Physicochemical and quality characteristics of cold-pressed hemp, flax and canola seed oils and functional properties of their seed cakes

by Sue-Siang Teh

Institution: University of Otago
Year: 0
Keywords: Cold-pressed; plant; fats; oils; hemp; canola; flax; polyphenols; microwave; PEF; ultrasonic; HPTLC; antioxidant; ACE-inhibitory-activity; protein-isolate; enzymatic-hydrolysis; proteases; protein-hydrolysates; peptides
Record ID: 1297879
Full text PDF: http://hdl.handle.net/10523/5670


New Zealand cold-pressed hemp, flax and canola seed oils were analyzed for their fatty acid compositions, tocopherols, β-carotene, chlorophyll, total phenolics, flavonoids, color, quality, melting and crystallization characteristics. The dominant fatty acid of canola, hemp and flax seed oils was oleic (57.0 ± 0.0%), linoleic (55.7 ± 0.3%) and linolenic acids (58.7 ± 1.2%), respectively (P < 0.05). Hemp seed oil contained the highest tocopherol, flavonoid and phenolic acid contents. There was a significant difference in color of the oils (P < 0.05) due to the chlorophyll content. Melting and crystallization transitions and enthalpy heat change (∆H) values varied for the three oils in the order canola > flax > hemp. All oils had low moisture and volatiles, unsaponifiable matter and free fatty acids content. Peroxide value, p-anisidine, conjugated dienoic acid, acid value, specific extinction of cold-pressed oils at 232 and 270 nm were under the value of limit allowed in general regulations. Defatted hemp, flax and canola seed cakes were extracted with different solvent systems namely methanol, ethanol, acetone, methanol 80%, acetone 80% and mixed solvent of methanol:acetone:water (MAW, 7:7:6, v/v/v). Each extract was analyzed for antioxidant capacity using ferric reducing/antioxidant power (FRAP) and 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assays. MAW exhibited the highest extraction of phenolic and flavonoid contents in the seed cakes, followed by acetone 80% and methanol 80%. The antioxidant capacity was proportional to the polyphenols recovery in the extracts. Canola seed cakes possessed the highest recovery of polyphenols and antioxidant capacity, followed by hemp and flax seed cakes. MAW extract of canola contained total phenolic content of 2104.67 ± 2.52 mg GAE/100 g fresh weight; total flavonoids of 37.79 ± 0.04 mg LUE.100 g-1 fresh weight; percentage inhibition of DPPH˙ of 33.03 ± 0.38%; total antioxidant capacity (TAC, FRAP assay) of 8.78 ± 0.07 μmol Fe (II).g-1 fresh weight. Identification of individual polyphenol compounds were performed HPLC. MAW extract of canola had the highest (P < 0.05) concentration of all individual polyphenols except gallic acid and catechin. Highest concentration of quercetin and luteolin in MAW extract of hemp was obtained among all solvent systems. The effectiveness of ultrasonic extraction of phenolics and flavonoids from defatted hemp, flax and canola seed cakes was compared to the conventional extraction method. Ultrasonic treatment at room temperature showed increased polyphenol extraction yield and antioxidant capacity by two-fold over the conventional extraction method. Different combinations of ultrasonic treatment parameters consisting of solvent volume (25, 50, 75 and 100 mL), extraction time (20, 30 and 40 min) and temperature (40, 50, 60 and 70ºC) were selected for polyphenol extractions from the seed cakes. The chosen parameters had a significant effect (P < 0.05) on the polyphenol extraction yield and subsequent antioxidant capacity from the seed…