Agriculture Reference
In-Depth Information
Juiciness
Juiciness as perceived by the consumer is greater the more juice is released on
chewing, the greater the force with which it is released, the higher its water
content and the lower its viscosity and content of suspended solids. Juiciness
requires a cohesive network of large, turgid, thin-walled cells. If the middle
lamella is stronger than the cell walls, the cells fracture on biting and juice
is released; if it is weaker, then the fracture is between cells, the juice is not
released and the fruit is perceived as non-juicy (Szczesniak and Ilker,
;
Boulton
et al.
,
;Tu
et al.
,
). Although juiciness is often associated
with fruit firmness (Kingston,
) apple cultivars with similar
textural properties may differ in juiciness (Corrigan
et al.
,
;Tu
et al.
,
). Juice content
can be determined by expressing the juice from a known volume or weight of
apple cortical tissue under known force and expressing the results as mg or ml
per gram of tissue (Smith,
). The area of spread of juice from the freshly
cut surface of apple slices on CuSO
-treated filter paper is highly correlated
with sensory panel ratings of juiciness (Boulton
et al.
,
).
Sugar and acid content
Apple taste is primarily related to the amount of sugar and acid in the fruit
tissues and to the balance between these. In pears acidity is considerably lower
than in apples and may be undetectable as a component of taste.
Fructose, glucose, sucrose and sorbitol are the main fruit sugars. Fructose is
themainsugarinmatureapplesofmostcultivars,including'GoldenDelicious'
(Pavel and DeJong,
) and 'Fuji' (Drake
et al.
,
). Sucrose predominates
in 'Cox's Orange Pippin' (Pavel and De Jong,
). European and Asian pears
alsoaccumulatehighamountsofsucroseduringfruitripening(Moriguchi
et al.
,
).
Malic acid is the main organic acid in apples and pears but some apple cul-
tivars also have appreciable amounts of citric acid (
-
% in 'Fuji' according
to Hong
et al.
,
). Citric acid may exceed malic in some pear cultivars
(Ulrich,
) and both apples and pears have smaller quantities of quinic,
galactouronic, chlorogenic and other acids.
Total and reducing sugars are measured by standard chemical and enzym-
atic procedures (Smith,
). Alternatively, a few drops of juice are placed
on the prism of a refractometer and results read as percentage soluble solids at
◦
C. Measurement of specific sugars is by HPLC. Acidity is best measured as
titratable acidity but can also be recorded as pH using indicator paper strips.
Measured levels of percentage sugar and pH are closely correlated with
taste assessments as long as the range is wide, e.g. between seedling cultivars,
but taste does not discriminate well within extremes of sugar content or acidity.
