoretical calculation

Extraction method C3G C3L C3MG C3ML QDGCFE 0.92 0.30 2.31 0.82 0.55

Conventional extraction 0.79 0.26 2.02 0.72 0.48Static batch extraction 0.68 0.22 1.57 0.61 0.41Theoretical calculation 1.08 0.37 2.71 1.02 0.61

References

[1] E. V. Petersson, J. Liu, P. J. R. Sjoberg, R. Danielsson, C. Turner, Anal. Chim. Acta 663 (2010) 27-32.

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