Agriculture Reference
In-Depth Information
Table 8.5
Vitamin Content (mg/100g) in Three
Avocado Cultivars.
Vitamins
QUALITY COMPONENTS AND INDICES
The major quality criteria used for avocado fruit are size,
skin colour, firmness and freedom from wounds, blemishes,
insect damage, residues and other contaminants. When
ripe, the key quality indices are absence of diseases, physi-
ological disorders, and physical damage. Many of these
quality factors are cultivar-dependent and consumer
preference for size, shape and colour can vary from region
to region. There are significant differences in size, texture,
and flavour between the different cultivars.
Freshly harvested avocados tend to have 'green' skins,
although 'Hass' fruit that are harvested late in the season
may have some skin darkening at harvest. The peel of ripe
'Hass' and 'Lamb Hass' avocados should have a dark,
purple-black or black skin while green-skinned cultivars
remain green when ripe. Pulp colour, texture and flavour
when ripe are cultivar-specific.
California avocados are graded as No. 1 or No. 2. Florida
avocados are graded as U.S. No. 1, U.S. No. 2 and U.S.
Combination. However, only some Florida varieties are
graded, while the others are marketed as unclassified. In
California, fruit are weight sized into the following
categories: 20 (532 to 624 g), 24 (447 to 532 g), 28 (390
to 447 g), 32 (333 to 397 g), 36 (298 to 354 g), 40 (269 to
326 g), 48 (213 to 269 g), 60 (177 to 213 g), 70 (135 to
177 g) and 84 (106 to 135 g), indicating the count for 11 kg
packs, and half these values for flats (or single layer trays).
Florida fruit are packed by count. Regulations specify that
the pack shall be at least fairly tight and that the weight of
the smallest fruit in any container shall not be less than
75% by weight of the largest fruit in the container.
Commonly used counts for Florida packages are 6, 7, 8, 9,
10, 12, 14, 16, 18, 20 and 24 counts.
Food safety has become an important issue with strict
guidelines now being set by the food industry. The major
retailer chains invest heavily into promoting brand names
and avoid adverse publicity that might arise from product
exceeding the legal limits set for pesticide residues.
'Fuerte'
'Hass'
'Anaheim'
Thiamine
0.12
0.09
0.08
Riboflavin
0.22
0.23
0.21
Niacin
1.45
2.16
1.56
Pantoteic acid
0.90
1.14
1.11
Pyridoxine
*
0.61
0.62
0.39
Folic acid
0.03
0.04
0.018
Biotin
0.005
0.006
0.0034
*Including pyridoxal y pyridoxamine.
Besides being a source of energy and vitamins, avocados
also contain several phytochemicals that are thought to be
beneficial for health. Therefore, avocado is considered by
some as 'functional food' (Mazza 1998). Some nutraceutical
ingredients that have been found in avocado pulp are
antioxidants, such as tocopherols (about 4.3 UI/100 g) and
glutathion (18 mg/100g). It has also been reported that
avocado is a source of lutein (contain up to 248 mg/100g).
The amount of β-sitosterol in this fruit is comparable to that
found in soy and olives. An avocado-enriched diet produced
a significant reduction in low-density lipoproteins and total
cholesterol in patients with high-cholesterol levels, while
diets enriched with soy and sunflower did not change the
total cholesterol concentrations (Carranza
et al
. 1997).
Pigments are important contributors to the appearance and
healthful properties of both avocado fruit and oil. Ashton
et al
. (2006) identified in the skin, flesh, and oil of avocado
fruit lutein, α-carotene, β-carotene, neoxanthin, violaxanthin,
zeaxanthin, antheraxanthin, chlorophylls a and b, and
pheophytins a and b with the highest concentrations of all
pigments in the skin. Chlorophyllides a and b were identified
in the skin and flesh tissues only. As the fruit ripened and
softened, the skin changed from green to purple/black. The
levels of carotenoids and chlorophylls did not change
significantly during ripening. As fruit ripened, the total
chlorophyll level in the oil from the flesh sections remained
constant but declined in the oil extracted from the skin. Skin
of 'Hass' avocados changes colour from green to purple/
black as fruit ripen. This colour change is important as an
indicator of ripeness. Colour change in 'Hass' avocados from
green to purple, then black, results from an initial decrease in
chlorophyll content, followed by an increase in the levels of
the anthocyanin, cyanidin 3-O-glucoside (Cox
et al
. 2004).
Total anthocyanins in skin tissue increased during ripening,
but this increase was due almost entirely to a single
anthocyanin; cyanidin 3-O-glucoside (Cox
et al
. 2004).
MAJOR CAUSES OF POST-HARVEST LOSSES
Coursey (1971) reported that the post-harvest losses of
avocado were estimated as 43%, and smooth skin varieties
are more prone to physical injuries during handling and
transport than the rough skin varieties. Some of the most
important causes of post-harvest losses in avocado include
mechanical damage, physiological disorders especially
chilling injury (CI), decay and insects. Avocado is a
subtropical fruit sensitive to CI (Pesis
et al
. 1994). The
main symptoms are black stains in the epidermis and a grey
or brown discolouration in the mesocarp. Morris (1982)
