人乳脂中甘油三酯分析方法及组成的研究进展

人乳脂对于婴儿的生长发育有举足轻重的作用。人乳脂是甘油三酯组成最复杂的脂类,详细分析人乳脂中甘油三酯的组成是油脂领域的一大难题。介绍了人乳脂中甘油三酯的分析方法,并比较了国内外人乳脂中甘油三酯的组成。总结了泌乳时期、母亲饮食等因素对人乳脂中甘油三酯组成的影响。对于了解人乳脂的生理功能和人乳替代脂的开发具有重要意义。     

Controlling fat bloom formation in chocolate – Impact of milk fat on microstructure and fat phase crystallisation

The partial replacement of cocoa butter (CB) with milk fat (MF) strongly influences micro-scale topographic evolution and fat phase crystallisation in milk chocolate. Adding MF reduces the incidence of large surface crystals and the number and diameter of amorphous, welled CB deposits (‘cones’), with a concurrent decrease in initial surface roughness (p < 0.05) and rate of surface coarsening. Presence of MF also slows the solidification of the cones into disorganised crystalline masses. Finally, MF reduces the initial solid fat content, and slows the rate of change in whiteness index, as well as the form V to VI polymorphic transition. Fat crystal growth is accelerated by repeated temperature-cycling (26–29 °C) compared to isothermal conditioning (26 °C). However, cone hardening occurs more rapidly when isothermally-stored. Irrespective of fat composition and storage conditions, fat crystal growth, welling and ultimately fat bloom begin only at specific locations on the chocolate surface, suggesting that chocolate’s microstructural heterogeneity is responsible for distinct surface fat crystallisation pathways.     

Fractionation of milk fat by short-path distillation

Fractionation of milk fat by short-path distillation changes the chemical composition and physical properties of the resulting fractions. Increases in distillation temperature from 125 to 250 degrees C increased distillate yield from 0.3 to 42.7% (wt/wt). The distillate was enriched in short- and medium-chain fatty acids and low molecular weight acylglycerols, while the retentate was enriched in long-chain saturated and unsaturated fatty acids as well as high molecular weight acylglyerols. As distillation temperature increased, dropping points of the distillate increased. Relative to native milk fat, the solid fat content (SFC) vs. temperature melting profile of the distillate was depressed and that of the retentate was augmented, which correlated with the saturated long-chain fatty acid content in the fractions. Retentate crystallization parameters obtained by fitting the Avrami model to SFC-time data, did not change as a function of distillation temperature, but varied as a function of the degree of undercooling. Changes in microstructure observed by polarized light microscopy also appeared to be solely a function of the degree of undercooling, with no observable differences between retentates obtained at the different distillation temperatures. In addition, no changes in the retentate's free energy of nucleation (deltaGc) as a function of distillation temperature were found. The compressive storage modulus of the crystallized retentate increased as a function of increasing distillation temperature.     

Continuous Supercritical Fluid Processing of Anhydrous Milk Fat in a Packed Column

A continuous supercritical carbon dioxide processing system was designed, built and operated to investigate its performance for fractionation of anhydrous milk fat (AMF). Packed columns showed mass transfer efficiencies five times greater than a spray column, Short- and medium-chain fatty acids were concentrated in the extract fractions and their amounts decreased as separation pressure increased. The ratio of unsaturated to saturated fatty acids in the raffinate fraction was 0.68 compared to 0.52 in the original AMF. The proportions of low-melting triglycerides in the range —42 to 15°C were greater in the extract fractions (44–72%) compared to the original AMF (29%).     

Effects of canola oil dilution on anhydrous milk fat crystallization and fractionation behavior

Blends of anhydrous milk fat (AMF) and canola oil (CO) were cooled from 35 to 5°C at 0.1°C/min, held for 24 h, and centrifuged to separate the liquid and crystalline fractions. The blends’ crystallization behaviors and microstructures depended on the level of CO present. Onset and half times of crystallization reflected a slower crystallization mechanism at higher levels of CO dilution. These differences were accompanied by a change in microstructure from large spherulites to smaller particles. The biggest change occurred between the 1:4 and 1:5 blends. Canola oil dilution also influenced the polymorphism of milk fat. Whereas only the β′ polymorph was observed in the crystallized 1:2 blend, the β polymorph predominated in the 1:8 blend. Some solubilization of AMF solids into CO was observed. This increased gradually with increasing CO concentration. Compositional analysis revealed the exchange of AMF and CO species between the liquid and crystalline fractions. The crystalline fractions were slightly enriched in AMF triacylglycerols, particularly with the more dilute blends (1:7 and 1:8). Large amounts of oil were trapped in the crystalline fractions, particularly for the concentrated AMF:CO blends where the β′ crystals and spherulitic microstructures were observed. Although the solid fat content profiles of the fractionated blends were marginally higher than those of the starting blends, the samples were very soft and oily. This strategy of using CO to fractionate milk fat was limited by the poor separation of solids and liquid during centrifugation.     

A further investigation of the influence of dietary protected lipid supplements on the characteristics of cows' milk fat

Dairy cows were offered diets containing three commercially available lipid supplements to determine their effect on milk fat composition and melting properties. Changes in fatty acid composition were observed. These were similar irrespective of supplement and agreed with the general trends reported in the literature. Changes in triglyceride composition were also found and these again were similar irrespective of supplement. However, the melting behaviour of the milk fats was different and may possibly be explained by changes in triglyceride structure. Compatibility of the dietary modified milk fats in mixtures with cocoa butter was examined using iso-solid diagrams produced by a computer-aided modelling technique. The differences in compatibility observed were small in magnitude but may still be important to the chocolate manufacturer.     

On the fractional melting of milk fat and the properties of the fractions

Standard methods of fractionating milk fat from the melt produce solid fractions that exhibit melting at temperatures considerably lower than that used for the fractionation. The use of high concentrations of aqueous detergent, in the presence of ammonia as an aid to centrifugation, has resulted in this solid material being sub-fractionated into a semi-solid, plastic material and a crystalline solid. The technique may be applied directly to milk fat to produce three fractions at a given fractionation temperature. Fatty acid compositions and separations according to triglyceride number are recorded for the parent fats and their fractions. Melting fingerprints, obtained by differential scanning calorimetry, are shown for the various samples, and the heats of melting are discussed.     

Lipase mediated upgradation of dietary fats and oils

In the present scenario, fats and oil modification is one of the prime areas in food processing industry that demands novel economic and green technologies. In this respect, tailored vegetable oils with nutritionally important structured triacylglycerols and altered physicochemical properties have a big potential in the future market. In this context, it is well established that lipases especially microbial lipases, which are regiospecific and fatty acid specific, are of immense importance and hence could be exploited for retailoring of vegetable oils. Further, of the bulk available, cheap oils could also be upgraded to synthesize nutritionally important structured triacylglycerols like cocoa butter substitutes, low calorie triacylglycerols, PUFA-enriched and oleic acid enriched oils. It is also possible to change the physical properties of natural oils to convert them into margarines and hard butter with higher melting points or into special low calorie spreads with short or medium chain fatty acids. Today, by and large, fat and oil modifications are carried out chemically following the method of directed inter-esterification. The process is energy intensive and non-specific. Lipase mediated modifications are likely to occupy a prominent place in oil industry for tailoring structured lipids since enzymatic modifications are specific and can be carried out at moderate reaction conditions. However, as a commercial venture, lipases are yet to be fully exploited. Once the technologies are established, the demand of lipases in oil industry is expected to increase tremendously in the near future for specific modifications of fats and oils to meet the changing consumers' dietary requirements.     

The influence of diet and breed of cow on the efficiency of conversion of milk constituents to curd in cheese manufacture

The influence of diet on the efficiency of conversion of milk solids to cheese in two breeds of cow, viz. Jersey and Friesian, was examined. An increase in the efficiency of conversion of milk solids to cheese in Jersey milks produced from cows on winter diets as compared with a typical summer diet was shown to be associated with an improvement in the level of fat retention in curd. The difference in fat retention could to some extent be related to the overall fat content of the milk, the casein to fat ratio and the distribution in the size of the fat globules but these factors when considered collectively or independently could not adequately explain the differences in fat retention observed in these experiments. The level of fat retention in curd was not influenced by the thermal properties of the mik fat.     

天然牛乳脂肪分离及应用研究进展

牛乳脂肪(乳脂)是一种天然的牛奶成分,主要加工成稀奶油、奶油和奶油粉等产品,具有良好的风味和营养价值。随着人们对乳脂营养价值及风味的认识更为全面,我国天然乳脂消费和加工逐年增加。为了扩大乳脂产品的应用范围,越来越多的改性技术被用于优化乳脂类产品,本文对适用于乳脂的不同物理改性技术进行了综述,着重探讨以干法分提为主的现有改性技术中存在的问题和局限,并概述了干法分提技术在奶油产品中的应用,从而为乳脂深加工提供参考。     

Fractionation of buffalo butter oil by supercritical carbon dioxide

Buffalo butter oil was fractionated by supercritical carbon dioxide into four fractions (F₁-F₄). Fractionation was performed at 50 and 70 °C over a pressure range of 10.9-40.1 MPa. Short chain fatty acids (C₄-C₈), medium chain fatty acids (C₁₀-C₁₄) and saturated fatty acids were decreased from F₁ to F₄, while long chain fatty acids (C₁₆-C_18:3) and unsaturated fatty acids were increased. Triacylglycerol molecular species exhibited a similar trend as fatty acids. Cholesterol was concentrated in F₁, and with increasing the fluid density, it decreased by more than 50% in F₄. Substantial changes occurred in the chemical composition of the fractions led to distinctive differences in their thermal profile and solid fat content. Fractions obtained in the initial stages of the fractionation exhibited lower melting behavior that obtained in the late stages.     

Sub-ambient differential scanning calorimetry of lard and lard contaminated by tallow

DSC scans of lard, cow tallow and admixtures were determined by cooling from 70 to −50°C. Analysis of the thermograms indicated that tallow could be detected in lard at concentrations above 1%, although the relative error of determination was large. For mixtures with tallow contents in the range of 6–26%, the relative error in the estimation of tallow content was in the range of 10–1%, respectively.     

Cocoa butter substitutes from sal (Shorea robusta) fat

Commercial sal fats vary in solidification properties and are unsuitable for use as cocoa butter extenders without further processing. Solvent and melt fractionation processes were used and the fractions were evaluated. One type could be satisfactorily fractionated by solvent or by melt fractionation at 23°C to obtain a stearin (yield 75–85%) of satisfactory quality, but the other could only be satisfactorily processed by melt fractionation at 38°C, removing about 10% stearin. The processing requirement of the fat can be assessed easily by determining the cooling curve.