Study On Preparation Of Zero Trans Fatty Acid Baked Shortening From Cottonseed Oil

Shortening is a kind of plastic fats widely used in the bakery and frying food,which introduces a crisp or softening effect on food products.The proportion of base stock in the shortening is as high as 99%.This base stock often involves the use of partially hydrogenated oil which contains sufficient trans fatty acids（TFAs）that endanger human health.In order to decrease the content of TFAs in shortening,a zero-trans fatty acid bakery shortening was prepared by hydrogenation,physical blending and enzymatic interesterification using cottonseed oil（CSO）and the fractionation fat of CSO as raw materials.The hydrogenation of refined cottonseed oil was carried out with nickel as catalyst.The effects of nickel loading,reaction temperature,reaction time and stirring velocity on the iodine value and relative content of TFAs of hydrogenated cottonseed oil were investigated.On the basis of single factor,the process conditions of extreme hydrogenation of cottonseed oil were optimized by response surface method.The optimum conditions for the fully hydrogenation of cottonseed oil were as follows:nickel loading 0.08%,stirring velocity 617 r/min,reaction temperature 138°C,reaction time 115 min.Under these conditions,the iodine value and relative content of trans fatty acids of fully hydrogenated cottonseed oil（FHCSO）were 2.4g/100 g and 0.19%,respectively,and the melting point was 65.3°C.The solid fat content（SFC）of fully hydrogenated cottonseed oil was basically unchanged with the increase of temperature in the range of 0～50°C,decreased sharply in the range of 50～65°C,and the plastic range was narrow.The fatty acid composition was mainly palmitic acid（19.9%）and stearic acid（73.7%）.The melting and crystallization curves showed that the melting range was relatively concentrated and the composition was single.The polymorphic form of the FHCSO wasβ’.The crystal morphology of FHCSO was divergent leaf shape and aggregated to form crystal clusters,and the crystal clusters were closely distributed.Prepared FHCSO was mixed with CSO and the fractionation fat of CSO with different mass ratios,and Lipozyme RM C was used as catalyst for enzymatic interesterification.Enzymatic interesterification conditions were determined by measuring the SFC of the oil and fat before and after the interesterification reaction.The enzymatic interesterification fat was further physically blended with the fractionation fat of CSO to determine the final ratio of shortening base stock.The results indicated that compared with the physical blended fat and interesterification fat of FHCSO and the fractionation fat of CSO,the compatibility of CSO and FHCSO interesterification fat was good,and the SFC（41.5%）of interesterification fat with the ratio of CSO:FHCSO=2:3 at 10°C was almost the same as that of commercial shortening,which ensured the plasticity of plastic fat at low temperature.The content of medium-low melting point triglycerides（TAGs）increased and the slip melting point（SMP）decreased to 52.3°C,which was more suitable as the raw material of shortening base stock.The SFC-20°C and SMP of CSO:FHCSO=2:3 interesterification fat were used as the investigation indexes.The reaction temperature,enzyme dosage and reaction time in the interesterification reaction process of CSO and FHCSO were optimized by single factor.Preliminary optimized reaction conditions were determined as follows:reaction temperature60°C,enzyme dosages 8 wt%,reaction time of 60 min.Interesterification fat prepared under the preliminary optimization conditions was physically blended with the fractionation fat of CSO for different mass ratios.It was found that when the mass ratio of CSO and FHCSO interesterification fat to the fractionation fat of CSO was 3:7,the SFC curve of the obtained blended fat tended to coincide with the commercial shortening,so it was determined as the decisive ratio for the preparation of shortening base stock.The acid value,peroxide value,insoluble impurities content,moisture and volatile matter content of the self-made shortening base stock were consistent with the national standard.The main fatty acids were palmitic acid（34.94%）,stearic acid（15.16%）,oleic acid（10.45%）,linoleum acid（38.28%）,and TFAs were not detected.The triglyceride composition and thermal properties of shortening base stock were analyzed.It was found that the shortening base stock mainly contained diunsaturated-monosaturated（U₂S）,triunsaturated（U₃）and disaturated-monounsaturated（S₂U）TAGs,and its end endothermic peak temperature was 45.3°C,which corresponded to the measured SMP of 45°C.The analysis of polymorphic form and crystal morphology of shortening base stock showed that the crystal form was small and dense needle-shapedβ’crystal form.The effects of emulsifier Span-60,Glycerol monostearate（GMS）and lecithin on the aeration and water absorption of self-made shortening were studied by using the aeration and water absorption of commercial shortening as reference indexes.The emulsifier was compounded and the compound emulsifier formula was optimized by mixture regression design.Finally,the emulsifier formula was determined to be lecithin:GMS:Span-60 mass ratio of 3.95:3.27:2.78.The laboratory finished shortening was prepared with 1%compound emulsifier and 99%self-made shortening base stock,and the appearance,physical and chemical indexes of the laboratory finished shortening were compared with those of the commercially available anhydrous shortening.The results showed that the self-made shortening was milky white,and the ingredients were only fat and emulsifier,while the commercially obtainable shortening was yellow,the ingredients table was more complex,and the other physical and chemical indexes of the two were similar.Two kinds of shortening were used to make traditional pound cake,and the sensory and texture of the cake were analyzed.It was noted that the sensory effect and texture characteristics of the cake baked with two kinds of shortening were similar.Laboratory homemade shortening is a favourable zero trans fatty acid bakery shortening.