They promote extraction by breaking down the cell walls of the structures containing the oils and hence can also lead to the extraction of essential nutraceutical and antioxidant compounds with lesser degenerative effects on the cells.Ultrasound assisted extraction of hemp seed oils was performed by Lin and his group as well as and Esmaeilzadeh Kenari and associates on hemp seeds and increased extraction yields were reported as compared to traditional extraction methods.A slightly modified ultrasound extraction method was also proposed in which solvent extraction using a Soxhlet apparatus was supplemented using ultrasound applied using an ultrasound probe.This coupled effect of conventional Soxhlet extraction along with ultrasound extraction led to an increased oil yield.Rezvankhah and his team studied the effects of Microwave assisted extraction on hemp seed oils and reported that the method was more time efficient as compared to traditional Soxhlet extraction.The oils produced were also of higher quality.Similarly,it was also reported that Microwave assisted extraction of oils from pongamia pinnata seeds was quicker and had no adverse effect on the quality of oils as compared to other conventional methods.Previously,hemp did not receive significant attention because of legal issues concerned with hemp cultivation.According to the 2018 reports by Health Canada,77,800 acres of industrial hemp were planted in Canada out of which 33,000 acres were planted in Alberta,27,100 acres in Saskatchewan,and 11,500 acres in Manitoba.It is estimated that roughly 90% of the total seed for hemp cultivation is produced in Canada which contains mostly Canadian developed varieties.Thus,it is evident that with increasing awareness there is a significant increase in hemp cultivation as well as the number of hemp processing plants leading to more research focusing on hemp seeds,grow rack especially oils extracted from hemp hearts.
Although there are previous research reports concerning the extraction of hemp oils,the literature is scanty and the scientific community lacks a thorough comparison between the effect of different extraction techniques on the quality of oils produced from hemp seeds.Previous research has mostly focused on the extraction and analysis of hemp seed oil using a single technique or a comparison between two techniques.However,a comprehensive comparative analysis of different extraction techniques for hemp heart oils operating at different temperature ranges have not been performed previously.Thus,the major objectives of the study were to Compare the extraction efficiencies of three different extraction techniques-microwave,ultrasound and cold pressing for the extraction of hemp seed oils by varying particle size and extraction conditions to obtain maximum yield.Analyze the physicochemical properties,fatty acid composition,free radical scavenging activity,and inherent chemical composition of the extracted oils to determine the quality and,understand the nature of the oils in order to suggest probable areas of application.These results indicated that the ultrasound is more effective in the first 30 min and with an increase in time,a decreasing trend in the yield was noticed.This may be attributed to the fact that due to increased time periods; ultrasound waves can disrupt more hemp heart cell walls leading to increased penetration of the solvent inside the cells resulting in more extraction.Again,the slight decrease in the extraction yield can be hypothesized to have been caused by prolonged exposure time as a result of which ultrasound oxidation of the edible oils take place either by thermal degradation or sonolysis,which can be attributed to the phenomenon of “cavitation”.Cavitations are micro-mechanical shocks affecting the structural and functional components of the cells and such an increased phenomenon in the cells lead to lipid oxidation and deterioration.This phenomenon may have resulted in a slight decrease in the oil yield upon increasing the ultrasound time.Further,an increase in the rate of cavitation leads to excessive breakdown of the cell membranes and cell walls,thus exposing the hydrophobic fatty acid tail of the phospholipids.
This might cause binding of the oil to the phospholipid and lower its extractability by the solvent.Therefore,excessive ultrasound can have a delirious effect on extraction.Again,the ultrasound time was optimized at 30 min and 60 min respectively to understand the effect of UAE power on the yield.Ultrasound powers of 20 W,130 W,and 200 W were used for UAE time of 60 min which is represented in Figure S3.On the other hand,130 W and 200 W were used for 30 min.The yields obtained by varying the ultrasound power at 60 min was not found to be significantly different.With an increase in power,the yield gradually increased and the maximum yields of 46.8 ± 3.25% and 44.9 ± 3.11% were produced at 200 W for 30 min and 60 min respectively.It can be hypothesized that when the ultrasound power is low,the energy produced by the ultrasound probe is not enough to cause the propagation of ultrasound pressure waves to cause cavitation.The results obtained are on par with previous research led by Lin et al.,who also reported that the maximum extraction yield is achieved for 200 W.The slight decrease in the yield% for 130 W and 60 min run time may be attributed to sonolysis and the cavitation phenomena.The maximum extraction yield was obtained for ultrasound power of 200 W and 30 min which was considered for further experiments.Means in the same column followed by different superscripts are significantly different.the yields except for the minimum and maximum values obtained.A comparative analysis of the extraction yields is presented in Figure S6.Results reported that there existed a significant difference between the yield obtained by CP and MW,but not between CP and UAE or UAE and MW.MW extraction produced the maximum oil yield of 54 ± 3.8% followed by 47 ± 1.97% for UAE,and 41 ± 2.82% for CP.This can be attributed to microwaves causing increased rupture of the cell walls resulting in lipolysis and proteolysis of the cell wall materials,and thus enhancing the penetration of the solvent inside the cells to extract the oil.Moreover,a temperature of 70 °C and MW exposure time of 15 min led to a movement in the media due to a reduction in solvent viscosity which enhanced the extraction yield.The mechanical effect of ultrasound promotes the release of soluble compounds from the plant material disrupting the cell walls,enhancing mass transfer,and facilitating the solvent to access the cellular contents.On the other hand,microwaves lead to an increased solvent penetration into the matrix due to the movement of dissolved ions and as a result,causes increased extraction of intracellular materials.It can further be hypothesized that ultrasound waves may have caused the lipoprotein cell membrane to break and retain some of the oils,thus reducing its extractability which led to a lower yield as compared to MW extraction.Cold pressing is a mechanical extraction technique and hence the yield is fairly less compared to the other two techniques.Overall,it can be concluded that the yield obtained by each extraction technique was more compared to the yields produced by hemp cultivars in Turkey and Pakistan.
The presence of antioxidants like tocopherols in higher concentrations in CP oils can be a reason for a higher induction time since we know that these antioxidants act as free radical scavengers and singlet oxygen quenchers.It is also known that factors like the processing and storage treatment as well as the fatty acid composition of the oil play a key role in determining the oxidative stability.Since cold pressing took place at room temperature ,it was highly likely that the oxidation reaction did not initiate during its storage leading to a higher induction time during the analysis.Electro paramagnetic resonance spectroscopy has found a wide variety of applications in detecting free radicals owing to its high sensitivity to the unpaired electrons.The close interaction of DPPH with the free radical scavengers present in the hemp seed oils presented a reduced signal intensity relative to the DPPH stock solution EPR spectrum.DPPH scavenging activity of the hemp seed oils is reported in Table 4; the addition of 0.2 g of hemp seed oils to 1 ml of DPPH stock solution quenched more than 93% of free radicals that are present in DPPH for all the oil samples in the first two hours.The declining trend in the spectral intensity for the oil sample is observed from Fig.5 and relative to the DPPH spectra.Among the three extraction techniques,UAE and MW oils have lower antioxidant activity relative to CP oil.During the extraction,cold-pressed seeds and oil were not exposed to the higher temperature like MW and UAE techniques.Due to the high-temperature processing,thermally sensitive antioxidant compounds were destroyed in MW and UAE hemp seed oils.On the other hand,CP hemp seed oil was extracted at room temperature,thereby,greenhouse grow tables the antioxidant activity of the CP is higher than MW and UAE.Further,the antioxidant activity of the oils was evaluated at 20 h,therefore the DPPH stock solution allows the dissolution of both DPPH and lipid-associated antioxidants that are present in the hemp seed oils.Upon analyzing the spectra at 20 h,enhanced scavenging activity was observed by the antioxidant compounds present in the hemp seed oils.After 20 h,1 – 3% increment in the antioxidant activity was noticed relative to at 2 h,i.e.,within 20 h of reaction with DPPH,hemp seed oils quenched or neutralized the synthetic-free radicals present in the DPPH,primary and secondary oxidation products from the hemp seed oils.As discussed in the previous section,GC–MS analysis of the hemp seed oils revealed the presence of -tocopherols,sitosterols,stigmasterol that may be hypothesized to be primarily responsible for the antioxidant properties shown by the oils.The free radical scavenging activity of the hemp seed oils showed that they are capable of quenching the reactive oxygen species and their derivatives in short time owing to the fast reactivity of the antioxidant compounds in hemp seed oils.Therefore,it was anticipated that the presence of antioxidants in the hemp seed oils,could be a value-added feedstock for the production of pharmaceuticals and nutraceuticals as reported by Polovka in his research.
Hemp has a long cultivating history all over the world,with the earliest report in Chinese ancient literatures dating back to 4000 BC.Traditionally,hemp has been widely used in textile,building materials,and paper,as well as herb medicines.In general,there are two types of hemp plants: the fifi ber type and the cannabinoids type.The fiber type hemp plants are tall and are harvested for fibers and seeds.However,they are very low in cannabinoids contents.On the other hand,the cannabinoids type hemp plant is shorter in heights and is rich in cannabinoids contents.Depending on the level of tetrahydrocannabinol in the plant,the hemp can be further classified into industrial hemp and marijuana.In recent years,the bioactive compounds,including oils,protein,cannabinoids and terpenes,etc.,in hemp plants have drawn increasing interests in both scientific research and product development.As the results,the cultivation area and production of hemp have been increasing.In 2019,the bearing acreage of hemp in the US,China,Europe and Canada were 465 787,164 819,138 863,and 92 504 acres,respectively.The global hemp industry is projected to reach $10.6 billion by 2025.Hemp seed protein contains the full essential amino acids profile required by humans,and the hemp protein isolate shows higher nutritional values than the soy protein isolates.Particularly,the contents of omega-6 to omega-3 fatty acids in hemp oil have a ratio of 3:1,which is recommended for healthy human diet.Cannabinoids such as cannabidiol ,THC,cannabigerol and cannabinol ,etc.,are gaining increasing interests in biomedical and pharmaceutical applications.Among them,CBD is the most popular topic in scientific research and hemp industry,which shows functionality in facilitating pain relief,reducing anxiety/distress,and promoting relaxation without any psycho-activities.CBD has already been applied in cosmetics industry and food products.In addition,terpenes,another group of bio-active compounds that define the characteristic aroma of the plant,are also drawing more attention together with CBD.Hemp terpenes show excellent anti-inflammatory,anti-cancer values and antioxidant activities,etc.,and have been proven to have an ‘entourage effect’ with CBD,improving CBD functionality.With these excellent pharmaceutical and nutritional values,hemp CBD and terpenes are expected to be used as future functional food ingredients,catching the wind of booming functional foods market.Currently,applications of CBD in foods are limited by several important factors: 1) Global legal regulations are still strict,which in general,prohibit the addition of CBD in any foods,beverages or supplements.However,these ever-changing regulations are opaque and varies from country to country; 2) The consumer base of hemp CBD is relatively weak.The word ‘CBD’ is unfamiliar to food consumers,and for most cultures in the world,habitual thinking associates the word ‘hemp cannabinoids’ to ‘drug’,insinuating that it is illegal and bad for human health.This further illustrates the need for the functionality and health benefits of CBD to be studied and verified; 3) Effective incorporation of the hemp CBD in conventional food products has not been extensively studied and reported,which are essential for the development of potential products; 4) Hemp plants have high yield and high moisture contents at harvest,which increases vulnerability to quality deterioration and microbial spoilage.Conventional natural drying process has low efficiency and causes product loss.