Thermal processing of carrots: Lycopene stability and isomerisation with regard to antioxidant potential

The thermal stability of lycopene was evaluated in a carrot cultivar with a high lycopene content (Daucus carota var. Nutri Red) by (a) exposure of carrot homogenates (with/without the addition of oil) to temperatures ranging from 25 to 140 °C; (b) applying convection and microwave vacuum drying to carrot slices. Heating carrot homogenates at temperatures above 100 °C initiated isomerisation of all-trans-lycopene under non-oxidising conditions, as indicated by a significant increase in 9-cis-lycopene. Isomerisation was enhanced at short treatment times, when sunflower oil was added prior to thermal treatment. Independent from an oil supplement, all-trans-lycopene was degraded at temperatures above 70 °C. The ratio of all-trans- to total-cis-isomers changed from 90:10 to 40:60, indicating a higher lycopene bioavailability due to generated cis-isomers. In oil containing carrot homogenates antioxidant properties of the methanol-soluble components raised after heat treatment at 130 °C for 0.5 h. Lycopene remained stable in dried carrots.     

Influence of extraction with ethanol or ethyl acetate on the yield of lycopene, β-carotene,phytoene and phytofluene from tomato peel powder

This study evaluated the extraction yield of the food grade solvents ethanol and ethyl acetate by extracting lycopene, β-carotene, phytoene and phytofluene from tomato peel powder at varying heating intensities, and the influence of the solvent and heating intensity on carotenoids isomerization and degradation during extraction. The heat treatments assayed were 25, 35, 50 and 60 °C which were applied for periods of 5, 10, 20, 30 or 40 min. The carotenoid yield was higher in the extractions with ethanol than with ethyl acetate. In general, the temperature increase caused an increase in the carotenoid concentrations; however in the extractions performed with ethanol at 60 °C, the yield of (all-E)-lycopene and their (Z)-isomers was lower than at 50 °C. This could indicate that a great isomerization is produced in the high temperature extractions with ethanol but the oxidative degradation is the predominant reaction. On the contrary, the obtained results in the extractions with ethyl acetate indicate that the isomerization is the predominant reaction.     

Lycopene degradation and isomerization in tomato dehydration

Lycopene is an important nutrient, since it appears to provide protection against a broad range of epithelial cancers. Tomatoes and tomato products are the major source of lycopene, and are considered to be an important source of carotenoids in the human diet. Biodegradation of lycopene not only affects the attractive color of the final products, but also their nutritive value. The main cause of lycopene degradation in tomato dehydration is isomerization and oxidation. The objectives of this study were to determine the retention of total lycopene and isomerization in different dehydration methods, and to optimize processing technology for the retention of lycopene biological potency in the tomato products. Experiments were carried out to compare the effect of osmotic treatment, vacuum-drying, air-drying and their combination on the retention of lycopene bioactivity. Firstly a skin treatment was applied to the tomatoes, following an osmotic treatment at 25°C in 65°Brix sucrose solution for 4 h, then vacuum-drying at 55°C for 4–8 h, or air-drying at 95°C for 6–10 h. In the fresh tomato samples, lycopene content is 75.5 μg/100 g on dry weight basis. Lycopene occurs in nature primarily in the more stable all-trans form. A significant increase in the cis-isomers with simultaneous decrease in the all-trans isomers can be observed in the dehydrated tomato samples in the different dehydration methods. The cis-isomers increased with temperature and processing time. In the osmotic treatment, the predominating mechanism is isomerization of lycopene. Since the total lycopene content remained essentially constant, but the distribution of trans- and cis-isomers changed. In the air-drying processing, isomerization and oxidation (autoxidation) as two strong factors affected simultaneously the decrease of total lycopene content, distribution of trans-and cis-isomers, and biological potency. A possible explanation of this result is that sugar enters the tomato matrix and strengthen the binding force on lycopene in the tomato matrix. Osmotic solution (sugar) remaining on the surface layer of the tomato prevents oxygen from penetrating and oxidizing lycopene. The osmotic treatment could reduce lycopene losses in comparison with other dehydration methods.     

Cis-trans isomerisation of lycopene and colour stability of foam—mat dried tomato powder during storage

Tomato powder with ～3% moisture was obtained by foam-mat drying tomato paste (29% solids). Samples of powder were stored at various temperatures (?10° +2° +20° and +37°c), atmospheres (air, nitrogen) and humidities (with and without in-package desiccation), and colour changes were observed for periods of up to 1 year. The main cause of colour fading was the oxidation of lycopene. However, another phenomenon, trans—cis isomerisation of all-trans lycopene, can occur, with apparent loss of coloration, which is later restored by re-isomerisation. The existence of this mechanism was demonstrated by simultaneous measurements of total liposoluble colour at 420 nm and separations of carotenoid pigments by column chromatography on Al₂O₃. Neo-lycopene A (6-mono-cis-lycopene) and at least one other cis-lycopene isomer were found in fresh powder and in samples stored up to 5 months. cis-Isomers were more susceptible to oxidation. Colour changes depend upon the interplay of isomerisation and oxidation; in some cases, tomato powder was more intensively coloured after storage than when fresh. Storage at +20°c was more favourable for colour retention than storage at +2°c, or — 10°c. Excessive desiccation strongly promoted oxidation losses. Storage in an inert atmosphere improved colour retention. At +37°c non-enzymic browning, accompanied by formation of water, caused rapid darkening although carotenoid pigments were not lost to a great extent.     

Comparison of lycopene stability in water- and oil-based food model systems under thermal- and light-irradiation treatments

Lycopene can undergo degradation via isomerization and oxidation during processing and storage. These degradative reactions affect its bioactivity and health benefit functionality. Degradation kinetics and isomerization of lycopene in water- and oil-based tomato model systems were investigated as a function of thermal treatments and light irradiation. Results showed that 80 and 100 °C heating favoured the stability of lycopene in oil-based tomato products. The high heating temperatures (120 and 140 °C) increased isomerization of lycopene and resulting in degradation of total lycopene and cis-isomers in both water- and oil-based tomato products. However, the levels of degradation of total lycopene contents and cis-isomers were greater in water-based samples than in oil-based model systems under different treatments. Heat and light both promoted lycopene isomerization of the all-trans form to the cis-isomers and further oxidation of cis-isomers. The major effect of thermal degradation and photosensitized oxidation was a significant decrease in the total lycopene content, especially the content of cis-isomers. These research results could be useful in assisting industry to improve processing technology and to improve the nutritional value and health-benefits of tomato-based foods.     

Effects of supercritical fluid extraction parameters on lycopene yield and antioxidant activity

The effects of various parameters of supercritical carbon dioxide (SC-CO₂) fluid extractions of tomato skins on the extraction yields and antioxidant activities of lycopene-rich extracts were investigated. A Box–Behnken design was applied to study the effects of three independent variables (temperature ranging from 40 to 100 °C, pressure ranging from 20 to 40 MPa, and flow rate ranging from 1.0 to 2.0 mL/min) on lycopene yield. The model showed good agreement with the experimental results, by the coefficient of determination (r² = 0.9834). Temperature, pressure, and the quadratic term for the temperature of SC-CO₂ extraction were large significantly positive factors affecting lycopene yield (P < 0.05). The maximum total lycopene content of 31.25 μg/g of raw tomato was extracted at the highest temperature of 100 °C, 40 MPa and 1.5 mL/min. TEAC assay was applied to assess the antioxidant activity of lycopene-rich extracts from SC-CO₂ fluid extraction. The effects of SC-CO₂ fluid extraction parameters on the antioxidant activities of the extracts differed with the yield. For each unit of lycopene extract, the antioxidant activity level was constant below 70 °C, but then gradually decreased above 70 °C due to isomerization occurring as a result of the higher temperature. The ratio of all-trans-lycopene to the cis-isomers changed from 1.70 to 1.32 when the operating temperature was adjusted from 40 to 100 °C, indicating an increased bioavailability due to the generation of the cis-isomers. No significant effects of pressure or flow rate of SC-CO₂ fluid extraction on the antioxidant activity were observed.     

Identification and Quantification of All-Trans-Zeaxanthin and Its Cis-Isomers During Illumination in a Model System

The degradation and isomerization of all-trans-zeaxanthin in a model system during illumination, in the absence or presence of iodine, were investigated. A high-performance liquid chromatography method was developed using the C-30 column to separate all-trans-zeaxanthin and its cis-isomers. Three mono-cis-isomers and four di-cis-isomers were assigned by high-performance liquid chromatography-photo diode array detection-atmospheric pressure chemical ionization-mass spectrometry (HPLC-DAD-APCI-MS), namely, 15/15’-cis-, 13/13’-cis-, 9/9’-cis-13,15-di-cis-, 9,15-di-cis-, 9,13-di-cis-, and 9,9’-di-cis-zeaxanthin. 13/13’-cis- and 9, 13-di-cis-zeaxanthin were the major cis-isomers of zeaxanthin formed during illumination. Di-cis-zeaxanthin was favored during illumination in the presence of iodine. The degradation of total amount of all-trans-zeaxanthin during illumination was found to fit a first-order model. The degradation rate of iodine-catalyzed photoisomerization of all-trans-zeaxanthin was faster than that of non-iodine-catalyzed photoisomerization. Isomerization and degradation of all-trans-zeaxanthin and its cis-isomers during illumination proceeded simultaneously.     

Effects of a hydrodynamic process on extraction of carotenoids from tomato

We evaluated the results of using a proprietary hydrodynamic method, which was introduced with the hope of increasing accessibility of beneficial nutrition-enhancing fruit and vegetable products. Tomato, a major dietary source of carotenoids, notably lycopene, was tested because of its many health benefits to consumers. Samples before and after treatment were compared for lycopene, phytoene, and phytofluene contents. Extractable lycopene and other carotenoids increased significantly. In nature, lycopene exists almost exclusively as the all-trans stereoisomer. Cis-lycopene isomers form during cooking and digestion, resulting in higher percentages in plasma and tissues than ingested. Cis-lycopene isomers are more bioavailable than all-trans lycopene. Extraction using this proprietary method increased extracted cis-lycopene to as high as 43% of the total lycopene, indicating increased isomerisation. This method could therefore contribute significantly to the delivery of health benefits of biologically available lycopene from tomato products for metabolic functions.     

Innovative extraction procedure for obtaining high pure lycopene from tomato

Many researchers have studied the biological effects of carotenoids and the more appropriate procedure for extracting them from vegetable sources. In this work we propose a rapid and low-cost procedure to extract lycopene from tomato in order to by-pass the problems related to the high cost of this molecule. Following this procedure we have obtained over 95% pure all-trans-lycopene checked by DAD-HPLC coupled with mass-spectrometer equipped with APCI source and by UV–Vis spectroscopy. Moreover, in order to evaluate the effectiveness of this procedure, we have assayed the capacity of the extracted lycopene to inhibit proliferation in T-lymphocyte jurkat J32 cells in comparison with authentic standard all-trans-lycopene. On this cellular line both standard lycopene and extracted lycopene tended to be dose-dependent but this latter seems to be more active even at lowest concentration.     

Thermal degradation of all-trans-β-carotene in the presence of phenylalanine

Solutions of all-trans-β-carotene in liquid paraffin were stirred under air at 210°C for 15 min in the presence and absence of various amino acids. After cooling, the absorbance values at 460 nm of model systems containing all-trans-β-carotene and phenylalanine, cysteine or tryptophan were 34–58 times higher than that obtained on heating in the absence of an amino acid. Based on absorbance values at 420 nm, 86% of the coloured material present on heating the all-trans-β-carotene-phenylalanine model system at 210°C for 15 min was retained by the liquid paraffin on methanol extraction. The liquid paraffin phase remaining after methanol extraction was analysed by reverse-phase HPLC and three major components were identified as all-trans-β-carotene and two degradation products of all-trans-β-carotene, ie 9-cis-β-carotene and a furanoid diepoxy derivative. None could be detected on heating all-trans-β-carotene alone, suggesting that its degradation was retarded on heating in the presence of phenylalanine.     

A Simple and Fast HPLC Method to Determine Lycopene in Foods

Carotenoids, among which lycopene—the principal pigment found in tomatoes—are lipophilic compounds which play a very important role in human health and nutrition. They are also recognised as strong antioxidants due to their ability to trap singlet oxygen and eliminate the peroxyl radical. The availability of reliable information on lycopene content of foods is essential both for the evaluation of diet and for epidemiological research relating the intake of lycopene. This paper describes a simple and fast HPLC/UV method for lycopene determination in a wide range of food products. All-E-lycopene together with its Z isomers were eluted isocratically using a carotenoid C30 reversed-phase column. The in-house validated HPLC method had a limit of quantification of 60 ng lycopene/g product and high precision and accuracy. The analytical method was successfully applied to several food products such as raw vegetables and fruits and also processed foods. Tomato and tomato-containing products contained the highest amounts of lycopene. While raw foods and minimally processed foods contained above 94% of all-E-lycopene, processed foods (such as soups, pasta sauces, pizza and cheese) contained from 76% to 87% of all-E-lycopene.     

Volatile chemical and carotenoid profiles in watermelons [Citrullus vulgaris (Thunb.) Schrad (Cucurbitaceae)] with different flesh colors

Twelve watermelon [Citrullus vulgaris (Thunb.) Schrad (Cucurbitaceae)] cultivars with different flesh colors were analyzed by HPLC, GC-FID, and GC-MS for their differences in carotenoid, soluble sugar, organic acid, and flavor. Results showed that all-trans violaxanthin, 9-cis-violaxanthin, and luteoxanthin were the main carotenoid esters in watermelons with yellow flesh. However, watermelons with red flesh were rich in all-trans lycopene and their cis-isomers. High concentrations of β-carotene and pro-lycopenes were found in watermelon with orange-yellow flesh. Large variations in the sucrose concentration were observed among the different watermelons. Sucrose and/or fructose were the dominant sugars, while citric acid and malic acid were the main organic acids in watermelon flesh. Limonene was detected in the watermelon flesh of all investigated genotypes. Interestingly, partial correlation analysis of the chemical concentrations revealed 2 significant (p<0.01) positive correlations between β-ionone and β-carotene, and between (E)-geranyl acetone and prolycopenes.     

Stability of carotenoids in tomato juice during processing

The stability of carotenoids in tomato juice as affected by various processing treatments was studied. Fresh tomatoes were crushed, hot-broken at 82 °C, screened and the juice was subjected to the following treatments: (1) heated at 90 °C for 5 min prior to canning; (2) heated in water at 100°C for 30 min after canning; (3) heated at 121°C for 40 s before canning (high-temperature-short-time treatment). The results showed that 16 carotenoids, including all-trans plus cis forms of lutein, lycopene and -carotene, were present in tomato juice. Most cis isomers of carotenoids showed inconsistent change during heating. The high-temperature-short-time treatment generated the highest yield of all-trans plus cis forms of lutein and lycopene, followed by heating at 90 °C for 5 min and heating in water at 100 °C for 30 min. Only a minor change in -carotene was observed for these heating treatments.     

Comparison of thermal,ultraviolet-c,and high pressure treatments on quality parameters of watermelon juice

The effect of thermal, ultraviolet-c, and high pressure treatments on colour, browning degree, dynamic viscosity, and lycopene content of watermelon juice was evaluated based on its pectin methylesterase residual level. Each treatment had a different impact on parameters studied. Ultraviolet-c treatments were rapid and effective to inactivate the pectin methylesterase of the watermelon juice compared to the thermal and high pressure treatments in the same time and temperature. High pressure treatments at 600 MPa kept the colour of the treated watermelon juice close to an untreated one, and that at 600–900 MPa held the browning degree and dynamic viscosity of the treated watermelon juice comparable to an untreated one. Moreover, the high pressure treatment had a slight impact on the all-trans-lycopene, total cis-lycopene, and total lycopene concentration of the watermelon juice compared to the other treatments. In summary, the high pressure treatment showed the lowest changes in colour, dynamic viscosity, browning degree, and lycopene content of the treated watermelon juice amongst the three treatments.     

Ultra-performance liquid chromatographic separation of geometric isomers of carotenoids and antioxidant activities of 20 tomato cultivars and breeding lines

All-trans-lutein, lycopene, β-carotene and their 22 cis-isomers in 20 tomato breeding were separated and identified by a rapid and sensitive UPLC method using a 1.7 μm C₁₈ column and a new gradient mobile phase based on methanol-MTBE-water in 15 min. All-trans-carotenoids were predominant, but 9-cis, 13-cis-lutein, 5-cis, 9-cis, 13-cis, 15-cis, di-cis-lycopene, 9-cis, 13-cis, 15-cis and di-cis-β-carotene were also found. The cis-isomers were identified using absorption around 330 nm and the Q-ratio. The total antioxidant activities as evaluated by PCL and DPPH assays were found to correlate well with the total carotenoid content, but not with the individual carotenoid or its different isomers. This paper provides an efficient analytical method for obtaining a complete picture of carotenoids in tomatoes. It can be a valuable tool for plant breeders, food processors and researchers in developing designer tomatoes and tomato-products with unique carotenoid compositions, and functional properties.     

Influence of the heating temperature on the fat composition of milk fat with emphasis on cis-/trans-isomerization

Milk fats from barn and pasture feeding (WMF and SMF) were analysed for changes in the content of fatty acids, triglycerides and cholesterol after 15-minute heating at 200, 225, 250, 275 and 300°C, respectively. The lower temperatures of 200 and 225°C are realistic in cooking and frying processes, whereas temperatures of 250 to 300°C were chosen to show the effects of overheating the fat. The main focus was put on identification and quantitation of individual isomers of C18 : 1 (trans δ4, δ5 to δ16, cis δ9 to δ15) as well as of C18 : 2 including the conjugated linoleic acid (CLA) isomer cis δ9, trans δ11. The trans isomers among these fatty acids are of great importance as regards nutritional physiology. Furthermore, determinations of the content of α-tocopherol and of free fatty acids as well as of the iodine and peroxide value were performed. Primarily, with rising temperature there was an increase of the elaidic acid (trans δ9) content from 0.3% to 0.5% (WMF) and from 0.2% to 0.7% (SMF) between the base fat and 300°C, whereas in this range the vaccenic acid (trans δ11) content decreased from 1.1% to 0.9% (WMF) and from 3.8% to 3.4% (SMF). The other trans-C18 : 1 isomers as well as the cis isomers δ12 to δ15 exhibited no general trend at these temperatures. The content of oleic acid strongly decreased with the WMF (max. 2.90%), whereas there was no comparable decrease with the SMF (max. 0.48%). This effect possibly was attributable to the content of α-tocopherol being higher by relatively 71% in the SMF. At the higher temperatures particularly strong decreases (base fat → 300°C) were found for cis δ9, cis δ12, trans δ11, cis δ15, cis δ9, trans δ11 (CLA) and linoleic acid (WMF: 1.55 → 0.67%, 0.17 → 0.09%, 0.50 → 0.03%, 0.42 → 0.06%; SMF: 1.05 → 0.67%, 0.54 → 0.38%, 1.71 → 0.35%, 0.61 → 0.17%). All together, absolute losses of fatty acids amounted to max. 4.6% and 6.5% (SMF and WMF, resp.). As losses of linoleic and linolenic acids were not compensated by formation of isomerization products, formation of oxidation products possibly having a high health-threatening potential must have taken place to a greater extent. On the other hand, a great part of these oxidation products are volatile and their amount in the remaining fat was not recorded by the analytical method applied. Anyway, isomerization and oxidation are low at 200°C, but these undesirable effects strongly increase with higher temperatures.     

Effect of illumination and chlorophylls on stability of tomato carotenoids

Lipidic extract from tomato peels, or tomato peels plus stalks, dissolved in ethanol were submitted to illumination. Lycopene, β-carotene, phytoene and phytofluene isomerisation and degradation, during storage at room temperature for 28 days, were studied. Degradation of chlorophylls a and b were analysed in lipidic extracts from stalks. Total lycopene and all-E-lycopene degradation was found to fit to a first-order model. The degradation rate constant was lower in extracts from peels −0.0137 (all-E-lycopene) and −0.0737 (total lycopene), than in those from peel plus stalk −0.0415 (all-E-lycopene) and −0.0854 (total lycopene). Z-lycopene isomers showed an inconsistence change during storage, in all analysed samples. Concentration of β-carotene from extracts of tomato peels plus stalks decreased slightly during storage. Phytoene and phytofluene degradation were not significantly affected by both storage conditions and chlorophylls. The obtained results showed that some compounds from stalks, such as chlorophylls, could favour lycopene and β-carotene degradation during storage under illumination.     

Effects of supercritical CO2 fluid parameters on chemical composition and yield of carotenoids extracted from pumpkin

Pumpkin is a traditional food that is grown extensively worldwide and is believed to be beneficial to human health due to its high contents of carotenoids. The carotenoids in pumpkin were extracted by organic solvents and by supercritical carbon dioxide (SC-CO₂), and then they were identified, quantified, and compared. β-carotene (31 to 40 g per 100 g of total carotenoids) was the predominate carotenoid in pumpkin. Lutein and lycopene contents were much higher in SC-CO₂ extracts than those in organic solvent extract. Cis-β-carotene increased by more than two times in the SC-CO₂ extracts, even at a relatively low temperature of 40 °C, over those in the solvent extracts, indicating both enhanced solubility and isomerization from trans- to cis-β-carotene. The influences of modifier (10 mL/100 mL), temperature (40-70 °C), and pressure (25-35 MPa) of SC-CO₂ extraction on the change of carotenoid yields were also investigated. The highest yield (109.6 μg/g) was obtained at 70 °C and 35 MPa, with a 73.7% recovery. Selective extraction could be achieved by adjusting the temperature and pressure. Higher proportions of all-trans-β-carotene extracts were achieved at 40 °C under both 25 MPa and 35 MPa conditions. In order to extract more cis-isomers, a higher temperature of 70 °C was preferred.     

Beta-carotene isomerisation in mango puree as influenced by thermal processing and high-pressure homogenisation

The present study describes a case study on mango puree, in which focus is given to the effect of thermal processing (100–130 °C, 0–80 min) and high-pressure homogenisation (0–1300 bar) on the isomerisation of β-carotene. Both unit operations are of relevance for the production of mango puree. β-Carotene is an essential micronutrient which is present in a high amount in most mango cultivars, and it is important for human health due to its antioxidant and provitamin A capacity. It is known that these health-related properties of β-carotene are negatively affected by the conversion to cis-isomers. The results have shown that during high-pressure homogenisation of mango puree, β-carotene isomerisation was negligible. During thermal processing, on the other hand, an increase in β-carotene cis-isomer formation with increasing treatment intensity could be observed, although high temperatures and/or long treatment times were required to observe clear additional isomer formation. From a kinetic point of view, a fractional conversion model could be used to model the all-trans-β-carotene isomerisation in mango puree in the temperature and time range studied. In general, it can be concluded that a high percentage of β-carotene is present as cis-isomers in raw mango puree. Furthermore, only intense thermal processing of mango puree leads to the formation of additional cis-isomers in relevant amounts.     

Effects of Heat Treatment on the Carotenoid and Tocopherol Composition of Tomato

Abstract: The objective of this study was to determine the influence of thermal processing on the assessment of tocopherols and carotenoids, as well as their isomer formation in tomatoes. The sliced tomatoes were heated in an oven at 100, 130, and 160 °C for 5, 10, and 20 min, then freeze‐dried. Freeze‐dried samples were finely ground and the analysis was performed on lyophilized samples. The average concentrations of total lycopene, lutein, β‐carotene, α‐tocopherol, and γ‐tocopherol in fresh tomatoes (in 100 g dry weight) were 21.2, 1.1, 2.7, 8.0, and 2.5 mg, respectively. Oven baking of tomato at 160 °C for 20 min led to a significant increase in the apparent measurement of lycopene, β‐carotene, and α‐tocopherol content by 75%, 81%, and 32%, respectively. Heating induced isomerization of (all‐E) to various (Z) isomers of lycopene, and we found that the total (Z)‐lycopene proportion in the tomatoes increased with longer heating time. (All‐E)‐lycopene constituted 75.4% in fresh tomatoes and decreased to 52.5% in oven‐baked tomatoes (160 °C, 20 min), while (5Z)‐lycopene increased from 9.4% to 17.9% of total lycopene. However, β‐carotene release and isomerization was less influenced by the heat treatment than that of lycopene. These results suggested that thermal processes might break down cell walls and enhance the release of carotenoids and tocopherols from the matrix, as well as increase isomerization of lycopene and β‐carotene.