Chemical composition and functional characterization of commercial pumpkin seed oil

Giuseppe Procida

, Bruno Stancher

, Francesca Cateni

and Marina Zacchigna

1

Department of Chemical and Pharmaceutical Sciences, P.zle Europa 1, 34127 Trieste

Department of Industrial Engineering and Information, Via A. Valerio 10, 34127 Trieste,

Chemical composition and functional characterization of commercial

pumpkin seed oil

Results

On the basis of the data reported in Table, as concerning aldehydes, significative differences are relative especially to compounds C4 (isobutanal, 3-methylbutanal and 2-methylbutanal). Generally, in samples from Slovenia, a major presence of all three aldehydes was observed. On the contrary, in three analyzed italian samples the concentration of the above aldehydes is lower of an order of magnitude: probably, slovenian samples could have been subjected to a more intense roasted process. Such compounds could be used as markers in order to define the roasted conditions followed before the extraction of the seeds oil.

The sulfur compounds are surely relevant for a definition of the flavour of the analyzed oils. In this case, it is important to remark the high concentration, particurarly of methanethiol, dimethylsulfide and dimethyldisulfide in samples 5 and 10 of Slovenian production. These substances, obtained via Strecker degradation, affect strongly the sensorial characteristics and could be connected to the roasted conditions employed: indeed sample 5 possesses a higher content in sulfur and aldehydic C4 compounds. The comparison of the data relative to the identified furans confirms the observations concerning the aldehydic and sulfur compounds: in particular, in samples 5 and 10 a major concentration of 2-methyltetrahydrofuran-3-one (3.44 and 3.72 g kg-1) and furfural (0.25 and 0.64 g kg -1) was reported. The content of such compounds, derived from the degradation of carbohydrates, is directly connected to the intensity of the roasting process conditions, as already reported in literature (1).

Also as concerning the pyrazine content, a higher content in samples 5 and 10 was reported: in particular, in sample 10 a concentration of 2-methylpyrazine (5.51 g kg-1) and 2,5-dimethylpyrazine (6.82 g kg-1) five times higher respect to the other analyzed samples was observed. Results previously reported in literature,1 indicate that the presence of pyrazines was directly related to the intensity of the thermal process of the seeds, prior to the oil pressing. The results of our analysis, carried out on commercial products, clearly show that in pumpkin oils it is possibile to individuate some classes of compounds as markers of the roasting process conducted on the seeds: the concentration of the aldehydic C4 compounds, of the sulfur compounds, furans and pyrazines, considerably increases on the basis of roasting grade. The presence of the sulfur compounds and of various pyrazines is a determining factor for the characteristic aromatic profile of this type of product.

INTRODUCTION

Pumpkin (Cucurbita pepo L.) seed oil is a common salad oil in southern Austrian region (Styria), Slovenia and Ungheria. This oil was obtained from the seeds of Steirischer Olkurbis pumpkin, the only one variety employed of the 800 different types, with seeds without rinds of a dark green color. The pumpkin seed oil is mainly produced by a traditional method: the cleaned seeds were dried, grounded, kneaded, roasted and subsequently pressed at elevated temperatures (100-130°C). During the roasting process of pumpkin seeds a rather high number of compounds could be identified in the volatile fraction belonging to the chemical classes of alcohols, aldehydes, ketones, sulfur compounds, furans and pyrazines, respectively (1).

The aim of the present investigation is to study the characteristics of two classes of products present on the market: pumpkin seeds oil for dietary and therapeutic use. The seeds of the first group, collected in Slovenia, should be roasted before extraction at high temperature, while the seeds of second group, collected in Italy, should have had mild conditions. The aim of this study is the evaluation of the qualitative and quantitative profile of the volatile fractions in pumpkin seed oil using a dynamic headspace gas chromatography-mass spectrometry (DHS-GC-MS) technique in order to evaluate the possibility of discriminating the samples on the basis of these compounds.

References

1)Siegmund B and Murkovic M, Changes in chemical composition of pumpkin seeds during

theroasting process for production of pumpkin seed oil (Part 2: volatile compounds). Food Chem 84: 367-374 (2004).

2)Barcarolo R and Casson P, Modified capillary GC/MS system enabling dynamic head space sampling with on-line cryofocusing and cold on column injection of liquid samples. J High Resol

Chromatog 20: 24-28 (1997).

Volatile Compounds (µg/kg) in the examined samples of pumpkin seed oil.

Rt Compounds 7 8 9 10 11 12 3.9 methanol 3.77 4.7 3.95 5.03 2.08 3.68 4.04 acetaldehyde 39.02 55.84 47.93 72.5 21.88 9.34 4.56 methanethiol 21.42 0.85 26.91 44.9 0.04 0.42 4.66 methylformate 3.44 14.28 2.52 8.89 7.83 16.17 5.25 ethanol 132.8 78.17 125.8 61.1 98.74 41.98 6.49 acetone 86.76 147.8 71.75 118 163.2 128.5 7.54 ethylformate 0.32 5.22 n.d. n.d. 2.6 9.02 7.76 dimethylsulfide 0.22 0.44 8.41 3.98 0.07 1.8 8.11 methylacetate 7.89 15.88 8.41 41.1 26.28 37.09 8.61 carbon disulfide 0.12 0.38 0.09 1.3 n.d. 0.34 8.71 dimethylsulfone 0.68 0.81 1.08 0.46 0.05 0.56 9.44 isobutanal 90.41 78.71 124.1 234 39.06 117.7 9.98 2-butenal (crotonal) 3.31 25.42 1.45 2.54 24.24 15.93 10.88 2,3-butanedione 0.64 0.22 12.52 4.63 0.25 0.26 11.13 butanal 3.7 29.94 1.4 7.98 16.09 26.46 11.34 2-butanone 19.6 63.33 22.58 40.3 77.8 52.59 12.31 ethylacetate 1.91 1.66 2.15 1.94 22.57 1.7 12.97 isobutanol 0.12 0.23 0.1 0.5 0.36 0.22 14.53 3-methylbutanal 113.1 131.1 159.3 303 34.87 176.1 14.77 2-pentanone n.d. n.d. n.d. n.d. 0.32 n.d. 14.88 butylformate n.d. n.d. n.d. n.d. 0.49 n.d. 15.05 2-methylbutanal 72.74 70.17 106.1 232 35.62 106.4 15.94 1-penten-3-ol 0.37 0.55 0.16 0.79 0.97 0.69 16.74 pentanal 13.65 32.88 7.54 28.4 48.02 39.35 19.29 2-methyl-2-butenal 0.33 0.57 0.29 1.82 1.15 0.62 19.64 dimethyldisulfide 0.53 0.42 1.32 20.7 1.82 0.89 20.29 1-pentanol 0.75 0.38 n.d. 2.25 6.92 0.58 21.51 2-hexanone 0.29 0.32 0.11 0.79 1.41 0.45 22.04 hexanal 39.14 112.7 12.1 53.02 95.43 104.4 22.44 2-methyltetrahydrofuran-3-one 0.12 n.d. 0.91 3.72 n.d. n.d. 23.38 2-methylpyrazine 0.53 1.23 0.62 5.51 1.58 1.63 23.81 furfural 0.13 0.17 0.18 0.64 0.26 n.d. 24.68 2-hexenal 0.3 0.25 0.11 0.2 0.22 0.25 26.28 2-heptanone 1.3 1.1 0.64 4.53 3.43 0.92 26.82 heptanal 0.86 1.13 0.42 2.6 0.93 1.41 27.48 2,6-dimethylpyrazine 1.1 1.05 1.53 6.82 1.08 0.25 29.34 2-heptenal 7.33 0.41 2.1 1.06 4.95 3.56 30.62 _{2-octanone 0.21 0.11 0.05 0.34 0.2 0.08} 30.76 _{dimethyltrisulfide n.d. n.d. 0.16 2.12 n.d. n.d.} 30.83 _{2-pentylfuran 0.53 0.31 0.12 1.32 0.33 0.11} 31.18 _{octanal 0.44 0.29 0.24 1.45 0.25 0.28} 31.39 _{5-methyl-2-ethylpyrazine 0.24 0.07 0.13 1.16 0.12 0.05} 35.24 _{nonanal 0.6 0.56 0.55 1.96 0.65 0.57}

Volatile compounds (µg/kg) in the examined samples of pumpkin seed oil.

Rt Compounds 1 2 3 4 5 6 3.9 methanol 3.11 3.71 0.51 2.9 6.18 0.97 4.04 acetaldehyde 35.92 85.49 1.94 37.38 132.7 16.55 4.56 methanethiol n.d. 6.81 n.d. 17.03 104.7 0.04 4.66 methylformate 3.83 23.61 0.16 6.26 11.77 1.1 5.25 ethanol 27.83 93.09 44.91 39.19 156.8 76.86 6.49 acetone 195.4 273.6 26.1 101.8 171.5 166.7 7.54 ethylformate 18.38 1.44 0.21 n.d. 0.24 1.27 7.76 dimethylsulfide n.d. n.d. 0.5 0.41 21.46 n.d. 8.11 methylacetate 1.95 36.93 0.7 27.9 70.55 3.49 8.61 carbon disulfide n.d. 1.01 0.36 1.5 1.21 n.d. 8.71 dimethylsulfone 0.32 0.81 0.22 0.45 0.65 0.33 9.44 isobutanal 19.81 21.65 2.81 136.9 290.9 14.92 9.98 2-butenal (crotonal) 35.14 4.45 0.27 1.09 2.91 34.16 10.88 2,3-butanedione 0.45 0.15 2.11 0.67 8.82 1.25 11.13 butanal 22.39 11.47 2.49 4.58 5.88 16.61 11.34 2-butanone 28.4 152.8 19.87 27.5 47.29 88.3 12.31 ethylacetate 2.93 10.27 1.26 1.78 4.74 62.37 12.97 isobutanol 1.3 0.81 2.63 0.55 1.04 0.24 14.53 3-methylbutanal 51.65 203.9 10.37 144.8 397.1 43.26 14.77 2-pentanone 1.05 0.59 n.d. n.d. n.d. 0.65 14.88 butylformate 0.11 0.23 1.38 n.d. n.d. 0.09 15.05 2-methylbutanal 20.74 20.6 1.79 118.3 260.9 13.94 15.94 1-penten-3-ol 1.76 0.7 0.33 n.d. 0.44 1.28 16.74 pentanal 53.6 25.28 8.22 13.02 16.86 28.98 19.29 2-methyl-2-butenal 0.41 0.87 n.d. 1.11 1.17 0.69 19.64 dimethyldisulfide 0.41 1.06 0.26 4.63 22.84 0.44 20.29 1-pentanol 1.59 1.2 3.28 1.42 2.22 1.01 21.51 2-hexanone 0.62 0.77 0.3 0.4 0.29 1.69 22.04 hexanal 187.2 110.2 18.63 30.1 33.4 120.6 22.44 2-methyltetrahydrofuran-3-one n.d. 2.31 0.03 1.3 3.44 n.d. 23.38 2-methylpyrazine 1.19 1.01 0.05 0.93 1.49 0.76 23.81 furfural 0.17 0.2 n.d. 0.1 0.25 0.03 24.68 2-hexenal 0.59 0.29 n.d. 0.21 0.1 0.22 26.28 2-heptanone 1.67 2.3 0.73 2.39 1.3 2.18 26.82 heptanal 2.14 1.62 0.38 1.83 0.96 0.78 27.48 2,6-dimethylpyrazine 0.81 1.27 0.11 1.67 2.94 0.89 29.34 2-heptenal 13.12 3.02 n.d. 1.13 2.48 2.89 30.62 _{2-octanone 0.32 0.57 0.05 0.22 0.15 0.34} 30.76 _{dimethyltrisulfide n.d. n.d. n.d. 0.79 1.58 0.11} 30.83 _{2-pentylfuran 0.94 1.01 0.83 0.53 0.81 0.44} 31.18 _{octanal 0.57 0.73 n.d. 1.39 0.55 0.42} 31.39 _{5-methyl-2-ethylpyrazine 0.28 0.27 n.d. 0.23 0.43 0.07} 35.24 _{nonanal 0.68 0.76 0.49 2.33 1.27 0.45}

Experimental

12 samples of various origin of pumpkin seeds oil were analyzed. In particular three samples are from Italy (1, 2 and 3) and nine from Slovenia.