A GUIDE TO CAROTENOID ANALYSIS IN FOODS

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14 A Guide to Carotenoid Analysis in Foods SOME PHYSICOCHEMICAL PROPERTIES OF <strong>CAROTENOID</strong>S A good understanding of some of the physical and chemical properties of carotenoids allows analysts to determine carotenoids with greater ease and reliability. Solubility With very few exceptions, carotenoids are lipophilic. They are insoluble in water and soluble in organic solvents, such as acetone, alcohol, ethyl ether, chloroform, and ethyl acetate. Carotenes are readily soluble in petroleum ether, hexane, and toluene; xanthophylls dissolve better in methanol and ethanol. Crystalline carotenoids may be difficult to dissolve in the above solvents but do dissolve in benzene and dichloromethane (Schiedt and Liaaen-Jensen 1995). Solubility of both ß-carotene and the xanthophyll lutein in tetrahydrofuran was shown to be excellent (Craft and Soares 1992). Light Absorption The conjugated double-bond system constitutes the light-absorbing chromophore that gives carotenoids their attractive color and provides the visible absorption spectrum that serves as a basis for their identification and quantification. The color enables analysts to monitor the different steps of carotenoid analysis. Loss or change of color at any time during the analysis gives an immediate indication of degradation or structural modification. The color permits visual monitoring of the separation of carotenoids in open-column chromatography, and mainly for this reason this classical technique is still a viable option for quantitative analysis of carotenoids. The ultraviolet and visible spectrum is the first diagnostic tool for the identification of carotenoids. The wavelength of maximum absorption (λmax) and the shape of the spectrum (spectral fine structure) are characteristic of the chromophore. The structure-spectrum relationship has been extensively discussed. The λmax values of common carotenoids, taken mainly from Britton’s (1995) compilation, are shown in Table 7 and will be discussed in relation to the structures by using the absorption in petroleum ether. Most carotenoids absorb maximally at three wavelengths, resulting in three-peak spectra (Figure 8). The greater the number of conjugated double bonds, the higher the λmax values. Thus, the most unsaturated acyclic carotenoid lycopene, with 11 conjugated double bonds, is red and absorbs at the longest wavelengths (λmax at 444, 470, and 502 nm) (Figure 8). At least 7 conjugated double bonds are needed for a carotenoid to have perceptible color. Thus, ζcarotene is light yellow. Being also acyclic, its spectrum has three well-defined peaks, but these are at wavelengths much lower than those of lycopene (λmax at 378, 400, and 425 nm), commensurate with Absorbance 350 400 450 500 550 Wavelength (nm) Figure 8. Visible absorption spectra of lycopene ( ____ ), γ-carotene (- - -), β-carotene (-.-.-.), and α-carotene (....) in petroleum ether.
Some Physicochemical Properties of Carotenoids 15 Table 7. Ultraviolet and visible absorption data for common food carotenoids Carotenoid Solvent λmax, nm a % III/II b Antheraxanthin Chloroform Ethanol 430 422 456 444 484 472 55 Hexane, petroleum ether 422 445 472 60 Astaxanthin Acetone Benzene, chloroform 480 485 0 0 Ethanol 478 0 Petroleum ether 468 0 Auroxanthin Acetone 381 402 427 101 Chloroform 385 413 438 Ethanol, petroleum ether 380 400 425 102 Bixin Chloroform 433 470 502 Ethanol 429 457 484 Petroleum ether 432 456 490 Canthaxanthin Chloroform 482 0 Ethanol 474 0 Petroleum ether 466 0 Capsanthin Ethanol 476 Petroleum ether (450) 475 505 Capsorubin Petroleum ether (455) 479 510 α-Carotene Acetone 424 448 476 55 Chloroform 433 457 484 Ethanol Hexane, petroleum ether 423 422 444 445 473 473 55 β-Carotene Acetone (429) 452 478 15 Chloroform Ethanol (435) (425) 461 450 485 478 25 Hexane, petroleum ether (425) 450 477 25 β-Carotene-5,6-epoxide Ethanol 423 445 474 β-Carotene-5,8-epoxide Ethanol 407 428 452 β-Carotene-5,6,5´,6´-diepoxide Ethanol 417 440 468 β-Carotene-5,8,5´8´-diepoxide Ethanol 388 400 425 δ-Carotene Chloroform 440 470 503 Petroleum ether 431 456 489 85 γ-Carotene Acetone Chloroform 439 446 461 475 491 509 Ethanol 440 460 489 35 Hexane, petroleum ether 437 462 494 40 ζ-Carotene Ethanol 377 399 425 Hexane, petroleum ether 378 400 425 103 Crocetin Chloroform Ethanol 413 401 435 423 462 447 Petroleum ether 400 422 450 α-Cryptoxanthin/Zeinoxanthin Chloroform Ethanol 435 423 459 446 487 473 60 Hexane 421 445 475 60 β-Cryptoxanthin Chloroform Ethanol (435) (428) 459 450 485 478 27 Petroleum ether (425) 449 476 25 Echinenone Acetone Chloroform 460 471 0 Ethanol 461 0 Petroleum ether 458 (482)
Page 1 and 2: A GUIDE TO CAROTENOID ANALYSIS IN F
Page 3 and 4: The use of trade names and commerci
Page 5 and 6: iv A Guide to Carotenoid Analysis i
Page 7 and 8: NATURE OF CAROTENOIDS IN FOODS Food
Page 9 and 10: Nature of Carotenoids in Foods 3 pr
Page 11 and 12: Nature of Carotenoids in Foods 5 As
Page 13 and 14: Nature of Carotenoids in Foods 7 Ta
Page 15 and 16: Nature of Carotenoids in Foods 9 Ta
Page 17 and 18: Nature of Carotenoids in Foods 11 I
Page 19: Nature of Carotenoids in Foods 13 c
Page 23 and 24: Some Physicochemical Properties of
Page 29 and 30: General Procedure and Sources of Er
Page 41 and 42: Do’s and Don’ts in Carotenoid A
Page 43 and 44: Sampling and Sample Preparation 37
Page 45 and 46: Sampling and Sample Preparation 39
Page 47 and 48: Open-column Method 41 OPEN-COLUMN M
Page 49 and 50: Open-column Method 43 than that of
Page 51 and 52: Open-column Method 45 Methylation o
Page 53 and 54: High-Performance Liquid Chromatogra
Page 55 and 56: High-Performance Liquid Chromatogra
Page 57 and 58: Conclusive Identification 51 CONCLU
Page 59 and 60: Conclusive Identification 53 Zeaxan
Page 61 and 62: Method Validation and Quality Assur
Page 63 and 64: Method Validation and Quality Assur
Page 65 and 66: Calculation of Retention in Process
Page 67 and 68: References 61 Emenhiser C, Sander L
Page 69 and 70: References 63 spinach. J Food Sci 5
Page 71:
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A GUIDE TO CAROTENOID ANALYSIS IN FOODS

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