基于植物油可见吸收光谱的相关系数鉴别特级初榨橄榄油

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王泓鹏, 万雄. 基于植物油可见吸收光谱的相关系数鉴别特级初榨橄榄油. 光谱学与光谱分析, 2018,38(9): 2814-2819
WANG Hong-peng, WAN Xiong. Distinguishing Extra Virgin Olive Oil Based on the Correlation Coefficient of Visible Absorption Spectrum of Vegetable Oil. Spectroscopy and Spectral Analysis, 2018,38(9): 2814-2819. 复制到剪切板

Doi: 10.3964/j.issn.1000-0593(2018)09-2814-06
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光谱学与光谱分析所有

基于植物油可见吸收光谱的相关系数鉴别特级初榨橄榄油

王泓鹏, 万雄^*

中国科学院空间主动光电技术重点实验室, 中国科学院上海技术物理研究所, 上海 200083

*通讯联系人 e-mail: wanxiong@mail.sitp.ac.cn

作者简介: 王泓鹏, 1989年生, 中国科学院上海技术物理研究所助理工程师 e-mail: wanghongpeng813@163.com

收稿日期: 2016-12-02 接受日期: 2017-10-09

基金项目: 中国科学院上海技术物理研究所创新专项种子基金项目(CX-110), 国家自然科学基金项目(81260225, 51428302), 国家高技术研究发展计划“863”项目(2015AA021103), 中国科学院重点实验室基金项目(CXJJ-14-S134)和中国科学院“百人计划”择优项目资助

摘要

目前市场上的橄榄油品牌很多, 质量参差不齐, 亟需完善橄榄油的等级分类检测和特级初榨橄榄油的鉴别方法。可见吸收光谱光谱法可在不直接接触样品的情况下对样品进行无添加试剂的探测, 因此为实现特级初榨橄榄油的鉴别, 采用可见吸收光谱法对不同种类植物油进行了光谱测量。实验结果发现特级初榨橄榄油在500~780 nm波段内具有4个明显的吸收峰, 而其他种类植物油在此波段内吸光度较弱或无吸收峰, 且同种植物油不同品牌之间的光谱特征极其相似。采用相关系数比对不同种类植物油可见吸收光谱, 分别计算了四个不同波长范围内植物油的可见吸收光谱的相关系数, 实验发现不同波长范围内的植物油可见光谱相关系数差别较大。在520~700 nm范围内, 特级初榨橄榄油间的光谱相关系数在0.999 6以上, 特级初榨橄榄油与其他种类植物油的光谱相关系数均低于0.267 8, 特级初榨橄榄油与其他等级橄榄油的光谱相关系数在0.194 6~0.835 8之间。研究结果表明可见吸收光谱相关系数法是一种快速非接触式鉴别特级初榨橄榄油的可行性方法。建立了一种特级初榨橄榄油快速鉴别方法, 即可见吸收光谱相关系数法。该方法在特级初榨橄榄油的实际鉴别中具有一定的应用价值。

关键词: 吸收光谱; 相关系数; 特级初榨橄榄油; 可见光; 植物油

中图分类号:O675.3 文献标识码:A

Distinguishing Extra Virgin Olive Oil Based on the Correlation Coefficient of Visible Absorption Spectrum of Vegetable Oil

WANG Hong-peng, WAN Xiong^*

Key Laboratory of Space Active Opto-Electronics Technology, Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, Shanghai 200083, China

Abstract

Currently there are many brands of olive oil on the market, and the quality of olive oil is uneven, so it is an urgent need to improve the classification of olive oil classification and extra virgin olive oil ide.pngication method. Visible absorption spectroscopy can be used to detect non-added reagents without direct contact with the sample. Therefore, for the purpose of distinguishing extra virgin olive oil, the spectroscopic measurement of different kinds of vegetable oils was carried out by visible absorption spectroscopy. In order to distinguish the extra virgin olive oils, spectroscopic measurements of different kinds of vegetable oils were carried out using visible absorption spectroscopy. It was found that the extra virgin olive oil had four distinct absorption peaks in the wavelength of 500~780 nm, while other kinds of vegetable oils had weak or no absorption in this band. what’s more, the spectral characteristics of the same brand of vegetable oil were very similar. The correlation coefficients of the visible absorption spectra of vegetable oils in four different wavelength ranges were calculated, and the correlation coefficients of the visible absorption spectra of different kinds of vegetable oils were compared. The results showed that the spectral correlation coefficients of the extra virgin olive oils in the wavelength range of 520~700 nm were 0.999 6. The spectral correlation coefficients between extra virgin olive oil and other kinds of vegetable oil were lower than 0.267 8, and the correlation coefficients between extra virgin olive oil and other olive oils were between 0.194 6 and 0.835 8. The results showed that the correlation coefficient method of visible absorption spectra is a fast and non-contact method for distinguishing extra virgin olive oil. In this paper, a method for rapid ide.pngication of extra virgin olive oil was established, that is, the correlation coefficient method of visible absorption spectrum. The method has a certain application value in the actual ide.pngication of extra virgin olive oil.

Key words: Absorption spectroscopy; Correlation coefficient; Extra virgin olive oil; Visible light; Vegetable oil

文章图片

引言

橄榄油是橄榄果直接冷榨而成, 严格的加工工艺使橄榄油保留了大量的天然营养成分, 其中特级初榨橄榄油是等级最高, 质量最好, 最符合人体吸收的天然产品。而橄榄果渣油是将物理冷榨后的橄榄果果渣经化学法提取制成, 在国际上橄榄果渣油是禁止食用的。自2000年后国内橄榄油的进口量与日俱增, 由原来的年进口量几百吨增长到现在年进口量3.86万吨(2015年), 其原因主要是中国的地理环境不适合大量生产橄榄油, 以2014年为例中国橄榄油的总产量不到两千吨, 这根本满足不了国内橄榄油市场的需求。因此, 国外橄榄油生产大国争相逐鹿中国市场, 并加大开拓中国市场的力度。全世界优质橄榄油的年产总量有限, 国外橄榄油生产大国在保障本国优质橄榄油供应的情况下, 可出口的优质橄榄油总量是有限的, 此外中国各地具备橄榄油检测能力的机构少的现象, 导致许多橄榄油生产大国向中国大量倾销劣质橄榄油, 甚至是工业级橄榄油。因此目前国内橄榄油市场十分混乱, 容易出现掺杂和以次充好的现象, 如用果渣油冒充初榨橄榄油、标签乱贴和生产日期随意更改、未按规定标定橄榄油等级、橄榄油名称乱象等。因此, 亟需完善橄榄油的等级分类检测和特级初榨橄榄油的鉴别方法。

橄榄油的光谱检测法已进行了相对广泛的研究, 例如红外光谱法^{[1, 2]}、拉曼光谱法^{[3, 4, 5]}、荧光光谱法^{[6, 7]}以及紫外光谱法^{[8, 9]}。紫外分光光度法根据208~210和310~320 nm处最大紫外吸收来判断特级初榨橄榄油中是否掺有精炼油。 Torrecilla等^[10]用紫外-可见分光光度法鉴别特级初榨橄榄油中掺入精炼橄榄油和精炼油橄榄果渣油。以上研究为可见吸收光谱在特级初榨橄榄油鉴定中的应用打下了一定的基础。

本工作对十种植物油进行了可见吸收光谱测量, 针对特级初榨橄榄油的鉴定问题, 提出一种基于植物油可见吸收光谱的相关系数鉴别特级初榨橄榄油的方法。

1 实验部分

1.1 仪器

实验采用岛津公司SolidSpec-3700/3700DUV分光光度计, 光谱范围185~3 300 nm。其可见光区的探测器为光电倍增管(PMT), 波长采样间隔1 nm, 波长扫描速度5 000 nm· min^-1, 波长重复性± 0.08 nm, 分辨率0.1 nm, 基线平整度± 0.002 Abs(320~1 600 nm的可见光区)。实验中采用石英比色皿(厚度1 cm)。

1.2 样本采集

实验所用的植物油均来自江西省南昌市某大型超市(花生油为两种不同产地的自榨花生油), 不同品牌的特级初榨橄榄油三种, 稻米油、葵花油、精炼橄榄油及花生油各两种, 橄榄果渣油、菜籽油、玉米油、大豆油、茶油各一种, 均由江西省粮油质量监督检验中心检测。

1.3 光谱采集

光谱采集流程: 控制室温恒定, 保证采集时植物油的温度恒定为25 ℃。调试光谱检测仪, 选定测量光谱的波长范围、光谱带宽等, 并使用移液枪将样本注入石英比色皿中(约2/3的含量)。最后分别采集不同种类植物油的可见吸收光谱如图1所示。

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	图1 植物油可见吸收光谱Fig.1 The visible absorption spectrum of vegetable oils

1.4 谱图预处理

为更好地提取每种植物油的可见吸收光谱指纹特征以及处理数据的方便, 把光谱吸光度数据映射到0~1范围之内处理(即归一化处理), 如图2所示。

	Figure Option View Download New Window
	图2 归一化的植物油可见吸收光谱Fig.2 The normalized visible absorption spectrum of vegetable oils

2 结果与讨论

2.1 植物油可见吸收光谱

特级初榨橄榄油三种品牌(阿格利司牌、范尼奥牌以及萨巴哈比牌)分别标注为Virgin olive oil 1, Virgin olive oil 2, Virgin olive oil 3, 所测得的可见吸收光谱如图3(a)所示。稻米油、葵花油、精炼橄榄油、花生油各两种品牌分别标注为Rice bran oil 1, Rice bran oil 2, Palm olive oil 1, Palm olive oil 2, Refined olive oil 1, Refined olive oil 2, Peanut oil 1, Peanut oil 2, 所测得的可见吸收光谱如图3(b)— (e)所示。橄榄果渣油、菜籽油、玉米油、茶油各一种分别标注为Pomace olive oil, Rapeseed oil, Corn oil和Camellia oil, 所测得的可见吸收光谱如图3(f)所示。

2.2 可见吸收光谱分析

采用相关系数评估各种植物油可见吸收光谱的相似性, 相关系数r可定义为式(1)

$r = \frac{\overset{n}{\sum_{i = 1}} (x_{i} - \overset{̅}{x}) (y_{i} - \overset{̅}{y})}{\sqrt[]{\overset{n}{\sum_{i = 1}} (x_{i} {- \overset{̅}{x})}^{2} \overset{n}{\sum_{i = 1}} (y_{i} {- \overset{̅}{y})}^{2}}}$ (1)

|r|的取值范围在0~1之间, 其大小可以反映出不同光谱指纹特征的相似度, 即当|r|=1时, 不同光谱指纹特征完全一样; |r|越小, 反映出的光谱指纹特征相似度越低。所有植物油可见吸收光谱之间的相关系数如表1所示。

	Figure Option View Download New Window
	图3 不同植物油可见吸收光谱 (a): 初榨橄榄油; (b): 稻米油; (c): 葵花油; (d): 精制橄榄油; (e): 花生油; (f): 其他植物油Fig.3 The visible absorption spectrum of vegetable oils (a): Virgin olive oils; (b): Rice bran oils; (c): Palm olive oils; (d): Refined olive oils; (e): Peanut oils; (f): Other oils

表1 不同植物油的光谱相关系数 Table 1 The spectral correlation coefficients of the different vegetable oils

图4为不同种类不同个体间在不同波段的可见吸收光谱相关系数的雷达图。

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View Download New Window

图4 相关系数雷达图
(a): 320~780 nm吸收光谱相关系数(0~1); (b): 320~780 nm吸收光谱相关系数(0.99~1);
(c): 400~780 nm吸收光谱相关系数(0~1); (d): 400~780 nm吸收光谱相关系数(0.99~1);
(e): 500~780 nm吸收光谱相关系数(0~1); (f): 500~780 nm吸收光谱相关系数(0.99~1);
(g): 520~780 nm吸收光谱相关系数(0~1); (h): 520~780 nm吸收光谱相关系数(0.99~1);
(i): 650~780 nm吸收光谱相关系数(0~1); (j): 650~780 nm吸收光谱相关系数(0.99~1)Fig.4 The radar plot of correlation coefficients r
(a): The correlation coefficients (0~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 320~780 nm;
(b): The correlation coefficients (0.99~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 320~780 nm;
(c): The correlation coefficients(0~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 400~780 nm;
(d): The correlation coefficients(0.99~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 400~780 nm;
(e): The correlation coefficients(0~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 500~780 nm;
(f): The correlation coefficients(0.99~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 500~780 nm;
(g): The correlation coefficients(0~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 520~780 nm;
(h): The correlation coefficients(0.99~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 520~780 nm;
(i): The correlation coefficients(0~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 650~780 nm;
(j): The correlation coefficients(0.99~1) of visible absorption spectrum of virgin olive oils in the wavelength range of 650~780 nm

比较图4(a)— (j), 发现在520~700 nm波段内不同品牌特级初榨橄榄油的可见光谱相关系数最高, 即光谱相关度最好。在520~700 nm波段内, 不同品牌特级初榨橄榄油的光谱相关系数高达0.999 6以上, 与其他种类植物油的光谱相关系数均低于0.267 8, 而与其他等级橄榄油的光谱相关系数取值范围在0.194 6~0.835 8之间(表2)。

表2 520~700 nm内所有植物油光谱的相关系数 Table 2 The spectral correlation coefficients among all whole vegetable oils in the wavelength range of 520~700 nm

	Camellia oil	Corn oil	Rapeseed oil	Rice bran oil 1	Rice bran oil 2	Virgin olive oil 1	Virgin olive oil 2	Virgin olive oil 3	Peanut oil	Pomace olive oil	Refined olive oil 1	Refined olive oil 2	palm oil1	palm oil2	soybean oil
Camellia oil	1	0.793	0.814	0.789 3	0.759	0.060 8	0.067 2	0.09	0.795 6	0.821 8	0.413 5	0.705 3	0.799 9	0.751	0.833 5
Corn oil	0.793	1	0.972	0.995 1	0.990 4	0.137 6	0.149	0.173 7	0.993 9	0.796	0.410 4	0.576 1	0.987 9	0.980 3	0.978 7
Rapeseed oil	0.814	0.972	1	0.982 9	0.981	0.213 5	0.224 7	0.255 9	0.970 3	0.898 2	0.332 4	0.618 2	0.979 9	0.967 3	0.975 3
Rice bran oil 1	0.789 3	0.995 1	0.982 9	1	0.997 1	0.203 6	0.215 1	0.240 9	0.988	0.823 5	0.348	0.555	0.990 7	0.982 3	0.977 4
Rice bran oil 2	0.759	0.990 4	0.981	0.997 1	1	0.205 2	0.217 3	0.243 3	0.983 6	0.817 3	0.337 6	0.538 9	0.985 9	0.984 4	0.969 4
Virgin olive oil 1	0.060 8^①	0.137 6^①	0.213 5^①	0.203 6^①	0.205 2^①	1^②	0.999 6^②	0.997 5^②	0.087 9^①	0.194 6^③	0.835 8^③	0.424 1^③	0.158 6^①	0.184 1^①	0.139 2^①
Virgin olive oil 2	0.067 2^①	0.149^①	0.224 7^①	0.215 1^①	0.217 3^①	0.999 6^②	1^②	0.997 3^②	0.099 3^①	0.203 1^③	0.830 6^③	0.423^③	0.169 1^①	0.195 9^①	0.150 2^①
Virgin olive oil 3	0.09^①	0.173 7^①	0.255 9^①	0.240 9^①	0.243 3^①	0.997 5^②	0.997 3^②	1^②	0.125 7^①	0.244 5^③	0.814^③	0.379 2^③	0.197 6^①	0.220 9^①	0.177 6^①
Peanut oil	0.795 6	0.993 9	0.970 3	0.988	0.983 6	0.087 9	0.099 3	0.125 7	1	0.803 7	0.456 2	0.618 1	0.986 3	0.976 5	0.979 6
Pomace olive oil	0.821 8	0.796	0.898 2	0.823 5	0.817 3	0.194 6	0.203 1	0.244 5	0.803 7	1	0.277 5	0.733 2	0.837 7	0.795 6	0.849 5
Refined olive oil 1	0.413 5	0.410 4	0.332 4	0.348	0.337 6	0.835 8	0.830 6	0.814	0.456 2	0.277 5	1	0.739 4	0.39	0.350 6	0.409 1
Refined olive oil 2	0.705 3	0.576 1	0.618 2	0.555	0.538 9	0.424 1	0.423	0.379 2	0.618 1	0.733 2	0.739 4	1	0.607 7	0.548	0.632 6
palm oil1	0.799 9	0.987 9	0.979 9	0.990 7	0.985 9	0.158 6	0.169 1	0.197 6	0.986 3	0.837 7	0.39	0.607 7	1	0.973 5	0.976 3
palm oil2	0.751	0.980 3	0.967 3	0.982 3	0.984 4	0.184 1	0.195 9	0.220 9	0.976 5	0.795 6	0.350 6	0.548	0.973 5	1	0.960 6
soybean oil	0.833 5	0.978 7	0.975 3	0.977 4	0.969 4	0.139 2	0.150 2	0.177 6	0.979 6	0.849 5	0.409 1	0.632 6	0.976 3	0.960 6	1

注: ①为特级初榨橄榄油与其他种类植物油的可见吸收光谱相关系数; ②为特级初榨橄榄油间的可见吸收光谱相关系数; ③为特级初榨橄榄油与不同等级橄榄油的可见吸收光谱相关系数

表2 520~700 nm内所有植物油光谱的相关系数 Table 2 The spectral correlation coefficients among all whole vegetable oils in the wavelength range of 520~700 nm

3 结论

采用可见光波段(380~780 nm)分别对特级初榨橄榄油、精炼橄榄油、橄榄果渣油、菜籽油、玉米油、大豆油、稻米油、葵花油、自榨花生油以及茶油进行了可见吸收光谱测量, 并分别计算了各样品光谱间的相关系数。研究结果表明: 通过分析不同植物油不同波段可见吸收光谱相关系数, 对比不同植物油间的光谱相关系数, 可以达到鉴别特级初榨橄榄油的目的。尤其在520~700 nm波段内, 不同品牌特技初榨橄榄油的光谱相关度高达0.999 6以上, 与其他种类植物油的光谱相关度均低于0.267 8, 而与其他等级橄榄油的光谱相关度取值范围在0.194 6~0.835 8之间, 本研究表明可见吸收光谱相关系数在鉴别特级初榨橄榄油方面是可行的。该研究对于制定或完善符合当前橄榄油检测要求的国家标准, 以及规范国内橄榄油市场具有一定的参考意义。

The authors have declared that no competing interests exist.

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