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J. Nutr. First published December 3, 2008; doi:10.3945/jn.108.098947
 Journal of Nutrition, doi:10.3945/jn.108.098947
Vol. 139, No. 1, 44-50, January 2009
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© 2009 American Society for Nutrition

Nutrient Physiology, Metabolism, and Nutrient-Nutrient Interactions

Sweet Potato β-Carotene Bioefficacy Is Enhanced by Dietary Fat and Not Reduced by Soluble Fiber Intake in Mongolian Gerbils1,2

Jordan P. Mills3, Gaston A. Tumuhimbise4, Kazi M. Jamil5, Sagar K. Thakkar6, Mark L. Failla6,7 and Sherry A. Tanumihardjo3,*

3 Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin, Madison, WI 53706; 4 Department of Food Science and Technology, Makerere University, Kampala, Uganda; 5 International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka, Bangladesh 1212; and 6 Interdisciplinary Ph.D. Program in Nutrition, and 7 Department of Human Nutrition, The Ohio State University, Columbus, OH 43210

* To whom correspondence should be addressed. E-mail: sherry{at}nutrisci.wisc.edu.


   ABSTRACT
TOP
 ABSTRACT
Introduction
 Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 
Orange-fleshed sweet potato (OFSP) is an important source of β-carotene (βC). Provitamin A bioefficacy from plant foods is influenced by dietary fat and fiber. We fed 3% OFSP powder diets with varying amounts of fat and soluble fiber to vitamin A (VA)-depleted Mongolian gerbils (n = 85) for 3 wk (8 groups, n = 10/group; control, n = 9) following a baseline kill (n = 6). OFSP diets differing in fat (3, 6, and 12%) contained 0.24% soluble fiber. Two additional 3% OFSP diets contained 6% fat and 3 or 9% white-fleshed sweet potato (WFSP) powder with soluble fiber contents of 0.42 and 0.80%, respectively. Control, VA-, and βC-supplemented groups were included. Simulated digestion experiments compared the bioaccessibility of βC from boiled vs. oil stir-fried OFSP. All OFSP diets maintained VA status and 12% fat and WFSP-added diets improved VA status above baseline (P < 0.05). Bioefficacy, as bioconversion factors, in gerbils fed 12% fat (3.5 ± 1.4 µg βC:1 µg VA) was improved over the 3% fat and βC groups (6.5 ± 3.7 and 6.7 ± 3.7 µg βC:1 µg VA, respectively) (P < 0.05) but did not differ from WFSP-added groups or the 6% fat group with no WFSP. Stir-frying doubled the efficiency of βC incorporation into micelles during small intestinal digestion in support of the stimulatory effect of dietary fat on bioefficacy in vivo. Soluble fiber intake derived from WFSP did not influence bioefficacy. Replacing WFSP with OFSP will affect VA status if adopted by target groups.


   Introduction
TOP
 ABSTRACT
 Introduction
Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 
Vitamin A (VA)8 deficiency is the most common cause of childhood blindness worldwide (1), much of which can be attributed to VA-deficient diets (2). Animal foods with preformed VA, e.g. liver, eggs, and milk, are often too expensive for poor communities (3), making plant foods the primary sources of provitamin A in developing countries.

Bioavailability of β-carotene (βC) is affected by many factors (4). Recent studies show that minimal fat is necessary for in vitro formation of micelles (5) and absorption and conversion of βC to retinol (6). The food matrix and processing affect the bioaccessibility of provitamin A carotenoids (7). Some dietary fibers have been reported to reduce carotenoid absorption in women (8). Although different factors affecting bioavailability of carotenoids have been studied, knowledge of their interaction remains limited. Specifically, the influence of dietary fibers and fats on carotenoid bioavailability and bioefficacy has not been elucidated.

Biofortification of candidate crops to enhance provitamin A content represents a recent strategy to combat VA deficiency (9). Orange-fleshed sweet potato (OFSP) [Ipomoea batatas (Lam)] is a staple crop targeted for biofortification (10). Efforts to biofortify sweet potato have focused on increasing βC content and improving organoleptic qualities of commonly consumed varieties. Replacement of white-fleshed sweet potato (WFSP) with orange-fleshed varieties could benefit ~50 million children < 6 y of age at risk of VA deficiency (11).

Recent human interventions have focused on different aspects of βC bioavailability from OFSP. Using stable isotope methodology (12), bioconversion of sweet potato βC was 13.4 µg βC to 1 µg retinol9 in Bangladeshi men fed a daily snack of 80 g sweet potato. Liver reserves assessed with the modified relative dose response test improved with a daily portion of OFSP fed during school days to South African schoolchildren (13). Likewise, serum retinol concentrations improved in young children after the introduction of OFSP into Mozambique (14).

The Mongolian gerbil model (15) has been used to assess bioefficacy of {alpha}-carotene (16), βC (17–20), and β-cryptoxanthin (21) from supplements, carrots (17–19), maize (22), cassava (23), and green vegetables (23). The gerbil model provides estimates of dietary provitamin A bioefficacy and is ideal for studying whole-body metabolism. Bioaccessibility can be evaluated using in vitro methods that simulate oral, gastric, and small intestinal conditions. The formation of mixed micelles through bile salts (24) mediates the delivery of carotenoids to the brush border surface of enterocytes (25,26). The current study investigated the influence of dietary fat and soluble fiber in sweet potato on the VA bioefficacy of βC from OFSP using gerbils. The bioaccessibility of βC from boiled vs. oil stir-fried OFSP was examined using in vitro digestion to explain in vivo observations regarding the potentiating effect of dietary fat on bioefficacy.


   Materials and Methods
TOP
 ABSTRACT
 Introduction
 Materials and Methods
Results
 Discussion
 LITERATURE CITED
 
    Sweet potato preparations. Boiled (10–15 min) and peeled OFSP and WFSP cubes were forwarded from Bangladesh on dry ice by Dr. Marjorie Haskell (University of California-Davis) to University of Wisconsin for the gerbil study and to Ohio State University for simulated digestion. For gerbils, samples were freeze-dried and ground into powders with a coffee grinder. For simulated digestion experiments, OFSP cubes were thawed overnight at 4°C, immersed in 5 parts water, and boiled at 95°C for 5 min. One-half of the cubes were stir-fried in soybean oil (5% v:wt) in a stainless steel pan for 5 min at 95°C while constantly stirring with a stainless steel spatula. Samples were cooled for 10 min before storing in 50-mL polypropylene screw-cap tubes under nitrogen at –80°C. The cooking methods were similar to those that were employed in a human feeding intervention to determine the influence of stir-frying on bioefficacy.

    Analyses of sweet potato phenolic content and antioxidant capacity. Total phenolic concentration of sweet potato powder was determined (27) using gallic acid to quantify phenolics as gallic acid equivalents (28). Lipophilic and hydrophilic antioxidant capacities were determined with the 2, 2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation decolorization assay and expressed as Trolox equivalent antioxidant capacity (TEAC)/g sweet potato (29).

    Determinations of sweet potato protein, fat, and fiber. Crude protein analyses were performed according to the Kjeldahl procedure (30) with a boric acid modification (31). Analysis for fat content of sweet potato powders used a Folch extraction method (32). Briefly, sweet potato powder (10 g) was ground repeatedly in a mortar and pestle with dichloromethane and filtered into a 50-mL flask. An aliquot (10 mL) was transferred to a tube, dried under argon, and placed in a desiccator overnight under vacuum. The difference between the initial and final weight was considered extracted fat.

Insoluble fiber concentrations were determined with neutral and acid detergent methods after treatment with amylase (33). Total soluble fiber was determined gravimetrically after base treatment (34), {alpha}-amylase digestion of starch (35,36), and dialysis (36). OFSP and WFSP powders were dried overnight at 55°C. Duplicate samples were weighed (1 g) into 15-mL polypropylene tubes and treated with 1.5 mL NaOH (0.125 mol/L) for 20 min at 95°C. Starch was digested with {alpha}-amylase (Sigma) in Tris-acetate buffer (pH 6.0) overnight at 50°C and continued until starch was no longer detected. Following centrifugation at 4000 x g; 15 min, the supernatant was transferred and saved. The pellet was washed with hot water 2 times followed by washes with 95% ethanol, 80% ethanol, acetone, chloroform, and acetone. Supernatants from each wash were added to that collected from the amylase digestion and the pooled fractions were dialyzed to remove digestion products. The dialyzed supernatant was freeze-dried and the remaining pellet, which was considered the cell-wall residue fraction, was dried for several days at 55°C for determination of neutral sugar (37) and uronic acids (38) in the supernatant and cell wall residue.

    Gerbils and procedures. We obtained male 40-d-old Mongolian gerbils (n = 87) from Charles River Laboratories. Gerbils were housed in plastic cages and consumed feed and water ad libitum. Two gerbils did not adapt to the diet and were killed. Gerbils were weighed daily and monitored for health until all were thriving, at which time they were weighed every 2 d. Gerbils were killed by exsanguination under isoflurane anesthesia. Blood samples were centrifuged at 2200 x g; 15 min at 4°C in BD Vacutainer Gel and Clot Activator tubes (Becton Dickinson) for serum isolation. Livers were excised and stored at –80°C. All animal handling procedures were approved by the College of Agriculture and Life Sciences Animal Care and Use Committee of the University of Wisconsin-Madison.

    Experimental diets and study design. Gerbil feeds (Harlan-Teklad) were designed using carotenoid- and VA-free purified basal diets with added sweet potato powder (Table 1). For the 5-wk VA depletion phase, all gerbils (n = 85) were fed the basal diet with no added sweet potato followed by a baseline kill (n = 6). Gerbils were separated into 8 groups (n = 10/group) except control (n = 9) and fed diets containing 3% OFSP or WFSP for 3 wk. OFSP diets with no added WFSP contained 3, 6, or 12% fat and 0.24% soluble fiber (Table 1). Two additional OFSP diets with 6% fat contained WFSP at concentrations of 3 and 9% (0.42 and 0.80% total soluble fiber, respectively) for a total potato content of 3, 6, and 12%. Control, βC, and VA groups were fed 3% WFSP diets and supplemented orally with cottonseed oil, βC, or retinyl acetate in oil, respectively, twice daily using a positive displacement pipette. Fat concentrations were manipulated with different basal diets, whereas soluble fiber concentrations were manipulated by adding different amounts of WFSP (Table 1). All treatment diets contained equal concentrations of insoluble fiber (6%), consisting of cellulose from the purified diet and cellulose, hemicellulose, and lignin from the added sweet potato. The βC supplement matched the βC intake from the OFSP groups on the prior day. The amount of VA administered was calculated as 50% of the theoretical bioconversion rate of βC in the OFSP (12).


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  		TABLE 1 Composition of purified diets with added sweet potato powder fed to Mongolian gerbils1

 
    Preparation of βC and VA supplements. Doses were prepared by dissolving βC supplements (GNC) into hexanes and then cottonseed oil using sonication. Hexanes were removed by rotary evaporation and flushing with argon. Retinyl acetate (Sigma) was dissolved into cottonseed oil using sonication. Final concentrations of βC (0.86 x nmol in 1 µL) and VA (0.98 x nmol in 1 µL) were determined by dissolving an aliquot in hexanes and using the E1%1 cm (2592 for βC and 1810 for VA) at 450 and 325 nm, respectively.

    In vitro digestion of OFSP. Cooked sweet potatoes were subjected to simulated oral, gastric, and small intestinal phases of digestion as described previously (25,26). The quantity of βC transferred from the food matrix to the filtered aqueous fraction during simulated digestion procedure represents partitioning of the carotenoid in micelles, i.e. the vehicle for delivery of the pigment to small intestinal absorptive epithelium.

    Extraction and HPLC analyses of carotenoids. Sweet potato powder was weighed (10 and 40 mg for OFSP and WFSP, respectively), β-apo-8'-carotenal was added as an internal standard, and the mixture was extracted 3 times with hexanes (3 mL), mixed by vortex, and centrifuged. Extracts were washed with water (1 mL). The organic phase was dried under argon, redissolved in dichloroethane:methanol (200 µL, 50:50, v:v), and injected (25 µL) into an HPLC system (Waters) (16). HPLC-purified βC and absorption spectra were used for identification. Analyses of VA and carotenoids from serum and liver were conducted as published (16,18). Aliquots (1 mL) of digesta and micelle fraction were mixed with 4 mL tetrahydrofuran:hexane (1:1) containing 0.1% BHT after addition of 2 µg Sudan I in ethanol as internal standard. This was mixed on an automatic vortex (VWR DVX-2500) for 1 min at 2500 revolutions/min. Tubes were centrifuged at 2000 x g; 5 min at room temperature and the supernatant was transferred to a glass vial. Samples were extracted 2 more times or until the supernatant was colorless. Pooled organic layers were evaporated under nitrogen and the film reconstituted in 1 mL mobile phase. For OFSP, digesta, and micelle fractions, a Waters 2695 separation module, 2996 photodiode array detector, and YMC Carotenoid S-5 3 µm-C30 reversed-phase column (4.6 mm x 250 mm) at 25°C were used. Compounds in eluate were identified and quantified from all-trans βC standard. The mobile phases were methanol and 1 mol/L ammonium acetate (98:2) (solvent A) and methyl tertiary butyl ether (solvent B) with a gradient flow rate of 0.8 mL/min to 1.0 mL/min: 0–10 min, 80% A; 11–20 min, 60% A; 21–25 min, 40% A; 26–30 min, 80% A. Chromatograms were generated at 450 nm.

    Statistical analysis and calculations. We analyzed the animal data using SAS software (SAS Institute, version 8.2; 2001). Outcomes of interest (i.e. gerbil weights, feed and βC intakes, serum and tissue VA, and βC concentrations) were evaluated using ANOVA. Post hoc differences were determined using Fisher's least significant difference test. Bioconversion of provitamin A carotenoids to retinol was calculated using total liver VA of individual gerbils in the OFSP-fed and βC-supplemented groups compared with that of the VA-supplemented group corrected for the total liver VA of the control group. The effects of fat, fiber, protein, and βC intake on the efficiency of βC conversion to VA were evaluated by multiple linear regression. For the simulated digestion experiments, a minimum of 3 digestions were made for each style of prepared OFSP in an experiment and each experiment was replicated to generate 6 observations. Statistical analyses were performed using SPSS (version 14.0). Means were compared using ANOVA followed by Dunnett's post hoc test. Values are means ± SD. Significance was assessed at {alpha} < 0.05.


   Results
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
Discussion
 LITERATURE CITED
 
    Sweet potato composition. OFSP powder contained abundant βC, whereas WFSP contained a trace (Table 2). Total phenolic content and antioxidant activities were higher in OFSP. The 2 varieties were similar in fat and fiber content, whereas protein and starch differed. Insoluble and soluble fiber concentrations were slightly higher in OFSP than in WFSP powder (Table 2).


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  		TABLE 2 Composition of boiled, then freeze-dried, sweet potato mixed into purified diets and fed to Mongolian gerbils1

 
    Neutral sugar and uronic acid analyses of isolated soluble fiber. Neutral sugar (37) and uronic acid (38) analyses of the supernatant and cell-wall residue fractions isolated from OFSP and WFSP confirmed previous reports that pectin is a major fiber type in sweet potato (41,42). Pectins (i.e. polymers of rhamnose, fucose, arabinose, and galactose) from OFSP and WFSP accounted for 28 and 58% of the total neutral sugars in the supernatant fraction, respectively, and 29 and 16% in the cell-wall residue fraction, respectively. Uronic acids, another class of pectins, were detected in low amounts (<1% of total soluble fiber) in the supernatant fractions from both sweet potatoes but not in the cell-wall fractions (Table 3).


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  		TABLE 3 Soluble fiber components of OFSP and WFSP powders

 
    Gerbil weights and intakes. Gerbil body weights (68.3 ± 6.9 to 75.3 ± 8.1 g) and liver weights (2.7 ± 0.6 to 3.4 ± 1.4 g) did not differ among the groups. Daily intake of the OFSP diet was significantly higher in the 3% fat group (5.5 ± 0.5 g) than in the 12% fat group (4.8 ± 0.5 g) but did not differ from the 6% fat group (5.3 ± 0.3 g) or the 6% fat groups with 3 and 9% WFSP (5.3 ± 0.5 and 5.2 ± 0.5 g, respectively). Total βC intake over the 3-wk treatment period ranged from 1612 ± 162 nmol for the 12% fat to 1869 ± 162 nmol for the 3% fat group. As with feed intake, total βC intake differed only between the 12 and 3% fat groups. The βC-supplemented group received 1765 nmol βC in oil over the 3-wk treatment period, which did not differ from the OFSP groups.

    Serum and liver VA and carotenoid concentrations. Serum retinol concentrations ranged from 1.38 ± 0.06 to 1.57 ± 0.25 µmol/L and did not differ. Total liver VA was higher in the VA-supplemented group than all others (P < 0.05) and higher in OFSP-fed and βC-supplemented groups than in the control group (P < 0.05) (Fig. 1). VA status was improved above baseline for gerbils in the 12 and 6% fat diets with 3 and 9% added WFSP (P < 0.05).


Figure 1
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  		FIGURE 1  Total liver VA in gerbils killed at baseline (Base) or fed 3% OFSP feeds with 3, 6, or 12% dietary fat, or the 6% fat OFSP feed with 3 or 9% added WFSP or 3% WFSP feed and supplemented with VA, βC (BC), or oil (Con) for 3 wk. Values are means ± SD, n = 10, 9 (control), or 6 (baseline). Means without a common letter differ, P < 0.05.

 
    OFSP βC bioconversion. OFSP βC bioefficacy was measured as conversion factors, i.e. βC intake (µg) necessary to yield 1 µg retinol. A correction factor was needed based on measured βC intake for each gerbil fed OFSP to account for differences in βC intake between groups and individual gerbils. The bioconversion factor of sweet potato βC in gerbils fed 12% fat was significantly lower than in gerbils fed the 3 and 6% fat supplemented with βC but did not differ from the groups fed 6% fat with or without added WFSP (Fig. 2). This indicated enhanced bioefficacy for the higher fat intake and no influence with higher soluble fiber intake.


Figure 2
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  		FIGURE 2  βC to VA conversion factors for gerbils fed 3% OFSP feeds with 3, 6, or 12% dietary fat (0.24% soluble fiber) (A) or fed the 6% fat OFSP feed with 3 or 9% added WFSP (0.42 and 0.80% soluble fiber, respectively) (B) compared with those given equivalent βC in oil as a daily supplement (BC). Values are means ± SD, n = 10. Means without a common letter differ, P < 0.05.

 
    Multiple linear regression. Efficiency of βC conversion to VA was positively associated with dietary fat in the univariate model (r = 0.31; P = 0.028), and after control for soluble fiber and protein intakes in the multivariate model (P = 0.011). Individual gerbil intake of βC was taken into account in the conversion factor calculation. Efficiency of conversion was not associated with soluble fiber intake alone or in other models containing covariates in all possible configurations. Efficiency of conversion was negatively associated with βC intake (r = –0.33; P = 0.010) and after control for fat, fiber, and protein (P = 0.042). Liver βC concentration was positively associated with fat intake after adjustment for total βC intake (P = 0.009).

    Micellarization of βC after simulated digestion. The same boiled OFSP cultivar fed to gerbils as freeze-dried powder was subjected to simulated digestion after additional boiling for 5 min or additional boiling followed by stir-frying in oil. The major cis isomer, 13-cis βC, accounted for only 4 and 6% of the total βC in boiled and boiled plus stir-fried OFSP, respectively. Recovery of βC after simulated digestion was 74% in the boiled and 58% in the stir-fried OFSP, whereas recovery of the internal standard (i.e. Sudan I) during extraction (26) was always >90%. Stir-frying the OFSP in soybean oil clearly enhanced the efficiency of micellarization of total βC by 90% (Fig. 3; P < 0.05). The quantities of total βC and all-trans βC that partitioned into micelles during simulated digestion of stir-fried OFSP was greater than that during digestion of boiled OFSP (P < 0.05), whereas the quantity of 13-cis βC transferred into micelles did not differ (Fig. 3). Micellarization of all-trans βC during small intestinal digestion of boiled OFSP was inefficient (1.2 ± 0.19%), less than that of 13-cis βC (12.7 ± 0.98%; P < 0.05), and enhanced when boiled OFSP was stir-fried in 5% soybean oil prior to in vitro digestion (2.8 ± 0.25%; P < 0.05).


Figure 3
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  		FIGURE 3  Stir-frying in soybean oil promotes micellarization of βC during simulated digestion of OFSP. Means for the amount of total βC and its isomers incorporated into micelles during simulated digestion are compared for boiled and boiled plus stir-fried OFSP. Data are means ± SD, n = 6. The quantities of total βC and the isomers in boiled compared with boiled plus stir-fried without a common letter differ, P < 0.05.

 

   Discussion
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
LITERATURE CITED
 
The influence of fat and soluble fiber on VA bioefficacy of βC from OFSP was determined. Fat enhanced βC bioefficacy as evidenced by higher liver VA storage and more efficient βC conversion to VA in gerbils fed higher fat. It has been suggested that a minimal amount of fat (3–5 g) is required for optimal absorption of βC (6,43), but other work has demonstrated that the threshold for optimal absorption of carotenoids may exceed 6 g of fat (44). We observed a positive linear relationship between fat and βC bioefficacy, represented as conversion factors (21). The amounts fed (3, 6, and 12%) were similar to diets consumed in some developing countries, where VA deficiency is prevalent and sweet potato intake is high (11).

Recovery and micellerization of βC from OFSP during simulated digestion were substantially improved by stir-frying compared with boiling. This supports the likelihood that more efficient conversion of βC to VA in gerbils fed the 12% fat compared with the 3% fat was due to greater bioaccessibility of OFSP βC. This observation in vitro helps to explain the positive association between fat intake and βC bioefficacy in vivo. Dietary fat provides a sink for deposition of carotenoids during early stages of digestion, stimulates the secretion of bile acids and lipases, enhances the formation of mixed micelles that shuttle carotenoids to the brush border, and promotes the assembly and secretion of chylomicra that transfer carotenoids and retinyl esters into lymph.

Because dietary fiber, and particularly soluble fibers, may decrease carotenoid bioavailability (8), specified amounts of soluble fiber derived from WFSP were mixed with OFSP. The amount of insoluble fiber, quantified as cellulose, hemicellulose, and lignins, was constant to ensure that the influence of dietary fiber on βC bioefficacy was limited to soluble fiber. Increased intake of soluble fiber did not reduce βC bioefficacy, in contrast to previous studies in gerbils (19) and humans (8). The added pectin or β-glucans in the prior gerbil study (19) were at concentrations 7.5–25 times greater than those used in the current study. Intake of the 2 diets with higher soluble fiber in the current study resulted in greater liver VA storage and lower conversion factors than diets with lower soluble fiber and similar concentrations of other dietary components thought to affect carotenoid bioefficacy, such as dietary fat. In contrast to the aforementioned study in gerbils (19), soluble fiber concentrations were manipulated by adding amounts of WFSP that could be achieved through biofortification.

A strength of this study is that we assessed the interaction between the βC and soluble fibers in sweet potato directly, as consumed from the actual food, rather than adding isolated fibers to the diet in an attempt to recreate the soluble fiber composition of whole foods. This method simulates intake of OFSP as a staple food. Assessment of the influence of soluble fiber intake on provitamin A carotenoid conversion to VA is complicated by the varying analytical and nutritional classifications of fiber types. Little work has been done to compare the influence of different types of soluble fiber, i.e. pectin vs. β-glucans studied by Deming et al. (19), on provitamin A bioefficacy. Thus, future investigations that include whole-food sources of soluble fiber should include the quantification of the different fiber types. Furthermore, we did not assess the influence of different types of dietary fat on bioefficacy, another question that remains relatively unexplored. Chain length and degree of fatty acid saturation may affect provitamin A bioefficacy.

βC conversion to VA was more efficient in gerbils fed OFSP than supplements, although bioefficacy varied widely between gerbils and the different dietary fat and fiber intakes. This measure of individual variability reflects that in humans. Intake of OFSP led to lower conversion factors despite βC intakes equivalent with the βC supplement. This finding conflicts with a carrot feeding study, where supplemental βC given as a carrot extract in oil resulted in greater storage of VA in liver compared with intake of equivalent βC from carrot powder (18), but agrees well with data from gerbils fed biofortified maize (21,22). βC in sweet potato chromoplasts may be more bioaccessible than crystalline βC in the carrot matrix (45).

WFSP is often preferred to OFSP, partially due to greater dry matter. In the current study, increasing dry matter with the addition of WFSP did not negatively affect βC bioefficacy; in fact, the addition of WFSP appeared to enhance the conversion of βC to VA. Thus, biofortification efforts can focus on increasing both the dry matter and βC of OFSP to improve consumer acceptability. Additionally, OFSP contained greater concentrations of fat, protein, and dietary antioxidants than WFSP, underscoring the potential benefits of replacing white with orange varieties (11,23). Changing behavior at the family and community levels can require substantial investment in nutrition education and infrastructure (46), but such effort can achieve the desired positive impact on VA status as demonstrated by a recent intervention with OFSP in Mozambique (14). Introduction of OFSP to households, integrated with increasing access to OFSP vines and improved nutrition knowledge that created greater demand for OFSP, increased provitamin A intake and serum retinol concentrations among children living in the region.


   ACKNOWLEDGMENTS
 
We thank Marjorie Haskell, University of California-Davis, for sending sweet potato from Bangladesh; Kenneth Brown, University of California-Davis, for supporting the comparison of in vitro, animal, and human models; and Barbara Mickelson, Harlan-Teklad, for assistance with the diets. We thank Ting Sun for assistance in developing the antioxidant capacity assays. We also thank Diane Amundson, Jane Marita, Ron Hatfield, and Mary Beth Hall of the USDA Dairy Forage Research Center, University of Wisconsin-Madison for graciously sharing their expertise and facilities during the fiber and protein analyses and providing excellent guidance on data interpretation.


   FOOTNOTES
 
1 Supported by HarvestPlus contracts 2005X059.UWM and 8014.OSU; Hatch Wisconsin Agricultural Experiment Station WIS04975; Department of State Educational Partnerships Program, Nutrition Education and Policy: a partnership between UW-Madison and Makerere University S-ECAAS-04-GR-218(CS); and the Ohio Agriculture Research and Development Center. Back

2 Author disclosures: J. P. Mills, G. A. Tumuhimbise, K. M. Jamil, S. K. Thakkar, M. L. Failla, and S. A. Tanumihardjo, no conflicts of interest. Back

8 Abbreviations used: βC, β-carotene; OFSP, orange-fleshed sweet potato; TEAC, Trolox equivalent antioxidant capacity; VA, vitamin A; WFSP, white-fleshed sweet potato. Back

9 Bioconversion factors for provitamin A carotenoids are expressed as µg β-carotene equivalents to µg retinol. The molecular weight of β-carotene is 537 g/mol and retinol is 286 g/mol. Back

Manuscript received 25 August 2008. Initial review completed 1 October 2008. Revision accepted 22 October 2008.


   LITERATURE CITED
TOP
 ABSTRACT
 Introduction
 Materials and Methods
 Results
 Discussion
 LITERATURE CITED
 

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