Abstract
Uniaxial loading and organic solvent are small-scale oil expression methods used to evaluate the mechanical behavior, oil content, and oil efficiency of oil-bearing materials aimed at designing a low-cost mechanical pressing system. Bulk kernels of pressing height 40 mm were heated from 40 to 60 °C and compressed at maximum force of 60 kN and speeds from 4 to 8 mm/min. Relaxation times between 3 and 12 min were applied to assess the kernel oil efficiency. The kernel oil point was identified at deformation levels between 15 and 25 mm at a speed of 4 mm/min using a litmus test. The kernel oil was analyzed for peroxide value and free fatty acid. Kernel oil content was determined by Soxhlet extraction. Increased speed caused a serration effect on the force–deformation curve leading to lower oil yield. Lower and upper oil point forces at 6.21 ± 0.58 and 10.61 ± 0.71 kN were observed to be useful for predicting the pressure for maximum output oil. The peroxide value and free fatty acid content of kernel oil decreased with increasing temperature, indicating its quality usage. The relaxation time of 12 min after compression increased kernel oil efficiency of 15.6%. In designing new presses, there is a need to consider compression and relaxation processes to reduce the residual kernel cake oil.
Highlights
Hazelnut (Corylus avellana L.) is a fruit consisting of a hard shell with a kernel inside it that is edible [1]
The effects of speed, temperature, and relaxation time on deformation, oil yield, oil expression efficiency, and energy of hazelnut kernels are presented in Tables 1–3, respectively
For a pressing vessel of diameter 60 mm and sample pressing height of 40 mm, kernel oil efficiency was achieved at a maximum force of 60 kN and speed of 4 mm/min
Summary
Hazelnut (Corylus avellana L.) is a fruit consisting of a hard shell with a kernel inside it that is edible [1]. The edible kernel is covered by a removable thin fibrous pellicle, with the internal tissue of the cotyledons consisting of parenchyma cells separated by very small intercellular spaces [2,3]. The tree crop belongs to the family Betulaceae and is grown in the Mediterranean Sea regions, mainly in Turkey, Spain, and Italy [4,5]. Turkey is the main producer and exporter with 420,000 tons/year (contributing around 70% of the total global production), followed by Italy with 120,572 tons/year, while Spain produces approximately 15,300 tons/year [6,7,8]. Hazelnuts are rich in antioxidant compounds such as tocopherols and polyphenols, unsaturated fatty acids, flavan-3-ols (flavanols) and proanthocyanidins, essential amino acids, dietary fibers, vitamins (E and B), and complex and essential minerals (Ca, Mg, P, K), which have a wide range of Processes 2020, 8, 957; doi:10.3390/pr8080957 www.mdpi.com/journal/processes
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