Bioaccessibility

The complex nature of the mass transfer of carotenoids to absorbable lipid species, the diversity of raw and processed foods consumed, and individual variations in the degree of mastication, will lead to differences in the amount of carotenoid that becomes bioaccessible and potentially available for absorption. By understanding the underlying mechanisms of these processes, for a wider range of fruit and vegetable constituents, it will become possible... 

In the in vitro digestion method, the compound of interest is transferred from the food matrix to a bile salt micelle suspension that simulates the in vivo digestion process. This in vitro digestion procedure was first developed to estimate iron availability from meals and since then has been modified and applied to studying carotenoid bioaccessibility from various food matrices. This approach assesses the bioaccessibility of the compound from a certain meal before it is presented to and taken up by intestinal cells. 

The bioaccessibility of a compound can be defined as the result of complex processes occurring in the lumen of the gut to transfer the compound from a non-digested form into a potentially absorbable form. For carotenoids, these different processes include the disruption of the food matrix, the disruption of molecular linkage, the uptake in lipid droplets, and finally the formation and uptake in micelles. Thus, the bioaccessibility of carotenoids and other lipophilic pigments from foods can be characterized by the efficiency of their incorporation into the micellar fraction in the gut. The fate of a compound from its presence in food to its absorbable form is affected by many factors that must be known in order to understand and predict the efficiency of a compound s bioaccessibility and bioavailability from a certain meal. ... 

The degree of lipophilicity of a pigment molecule can play a major role in its bioaccessibility. Obviously, a compound with a lower lipophilic character will be... 

Factors Influencing Bioaccessibility of Pigments from Foods... 

The degree of linkage of a compound may also affect its bioaccessibility in the gut. It is generally admitted that a compound linked with other molecules (e.g., via esterification, glycosylation, etc.) is not absorbed as well as its free form and thus it must be hydrolyzed in the gut in order to be taken up by enterocytes. Due to the presence of hydroxyl or keto groups on their molecules, the xanthophylls (lutein, zeaxanthin, and P-cryptoxanthin) are found in both free and esterified (monoester or diester) forms in nature, but few studies have been conducted to date to assess the bioavailabilities of these esters. 

The positions, numbers, and types of sugars on the anthocyanin molecule influence its bioaccessibility. Indeed, a recent human study reported that the acylation of anthocyaifins resulted in a sigififlcant decrease of anthocyanin recoveries in plasma and urine. In addition, anthocyanins form linkages with aromatic acids, aliphatic acids, and methyl ester derivatives, which can also affect their passage through the intestinal barrier. 

The release of a compound from the food matrix in which it is incorporated is a determining process for its bioavailability and is largely influenced by the physicochemical characteristics of the compound, the type of food matrix, the subcellular location of the compound in plant tissues, and the food processing. The, food matrix type greatly influences the compound bioaccessibility. 

Different factors inclnding nntrients, bile salts, pH, and microflora present in the gastrointestinal tract dnring the digestion process can affect the bioaccessibility of a compound (Table 3.2.1). The compoimd of interest is generally consiuned together with other nutrients present in the meal and, once the compound and these nutrients are released from the food matrix during the same period, they may interact in the intestinal liunen. 

Dietary fats, libers, and other carotenoids have been reported to interfere with carotenoid bioaccessibility. It is clear that by their presence in the gut, lipids create an environment in favor of hydrophobic compounds such as carotenoids. When arriving in the small intestinal lumen, dietary fats stimulate bile flow from the gallbladder and therefore enhance the micelle formation, which in turn could facilitate the emulsification of carotenoids into lipid micelles. Without micelle formation, carotenoids are poorly absorbed a minimum of 3 g of fat in meal is necessary for an efficient absorption of carotenoids, except for lutein esters that require higher amounts of fat. ... 

FIGURE 5.1 Pathways of bioaccessibility, biouptake, and bioavaUabUity leading to exposure. Source Modified from Escher and Hermens 2002.)... 

Geography and habitat variability affect MeHg prodnctiorr, bioaccessibility, and uptake into wildlife. Interpretation of mercttry in wildlife also reqtrires a working knowledge of sex, age, and tissue differences (Evers et al. 2005). Biogeochemical differences in aquatic and terrestrial systems are partictrlarly important determinants of Hg methylation, as discussed in previons chapters for water and fish. 

Physical and Chemical Properties. The physical and chemical properties of lead and its compounds are sufficiently well defined to allow an estimation of the environmental fate of lead to be made (Howe 1981 HSDB 1996 Lide 1996 Merck 1989 Sax 1984 Sax and Lewis 1987). Availabilities of the various forms need to be modeled and the connectivities to bioaccessabilities and bioavailabilities determined. 

Martins MAM, Ferreira IC, Santos IFM, Queiroz MJ, Lima N (2001) Biodegradation of bioaccessible textile azo dyes by Phanerochaete chrysosporium. J Biotechnol 89 91-98... 

Hamel S.C., Buckley B., Lioy P.J. Bioaccessibility of metals in soils for different liquid to solid ratios in synthetic gastric fluid. Environ Sci Technol 1998 32 358-362. 

Influence of soil geochemical and physical properties on the sorption and bioaccessibility of chromium(III). J Environ Qual 2003 32 129-137. 

Bioavailability issues have been reviewed previously (Mihelcic etal. 1993 Boesten 1993 Baveye and Bladon 1999 Ehlers and Luthy 2003). In this review, we discuss specifically the bioavailability of soil- or sediment-sorbed organic contaminants to pollutant-degrading bacteria. Direct uptake of sorbed contaminants is perhaps the most controversial and least understood process. The definition of bioavailability given by Alexander (2000) will be used in this review. The term bioaccessibility encompasses what is immediately available plus that which may become available, whereas bioavailability refers to what is available immediately. 

Gofii I, Serrano J and Saura-Calixto F. 2006. Bioaccessibility of beta-carotene, lutein, and lycopene from fruits and vegetables. J Agric Food Chem 54 5382-5387. 

Omelas-Paz JJ, Failla ML, Yahia EM and Gardea-Bejar AA. 2008b. Impact of the stage of ripening and dietary fat on in vitro bioaccessibility of (1 carotene in Ataulfo mango. J Agric Food Chem 56 1511-1516. 

DF and antioxidants are generally addressed separately as groups of food constituents in both chemical and nutritional studies. However, it is a little-known fact that a substantial proportion of the antioxidant polyphenols and carotenoids contained in fruit and vegetables are linked to DF (Saura-Calixto and others 2007), and some of the postulated benefits of fiber intake can be attributed to these associated compounds. These compounds are not bioaccessible in the human small intestine, but they... 

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