Impact of Species and Variety on Concentrations of Minor Lipophilic

Article pubs.acs.org/JAFC

Impact of Species and Variety on Concentrations of Minor Lipophilic Bioactive Compounds in Oils Recovered from Plum Kernels Paweł Górnaś,*,† Magdalena Rudzińska,§ Marianna Raczyk,§ Inga Mišina,† Arianne Soliven,# † Gunars and Dalija Segliņa† ̅ Lacis, ̅ †

Institute of Horticulture, Latvia University of Agriculture, Graudu 1, Dobele, LV-3701 Latvia Institute of Food Technology of Plant Origin, Faculty of Food Science and Nutrition, Poznań University of Life Sciences, Wojska Polskiego 31, 60-624 Poznań, Poland # Australian Centre for Research on Separation Sciences (ACROSS), School of Science and Health, Western Sydney University (Parramatta), Sydney, NSW, 2150 Australia §

ABSTRACT: The profile of bioactive compounds (carotenoids, tocopherols, tocotrienols, phytosterols, and squalene) in oils recovered from the kernels of 28 plum varieties of hexaploid species Prunus domestica L. and diploid plums Prunus cerasifera Ehrh. and their crossbreeds were studied. Oil yields in plum kernels of both P. cerasifera and P. domestica was in wide ranges of 22.6− 53.1 and 24.2−46.9% (w/w) dw, respectively. The contents of total tocochromanols, carotenoids, phytosterols, and squalene was significantly affected by the variety and ranged between 70.7 and 208.7 mg/100 g of oil, between 0.41 and 3.07 mg/100 g of oil, between 297.2 and 1569.6 mg/100 g of oil, and between 25.7 and 80.4 mg/100 g of oil, respectively. Regardless of the cultivar, β-sitosterol and γ-tocopherol were the main minor lipophilic compounds in plum kernel oils and constituted between 208.5 and 1258.7 mg/100 g of oil and between 60.5 and 182.0 mg/100 g of oil, respectively. Between the studied plum species, significant differences were recorded for δ-tocopherol (p = 0.007), 24-methylenecycloartanol (p = 0.038), and citrostadienol (p = 0.003), but they were insufficient for discrimination by PCA. KEYWORDS: tocopherols, tocotrienols, phytosterols, squalene, plum kernel oils, Prunus, byproducts

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bacteria and fungi.14 Carotenoids have important functions in human nutrition. β-Carotene, one of the major carotenoids in the plant world, exhibits pro-vitamin A activity, whereas certain plasma carotenoids and tocopherols are related inversely to prostate-specific antigen levels at various time points.15 Therefore, greater intake of foodstuffs rich in tocopherols and carotenoids might be beneficial to men with prostate-specific antigen-defined prostate cancer recurrence.15 Squalene (2,6,10,15,19,23-hexamethyl-2,6,10,14,18,20-tetracosahexane) is a triterpenic hydrocarbon precursor of vitamin D, cholesterol, and steroid hormones. The richest source of squlene is shark liver;16 however, a significant amount can be also found in extra-virgin olive oil.16 Squalene protects against oxidative DNA damage in human mammary epithelial cells by reducing levels of reactive oxygen forms and thereby plays a significant role in the prevention of human breast cancer.17 Agro-industrial byproducts are promising unconventional alternative sources of natural bioactive compounds; however, the impact of the variety has not been investigated in sufficient detail, especially in the case of industrial wastes. Plums belong to several species of the genus Prunus and their multiple interspecific hybrids and are represented by a great diversity of cultivars developed in different countries, which may significantly affect the content of bioactive compounds in the plant

INTRODUCTION During the past decade increased production of fruits has been reported on the global scale. The most popular group of processed fruits includes plums (Prunus spp.), with world production for the year 2012 reaching almost 11 million tons.1 The processing of plums into jams, juices, and dried fruits generates tonnes of byproducts in the form of fruit pits. Fruit pits and seeds have great potential as an unconventional valuable source of oil, rich in bioactive compounds such as phytosterols, tocochromanols, carotenoids, and squalene,2−5 characterized by high biological activity. Plant stanols and sterols belong to the group of compounds known as phytosterols. Phytosterols are steroid compounds consisting of a cholesterol skeleton with carbon side chains. The most common forms of phytosterols in the plant world are β-sitosterol, stigmasterol, and campesterol. Phytosterols have a significant impact on human health; for instance, they have the ability to reduce the levels of cholesterol in blood serum.6 “Tocochromanols” is the collective term for the homologues of tocopherol and tocotrienol, all of which are active forms of vitamin E and are synthesized only in photosynthetic organisms. Concentrations of vitamin E active forms vary significantly not only between various plant species but also for different vegetative parts.7 Tocochromanols have demonstrated unique physicochemical activity in model8−11 as well in biological12,13 systems. Carotenoids include over 700 different compounds described as natural isoprenoid pigments, which are synthesized in photosynthetic organisms and some nonphotosynthetic, for instance, © 2016 American Chemical Society

Received: Revised: Accepted: Published: 898

November 6, 2015 December 24, 2015 January 5, 2016 January 5, 2016 DOI: 10.1021/acs.jafc.5b05330 J. Agric. Food Chem. 2016, 64, 898−905

Article

Journal of Agricultural and Food Chemistry m = c × MW × V

material. Therefore, in the present study the fruit kernels were recovered from 28 samples of various plum varieties of hexaploid species Prunus domestica L. and diploid plums Prunus cerasifera Ehrh. and their crossbreeds, with different countries of origin. Hence, the aim of the investigation was to determine the influence of plum variety and species on oil yield and concentration of tocochromanols, carotenoids, phytosterols, and squalene and to investigate the association between oil yield and concentration of bioactive compounds.

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where c is the concentration (mol/L), A is the absorbance, ε is the molar extinction coefficient (L/mol × cm), l is the path length (cm), m is the mass of total carotenoids in study amount of the sample (g), MW is the molecular weight (g/mol), and V is the volume of solution (L). Contents of Phytosterols, Cholesterol, and Squalene. Contents of plant sterols, cholesterol, and squalene were determined according to the AOCS.22 In brief, the oil sample (50 mg) was saponified with 1 M KOH in methanol for 18 h at room temperature, and then unsaponifiables were extracted three times with n-hexane/ tert-butyl methyl ether (1:1, v/v). After silylation using a Sylon BTZ, phytosterols, cholesterol, and squalene were separated on a HP 6890 gas chromatograph (GC) (Hewlett-Packard, Wilmington, DE, USA) equipped with a DB-35MS capillary column (25 m × 0.20 mm × 0.33 μm; J&W Scientific, Folsom, CA, USA) and flame ionization detector (FID). Samples of 0.5 μL were injected in splitless mode. Column temperature was held at 100 °C for 5 min, then programmed to 250 °C at 25 °C/min, held for 1 min, then further programmed to 290 °C at 3 °C/min, and held for 20 min. Hydrogen was used as a carrier gas at a flow rate of 1.5 mL/min. Temperature of the injection port was held at 290 °C. FID detector temperature was set at 300 °C with the limit of detection of 0.01 μg/g. An internal standard, 5α-cholestane, was used for sterol, cholesterol and squalene quantifications. Campesterol, stigmasterol, and β-sitosterolthe most common phytosterols in various plants23as well as cholesterol and squalene were identified by comparison with retention time of standards. Other phytosterols, due to lack of standards on the market, were identified on the Agilent Technologies 7890A GC equipped with triple quadrupole mass analyzer VL MSD 5975C (Agilent Technologies, Santa Clara, CA, USA). GC-MS was run using the same chromatographic conditions as described above for GC-FID. Mass spectra were collected in electron impact mode (70 eV), and masses were scanned from 100 to 600 Da. Both instruments, GC-FID and GC-MS, were calibrated using available standards (brassicasterol, campesterol, stigmasterol, β-sitosterol, cholesterol, and squalene) before analysis of samples. The Kovats retention indices24 were calculated between GCFID and GC-MS to confirm correctness of sterol identification. Statistical Analysis. The results were presented as means ± standard deviation (n = 3) from three independent batches (each batch was collected from different trees) of ground kernels. A p value ≤0.05 was used to denote significant differences between mean values determined by one-way analysis of variance (ANOVA). The Bonferroni post hoc test was used to denote statistically significant values at p ≤ 0.05. The relationship between analyzed variables was assessed by Pearson’s correlation coefficient. Its significance was evaluated by Student’s t test. Linear regression model (y = ax + b) was calculated additionally for analysis of significant relationship between parameters. Analyses mentioned above as well as principal component analysis (PCA) of minor lipophilic compounds in plum kernel oil samples were performed with the assistance of Statistica 10.0 (StatSoft, Tulsa, OK, USA) software.

MATERIALS AND METHODS

Reagents. Methanol, 2-propanol, tert-butyl methyl ether, n-hexane (HPLC grade), 5α-cholestane (≥97%, GC), and brassicasterol, campesterol, stigmasterol, β-sitosterol, cholesterol, and squalene (≥95%, GC) were purchased from Sigma-Aldrich (Steinheim, Germany). Tocopherol and tocotrienol homologues (α, β, γ, and δ) (>95%, HPLC) were obtained from Merck (Darmstadt, Germany) and LGC Standards (Teddington, Middlesex, UK), respectively. Sylon BTZ and fatty acid methyl ester mix were received from Supelco (Bellefonte, PA, USA; and Steinheim, Germany, respectively). Plant Material. Twenty-eight plum varieties of hexaploid species P. domestica L. and diploid plums P. cerasifera Ehrh. and their crossbreeds (Table 1) at the full-maturity stage were harvested in August and September 2013 at the Latvia State Institute of FruitGrowing (LSIFG) (GPS location: 56°36′39″ N; 23°17′50″ E). Detailed information about plant material has been reported previously.2 Undamaged kernels, obtained by removing the outer shells from the fruit pits, were frozen (−18 °C) and subsequently freeze-dried using a FreeZone freeze-dry system (Labconco, Kansas City, MO, USA) at a temperature of −51 ± 1 °C under vacuum of 0.055−0.065 mbar for 48 h. The kernels (50 ± 5 g) were milled with a Knifetec1095 universal laboratory mill (Foss, Höganäs, Sweden) to pass through a sieve of 0.75 mm mesh size to finally obtain a powder. Dry weight basis (dw) in studied samples was measured gravimetrically. Oil Extraction. Oil was extracted according to an earlier reported method.18 In brief, ground fruit kernels (5 g) were supplemented with 25 mL of n-hexane (Sigma-Aldrich) in a centrifuge tube and mixed on a Vortex REAX top (Heidolph, Schwabach, Germany) at 2500 rpm (1 min). Samples were subjected to ultrasound treatment in the Sonorex RK 510 H ultrasonic bath (Bandelin Electronic, Berlin, Germany) (5 min, 35 °C) and centrifuged on a 5804 R centrifuge (Eppendorf, Hamburg, Germany) (10000g, 5 min, 21 °C). The supernatant was collected in a round-bottom flask, and the remaining solid residue was re-extracted (twice) as described above. The combined supernatants were evaporated in a Laborota 4000 vacuum rotary evaporator (Heidolph) at 40 °C until constant weight. The oil content was expressed in percent (w/w) dw (dry weight basis, measured gravimetrically) of kernels. Tocopherol and Tocotrienol Homologue Determination. The oil samples (0.1 g) were diluted in 2-propanol until 10 mL using a volumetric flask as was described by Górnaś.19 Tocochromanols were determined by RP-HPLC/FLD using a pentafluorophenyl (PFP) column (ensured separation of two tocopherol and tocotrienol isomers, β and γ) on a Shimadzu HPLC system (Shimadzu Corp., Kyoto, Japan), according to the method previously developed and validated.20 The limits of detection (LODs) for tocopherols (Ts) and tocotrienols (T3s) were as follows: 0.051, 0.018, 0.022, 0.044, 0.061, 0.027, 0.030, and 0.019 mg/L for α-T, β-T, γ-T, δ-T, α-T3, β-T3, γ-T3, and δ-T3, respectively. Total Carotenoids Determination. A 0.2 g oil sample was diluted by n-hexane in a 5 mL volumetric flask, and the absorbance was measured at 450 nm with a UV-1800 spectrophotometer (Shimadzu). The total carotenoids concentration in oil samples was quantitated spectrophotometrically using the molar extinction coefficient for all-trans-β-carotene (ε = 139049) and converted equations of the Beer−Lambert law and molar concentration21

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RESULTS AND DISCUSSION Oil Yield in Plum Kernels. Oil yield in the investigated plum kernels varied considerably (p ≤ 0.05) and ranged from 22.6 to 53.1% (w/w) dw in the varieties ‘Plamennaya’ and PU 16764, respectively (Table 1). Both samples belong to the diploid plums P. cerasifera. In the hexaploid plums P. domestica, the oil yield was noted in the range between 24.2 and 46.9% (w/w) dw in the cvs. ‘Renklod Rannij Doneckij’ and ‘Renklod Uljanisceva’, respectively. The minimal and maximal oil concentrations in samples of both species P. cerasifera and P. domestica were similar. This observation leads to the conclusion that regardless of species, a comparable range of oil yield in plum kernels may be found. A wide range of oil yield in plum kernels has also been reported in the literature, from 32% in P. domestica25 to 53.5% in Prunus spinosa.26 Nevertheless, in

c = A /ε × l 899

DOI: 10.1021/acs.jafc.5b05330 J. Agric. Food Chem. 2016, 64, 898−905

FRA FRA LVA UKR GBR GBR

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

Aženas

Mirabelle de Nancy

Lotte

Renklod Rannij Doneckij

Blue Perdrigon

Kirke DEU RUS USA RUS SWE SWE LVA USA LVA GBR LVA GBR

P. domestica L.

Renklod Uljanisceva P. domestica L.

P. domestica L.

P. cerasifera Ehrh.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

P. domestica L.

Stanley

Plamennaya

Experimentalfältets Sviskon

1228C

Karsavas ̅

Tragedy

Sonora

Victoria

Minjona

Duke of Edinburgh

Tegera

SWE

RUS

Kubanskaya Kometa P. cerasifera Ehrh. × P. salicina Lindl.

(P. salicina Lindl. × P. americana March. × P. simonii Carr.) × P. cerasifera var. pissardii Ehrh.

EST

P. domestica L.

Suhkruploom

BPr 7413

LVA

39.7 0.7g,h,i 29.1 0.6c 28.6 0.5c 41.4 0.5i,j,k 42.0 0.6j,k,l 41.5 0.5i,j,k 32.4 0.4d 24.2 0.5a 39.4 0.5g,h 41.5 0.5i,j,k 33.7 0.6d,e 46.9 1.0o,p 42.4 0.5k,l,m 22.6 0.3a 35.2 0.3e,f 35.1 0.4e,f 42.8 0.6k,l,m 26.1 0.5b 27.5 0.5a,b 35.6 0.6f 40.4 0.7h,i,j 38.6 0.5g

country of origin oil yield (%, w/w dw)

P. domestica L.

species

Lase ̅

variety 9.2 0.1e,f 16.0 0.2i 17.2 0.2m,n 8.3 0.1d 9.5 0.1f 5.8 0.1b 18.1 0.1o 13.5 0.1j 12.3 0.2i 5.7 0.1b 19.9 0.3p 7.7 0.1c 11.8 0.1h,i 16.8 0.2m 9.6 0.1f 8.7 0.2d,e 7.4 0.2c 14.7 0.2k 17.5 0.3n 11.6 0.2g,h 8.4 0.1d 11.4 0.3g,h

α-T 0.2 0.0a 0.2 0.0a 0.3 0.0a,b 0.2 0.0a 0.3 0.0a,b 0.2 0.0a 0.4 0.0b 0.2 0.0a 0.3 0.0a,b 0.1 0.0a 0.4 0.0b 0.2 0.0a 0.7 0.0c 0.3 0.0a,b 0.2 0.0a 0.1 0.0a 0.2 0.0a 0.3 0.0a,b 0.3 0.0a,b 0.2 0.0a 0.2 0.0a 0.3 0.0a,b

β-T 97.7 0.8i 104.3 0.9j 170.6 0.7o 83.8 0.9e 97.6 0.4i 86.6 0.9e 127.8 1.1l 182.0 1.1p 90.7 0.9f,g 79.9 1.1d 131.4 1.8m 97.5 0.7i 96.5 0.9h,i 120.7 1.2k 76.2 1.1c 162.6 1.4n 90.3 1.0f 165.4 1.4n 129.0 1.2l,m 97.6 1.0i 93.8 0.9g,h 131.2 1.3m

γ-T 6.7 0.1l 5.6 0.1j,k 6.9 0.0l 3.0 0.0c,d 5.3 0.0i,j 3.9 0.0f 8.2 0.1n 11.6 0.1r,q 3.6 0.1e,f 5.2 0.1h,i 9.6 0.2o 6.7 0.1l 11.2 0.1r 4.8 0.1g 2.9 0.0c 10.5 0.3p 3.5 0.1e 10.4 0.2p 9.6 0.1o 3.7 0.1e,f 4.9 0.1g,h 8.3 0.2n

δ-T 0.5 0.0b,c 2.9 0.0n 1.4 0.0h 0.1 0.0a 0.7 0.1d,e 0.5 0.0b,c 1.4 0.1h 0.7 0.0d,e 0.4 0.0b 1.2 0.1g 0.4 0.1b 0.4 0.0b 0.1 0.0a 0.2 0.0a 0.7 0.1d,e 0.9 0.0f 0.3 0.0a,b 0.8 0.0e,f 2.4 0.1m 0.9 0.0f 0.9 0.0f 0.5 0.0b,c

α-T3 0.2 0.0a,o 0.8 0.0f 0.3 0.0b,c 0.1 0.0a 0.4 0.0c,d 0.2 0.0a,b 0.8 0.0f 0.6 0.0e 0.2 0.0a,b 0.5 0.0d,e 0.5 0.0d,e 0.2 0.0a,b 0.1 0.0a 0.3 0.0b,c 0.2 0.0a,b 0.8 0.0f 0.2 0.0a,b 0.3 0.0b,c 1.4 0.0g 0.3 0.0b,c 0.2 0.0a,b 0.2 0.0a,b

γ-T3

tocochromanols (mg/100 g oil)

Table 1. Oil Yield Recovered from Kernels of 28 Plum Varieties and Content of Tocochromanols and Carotenoidsa

114.6 0.8i 129.9 1.2k 196.7 0.9q 95.5 1.0d,e 113.7 0.3i 97.3 1.0e 156.7 1.3n 208.6 1.3s 107.4 0.9g 92.6 1.4c,d 162.2 2.3o 112.8 0.7h,i 120.3 1.2j 143.1 1.0l 89.8 1.2c 183.5 1.3p 101.8 1.3f 191.8 1.2r 160.2 1.7n,o 114.3 1.1i 108.4 1.1g 151.9 1.7m

total Ts + T3s 1.41 0.0f,g,h 1.00 0.0d,e,f 0.69 0.0b,c,d 0.71 0.0b,c,d 2.21 0.0i,j 0.97 0.0d,e,f 2.43 0.0j 0.91 0.0c,d,e 1.88 0.0h,i 3.00 0.0k,l 3.07 0.0l 1.09 0.0e,f,g 1.12 0.0e,f,g 0.91 0.0c,d,e 1.03 0.0d,e,f 1.58 0.0g,h 1.10 0.0e,f,g 1.14 0.0e,f,g 2.53 0.0j,k 1.39 0.0f,g,h 1.75 0.0h,i 1.49 0.0f,g,h

total carotenoids (mg/100 g oil)

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Italic values correspond to standard deviations (n = 3). Different letters in the same column indicate statistically significant difference at p < 0.05. T, tocopherol; T3, tocotrienol; dw, dry weight basis; LVA, Latvia; EST, Estonia; RUS, Russia; SWE, Sweden; FRA, France; UKR, Ukraine; GBR, Great Britain; DEU, Germany; USA, United States.

0.0a,b,c 0.8a 0.0a 0.0c,d 0.1a 0.7a 0.0a 0.1c 0.5p

those studies only one and three different cultivars of plums were investigated, respectively. Other factors that may have had a significant impact on the oil yield in the plant material include abiotic factors27 and the oil extraction method.28 The abiotic factors and extraction method were the same for all samples in this study, hence demonstrating the plum variety is a key factor affecting the oil yield in kernels (p ≤ 0.05) (Table 1). Considerable variation of the oil content was reported also in kernels and seeds of other plants belonging to the Rosaceae family, for example, different cultivars of almond (Prunus dulcis (Miller) D.A. Webb),29,30 sour cherry (Prunus cerasus L.),31 and pear (Pyrus communis L.).32 Content of Tocochromanols in Plum Kernel Oils. Four tocopherol (α, β, γ, and δ) and two tocotrienol homologues (α and γ) were identified in all plum kernel oils (Table 1). γ-T was a predominant form with the concentration range 60.5− 182.0 mg/100 g oil in cvs. ‘Liesma’ and ‘Renklod Rannij Doneckij’, respectively. Both species P. domestica and P. cerasifera had comparable ranges of γ-T levels (76.2−182.0 and 60.5−170.6 mg/100 g oil, respectively). Nevertheless, the average concentration in samples of species P. domestica was higher than in P. cerasifera (110.6 and 92.7 mg/100 g oil, respectively). Relatively high amounts were noted for α-T especially in cvs. ‘Suhkruploom’, ‘Plamennaya’, ‘Kubanskaya Kometa’, ‘Sonora’, ‘Lotte’, and ‘Tegera’ characterized by the amount above 15 mg/100 g oil. However, in varieties ‘Mirabelle de Nancy’, ‘Kirke’, and PU 16764, significantly lower (p ≤ 0.05) concentrations of α-T, 3−5-fold in comparison to cv. ‘Tegera’, were noted (Table 1). The level of δ-T was about 2-fold lower in comparison to concentration of α-T in the studied samples. Moreover, the difference between the lowest and highest amounts of δ-T was 7-fold in varieties 20651 and ‘Renklod Rannij Doneckij’, respectively. Levels of β-T, α-T3, and γ-T3 were below 3 mg/100 g oil, significantly lower (p ≤ 0.05) than noted for α-T and γ-T. The difference between the lowest and highest values for β-T, α-T3, and γ-T3 were, respectively, 7-, 29-, and 14-fold. In oils obtained from 17 almond cultivars, greater differences in concentration of the tocochromanols with minor levels and lower with high amount were observed.33 A similar observation was noted in the present study. For α-T and β-T in both species, P. domestica and P. cerasifera, were recorded similar average concentrations (11.3 vs 10.0 and 0.2 vs 0.2 mg/100 g oil, respectively); however, in the cases of δ-T, α-T3, and γ-T3 the average values were almost 2-fold higher in P. domestica compared with P. cerasifera (6.9 vs 3.6, 0.8 vs 0.5, and 0.4 vs 0.2 mg/100 g oil, respectively). Total concentration of tocochromanols in most plum kernel oil samples was significantly different (p ≤ 0.05) and was characterized by a high, wide range (70.7−208.7 mg/100 g oil in cvs. ‘Liesma’ and ‘Renklod Rannij Doneckij’, respectively), which covered the total tocochromanols concentration reported in oils recovered from such fruit seeds as apple, red currant, gooseberry, grape, Japanese quince, watermelon, and canary melon, but lower than in pomegranate and sea buckthorn.34 Significantly lower concentrations of total tocochromanols were reported in three samples of oil recovered from plum kernel originating from Turkey.26 This difference may have been due to different abiotic factors, cultivar, or plant origin. On the basis of the percentage calculation, γ-T in plum kernel oils constituted 80.2−90.5% of total tocochromanols with the average 85.4%. An almost identical percentage (85.5%) of γ-T in plum kernel oil originating from Egypt was reported previously.25 γ-T was also reported to be a predominant form of

a

0.0a

0.56 72.4

0.7b 0.0a

0.1 0.6

0.0a 0.1e

1.7 62.7

0.5c,d 0.0a

0.1 7.3

0.1a 0.6r

LVA P. cerasifera Ehrh. 20651

47.7

0.0f,g,h

0.41 85.9 0.1 0.1 3.5 77.8 0.1 4.3 LVA P. cerasifera Ehrh. PU 16764

53.1

1.41 108.1

0.8g 0.0a,b

0.2 0.4

0.1b 0.1m

7.6 92.4

0.7f,g 0.0a 0.1c

0.2 7.3

0.6n,o

UKR P. domestica L. Oda

45.6

0.0a,b 0.6a 0.0a 0.0b 0.1b 0.6a 0.0a 0.1c 0.4p

0.0c,d,e

0.47 70.7

0.9b 0.0a,b

0.1 0.4

0.0b,c 0.1d,e

2.1 60.5

0.9b 0.0a

0.1 7.4

0.1d 0.4l,m

LVA P. cerasifera var. pissardii Ehrh. Liesma

47.8

0.0i,j

0.90 85.3 0.2 0.5 3.3 72.6 0.2 LVA

8.5

2.12

P. cerasifera Ehrh. × P. salicina ssp. ussuriensis Koval. et Kost.

43.5

1.0g,h 0.0a 0.0c,d 0.1k 0.8f,g

Alvis

variety

0.0a 0.1g 0.6m,n

total Ts + T3s

109.2 0.1

γ-T3 α-T3

0.6 5.8

δ-T γ-T

91.5 0.2

β-T α-T

11.0 44.2

country of origin oil yield (%, w/w dw)

GBR

tocochromanols (mg/100 g oil)

Table 1. continued

species P. domestica L. Greengage

total carotenoids (mg/100 g oil)

Journal of Agricultural and Food Chemistry

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cholesterol in the studied samples amounted to 6-, 7-, 16-, 6-, 30-, 10-, 9-, 30-, 23-, 9-, 6-, and 4-fold for cholesterol, campesterol, Δ5-stigmasterol, β-sitosterol, sitostanol, Δ5-avenasterol, Δ7-stigmasterol, cycloartenol, Δ7-avenasterol, 24-methylenecycloartanol, citrostadienol, and others (unidentified), respectively (Table 2). A significantly lower difference, 2−3fold, in the concentration of the individual phytosterols in oils recovered from kernels of nine apricot cultivars was reported.39 However, in a study in which 15 varieties of apricot were tested, the difference in levels of some phytosterols reached even 8-fold.40 This observation allows one to conclude that higher differences in the concentration of some bioactive compounds can be expected with greater numbers of tested samples. A 5-fold difference between the lowest and highest amount of

tocopherol for other fruit kernels and seeds of plants belonging to the Rosaceae family, for example, different cultivars of apricots (Prunus armeniaca L.), 91−95%;35 sweet cherry (Prunus avium L.), 85−89%;3 and pears (Pyrus communis L.), 84−88%.36 However, some exceptions include apple (Malus domestica Borkh.) seeds37 and Japanese quince (Chaenomeles japonica (Thunb.) Lindl. ex Spach) seeds,38 where γ-T comprising 1−24 and 2% of the total tochochromanols detected, respectively, were reported. Content of Phytosterols and Cholesterol in Plum Kernel Oils. The contents of 10 identified phytosterols and cholesterol in kernel oils recovered from different plum varieties varied significantly (p ≤ 0.05) (Table 2). The difference in concentration of individual phytosterols and

Table 2. Content of Cholesterol, Phytosterols, and Squalene in Kernel Oils Recovered from 28 Plum Varietiesa phytosterols (mg/100 g oil)

seed oils Lase ̅

cholesterol 17.2 0.8e,f,g

Suhkruploom

22.7

Kubanskaya Kometa

55.4

BPr 7413

16.6

Aženas

19.7

Mirabelle de Nancy

11.2

Lotte

26.1

0.4h,i,j 0.6r 1.1e,f 1.09

34.4 1.5m,n

Blue Perdrigon 15.8 0.9e,f Kirke

28.5 1.4l,m

Tegera

14.3 0.6a,b,c 33.5 0.6h 37.2 0.8i 13.2 0.7a,b 17.9 0.49 15.5

Δ5avenasterol

Δ7stigma- cycloarsterol tenol

Δ724avena- methylene- citrostasterol cycloartanol dienol

others

4.6

48.6

5.2

1.1

1.2

5.6

0.3g,h

0.2a,b

0.2c,d,e

7.6

0.5

0.4

0.3j,k,l

0.1a

0.1a

0.4k,l

8.0

3.2

2.3

9.6

0.3k,l

0.2f,g

0.2f,g,h

0.4i,j

4.2

2.8

2.7

6.4

0.3f,g

0.2e,f

0.2h,i,j

0.2c,d

0.6l

0.2b,c,d

2.8

1.3

1.2

9.6

8.1

6.2

0.29

0.29

0.29

0.59

0.29

0.79

3.2

0.8

0.6

3.3

3.7

3.4

0.2d,e,f

0.1a,b

0.2a,b,c

0.2a,b

0.2a

0.5a

8.4

3.2

3.3

9.1

0.6l,m

0.3f,g

0.2j,k

0.1h,i,j

0.3g,h,i

0.6d,e,f

6.4

1.3

1.1

7.6

6.1

5.4

0.3h,i,j

0.2b,c,d 0.2b,c,d

0.3f,g,h

0.4b,c

0.4b

1.9

0.8

6.6

5.9

5.4

0.3d,e,f 7.4 0.3h,i,j 3.6 0.3c,d,e 2.7 0.2b,c,d 5.1 1.59 4.2

1.0b,c,d 0.4b,c,d 0.3d,e,f 0.4k,l

Renklod Rannij Doneckij

campesterol

31.1 2.5l.m

Renklod Uljanisceva

30.9

Stanley

25.1

Plamennaya

35.3

Experimentalfältets Sviskon

19.6

1228C

50.5

2.3l,m 0.6j,k 1.0m,n 1.8f,g,h

2.9p Karsavas ̅

35.8

Tragedy

59.0

1.0n 2.5s

32.3 0.4h 44.8 1.6j 12.2 0.4a 32.9 0.3h 58.8 1.4l,m 30.6 0.4g,h 30.9 0.7g,h 54.7 0.8k 32.5 1.6h 61.8 1.4m 28.9 1.3g 56.8 1.4k,l

total of phytosterols + cholesterol squalene (mg/100 g oil) (mg/100 g oil)

Δ5stigmaβsitostasterol sitosterol nol

4.2 0.2d,e,f 5.4 0.4f,g,h 4.3 0.3d,e,f 7.5 0.3h,i,j 9.6 0.7j,k 3.5 0.3c,d,e 7.5 0.4h,i,j 18.7

304.8 12.6d,e 473.8 13.1f,g 556.1 25.2h 285.2

14.09 256.0

20.7f 550.4 35.1h 247.0

17.4g,h 894.7 27.0k 456.5 22.8f 478.1 18.6f,g 988.3 21.5l

8.5 0.4i,j 11.1 0.2k

0.7 0.1a 3.8 2.9 0.29 5.6 11.7 0.8k,l 1.5 0.2a,b 1.7

21.5b,c,d 0.2a,b,c 534.7

660.8

6.5

0.2a,b

3.1b,c,d 0.5g,h 445.8

8.7

0.3g,h,i

1.3

13.1c,d,e 0.3e,f,g 253.1

2.7l 0.3i,j

5.0 0.3f,g

35.9i 804.4 19.1j 442.8 27.3f 896.2 33.2k

0.7f 74.8 1.0k 68.6 0.6j 62.4 1.6i 38.5 0.9e 19.6 0.2a,b 47.8 0.9f 25.4 1.3c,d 27.8 0.9d

9.4

62.5

0.7j

1.0i

19.6

78.5

1.1n,o 12.8 0.4l,k,m 11.4 0.7j,k 13.5 1.1l,m 18.8 0.9n 14.6 0.7m 11.0 0.8i,j,k 21.2 0.7o

1.0k 47.5 0.8f 48.3 0.9f 154.8 4.2m 60.1 1.4h,i 54.5 1.1g 45.3 0.8f 74.9 2.4k

2.2

12.5 0.4l 11.9

0.2a,b

0.1a,b

0.2f,g,h

8.9

3.3

3.8

0.4l,m

0.2f,g

0.1k,l

0.8o

1.4

4.0

9.4

8.2

0.2a

0.4g,h,i 0.4m

5.7

4.4

3.1

0.3h,i

0.3h,i

0.4i,j,k

5.6

2.3

4.2

0.4h,i

0.3d,e,f 0.2l

0.4j,k

4.7

1.3

7.5

0.9n

0.3i

0.2c,d,e

1.3f,g,h

9.6

7.8

4.2

8.5

0.3m

1.0j

0.3l

0.4g,h,i

13.3

0.3c,d,e 25.5

0.2g,h,i 27.6 0.8p 10.6

0.4h,i

0.2b,c

8.7

8.8

0.3d,e,f 16.7 0.6j 23.3

11.0

0.5b,c 15.3 0.4j 16.1 0.5j 19.2 0.7k 11.8 0.4i 15.3 2.4j 11.9 0.6i

12.0c,d 651.4

0.3g,h,i 13.6 0.4k

23.9h

6.4

429.7

15.69 327.2 3.0a,b

7.2

610.0

30.4f,g 331.7

0.3b

21.1a,b

11.0

743.1

0.9j,k

17.8g,h

9.9

1141.3

0.8h,i,j 13.3 0.4k

28.4e,f

7.8

643.5

0.5e,f,g 12.7 0.7k

28.8l 852.7

0.4i,j

34.5i

2.4

0.8n

0.4g,h,i

0.7f,g,h

6.5

2.4

2.3

4.9

7.3

9.3

0.5h,i,j

0.4d,e,f 0.2f,g,h

9.6

3.4

0.3m

0.3f,g,h 0.5l 902

0.9m

0.5g,h,i

8.3

1046.3 18.7j 605.0

0.5h,i,j 0.7k

18.6e,f 1320.1

10.2

13.2

26.2k 655.1

0.2g,h,i

0.4c,d,e

21.6e 690.0

2.6

11.4

16.9cd 366.4

0.4e,f

0.3b,c

11.8e,f 774.9

0.9i,j,k

15.9

10.4

431.7

6.7

4.1

23.4

11.6

30.0e 1176.8 37.3k

28.3 0.6a,b,c 35.4 0.4f,g 50.5 0.9k 25.7 0.7a 43.1 0.7i 33.3 0.5d,e,f 39.3 0.6h 27.7 1.1a,b 26.2 0.6a 80.4 0.7o 49.2 1.4j,k 73.0 1.3n 47.4 1.5j,k 46.5 1.0i,j 36.1 0.7f,g,h 63.6 1.0m 60.7 1.7m 38.9 0.9g,h

DOI: 10.1021/acs.jafc.5b05330 J. Agric. Food Chem. 2016, 64, 898−905

Article

Journal of Agricultural and Food Chemistry Table 2. continued phytosterols (mg/100 g oil)

seed oils Sonora

cholesterol 44.9 1.1o

Victoria

15.6

Minjona

14.9

1.1d,e,f 1.5c,d,e

campesterol

Δ5stigmaβsitostasterol sitosterol nol

Δ5avenasterol

Δ7stigma- cycloarsterol tenol

Δ724avena- methylene- citrostasterol cycloartanol dienol

others

84.7

19.4

91.6

2.3

0.7

8.6

1.6n 20.8 1.5e,f 22.3 1.1f

0.5l 8.3 1.0i,j 5.0 0.6d,e,f

Duke of Edin- 21.3 18.9 burgh 1.1g,h,i 0.8e

0.2e,f,g

Greengage

14.6

2.3

Alvis

11.0

0.6c,d,e 1.5a,b,c Liesma

9.5 0.3a

Oda

16.0 1.0e,f

PU 16764

15.4 0.9d,e,f

20651

10.9 0.7a,b

a

18.1 1.1d,e 15.6

5.1

0.3a,b,c 3.2

0.6b,c,d 0.4c,d,e 15.0

2.2

0.5b,c,d 0.2a,b,c 17.5 1.2c,d,e 13.3 0.6a,b 14.9

3.3 0.2c,d,e 1.2 0.3a 1.8

0.5b,c,d 0.4a,b

1258.7 38.3m 333.4 17.4e 284.2

0.8 0.2a 7.2 0.6h 5.5

15.8c,d,e 0.3g,h 339.8 19.5e 280.3

9.6 0.6i,j 5.6

12.5c,d,e 0.4g,h 235.8

2.7

10.7b,c,d 0.4c,d,e 208.5 16.4a 252.9

2.2 0.2b,c,d 4.2

12.9b,c,d 0.3e,f,g 208.7 14.2a,b 216.7

3.6 0.3d,e,f 4.3

12.5a,b,c 0.5e,f,g

2.2l 21.0 0.8b,c 16.4 0.4a,b 29.8 1.1o 28.1 1.0d 62.5 1.9i 57.5 0.9g,h 16.0 0.8a 29.4 0.7d 35.1 0.6e

15.0

27.3

15.5

total of phytosterols + cholesterol squalene (mg/100 g oil) (mg/100 g oil) 1569.6

0.3b,c,d 0.7k

0.2a,b,c

1.0o,p

0.5j

0.3g,h,i

4.1

1.8

0.9

7.1

9.4

7.1

0.2e,f,g

0.3c,d,e 0.1b,c,d

0.5e,f,g

0.4e,f,g

0.3d,e,f

3.3

0.8

1.3

7.4

5.5

6.3

0.2d,e,f

0.2a,b

0.2c,d,e

0.4f,g,h

0.3a,b

0.2b,c,d

5.6

1.3

2.7

8.7

8.4

6.6

0.3h,i

0.2b,c,d 0.3h,i

0.6g,h,i

0.5d,e,f

0.4b,c,d

3.6

1.2

6.8

6.5

6.5

0.4d,e,f

0.2a,b,c 0.3e,f,g

0.3d,e,f

2.6

2.5

1.5

4.5

2.0

436.6

6.7

0.2d,e,f

0.3a,b

1.3

4.2

0.7c,d,e

0.2c,d

0.2f,g,h 0.1c,d,e

0.2a,b

0.4j

0.4b,c

3.5

0.8

1.4

7.6

7.6

6.3

0.2d,e,f

0.2a,b

0.1c,d,e

0.4c,d,e

0.4f,g,h

0.7b,c,d

2.2

2.3

0.6

3.0

0.1a,b,c

0.2d,e,f 0.1a,b

0.1a

0.7i

0.3b,c

2.5

3.2

1.0

3.7

9.5

5.5

0.2b,c,d

0.4a,b

0.4f,g,h

0.4b,c

5.6

5.6

15.4b,c 370.0

3.4

11.8

21.2d 375.7

0.3b,c,d 0.2e,f

0.3b,c,d 0.1f,g

1.0k,l

15.3b,c 457.8

2.7

15.5

19.5c,d 372.9

0.4b,c,d 0.6b,c,d 21.4

37.7m

11.8a,b,c 327.5 16.6a,b 336.8 15.0a,b 297.2 14.4a 309.0 13.9a,b

54.6 1.9l 28.3 0.7a,b,c 30.6 1.8b,c,d 34.3 1.2e,f 27.2 0.8a,b 31.5 0.8c,d,e 27.4 1.1a,b 33.7 0.8d,e,f 43.5 1.4i 47.3 1.2j,k

Italic values correspond to standard deviations (n = 3). Different letters in the same column indicate statistically significant differences at p < 0.05.

total phytosterol concentration was recorded for the investigated plum kernel oil samples (297.2−1569.6 mg/100 g oil in varieties PU 16764 and ‘Sonora’, respectively). In the case of total tocochromanols, this difference was only 3-fold. In half of the tested samples the levels of total phytosterols were below 500 mg/100 g oil, and only five varieties had concentrations above 1000 mg/100 g oil. β-Sitosterol was the predominant phytosterol in each variety and consisted of 64−80% of the total detected phytosterols. The predominance of β-sitosterol and its wide range in different varieties is not surprising, because a similar observation was reported previously in seed oils recovered from different apple cultivars. 18 Other phytosterols for which significant quantities in plum kernel oils were recorded included Δ5-avenasterol and campesterol (4−18 and 3−6%, respectively). In the context of phytosterols certain differences between species were observed. P. domestica had higher average percentage of β-sitosterol and lower average percentage of Δ5-avenasterol compared with P. cerasifera, 75 and 7 vs 69 and 13%, respectively. Four of the main phytosterols, β-sitosterol, isofucosterol (Δ5-avenasterol), campesterol, and stigmasterol, had similar percentage shares in comparison to a previous investigation.25 Content of Carotenoids and Squalene in Plum Kernel Oils. In samples of species P. cerasifera lower concentrations of carotenoids (0.41−0.91 mg/100 g oil in varieties PU 16764 and ‘Plamennaya’, respectively) compared to P. domestica (0.91− 3.07 mg/100 g oil in cvs. ‘Renklod Rannij Doneckij’ and ‘Tegera’, respectively) were noted. Recorded levels of carotenoids in plum kernel oils were marginally higher than reported in apple seed oils (0.10−1.58 mg/100 g oil)41 and significantly lower than in crude palm oil (50−70 mg/100 g oil).42

The content of squalene in both plum species was dependent on the variety and ranged from 25.7 to 80.4 mg/100 g oil in varieties BPr 7413 and ‘Kirke’, respectively, with an average concentration of 41.6 mg/100 g oil. The concentration of squalene in plum kernel oils was higher compared to previously reported levels in dessert apple seed oils (9.0−34.0 mg/100 g oil)18 and lower than in virgin olive oils (80−1300 mg/100 g oil).17 To the best of our knowledge this is the first report about carotenoids and squalene being present in plum kernel oils and, therefore, direct comparison is not possible. Associations between Oil Yield and Contents of Lipophilic Bioactive Compounds in Plum Kernel Oils. The β-sitosterol and total phytosterols in oil samples recovered from different cultivars of crab and dessert apple seeds were previously reported to be negatively correlated with the obtained oil yield.18 A similar phenomenon was found also in the present study. Significant trends occurred between oil yield in plum kernels and the concentration of total phytosterols and tocochromanols (R2 = 0.536, p ≤ 0.00001; and R2 = 0.635, p ≤ 0.000001, respectively). In the case of total carotenoids no trend was found (R2 = 0.028, p ≤ 0.5). Moreover, when the oil samples were divided with respect to species, the observed associations between oil yield and minor bioactive compounds (phytosterols, tocochromanols, and carotenoids) for P. cerasifera were higher (R2 = 0.882, p ≤ 0.005; R2 = 0.697, p ≤ 0.05; and R2 = 0.506, p ≤ 0.1) than for P. domestica (R2 = 0.390, p ≤ 0.005; R2 = 0.588, p ≤ 0.0001; and R2 = 0.0001, p ≤ 1.0). The observed phenomena indicate that higher oil yield in plum kernels results in a lower concentration of tocochromanols and phytosterols. 903

DOI: 10.1021/acs.jafc.5b05330 J. Agric. Food Chem. 2016, 64, 898−905

Article

Journal of Agricultural and Food Chemistry

unconventional bio-oil from by-products for the pharmaceutical and cosmetic industry. Ind. Crops Prod. 2013, 48, 178−182. (6) Chen, Z.-Y.; Jiao, R.; Ma, K. Y. Cholesterol-lowering nutraceuticals and functional foods. J. Agric. Food Chem. 2008, 56, 8761−8773. (7) Munné-Bosch, S.; Alegre, L. The function of tocopherols and tocotrienols in plants. Crit. Rev. Plant Sci. 2002, 21, 31−57. (8) Dwiecki, K.; Górnaś, P.; Jackowiak, H.; Nogala-Kałucka, M.; Polewski, K. The effect of D-α-tocopherol on the solubilization of dipalmitoylphosphatidylcholine membrane by anionic detergent sodium dodecyl sulfate. J. Food Lipids 2007, 14, 50−61. (9) Dwiecki, K.; Górnaś, P.; Wilk, A.; Nogala-Kałucka, M.; Polewski, K. Spectroscopic studies of D-α-tocopherol concentration-induced transformation in egg phosphatidylcholine vesicles. Cell. Mol. Biol. Lett. 2007, 12, 51−69. (10) Nogala-Kałucka, M.; Dwiecki, K.; Siger, A.; Górnaś, P.; Polewski, K.; Ciosek, S. Antioxidant synergism and antagonism between tocotrienols, quercetin and rutin in model system. Acta Aliment. 2013, 42, 360−370. (11) Neunert, G.; Górnaś, P.; Dwiecki, K.; Siger, A.; Polewski, K. Synergistic and antagonistic effects between alpha-tocopherol and phenolic acids in liposome system: spectroscopic study. Eur. Food Res. Technol. 2015, 241, 749−757. (12) Eitenmiller, R.; Lee, J. Vitamin E: Food Chemistry, Composition, And Analysis; Dekker: New York, 2004. (13) Aggarwal, B. B.; Sundaram, C.; Prasad, S.; Kannappan, R. Tocotrienols, the vitamin E of the 21st century: its potential against cancer and other chronic diseases. Biochem. Pharmacol. 2010, 80, 1613−1631. (14) Aust, O.; Sies, H.; Stahl, W.; Polidori, M. C. Analysis of lipophilic antioxidants in human serum and tissues: tocopherols and carotenoids. J. Chromatogr. A 2001, 936, 83−93. (15) Antwi, S. O.; Steck, S. E.; Zhang, H.; Stumm, L.; Zhang, J.; Hurley, T. G.; Hebert, J. R. Plasma carotenoids and tocopherols in relation to prostate-specific antigen (PSA) levels among men with biochemical recurrence of prostate cancer. Cancer Epidemiol. 2015, 39, 752. (16) Camin, F.; Bontempo, L.; Ziller, L.; Piangiolino, C.; Morchio, G. Stable isotope ratios of carbon and hydrogen to distinguish olive oil from shark squalene-squalane. Rapid Commun. Mass Spectrom. 2010, 24, 1810−1816. (17) Warleta, F.; Campos, M.; Allouche, Y.; Sánchez-Quesada, C.; Ruiz-Mora, J.; Beltrán, G.; Gaforio, J. J. Squalene protects against oxidative DNA damage in MCF10A human mammary epithelial cells but not in MCF7 and MDA-MB-231 human breast cancer cells. Food Chem. Toxicol. 2010, 48, 1092−1100. (18) Górnaś, P.; Rudzińska, M.; Segliņa, D. Lipophilic composition of eleven apple seed oils: a promising source of unconventional oil from industry by-products. Ind. Crops Prod. 2014, 60, 86−91. (19) Górnaś, P. Unique variability of tocopherol composition in various seed oils recovered from by-products of apple industry: rapid and simple determination of all four homologues (α, β, γ and δ) by RP-HPLC/FLD. Food Chem. 2015, 172, 129−134. (20) Górnaś, P.; Siger, A.; Czubinski, J.; Dwiecki, K.; Segliņa, D.; Nogala-Kalucka, M. An alternative RP-HPLC method for the separation and determination of tocopherol and tocotrienol homologues as butter authenticity markers: a comparative study between two European countries. Eur. J. Lipid Sci. Technol. 2014, 116, 895−903. (21) Britton, G. UV/visible spectroscopy. In Carotenoids; Britton, G., Liaaen-Jensen, S., Pfander, H., Eds.; Birkhauser Verlag: Basel, Switzerland, 1995; Vol. 1B, pp 13−62. (22) AOCS Official Method Ch 6-91. Determination of the composition of the sterol fraction of animal and vegetable oils and fats by TLC and capillary GLC. Official Methods and Recommended Practices of the American Oil Chemists’ Society, 4th ed.; American Oil Chemists’ Society: Champaign, IL, USA, 1997.

PCA was applied to discriminate species of tested plum samples according to the content of minor lipophilic bioactive compounds in the kernel oils. The results of the PCA did not group tested varieties according to species (results not shown). ANOVA was applied to select the compounds that have statistically significant differences between tested plum species. Three compounds were identified, which possibly can ensure PCA discrimination between species: δ-T (p = 0.007), 24-methylenecycloartanol (p = 0.038), and citrostadienol (p = 0.003). However, even these selected compounds did not group plum varieties according to species (results not shown), which can be explained by an insufficient level of differences or their inconsistency. It should be also mentioned that tested P. cerasifera plums are not homogeneous; they include interspecific crosses with other plums such as Prunus salicina Lindl., Prunus americana March., and Prunus simonii Carr., increasing the diversity of this group and therefore possibly overlapping with P. domestica plums. In summary, the present study has demonstrated that kernel oils recovered from 28 different plum varieties are a rich source of bioactive compounds. Nevertheless, the oil yield, as well the content of lipophilic bioactive compounds in oil, namely, tocopherols, tocotrienols, carotenoids, phytosterols, and squalene, was significantly affected by the variety. Significant correlations were found between oil yield in plum kernels and the amount of tocochromanols and phytosterols, which could be applied as a preliminary tool for the prediction of their concentrations in the future studies. Minor differences in the composition and content of bioactive compounds identified in kernel oils of diploid plums P. cerasifera Ehrh. and their crossbreeds compared to hexaploid species P. domestica L. were not sufficient for their clear discrimination by PCA.

■

AUTHOR INFORMATION

Corresponding Author

*(P.G.) Phone: +371-63722294. Fax: +371-63781718. E-mail: [email protected]. Funding

This research was supported by the Ministry of Agriculture Republic of Latvia Project 070515/S2P. Notes

The authors declare no competing financial interest.

■

REFERENCES

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DOI: 10.1021/acs.jafc.5b05330 J. Agric. Food Chem. 2016, 64, 898−905

Article

Journal of Agricultural and Food Chemistry

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DOI: 10.1021/acs.jafc.5b05330 J. Agric. Food Chem. 2016, 64, 898−905