| Conjugated linoleic acid(CLA)is a secondary derivative of linoleic acid,which is a general term of fatty acids with spatial and positional isomers of linoleic acid and has various physiological functions.At present,conjugated linoleic acid in the market is mostly prepared by isomerizing raw grease rich in linoleic acid to obtain mixed fatty acids containing conjugated linoleic acid.Coffee grounds is a renewable biomass containing various bioactive substances.The content of linoleic acid in coffee grounds oil is relatively high,which can be used as a raw material for preparing conjugated linoleic acid.In this paper,waste coffee grounds was used as raw material,coffee grounds oil was extracted by enzymatic method,conjugated linoleic acid was prepared from coffee grounds oil,and conjugated linoleic acid powder was obtained by inclusion with β-cyclodextrin.The research results are as follows:1.Enzymatic extraction of coffee grounds oil: In this study,pretreatment methods,enzyme types and pretreatment conditions were selected firstly,and then the effects of solid-liquid ratio,temperature,p H,enzyme addition amount and enzymolysis time on the oil extraction rate were evaluated by single factor experiment.Furthermore,the extraction parameters were optimized by combining the three factors of enzyme addition amount,p H and enzymolysis time,which had a significant impact on the oil extraction rate,with response surface design.The results showed that the optimal extraction conditions of coffee grounds oil were as follows: solid-liquid ratio 1:10(100℃ hot water),p H 8 alkali pretreatment for 45 min,neutral protease 2%(w/w),p H 6.5,enzymolysis temperature48℃,enzymolysis time 16 h.Under the optimal conditions,the oil extraction rate of coffee grounds oil was 74.2%±0.74%.The fatty acid composition of the extracted coffe grounds oil was determined,in which the linoleic acid content was 42.1%±0.46%.The physical and chemical indexes of acid value(AV)and peroxide value(POV)met the requirements of the national standard for vegetable oil food safety.In this study,coffe grounds oil was extracted by enzymatic method.The reaction conditions were mild.The organic solvent was not used,and it was green and safe.It could provide technical support for deep processing and high value-added conversion of coffee grounds.2.Preparation of conjugated linoleic acid from coffe grounds oil: The effects of microwave power,KOH/coffe grounds oil mass ratio,propylene glycol/coffe grounds oil mass ratio and microwave heating time on the conjugation conversion rate of linoleic acid were evaluated by single-factor experiments.The process parameters for preparing CLA from coffe grounds oil were further optimized by combining with response surface methodology.The optimal process conditions were obtained as follows: microwave heating power 450 W,KOH/coffe grounds oil mass ratio 0.5:1,propylene glycol/coffe grounds oil mass ratio 4:1,microwave heating time 35 min.The fatty acid mixture containing conjugated linoleic acid was then obtained.The conjugated conversion rate of linoleic acid in coffe grounds oil was 88.9%±0.32%,and the physical and chemical indexes met the national standard for vegetable oil food safety.In this study,the conjugated linoleic acid was prepared from coffe grounds oil for the first time.The reaction time was short and the conversion rate was high.The results showed that the conjugated conversion process of linoleic acid in coffe grounds oil was feasible.3.Preparation of conjugated linoleic acid powder: The effects of the mass ratio of conjugated linoleic acid to β-cyclodextrin saturated solution,the inclusion stirring temperature and the inclusion stirring time on the inclusion rate of conjugated linoleic acid powder were evaluated by single factor experiment.The optimal process parameters for preparing conjugated linoleic acid powder were obtained by orthogonal experiment design:1:1 mass ratio of the saturated solution of conjugated linoleic acid and beta-cyclodextrin,the inclusion stirring temperature of 55℃,and the inclusion stirring time of 3 h.Under these conditions,the inclusion rate was 77.6%±0.89%.The powder was characterized by Fourier transform infrared spectroscopy,X-ray diffraction,scanning electron microscopy and other structural features,which confirmed that the conjugated linoleic acid andβ-cyclodextrin formed a stable inclusion compound.The powder fluidity and performance measurement test showed that the conjugated linoleic acid powder had good fluidity.The stability test results showed that the conjugated linoleic acid powder had significantly higher stability than the conjugated linoleic acid powder.To sum up,in this study,oil was extracted from coffee grounds to prepare high-value-added products,which would turn coffee grounds into valuable waste.It provided a new use for recycling coffee grounds waste recycling resources and improved the commercial value of coffee grounds. |
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