Industrial by-products of plum Prunus domestica L. and Prunus cerasifera Ehrh. as potential biodiesel feedstock: Impact of variety

Industrial Crops and Products 100 (2017) 77–84

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Industrial by-products of plum Prunus domestica L. and Prunus cerasifera Ehrh. as potential biodiesel feedstock: Impact of variety b ´ Paweł Górna´s a,∗ , Magdalena Rudzinska , Arianne Soliven c a

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, Pozna´ n University of Life Sciences, Wojska Polskiego 31, 60-624 Pozna´ n, Poland c Australian Centre for Research on Separation Sciences (ACROSS), School of Science and Health, University of Western Sydney (Parramatta), Sydney, NSW, Australia b

a r t i c l e

i n f o

Article history: Received 18 September 2016 Received in revised form 5 February 2017 Accepted 12 February 2017 Keywords: By-products Plum kernel oil Prunus domestica L Prunus cerasifera Ehrh Fatty acid Biodiesel

a b s t r a c t Kernels recovered from fruit pits (industrial by-products) of twenty-eight plum varieties of two species Prunus domestica L. and Prunus cerasifera Ehrh. were studied as potential biodiesel feedstock. The lowest (22.7% (w/w) on dry weight basis (dw)) and the highest (53.2% (w/w) dw) oil yields in the tested varieties differed by almost two-fold. The levels of oleic and linoleic acids, the two dominant fatty acids in plum kernel oils, were significantly (p ≤ 0.05) affected by the variety and ranged between 46.2–70.7% and 22.6–45.3%, respectively. Two significant correlations were found between the oil yield in kernels of different plum varieties of both species and two fatty acids, oleic and linoleic acids. The European biodiesel standards of kinematic viscosity, cetane number, density and iodine value were met for all studied samples. Recorded differences between minimum and maximum value of individual biodiesel parameters obtained for various plum varieties were: 4.7 (cetane number), 0.20 mm2 /s (kinematic viscosity), 0.0022 g/cm3 (density), 0.01 MJ/kg (higher heating value), 2.63 ◦ C (CFPP), 2.61 h (induction period) and 14.7 I2 /100 g (iodine value). The logarithmic regression model in comparison to linear regression model, better expressed the relationship between physicochemical properties of biofuel and the PUFA/(SFA + MUFA) ratio; where PUFA, SFA and MUFA are the sum of polyunsaturated, saturated and monounsaturated fatty acids, respectively. Regardless of the species, P. cerasifera Ehrh. vs. P. domestica L., a similar variation of all study parameters was noted. © 2017 Elsevier B.V. All rights reserved.

1. Introduction Plums (Prunus spp.) are amongst the most popular processed fruits, with the global production in 2013 reaching 11.5 million tons (FAOSTAT, 2016). During processing into dry fruits, jams and juices, tones of fruit pits are generated (agro-industrial by-products). As the world production of plums and the amount of agro-industrial by-products both continue to rise (FAOSTAT, 2016), targeted utilization of fruit pits will benefit to the environment and industry. The plum pits has been considered as liquid (kernel oil) and solid (outer shells) biofuel (Kostic´ et al., 2016), a new and cheap source of bioactive peptides (González-García et al., 2014), active carbons (Nowicki et al., 2010b), and carbonaceous adsorbents (Nowicki et al., 2010a). None of these works took into account the impact

∗ Corresponding author. E-mail address: [email protected] (P. Górna´s). http://dx.doi.org/10.1016/j.indcrop.2017.02.014 0926-6690/© 2017 Elsevier B.V. All rights reserved.

of the plum species and genotype (variety). While, the utility value of the agro-industrial by-products obtained from the processing of stone fruit can vary considerably due to the impact of cultivar on biochemical composition of raw material (Górna´s et al., 2016a, 2016b, 2016c). In the past decade, unconventional oils have gained more attention due to their useful properties in various industries (Górna´s and ´ Rudzinska, 2016; Górna´s et al., 2013). In a number of reports, the oils recovered from fruit seed and kernel by-products have been considered as potential biodiesel feedstock instead of being dis´ carded as industrial waste (Górna´s and Rudzinska, 2016; Gumus and Kasifoglu, 2010; Karmakar et al., 2010; Kostic´ et al., 2016; Rashid et al., 2013). Agro-industrial by-products are a promising feedstock for biodiesel production due to their low costs (Górna´s ´ and Rudzinska, 2016; Kostic´ et al., 2016) and alternative for common oils used in food production e.g. rapeseed oil. However, to reach the economic benefits in the biodiesel production the potential raw material should be rich in oil. The kernels recovered from

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P. Górna´s et al. / Industrial Crops and Products 100 (2017) 77–84

the plum pits are a valuable source of oil which can yield over 50%, although large variations have been reported in different studies (Górna´s et al., 2016b; Kamel and Kakuda, 1992; Kostic´ et al., 2016; Matthäus and Özcan, 2009; Picuric-Jovanovic et al., 1997). Beside the oil yield, the composition of fatty acids in potential feedstock is one of the most important factor that impacts the quality of biodiesel and decision for future production possibilities (Ramos et al., 2009). Plums belong to the genus Prunus with several species, moreover great diversity of cultivars developed and cultivated in different countries can be found; all of which may significantly affect the oil yield and fatty acid composition in the plant material. Thereby, the economic benefit and stable quality of the biofuel obtained from different batch of the plant material must be taken into consideration before utilization as feedstock in biodiesel production, due to the chemical composition diversity of the raw material. Hence, species and variety selection for industrial application becomes a very critical factor. Since in most of the previous studies about plum kernel oils, the impact of variety was not taken into account and is lack information about the P. cerasifera Ehrh. the present studies has been performed. In order to ensure the extensive characterization of the potential application of different plum kernel oil as a biodiesel feedstock, twenty-eight plum samples of two species P. domestica L. and P. cerasifera Ehrh. that originated from different countries were selected and examined for their potential application in the biodiesel industry.

2. Materials and methods 2.1. Reagents All used in this work reagents, except n-hexane (HPLC grade), were of analytical grade received from Sigma-Aldrich (Steinheim, Germany). The fatty acid methyl ester mix was purchased from Supelco (Steinheim, Germany).

2.2. Plant material Twenty-eight plum samples, including seven samples of diploid plums P. cerasifera Ehrh. and its crossbreeds (20651, ‘Alvis’, BPr 7413, ‘Kubanskaya Kometa’, ‘Liesma’, ‘Plamennaya’ and PU 16764) and twenty-one samples of hexaploid species P. domestica L. (1228C, ‘Aˇzenas’, ‘Blue Perdrigon’, ‘Duke of Edinburgh’, ‘Experi¯ ¯ mentalfältets Sviskon’, ‘Greengage’, ‘Karsavas’, ‘Kirke’, ‘Lase’, ‘Lotte’, ‘Suhkruploom’, ‘Minjona’, ‘Mirabelle de Nancy’, ‘Oda’, ‘Renklod Rannij Doneckij’, ‘Renklod Uljanisceva’, ‘Sonora’, ‘Stanley’, ‘Tegera’, ‘Tragedy’ and ‘Victoria’) were collected at full fruit maturity (August–September, 2013) at the Latvia State Institute of FruitGrowing, Dobele, Latvia (GPS location: N: 56◦ 36 39 E: 23◦ 17 50 ). During the variety selection, mainly two criteria were taken into account, present – popularity of the specific cultivar in different countries and future – perspectives of the tested variety from the agronomic and economic point of view. The fruits were harvested from at least three different plum trees for each variety. Detailed information about plant material has been reported previously (Górna´s et al., 2015). The present study was carried out in parallel with published data (Górna´s et al., 2016b); however both experiments were conducted independently of each other and were designated for different application. Briefly, harvested plums of each variety were divided into four nearly identical batches (n = 4), in terms of quantity, and processed separately. After plum processing the fruit pits were recovered manually and crushed using a hammer to remove the kernels. The whole healthy kernels (25 ± 2 g), for each batch (n = 4), were frozen (−18 ◦ C), freeze dried (−51 ± 1 ◦ C, 0.055–0.065 mBar, 48 h) (FreeZone, Labconco,

Kansas City, MO, USA) and milled (KnifetecTM 1095, Foss, Höganäs, Sweden). 2.3. Oil extraction Oil was extracted according to method described by Górna´s et al. (2014). Briefly, 5 g of ground plum kernels were placed in a centrifuge tube, supplemented with 25 mL of n-hexane, mixed for 1 min (Vortex REAX top, Heidolph, Schwabach, Germany) and subsequently subjected to ultrasound treatment (5 min, 35 ◦ C) (Sonorex RK 510 H, Bandelin electronic, Berlin, Germany) and finally centrifuged (5 min, 10000 × g, 21 ◦ C) (Centrifuge 5804 R, Eppendorf, Hamburg, Germany). The supernatant was collected in a round bottom flask and the remaining solid residue was reextracted (twice) as described above. The combined supernatants were vacuum-evaporated until constant weight. The oil yield was expressed in% (w/w) dry weight basis (dw), measured gravimetrically, of kernels. For all study samples, the oil was extracted once for each of the four independent batches of milled kernels (n = 1 × 4). 2.4. Fatty acid determination The fatty acids in plum kernel oils, after their esterification to the fatty acid methyl esters (FAME) according to protocol AOCS (2005) has been determined via gas chromatography (GC). Detailed information about the type of the GC, it configuration and all separation parameters has been reported previously (Górna´s et al., 2016c). For all study samples, the fatty acids were examined once for each of the four independent batches of oil (n = 1 × 4). 2.5. Physicochemical properties of biodiesel All biodiesel properties were calculated empirically using previously developed equations (Park et al., 2008; Ramírez-Verduzco et al., 2012; Ramos et al., 2009; Wang et al., 2012) which were proposed as a low cost and rapid alternative method for preliminary screening of potential biodiesel feedstock, based on the FAME of the sample. 2.5.1. Kinematic viscosity ln(i ) = −12.503 + 2.496 × ln(M i ) − 0.178 × N

(1)

where i is the kinematic viscosity at 40 ◦ C of the ith FAME in mm2 /s, Mi is the molecular weight of the ith FAME and N is the number of double bounds (Ramírez-Verduzco et al., 2012). 2.5.2. Cetane number i = −7.8 + 0.302 × M i − 20 × N

(2)

where i is the cetane number of the ith FAME, Mi is the molecular weight of the ith FAME and N is the number of double bounds (Ramírez-Verduzco et al., 2012). 2.5.3. Higher heating value 1794 ␦i = 46.19 − − 0.21 × N Mi

(3)

where ıi is the higher heating value of the ith FAME in MJ/kg, Mi is the molecular weight of the ith FAME and N is the number of double bounds (Ramírez-Verduzco et al., 2012). 2.5.4. Density ␳i = 0.8463 +

4.9 + 0.0118 × N Mi

(4)

P. Górna´s et al. / Industrial Crops and Products 100 (2017) 77–84

where i is the density at 20 ◦ C of the ith FAME in g/cm3 , Mi is the molecular weight of the ith FAME and N is the number of double bounds (Ramírez-Verduzco et al., 2012). fb =

n 

79

All analyses were performed with the assistance of Statistica 10.0 (StatSoft, Tulsa, OK, USA) software. 3. Results and discussion

Zi × fi

(5) 3.1. Factors impact the oil yield in plum pits

i=1

where f is a function that represents any physical property (the subscripts b and i refer to the biodiesel and the pure ith FAME, respectively), Zi is the mass or mole fraction of the ith FAME. The function fb must be replaced by the variables b , ln(b ), b and ıb in order to specify the cetane number, natural logarithm of kinematic viscosity, density and higher heating value of biodiesel, where as the function fi must be interchanged by the variables i , ln(i ), i and ıi in order to specify the properties of the individual ith FAME (Ramírez-Verduzco et al., 2012). 2.5.5. Iodine value IV = 0.6683 × DU + 25.0364

(6)

DU = (MUFA Cn : 1, wt.%) + 2 × (MUFA Cn : 2, wt.%) + 3 × (MUFA C n : 3, wt.%) + 4 × (MUFA Cn : 4, wt.%)

(7)

where IV is the iodine value, DU is the degree of unsaturation, MUFA Cn :1, MUFA Cn :2, MUFA Cn :3 and MUFA Cn :4 is the amount of monounsaturated and polyunsaturated fatty acids (wt.%), respectively (Wang et al., 2012). 2.5.6. Cold filter plugging point CFPP = 3.1417 × LCSF − 16.477

(8)

LCSF = 0.1 × C16(wt.%) + 0.5 × C18(wt.%) + 1 × C20(wt.%) + 1.5 × C22(wt.%) + 2 × C24(wt.%)

(9)

where CFPP is the cold filter plugging point, LCSF is the long chain saturated factor and C16, C18, C20, C22 and C24 is the amount of long chain saturated fatty acids (wt.%) present in the oil (Ramos et al., 2009). 2.5.7. Induction period (oxidation stability) 117.9295 + 2.5905 Y= X

(10)

where Y is the induction period (h) and X is the content of linoleic and linolenic acids (0 < X < 100) (wt.%) (Park et al., 2008). 2.6. Statistical analysis The results of each experiment are presented as means ± standard deviation from four independent batches of raw material for each variety (n = 1 × 4). The sum of SFA, MUFA and PUFA (%), and fatty acids ratios as well as all biodiesel parameters were calculated based on the mean values of fatty acids and fatty acid methyl esters composition, respectively, for each oil sample and, therefore for those parameters the standard deviation has been not provided. The 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 analysed variables was assessed by Pearson’s correlation coefficient. Its significance was evaluated by Student’s t-test. Linear regression model (y = ax + b) and logarithmic regression model (y = alnx + b) were calculated additionally for the analysis of significant relationships between parameters.

The plum pits, depending on the cultivar, constitute between the 3.2–5.5% (w/w), on average 4.3% (w/w), of fresh fruits (data not shown). For breeders it is not a significant amount and factor of plum cultivation, but from the viewpoint of the processing, while the plum flesh and skin are a main raw material and fruit pits are by-products) already so. Since, the oil is obtained from the kernels recovered from the fruit pits, the percentage between the kernels and plum pits was determined (Table 1). A similar range, the average and standard deviation of kernels amount in fruit pits of different plum varieties between the P. cerasifera Ehrh. and P. domestica L. was found (Table 1). The plum kernels, of both species, constitute between the 11.2–23.8% (w/w) of fresh plum pits. The amount of kernels in different plum pits was significantly related with the variety (p ≤ 0.05). In five cultivars ‘Aˇzenas’, ‘Kubanskaya Kometa’, ‘Plamennaya’, ‘Sonora’ and ‘Suhkruploom’ the kernels constituted ≤ 15% (w/w) of fresh plum pits, while for the other varieties the values were approximately 20 ± 3% (w/w) of fresh fruit pits. On average, taking on account both species, 19.1 ± 3.3% (w/w) of fresh fruit pits were kernels. The oil yield from an economic perspective is a key factor to determine the suitability of potential feedstock for biodiesel production. In line with our previous study (Górna´s et al., 2016b), there was a significant impact of the variety (p ≤ 0.05) on the oil yield in the plum kernels. The recorded difference between the highest and the lowest level of oil was almost two and a half-fold, while the average content of all tested samples was 38.2% (w/w) dw (Table 1). In previous studies, little focus was placed on the impact of the variety on the oil yield of plum kernels, with the exception of a report where three plum cultivars, two P. domestica and one P. spinosa, were investigated (Matthäus and Özcan, 2009). Significant impacts on the oil yield of plum kernels have also been related to the extraction technique (Kostic´ et al., 2016). The reported oil content in plum kernels varies, with amounts of 32% in P. domestica (Hassanein, 1999), 35.8% in P. domestica (Kostic´ et al., 2016), 47.1–47.8% in P. domestica and 53.5% in P. spinosa (Matthäus and Özcan, 2009), similar to the observations of this present study. Due to the large variation of the oil yield in plum kernels, this piece of information must be studied before their consideration as feedstock for biodiesel production. On the assumption, 1333 trees on one hectare (planting spacing 5 × 1.5 m), the average fruit yield from one tree 15 kg, the average percentage weight of plum pits in relation to the fresh fruits 4.3% (w/w), the average water content in fresh kernels 50% (w/w), the average percentage weight of kernels in relation to the plum pits 19.1% (w/w), the average oil yield in dry weight of kernels 38.2% (w/w) will amount 31.4 kg of plum kernel oil. The amount of plum kernel oil that can be obtained from one hectare is rather not relevant for the growers, but for the processing industry, due to the large quantities of fruit pits can bring additional economic benefits and environmental, related with the management of agro-industrial by-products. 3.2. Fatty acid composition Eight and nine fatty acids in the kernel oils of the plum P. cerasifera Ehrh. and P. domestica L. were identified, respectively (Table 1). Regardless of species and varieties, the oleic (C18:1) and linoleic (C18:2) acids were the predominant forms and ranged between 46.2–70.7% and 22.6–45.3%, respectively. In both species,

80 Table 1 Content of kernels in fresh plum pits (%, w/w), oil yield (% (w/w) dw), fatty acid composition (%), sum of SFA, MUFA and PUFA (%), and fatty acids ratios recorded in twenty eight varieties of plum P. cerasifera Ehrh. (n = 7) and P. domestica L. (n = 21). Variety

P. domestica L. 1228C Aˇzenas Blue Perdrigon Duke of Edinburgh Experimentalfältets Sviskon Greengage ¯ Karsavas Kirke ¯ Lase Lotte Minjona Mirabelle de Nancy Oda Renklod Rannij Doneckij Renklod Uljanisceva Stanley Suhkruploom Tegera Tragedy Sonora Victoria Min Max Mean S.D.

20.1 1.5c,d,e,f,g,h 19.0 1.4c,d,e,f,g,h 17.3 1.3b,c,d,e 14.6 1.5a,b 22.3 2.3e,f,g,h 1.3a,b 14.3 1.3h 23.7 14.3 23.7 18.8 3.6

Oil yield (% (w/w) dw)

Fatty acid (%)

C8:0

C16:0

C16:1

47.8 43.6 41.3 28.7 47.8 22.7 53.2 22.6 53.1 40.7 11.1

0.5q 0.4n,o 0.4k,l 0.4d,e 0.4q 0.3a 0.5r

nd nd nd nd nd nd nd 0.0 0.0 0.0 0.0

4.5 0.0c,d 4.2 0.0a 4.4 0.0b 5.8 0.0n 4.3 0.0b 4.9 0.0f 4.6 0.0d 4.2 5.8 4.7 0.5

0.4 0.3 nd 0.6 0.4 0.6 0.5 0.0 0.6 0.4 0.2

0.0b 0.0a 0.0d 0.0b 0.0d 0.0c

C18:0

C18:1

C18:2

␣-C18:3

1.20.0d,e 1.7 0.0j 1.0 0.0b 0.9 0.0a 1.6 0.0i 0.8 0.0a 1.3 0.0f,g 0.8 1.7 1.2 0.3

67.50.4n,o 69.8 0.3q 61.0 0.2i 47.5 0.2b 70.30.3q,r 53.5 0.2f 70.7 0.3r 47.5 70.7 62.9 9.3

25.1 0.4f 23.8 0.3b,c 33.6 0.3l 45.3 0.2q 23.1 0.3a,b 40.1 0.3n 22.6 0.4a 22.6 45.3 30.5 9.2

0.1 0.1 nd nd 0.1 nd 0.1 0.0 0.1 0.0 0.0

23.8 15.5 22.2 22.3 23.6

1.1h 1.7a,b,c 2.5e,f,g,h 1.7e,f,g,h 1.8g,h

35.0 42.0 39.6 38.7 35.4

0.3g,h 0.5l,m 0.5i,j 0.5i 0.5h

nd nd nd 0.50.0d nd

6.3 0.0o 5.6 0.0l 4.8 0.0e 5.3 0.0j,k 4.9 0.0f

1.0 0.0k,l 1.10.0m,n 0.8 0.0f 0.7 0.0e 0.90.0h,i,j

1.3 0.0f,g 2.00.0l,m 1.9 0.0l 1.1 0.0c 1.1 0.0c

54.5 0.2g 66.2 0.2m 68.4 0.2p 50.8 0.2e 63.7 0.3k,l

36.9 0.2m 25.1 0.3f 24.10.2c,d,e 41.5 0.2o 29.3 0.3i

nd nd nd nd nd

17.5 22.8 18.2 19.4 17.1 17.2 22.0 18.0 18.0 19.5 16.6 11.2 22.8 20.0 15.8 21.3 11.2 23.8 19.3 3.2

1.3b,c,d,e,f 1.4f,g,h 2.0b,c,d,e,f,g 2.0c,d,e,f,g,h 1.6b,c,d,e 1.1b,c,d,e 1.2d,e,f,g,h 1.2b,c,d,e,f 1.8b,c,d,e,f 1.4c,d,e,f,g,h 1.5a,b,c,d 1.4a 1.7f,g,h 2.1c,d,e,f,g,h 1.2a,b,c 2.1d,e,f,g,h

44.1 42.8 41.4 39.8 32.3 40.6 41.6 45.7 24.2 46.9 42.5 29.3 33.8 26.3 27.4 35.7 24.2 46.9 37.3 6.5

0.5o 0.5m,n,o 0.5k,l 0.6j 0.4f 0.7j,k 0.5k,l,m 0.5p 0.4b 0.8p,q 0.5l,m,n 0.7e 0.5g 0.6c 0.5c,d 0.5h

0.30.0c nd nd nd nd 0.10.0a nd nd nd nd nd nd nd 0.50.0d 1.30.0e 0.20.0b 0.0 1.3 0.1 0.3

4.5 0.0c 5.2 0.1h,i 4.8 0.0e 4.5 0.0c,d 5.8 0.0n 5.2 0.0h,i 5.2 0.0h,i 5.2 0.0h,i 6.4 0.1o 5.1 0.0g,h 5.4 0.0k 5.6 0.0l,m 7.5 0.0p 5.70.0m,n 5.30.0i,j,k 5.0 0.1f,g 4.5 7.5 5.4 0.7

0.4 0.0b 0.8 0.0f 0.9 0.0g 0.7 0.0e,f 1.10.0m,n 1.0 0.0j,k 1.10.0m,n 0.9 0.0g,h 1.1 0.0n 1.0 0.0j,k,l 1.0 0.0i,j,k 0.90.0g,h,i 1.4 0.0o 0.9 0.0g,h 0.8 0.0f 1.0 0.0l,m 0.4 1.4 0.9 0.2

2.3 0.0n 1.20.0d,e 2.0 0.0m 1.3 0.0f,g 1.40.0g,h 1.9 0.0k,l 1.6 0.0i 1.6 0.0i 1.20.0c,d 1.6 0.0i 1.4 0.0h 1.9 0.0k 1.0 0.0b 1.3 0.0e,f 1.6 0.0i 1.6 0.0i 1.0 2.3 1.5 0.4

68.40.4o,p 63.2 0.2k 67.50.2n,o 67.1 0.3n 59.6 0.3h 64.3 0.3l 62.3 0.2j 65.8 0.3m 46.2 0.2a 67.3 0.2n 61.1 0.3i 51.0 0.3e 49.7 0.2d 48.7 0.3c 54.1 0.3f,g 63.1 0.3j,k 46.2 68.4 60.2 7.4

23.90.4b,c,d 29.3 0.2i 24.80.2d,e,f 26.3 0.2g 32.2 0.3k 27.2 0.3h 29.9 0.3i 26.3 0.3g 45.1 0.3q 25.0 0.2e,f 31.1 0.3j 40.6 0.3n,o 40.4 0.2n 42.6 0.2p 36.2 0.2m 29.1 0.3i 23.9 45.1 31.8 6.9

0.1 0.2 nd nd nd nd nd 0.1 nd nd nd nd nd 0.2 0.3 nd 0.0 0.3 0.1 0.1

0.1 0.3

5.2 0.7

0.8 0.3

1.5 0.4

60.8 7.8

31.4 7.4

0.1 0.1

P. cerasifera Ehrh. and P. domestica L. 19.1 Mean 3.3 S.D.

38.2 7.8

0.0a 0.0a

0.0a 0.0a

0.0a 0.0b

0.0a

0.0b 0.0c

Sum of fatty acids (%)

Fatty acids ratios

C20:0

C20:1

SFA

MUFA

PUFA

UFA/SFA

PUFA/ (SFA + MUFA)

0.10.0a 0.10.0a nd nd 0.10.0a nd 0.10.0a 0.0 0.1 0.1 0.1

0.90.0c nd nd nd nd nd 0.10.0a 0.0 0.9 0.1 0.3

5.9 6.0 5.4 6.6 6.1 5.8 6.1 5.4 6.6 6.0 0.4

68.9 70.1 61.0 48.1 70.7 54.1 71.3 48.1 71.3 63.5 9.3

25.2 23.9 33.6 45.3 23.2 40.1 22.6 22.6 45.3 30.6 9.2

16.0 15.6 17.6 14.1 15.5 16.4 15.5 14.1 17.6 15.8 1.1

0.3 0.3 0.5 0.8 0.3 0.7 0.3 0.3 0.8 0.5 0.2

nd nd nd nd nd

nd nd nd nd nd

7.6 7.6 6.7 7.0 6.1

55.5 67.3 69.2 51.5 64.7

36.9 25.1 24.1 41.5 29.3

12.2 12.1 13.9 13.4 15.5

0.6 0.3 0.3 0.7 0.4

0.20.0b 0.10.0a nd nd nd nd nd nd nd nd nd nd nd nd 0.20.0b nd 0.0 0.2 0.0 0.1

0.10.0a 0.10.0a nd nd nd nd nd nd nd nd nd nd nd 0.20.0b 0.20.0b nd 0.0 0.2 0.0 0.1

7.2 6.5 6.8 5.9 7.1 7.3 6.8 6.8 7.5 6.8 6.8 7.5 8.5 7.5 8.4 6.8 5.9 8.5 7.1 0.6

68.8 64.1 68.4 67.9 60.7 65.3 63.3 66.7 47.3 68.3 62.1 51.9 51.2 49.7 55.1 64.1 47.3 69.2 61.1 7.3

24.0 29.4 24.8 26.3 32.2 27.4 29.9 26.5 45.1 25.0 31.1 40.6 40.4 42.8 36.5 29.1 24.0 45.1 31.8 6.9

13.0 14.4 13.6 16.0 13.0 12.7 13.7 13.7 12.3 13.8 13.7 12.3 10.8 12.3 10.9 13.7 10.8 16.0 13.2 1.3

0.3 0.4 0.3 0.4 0.5 0.4 0.4 0.4 0.8 0.3 0.5 0.7 0.7 0.7 0.6 0.4 0.3 0.8 0.5 0.2

0.0 0.1

0.1 0.2

6.8 0.8

61.7 7.7

31.5 7.4

13.8 1.7

0.5 0.2

Italic values correspond to standard deviations of independent analyses from four batches of each sample (n = 1 × 4). Different letters in the same column indicate statistically significant differences at p < 0.05. SFA, sum of saturated fatty acids; MUFA, sum of monounsaturated fatty acids; PUFA, sum of polyunsaturated fatty acids; UFA, sum of unsaturated fatty acids. SFA, MUFA, PUFA, UFA were calculated based on the mean values of fatty acids composition for each oil sample (n = 28).

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P. cerasifera Ehrh. 20651 Alvis BPr 7413 Kubanskaya Kometa Liesma Plamennaya PU 16764 Min Max Mean S.D.

Content of kernels in fresh plum pits (%, w/w)

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Fig. 1. A correlation between oil yield in kernels of twenty eight plum varieties (% (w/w) dw) and content of oleic acid (%) and linoleic acid (%) in these oils, based on the: P. cerasifera Ehrh. including its crossbreeds (n = 7) (A and B); P. domestica L. (n = 21) (C and D); combined (n = 28) (E and F), respectively.

similar variation of C18:1 and C18:2 levels has been observed with the average amount 62.9 and 30.5%, and 60.2 and 31.8% in P. cerasifera Ehrh. and P. domestica L., respectively. With the exception of two cultivars ‘Kubanskaya Kometa’ and ‘Renklod Rannij Doneckij’ where oleic and linoleic acids were nearly identical, the oleic acid consisted of over 49% of the total fatty acids, and over 60% was observed for almost 70% of samples. Approximately tenfold lower content of palmitic acid (C16:0) (4.2–7.5%) in relation to C18:1 in plum kernel oils was recorded. Several fold lower amount of palmitoleic (C16:1) (0.0–1.4%) and stearic (C18:0) (0.8–2.3%) acids in relation to C16:0 was noted. The caprylic acid (C8:0), alphalinolenic acid (␣-C18:3), eicosanoic acid (C20:0) and eicosenoic acid (C20:1) were found only in few samples in low amounts (0.1–1.3%). The C8:0 was not identified in any of the P. cerasifera Ehrh. samples. The levels of individual fatty acids in the tested oils were significantly (p ≤ 0.05) affected by the variety (Table 1). The oleic and linoleic acids have been reported previously as predominant fatty acids of plum (P. domestica L. and P. spinosa L.) kernel oils (Kamel and Kakuda, 1992; Kostic´ et al., 2016; Matthäus and Özcan, 2009; Picuric-Jovanovic et al., 1997), however in previous reports the impact of the variety was not tested, with exception of study conducted by Matthäus and Özcan (2009) where two cultivars of species P. domestica L. were tested. In all previous studies on plum P. domestica L. kernel oils, the oleic acid was a predominant fatty acid and constituted over 60% of the total detected fatty acids. While, in P. spinosa L., similar levels of oleic and linoleic acids were reported (Matthäus and Özcan, 2009). For the first time, this study investigated the composition of the fatty acids of seven diploid plums P. cerasifera Ehrh. and its crossbreeds. Regardless of species, similar variation of the fatty acid composition in the plum kernel oils was observed, thus emphasizing the importance of variety. The significant impact of the cultivar on the composition of the fatty acids in different fruit (sweet and sour cherry) kernel

oils has been reported previously (Górna´s et al., 2016a, 2016c). Monounsaturated fatty acids dominated in kernel oils recovered from different plum varieties (61.7%) followed by polyunsaturated fatty acids (31.5%) and the lowest levels were noted for the saturated fatty acids (6.8%). The ratios of fatty acids UFA/SFA and PUFA/(SFA + MUFA) in plum kernel oils were in the range of 10.8–17.6 and 0.3–0.8, respectively (Table 1). As was suggested previously, a PUFA/(SFA + MUFA) ratio of ≤ 1 may indicate a feedstock characterized by favorable properties of biodiesel, however the saturation level of the fatty acids as well as their length need to be taken into account due to the critical impact on the ´ CFPP value of potential biodiesel feedstock (Górna´s and Rudzinska, 2016). 3.3. Oil yield vs. fatty acid composition Significant correlations between oil yield in kernels of different plum varieties of both species and two fatty acids, oleic and linoleic, were found. Positive correlations for oleic acid (r = 0.906, p < 4.9 × 10−03 ; r = 0.813, p < 7.6 × 10−06 and r = 0.844, p < 1.6 × 10−08 ) (Fig. 1A,C,E) and a negative for linoleic acid (r = −0.912, p < 4.3 × 10−03 ; r = −0.806, p < 1.0 × 10−05 and r = −0.839, p < 2.4 × 10−08 ) (Fig. 1B,D,F) were found for samples of P. cerasifera Ehrh., P. domestica L. and both species together, respectively. Similar correlations between oil content and levels of oleic and ␣-linolenic acids have been reported in seeds of various dessert and crab apple cultivars (Górna´s et al., 2014). This relationship demonstrated that with increasing oil yield in plum kernels, a higher content of oleic acid and lower levels of linoleic acid can be expected. Hence, plum kernels characterised by high oil yield may be considered for future application in biodiesel production, not only due to the oil content, but also due to the high levels of oleic acid, which have better biodiesel properties

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Table 2 Physicochemical properties of biodiesel from kernel oils of twenty eight varieties of plum P. cerasifera Ehrh. (n = 7) and P. domestica L. (n = 21). Cetane number

Kinematic viscosity at 40 ◦ C (mm2 /s)

Density at 20 ◦ C (g/cm3 )

Higher heating value (MJ/kg)

Cold filter plugging point (◦ C)

Induction period (h)

Iodine value

P. cerasifera Ehrh. 20651 Alvis BPr 7413 Kubanskaya Kometa Liesma Plamennaya PU 16764 Min Max Mean S.D.

57.4 57.7 55.6 53.2 57.8 54.2 57.9 53.2 57.9 56.2 1.9

4.41 4.41 4.33 4.22 4.42 4.26 4.42 4.22 4.42 4.35 0.08

0.8770 0.8768 0.8781 0.8793 0.8768 0.8788 0.8767 0.8767 0.8793 0.8776 0.0011

39.85 39.86 39.83 39.79 39.86 39.81 39.86 39.79 39.86 39.84 0.03

−12.73 −12.02 −13.51 −13.31 −12.21 −13.65 −12.55 −13.65 −12.02 −12.85 0.64

7.26 7.52 6.10 5.19 7.67 5.53 7.80 5.19 7.80 6.73 1.09

104.9 103.9 110.7 117.7 103.4 114.8 103.0 103.0 117.7 108.3 6.1

P. domestica L. 1228C Aˇzenas Blue Perdrigon Duke of Edinburgh Experimentalfältets Sviskon Greengage ¯ Karsavas Kirke ¯ Lase Lotte Minjona Mirabelle de Nancy Oda Renklod Rannij Doneckij Renklod Uljanisceva Stanley Suhkruploom Tegera Tragedy Sonora Victoria Min Max Mean S.D.

55.1 57.6 57.7 53.9 56.5 57.7 56.5 57.6 57.1 56.0 57.0 56.5 57.1 53.4 57.5 56.2 54.4 54.4 53.7 54.9 56.6 53.4 57.7 56.1 1.4

4.29 4.39 4.40 4.24 4.35 4.41 4.36 4.40 4.38 4.33 4.37 4.35 4.38 4.22 4.39 4.34 4.27 4.25 4.23 4.26 4.35 4.22 4.41 4.33 0.06

0.8782 0.8768 0.8768 0.8789 0.8775 0.8768 0.8775 0.8769 0.8771 0.8777 0.8772 0.8775 0.8771 0.8792 0.8769 0.8776 0.8787 0.8786 0.8790 0.8783 0.8774 0.8771 0.8792 0.8777 0.0008

39.81 39.84 39.85 39.78 39.83 39.84 39.84 39.85 39.85 39.82 39.83 39.83 39.84 39.79 39.85 39.83 39.81 39.79 39.77 39.75 39.83 39.85 39.85 39.82 0.03

−12.43 −11.57 −11.93 −13.03 −13.15 −11.02 −12.56 −11.76 −12.94 −12.52 −11.80 −12.36 −12.34 −12.62 −12.32 −12.54 −11.78 −12.61 −12.67 −11.58 −12.36 −13.15 −11.02 −12.28 0.54

5.79 7.29 7.49 5.43 6.62 7.50 6.60 7.35 7.08 6.26 6.89 6.54 7.05 5.20 7.32 6.38 5.49 5.51 5.35 5.82 6.64 5.20 7.50 6.46 0.77

111.5 103.5 103.5 115.0 107.4 103.2 107.3 103.8 105.5 108.6 105.4 107.3 105.1 117.0 104.0 108.1 114.0 113.2 115.6 110.9 106.8 103.2 117.0 108.4 4.4

4.34 0.07

0.8777 0.0009

39.82 0.03

−12.42 0.61

6.52 0.85

108.4 4.7

Variety

P. cerasifera Ehrh. and P. domestica L. Mean 56.1 S.D. 1.5

Values provided in table above were calculated empirically based on the mean values of fatty acid methyl esters determined for each oil sample (n = 28) listed in Table 1.

relative to linoleic acid (Ramos et al., 2009). These associations may provide a preliminary estimation of the oleic and linoleic acid content in plum kernels based upon the known oil yield. Moreover, the positive correlation found between oil yield and oleic acid regardless of the variety, may be applied as a first indicator of the plum kernel sample’s quality as a biodiesel feedstock candidate. 3.4. Biodiesel properties European biofuel standards are more restrictive in comparison with U.S. standards, and in accordance to good biodiesel quality, they should be characterized by the parameters such as: kinematic viscosity at 40 ◦ C between 3.5 and 5.0 mm2 /s, cetane number 51 and above, density at 20 ◦ C between 860 and 900 kg/m3 , iodine value below 120 g I2 /100 g and induction period (oxidation stability) at 110 ◦ C at least 6 h (Hoekman et al., 2012). The European biofuel standards of cetane number (53.2–57.9), kinematic viscosity (4.22–4.42 mm2 /s at 40 ◦ C), density (0.8771–0.8793 g/cm3 at 20 ◦ C) and iodine value (103.0–117.7) were met by all tested samples (Table 2). Similar values of kinematic viscosity, density and iodine values to those obtained in the present study, have been reported also for a plum (P. domestica L.) kernel oil recovered from the fruit stones generated by the local food processing factory in Serbia (data obtained experimentally) (Kostic´ et al., 2016).

The induction period above 6 h was reached by almost 70% of all tested samples, while 30% had values that ranged from 5.2–5.8 h. ´ Nevertheless, as previously reported by Górna´s and Rudzinska (2016), a large discrepancy was found between the values of experimental and calculated induction period values, probably due to the impact of natural antioxidants e.g. carotenoids and tocochromanols present in the oils, which were not taken into account during the theoretical calculation of induction period. Plum kernel oils are rich in tocochromanols and carotenoids (Górna´s et al., 2016b), therefore the actual induction periods may be higher than values calculated in the present study, based on the previously proposed equation. European standards for biodiesel define maximum levels of the linolenic acid methyl ester and polyunsaturated fatty acid methyl esters with four double bonds, which are set at the level of 12 and 1%, respectively. Lack of fatty acid methyl esters with four double bonds and 0.0-0.3% of linolenic acid methyl ester were detected in the tested samples. Neither the U.S. nor European biofuel standards define a specification for the heating value (MJ/kg) due to expected lower mass energy content for the biodiesel (about 10%) compared to petroleum diesel, and the cold filter plugging point (CFPP) (◦ C) due to considerable seasonal, as well as geographic temperature variability. Nonetheless, the CFPP is a very important parameter (Hoekman et al., 2012). All investigated samples had very

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Table 3 A correlation between physicochemical properties of biodiesel and the PUFA/(SFA + MUFA) ratio from studied kernel oils of twenty eight varieties (n = 28) of plum P. cerasifera Ehrh. (n = 7) and P. domestica L. (n = 21). PUFA/(SFA + MUFA) ratio of plum kernel oils (n = 28)

Cetane number*

Kinematic viscosity at 40 ◦ C (mm2 /s)*

Denisity at 20 ◦ C (g/cm3 )*

Heating value (MJ/kg)*

Cold filter plugging point (◦ C)*

Induction period (h)*

Iodine value*

Correlation coefficient** Indicate significance (p-value)** Correlation coefficient*** Indicate significance (p-value)***

0.994 3.1 × 10−26 0.998 2.9 × 10−32

0.985 1.7 × 10−21 0.993 7.1 × 10−26

0.993 5.5 × 10−26 0.996 2.6 × 10−29

0.882 5.5 × 10−10 0.897 1.0 × 10−10

0.431 2.2 × 10−2 0.445 1.8 × 10−2

0.969 3.1 × 10−17 0.992 5.9 × 10−25

0.993 2.8 × 10−25 0.994 9.7 × 10−27

* Values provided in table above were determined based on the values of PUFA/(SFA + MUFA) ratio and specific biodiesel parameter for each oil sample (n = 28) listed in Tables 1 and 2. ** Linear regression model. *** Logarithmical regression model.

similar values of CFPP ((−13.65)–(−11.02)) and heating value (39.75–39.86) (Table 2). The recorded differences between minimum and maximum value of individual biodiesel parameters obtained for various plum varieties were not substantial in most cases and were as follows 4.7 (cetane number), 0.20 (kinematic viscosity), 0.0022 (density), 0.01 (higher heating value), 2.63 (CFPP), 2.61 (induction period) and 14.7 (iodine value). Regardless of the species, P. cerasifera Ehrh. vs. P. domestica L., a similar variation of value for individual biodiesel parameters was found. Relatively low differences between minimum and maximum value of tested biodiesel parameters obtained for different plum varieties allow concluding that regardless of cultivar all plum kernel oils can be considered as a valuable feedstocks for biodisel production. Similar observation has been reported in 17 germplasm accessions of Siberian apricot (Prunus sibirica L.) (Wang, 2012). 3.5. Physicochemical properties of biodiesel vs. the PUFA/(SFA + MUFA) ratio Based upon the results obtained from the seed oils of nine fruit species, the PUFA/(SFA + MUFA) ratio may be applied for rapid preliminary screening of potential biofuel feedstock due to significant correlation with biodiesel properties such as cetane number, kinematic viscosity, oxidation stability, iodine value and heating ´ value (Górna´s and Rudzinska, 2016). Similar results were observed in the present study, however, greater values of the correlation coefficient between physicochemical properties of biodiesel and the PUFA/(SFA + MUFA) ratio were recorded via logarithmic regression model rather than fitting to a linear regression model (Table 3). Therefore, the logarithmic regression model should be applied in future investigations to estimate more accurately the physicochemical properties of biodiesel feedstock. No correlations we found for the CFPP value, which was also the case for previ´ ous study (Górna´s and Rudzinska, 2016). This observation is not surprising, since it has been reported that the CFPP value is not correlated with the amount of the individual unsaturated fatty acid in tested sample (Park et al., 2008). 4. Conclusion The plum variety has shown to be a crucial factor affecting the kernels amount in fruit pits, oil yield in kernels and the fatty acids composition of the kernel oils consequently economic profit and the quality of biodiesel. Regardless of the species, P. cerasifera Ehrh. vs. P. domestica L., a similar variation of all study parameters was noted. All tested samples met the European specification for biodiesel in terms of cetane number, kinematic viscosity, density, iodine value and almost 70% of tested samples met the requirements of induction period. The logarithmic regression model perfectly reflects the relationship between the

PUFA/(SFA + MUFA) ratio and physicochemical properties of biodiesel, with the exception of CFPP value. Such relationships may further serve as rapid screening of the biodiesel properties of the potential feedstock. Acknowledgment ¯ ıte for her assisI would like to kindly acknowledge Dr. Ilze Grav¯ tance. References AOCS, 2005. Official Method Ce 1h-05 determination of cis-, trans-, saturated, monounsaturated and polyunsaturated fatty acids in vegetable or non-ruminant animal oils and fats by capillary GLC. In: Official Methods and Recommended Practices of the American Oil Chemists’ Society, 5th ed. American Oil Chemists’ Society, USA. FAOSTAT, 2016. FAO Statistical Database, http://faostat3.fao.org. (Accessed 14 July 2016). ´ Górna´s, P., Rudzinska, M., 2016. Seeds recovered from industry by-products of nine fruit species with a high potential utility as a source of unconventional oil for biodiesel and cosmetic and pharmaceutical sectors. Ind. Crops Prod. 83, 329–338. Górna´s, P., Siger, A., Seglin¸a, D., 2013. Physicochemical characteristics of the cold-pressed Japanese quince seed oil: new promising unconventional bio-oil from by-products for the pharmaceutical and cosmetic industry. Ind. Crops Prod. 48, 178–182. ´ Górna´s, P., Rudzinska, M., Seglin¸a, D., 2014. Lipophilic composition of eleven apple seed oils: a promising source of unconventional oil from industry by-products. Ind. Crops Prod. 60, 86–91. ¯ ıte, I., Lacis, ¯ Górna´s, P., Miˇsina, I., Grav¯ G., Radenkovs, V., Olˇsteine, A., Seglin¸a, D., Kaufmane, E., Rubauskis, E., 2015. Composition of tocochromanols in the kernels recovered from plum pits: the impact of the varieties and species on the potential utility value for industrial application. Eur. Food Res. Technol. 241, 513–520. Górna´s, P., Rudzinska, M., Raczyk, M., Miˇsina, I., Seglina, D., 2016a. Impact of cultivar on profile and concentration of lipophilic bioactive compounds in kernel oils recovered from sweet cherry (Prunus avium L.) by-products. Plant Foods Hum. Nutr. 71, 158–164. ¯ Górna´s, P., Rudzinska, M., Raczyk, M., Miˇsina, I., Soliven, A., Lacis, G., Seglina, D., 2016b. Impact of species and variety on concentrations of minor lipophilic bioactive compounds in oils recovered from plum kernels. J. Agric. Food Chem. 64, 898–905. ´ Górna´s, P., Rudzinska, M., Raczyk, M., Miˇsina, I., Soliven, A., Seglin¸a, D., 2016c. Composition of bioactive compounds in kernel oils recovered from sour cherry (Prunus cerasus L.) by-products: impact of the cultivar on potential applications. Ind. Crops Prod. 82, 44–50. González-García, E., Marina, M.L., García, M.C., 2014. Plum (Prunus domestica L.) by-product as a new and cheap source of bioactive peptides: extraction method and peptides characterization. J. Funct. Foods 11, 428–437. Gumus, M., Kasifoglu, S., 2010. Performance and emission evaluation of a compression ignition engine using a biodiesel (apricot seed kernel oil methyl ester) and its blends with diesel fuel. Biomass Bioenergy 34, 134–139. Hassanein, M.M.M., 1999. Studies on non-traditional oils: l. Detailed studies on different lipid profiles of some Rosaceae kernel oils. Grasas Aceites 50, 379–384. Hoekman, S.K., Broch, A., Robbins, C., Ceniceros, E., Natarajan, M., 2012. Review of biodiesel composition, properties, and specifications. Renew. Sustain. Energy Rev. 16, 143–169. Kamel, B.S., Kakuda, Y., 1992. Characterization of the seed oil and meal from apricot, cherry, nectarine, peach and plum. J. Am. Oil Chem. Soc. 69, 492–494. Karmakar, A., Karmakar, S., Mukherjee, S., 2010. Properties of various plants and animals feedstocks for biodiesel production. Bioresour. Technol. 101, 7201–7210.

84

P. Górna´s et al. / Industrial Crops and Products 100 (2017) 77–84

´ M.D., Veliˇckovic, ´ A.V., Jokovic, ´ N.M., Stamenkovic, ´ O.S., Veljkovic, ´ V.B., 2016. Kostic, Optimization and kinetic modeling of esterification of the oil obtained from waste plum stones as a pretreatment step in biodiesel production. Waste Manag. 48, 619–629. Matthäus, B., Özcan, M.M., 2009. Fatty acids and tocopherol contents of some Prunus spp. kernel oils. J. Food Lipids 16, 187–199. Nowicki, P., Skrzypczak, M., Pietrzak, R., 2010a. Effect of activation method on the physicochemical properties and NO2 removal abilities of sorbents obtained from plum stones (Prunus domestica). Chem. Eng. J. 162, 723–729. Nowicki, P., Wachowska, H., Pietrzak, R., 2010b. Active carbons prepared by chemical activation of plum stones and their application in removal of NO2 . J. Hazard. Mater. 181, 1088–1094. Park, J.-Y., Kim, D.-K., Lee, J.-P., Park, S.-C., Kim, Y.-J., Lee, J.-S., 2008. Blending effects of biodiesels on oxidation stability and low temperature flow properties. Bioresour. Technol. 99, 1196–1203. Picuric-Jovanovic, K., Vrbaski, Z., Milovanovic, M., 1997. Aqueous-enzymatic extraction of plum kernel oil. Lipid/Fett 99, 433–435.

Ramírez-Verduzco, L.F., Rodríguez-Rodríguez, J.E., del Rayo Jaramillo-Jacob, A., 2012. Predicting cetane number, kinematic viscosity, density and higher heating value of biodiesel from its fatty acid methyl ester composition. Fuel 91, 102–111. Ramos, M.J., Fernández, C.M., Casas, A., Rodríguez, L., Pérez, Á., 2009. Influence of fatty acid composition of raw materials on biodiesel properties. Bioresour. Technol. 100, 261–268. Rashid, U., Ibrahim, M., Yasin, S., Yunus, R., Taufiq-Yap, Y.H., Knothe, G., 2013. Biodiesel from Citrus reticulata (mandarin orange) seed oil, a potential non-food feedstock. Ind. Crops Prod. 45, 355–359. Wang, L.-B., Yu, H.-Y., He, X.-H., Liu, R.-Y., 2012. Influence of fatty acid composition of woody biodiesel plants on the fuel properties. J. Fuel Chem. Technol. 40, 397–404. Wang, L., 2012. Evaluation of Siberian apricot (Prunus sibirica L.) germplasm variability for biodiesel properties. J. Am. Oil Chem. Soc. 89, 1743–1747.