建立食品和脂肪中的不饱和程度

在当今的食品行业中，重要的是要了解不饱和水平以及可食用油和脂肪中的顺式和反式异构体含量的相对量，这在过程和质量控制方面都是必不可少的，并代表了必要的营养数据食品标签。

全部的unsaturation of oils and fatsis represented as the Iodine Value (IV), which is presently measured through standard titration techniques. Techniques like FTIR are used to measure trans isomer content, while gas chromatography (GC) is used to determine the composition of lipid fatty acids. Conversely, these methods are not suitable for on-line process control due to chromatographic time limitations, infrared (IR) absorption by water, and rigorous sampling needs.

Raman spectroscopy is considered to be a suitable method to make on-line determination of total unsaturation and顺式/译以快速准确的方式在油和脂肪中的异构体含量。在FT-Raman的帮助下，已经出现了该分析的离线演示。本文提供了证明，可以使用用于过程控制的色散拉曼仪器轻松执行此类分析。

Experimental Procedure

一种fully incorporated, remote Kaiser Optical Systems HoloProbe™ analyzer, equipped with 10 mW of 532 nm incident laser light, was used to obtain the data. The entire Raman spectrum was obtained in a single exposure by means of a HoloPlex™ grating, and enabled quantitative analysis across the whole quantified range. Based on the sample, integration times spanned between 60 and 300 seconds.

确定总不饱和

植物油，人造黄油，黄油和蔬菜的拉曼光谱从1150厘米到1775厘米^–1如图1所示。

Figure 1.背景校正的拉曼商业食品和脂肪的光谱。乐队为1165和1525厘米^–1黄油和人造黄油光谱归因于着色剂β-胡萝卜素。

可以通过估计集中在1661 cm的C = C拉伸（νc= C）的比率来实现总不饱和度的定量确定^–1到ch₂剪裁变形（ΔCH₂）1444厘米^–1。当ΔCH的相对强度₂and νC=C were compared, it was observed that butter had the maximum percentage of saturated fat. However, vegetable oil was found to have the least saturation, while margarine and vegetable shortening come between these two extremes. This corresponds with what is qualitatively known beforehand. Vegetable shortenings and vegetable oils are better than animal shortenings in terms of nutritional viewpoint because they have less saturated fat.

顺式异构体内容

TheRaman spectrum也可以用来测量顺式异构体含量。在1272厘米^–1，该频带是平面内= CIS双键中的平面内= C – H变形的结果。顺式异构体含量可以通过该带的强度与1306 cm处的相比甲基扭曲振动的强度直接测量^–1。

This is clearly shown by making a comparison between the Raman spectrum of vegetable oil and the partly hydrogenated vegetable shortening. Hydrogenation leads to a preferential decrease in the cis/trans isomer ratio. In Figure 1, it is seen that unhydrogenated vegetable oil has considerably more cis isomer character as opposed to the partly hydrogenated vegetable shortening.

高度荧光样品的背景校正

背景校正的花生和植物油的完整拉曼光谱如图2所示。背景水平比ΔCH₂vibration intensity emerges in parentheses by individual spectra.

Figure 2.Background-corrected spectra of vegetable and peanut oils.

在商业样品中，清楚地看到了荧光，这是由于各种着色剂引起的。图2显示，尽管存在相当大的背景，但可以立即查看从这些样本组获得的拉曼光谱。具有可感知激发的分散性拉曼为FT-Raman提供了明显的好处，尤其是在荧光不会压倒的情况下。得益于高效的CCD检测器和ν拉曼强度依赖性，灵敏度得到进一步提高。或者，可以使用较长的入射波长来减少或防止荧光。一种RamanRxn1™ analyzerfitted with a 785 nm NIR laser is ideal for this application.

结论

RamanRXN1分析仪提供了高吞吐量，并可以使用短曝光时间和低激光功率来执行远程拉曼测量。该分析仪是紧凑的，具有强大的设计，并且具有最小的实用性要求，这使其适合实验室环境以外的应用。拉曼光谱法可用于在线确定脂肪和油的商业样品中的顺式异构体含量和总不饱和度。

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