HIU treatment can reduce the particle size,increase solubility and improve the emulsification characteristics of protein.In Zhao et al.’s study,the solubility,foaming and emulsification of perilla protein isolate were improved after ultrasonic treatment.Meanwhile,the interfacial waves and cavitation bubbles generated by the sound field broke up the oil droplets,reducing the emulsion droplet size.In addition,the mechanical shearing,thermal effects,dynamic stirring and turbulence generated by ultrasonic would further process the emulsion and change the emulsion properties.Taha et al.investigated ultrasonic-assisted emulsions stabilized with different plant and animal proteins and found that ultrasonic treatment increased the interfacial protein content and thermal stability.Wang et al.has studied the effect of different HIU powers on soybean isolate protein-pectin emulsions and the its stability was highest at 450 W.HIU has been considered as a green,safe and efficient method to assist in the preparation of emulsions.In this study,the HSO emulsions stabilized with hemp seed protein were prepared and the effects of different HIU treatment powers on the physicochemical properties,microstructure and stability of the emulsions were investigated.The emulsification properties,particle size and potential of the emulsions under different conditions were explored in the study,and the effects of HIU treatment on the thermal and oxidative stability of the emulsions were discussed.We expect the HIU treatment to improve the emulsification performance of HPI,marijuana grow system enhance the stability of HSO emulsions,improve the retention of THC,and further expand the application of processed products from hemp seeds in the food industry.
The amount of protein adsorbed and loaded at the emulsion interface is an important indicator of the stability of the emulsion.The higher the amount of protein adsorbed at the interface,the more stable the oil in-water emulsion will be during storage.The interfacial protein distribution of the emulsions treated with different HIU power can be seen in Fig.3.With the increase of HIU power,the adsorbed protein content showed a trend of increasing and then slightly decreasing,while the non-adsorbed protein content showed the opposite trend.At a treated power of 450 W,the adsorbed protein content reached 30.12% and the non-adsorbed protein content reached 69.88%.This result proved that the HIU treatment benefited the adsorption of HPI on the HSO surface.At that time,HIU may lead to the decrease of HSO oil droplet size and increase of surface area,which was one of the reasons for the increase of adsorbed protein content.In addition,HIU reduced the particle size of HPI ,which accelerated the diffusion rate of protein and made it easier to rearrange at the oil-water interface to reduce interfacial tension,which can improve emulsion stability.Interestingly,when the HIU power was increased to 600 W,the adsorbed protein content decreased slightly to 27.69%.This phenomenon was consistent with some existing studies,where too high a power can lead to the phenomenon of “overprocessing”,where the emulsion showed a tendency to re-agglomerate,increasing the emulsion particle size,which was detrimental to the stability of the emulsion.The same was found in a study by Li et al on casein emulsified soybean oil,where prolonged sonication reduced the amount of adsorbed protein in the casein emulsion,though not significantly.HIU treatment alters the emulsifying properties while also improving the stability of the emulsion.In processing and production,changes in temperature may change the interfacial behavior and the aggregation degree of proteins,so the evaluation of the thermal stability of HIU assisted prepared emulsion samples is necessary.
The effect of different HIU power on the particle size distribution of the heat-treated emulsions is shown in Fig.4.The emulsions without HIU treatment have the largest D43,and poor dispersion.This phenomenon implied that heat treatment led to the formation of protein aggregates,which resulted in larger emulsion sizes and in homogeneous particle size distributions.As a control group,the emulsions without ultrasonic treatment,formed protein aggregates under heating conditions,resulting in larger emulsion sizes and non-uniform particle size distribution.Meanwhile,the D43 of the emulsion droplets decreased significantly after the HIU treatment.Among them,the smallest D43 of the emulsion was 985.74 ± 64.89 nm at a power of 450 W.The dispersion of the emulsion was also improved at this time,and the thermal stability reached the best compared with the other treatment powers selected.This conclusion was also demonstrated in the study by Li et al.The ultrasonicated oat proteins showed smoother fluctuations in particle size during heating and had better resistance to thermal aggregation.At a power of 600 W,the D43 of the emulsion showed a rebound,which was in agreement with the results in 3.4,probably owing to the excessive ultrasonic intensity affecting the emulsion stability.THC is an unstable polyphenol in HSO and is subject to oxidative degradation during storage,thus the retention rate of THC in emulsions can be used as an indicator to evaluate the stability of emulsions.The THC retention rates of the emulsions under different power HIU treatments after storage for 0,5,10,15,20,25,and 30 d are shown in Fig.5.The THC retention rate of all emulsions showed a decreasing trend as the storage time increased,and the retention rate of the emulsions without HIU treatment decreased to 65.92% after 30 days of storage,while the rest of them were above 75%.Furthermore,the THC retention rate for 30 Days was the first to increase and then decrease with increasing ultrasonic power,and the highest value occurred at a power of 450 W with 87.64%.After increasing the power to 600 W,the THC retention decreased to 81.25%.
It can be concluded that HIU treatment promoted the formation of a denser and thicker interfacial layer of the emulsion,which hindered the diffusion of oxygen and oxidant,thereby avoiding the oxidative degradation of THC.This was also discussed in Sun et al.’s study,where ultrasonic treatment-assisted α-tocopherol/caseinstabilized grape seed oil emulsions were effective in inhibiting the formation of oxidative radicals in the oil and avoiding molecular degradation.At an ultrasonic power of 600 W,a decrease in THC retention rate was observed.The appearance of this phenomenon was associated with the HIU treatment promoting the dissociation of water molecules and the production of free radicals.The rupture of cavitation bubbles generated by ultrasonics can produce free radicals,and the amounts of free radicals would be approximately proportional to the ultrasonic power.Thus,at a treatment power of 600 W,free radicals caused oxidative degradation of THC,leading to a decrease in THC retention rate.The POV value is the degree of oil oxidation,which mainly determined the hydroperoxides produced by the reaction of unsaturated fatty acids with oxygen,and can be used to evaluate the oxidative stability of the emulsion.The POV of HSO emulsions treated with different power HIU at days 0,5,10,15,20,25 and 30 are shown in Fig.6.The POV of all HSO emulsions increased with the storage time within 30 d.It can be observed that the POV values during storage of the emulsions were significantly reduced after treatment compared to those of the non-HIU treated emulsions during storage 10–30 d.This phenomenon demonstrated that the HIU treatment was able to inhibit the increase of hydroperoxides in HSO and improve the oxidative stability of the emulsions.This inhibition effect was optimal at a power of 450 W.The POV value of 4.6 μmol/L was the lowest value after 30 d storage.The reason for this phenomenon is in agreement with the findings in 3.2 and 3.4 above,that the 450 W-treated emulsion has the smallest particle size and the highest adsorbed protein content,where the reduction in particle size may enhance the vulnerability of the emulsion to oxygen reaction; Increased adsorption proteins allow faster scavenging of free radicals to inhibit lipid oxidation,thus improving the oxidative stability.This same phenomenon was also found in the study by Li et al.Appropriate sonication time helped to improve the oxidative stability of sodium caseinate – soybean oil emulsion.The POV value is 5.7 μmol/L at 600 W,which is higher than the emulsion at 450 W.This may be caused by the high sound field of HIU and the strong cavitation effect promoting the formation of highly reactive radicals ,which further synthesize hydrogen peroxide and oxidize HSO.Thus,while HIU treatment resulted in an increase in hydrogen peroxide content.At 450 W treatment power,it still decreased the POV value during storage and improved the oxidative stability of the emulsion.Bio-based materials have become increasingly popular for producing economical engineering materials in the building and construction industry.
Composites manufactured using the woody core of the hemp plant known as shiv have been adopted by the building industry.Lightweight composites from hemp shiv possess excellent hygroscopic,thermal and biodegradable properties.The hydrophilic nature of bio-based materials makes them incompatible with hydrophobic thermoset/ thermoplastic polymers.On the other hand,since the shiv competes with the binder for the available water,purely hydraulic binders like lime or cement cannot hydrate completely,leading to a powdery inner core in the hemp-lime walls which is poorly bound.The issue of adhesion with hemp-lime has stimulated considerable investment in hemp-specific lime based binders.The most recent generation of binders utilises high specific surface area lime in order to obtain a more reactive binder,however,they are still susceptible to adhesion issues.Pre-fabrication of panels or blocks ensures factory controlled conditions which reduce the extremes of adhesion issues ,but there still remains the inherent issue that the soluble sugars on the surface of the shiv interfere with the hydration of the binders,resulting in lower strength composites.The durability of the material is compromised due to high moisture uptake as colonial fungal growth is encouraged resulting in cell wall degradation.The major constituents of industrial hemp shiv are: cellulose ,hemicellulose ,lignin and other components such as extractives and ash.Extractives include numerous low molecular mass compounds such as fatty acids,waxes,sterols,triglycerides,steryl esters,glycosides,fatty alcohols,terpenes,phenolics,simple sugars,alkaloids,pectins,gums and essential oils.It is well known that extractives can be isolated using polar and non-polar solvents.Volatile extractives are represented by highly volatile compounds which can be separated by water distillation.They are mainly composed of monoterpenes and other volatile terpenes including terpenoids as well as many different low molecular weight compounds.Water-soluble compounds consist of various phenol compounds,carbohydrates,glycosides and soluble salts,which can be extracted by cold or hot water.Lipophilic extractives are insoluble in water but soluble in organic solvents such as hexane,dichloromethane,diethylether,cannabis vertical farming acetone or ethanol.Lipophilic extractives also known as plant-resins are divided into free acids,e.g.resin acid and fatty acid,and neutral compounds,e.g.fats and waxes.Extractives from bio-based materials can have a tacky nature forming pitch deposits which is considered to be a major problem in the paper and pulp industry.
Natural fibre composites have low durability and tend to absorb large amounts of moisture weakening interfacial adhesion and degradation,although this property can be improved by treatment of the fibres.Physical approaches such as plasma,ultraviolet or corona treatment modify the fibre surface for enhancing roughness and interfacial adhesion.Chemical treatments such as alkaline,silane and acetylation offer better improvements than physical methods enhancing hydrophobicity and roughness of the fibres resulting in better interfacial bonding.Addition of silica particles into polymeric matrix has also been used to enhance the mechanical properties of natural fibre reinforced composites.Hydrolysed silanes can chemically attach to the hydroxyl group of fibres,but they are known to provide only a limited improvement in the mechanical properties of the resulting fibre composite due to their physical compatibility with the matrix.The strength of natural fibre composites can be increased if covalent bonds are present between the silane treated fibre and matrix.Therefore there is a need to develop novel composites that possess good interfacial bonding and at the same time utilise the benefits of chemically treated bio-based aggregates being resistant to water and degradation.The work reported in this paper is carried out under the ISOBIO project which aims to develop hygrothermally efficient bio-based building insulation panels with low embodied energy and low embodied carbon.We have previously reported that the silica based treatment can provide hydrophobicity to hemp shiv without compromising its moisture buffering capacity as the pores are not totally blocked by the coating.The aim of this paper is to demonstrate the use of a hydrophobic silica treatment as a binder for hemp shiv to produce novel robust light weight composites with enhanced water resistance.The silica based binder was synthesised by hydrolysis and condensation of TEOS in ethanol and water.The reaction was catalysed by nitric acid.For the preparation of the silica,1 M of TEOS was added to a mixture of 4 M distilled water,4 M of absolute ethanol and 0.005 M of nitric acid.0.015 M of HDTMS was added to the above mixture as the hydrophobic agent.The sol was vigorously stirred at 40 °C and atmospheric pressure for nearly 2 h.The sols were allowed to age for 96 h in closed container at room temperature.For the preparation of the silica glass,the sol was aged in a container at room temperature until the gel point was reached.