COLD PRESSING, AMYGDALIN REMOVAL AND CLOSED-CYCLE VALORISATION OF STONE FRUIT KERNEL OILS: A MASS-BALANCE ASSESSMENT
- Authors
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Z.Z. Nematov
Navoi State University of Mining and Technologies, Navoi, Uzbekistan
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- Keywords:
- stone fruit kernel oil cold pressing amygdalin cyanogenic glycoside ethanolic extraction press cake valorisation mass balance waste-free processing
- Abstract
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Stone fruit processing in Uzbekistan generates a large kernel stream that is currently burnt or landfilled, although the kernel contains oil at a level comparable with conventional oilseeds. Three recovery routes petroleum-fraction extraction, hot pressing and cold pressing were compared on six kernel feedstocks, the sanitary and ecotoxicological status of the cold-pressed oils was evaluated, and a water-free route for removing amygdalin with closed-loop recovery of the extractant is reported. Extraction gave the highest yields (40.1–48.2 %), but cold pressing retained on average 77.7 % of the extraction yield while eliminating solvent residues and volatile organic emissions. The 22.3 % apparent shortfall is not a loss: it is recovered in the press cake, so that about 101 kg of oil per 1000 kg of kernel is exchanged for roughly 91 kg of additional cake. Amygdalin ranged from 0.0936 mg/kg in plum to 0.430 mg/kg in peach, a 4.6-fold spread across species grown on the same soils, and reached 0.761 mg/kg in the almond group, 1.52 times the 0.5 mg/kg limit. Toxic metals occupied 0.2–24.5 % of their permitted maxima, aerobic counts stayed below 10 CFU/g, and all indicators remained within specification over two years of ambient storage. Ethanolic extraction (96 % ethanol, oil : ethanol 1:1 v/v, 30–40 °C, 40 min) recovered amygdalin as a crystalline solid and returned the ethanol to the cycle. The mass balance on 1000 kg of dry kernel closes with 335 kg of purified oil, 655 kg of cake and 0.5 kg of amygdalin, 99.05 % of the feedstock entering a marketable or secondary stream. Because amygdalin content is species-determined rather than site-determined, targeting the purification step by species is proposed as the governing design principle.
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