Effect Of Oil-extraction Process On Phenolic Content And Antioxidant Activity Of Flaxseed Meal

Flaxseed meal is the main by-product of the oil-extract process of flaxseed oil,which is insufficient for development and utilization.Phenolic compounds are an important class of beneficial components in flaxseed,which not only give good stability to flaxseed oil in flaxseed cells,but also have many other physiological functions,such as effects on preventing or inhibiting breast cancer,anti-tumor,immune regulation and so on.In this paper,the flaxseed oil was prepared by the common oil-extract process to obtain the corresponding flaxseed meals.The effect of the oil-extraction process on the content of phenolic compounds and the free radical scavenging ability of flaxseed meal were studied.The compounds were added to flaxseed oil to evaluate the antioxidant properties of flaxseed meal polyphenols in oil systems.The research of the subject can provide theoretical guidance for the development and utilization of flaxseed meal.Firstly,the pretreatment conditions and HPLC parameters of the quantitative determination of flaxseed meal SDG were optimized,and the pretreatment process included ultrasonic assisted extraction and alkali hydrolysis.The conditions of ultrasonic assisted extraction were as follows:anhydrous methanol as extraction solvent,ratio of material to liquid 1:20(m:v),ultrasonic time 2 h,ultrasonic temperature 35?,ultrasonic power 800 W,ultrasonic extraction 3 times;alkaline hydrolysis The amount of alkali added during the process is the main influencing factor,and the optimum amount of alkali added is 3:1(volume-mass ratio of 0.3 mol/L NaOH solution to flaxseed meal).The optimized HPLC conditions are:column temperature 30?;UV detector,detection wavelength 280 nm;flow rate 0.8 mL/min,gradient elution,mobile phase A is 98%super Pure water(ie ultrapure water:acetic acid=98:2,V:V),mobile phase B is methanol,elution gradient is 85%A at 0 min,85%A at 20 min,72%A at 30 min,72%A at 40 min,45%A at 60 min,45%A at 70 min,15%A at 80 min,85%A at 81 min,and 85%A at 91 min.Ultrasound-assisted extraction,alkaline hydrolysis pretreatment combined with HPLC detection of SDG method is quick,convenient,safe and accurate.Secondly,the effects of oil-extraction process on the content of phenolic compounds in flaxseed meal were studied.The total phenolic content,flavonoid content and SDG content of hot-pressed flaxseed meal were compared between leaching and cold-pressing at different temperatures from 100? to 180?.The results showed that the content of phenolic compounds in flaxseed meal was closely related to the temperature of the oil-making process,and then decreased.The total phenolic content and flavonoid content of the flaxseed meal at160?were the highest,which were 20.67 mg GAE/g flaxseed meal,30.96 mg QE/g flaxseed meal;in terms of SDG content of flaxseed meal,its content varies with oil temperature and the flavonoid content and SDG content are different,and the SDG content increases with the oil temperature.High and elevated,the pretreatment of hot pressed flaxseed meal at 180? has the highest SDG content(20.48 mg/kg flaxseed meal).Thirdly,the methanol extracts of flaxseed meal(ie,extracts of phenolic compounds)of different oil-extract processes were evaluated for in vitro antioxidant performance by DPPH,FRAP and ABTS.The results showed that for the same flaxseed meal polyphenols,the free radical scavenging capacity of the three systems was:ABTS>DPPH>FRAP,and the ABTS system was about 10 times that of the other two systems;DPPH and FRAP scavenging capacity showed the law of increasing first and then decreasing.The DPPH free radical scavenging ability of flaxseed meal polyphenols in different oil production processes was123.52~154.84?mol TE/100g flaxseed meal.The FRAP free radical scavenging ability ranged from 76.12?mol TE/100g to 107.69?mol TE/100g.Among them,the DPPH and FRAP free radical scavenging ability were the most total phenolic compounds pretreated at160?,;polyphenolic compounds of flaxseed meal under different oil extraction processes.The changes of ABTS scavenging ability of flaxseed meal polyphenols in different oil-extract processes are different from those of DPPH and FRAP systems,and the influence of temperature is relatively small.The flaxseed meal polyphenols free radicals under different oil-making processes The scavenging capacity ranged from 900.89?mol TE/100g to 1504.13?mol TE/100g flaxseed meal.The 160? pretreated-hot pressed polyphenolic compound had the strongest DPPH free radical scavenging ability and the weakest extraction.Pearson correlation analysis between the free radical scavenging ability of flaxseed meal and the phenolic compound content of flaxseed meal was carried out.The results showed that the correlation between SDG content and DPPH free radical scavenging ability and ABTS·~+ion capacity was the most strong,flavonoids followed;flavonoids showed the strongest ability to reduce ferric iron(FRAP),followed by SDG;the correlation between total phenolic content and the ability to scavenge free radicals was the weakest.Finally,methanol extracts of flaxseed meal(ie,extracts of phenolic compounds)from different oil-exstract processes were added to fresh hot-pressed flaxseed oil for oven accelerated oxidation experiments to evaluate the phenolics of flaxseed meal in different oil-extracting processes.The antioxidant properties of the compound in an oil phase system.The results showed that the flaxseed phenolic compound extract showed very obvious anti-oxidation or pro-oxidation effect on hot-pressed flaxseed oil,and the anti-oxidation and oxidation-promoting effect depended on the addition amount of phenolic compound extract,the concentration of polyphenols in different oil-making processes of flaxseed meal will show good antioxidant performance when added,and vice versa may show prooxidation.Taking120%pretreatment of hot-pressed flaxseed meal as an example,the optimum addition amount is 10%.Under the added conditions,the oxidized value,anisidine value and total oxidation value of flaxseed oil are only oxidized for 5 days.12.51 mmol/kg,14.38 and 63.47,which was much lower than the index of linseed oil group.The peroxide value,anisidine value and total oxidation value were 23.57 mmol/kg,13.96 and 113.63,respectively.In order to ensure effective antioxidant action,the amount of flaxseed meal added in different oil-extracting processes is added according to the following principle:The total amount of phenolic compound extract is controlled at 1.0 mgGEA/g hot-pressed oil~1.5 mgGEA/g hot-pressed oil according to the total phenol content;based on the content of flavonoids,the amount of polyphenolic compound extract is controlled at 1.3 mgQE/g hot pressed flaxseed oil~2mgQE/g hot pressed flaxseed oil;the amount of polyphenolic compound extract is controlled at 1.3 mg/g~2.0 mg/g based on SDG content.mg/g hot pressed flaxseed oil hot pressed flaxseed oil.