Refining Of Rice Bran Miscella And Production Process Of Nutritional Rice Bran Oil

Rice bran oil is nutritious high-quality edible oil. But when using conventional refiningprocess of vegetable oil, it is difficult to obtain high-grade oil because of its high acid valueand deep color; the nutritional advantages of rice bran oil are reduced greatly, because of lowrefining yield, and the nutrients lost severely, and the harmful ingredients (trans fatty acid,TFA) are generated greatly. This paper aims to improve the refining technology of rice branoil, using miscella refining process, then reducing refining losses and retaining the nutrients(oryzanol, VEand sterols, etc.) of rice bran oil under the premise of obtaining high-grade ricebran oil, while reducing the generation of TFA.Deacidification is an important process in refining of rice bran oil, alkali refining is oneof the most commonly methods of deacidification. While the alkali refining of miscella notonly can maintain the advantages of alkali refining, but also beneficial to improving the alkalirefining yield, and reducing the losses of nutrients. The process conditions and process effectsof the miscella alkali refining were studied in this paper. And the optimum conditions wereobtained through the single factor experiments and orthogonal tests: reaction tempreture was55℃, total alkali were theory alkali combined with0.3%excess alkali of oil weight, miscellaconcentration40%(W/W), alkali concentration16°Bé. Under these conditions, the acid valueof the oil was reduced from28.6mg KOH/g to0.80mg KOH/g, the alkali refining yield was71.62%, the decolorization rate was42.73%, the loss rates of oryzanol, sterols and VEwere63.22%,43.76%and41.74%, respectively. Compared with the alkali refining of crude ricebran oil, the alkali refining yield was increased14.30%, the decolorization rate was increased5.26%, the loss rates of oryzanol and sterols were decreased30.56%and21.41%,respectively. So, for the rice bran oil with high acid value, there were obvious advantages onincreasing alkali refining yield, improving the color of oil and reducing the losses of nutrients,when using alkali refining of miscella.It can be seen from the miscella alkali refining results, for the crude rice bran oil withhigh acid value, alkali refining yield was very low and the loss rates of nutrients were stillhigh even miscella alkali refining was used. Two-stage alkali refining can reduce the alkali which added in each stage, then reduce the chance of neutral oil is saponified, and reduce thelosses of neutral oil and nutrients are adsorpted. The process conditions and process effects ofthe two-stage miscella alkali refining were also studied in this paper. And the optimumconditions were obtained through the single factor experiments and orthogonal tests, theconditions were: reaction temperature was55℃, miscella concentration was40%, acid valueof deacidified oil was reduced to14mg KOH/g from28.6mg KOH/g with12°Bé alkali inthe first stage, then it was reduced to below1mg KOH/g with20°Bé in the second stage.Under these conditions, the acid value of the oil was reduced from28.6mg KOH/g to0.67mg KOH/g, the alkali refining yield was78.24%, decolorization rate was68.25%, theLovibond color of the oil was Y35R11.0(25.4mm), the loss rates of oryzanol, sterols and VEwere51.09%,30.44%and32.67%, respectively. Compared with one-stage miscella alkalirefining, the alkali refining yield was increased9.19%, decolorization rate was increased3.92%, and the loss rates of oryzanol, sterols and VEwere decreased7.13%,1.75%and9.22%, respectively. Therefore, for the alkali refining of rice bran oil with high acid value,there were much more advantages on increasing alkali refining yield, and improving the colorof oil, and reducing the losses of nutrients when using two-stage alkali refining thanone-stage alkali refining of miscella.Bleaching is one of the difficulties in production of high grade rice bran oil. The deepcolor of crude rice bran oil is difficult to remove; excessive bleaching will increase theconsumption of adsorbent, increase the losses of neutral oil and nutrients, and also increasethe formation of TFA. The adsorption bleaching conditions of rice bran oil were studied andoptimized in this paper, decolorization rate, nutrients retention rates and TFA content wereused as the indexes of comprehensive effect of adsorption bleaching. The optimum conditionswere obtained through the single factor experiments and orthogonal tests, the conditions were:activated clay was used as decolorant, decolorant dosage3%of oil weight, bleachingtemperature was120℃, bleaching time was25min. Bleached rice bran oil was obtainedthrough the verification tests under these conditions, the Lovibond color of the oil was Y20R2.1(25.4mm), the decolorization rate was82.50%, the retention rates of oryzanol, sterolsand VEwere96.74%,90.60%and78.68%, respectively, and the TFA was not detected in alloil samples. Deodorization is essential and important in refining of rice bran oil. The nutrients in theoil will lose and TFA will generate during deodorization. The nutrients retention rates andTFA content were used as the indexes of comprehensive effect of deodorization, and theoptimum conditions were obtained through the single factor experiments and orthogonal test,the conditions were: deodorization time40min and deodorization temperature215℃, thesystem pressure was below400Pa, and the steam flow was constant. Deodorized rice bran oilwas obtained through the verification tests under the optimum conditions, the acid value ofthe oil was0.86mg KOH/g, the retention rates of oryzanol, sterols and VEwere97.54%,89.12%and88.36%, respectively, and the TFA was not detected.In order to reduce the acid value of rice bran oil and the losses of nutrients duringdeodorization, the process effects of two-stage deodorization were studied. Two-stagedeodorization aims to reduce the deodorization time under high temperature through devidedthe deodorization into lower temperature section and higher temperature section, the fractionwith lower boiling point was removed in the lower temperature section, and the fraction withhigher boiling point was removed in the higher temperature section, and then reducing theTFA formation, and increasing the retention of nutrients. The process conditions optionedwere: the deodorization temperature was190℃, the deodorization time was30min in thefirst stage; in the second stage, they were230℃and30min. Deodorized oil was obtainedunder the conditions, the acid value and color of the oil were reached the requirements of thetop grade of rice bran oil in national standard; compared with the conventional deodorizationunder the optimum conditions, the retention rates of oryzanol and VEwere almost the same,but the retention rate of sterol was increased6.38%, and the TFA content was reduced0.11%.So the two-stage deodorization process was much better than conventional deodorization onreducing acid value of oil, and retaining the nutrients, and reducing the TFA content ofdeodorized oil.