No abstract

This study is concerned with the effect of the process of roasting of naked pumpkin seeds prior to their pressing on the chemical composition and oxidative stability of the extracted oil. Ground seeds were roasted at temperatures of 90, 110, and 130°C for 30 and 60 min, according to the traditional technology of production of roasted pumpkin oil. Depending on the roasting conditions of the seeds, this treatment resulted in a significant increase of the contents of phospholipids (from 0.005 to 0.463%), total phenolic compounds (from 4.63 to 19.60 mg/kg), and total tocopherols (from 265.79 to 350.98 mg/kg) in oil. Higher contents of these minor components enhanced the oxidative stability of the oil, i.e., increased the induction period (from 4.50 to 12.93 h). However, at the same time, the applied thermal treatment generated an increase in the primary and secondary oxidation products, resulting in higher Totox values that could lower the quality of the oil.

Hemp seed oil press-cake as a by-product of cold-pressed oil processing and brown rice flour were used to design a functional gluten-free snack-type product-savory crackers. All crackers were high in minerals, fibers, and omega-3 fatty acids with a desirable omega-6/omega-3 fatty acids ratio. Green tea leaves were added to improve antioxidant activity, which greatly contributed to their functional properties. This qualified the crackers as a healthy snack with a minimal content saturated fatty acids and an abundance of polyunsaturated and monounsaturated fatty acids that originated from chia seeds residual oil present in the hemp flour.

The production of cold-pressed oil from nonroasted naked pumpkin seeds by pressing with screw presses started in the Republic of Serbia at the end of 1990s. This oil has the characteristic flavour of raw-dried seeds, and is a specific product of this region. The oil samples were prepared by pressing naked pumpkin seeds and pumpkin seeds with the hulls in a 3:2 ratio using a screw press. The changes of the oil sensory characteristics, basic chemical quality and oxidative stability were followed over a 2-year period. The results obtained showed that the oil sensory quality was stable during the first 12 months of storage, after which the flavour became musty. Although the chemical quality of the oil deteriorated to some extent, both the acid and peroxide values satisfied the legislative minimum during the whole investigation time. The oxidative stability of oil determined by a Rancimat apparatus was good, although the induction period after 2 years decreased by 25-40%. To ensure the use of only the highest quality oil, a 12-month shelf life is recommended.

Prolonged storage of frozen berries had some impact on the quality of the oils compared to the fresh sample. Free fatty acid content (FFA) and peroxide values (PV) increased in blackberry oil (BO) (from 1.18 to 3.54% oleic acid) and in raspberry oil (RO) (from 2.66 to 8.84% oleic acid). PV values were higher in the RO (increased from 4.82 to 13.97 mmol/kg) than in the BO (increased from 3.73 to 11.14 mmol/kg). Both oils were very high in omega‐6 FA (%): 63.66 ± 0.49 for BO and 54.94 ± 0.18 for RO, and omega‐3 FA (%): 14.77 ± 0.42 for BO and 32.38 ± 0.38 for RO, with their ratio of 1.8 and 4.5. Both oils have shown a very high level of α, β + γ, and δ‐tocopherols. Much higher levels of campesterols and stigmasterols were found in the BO, while the content of β‐sitosterols was much higher in the RO. Total phenolic content was much higher in the BO (∼27%). Our results demonstrated that pomace, despite longterm frozen storage, is a good raw material for oil extraction, as its oil composition remains stable. Chemical characteristics suggested that oils are of high quality and a possible source of functional ingredients. Practical applications: Pomace is a fruit processing waste, which is currently underutilized, and not used much for food production. Blackberry and raspberry seed pomaces that mostly consist of seeds are generated in large quantities. Both seed oils are of high quality and rich in essential omega fatty acids and very high content of bioactive compounds such as tocopherols, phenols, sterols, and carotenoids that have antioxidant properties. Due to their nutritional and antioxidant properties they are considered value‐added products that can be successfully used for functional and nutraceutical food products. The oils have high levels of oleic, omega‐6, and omega‐3 fatty acids and bioactive compounds including tocopherols, phenols, sterols, and carotenoids. Based on the research results, prolonged storage (8 months) of frozen blackberries and raspberries in sealed plastic bags at −18°C before further processing and use of the pomace as a by‐product can be recommended to the food industry.