Riboflavin digestion

Corylus heterophylla Fisch. ex Besser. C. mandshurica Maxim, ex Rupr. C. mandshurica Maxim, ex Rupr. f. brevituba (Kom.) Kitag. Zhen (Filbert) (seed) Beta-carotene, thiamine, riboflavin, niacin, ascorbic acid.50 To improve appetite, a digestive. 

N.A. Carotene, thiamine, nicotinic acid, riboflavin, folic acid, pantothenic acid, biotin, glutamic acid, serine, glycine, aminobutyric acid, globulin, amino acids.100 An antiseptic, aperient, depurative, digestive, pectoral, a folk remedy for asthma. 

Yeast protein is easily digested (87%) and provides amino acids essential to human nutrition. Most commercial yeasts show the following pattern of amino acids, among others, as percent of protein 8.2% lysine 5.5% valine 7.9% leucine 2.5% methionine 4.5% phenylalanine 1.2% tryptophan 1.6% cystine 4% histidine 5% tyrosine and 5% arginine. The usual therapeutic dose of dried yeast is 40 grams/day, which supplies significant daily needs of thiamine, riboflavin, niacin, pyridoxine, and general protein. 

The dried sludge residue contains proteins, fats, saccharides, vitamins (thiamine, riboflavin, niacin, pyridoxine, nicotinamide, biotin, etc.) and mineral salts. It therefore represents a potentionally suitable feed additive. Particularly in the case of plant fodders, it can increase their biological value, digestibility and degree of utilization. 

Plants and microorganisms synthesize riboflavin naturally. Some foods rich in riboflavin are brewer s yeast, dark green vegetables, mushrooms, legumes, nuts, milk and other dairy products, sweet potatoes, and pumpkins. Bacteria that live in the human digestive tract are also able to synthesize some riboflavin, but not enough to meet the body s requirement for the vitamin. 

The most common forms of vitamin B2 are riboflavin 5 -phosphate (FMN) and flavin adenine dinucleotide (FAD), which are best known for their participation as co-factors (ligands) to some of the enzymes involved in electron transfer chains. The ligand is usually coupled to enzymes through the phosphate moiety and therefore isolation from tissue can be achieved by either mild acid hydrolysis or by enzymatic digestion with an acid phosphatase. 

Vitamins are a well-known group of compounds that are essential for human health. Water-soluble vitamins include folate (vitamin B9) to create DNA. Folate also plays an important role in preventing birth defects during early pregnancy. Thiamine is the first vitamin of the B-complex (vitamin Bl) that researchers discovered. It allows the body to break down alcohol and metabolize carbohydrates and amino acids. Like many other B vitamins, riboflavin (vitamin B2) helps the body to metabolize carbohydrates, proteins, and fat. Niacin (vitamin B3) protects the health of skin cells and keeps the digestive system functioning properly. Pantothenic acid (vitamin B5) and biotin allow the body to obtain energy from macronutrients such as carbohydrates, proteins, and fats. Vitamin B6 (pyridoxine) acts as a coenzyme, which means it helps chemical reactions to take place. It also plays a vital role in the creation of nonessential amino acids. 

The inadequate intake of riboflavin seems to be the main cause for the deficiency of this vitamin, being common in populations whose diet lack dairy products and meat, and in anorexic individuals. Digestion and intestinal absorption disorders are other causes of disability, as observed in individuals with lactose intolerance, tropical sprue, coeliac disease and intestinal resection, as well as gastrointestinal and biliary obstruction. Other disorders such as diarrhoea, infectious enteritis and irritable bowel syndrome can cause poor absorption by increasing intestinal motility. Riboflavin deficiency also occurs in conditions such as chronic alcoholism, diabetes mellitus and inflammatory bowel diseases. 

Riboflavin is digested in the stomach and in the small intestine by the action of hydrochloric acid and specific enzymes, respectively. Absorption occurs in the small intestine by a Na -independent carrier. 

Sample treatment prior to SPE was required to convert FMN and FAD to riboflavin using a hot acid extraction procedure followed by enzymatic digestion, as the HPLC method applied allows the determination of only riboflavin. In this case, the recovery of riboflavin from FAD in pork samples was 94-98% with 2-4 hours of incubation time prolonging the incubation time to 24 hours did not improve the recovery. Indeed, the SPE procedure allowed a concentration factor of two to four fold, with recoveries for samples in the range 96-108%. The method was applied to 21 food samples, providing comparable results to the AO AC method (modified) apart from the crispbread sample. This was justified by the presence of a fluorescent contaminant in this sample that caused an overestimation of the amount of riboflavin in the fluorimetric, non-separative method. 

Table 18.2 Characteristics and figures of merit for solid-phase extraction of riboflavin and determination by HPLC-FL. The procedure proposed by Ollilainen el al. (1990) utilizes a silica Cl8 cartridge for selective extraction of riboflavin after acid and enzymatic digestion of samples. Riboflavin in the extract is quantified by HPLC using a reversed-phase column.

The analytical characteristics are presented in Table 18.5. The method was validated by application to CRM NIST 1846 (milk-based infant formula) and to CRM BCR 487 (pig liver), providing values that were statistically comparable to the certified values. Good precision and good recoveries (91-93%) were attained after addition to an energy drink. However, there is still a question about this method as no study has been undertaken regarding the MIP selectivity towards different forms of riboflavin, namely FMN and FAD. As pig liver was digested and treated with enzymes prior to analysis and the two other samples analyzed probably had mainly free riboflavin, no assumptions about the selectivity can be drawn from these results. 

Intestinal bioavailability of riboflavin from the diet depends on digestibility of the food, which alfects duration of the food in the gut, and is decreased by the consumption of alcohol, which inhibits the activity of FAD and FMN phosphatases, indispensable to their conversion into riboflavin before absorption (Figure 36.1). Simultaneously, the intestinal bioavailability is increased by secretion of bile salts these extend the transition of food in the intestinal tract and enhance riboflavin solubility and the permeability of the brush-border membrane (Ball 2004b). 

Figure 36.2 Riboflavin (RF) absorption and transport via the epithelium of the small intestine. The figure presents the fragments of the digestive tract involved in riboflavin absorption and a scheme of recognized mechanisms of this process.

Riboflavin needs to be present in the human typical diet, as animals, unlike many plants, fungi and bacteria, are unable to synthesize this molecule. Dietary intake of this vitamin includes free riboflavin and also its protein bound form, as FAD and FMN in flavoproteins (Figure 37.1 A). In the latter case, flavins need to be first released from carrier proteins during digestion and then hydrolysed to riboflavin by alkaline phosphatases and FMN/FAD pyrophosphatase in order to be absorbed at the small intestine. 

Figure 37.1 Riboflavin metabolism and cellular processing pathways. (A) Riboflavin and flavin intake is made via the diet, either in riboflavin-rich aliments or flavoproteins. In the latter, digestion in the stomach releases FAD and FMN cofactors. Riboflavin and flavins achieve a high concentration in the liver, spleen and cardiac muscle a concentration of about 30 nM riboflavin is also reached in the plasma circulation. (B) Riboflavin is imported into the cell and into the mitochondria via specific transporters (white circles in membranes). In the cytoplasm, flavin kinase (FK) and FAD synthetase (FADS) consecutively convert riboflavin into FMN and FAD, at the expense of ATP. An identical mechanism is also thought to be present inside the mitochondria, although a mitochondrial FK remains to be identified. FAD can also be imported into the mitochondria, or diffuse passively when the riboflavin concentrations are high. Figures reprinted from Henriques et al. (2010), with permission.

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