| Fenugreek(Trigonella foenum-graecum L.)is a traditional medicine and food dual resource,which is now widely cultivated in China.Fenugreek seeds contain 6-12% oil,and are rich in unsaturated fatty acid.In addition,the seed is also rich in dietary fiber,polysaccharide,protein,vitamins,minerals,alkaloids,flavonoids and saponins;and is widely known for its nutraceutical,medicinal,and pharmaceutical properties.Subcritical extraction technology has been widely used and studied in food industry,owing to its advantages,such as low cost,non-toxic,environmental friendly,low temperature extraction,high yield and high quality of the products.Based on the state of research and utilization of fenugreek seeds,subcritical extraction technology was employed to extract oil and volatile oil from the seeds,and the defatted meal was also been utilized for polysaccharide and protein extraction.The main research contents and conclusions are as follows:1.Extraction of fenugreek seed oil using subcritical butane: In this study,subcritical butane extraction was employed to extract oil from fenugreek seeds,and the process was optimized using response surface methodology.The optimum conditions were obtained as follows: particle size of 0.26 mm,extraction time of 32.80 min,and extraction temperature of 43.24 °C.No significant differences were found between the actual yield(7.17 ± 0.16%,n=3)and predicted value(7.18%)in the confirmatory experiment.Results revealed the acid value was slightly higher,the others physicochemical properties are better than the national standard of edible oils.The oxidation induction time(IT)of the oil was 2.850 h(at 120 °C),which was mainly due to the high content of unsaturated fatty acids.Thermogravimetric analysis showed that the oil had a sufficient thermal stability.There was no significant difference between the yields of subcritical extraction and accelerated solvent extraction,and they were both higher than that of Soxhlet extraction.Fatty acid composition of oils obtained by these methods showed negligible difference.All the oils were rich in linoleic acid(42.69%-42.80%),linolenic acid(26.01%-26.15%),and oleic acid(14.24%-14.40%).2.Study on the extraction of fenugreek seed volatile oil: The volatile oils of fenugreek seeds were prepared by subcritical butane,subcritical methyl ether,supercritical CO2 and ethanol extraction methods;the yields and the quality of volatile oils obtained by different methods were compared.Supercritical CO2 extraction has the highest yield of 0.41%,followed by subcritical methyl ether(0.38%),subcritical butane(0.33%)and ethanol extraction(0.24%).The results showed that the volatile oils extracted by subcritical(butane and methyl ether)and supercritical CO2 extraction had a very close appearance and aroma quality,and were superior to ethanol extraction.Total 47 compounds were identified from the volatile oils,mainly including fatty acids,terpenes,esters and ketones.All the volatile oils showed good effect in the flavoring and sensory evaluation of cigarettes.The volatile oils obtained by subcritical butane and methyl ether were investigated by Pyrolysis GC-MS,and total 138 compounds were identified from the pyrolysis products,in which 77 and 100 compounds were identified from subcritical butane and subcritical dimethyl ether extraction,respectively,including aldehydes,alcohols,acids,aromatic hydrocarbons,ketones and alkenes.And the aroma mechanism of pyrolysis process was analyzed.3.Subcritical water extraction and structure characterization of polysaccharide from fenugreek seed meal: Fenugreek seed polysaccharide was prepared by subcritical water extraction,and the process was optimized using response surface methodology.Results showed that the actual extraction rate(20.53 ± 0.31%)showed no significant difference with the predicted value(20.65%),at the optimum conditions,i.e.a liquid/solid ratio of 32:1,an extraction temperature 120 °C and an extraction time of 36 min.Crude FSP solution was applied to a DEAE-Sepharose Fast Flow column.Then the column was stepwise eluted with 0,0.1,0.3 and 0.5M aqueous solution of NaCl at a flow rate of 1 mL/min.Two completely separated fractions(FSP-1and FSP-2)were obtained.The molecular weights of FSP-1 and FSP-2 were 1587800 g/mol and 26753 g/mol,respectively.The monosaccharides of FSP-1 and FSP-2 are mainly mannose and galactose;Thermo gravimetric analysis showed that FSP-1 and FSP-2 had higher thermal stability.Results of monosaccharide composition,FT-IR,NMR and methylation analysis revealed that FSP-1 is a galactomannan(M/G=1.08),that is a backbone of ?4-D-Manp?1 and ?4,6-D-Manp?1 with a substitution of C-6-carbon atoms by a single D-Galp?1 residue.Scanning electron microscopy showed that the appearance of the two polysaccharide components were fibrous,the structure of FSP-1 was relatively dense and the surface was relatively smooth,FSP-2 was rough,and there were striations and holes.4.Preparation and characterization of concentrated protein from fenugreek seed meal: Fenugreek seed meal proteins,namely FPI-1 and FPI-2,were obtained using alcohol washing and alkali extraction/acid precipitation methods.The contents of protein in FPI-1 and FPI-2 were 72.33% and 91.42%,respectively.Total 17 kinds of amino acids were found in FPI-1 and FPI-2.And the contents of essential amino acids were 31.35% and 37.23%,for nonessential amino acids were 40.62% and 52.78%,respectively.FPI-2 was better than FPI-1 in total amino acid and essential amino acid content.The water absorption of FPI-1 and FPI-2 were 1.81 g/g and 2.63 g/g,respectively;for oil absorption were 3.42 mL/g and 5.27 mL/g,respectively.The emulsifying ability of FPI-2 was significantly higher than that of FPI-1(p < 0.05);the emulsifying ability of FPI-1 and FPI-2 at acid and alkali conditions was significantly higher than that in the isoelectric point.The emulsion stability of FPI-2 was higher than that of FPI-1 in all pH values.The emulsion stability of FPI-1 and FPI-2 was highest at pH 8.The foaming ability of FPI-2 was higher than that of FPI-1 in all pH values.The foaming ability of FPI-1 and FPI-2 was lowest at pH 4.5,and was highest at pH 8.The foaming stability of FPI-2 was higher than that of FPI-1 in all pH values.The foaming stability of FPI-1 and FPI-2 was the highest at p H 4.5.However,when the pH value was too acid or alkali,the foaming stability of FPI-1 and FPI-2 were decreased.In conclusion,systematic researches were carried out in this paper,to achieve a comprehensive development and utilization of fenugreek seeds.These provide technical and data support for fundamental research and industrial application of the oil,volatile oil,polysaccharide and protein of fenugreek seeds.And have important theoretical and practical significance for the development and utilization of fenugreek seeds. |
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