| Tiger nut oil is a new type of high quality edible oil,which is not only rich in unsaturated fatty acids such as oleic acid and linoleic acid,but also rich in minor active components such as vitamin E and phytosterol.The development and utilization of tiger nut oil will play an important role in relieving the pressure of oil self-sufficiency in China.Crude oil of tiger nut obtained directly by pressing or solvent extraction requires a series of refining processes to produce edible oil.Degumming and deacidification of crude oil are the key processes and important steps in refining process.However,the traditional degumming and deacidification processes currently have some disadvantages,such as large loss of neutral oil and micronutrients,waste water discharge and high energy consumption.The purpose of this subject is to explore the applicability of tiger nut oil to different degumming and deacidification processes,with a view to overcoming the above problems and obtaining high-quality tiger nut oil with high neutral oil yield and maximum retention of micronutrients.Firstly,most phospholipids in tiger nut oil are nonhydratable phospholipids(NHP),and using traditional hydration degumming alone cannot achieve a good degumming effeciency,while acid degumming can convert NHP into hydrated phospholipids which can be removed by hydration degumming.In this paper,the effects of acid type,mass fraction of citric acid solution,citric acid solution dosage(based on the mass of oil),water dosage(based on the mass of oil),acidification time,hydration time,reaction temperature on the acid degumming of tiger nut crude oil were studied,and the degumming conditions were optimized by response surface method.The results showed that using citric acid as an electrolyte had a better degumming effeciency than phosphoric acid.The optimum conditions were as follows:40%citric acid solution,0.20%acid dosage,acidification time 10 min,3.5%water dosage,hydration time 50 min,and reaction temperature 59℃.Under the optimum conditions,the degumming rate was 95.9±0.3%,and the phosphorus content was decreased from 207.6±2.3 mg/kg to 4.41±0.3 mg/kg,and sterol and V_Eretention rates were 90.80%and 91.30%,respectively.In summary,acid degumming can effectively remove phospholipids in tiger nut crude oil,with less loss of micronutrients.Secondly,in order to preserve the neutral oil component in the process of deacidification and selectively remove the free fatty acid(FFA)in tiger nut oil,the effect of lipases on the selective deacidification of tiger nut oil was investigated.Different lipases and acyl receptors were screened for the selective deacidification of tiger nut degummed oil by enzymatic esterification in the solvent free system.The effects of immobilized enzymes Novozym 435,Lipozyme RMIM,Lipozyme TLIM and liquid lipase Candia Antarctica Lipase B(CALB)on the deacidification effeciency of tiger nut degummed oil were compared.The results showed that not only good deacidification effeciency were obtained,but also selective deacidification effeciency were achieved through using the cheaper liquid lipase CALB and small molecular weight acyl acceptor anhydrous ethanol.In addition,the effects of reaction time,substrate ratio,enzyme dosage,reaction temperature and molecular sieves dosage on the selective deacidification of tiger nut oil were also discussed and optimized through response surface methodology.The optimal reaction conditions were obtained as follows:substrate ratio 10:1,reaction temperature 50℃,and enzyme dosage 3%.Under the optimal conditions for 5h,the acid value(AV)of the tiger nut degummed oil was decreased from 5.66±0.12 mg KOH/g to 0.29±0.02 mg KOH/g,and the triacylglyceride retention rate was higher than 94%.Meanwhile,the high contents of sterol(304.25±1.62mg/100g)and vitamin E(135.70±0.15 mg/kg)in tiger nut deacidified oil was also obtained.Finally,a one-step process of simultaneously degumming and deacidification in solvent system was used to remove the phospholipids and FFA from tiger nut crude oil.The miscella of tiger nut oil was used as the raw material.The soap generated by the reaction of Na OH solution and miscella of tiger nut oil was used to neutralize FFA and condense phospholipid micelles.The effects of reaction temperature,miscella oil concentration,reaction time,alkali concentration and excess alkali dosage on the simultaneous degumming and deacidification of the tiger nut crude oil were studied,and the response surface method was used to optimize the reaction conditions.The optimum conditions were as follows:the concentration of miscella oil 73%,the alkali concentration 12°Bé,and reaction temperature 58℃.After 75min,the phosphorus content and AV of tiger nut oil could be reduced to about 7 mg/kg and0.15 mg KOH/g,respectively,which satisfied the equirements of the first-grade edible oil.At the same time,the high neutral oil yield(94.77±0.12%)and low loss rates of sterols(15.67%)and V_E(6.63%)was obtained.The process of simultaneous degumming and deacidification of tiger nut crude oil in solvent system does not produce waste water and was friendly to neutral oil and micronutrients. |
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