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

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), 2.63ᵒC (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.