Bioaccessibility and Bioavailability of Bioactive Compounds in Food and Plant Determination - Natural Antioxidants and Biocides from Wild Medicinal Plants - page 49

the intestinal lumen and it is in the gastroin-
testinal tract where these compounds can
have substantial benefits, such as inhibition
of abnormal cell proliferation and protection
against the development of cancer.
Among the methods currently used to
estimate the bioavailability is the dialysis
process. In the study of apple polyphenols
mentioned above, also the amount of dia-
lysable polyphenols is calculated, wherein
the total dialysable polyphenols were lower
than the total soluble polyphenols in the
intestinal phase, indicating that the amounts
of potentially available polyphenols for
absorption are less than those bioaccessible
in intestinal digestion, by approximately
50% (Bouayed et al. , 2012). But dialysis is a
complex process affected by factors such as
volume, composition of the buffer used,
concentration of sugars in the sample or the
ability of certain molecules to bind to the
membrane. All these parameters can affect
the dialysance of a specific compound,
which cannot actually be attributed to
absorption of this compound in vivo or lev-
els of this compound in serum. Another
method for the study of bioavailability of
phenolic compounds is the use of Caco-2
cells. In a study of grape seed extract it was
observed that the phenol content was not
affected by gastric stimulation, but during
the intestinal digestion decreased due to
interaction with pancreatic proteins. Then,
in the presence of Caco-2 cells, all dimers
disappear, except (+)-catechin and
(−)-epicatechin that decreased 44% and
85%, respectively, after 2 h of intestinal
digestion. Compounds were not detected in
the basal compartment of the cell mono-
layer (Laurent et al. , 2007).
b-Carotene is the most common carote-
noid found in human tissue and plasma; after
crossing the intestinal wall the b-carotene is
converted to vitamin A and other metabolites.
The bioavailability of b-carotene depends
on the physicochemical state of the caroten-
oid in food, the type of processing/cooking,
presence of other nutrients, seasonal varia-
tion and geographical origin. In carrots,
carotenoids are present in semi-crystalline
form or associated with proteins embedded
in chromoplasts. Cooking vegetables rich in

carotenoids can lead to degradation and/or
isomerization of carotenoids. There are higher
amounts of trans b-carotene on micelles in
cooked carrots than in raw carrots; cooked
carrots also contain higher levels of the
13- cis isomer and 15- cis isomer. All trans
b-carotene isomers are more bioaccessible
from mashed than from cooked carrots. All
trans b-carotenes are absorbed faster than
the cis by Caco-2 cells. Therefore, cooking
the carrots increases the bioaccessibility
and bioavailability of all trans b-carotene
(Aherne et al. , 2010).
With respect to contaminants in marine
products, it has been observed that the effect
of cooking algae causes the elimination of
arsenic in the cooking water. The percent-
ages of dialysability found in raw algae are
comparable to those found in cooked algae,
except for sea lettuce, which yields a lower
percentage when it is cooked. The percent-
age of dialysability in cooked algae was
between 7.4 and 13.8%, which does not
vary much when compared with raw algae
(García-Sartal et al. , 2011).

4.8 The In Vitro Human
Digestive Process

Feeding methods in vivo , using animals or
humans, usually provide more accurate
results but are long and expensive, which is
why currently efforts are made in develop-
ing in vitro procedures. Table 4.1 shows the
conditions used for various simulated gas-
tric digestions. Enzymes commonly used in
in vitro digestion models are pepsin, pan-
creatin, trypsin, chymotrypsin, peptidase,
a-amylase, lipase, bile salts and mucin. The
simulation times vary according to the food
matrix being studied; small particles require
less digestion times than larger particles
(Hur et al. , 2011). Generally, gastric diges-
tion times of 1 h are used and intestinal
digestion times used are 2-6 h. Models of in
vitro digestion do not usually consider the
large intestine, because compound absorp-
tion generally occurs in the small intestine
(Brandon et al. , 2006). But there are studies
that do include the processes occurring in