| The physical and chemical properties were analyzed of rice bran stearin(RBS) which is the by-product during rice bran oil(RBO) winterization. Based on the physicochemical properties of RBS, RBS was used as liquid phase oil, and shortenings was prepared by means of enzymatic interesterification and physical blending with fat & oil of higher melting point as solid phase oil to form liquid-solid system. The present research provided a possible application of RBS in nutrition enriched and excellent properties shortening preparation, aiming at solving key problems concerning RBS, such as lack of related research and application and low added value.Firstly, 12 kinds of representative RBS(RBS1~RBS12) were analyzed for their physical and chemical properties. It is showed that RBS were semi-solid, flow and cloudy at room temperature. The properties of RBS are affected by the production places and refining processes obviously. The acid and peroxide value of RBS were significantly lower than the requirement of hygienic standard for edible vegetable oil. RBS mainly contained palmitic acid(17.76%~29.50%), oleic acid(37.99%~43.35%), linoleic acid(24.71%~37.91%), and 0.52%~3.34% of trans fatty acid. Main kinds of triglycerides were tri-unsaturated, mono-saturated and di-saturated triglycerides, but no tri-saturated triglycerides. In addition, RBS are abundant with micronutrients and has strong antioxidant capacity. 12 kinds of RBS can be divided into three categories based on their solid fat content(SFC) curves:(1) with steep SFC curves;(2) with flat SFC curves;(3) always below 6% at each test temperature. Though RBS has relatively poor plasticity, it still can be used as liquid phase of special oil for its unique richness in micronutrients.Secondly, RBS1 and fully hydrogenated soybean oil were used as liquid phase oil and solid phase respectively with additional coconut oil, and then the based oil for shortening was prepared by enzymatic interesterification. The influence of temperature, enzyme addition and reaction time on enzymatic interesterification were studied according to the melting point and SFC at 20℃ of the mixed system. The reaction reached equilibrium at 60℃, enzyme addition of 8%(on reaction substrates mass basis) and reaction time of 4 h. After reaction, the SFC curve became much smoother and plastic range got wider(SFC at 10~35℃ was changed from 34.0%~65.6%, 28.8%~60.0%, and 21.1%~55.6% to 10.8%~71.6%,6.2%~64.1%, and 2.0%~55.9%, respectively). The main polymorph changed from β to β’ and crystal diameter became significantly smaller and more uniform. The triacylglycerol composition significantly changed after interesterification. Besides, oryzanol, phytosterols and tocopherols were abundant and showed no significant decline after reaction.Thirdly, research on shortening preparation by physical blending using RBS, palm stearin(PS, P1~P4) was carried out, and compatibility of the RBS/PS binary blends were analyzed. Based on the compatibility analysis, binary blends with similar SFC to commercial shortenings(C1, C2) were finally acquired. Compatibility studies showed that RBS/PS had a good compatibility, of which RBS1/P2 is the best, and the △SFC is between ±2%; followed by RBS1/P3, the △SFC of binary system(P3 content of 40%~90%) is between ±2.5%; △SFC of other RBS/PS systems are between ±6%. Comparing SFC and slip melting point(SMP) with C1 and C2, the obtained shortening formulas were: C1, RBS1(RBS7, RBS12):P2=20:80; C2, RBS1:P1=70:30, RBS1(RBS7, RBS12)=40:60, RBS1:P3=60:40. Shortening formulas had a comparable SMP(38.1~42.7℃) and plastic range. RBS/PS blends has a β’ crystals and is rich in micronutrients, which might present better nutritional properties.Finally, several shortenings were prepared at laboratory scale, and were evaluated by baking experiment. The quality of bread prepared with experimental and commercial shortenings showed no significant difference(p>0.05). |
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