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1.
Carotenoids, lutein and zeaxanthin, found in fruits and vegetables, comprise the macula pigment of the eye. These carotenoids exist in plants as the all-trans geometric form; however, in human plasma, cis isomers of these carotenoids have also been identified. Thermal processing can induce carotenoid trans to cis isomerization. The aim of this research was to determine if thermal processing induces isomerization of lutein and zeaxanthin and to quantify the extent of this reaction. High-performance liquid chromatography was used to separate and quantitate geometric isomers of lutein and zeaxanthin. Isomers were tentatively identified by UV-visible absorbance spectra, comparison of retention times to those of isomerized standards using C(30) chromatography, and mass spectrometry. Thermal processing increased the percent cis isomers of lutein and zeaxanthin up to 22 and 17%, respectively. Further studies are needed to consider the physiological impact of consuming carotenoid isomers in processed vegetables.  相似文献   

2.
(13Z,13'Z,3R,3'R,6'R)-Lutein has been isolated and purified from extracts of marigold flowers, fresh raw kale (Brassica oleracea var. Acephala), and human plasma and fully characterized by (1)H and (13)C NMR, UV/vis, and MS. While the concentration of (13Z, 13'Z)-lutein in kale and human plasma compared to (all-E,3R,3'R, 6'R)-lutein was found to be quite low, this compound was readily isolated by fractional crystallization of lutein from marigold extracts. Thus, the mother liquors from two consecutive crystallizations of lutein from a saponified extract of marigold flowers were enriched in (13Z,13'Z)-lutein (8.7% of total carotenoids) and employed for the isolation of this compound by HPLC. The identity of the di-Z-lutein in kale and human plasma has been established by comparison of the HPLC-UV/vis-MS profiles of the purified compounds with those of a fully characterized sample, isolated from marigolds. 3-Hydroxy-beta,epsilon-caroten-3'-one and 3'-epilutein have also been identified in extracts from marigolds.  相似文献   

3.
Leafy vegetables [Basella rubra L., Peucedanum sowa Roxb., Moringa oleifera Lam., Trigonella foenum-graecum L., Spinacia oleracea L., Sesbania grandiflora (L.) Poir., and Raphanus sativus L.] that are commonly used by the rural population in India were evaluated in terms of their main carotenoid pattern. The extracted carotenoids were purified by open column chromatography (OCC) on a neutral alumina column to verify their identity by their characteristic UV-visible absorption spectra. Reverse-phase high-performance liquid chromatography (HPLC) on a C18 column with UV-visible photodiode array detection under isocratic conditions was used for quantification of isolated carotenoids. Acetonitrile/methanol/dichloromethane (60:20:20 v/v/v) containing 0.1% ammonium acetate was used as a mobile phase. The major carotenoids identified by both methods were lutein, beta-carotene, violaxanthin, neoxanthin, and zeaxanthin. Among the carotenoids identified, lutein and beta-carotene levels were found to be higher in these leafy vegetables. Results show that P. sowa and S. oleracea are rich sources of lutein (77-92 mg/100 g of dry wt) and beta-carotene (36-44 mg/100 g of dry wt) compared with other leafy vegetables. The purity of carotenoids eluted by OCC was clarified by HPLC, and they were found to be 92% +/- 3% for neoxanthin, 94% +/- 2% for violaxanthin, 97% +/-2% for lutein and zeaxanthin, and 90% +/- 3% for beta-carotene. It could be recommended to use P. sowa and S. oleracea as rich sources of lutein and beta-carotene for health benefits. The OCC method proposed is relatively simple and provides purified carotenoids for feeding trials.  相似文献   

4.
Besides the health benefits associated with whole-grain consumption, cereals are recognized sources of health-enhancing bioactive components such as carotenoids, which are a group of yellow pigments involved in the prevention of many degenerative diseases and which have been used for a long time as indicators of the color quality of durum wheat and pasta products. This work reports a fast, sensitive, and selective procedure for the extraction and determination of carotenoids from cereals and cereal byproducts. The method involves sample saponification and extraction followed by normal-phase high-performance liquid chromatography, allowing the separation of the main carotenoids pigments of cereals, especially lutein and zeaxanthin. An application of the established method to various species of cereals and cereal byproducts is also shown. The highest carotenoid levels were found in maize (approximately 11.14 mg/kg of dry weight), which contains high amounts of beta-cryptoxanthin (2.40 mg/kg of dry weight), and, among the cereals considered, has the highest content of zeaxanthin (6.43 mg/kg of dry weight) and alpha+beta-carotene (1.44 mg/kg of dry weight). With the exception of maize, lutein is the main compound found (from 0.23 to 2.65 mg/kg of dry weight in oat and durum wheat, respectively). Moreover, whereas alpha+beta-carotene and zeaxanthin are principally localized in the germ, lutein is equally distributed along the kernel.  相似文献   

5.
The present investigation aimed to expand the knowledge of bioaccessibility of carotenoids, tocopherols, and tocotrienols from cereal products such as pasta. Because most of the published approaches assessing the bioaccessibility of lipophilic micronutrients dealt with fruits and vegetables, a prevalent in vitro digestion procedure was modified. Additionally, several digestion parameters were evaluated with regard to their impact on the bioaccessibility of carotenoids and vitamin E from pasta. Overall, the estimated values were highly dependent on the amount of bile extract present in the digestive medium and to a lesser extent on the simulated gastric pH and the incubation time with digestive enzymes. The bioaccessibility of carotenoids and vitamin E from durum wheat pasta was quite high (71 ± 5 and 70 ± 4%, respectively), whereas these micronutrients were considerably less accessible from pasta containing 10% eggs (57 ± 1 and 49 ± 5%, respectively).  相似文献   

6.
Isomerization of carotenoids, which is often encountered in food processing under the influence of temperature and light, may play a role in the observed protective effects of this group of secondary plant products. Investigation of in vitro antioxidant activity of prominent carotenoid geometrical isomers was undertaken in light of recent reports illustrating a large percentage of carotenoid (Z)-isomers in biological fluids and tissues. Alpha-carotene, beta-carotene, lycopene, and zeaxanthin were isolated from foods or supplements and subsequently photoisomerized with iodine as a catalyst. Major Z-isomers of each carotenoid were fractionated by semipreparative C(30) HPLC. In vitro antioxidant activity of all isomers collected was measured photometrically using the Trolox equivalent antioxidant capacity (TEAC) assay. TEAC values of 17 geometrical isomers investigated ranged from 0.5 to 3.1 mmol/L. Three unidentified (Z)-isomers of lycopene showed the highest antioxidant activity, being significantly higher than the result for (all-E)-lycopene, which had approximately two times the activity of (all-E)-beta-carotene. On the other hand, (9Z)-zeaxanthin had a more than 80% lower TEAC value compared to that of (all-E)-lycopene. These results allow for the in vivo relevance of (Z)-isomers of carotenoids to be considered.  相似文献   

7.
Selected primitive and modern wheat species were evaluated on the basis of their carotenoid composition and effects of the genotype and environment on lutein using spectrometry and liquid chromatography. Carotenoids in the wheat extracts were identified and confirmed on the basis of their UV/vis and mass spectra compared with those of authentic standards. The protonated molecule (M + 1)+ at m/z 569 was the predominant ion for zeaxanthin compared to the fragment ion at m/z 551 for lutein. A similar carotenoid profile was obtained for the wheat species investigated, but significant differences were observed in the concentration of carotenoids. Einkorn (Triticum monococcum) exhibited the highest level of all-trans-lutein, averaging 7.41 microg/g with small amounts of all-trans-zeaxanthin, cis-lutein isomers, and beta-carotene. Durum, Kamut, and Khorasan (Triticum turgidum) had intermediate levels of lutein (5.41-5.77 microg/g), while common bread or pastry wheat (Triticum aestivum) had the lowest content (2.01-2.11 microg/g). Lutein in einkorn appeared to be influenced significantly by environmental growing conditions.  相似文献   

8.
Epidemiological studies have shown that consumption of carotenoid-rich fruits and vegetables is associated with a reduced risk of developing chronic diseases. beta-Carotene, alpha-carotene, and beta-cryptoxanthin are precursors of vitamin A, a nutrient essential for human health. However, little is known about the bioavailability of carotenoids from whole foods. This study characterized the intestinal uptake performance of carotenoids using monolayers of differentiated Caco-2 human intestinal cells and mimicked human digestion to assess carotenoid absorption from carrots and corn. Results showed that Caco-2 cellular uptake of beta-carotene and zeaxanthin was higher than that of lutein. Uptake performances of pure carotenoids and carotenoids from whole foods by Caco-2 cells were both curvilinear, reaching saturated levels after 4 h of incubation. The time kinetics and dose response of carotenoid uptake presented a similar pattern in Caco-2 cells after plating for 2 and 14 days. Furthermore, the applicability of this new model was verified with whole grain corn, showing that cooked corn grain significantly enhanced carotenoid bioavailability. These results support the feasibility of the in vitro digestion cell model for assessing carotenoid absorption from whole foods as a suitable and cost-effective physiological alternative to current methodologies.  相似文献   

9.
This study determined the lutein level in various green leafy vegetables (GLVs) and the influence of olive and sunflower oils on the postprandial plasma and eye response of dietary lutein in adult rats, previously induced with lutein depletion (LD). Fresh GLVs (n = 35) were assessed for lutein (L) and its isomer zeaxanthin (Z) levels by high-performance liquid chromatography and liquid chromatography-mass spectrometry. Among GLVs analyzed, Commelina benghalensis L. contained a higher level of L + Z (183 mg/100 g dry wt) and was used as a lutein source for feeding studies. Rats with LD were fed a diet containing powdered C. benghalensis (2.69 mg lutein/kg diet) with either olive oil (OO group), sunflower oil (SFO group), or groundnut oil (GNO group) for 16 days. The L + Z levels of the OO group were markedly (p > 0.05) higher than those of SFO and GNO groups, in plasma (37.6 and 40.9%) and eyes (22.7 and 30.8%), respectively. These results suggest that oleic acid or OO can be used as a suitable fat source to modulate the absorption of dietary lutein to manage age-related macular degeneration.  相似文献   

10.
The so-called "yellow pigment" content of durum wheat has been used for a long time as an indicator of the color quality of durum wheat and pasta products. For decades the chemical nature of these pigments has been assigned to carotenoids, mainly to the xanthophyll lutein and its fatty acid esters. The chemical composition of the yellow pigments of eight German durum wheat cultivars was studied. Grains were milled on a laboratory mill. Pigment extraction of millstream fractions was performed according to the optimized ICC standard method 152 procedure, and the chemical composition of the extract was analyzed by isocratic reversed phase high-performance liquid chromatography. all-trans-Lutein ranged from 1.5 to 4 mg kg(-1), and zeaxanthin was found in traces. No lutein esters and carotenes were detected. Surprisingly, the fraction of carotenoids of the complete yellow pigment content amounted to only 30-50% of the yellow pigment quantities, so there are still compounds in durum wheat not yet identified that contribute considerably to the yellow color of the grain extracts. The isolation and chemical identification of those pigments are under investigation.  相似文献   

11.
To evaluate the effect of storage temperature, the degradation kinetics of carotenoids in wholemeal and white flour of einkorn cv. Monlis and bread wheat cv. Serio, stored at -20, 5, 20, 30, and 38 degrees C, was assessed by normal-phase high-performance liquid chromatography. In Monlis, the carotenoids content (8.1 and 9.8 mg/kg for wholemeal and white flour, respectively) was 8-fold higher than in Serio (1.0 and 1.1 mg/kg). Only lutein and zeaxanthin were detected in bread wheat, while significant quantities of (alpha and beta)-carotene and beta-cryptoxanthin were observed in einkorn. Carotenoids degradation was influenced by temperature and time, following first-order kinetics. The degradation rate was similar in wholemeal and white flour; however, loss of lutein and total carotenoids was faster in Serio than in Monlis. The activation energy E(a) ranged from 35.2 to 52.5 kJ/mol. Temperatures not exceeding 20 degrees C better preserve carotenoids content and are recommended for long-term storage.  相似文献   

12.
Sixteen carotenoids were isolated from the flesh of Brazilian red guavas (Psidium guajava L.). Their structures were established by means of UV-visible, 400 and 500 MHz (1)H NMR, 120 and 125 MHz (13)C NMR, mass, and circular dichroism spectra. The carotenoids were identified as phytofluene, (all-E)-, (9Z)-, (13Z)-, and (15Z)-beta-carotene, (all-E)-gamma-carotene, (all-E)-, (9Z)-, (13Z)-, and (15Z)-lycopene, (all-E,3R)-beta-cryptoxanthin, (all-E, 3R)-rubixanthin, (all-E,3S,5R,8S)-cryptoflavin, (all-E,3R,3'R, 6'R)-lutein, (all-E,3S,5R,6R,3'S,5'R,8'R)-, and (all-E,3S,5R,6R,3'S, 5'R,8'S)-neochrome. Thirteen of the carotenoids identified are reported as guava carotenoids for the first time.  相似文献   

13.
OBJECTIVE: To evaluate responses to self-administered brief questions regarding consumption of vegetables and fruit by comparison with blood levels of serum carotenoids and red-cell folate. DESIGN: A cross-sectional study in which participants reported their usual intake of fruit and vegetables in servings per day, and serum levels of five carotenoids (alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin and lycopene) and red-cell folate were measured. Serum carotenoid levels were determined by high-performance liquid chromatography, and red-cell folate by an automated immunoassay system. SETTINGS AND SUBJECTS: Between October and December 2000, a sample of 1598 adults aged 25 years and over, from six randomly selected urban centres in Queensland, Australia, were examined as part of a national study conducted to determine the prevalence of diabetes and associated cardiovascular risk factors. RESULTS: Statistically significant (P<0.01) associations with vegetable and fruit intake (categorised into groups: /=4 servings per day) were observed for alpha-carotene, beta-carotene, beta-cryptoxanthin, lutein/zeaxanthin and red-cell folate. The mean level of these carotenoids and of red-cell folate increased with increasing frequency of reported servings of vegetables and fruit, both before and after adjusting for potential confounding factors. A significant association with lycopene was observed only for vegetable intake before adjusting for confounders. CONCLUSIONS: These data indicate that brief questions may be a simple and valuable tool for monitoring vegetable and fruit intake in this population.  相似文献   

14.
Phytochemical profiles and antioxidant activity of wheat varieties   总被引:18,自引:0,他引:18  
Whole grain consumption has been associated with reduced risk of chronic diseases, such as cardiovascular diseases and cancer. These beneficial effects have been attributed to the unique phytochemicals of grains that complement those found in fruits and vegetables. Wheat is one of the major grains in the human diet; however, little is known about the inherent varietal differences in phytochemical profiles, total phenolic and carotenoid contents, or total antioxidant activities of different wheat varieties, which ultimately influence the associated nutritional and health benefits of wheat and wheat products. The objectives of this study were to determine the phytochemical profiles and total antioxidant activity for 11 diverse wheat varieties and experimental lines. The profiles included free, soluble-conjugated, and insoluble-bound forms of total phenolics, flavonoids, and ferulic acids and carotenoid content including lutein, zeaxanthin, and beta-cryptoxanthin. The results showed that total phenolic content (709.8-860.0 micromol of gallic acid equiv/100 g of wheat), total antioxidant activity (37.6-46.4 micromol of vitamin C/g), and total flavonoid content (105.8-141.8 micromol of catechin equiv/100 g of wheat) did not vary greatly among the 11 wheat lines. However, significant differences in total ferulic acid content (p < 0.05) and carotenoid content (p < 0.05) among the varieties were observed, with carotenoid content exhibiting the greatest range of values. Carotenoid content among the 11 wheat varieties exhibited 5-fold, 3-fold, and 12-fold differences in lutein, zeaxanthin, and beta-cryptoxanthin, respectively. A synthetic wheat experimental line, W7985, gave the lowest carotenoid concentrations of any of the genotypes in this study. Such large genotypic differences in carotenoid content may open up new opportunities for breeding wheat varieties with higher nutritional value.  相似文献   

15.
Epidemiological studies have consistently demonstrated that there is an association between carotenoid-rich food intakes with a low incidence in chronic diseases. Nevertheless, there is not an association between the intake of total dietary carotenoids and chronic health incidence in the European population, probably because of different carotenoid food sources and bioavailability. The objective of this study was to evaluate the small and large intestine bioaccessibilities of major dietary carotenoids from fruits and vegetables in a common diet. A bioaccessibility model that includes enzymatic digestion and in vitro colonic fermentation was employed. Lutein presented greater small intestine bioaccessibility (79%) than beta-carotene (27%) or lycopene (40%). With regard to large intestine bioaccessibility, similar amounts of lycopene and beta-carotene were released from the food matrix (57%), whereas small amounts of lutein (17%) were released. These results suggest that 91% of the beta-carotene, lutein, and lycopene contained in fruits and vegetables is available in the gut during the entire digestion process. Colonic fermentation is shown to be important for carotenoid availability in the gut.  相似文献   

16.
The health-promoting effects of whole-grain consumption have been attributed in part to their unique phytochemical contents and profiles that complement those found in fruits and vegetables. Wheat is an important component of the human diet; however, little is known about the phytochemical profiles and total antioxidant activities of milled fractions of different wheat varieties. The objectives of this study were to investigate the distribution of phytochemicals (total phenolics, flavonoids, ferulic acid, and carotenoids) and to determine hydrophilic and lipophilic antioxidant activity in milled fractions (endosperm and bran/germ) of three different wheat varieties, two of which were grown in two environments. Grain samples of each of the wheat varieties were milled into endosperm and bran/germ fractions. Each fraction was extracted and analyzed for total phenolics, ferulic acid, flavonoids, carotenoid contents, and hydrophilic and lipophilic antioxidant activities. Total phenolic content of bran/germ fractions (2867-3120 micromol of gallic acid equiv/100 g) was 15-18-fold higher (p < 0.01) than that of respective endosperm fractions. Ferulic acid content ranged from 1005 to 1130 micromol/100 g in bran/germ fractions and from 15 to 21 micromol/100 g in the endosperm fractions. The bran/germ fraction flavonoid content was 740-940 micromol of catechin equiv/100 g. On average, bran/germ fractions of wheat had 4-fold more lutein, 12-fold more zeaxanthin, and 2-fold more beta-cryptoxanthin than the endosperm fractions. Hydrophilic antioxidant activity of bran/germ samples (7.1-16.4 micromol of vitamin C equiv/g) was 13-27-fold higher than that of the respective endosperm samples. Similarly, lipophilic antioxidant activity was 28-89-fold higher in the bran/germ fractions (1785-4669 nmol of vitamin E equiv/g). Hydrophilic antioxidant activity contribution to the total antioxidant activity (hydrophilic + lipophilic) was >80%. In whole-wheat flour, the bran/germ fraction contributed 83% of the total phenolic content, 79% of the total flavonoid content, 51% of the total lutein, 78% of the total zeaxanthin, 42% of the total beta-cryptoxanthin, 85% of the total hydrophilic antioxidant activity, and 94% of the total lipophilic antioxidant activity. Our results showed that different milled fractions of wheat have different profiles of both hydrophilic and lipophilic phytochemicals. These findings provide information necessary for evaluating contributions to good health and disease prevention from whole-wheat consumption.  相似文献   

17.
OBJECTIVES: Antioxidant nutrients like carotenoids, tocopherols and vitamin C have been suggested to protect against allergic rhinitis and allergic sensitisation but scientific evidence is scarce. The aims of the study were to measure the plasma concentration of six carotenoids, alpha- and gamma-tocopherol and vitamin C as biomarkers of the intake, absorption and subsequent metabolism of these nutrients, and to assess their association with allergic rhinitis and sensitisation. METHOD: Data from a cross-sectional study on representative dietary and lifestyle habits of the population of Bavaria, Germany, were analysed. The plasma levels of six carotenoids (alpha-carotene, beta-carotene, lycopene, lutein/zeaxanthin, canthaxanthin and cryptoxanthin) as well as of alpha-tocopherol, gamma-tocopherol and vitamin C were measured in 547 adults aged between 19 and 81 years. Participants with specific serum immunoglobulin E > or =700 U l(-1) were categorised as sensitised. The association of plasma antioxidant levels, allergic rhinitis and allergic sensitisation was assessed by means of unconditional logistic regression models. RESULTS: We observed a negative association between plasma total carotenoids and the prevalence of allergic rhinitis, with odds ratio (95% confidence interval) of 1.13 (0.54-2.39) for the second, 0.72 (0.33-1.58) for the third and 0.44 (0.19-1.03) for the fourth quartile of total carotenoids concentration (P for trend=0.0332); results for lycopene failed to reach statistical significance (P=0.0608). Other single carotenoids, tocopherols and vitamin C were unrelated to allergic rhinitis. Allergic sensitisation was negatively associated with plasma gamma-tocopherol, with odds ratio (95% confidence interval) of 0.92 (0.51-1.65) for the second, 1.00 (0.56-1.80) for the third and 0.45 (0.23-0.88) for the fourth quartile of plasma gamma-tocopherol concentration (P for trend=0.0410). No other antioxidant was significantly related to allergic sensitisation. CONCLUSIONS: High plasma carotenoid concentrations reflecting a diet high in various fruits and vegetables might have a protective effect on allergic rhinitis in adulthood.  相似文献   

18.
OBJECTIVE: To assess changes in carotenoid intake based on the variations in the consumption of fresh fruit and vegetables in the Spanish population over the period 1964-2004. DESIGN: Consumption data of fresh fruit and vegetables from Family Budget Surveys carried out in 1964, 1980, 1990 and 2004. Consumption data (g per person per day) accounted for >90% of fruit and vegetable consumption at each time point. Quality controlled high-performance liquid chromatography analysis of the carotenoid composition of Spanish fruit and vegetable was used. SUBJECTS: Randomly selected, private households throughout Spain (20,800 households in 1964, 30,311 households in 1980, 21,155 households in 1990 and 6000 households in 2004). Twelve vegetables and 16 fruits representing 89-96% of the total consumption of fresh fruit and vegetables were used. RESULTS: Individual consumption of fruit and vegetables has changed over this period, altering the total and individual intake of carotenoids. Total carotenoid intake increased from 2.5 mg per person per day in 1964 to 4.1 mg per person per day in 1990, with a decrease to 3.3 mg per person per day in 2004. These increments are due to an increase in lycopene, alpha- and beta-carotene, while a decrease in lutein and zeaxanthin is observed during the last decade. A continuous and consistent decrease in the relative contribution of lutein in the diet is observed over the period studied. CONCLUSION: Although the consumption of fruit and vegetables is still consistent with a Mediterranean-type pattern, modifications in the consumption of individual fruits and vegetables have provoked changes in total and specific carotenoid intake with potential relevance in human health.  相似文献   

19.
The influence of thermal treatment and light exposure on degradation and isomerization of the predominant carotenoids (lutein and beta-carotene) occurring in green leafy vegetables was assessed. The effect of lipid addition on carotenoid stability was also evaluated. For the first time, the stabilities of pure carotenoids and chloroplast-bound carotenoids were compared. Besides degradation, heating caused carotenoid isomerization in all samples. Whereas pure carotenoids favor 13-cis isomers, in native chloroplasts and heated chloroplasts 9-cis isomers were predominant. Illumination of freshly prepared chloroplast isolates caused an initial increase in the level of lutein (9.6%) and beta-carotene (29.8%), while pure carotenoids exhibited time-dependent degradation. The addition of lipids to chloroplast preparations had the reverse effects on the retention of both carotenoids after heating; isomerization was not significantly affected. It was demonstrated that carotenoid stability has to be evaluated for every individual pigment in its genuine environment. Stability data based on model systems (e.g., pure carotenoids) may not be transferred to complex food matrices without intensive investigation.  相似文献   

20.
Carotenoids in grapes of three Port winemaking cultivars were investigated. Extracts were obtained with n-hexane/diethyl ether mixtures (0/100; 20/80; 50/50; 100/0) and analyzed by normal and reversed phase HPLC-DAD. Selection and identification of peaks were based on spectroscopic characteristics - lambda(max), (%III/II) and k' values, leading to 28 probable carotenoids. Using pure standards, it was possible to identify seven compounds previously described (neochrome, neoxanthin, violaxanthin, flavoxanthin, zeaxanthin, lutein, and beta-carotene), one more type of neochrome reported here, for the first time, and in addition, two geometrical isomers of lutein and beta-carotene were tentatively described. The remaining 17 need to be further identified. High polarity solvent mixtures lead to qualitatively richer chromatograms. Reversed-phase separations allowed the detection of flavoxanthin and the possible geometrical isomer(s) of beta-carotene. Under normal phase, zeaxanthin was detected, and neochromes were better separated from neoxanthin. Extraction with 50/50 n-hexane/diethyl ether mixtures and reversed-phase conditions was the best combination for analysis of the carotenoids, known as precursors of compounds with high aroma impact in wines.  相似文献   

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