| China is the richest country in the world in terms of hemp resources,but there is a lack of research in the comprehensive utilization of hemp seeds.Hemp seeds contain rich and high quality oil and protein,and there have been successful cases of enzyme assisted aqueous extraction in the processing of high-oil and high-protein oilseeds.Therefore,this thesis takes peeled hemp seeds as the research object,and studies its applicable pretreatment methods and enzyme assisted aqueous extraction processing to achieve the goal of extracting oil and recovering fire hemp protein to the greatest extent while reducing processing water consumption and enzyme dosage.Firstly,three pretreatment methods,ultrasonic,acid immersion and ultrasound-assisted acid immersion,were identified through preliminary pre-experiments.It was found that the oil yield of hemp seeds increased to 82.23% after the combination of acid leaching and ultrasonic treatment,and not only the oil content in the emulsion decreased to 12.30%,but also the residual oil rate in the residue phase decreased from 4.23%to 2.14% in the single acid immersion treatment.After the ultrasound-assisted acid immersion pretreatment,about 68.54% of the protein was distributed in the aqueous phase and about 30.92% in the residue phase,and the percentage of protein distribution in the aqueous phase was lower than that in the control and ultrasonic treatment groups and higher than that in the acid immersion treatment group alone.The average particle size of the ultrasound-assisted acid immersion pretreatment group was reduced to 12.13μm after 3 times of shear crushing and 7 times of fine crushing,and the cell structure and lipid-protein complex were destroyed and a large number of lipid bodies were aggregated when combined with the results of laser confocal microscopy.The experimental results demonstrated that the ultrasound-assisted acid immersion pretreatment was suitable as a pretreatment condition for the new enzyme assisted aqueous extraction processing.Then,single-factor experiments were conducted to optimize the ultrasound-assisted acid immersion pretreatment and the enzyme assisted aqueous extraction processing respectively,using the extraction rate of clear oil and oil residue rate as indicators.The results of pretreatment process optimization were as follows:ultrasonic frequency of 200 W,ultrasonic time of 40 min,citric acid concentration of 0.4 mol/L and drying temperature of 40℃.The process optimization for the enzyme assisted aqueous extraction processing resulted in the following conditions:material-liquid ratio(w/v)1:3,pH 10.0,extraction temperature 60°C,and extraction time 1.5 h.The emulsion obtained was broken by using Bacillus subtilis protease and the breaking rate could reach 98.34%.The best process was verified several times and the final total oil extraction rate could reach 95.36%.Then,the quality analysis and storage stability of the extracted oil were studied.The results showed that the fatty acid composition of the oil was not affected by the enzyme assisted aqueous extraction processing with ultrasound-assisted acid immersion,and the content of trans fatty acids was low,only 0.071%;the content of active substances such as tocopherols and sterols in the oil was high,753.01 mg/kg and 2817.93 mg/kg,respectively;no additional harmful substances were produced by the enzyme assisted aqueous extraction processing with ultrasound-assisted acid immersion.The oil has a high food safety and excellent nutritional value.The storage stability of hemp seed oil was studied by Schaal accelerated storage experiment,and the addition of the antioxidant TBHQ played a significant role in inhibiting the oxidation of fire sesame oil.The results showed thatα-pinene,β-pinene,β-laurene,D-limonene andβ-staphylene accounted for the major components;the enzyme assisted aqueous extraction processing retained more characteristic flavor compounds and the pretreatment did not cause any loss of flavor components.Finally,the hemp seed protein,a by-product of the enzyme assisted aqueous extraction processing,was investigated.The solubility of the aqueous phase isolated hemp protein was slightly higher than that of the fire hemp meal protein.The Osborne classification showed that the vast majority of the fire hemp isolated protein was globulin(66.14%) and the main component of the hemp meal protein was glutenin(61.47%).The secondary and tertiary structures of the hemp proteins were studied by circular dichroism and endogenous fluorescence spectroscopy,and the results showed that acid immersion sonication increased the proportion ofα-helices to 31.17% and reduced the proportion ofβ-folds to 11.21%,exposing more hydrophobic groups.The properties of each group of fire hemp proteins were compared.For the hemp isolate protein,ultrasound-assisted acid immersion increased the surface hydrophobicity and improved the oil-holding property and emulsifying activity to7.14 g/g and 45.77 m~2/g,respectively;the hemp meal protein had higher emulsification stability,foaming property and foaming stability to 72.44%,125.69% and 88.96%,respectively,and the ultrasound-assisted acid immersion pretreatment did not have any significant effect on them.In vitro digestion simulation experiments were conducted to study the digestive characteristics of hemp protein,and the soluble nitrogen release of hemp protein isolate was higher than that of hemp meal protein,both of which were at a higher level;the in vitro digestibility of hemp protein was improved to a certain extent by ultrasound-assisted acid immersion pretreatment,and the soluble nitrogen release of the pretreated hemp protein isolate reached a maximum of 90.33%.In summary,the enzyme assisted aqueous extraction processing with ultrasound-assisted acid immersion pretreatment can be highly efficient in the simultaneous extraction of hemp oil and hemp protein with lower water and enzyme consumption,effectively controlling the cost.Oil and protein products both have excellent quality.Thus,it is a very promising hemp seed processing method. |
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