Soft Fruit - Crop Post-Harvest: Science and Technology - page 263

and soluble amino acids may also influence TSS. Typical
concentrations of fructose, glucose and sucrose found in
ripe strawberry cv. Elsanta range from 22 to 36 mg g −1 FW,
from 18 to 29 mg g −1 FW and from 23 to 28 mg g −1 FW,
respectively, and have been shown to be affected by
preharvest water deficit irrigation (Terry et al . 2007b).
Despite TSS being used ubiquitously by the strawberry
industry for quality control it should be limited to com-
parative studies when environmental variation is low (Olías
et al . 2001; Terry et al . 2005).

Colour and appearance
As soft fruit ripen an increase in anthocyanins is accompa-
nied by a decrease in chlorophyll content. The predominant
anthocyanins in all red strawberry cultivars and raspberry
fruit is pelargonidin 3-glucoside (Pg 3-gluc) and cyanidin
3-glucoside (Cy 3-gluc), respectively (Given
et al . 1988; João Melo et al . 2000). Typical concentrations
of Pg 3-gluc and Cy 3-gluc found in ripe strawberry cv.
Elsanta range from 110 to 150 μg g −1 FW and from 2 to
4 μg g −1 FW, respectively, and have been shown to be
affected by preharvest water deficit irrigation (Terry et al .
2007b). The accumulation of anthocyanins coincides
with the de novo induction of the activities of phenylala-
nine ammonia lyase (PAL) and uridine diphosphate
glucose:flavonol O 3 -D-glucotransferase (UDPGFT) (Given
et al . 1988; Cheng & Breen 1991). Despite final ripe fruit
colour being affected by environment there are distinct col-
our differences between genotypes (Table 11.2; Sacks &
Shaw 1994). Modest changes in anthocyanin content of
strawberry fruit during storage can occur according to
maturity, light and storage temperature (Sacks & Shaw
1993; Saks et al . 1996). Fruit glossiness also diminishes
post-harvest, particularly at temperatures greater than 5°C
and at low humidity (Ferreira et al . 1994). Distinct
differences in the level of anthocyanins were also found
amongst blackcurrant cultivars (McDougall et al . 2005;
Giné Bordonaba & Terry 2007). Increasingly, evidence
suggests that daily consumption of soft fruit, which
typically contain relatively high concentrations of
anthocyanins and other phenylpropanoids (e.g. flavonoids
and hydroxycinnamic acids; Aaby et al . 2005, 2007) with
high total antioxidant capacity (e.g. ORAC or FRAP
assays), may provide protection against cardiovascular
diseases and cancer ( cf . Seeram et al . 2006).

Organic acids
Citric, malic, ascorbic, oxalacetic, glyceric and glycolic
acids are the principle organic acids identified in strawberry
fruit. Acids affect flavour directly and can regulate cellular
pH, influencing fruit tissue colour. Total titratable acidity
(TTA), a measure of the buffering capacity of fruit, is
generally expressed as percent citric acid. Citric acid is the
predominate organic acid found in strawberry (Green 1971)
and decreases upon colour development on a per fruit basis.
Typical concentrations of citrate, malate and ascorbate
found in ripe strawberry cv. Elsanta range from 9 mg g −1
FW, 3 mg g −1 FW and 0.7 mg g −1 FW, respectively (Terry
et al . 2007b). Current standard product-orientated quality
control operations do not use TTA due to the cumbersome
and time-consuming nature of titrations (Terry et al . 2005).

Volatile compounds
Soft fruit aroma is influenced by a complicated assortment
of esters, alcohols, aldehydes, ketones, sulfur compounds
and furanones. Raspberry aroma can be approximated
relatively well by 4-(4-hydroxyphenyl)-butan-2-one;
referred to as the 'raspberry ketone' (Larsen & Poll 1990).
No single character impact compound (Baldwin 2002) is
responsible for the typical aroma of fresh strawberry,
however, ethyl/methyl esters and furaneol seem to be
important ( cf . Olías et al . 2001; Olbricht et al . 2008).
Aroma is affected by genotype, shading, harvest maturity
and post-harvest handling (Watson et al . 2002). Low
temperature storage, although desirable for extending
post-harvest life, can diminish emission of volatiles.

Sugars
It has been reported that the total soluble solid content
(TSS %) of strawberry fruit increases steadily during
development, from 5% in green fruit to 7.3% in overripe
(dark red) fruit (Spayd & Morris 1981). However,
depending on the environment and cultivar, the TSS of
fruit can vary between 4% and 12% Brix (Terry unpub-
lished). Maroto et al . (1986) reported that TSS hardly
changed during fruit development and ripening, with a
mean value of 8%. Although the absolute and relative con-
centrations of fructose, glucose and sucrose vary amongst
cultivars and degree of ripeness there is actually poor
correlation between sugar content and TSS (Shaw 1988;
Perez et al . 1997) and thus it is thought that organic acids

POST-HARVEST HANDLING
The highest quality soft fruit, after harvest, are regularly
shaped, glossy, fully coloured, firm and have achieved
maximum flavour and aroma. For strawberry fruit, a
healthy green calyx is also desirable. Fruit that are too
large can result in lower prices. Strawberry fruit destined
for export are occasionally picked at least three-quarters
ripe. Fruit at this stage generally develop adequate colour