光谱学技术在稀奶油乳脂肪研究中的应用
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摘要
乳脂肪是制备稀奶油的主要原料,不同产地的乳脂肪结构性能差异较大,进而影响稀奶油乳浊液各项性能。利用拉曼光谱动态光散射、近红外光稳定性分析等光谱学技术,研究了不同来源乳脂肪(MF-A,MF-B和MF-C)理化特性,并比较相应稀奶油的稳定性及粒径分布,以说明乳脂肪性能对稀奶油品质的影响。拉曼光谱结果显示:1 303和1 446cm~(-1)—CH_2振动, 2 800～3 000cm~(-1) C—H振动, 1 131cm~(-1) C—C振动的峰信号强弱顺序MF-A>MF-B>MF-C(p<0.05),说明MF-A饱和程度最高; 1 657 cm~(-1) CC振动,信号强弱顺序MF-C>MF-B>MF-A (p<0.05),说明MF-C中顺式不饱和脂肪酸含量最高,三种乳脂肪均为顺式不饱和脂肪酸,无反式脂肪酸。同时,碘值分析进一步验证MF-A饱和度最高,相应乳脂肪硬度大、稳定性和可塑性佳。在0～40℃范围内,不同温度下固体脂肪含量(SFC)由高到低为MF-A>MF-B>MF-C(p<0.05),说明相应的稀奶油宜在4℃贮藏, 10～15℃打发并裱花。在25℃等温结晶1 h,用偏光显微镜观察三个样品,发现MF-A冷却时最先形成晶核并诱导周围脂肪不断结晶而聚集形成小而密的结晶网络。MF-B为细微球晶与针状晶组成的晶体簇,晶体数量少,结晶网络不完整; MF-C晶体分布较为稀疏,数量极少,且晶体平均直径小于20μm。分别用三种乳脂肪制备稀奶油XMF-A, XMF-B, XMF-C,从粒径分布图中看出XMF-A基本为单峰,说明稀奶油乳浊液较稳定,脂肪球没有聚结,而XMF-B, XMF-C为双峰,说明脂肪球均发生了一定程度的聚结,且XMF-C平均粒径最大,所以XMF-C聚结程度高于XMF-B,平均粒径顺序为XMF-AXMF-B>XMF-C(p<0.05)。通过研究以连续相与分散相形式存在的乳脂肪理化特性,发现了脂肪组成、结构与结晶行为规律,探索了乳脂肪结晶对稀奶油品质的影响机制,旨在为制备不同需求乳制品提供原料选择的理论依据。
Milk fat is the main raw constituent of dairy cream. The source of the milk has a significant influence on its physicochemical properties and the presence of the dispersed phase in the emulsion, which, in turn, influences the quality of cream products. In this paper, Raman spectroscopy combined with dynamic light scattering, near infrared spectrum-stability analysis, and other spectroscopy techniques were used to study the physiochemical characteristics of milk fat from three different sources, namely MF-A, MF-B and MF-C, and to compare the corresponding stability of dairy cream. The Raman spectra results indicatedthat 1 303 and 1 446 cm~(-1) were —CH_2 vibrations, 2 800～3 000 cm~(-1)was a C—H vibration, and 1 131 cm~(-1) was a C—C vibration, ith a peak intensity of MF-A>MF-B>MF-C(p<0.05). These results established that MF-A had the highest degree of saturation. 1 657 cm~(-1) was a CC cis-stretching vibration, thus indicating that all samples contained cis-unsaturated fatty acids and had no trans-fatty acids. The peak intensity was MF-C>MF-B>MF-A(p<0.05), indicating that MF-C had the highest cis-unsaturated fatty acid content. Iodine analysis further showed that MF-A had the highest degree of saturation. Solid fat content(SFC) at different temperatures showed MF-A>MF-B>MF-C(p<0.05) in the heat range of 0～40 ℃. Therefore, dairy cream should be stored at around 4 ℃ and whipped cream at between 10 and 15 ℃. After isothermal crystallization at 25 ℃ for 1 h, the three samples were observed under a polarized light microscope: MF-A, which had a low iodine value and a high melting point, formed the nucleus quickly and induced the surrounding fat to crystallize continuously until aggregated to form a dense crystalline network; MF-B exhibited a combination of spherulites and needle-like crystals, and the crystal network was incomplete; MF-C crystals were sparsely distributed with the diameter of each crystal less than 20 μm. Subsequently, dairy creams XMF-A, XMF-B and XMF-C were prepared using MF-A, MF-B and MF-C, respectively. As can be seen in the particle size distribution chart, XMF-A is basically unimodal, suggesting that the cream emulsion was relatively stable and the fat globules were not coalesced. Both XMF-B and XMF-C are bimodal, suggesting partial coalescence of the fat globules, with XMF-C's degree of coalescence greater than that of XMF-B, providing XMF-C with the largest average particle size. The dynamic light scattering results recorded the average particle size of milk fat globules as follows: XMF-AXMF-B>XMF-C(p<0.05). The results of this research, which examines the physicochemical properties of milk fats in their continuous/dispersive phase and the mechanism of milk fat composition and crystallization behavior on dairy cream quality, thus provide a theoretical basis for the selection of raw materials in the preparation of a variety of dairy products.
Milk fat is the main raw constituent of dairy cream. The source of the milk has a significant influence on its physicochemical properties and the presence of the dispersed phase in the emulsion, which, in turn, influences the quality of cream products. In this paper, Raman spectroscopy combined with dynamic light scattering, near infrared spectrum-stability analysis, and other spectroscopy techniques were used to study the physiochemical characteristics of milk fat from three different sources, namely MF-A, MF-B and MF-C, and to compare the corresponding stability of dairy cream. The Raman spectra results indicatedthat 1 303 and 1 446 cm~(-1) were —CH_2 vibrations, 2 800～3 000 cm~(-1)was a C—H vibration, and 1 131 cm~(-1) was a C—C vibration, ith a peak intensity of MF-A>MF-B>MF-C(p<0.05). These results established that MF-A had the highest degree of saturation. 1 657 cm~(-1) was a CC cis-stretching vibration, thus indicating that all samples contained cis-unsaturated fatty acids and had no trans-fatty acids. The peak intensity was MF-C>MF-B>MF-A(p<0.05), indicating that MF-C had the highest cis-unsaturated fatty acid content. Iodine analysis further showed that MF-A had the highest degree of saturation. Solid fat content(SFC) at different temperatures showed MF-A>MF-B>MF-C(p<0.05) in the heat range of 0～40 ℃. Therefore, dairy cream should be stored at around 4 ℃ and whipped cream at between 10 and 15 ℃. After isothermal crystallization at 25 ℃ for 1 h, the three samples were observed under a polarized light microscope: MF-A, which had a low iodine value and a high melting point, formed the nucleus quickly and induced the surrounding fat to crystallize continuously until aggregated to form a dense crystalline network; MF-B exhibited a combination of spherulites and needle-like crystals, and the crystal network was incomplete; MF-C crystals were sparsely distributed with the diameter of each crystal less than 20 μm. Subsequently, dairy creams XMF-A, XMF-B and XMF-C were prepared using MF-A, MF-B and MF-C, respectively. As can be seen in the particle size distribution chart, XMF-A is basically unimodal, suggesting that the cream emulsion was relatively stable and the fat globules were not coalesced. Both XMF-B and XMF-C are bimodal, suggesting partial coalescence of the fat globules, with XMF-C's degree of coalescence greater than that of XMF-B, providing XMF-C with the largest average particle size. The dynamic light scattering results recorded the average particle size of milk fat globules as follows: XMF-A
引文
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[10] Edén J,Dejmek P,L?fgren R,et al.Int Dairy J,2016,61:176.
[2] Ullah R,Khan S,Khan A,et al.J.Raman Spectrosc.,2017,48(3):363.
[3] Zhou X,Chen L,Han J,et al.Int.J.Food Pro.,2016,20(10):2223.
[4] Tzompa-Sosa D A,Ramel P R,Van Valenberg H J,et al.J.Agr.Food Chem.,2016,64(20):4152.
[5] Queirós M S,Grimaldi R,Gigante M L.Food Res.Int.,2016,84:69.
[6] ZHAO Fang,PENG Yan-kun(赵芳,彭彦昆).Chinese Journal of Lasers(中国激光),2017,44(11):1111001.
[7] Buyukbese D,Rousseau D,Kaya A.Int.J.Food Pro.,2018,20(3):3015.
[8] Bayard M,Leal-Calderon F,Cansell M.Food Chem.,2017,218:22.
[9] Thiel A E,Hartel R W,Spicer P T.Journal of the American Oil Chemists’ Society,2017,94(2):325.
[10] Edén J,Dejmek P,L?fgren R,et al.Int Dairy J,2016,61:176.
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