The history of food composition information in the United States is traced from its earliest tabulations by Atwater and colleagues in the late nineteenth century to the present day. Early tabulations consisted of values for moisture, protein, fat, ash, carbohydrate, and energy. Tabulations of vitamins and minerals content of foods followed their discovery and development of analytical procedures. Although there were interim reports on the nutrient content of foods, the next complete tabulation of the composition of foods was published in 1945. This was followed by the famous Agricultural Handbook No. 8 in 1950, which was updated in 1963 and extensively revised and published 1976–1992. Online databases of food composition information followed printed tables and have advanced as the number of foods, food components and support data have increased. The most recent online information system is FoodData Central. Technological advances in the mid-20th century provided essential tools for the rapid analysis of nutrients and health-related components of foods and for the electronic management and dissemination of food composition information. At the same time, recognition that diet was a major component of cardiovascular disease stimulated extensive collaboration between NIH and USDA. A decade later the potential role of diet in the reduction of cancer risk was recognized. These events were a watershed for analyses and tabulation of nutrients and health-related components for several decades. Most recently the contribution of dietary supplements to the intake of nutrients and other health related components has been recognized, resulting in unique approaches to algorithms for reporting their content.

Several micronutrients common in the diets of human have been suggested to be associated with a reduction in the incidence of cancer or inhibition of carcinogen-induced neoplasia. The ability to establish a statistically sound relationship between dietary micronutrients and incidence of cancer requires accurate and precise food composition data. Technological advances in chemical instrumentation during the past two decades have provided analysts with powerful new tools to quantify low levels and various forms of nutrients in foods. Improvements in high performance liquid chromatography (HPLC) and particularly in column technology have been especially important in the development of new analytical techniques for several micronutrients. The chromatographic profiles of the varieties of squash described above demonstrate significant differences in qualitative distribution of carotenoids and the related fatty acid esters in different cultivars of this vegetable.

Food composition tables and databases provide the foundation on which food and nutrition research, policy, and practice are based. Some aspects of food composition are evident by merely seeing, tasting, or preparing the food. Sugar and salt are evident by taste, carotene by its orange color, and fat content by rendering. Other essential factors are impossible to identify without chemical analysis, and all require chemical analysis for an accurate estimate of amount present. The food label is probably the most accessible source of food data for the consumer; however, the student and researcher require a more comprehensive source of data. Analytical data may come from many sources including scientific literature, government sources, food industry laboratories, or from contractual studies. As a result, data from such diverse sources are often of uneven quality and lacking in detailed supporting documentation. Effective food composition databases must be routinely updated to keep pace with many developing phenomena.

The systematic chemical analysis of foods for human consumption in the United States had its origin with Wilbur O. Atwater. This activity began in the 1860s while Atwater was a student at Yale University and continued through his tenures at Wesleyan University and the Storrs (Connecticut) Experiment Station. These activities moved with Atwater to the USDA in Washington, DC and ultimately to the Henry D. Wallace Beltsville Agricultural Research Center in Beltsville, MD early in the 1900s. During the first half of the 20th century, food composition activities were guided by the discovery of new essential nutrients and the need to measure and tabulate their levels in foods. Later in the century, the association between diet and chronic diseases was recognized. As a result, collaborations were established between other food- and health-related government agencies, the food industry, and many universities. At the same time, computer and communication technology greatly advanced, which became integral to laboratory instrumentation and allowed data in the National Nutrient Databank System to be available electronically. Simultaneously, accuracy of analytical data came under scrutiny and a new paradigm was established in collaboration with governmental metrology units worldwide. Advances in computer technology and the increased focus on accuracy of analytical data subsequently led to the development of quality indicators for all food composition data. Recently, increased consumption of dietary supplements resulted in the broadening of food composition efforts and development of new collaborations with government agencies, several industries, and universities.

Anthocyanins (ACNs) are water-soluble plant pigments that have important functions in plant physiology as well as possible health effects. Over 100 common foods were screened for ACNs, and 24 of them were found to contain ACNs. Concentrations of total ACNs varied considerably from 0.7 to 1480 mg/100 g of fresh weight in gooseberry ('Careless' variety) and chokeberry, respectively. Not only does the concentration vary, but the specific anthocyanins present in foods are also quite different. Only six common aglycones, delphinidin, cyanidin, petunidin, pelargonidin, peonidin, and malvidin, were found in all of these foods. However, their sugar moieties and acylation patterns varied from food to food. Results from this study will add to the available data for the USDA Nutrient Database of flavonoids. On the basis of the concentration data and updated food intake data from NHANES 2001-2002, the daily intake of ACNs is estimated to be 12.5 mg/day/person in the United States. Of the different aglycones, cyanidin, delphinidin, and malvidin were estimated to contribute 45, 21, and 15%, respectively, of the total ACN intake. Nonacylated contributed 77% compared to 23% from acylated ACNs.

Analytical data are reported for 20 flavonoids (as aglycones) determined for more than 60 fresh fruits, vegetables, and nuts collected from four regions across the United States at two times of the year. Sample collection was designed and implemented by the Nutrient Data Laboratory (USDA). Analyses of eight flavan-3-ols (catechin, catechin gallate, epicatechin, epicatechin gallate, epigallocatechin, epigallocatechin gallate, gallocatechin, and gallocatechin gallate), six anthocyanins (cyanidin, delphinidin, malvidin, pelargonidin, peonidin, and petunidin), two flavanones (hesperetin and naringenin), two flavones (apigenin and luteolin), and two flavonols (myricetin and quercetin) were performed by the Food Composition Laboratory (USDA) using a hydrolysis method for the anthocyanidins, flavones, and flavonols and a direct extraction method for the flavan-3-ols and flavanones. Experimental results compare favorably (few statistically significant differences) to literature values in the flavonoid and proanthocyanidin database previously compiled by the Nutrient Data Laboratory. The results of this study showed a seasonal variation only for blueberries. This study also showed that the variation in the flavonoid content of foods, as purchased by the U.S. consumer, is very large. The relative standard deviation, averaged for each flavonoid in each food, was 168%.

Flavanones constitute the majority of flavonoids in citrus fruits such as sweet (Citrus sinensis) and sour oranges (C. aurantium) and their near relatives—tangerines/mandarins (C. reticulata), tangors and tangelos. The relevant chemical analytic literature was searched, abstracted, documented, standardized, examined for quality, enumerated, and summarized in a database for these citrus flavanones: hesperidin, naringin, narirutin, eriocitrin, neohesperidin, didymin, neoeriocitrin, and poncirin. Sour oranges had a distinct flavanone profile dominated by naringin and neohesperidin, and were highest in total flavanones (summed means) (48mg/100g aglycones). Total flavanones (summed means) in sweet oranges, tangerines, and tangors were similar (∼20mg/100g), and hesperidin and narirutin dominated the flavanone profiles for these three fruits. Total flavanones (summed means) in tangelos (30mg/100) were midway between sour and sweet oranges and the tangelo flavanone profile exhibited characteristics of both species. The database provides information on several varieties of citrus and eight flavanone compounds.

In order to develop a database for flavanones, the dominant flavonoid class in the genus citrus, the relevant scientific literature on flavonoids in grapefruit, lemons, and limes was searched, abstracted, documented, standardized by taxons and units (mg/100g) and examined for quality. Values for eight flavanones (didymin, eriocitrin, hesperidin, naringin, narirutin, neoeriocitrin, neohesperidin, poncirin) are presented. Grapefruit had a total flavanone content (summed means) of 27mg/100g as aglycones and a distinct flavanone profile, dominated by naringin. White grapefruit varieties tended to be slightly but not significantly higher in total flavanones than pink and red varieties. For lemons, total flavanones (summed means) were 26mg/100g and for limes 17mg/100g. The flavanone profiles of both lemons and limes were dominated by hesperidin and eriocitrin.

Proanthocyanidins, also called condensed tannins, are oligomers and polymers of monomeric flavans linked through specific single (B linkages) and double (A linkages) bonds. These secondary plant metabolites have substantial antioxidant activity. They are prevalent in some foods and dietary supplements including several berries, red grapes and their wines, and seeds, baking chocolate, cinnamon, pycnogenol, and Ginkgo biloba. Calculations based on limited food composition data suggest daily intakes of about 54 mg/day per person in the United States. Similar data are unavailable to estimate intakes from dietary supplements. Studies on digestion of proanthocyanidins indicates only monomers and dimers are absorbed; however, preliminary evidence suggests hydroxylated phenolic acids are important products of gastrointestinal microflora activity that also may be absorbed. Several types of investigations support improved vascular health after short- or long-term consumption of proanthocyanidins or foods and supplements that contain them. These effects include vasodilation, presumably as a result of increased NO production, decreased platelet aggregation, reduced sensitivity of low-density lipoproteins (LDL) to oxidization, and modulation of several reactions associated with inflammation. Studies with cranberries and cinnamon, both of which contain uniquely linked proanthocyanidins, support a role for bacterial antiadhesion and improved glucose metabolism in type 2 diabetics, respectively. Results from a variety of experiments indicate proanthocyanidins may modulate several reactions involved in cancer processes. A crucial research need is to identify further biologically active components of proanthocyanidins so that mechanisms of action at the tissue, cellular, and subcellular levels can be elucidated.

Fruits and vegetables are dietary components which convey numerous health benefits. Not only do fruits and vegetables contain many essential nutrients, but they also contribute to disease prevention. In the last decade, nutrition research has made great strides in identifying specific nutrients which have beneficial health effects and the mechanisms by which those health benefits are achieved. However, the ability of a specific nutrient to impart health benefits depends on the gastrointestinal tract’s ability to extract the nutrient from the plant material. The presence of a specific nutrient in a plant food is insufficient for providing health benefits if the bioavailability of that nutrient is very low. For example, spinach contains a high calcium content, but the presence of phytates and oxalates in spinach prevents the calcium from being absorbed in the gastrointestinal tract (Weaver et al., 1987; Heaney and Weaver, 1989; Peterson et al., 1992). Thus, calcium has a very low bioavailability from spinach.

Flavonoids and their polymers constitute a large class of food constituents, many of which alter metabolic processes and have a positive impact on health. Flavonoids are a subclass of polyphenols. They generally consist of two aromatic rings, each containing at least one hydroxyl, which are connected through a three-carbon "bridge" and become part of a six-member heterocyclic ring. The flavonoids are further divided into subclasses based on the connection of an aromatic ring to the heterocyclic ring, as well as the oxidation state and functional groups of the heterocyclic ring. Within each subclass, individual compounds are characterized by specific hydroxylation and conjugation patterns. Many flavonoids in foods also occur as large molecules (tannins). These include condensed tannins (proanthocyanidins), derived tannins and hydrolysable tannins. For proantho-cyanidins, three subclasses (15 characterized) have been identified in foods. Monomers are connected through specific carbon-carbon and ether linkages to form polymers. Derived tannins are formed during food handling and processing, and found primarily in black and oolong teas. Flavonoids are widely distributed in nature, albeit not uniformly. As a result, specific groups of foods are often rich sources of one or more subclasses of these polyphenols. The polyphenolic structure of flavonoids and tannins renders them quite sensitive to oxidative enzymes and cooking conditions. Scientists in several countries have estimated intakes of a few subclasses of flavonoids from limited food composition databases. These observations suggest large differences in consumption, due in part to cultural and food preferences among populations of each country.

A mixed food homogenate was prepared as a quality control material for two multi-center clinical feeding trials. Approximately 100 kg of homogenized human diet material was prepared under controlled conditions to maintain the stability of lipid components. More than 4800 20–25 g aliquots were prepared and stored at –60 °C in glass jars with Teflon-lined lids. The homogeneity of the composite was validated by analysis of moisture and total fat in aliquots taken throughout the dispensing sequence. A portion of the material was reserved at the National Institute of Standards and Technology and further characterized as SRM 1544-Fatty Acids in Diet Composite. Moisture, protein, ash, total lipid, fatty acids, cholesterol, sodium, potassium, calcium, and magnesium were assayed as part of routine quality-control analyses. Components were analyzed over a total time period ranging from 29 months (minerals) to 60 months (moisture), and up to 319 values per nutrient were generated. Results for all components assayed were stable over the time period studied. For example, moisture (n = 319; 60 months) ranged from 70.66 to 72.58 g/100 g with a mean, standard deviation (SD), and relative standard deviation (RSD) of 71.90, 0.27, and 0.4%, respectively. The range, mean, SD, and RSD for cholesterol (mg/100 g; n = 98; 49 months) were 13.54–17.96, 15.14, 0.64, and 4%.

The critically acclaimed laboratory standard for more than forty years, Methods in Enzymology is one of the most highly respected publications in the field of biochemistry. Since 1955, each volume has been eagerly awaited, frequently consulted, and praised by researchers and reviewers alike. Now with more than 300 volumes (all of them still in print), the series contains much material still relevant today-truly an essential publication for researchers in all fields of life sciences. This volume presents an extensive collection of new methodologies to aid progress in solving unanswered questions concerning the bioavailability and metabolism of flavonoids and polyphenols, their biochemical and molecular biological effects on cell regulation, and their effects on health. Major topics in this volume include sources, characterization, analytical methods, bioavailability, antioxidant action, and biological activity.

Tea consumption has been associated with reduced risk of both cancer and cardiovascular disease in population studies, but clinical data demonstrating bioavailability of the individual catechins and other polyphenolic components of tea are limited. This study assessed the apparent bioavailability of the prominent catechins from black tea in humans drinking tea throughout the day. After 5 d of consuming a low flavonoid diet, subjects drank a black tea preparation containing 15.48, 36.54, 16.74, and 31.14 mg of (-)-epigallocatechin (EGC), (-)-epicatechin (EC), (-)-epigallocatechin gallate (EGCG) and (-)-epicatechin gallate (ECG), respectively, at four time points (0, 2, 4 and 6 h). Blood, urine and fecal specimens were collected over a 24- to 72-h period and catechins were quantified by HPLC with coularray detection. Plasma concentrations of EGC, EC and EGCG increased significantly relative to baseline (P < 0.05). Plasma EGC, EC and EGCG peaked after 5 h, whereas ECG peaked at 24 h. Urinary excretion of EGC and EC, which peaked at 5 h, was increased relative to baseline amounts (P < 0.05) and fecal excretion of all four catechins was increased relative to baseline (P < 0.05). Approximately 1.68% of ingested catechins were present in the plasma, urine and feces, and the apparent bioavailability of the gallated catechins was lower than the nongallated forms. Thus, catechins were bioavailable. However, unless they are rapidly metabolized or sequestered, the catechins appeared to be absorbed in amounts that were small relative to intake.

The plant lignans, secoisolariciresinol (SEC) and matairesinol (MAT) are converted to the metabolites, enterodiol (ED) and enterolactone (EL), known as the mammalian lignans in the gastrointestinal tract. In vitro, mammalian lignans may have both estrogenic and antiestrogenic properties. Increased consumption of lignan-rich foods through the addition of brans, oilseeds and cereals in bread, muffins, health bars and breakfast cereal or emphasis on fruits and vegetables in a balanced diet has lead to the need for reliable data on lignan content in foods. The quantitative determination of the lignans to date by a direct method has involved hydrolysis of the glycoside and analysis of the resulting aglycones (SEC and MAT). The in vitro fermentation methodology, which simulates colonic fermentation with fecal microflora, has been utilized in the indirect analysis of foods where ED and EL are measured as an indication of the plant lignans. A compilation of the available data on the lignan content of various food groups and the assessment of these data by contrasting two different analytical methodologies are given. In general, in vitro fermentation gave higher values, compared to direct analysis, for most foods for which comparisons could be made.