Blackberry (Rubus fruticosus L.) and raspberry (Rubus idaeus L.) seed oils extracted from dried press pomace after longterm frozen storage of berries can be used as functional food ingredients

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Abstract

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.

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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.

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