Abstract

The aim of work were the investigations on the using of the rapeseed oil in the milk fat modification. In the work used two raw materials - with a different characteristic of fatty acids - rapeseed oil and milk fat. Rapeseed oil contains about 90% unsaturated fatty acids (mono- and polienic) - milk fat about 70% saturated fatty acids. Modification through undirect interesterification the mixture of rapeseed oil and milk fat in different proportions was carried out. The effect of this process were restructuring of triacylglycerol and in consequence changes of reologhical properities obtained fat. The results of work indicated on partially elimination saturated fatty acids from internal position sn-2 TAG MF and introducing in this place unsaturated FA C-18 number, from rapeseed oil, nondestructing of this fatty acids. The new TAG characterized the lower hipercholesterolemic action of comparising with TAG from milk fat.

Introduction

The aim of work were investigations on obtaining of new type of fats with a new triacylglycerols structure (TAG) on the way chemical and phisycal modificatiom and reologhical behaviour determination.

Experimental

Materials and methods used

The rapeseed oil is widley accepted as a highly nutritious dietary fat source. The main raw material for oil manufacturing in Poland is rape seed of "double zero" variety. The another different fat material is butter. The TAG of milk fat consist of about 70% saturated fatty acids and opposite the TAG of rapeseed oil consist of about 90% unsatureted fatty acids (mono-, di- and polienoic).

The following processes were applied:

• dry fractionation of milk fat,
• "blending",
• the chemical interesterification using sodium methylate as acatalyst,
• filtration and drying under vacuum.

The following methods were applied:

• solid phase content determination by NMR technique using a Bruker "Minispec PC - 120",
• fatty acids composition analysis by gas chromatograph, Hewlett-Packard,
• melting point detrmination in open sealed capilary tube,
• triacylglycerols (TAG) structure determination using pancreatic lipase, TLC and GC,
• determination of sterols and tocopherols by GC and HPLC.

In the first stage this work the anhydrous milk fat (AMF) from domestic butter was obtained. The next high melting fraction - HMF, melting point 42ºC (stearin 1) and middle melting fraction - MMF, melting point 33ºC (stearin 2) by dry fractionation were obtained (chart 1). These fats were as the raw materials in interesterification processes with and without rapeseed oil blends in different proportions.

TABLE 1.Changes of the solid fat content of fat mixture before and after interesterification

( AMF - rapeseed oil)

The melting profiles of milk fat before and after interesterification were different - fig. 1.

The interesterified fat, characterized the lower solid phase content in temperature range between 0ºC to 18 ºC and the higher solid phase content in 18ºC to 35ºC, comparing with MF before interesterification. In the case the butter fat - rapeseed oil mixture interesterification, in different mass proportions (table 1), the result indicated lowering melting profiles, in all areas of temperatures. The next investigations interesterification processes the HMF (mp. 42ºC) and rapeseed oil mixture, indicated in general lowering of solid phase content and melting point. The determination of triacylglycerols structure (TAG) by hydrolysis using pancreatic lipase, indicated partially elimiantion of saturated fatty acids from sn-2 position and introducing in this place unsaturated fatty acids C 18-number (oleic and linoleic) from sn-1,3 position of rapeseed oil. The efect of this modification were lowering of hipercholesterolemc action TAG of milk fa (Gurr M.). The sterols and tocopherols changes befor and after interesterifications processes in studies mixture,were at a low level. In the case interesterified fat, AMF-RO 6:4, the level was: cholesterol - 116,5mg/100g, brassicasterol - 31,3 mg/100g, campasterol - 100,7 mg/100g, ß - sitosterol - 142,4 mg/100g, Δ 5 avenasterol - 5,8 mg/100g, α-tocopherol - 9,3 mg/100g, β+γ tocopherol - 11,3 mg/100g.

Conclusions

The modification of milk fat and rapeseed oil mixture let to obtain a new type fats with different TAG structure and melting behaviour.

The obtained interesterificated fats characterized higher level unsaturated fatty acids in the sn-2 position of TAG,compared to milk fat (important for human metabolism).

Some the obtained interesterified fats allow for preparation fat blends, margarine bases and spreads with very good spreadable at refrigerator temperature.

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