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U.S. Department of Agriculture, Agricultural Research Service, Phytonutrients Laboratory, Beltsville Human Nutrition Research Center and
* Biometrical Consulting Service, Beltsville, MD 20705;
U.S. Department of Agriculture, Agricultural Research Service, South Central Agricultural Research Laboratory, Lane, OK 74555; and
** U.S. Department of Agriculture Citrus and Subtropical Products Laboratory, Winter Haven, FL 33881
3To whom correspondence should be addressed. E-mail: clevideb{at}ba.ars.usda.gov.
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ABSTRACT |
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 TOP ABSTRACT SUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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KEY WORDS: • lycopene • ß-carotene • bioavailability • watermelon • tomato
Watermelon is one of few foods rich in lycopene, a nonprovitamin A carotenoid that has up to twice the antioxidant capacity of ß-carotene in vitro (1 –3 ). Data from epidemiological studies suggest lycopene may have protective effects against certain types of cancers (4 –7 ) and cardiovascular disease (8 ,9 ).
Previous investigations of lycopene bioavailability have focused on tomato products (10 –18 ), which represent 80% of lycopene intake in the U.S. diet (19 ). Other natural food sources of lycopene include guava, pink grapefruit, apricots, persimmons and red-fleshed papaya, although the contribution of these foods to dietary lycopene is limited (19 –21 ). The mean lycopene concentration of watermelon (4868 µg/100 g) is about 40% higher than the year-round mean for raw tomato (3025 µg/100 g) (21 ), and watermelon ranks 5th among the major contributors of lycopene in the U.S. diet (19 ). However, the bioavailability of lycopene from watermelon has not been evaluated.
Carotenoid absorption from plants is generally poor relative to carotenoid supplements (12 ) and varies with several factors, including accessibility from the plant matrix (22 ). The crystalline nature of lycopene in tomato may account in part for its apparently low absorption efficiency from the tomato plant matrix (16 ,23 ). The bioavailability of both lycopene and ß-carotene from tomato products has been shown to increase with heat and/or homogenization, processes that break down plant cell walls, allowing release of carotenoids (16 ). Although trans isomers of lycopene are generally stable in the plant matrix, once liberated they are susceptible to heat-induced isomerization to cis isomers (24 ), which may be more readily absorbed (10 ,25 ). Watermelon has a carotenoid profile similar to that of tomato (26 ), but it is not typically heat treated, a factor that might be expected to limit lycopene bioavailability.
The primary objective of this study was to assess the bioavailability of lycopene from watermelon juice using tomato juice as a comparative lycopene-rich food. As secondary objectives, we sought to determine whether a measurable dose-response in plasma lycopene occurs when the amount of watermelon juice consumed is doubled and to compare the plasma lycopene response to tomato and watermelon juices providing a similar amount of lycopene. Plasma responses from other carotenoids present in watermelon and tomato, including ß-carotene, phytoene and phytofluene, were also examined.
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SUBJECTS AND METHODS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Over 19 wk, subjects consumed three of four possible treatments according to a repeated-measures crossover design. Treatments were as follows: 1) C-0, control or base diet only; 2) W-20, base diet plus 20.1 mg/d lycopene and 2.5 mg/d ß-carotene from watermelon; 3) W-40, base diet plus 40.2 mg/d lycopene and 5.0 mg/d ß-carotene from watermelon; and 4) T-20, base diet plus 18.4 mg/d lycopene and 0.6 mg/d ß-carotene from tomato juice. Subjects consumed W-20 and C-0 in separate treatment periods, plus either T-20 or W-40 in a third treatment period. Twelve distinct treatment sequences (i.e., triplets) were assigned to 24 subjects, with each sequence order assigned to two subjects. Subjects were matched by gender, age and body mass index (BMI) to have a nonbiased profile of subjects represented in the split treatments (W-40 and T-20).
Four-week washout periods, during which subjects limited consumption of lycopene-containing foods, were completed between treatment periods 1 and 2, and 2 and 3 to minimize carryover effects on plasma lycopene. A 2-wk washout period was completed before treatment period 1 to allow plasma lycopene to reach stable baseline levels before treatment. Subjects consumed their own foods, but kept written records of fruit, vegetable and beverage intake during the washout periods.
Subjects.
The Committee on Human Research of the Johns Hopkins School of Public Health and Hygiene approved the study procedures. Before enrollment in the study, subjects signed consent forms. Twelve men and 12 women, all healthy, nonsmoking and between the ages of 36–69 y from the Beltsville, MD area were recruited. Subjects’ mean BMI was 27 ± 4 kg/m2 (range: 20–35 kg/m2) and mean age was 51 ± 10 y. Subjects were determined to be healthy by a physician and by routine blood and urine indicators, height, weight and blood pressure. Subjects had no hyperlipidemias, current pregnancy, diabetes, liver disease or kidney disease. Subjects did not take lipid-lowering drugs or supplements high in carotenoids. Eleven men and 11 women completed all three treatments; one subject dropped out of the study before the first treatment and another completed only the C-0 and W-20 treatments.
Watermelon juice.
Watermelon juice was prepared at the USDA Citrus and Subtropical Products Lab (Winter Haven, FL) from Millionaire variety seedless SunripeTM watermelons (Falls Church, VA). Melon flesh was fed into a screw finisher and the pulp was forced through a stainless steel screen tube with perforations of 0.1 mm diameter. The juice was bottled in 0.25 L–capacity high density polyethylene containers (each 260 g or 
1 cup) and frozen immediately without pasteurization. Bottling, freezing and microbial analysis of the juice was done by The Fresh Juice Company/Saratoga Bottling Co. (Winter Haven, FL). The juice was maintained for 1–6 mo at -20°C before consumption or food analysis.
Watermelon juice was thawed in the refrigerator 1–2 d before serving to subjects. Three containers, one at each meal, were provided daily for the W-20 treatment, whereas two containers were provided at each meal for the W-40 treatment. Mean doses of individual carotenoids for each treatment are shown in Table 1 . Watermelon juice provided 150 kJ energy per 100 g (Covance Laboratories, Madison, WI), and contained <0.1 g/100 g total dietary fiber by AOAC Method 991.43 (Medallion Labs, Minneapolis, MN).
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A single lot of commercially available canned tomato juice was purchased locally (Greenbelt, MD), and was not given further heat treatment. For the T-20 treatment, two servings (122 g each, 0.5 cup) of tomato juice were given daily at breakfast and at dinner. Tomato juice provided 84 kJ energy per 100 g (Covance Laboratories) and 0.6 ± 0.05 g total dietary fiber per 100 g (Medallion Labs). The actual amount of lycopene provided with the tomato juice treatment (18.4 mg) was slightly less than the desired dose of 20 mg lycopene because of natural product variability.
Controlled diet.
Subjects were fed controlled, weight-maintenance diets at the Beltsville Human Nutrition Research Center (BHNRC) Human Study Facility. Menus, ranging from 6700 to 15,000 kJ, were prepared in 840-kJ increments by proportionately scaling each food item. Subjects were weighed daily and the diet was adjusted if necessary to maintain starting body weights. Breakfast and dinner were consumed in the dining facility Monday through Friday under the supervision of a registered dietitian. Lunches and weekend meals, including treatments, were packed for take-out. Proportions of macronutrients in the base diet were controlled within narrow ranges and provided a mean of 34% energy from fat, 15% from protein and 51% from carbohydrate. Macronutrient contents of the base diets were calculated using Nutritionist FiveTM (First DataBank; San Bruno, CA), with nutrient values from the USDA Nutrient Database for Standard Reference, Release 14 (28 ). Diets were designed to meet the recommended dietary allowances of known required nutrients.
Diets provided a stable, daily intake of nonlycopene carotenoids, which were held constant as a function of energy required to maintain body weight. The carotenoid content of the base diet was calculated using the 1998 USDA-NCC Carotenoid Database for U.S. Foods (21
). For example, the 10,040 kJ (2400 kcal) diet contained a mean of 2.2 mg carotenoids, including 
-carotene (0.03 mg), ß-carotene (0.84 mg) and lutein/zeaxanthin (1.3 mg). Once per wk, subjects consumed a salad dressing containing 0.9–2.0 mg lycopene, depending on the energy level of the base diet. This was the only source of lycopene on the C-0 (base) diet.
Samples.
Blood samples from fasting subjects were collected at the onset of the study ("preintervention baseline") and then weekly during each 3-wk treatment period. Duplicate blood samples were collected at treatment baseline (wk 0) and at the end of treatment (wk 3). The preintervention baseline sample was taken before the first washout period. "Treatment baseline" or wk 0 samples were collected immediately after a washout period.
Plasma and food analysis.
Plasma samples (800 µL) were precipitated with an equal volume of ethanol containing the internal standard ß-apo-8'-carotenal, and then extracted with 2 volumes of hexane. The combined extracts were dried under N2, then reconstituted with 400 µL mobile phase consisting of acetonitrile:methylene chloride:methanol (65:25:10, v/v/v), 1 g/L butylated hydroxytoluene and 0.1 mL/L N,N-diisopropylethylamine. The sample was then divided into two equal portions for analyses on two analytical HPLC systems, as described below.
Quantitative analyses of total lycopene (cis plus trans), ß-carotene, phytoene, phytofluene, retinol and lutein were performed using a 5-µm reverse-phase C18 Microsorb MVTM column (250 x 4.6 mm) from Varian (Walnut Creek, CA) and a 5-µm C18 BrownleeTM guard column (30 x 4.6 mm) from Alltech (Deerfield, IL). Isocratic elution was performed within 30 min at 20°C at a flow rate of 0.8 mL/min, using an automated Hewlett–Packard (Palo Alto, CA) 1050 Series HPLC system.
Percentages of all trans and cis isomers of lycopene were determined and isomers identified using a gradient elution method (14 ), as modified by Holloway et al. (29 ). Briefly, a 3-µm C30 carotenoid column (4.6 x 250 mm) and guard column (4.6 x 20 mm), both YMCTM columns from Waters Corp. (Franklin, MA), and an Agilent 1100 HPLC system were used. Four cis isomers of lycopene were tentatively identified by retention time and spectra (14 ,29 ,30 ): 15-, 13-, 9- and 5-cis. Three peaks representing unknown isomers were combined and presented as "other"-cis isomers and included an isomer that was spectrally similar to the 9-cis isomer.
Accuracy of the HPLC systems was checked by analysis of Standard Reference Material 968C (National Institute of Standards and Technology, Gaithersburg, MD) and by daily analysis of pooled plasma samples, which were used as secondary reference standards. Carotenoids and retinol were identified by retention times and UV-vis spectra and quantified by reference to standard curves of response values (area of analyte relative to internal standard). All-trans lycopene (Indofine, Somerville, NJ) was used as the standard for total, all-trans and cis isomers of lycopene. HPLC-grade solvents were from Fisher Scientific (Fairlawn, NJ). ß-Apo-8'-carotenal was from Fluka Chemical (Milwaukee, WI) and all other carotenoid standards were from Sigma– Aldrich (St. Louis, MO).
Watermelon and tomato juice samples were evaluated in our laboratory using the extraction method of Tonucci et al. (31 ) and analysis by HPLC, as described for plasma. Food analyses were conducted at the beginning and end of the study to verify the stability of total lycopene and percentages of cis and trans lycopene during storage. Watermelon juice sampled from six cases contained 2.6 ± 0.15 mg lycopene, 0.32 ± 0.03 mg ß-carotene, 0.12 ± 0.01 mg phytoene and 0.06 ± 0.01 mg phytofluene per 100 g serving. Watermelon juice contained 93.7 ± 0.8% of lycopene in the trans isomer form, with the remainder (6.3%) as cis isomers, predominantly 5-cis (3.7%) and 13-cis (1.7%), with smaller amounts of "other"-cis (0.6%), 9-cis (0.2%) and 15-cis (0.1%) isomers present. Tomato juice sampled from eight cases contained 7.6 ± 1.1 mg lycopene, 0.23 ± 0.03 mg ß-carotene, 0.90 ± 0.06 mg phytoene and 0.52 ± 0.03 mg phytofluene per 100 g serving. Tomato juice contained 89.2 ± 0.6% trans lycopene, with the remainder (10.8%) as cis isomers, including 4.1 and 3.3% as 5-cis and "other"-cis isomers, respectively. Smaller amounts of 13-cis (2.0%), 9-cis (1.2%) and 15-cis (0.3%) isomers were present.
Statistics.
A linear mixed model ANCOVA (32 ,33 ) was fit to response variables: total lycopene, cis lycopene (total cis lycopene, including 15-, 13-, 9-, 5- and "other"-cis isomers), trans lycopene, ß-carotene, retinol, lutein, phytoene and phytofluene using SAS version 8.2 (SAS Institute, Cary, NC). The model contained effects of gender, period (treatment period 1, 2 or 3), carryover, treatment, gender x treatment, subject and subject x period, as well as potential covariates of age, preintervention baseline concentration, BMI and wk within treatment period. The response data were log10 transformed to obtain normally distributed model residuals. The Akaike’s information criterion, goodness-of-fit statistic, identified appropriate correlation structures for the ANCOVA models. No correlations were detected among treatment periods, although a significant first-order autoregressive correlation structure was identified, and subsequently modeled, among measurements observed from wk-to-wk within periods.
Effects of treatment period and carryover were modeled and removed from the data variability before the population marginals [i.e., least squares means (LSM) ± SEM] were estimated for the treatment and gender comparisons. Where the covariate level significantly affected response values, mean comparisons were conducted at minimum, mean and maximum covariate values. Where covariates did not produce a significant interaction effect with treatment, overall treatment means were calculated, combining data from both genders and setting each covariate to its mean. Bonferroni-adjusted mean comparisons were conducted to ensure an experimental = 0.05 type I error rate for all means comparisons, which are described below.
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RESULTS |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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For plasma total lycopene, effects of gender, gender x wk, treatment, treatment x wk and treatment x wk2 effects were significant. The wk and preintervention baseline covariates were significant, with log10 lycopene changing both as a linear and quadratic function of wk and as a linear function of preintervention baseline plasma lycopene. Linear models of plasma lycopene fit to each treatment as a function of wk, including both genders and setting the covariate for preintervention baseline lycopene at the mean, are shown in Figure 1A . The LSM for plasma lycopene for W-20, W-40 and T-20 treatments were significantly greater than control at wk 1, 2 and 3 (Table 2 ). There were no significant differences in plasma lycopene LSM for the W-20, W-40 and T-20 treatments at any time. The W-40 treatment produced a twofold increase in plasma lycopene at wk 3, reaching a mean of 1183 nmol/L. This value was not significantly different from the LSM for W-20 (1078 nmol/L) or T-20 (960 nmol/L) treatments at wk 3.
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The increase in plasma total lycopene with watermelon or tomato treatments was attributed to increases in both cis and trans isomers of lycopene (Fig. 2 ). Baseline-adjusted values were obtained by subtracting wk 0 values for cis and trans lycopene from the corresponding wk 3 values for each individual subject. LSM of baseline-adjusted values were then generated for each treatment. There were significant increases from wk 0 to wk 3 in both cis and trans lycopene for W-20, W-40 and T-20 treatments that did not occur for C-0. The increase in trans lycopene was significantly greater for the W-20 and W-40 treatments than for T-20, although the increase in cis lycopene did not differ among W-20, W-40 and T-20 treatments. The cis and trans lycopene concentrations decreased similarly after the C-0 treatment.
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DISCUSSION |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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20 mg/d lycopene from either watermelon or tomato juice resulted in a 100 to 200% increase in plasma lycopene in human subjects. Heat treatment was thus not required for lycopene absorption from fresh-frozen watermelon juice.
Although there has been some doubt about the bioavailability of lycopene from tomato juice (4
,12
), we demonstrated an increase in plasma lycopene from 428 to 960 nmol/L over 3 wk using 18.4 mg/d lycopene from 240 g (1 cup/d) of tomato juice. This finding is in agreement with that of Sakamoto et al. (13
), who reported an increase in plasma lycopene from 425 to 807 nmol/L over 4 wk using 18 mg/d lycopene from tomato juice. Similarly, Paetau et al. (18
) reported an increase in plasma lycopene from 580 to 820 nmol/L over 4 wk using 75 mg/d lycopene from tomato juice. Single-dose studies have not consistently shown changes in plasma lycopene with commercially processed tomato juice unless it is given additional heat treatment (10
,11
). However, the triacylglycerol-rich lipoprotein fraction of plasma has been shown to respond to raw (15
) and canned tomatoes (16
), suggesting whole plasma may not reveal small lycopene responses to single meals.
After W-20, W-40 and T-20 treatments, plasma lycopene concentrations were significantly elevated above control by wk 1, reaching a maximum at wk 2 and a plateau between wk 2 and wk 3. This plateau effect was reported previously (18 ) in response to continued doses of lycopene supplements or tomato juice. In the W-40 treatment, the watermelon dose was doubled, although the plasma lycopene response was similar to that for W-20. Similarly, Sakamoto et al. (13 ) reported no difference in plasma lycopene concentrations in treatment groups fed 18 and 36 mg lycopene/d from tomato juice for 4 wk. These chronic study data support findings from acute studies that suggest absorption of lycopene is more efficient at lower doses (10 ,34 ). It is not clear whether this apparent reduction in absorption efficiency is attributable to a greater proportion of the lycopene dose being excreted or metabolized or to an accumulation of lycopene in nonplasma tissues. Lycopene has been shown to accumulate in prostate tissue of men consuming tomato products (35 ), and it is possible that lycopene accumulates in tissues other than plasma in a dose-responsive manner.
Gender effects were significant for both ß-carotene and lycopene, whereas BMI was not a significant covariate for either ß-carotene or lycopene, and age was a significant covariate for ß-carotene only. Serum concentrations of ß-carotene were previously found to be lower in men than in women (36 ,37 ), as found in the present study. Serum concentrations of lycopene (total, cis and trans) were greater in women than in men at baseline, whereas this difference remained only for cis lycopene after treatment. Previous studies have not shown a consistent relationship between gender and plasma lycopene (20 ). BMI did not remain a significant covariate for ß-carotene or lycopene once factors such as age, preintervention baseline carotenoids and gender were included in the models. We did not, however, assess the effect of body weight alone on carotenoid response. Previous studies found that ß-carotene, but not lycopene, was inversely associated with BMI (36 –38 ). Log10 ß-carotene increased linearly with age in the present study, a finding that agrees with some studies (36 ,37 ) but not others (38 –41 ).
Tomato products are typically 90% or greater trans lycopene (24 ). In contrast, plasma carotenoids are generally >50% cis lycopene (42 ,43 ). The relative percentages of cis and trans isomers in plasma have been suggested to represent an equilibrium state in plasma (25 ,30 ). In the present study, trans (30–32%) and 5-cis (29–31%) lycopene isomers predominated at baseline, a finding consistent with other reports (29 ,43 ,44 ). The percentage trans remained similar at wk 3 of C-0 (27%) treatment, but increased significantly from wk 0 to wk 3 for W-20 (44%), W-40 (46%) and T-20 (38%) treatments. Similarly, Holloway et al. (29 ) reported that 40–45% of plasma lycopene in human subjects was in the trans form after 2 wk supplementation with 21 mg/d tomato paste (84% trans). They also reported a greater (nonsignificant) percentage of cis isomers in HDL than in either LDL or VLDL, and suggested cis-lycopene may be taken up from tissues by HDL in a manner analogous to reverse cholesterol transport. These data (29 ) and those from the present study suggest that, in addition to equilibrium forces that may influence isomer distribution in plasma, the relative proportions of cis and trans isomers are influenced by the balance between uptake and clearance of plasma lycopene by lipoproteins.
Both trans and cis isomers of lycopene in plasma were significantly greater than those for C-0 after W-20, W-40 and T-20 treatments, despite the fairly low concentration of cis lycopene isomers in the lycopene-containing treatments (<11%). This is in agreement with earlier human studies, in which an increase in both trans and cis isomers of plasma lycopene occurred after a single dose of heated tomato juice (15 ) and a 15-d dietary intervention with vegetable juice and tomato sauce (14 ). Accumulating evidence in humans (10 ,15 ) and in animal models (25 ) supports the hypothesis that cis lycopene is preferentially absorbed. Isomerization of trans to cis lycopene is likely to occur during digestion (30 ), but only after trans lycopene is released from the food matrix, in which it is fairly stable (24 ). The increase in trans lycopene was greater for W-20 (and W-40) than for T-20, a finding that may be explained by the difference in trans lycopene consumed per day for the W-20 (18.9 mg trans) and T-20 (16.4 mg trans) doses. Another possibility is that trans lycopene was more readily released from the watermelon matrix than from tomato, although this latter explanation is speculative.
Absorption of carotenoids from plants is influenced by matrix features including the type of chromoplast(s) present and the association of protein with carotenoids (45 ). In the red tomato, lycopene accumulates in long crystalloids, whereas ß-carotene is dissolved in lipid droplets or globules (46 ). This difference in chromoplast types may explain the preferential absorption of ß-carotene from tomato products (16 ). Red watermelon and red tomato have similar carotenoid patterns (26 ), and both have crystalline chromoplasts containing lycopene (46 –48 ), but other similarities or differences in ultrastructure and release of carotenoids during digestive processes remain to be elucidated.
Plasma ß-carotene increased fairly linearly and significantly after W-20 and W-40 treatments, although the plasma response did not differ between these treatments. This may be explained by the large interindividual variation in responses and the reduction in statistical power that occurred because only half of subjects consumed the W-40 treatment. A ß-carotene response was not seen for the T-20 treatment, which contained less ß-carotene than did the W-20 or W-40 treatments. Previous studies showed significant increases in plasma ß-carotene after consumption of 1 mg ß-carotene for 4 d from heated-homogenized tomatoes (16 ) and after consumption of 0.6 mg (13 ) and 2.1 mg (18 ) ß-carotene from tomato juice over 4 wk. Although the dose of ß-carotene provided in the T-20 treatment was small (0.6 mg), the low-carotenoid background diet of the present study produced a general downward trend in plasma carotenoids, which may have masked subtle changes in plasma ß-carotene that might have occurred with the T-20 treatment. ß-Carotene absorption from watermelon appeared to be more responsive to dose than was lycopene, a finding in agreement with animal studies that showed the absorption efficiency of lycopene to be poorer than that of other carotenoids (49 ,50 ).
Phytoene and phytofluene are of interest because they may have protective effects against chronic disease (51 –53 ). Both phytofluene and phytoene concentrations doubled after 3 wk of T-20 treatment, which is consistent with a previous study (18 ). Phytoene was bioavailable from both tomato and watermelon juices, but particularly from tomato juice. Plasma phytofluene increased for T-20 only, although this increase was dramatic despite the fairly small amount (1.1 mg) present in the tomato juice. The significant interactions observed for phytoene (treatment x age) and phytofluene (treatment x preintervention baseline) may not be biologically relevant, given that they were not consistent for the two watermelon treatments.
The means for plasma lycopene at wk 0 (377–452 nmol/L) are similar to the 50th percentile value of 410 nmol/L for adults over age 20 y based on data from NHANES III (54
) and baseline values from previous studies (55
,56
). The population marginal means (LSM) at wk 0 baseline in the present study, although lower than those in some studies (12
,44
), were not atypical. The LSM for plasma lycopene after 3 wk of consumption of dietary treatments including watermelon or tomato juice ranged from 960 to 1183 nmol/L, values that are consistent with lycopene supplementation studies (13
,18
) and also within ranges reported for free living adults (44
,54
). NHANES III data show that the 50th, 90th and 99th percentiles for mean, 1-d intake of lycopene from food are 2.1, 22.3 and 65.5 mg/d, respectively (57
). The dietary intervention with T-20 and W-20 treatments was within the 90th percentile for usual intake for the U.S. diet, whereas that for W-40 was close to the upper end of the typical U.S. intake. If the mean lycopene concentration of watermelon is 4800 µg/100 g (21
) and 1 wedge (1/16th) of a medium-sized watermelon weighs 286 g, and 48% or 137 g of this is the edible portion (27
), then 20 mg of lycopene could be obtained from three wedges of watermelon. Similarly, if 1 cup diced watermelon (152 g edible portion) provides a mean of 7.3 mg lycopene, then 2
cups watermelon would provide 20 mg of lycopene. The dose of lycopene provided and resulting plasma levels in this study are physiologically relevant based on these comparisons.
In healthy human subjects, in the presence of ample fat, lycopene was bioavailable from watermelon juice and produced an increase in plasma lycopene similar to that of tomato juice. This is the first report to demonstrate that lycopene is bioavailable from a watermelon product. We used watermelon in juice form to provide a consistent product across the months of controlled feeding. This would not have been possible with the whole fruit because of the large interindividual variability in lycopene content of watermelons (58 ). Although use of the juice limits the extrapolation of our data to whole watermelon, the juice contained pulp from fresh watermelon and was not heat processed, factors supporting the concept that lycopene is bioavailable from whole watermelon.
In conclusion, we evaluated lycopene bioavailability from two food sources, with no additional heat treatment, and found that lycopene was bioavailable from both fresh-frozen watermelon and canned tomato juices. Plasma concentrations of lycopene were significantly and similarly elevated from 18 to 20 mg lycopene per day from fresh-frozen watermelon juice or canned tomato juice. Heat treatment was not necessary for lycopene absorption from watermelon juice. There was no apparent dose– response effect for plasma lycopene when the amount of watermelon juice consumed was doubled. Watermelon may serve as a bioavailable source of lycopene in the diet.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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2 Supported by the National Watermelon Promotion Board, Orlando, FL, and the Beltsville Human Nutrition Research Center, USDA– ARS, Beltsville, MD.
4 Abbreviations used: BMI, body mass index; C-0, control or base diet; LSM, least squares mean(s); LYC, lycopene; T-20, 18.4 mg/d lycopene from tomato juice; W-20, 20.1 mg/d lycopene from watermelon juice; W-40, 40.2 mg/d lycopene from watermelon juice.
Manuscript received 4 October 2002. Initial review completed 4 November 2002. Revision accepted 13 January 2003.
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LITERATURE CITED |
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TOPABSTRACTSUBJECTS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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