Vitamins in Fleshy Fruits - Fruit Ripening: Physiology, Signalling and Genomics - page 130

vitamin C content), postharvest storage
conditions (reviewed by Lee and Kader,
2000) and whether the product is
consumed raw or transformed by cooking
(vitamin C is heat labile, but cooking can
increase the bioavailability of carotenoids).
In this chapter, we will focus on three
vitamins for which fl eshy fruits are
important sources in the human diet: two
fat-soluble vitamins, the provitamin A
carotenoids, which are precursors of
vitamin A (retinoids), and vitamin E
(tocopherols), and the water-soluble vitamin
C (ascorbate). State-of-the-art research on
vitamins in plants and their potential
benefi ts in promoting human health have
been outlined in a recent review (Fitzpatrick
et al. , 2012). The reader can also refer to two
recent volumes of Advances in Botanical
Research dedicated to vitamins in plants
(Rébeillé and Douce, 2011a,b) for more
detailed knowledge on specifi c vitamins. In
the fi rst part of the chapter, a general
overview will be given for each vitamin: its
physiological role in plants, the bio-
synthetic pathways in fl eshy fruits and
regulation by genetic factors, and environ-
mental cues in terms of fruit development
and during postharvest storage. In the
second part, we will review the various
strategies currently being undertaken to
improve the vitamin content of fl eshy fruits.

8.2.1 Role of vitamin A in humans and
plants

Provitamin A carotenoid pigments found
in fruits are embedded in chloroplasts and
chromoplasts, which are complex cellular
structures. During digestion, highly lipo-
philic carotenoids are freed from embed-
ded food matrices and incorporated into
lipid-containing water-miscible micellar
solutions, a process that permits their
passage into the lipid-rich membrane of
intestinal mucosal cells. Fruit processing
(e.g. thermal treatments, high-pressure or
microwave preservation), which disrupts
fruit chromoplasts and helps the con-
stitution of emulsions, contributes to
increase the bioaccessibility of provitamin
A (Svelander et al. , 2011).
Vitamin A is essential to humans and is
needed in small amounts for the visual
system, in the retina of the eye, for normal
development and growth, for dif-
ferentiation of epithelial cells and for
immune function. Vitamin A defi ciency is
frequent in economically deprived popu-
lations, in which it is the major cause of
blindness and one of the important reasons
for child mortality. Defi ciency in de-
veloped countries, although less acute and
frequent, can be responsible for night
blindness. Other human diseases triggered
by vitamin A defi ciency are mostly linked
to its effect on epithelial cells (e.g. in-
creased sensitivity to pathogens, reduced
immunity).
In plants, carotenoids are essential
components of the photosynthetic system,
in which they contribute to the stabiliz-
ation of lipid membranes and to light
harvesting for photosynthesis. Because of
their chemical properties, they have a
crucial function in protecting the photo-
synthetic apparatus against chlorophyll
bleaching in intense light. In addition,
carotenoids are precursors of the plant
hormone abscisic acid (ABA). Carotenoids
are also natural pigments acting as
colouring agents in fl owers and fruits,
where their function is to attract animals to
disseminate the seeds.

8.2 Provitamin A Biosynthesis and
Regulation in Fleshy Fruits

Vitamin A comprises several compounds,
among which the most abundant and active
is retinol. In plants and fruits, several
precursors of retinol known as provitamin
A can be found. They mainly include D - and
E -carotene and E -cryptoxanthin, which are
orange-red carotenoids found in chloro-
plasts and chromoplasts. Plant carotenoids
are C40 isoprenoids with polyene chains
that may contain up to 15 conjugated
double bonds. Carotenoids provide most
of the provitamin A in the diet, with
E -carotene being converted the most effi -
ciently to vitamin A.