Riboflavin Content Research Articles

Ectopic Expression of the Rice Lumazine Synthase Gene Contributes to Defense Responses in Transgenic Tobacco

Lumazine synthase (LS) catalyzes the penultimate reaction in the multistep riboflavin biosynthesis pathway, which is involved in plant defenses. Plant defenses are often subject to synergistic effects of jasmonic acid and ethylene whereas LS is a regulator of jasmonic acid signal transduction. However, little is known about whether the enzyme contributes to defense responses. To study the role of LS in plant pathogen defenses, we generated transgenic tobacco expressing the rice (Oryza sativa) LS gene, OsLS. OsLS was cloned and found to have strong identity with its homologues in higher plants and less homology to microbial orthologues. The OsLS protein localized to chloroplasts in three OsLS-expressing transgenic tobacco (LSETT) lines characterized as enhanced in growth and defense. Compared with control plants, LSETT had higher content of both riboflavin and the cofactors flavin mononucleotide and flavin adenine dinucleotide. In LSETT, jasmonic acid and ethylene were elevated, the expression of defense-related genes was induced, levels of resistance to pathogens were enhanced, and resistance was effective to viral, bacterial, and oomycete pathogens. Extents of OsLS expression correlated with increases in flavin, jasmonic acid, and ethylene content, and correlated with increases in resistance levels, suggesting a role for OsLS in defense responses.

Estimación del contenido de hierro, ácido fólico, tiamina, riboflavina y niacina en alimentos elaborados con harina de trigo enriquecida

Background The enrichment of the wheat flour with iron, thiamine, riboflavin, niacin, and folate, has been a relevant nutrition strategy in the prevention of moderate deficiency of certain vitamins and minerals in many countries, because it is a widely consumed commodity, cheap, highly accepted by the population and consumed daily. In Argentina the law 25.630 “Prevention of anaemia and neural tube defects” sets that provision. Aim The aim of this work was to assess iron, thiamine, riboflavin, niacin, folic acid content in food elaborated with enriched wheat flour. Material and methods This observational, descriptive, cross-sectional study was carried out on a random sample of bakeries and industries willing to provide information; nutritional labelling data were also considerate. Results Values (mg/100g) for the content of iron, thiamine, riboflavin, niacin and folic acid in foods elaborated with fortified wheat flour were compiled from data provided by ten bakeries of Rufino and Rosario city (Santa Fe), two factories of pasta and data declared in food labels. Grisines, industry prepared tart pastry and common French bread were the food items with a higher iron content. Conclusions Estimations of nutrient content in foods based on calculations, as done in this study, are less accurate than those based on chemical analysis of foods that could be incorporated into food composition tables.

Carotenoid and riboflavin content of banana cultivars from Makira, Solomon Islands

The Solomon Islands face problems of vitamin A deficiency and infectious diseases, including malaria. It is essential to identify nutrient-rich indigenous foods for preventing and alleviating these diseases. Previous work in Micronesia identified yellow/orange-fleshed carotenoid-rich banana cultivars, in particular Fe’i cultivars (characterized by upright bunches), with potential to alleviate vitamin A deficiency. Although there is a great diversity of Solomon Islands bananas, little is documented about these cultivars and their nutrient content. Using an ethnographic approach, this study aimed to identify nutrient-rich cultivars and to collect information relating to production and consumption. Seven Fe’i cultivars (not previously analyzed) and three non-Fe’i cultivars were assessed for flesh color, fruit size and other attributes and analyzed for provitamin A carotenoids (β- and α-carotene), total carotenoids and riboflavin. Five Fe’i and two non-Fe’i cultivars were identified as carotenoid-rich. Of 10 cultivars analyzed the concentrations of β-carotene equivalents ranged from 45 to 7124 μg/100 g. Compared to cultivars with light-colored flesh, the yellow/orange-fleshed cultivars generally contained higher carotenoid concentrations. All Fe’i cultivars contained riboflavin, from 0.10 to 2.72 mg/100 g, some having substantial concentrations. The nutrient-rich cultivars, including Fe’i, should be promoted for their potential to contribute to vitamin A intake and overall health.

Studies on the Riboflavin Contents in Yoghurt

Studies on the Riboflavin Contents in Yoghurt

Effect of domestic processing techniques on the nutritional quality of the soybean

Food legumes are widely consumed all over the world as these are good sources of dietary proteins, carbohydrates and minerals. Common domestic processing techniques like soaking, germination and cooking enhance the digestibility and nutritive value of legumes. The effects of soaking, germination (1, 2 and 3 day) and cooking (microwave, pressure and ordinary cooking) were studied on the carbohydrates, crude protein, mineral and vitamin content of soybean. Germination (2nd day) leads to significant increases in the sugar, crude protein, Ca, Cu, Mn, Zn, riboflavin, niacin and ascorbic acid content. Microwave cooking resulted in greater retention of minerals and vitamins as compared to pressure cooking and ordinary cooking. Based on the results, germination (day 2) for soybean should be popularised as a simple process for naturally fortifying food with essential minerals and vitamins. While amongst cooking methods, microwave cooking could be suggested for soybean preparation.

Effect of Fasting on the Urinary Excretion of Water-Soluble Vitamins in Humans and Rats

Recent studies showed that the urinary excretion of the water-soluble vitamins can be useful as a nutritional index. To determine how fasting affects urinary excretion of water-soluble vitamins, a human study and an animal experiment were conducted. In the human study, the 24-h urinary excretion of water-soluble vitamins in 12 healthy Japanese adults fasting for a day was measured. One-day fasting drastically decreased urinary thiamin content to 30%, and increased urinary riboflavin content by 3-fold. Other water-soluble vitamin contents did not show significant change by fasting. To further investigate the alterations of water-soluble vitamin status by starvation, rats were starved for 3 d, and water-soluble vitamin contents in the liver, blood and urine were measured during starvation. Urinary excretion of thiamin, riboflavin, vitamin B(6) metabolite 4-pyridoxic acid, nicotinamide metabolites and folate decreased during starvation, but that of vitamin B(12), pantothenic acid and biotin did not. As for blood vitamin levels, only blood vitamin B(1), plasma PLP and plasma folate levels decreased with starvation. All water-soluble vitamin contents in the liver decreased during starvation, whereas vitamin concentrations in the liver did not decrease. Starvation decreased only concentrations of vitamin B(12) and folate in the skeletal muscle. These results suggest that water-soluble vitamins were released from the liver, and supplied to the peripheral tissues to maintain vitamin nutrition. Our human study also suggested that the effect of fasting should be taken into consideration for subjects showing low urinary thiamin and high urinary riboflavin.

Effect of flour extraction rate and baking process on vitamin B1 and B2 contents and antioxidant activity of ginger-based products

The effect of flour extraction rate and baking on thiamine (vitamin B1) and riboflavin (vitamin B2) content and antioxidant capacity of traditional ginger cake was studied and then compared to white wheat bread. Ginger cake was formulated either with whole-grain (100% extraction rate) or with brown (92% extraction rate) rye flour and baked at 180 °C for 18 min. The antioxidant capacity was evaluated in terms of radical scavenging activity against peroxyl (ROO·) and superoxide anion radicals (O2·−). Thiamine content in rye doughs (F-100% and F-92%) was found to be 38% lower when compared to wheat dough. In contrast, whole-grain and brown rye doughs exhibited an almost fourfold higher riboflavin content than wheat dough. Rye dough baking led to reductions in thiamine (from 53 to 65%) and riboflavin (from 69 to 71%) contents. Likewise, thiamine and riboflavin contents in wheat dough were also reduced (56 and 10%, respectively) after baking; however, ginger cake with whole-grain rye flour exhibited significantly higher thiamine and riboflavin contents. Rye doughs and ginger cakes showed higher scavenging activities against ROO· radicals when compared to that of wheat dough and bread. Thus, baking significantly enhanced ROO· scavenging properties of ginger cakes while only a slight increase was observed in wheat bread. In contrary, baking gave rise to a decrease in SOD-like activity both in ginger cake or wheat bread. Our findings suggest that formulation with whole-grain rye flour can potentially increase B1 and B2 vitamin contents as well as the ROO· scavenging capacity of traditional ginger cake.

Effect of Processing Methods on the In Vitro Protein Digestibility and Vitamin Content of Edible Winged Termite (Macrotermes subhylanus) and Grasshopper (Ruspolia differens)

The influence of processing methods of toasting and solar drying on the in vitro protein digestibility and vitamins content of edible winged termites, green grasshoppers, and brown grasshoppers consumed in Siaya, district of Kenya, was determined using standard methods. Analysis was done on fresh, toasted, toasted dried, and fresh dried insect samples. There was no significant change (p > 0.05) in protein digestibility in the termite samples, while a significant decrease (p ≤ 0.05) in the grasshopper samples was observed on toasting and drying. There was a significant reduction (p ≤ 0.05) in riboflavin content with 4.18 mg/100 g in fresh termites, 2.76 mg/100 g in toasted termites, 2.26 mg/100 g in fresh dried termites, and 1.50 mg/100 g in toasted dried termites on processing. There was also a significant reduction (p ≤ 0.05) in niacin content in the grasshoppers with 3.61 mg/100 g in fresh green grasshopper, 3.28 mg/100 g in toasted green grasshopper, 3.22 mg/100 g in fresh dried green grasshoppers, and 3.06 mg/100 g in toasted dried green grasshoppers. A significant reduction (p ≤ 0.05) in retinol content with 2.24 μg/g in fresh termites, 1.56 μg/g in toasted termites, 1.02 μg/g in toasted dried termites, and 0.98 μg/g in fresh dried termites was also reported. The processing methods of the insects affected their nutrient potential as evidenced by the changes in protein digestibility and vitamins content. Therefore, optimal processing methods need to be investigated even as we promote commercialization of these insects.

RHEOLOGICAL AND SENSORY QUALITY OF READY‐TO‐BAKE CHAPATTI DURING FROZEN STORAGE

ABSTRACT The effect of prolonged frozen storage at −18C, on the textural and sensory properties of ready‐to‐bake frozen chapatti (R‐BFC) was evaluated. The R‐BFC samples were prepared from normal‐ (control) and microwave‐treated (18% moisture content for 80 s) wheat grains. Results showed that the extensibility of dough and maximum load for resistance increased gradually in both the samples during frozen storage; however, the increase was lesser in the treated ones. Chapattis prepared from both R‐BFC samples exhibited higher hardness, cohesiveness, chewiness and lower springiness values during frozen storage. Microwave‐treated R‐BFC samples were rated as better retained in color, texture and overall acceptability scores as compared with control, up to 6 months of storage at −18C. Thiamin and riboflavin contents were monitored during frozen storage and a loss of 12.0–14.5% in thiamin and 4–6% in riboflavin after 6 months of frozen storage was recorded.PRACTICAL APPLICATIONSDuring frozen storage, various physical, rheological and sensory changes occur in the food products, which determine the consumer's acceptability. The results of this study will help to establish quality of the frozen chapattis with respect to texture, color and aroma which will meet the consumer's acceptance. The protocol for the storage of frozen chapattis will help the industry to deliver the product of optimum quality.

Riboflavin content of coelomocytes in earthworm ( Dendrodrilus rubidus) field populations as a molecular biomarker of soil metal pollution

The effect of Pb + Zn on coelomocyte riboflavin content in the epigeic earthworm Dendrodrilus rubidus inhabiting three metalliferous soils and one reference soil was measured by flow cytometry and spectrofluorimetry. A reciprocal polluted↔unpolluted worm transfer experiment (4-week exposure) was also performed. High proportions of autofluorescent eleocytes were counted in worms from all localities, but intense riboflavin-derived autofluorescence was detectable only in reference worm eleocytes. Other findings were: (i) fluorophore(s) other than riboflavin is/are responsible for eleocyte autofluorescence in residents of metalliferous soils; (ii) riboflavin content was reduced in the eleocytes of worms transferred from unpolluted to metal-polluted soil; (iii) the riboflavin content of D. rubidus eleocytes is a promising biomarker of exposure; (iv) COII mitochondrial genotyping revealed that the reference population is genetically distinct from the three mine populations; (v) metal exposure rather than genotype is probably the main determinant of inter-population differences in eleocyte riboflavin status.

The Effect of Soaking, Boiling and Fermentation with Rhizopus oligosporus on the Water Soluble Vitamin Content of Bambara Groundnut

Effect of treatment conditions (soaking, boiling and fermentation with Rhizopus oligosporus (SBF)) on the water soluble vitamins and trypsin inhibitor of bambara nut flour (Vigna subterranea (L) Verdc) was investigated. It was observed that the thiamine content decreased by 5%, riboflavin 6.2%, folacin 9.6%, niacin 10.2% and biotin 14% after 24 h of soaking at room temperature. Treatment by boiling for 45 min revealed that there was a further decrease of 52.4%, 56.2%, 35.0%, 70.0% and 48.3% in the values of thiamine , riboflavin, folacin, niacin and biotin respectively. However, fermentation with Rhizopus oligosporus for 24 h significantly reduced the thiamine content from the original value of 0.47+0.13-0.1 9+0.02 mg/100g, while riboflavin content increased significantly from 0.15+0.06-0.17+0.01 mg/100 g, folacin 0.16+0.02-0.23+0.03 mg/100 g, niacin 1.88+0.09-2.16±0.00 mg/100 g and biotin 0.10+0.02-0.16±0.05 mg/100 g (P < 0.05). Trypsin Inhibitor Activity (TIA) decreased by 22.1% after soaking for 24 h at room temperature and further decreased by 72% after boiling for 45 mins. Conversely, during fermentation period of 24 h, the TIA increased significantly from 0.71+0.62-1.33±0.59 mg/100 g protein (P < 0.05).

Electrochemically deposited boronate affinity extracting phase for covalent solid phase microextraction of cis-diol biomolecules

A new format of solid phase microextraction (SPME), boronate affinity SPME, was proposed for the first time for covalent extraction of cis-diol containing biomolecules. This new SPME format is based on the reversible complex formation between boronic acids and 1,2- and 1,3-cis-diols. The complex formation and dissociation can be facilely controlled by changing pH. An extracting phase of poly-3-aminophenylboronate (polyAPBA) electrochemically deposited on a metal wire was employed to demonstrate the concept of this new methodology. Catechol and riboflavin were used as the test analytes, and the SPME extraction was combined off-line with high-performance liquid chromatographic (HPLC) separation followed by UV absorbance or fluorescence detection. Fundamental aspects, such as selectivity, extraction/desorption equilibrium, linearity, effect of competing compounds, reproducibility and life-time, were first investigated. Then the developed method was applied to beer samples since the content of riboflavin plays an important role in the flavor stability of beverages. Excellent performance of the SPME fibers was observed for both standard and real samples. Particularly, the expected excellent features of the polyAPBA extracting phase were experimentally verified, which include specific selectivity, eliminated matrix effect and manipulable capture/release. The new methodology of SPME can be a promising tool since a lot of 1,2- and 1,3-cis-diol-containing compounds are of great biological importance.

Qualitative changes in Pleurotus ostreatus (Jacq.: Fr.) Kumm. mushrooms resulting from different methods of preliminary processing and periods of frozen storage

AbstractBACKGROUND: The aim of this study was to investigate the effect of different methods of preliminary processing and periods of frozen storage on the quality of Pleurotus ostreatus (Jacq.: Fr.) Kumm. mushrooms. In pre‐processing, mushrooms were blanched or soaked and blanched in water as well as in aqueous solutions of citric acid, L‐ascorbic acid and/or lactic acid. During 12 months of storage at −25 °C, sensory evaluations, instrumental colour measurements and chemical analyses of the frozen products were carried out every 4 months.RESULTS: The greatest changes resulting from technological treatment were found in flavour. At the end of the storage period the content of thiamine and riboflavin decreased by 14–65% and 3–13% respectively compared with the raw material. This was accompanied by changes in total acidity and vitamin C content within the ranges − 56 to + 61% and − 97 to + 5% respectively.CONCLUSION: Based on the results of the sensory evaluation, a maximum storage period of 4 months was set for the frozen product obtained from unblanched mushrooms. Mushroom products pre‐processed in aqueous solutions with added substances may be stored for 8 months and those blanched in water for 12 months. Copyright © 2009 Society of Chemical Industry

Effect of Flour Extraction Rate and Baking on Thiamine and Riboflavin Content and Antioxidant Capacity of Traditional Rye Bread

The effect of rye flour extraction rates and baking on thiamine and riboflavin content, and antioxidant capacity of traditional rye bread were studied and compared with white wheat flour. The content of thiamine was higher (10.9%) in rye dough formulated with dark rye flour (F-100%; extraction rate of 100%) than in rye dough formulated with brown rye flour (F-92%; extraction rate of 92%) that was similar to dough made with wheat flour. The riboflavin content in rye dough made from flour F-100% was also higher (16%) than in dough formulated with flour F-92%, and both provided larger riboflavin content than wheat dough. Baking led to reductions in thiamine of 56% for wheat bread and of 20% for both rye breads; however, this process caused only a 10% decrease in riboflavin for wheat bread and a 30% decrease for rye breads. Trolox equivalent antioxidant capacity, peroxyl radical scavenging capacity, DPPH radical scavenging activity, and Folin-Ciocalteu reducing capacity were higher in rye than in wheat dough and bread. Baking process produced slight changes in antioxidant activity, except for Superoxide Dismutase-like activity where a sharp decrease was observed. Our findings showed that rye breads are an important source of B vitamins and rye breads formulated with dark and brown flours showed better antioxidant properties than wheat bread. Therefore, rye breads should be more widely recommended in human nutrition.

New antioxidant protein in seaweed (Porphyra yezoensis Ueda)

Gel filtration was used to partially purify the antioxidizing component of a crude extracted solution of seaweed (Porphyra yezoensis Ueda), and its properties were studied. The antioxidizing effect did not decrease after dialysis or heating. The finding of no change after dialysis suggested that the compound was of high molecular weight, estimated at 52.2 kDa by gel filtration chromatography. The antioxidizing effect decreased with irradiation, accompanied by a parallel decrease in the riboflavin content. The antioxidizing component of this 52.2-kDa fraction may be a protein-bound riboflavin. The structural of protein-bound riboflavin in seaweed was analyzed with hydrogen-1 nuclear magnetic resonance, and the results suggested that the 52.2-kDa fraction was riboflavin. We found an antioxidizing component in seaweed (P. yezoensis Ueda). This antioxidizing component is estimated at 52.2 kDa and may be a protein-bound riboflavin.

Riboflavin in Asian noodles: The impact of processing, storage and the efficacy of fortification of three product styles

Asian noodle products are a staple food in many countries, representing the end-use of approximately one eighth of all wheat produced globally. Relatively little has been published on the contribution of Asian noodles to dietary intakes of essential nutrients including the B group vitamins. Therefore, the aim of this study has been to investigate the factors influencing the retention of riboflavin in these products. The three most common styles of Asian noodles (white salted, yellow alkaline and instant) have been prepared under controlled laboratory conditions and riboflavin contents measured at each stage of processing. The stability varied markedly between the different styles with losses occurring at each step. Declines ranging from 27% to 38% of the initial riboflavin levels were found in fortified noodles prior to cooking. During boiling at the optimum temperature, further decreases occurred resulting in overall losses of 52–74% of the amounts incorporated into the various formulations. The presence of alkaline salts as ingredients appeared to be the primary factor influencing the extent of losses in the three styles. White salted and instant Asian noodles are effective vehicles for enhancing dietary intakes of riboflavin.

Riboflavin content in lupine seeds and blood plasma riboflavin status in broilers fed diets containing high levels of lupine seeds

AbstractBACKGROUND: The potential of lupine as a source of protein and other nutrients in poultry has attracted considerable attention in countries dependent on imports of soybean meal (SBM), as well as in organic farming. Nutritional aspects of riboflavin in lupines are poorly understood. This work evaluated riboflavin content in whole and dehulled seeds of three lupines (L. albus, L. angustifolius, L. luteus) and riboflavin status in broiler fed diets containing high levels of lupine seeds in comparison to SBM.RESULTS: Riboflavin is concentrated mainly in lupine cotyledons, predominantly as flavin mononucleotide. Its content in whole seeds ranged from 2.07 to 2.70 mg kg−1, and was comparable to content in SBM (2.35 mg kg−1). In comparison to the SBM‐fed group, broilers fed lupine diets showed higher plasma riboflavin (P &lt; 0.05), but their growth rate and feed intake parameters were significantly lower (P &lt; 0.05).CONCLUSION: Lupine seeds contain moderate to high levels of riboflavin. Feeding diets containing high levels of lupine seeds did not have adverse effects on plasma riboflavin status in broilers. Poor performance of broilers fed lupine diets is not associated with inadequacy of riboflavin. Copyright © 2008 Society of Chemical Industry

The effect of preliminary processing and period of storage on the quality of frozen Boletus edulis (Bull: Fr.) mushrooms

This paper investigates the effect on the quality of frozen Boletus edulis (Bull: Fr.) mushrooms of blanching or soaking and blanching in aqueous solutions containing combinations of added substances safe for human consumption, or period of frozen storage. During 12 months of storage, sensory evaluations, instrumental colour measurements and chemical analyses of the frozen products were carried out every four months. Based on the results of the sensory evaluation, a maximum storage period of four months was set for the frozen product obtained from unblanched mushrooms. Frozen products having undergone preliminary processing retained good sensory quality for up to 12 months. Soaking, blanching and freezing resulted in the appearance of colours, such as yellow, honey and pink–violet. As a result of freezing, decreases in the contents of thiamine, riboflavin and vitamin C were noted. Blanching in water, as a method of pre-processing, was sufficient for maintaining acceptable sensory quality.

Efficacy of gamma irradiation for protection against postharvest insect damage and microbial contamination of adlay

This study examines the protective effects of gamma irradiation against postharvest insect damage and microbial contamination and its effect on the nutritive value of adlay ( Coix lacryma-jobi L.). Adlay was treated with doses of 0–20 kGy gamma irradiation and subsequently stored at ambient temperature. The number of insects, microbial quality and chemical properties of irradiated and non-irradiated adlay were evaluated immediately after treatment and after 6 months of storage. Before irradiation, total aerobic microbial counts ranged from 5.6 × 10 2 to 1.4 × 10 5 CFU g −1 and the mean total number of insects was 3.2 ± 2.1 per 100 g of polished kernel. Two kilograys was the lowest dose that provided 100% insect control. A radiation-resistant bacterium, Deinococcus radiodurans RC1, was found in 2 of 10 adlay samples. Four kilograys was a sufficient dose for Enterobacteriaceae inactivation, and 6 kGy was a sufficient dose for yeast and fungi inactivation. Twenty and 8 kGy sufficed for the inactivation of all mesophilic microbes in samples with and without D. radiodurans, separately. Moreover the moisture, ash, crude fiber, crude fat, crude protein and riboflavin content all remained constant. However, 8 kGy irradiation reduced vitamin B1 concentration by 24.2%, but did not measurably reduce the amount of amino acids, except methionine and cysteine. Fatty acid contents did not alter after 8 kGy irradiation, but changes were observed after the 6 months of storage. These changes caused by irradiation were no greater than those caused by the 6-month storage. Irradiation up to 8 kGy did not markedly increase the acid value, but did increase the peroxide value to 13% of the initial value right after irradiation. However, significant changes in acid value and peroxide value were noted after 6 months of storage both in non-irradiated and post-irradiated storage samples. Additionally, 8 kGy irradiation did not significantly change the adlay appearance. The improvement in the hygiene of this vital food source compensates for the small loss of some nutritional constituents. Hence 8 kGy of gamma irradiation can be used in cold decontamination of adlay to prolong shelf-life, to improve postharvest quality, and to reduce the risk of food-borne disease.

Proliferation of Peripheral Blood Mononuclear Cells Increases Riboflavin Influx

Abstract. Previously we demonstrated that proliferation of peripheral blood mononuclear cells (PBMC) causes a five-fold increase in cellular uptake of biotin; this increase is mediated by an increased number of biotin transporters on the PBMC surface. In the present study, we investigated the specificity of this phenomenon by determining whether the cellular uptake of riboflavin also increases in proliferating PBMC and whether the increase is also mediated by an increased number of transporters per cell. We characterized [3H]riboflavin uptake in both quiescent and proliferating PBMC. In quiescent PBMC, [3H]riboflavin uptake exhibited saturation kinetics and was reduced by addition of unlabeled riboflavin (P < 0.05) or lumichrome (P < 0.01). These observations are consistent with transporter-mediated uptake. [3H]Riboflavin uptake was reduced at 4°C compared with 37°C (P < 0.01) and by 2,4-dinitrophenol (P < 0.05) but not by ouabain or incubation in sodium-free medium. These data provide evidence for an energy-dependent but sodium-independent transporter. Proliferating PBMC accumulated approximately four times more [3H]riboflavin than quiescent PBMC (P < 0.05). Because both transporter affinity and transporter number per cell (as judged by maximal transport rate) were similar in quiescent and proliferating PBMC, we hypothesize that the increased riboflavin uptake by proliferating PBMC reflects only increased cellular volume. To test this hypothesis, PBMC volume was reduced using hyperosmolar medium; [3H]riboflavin uptake decreased to about 50% of isotonic controls (P < 0.01). Thus we conclude that proliferating PBMC increase cellular content of riboflavin and biotin by two different mechanisms.