Rheological Characteristics of Apple Skin and Apple Firmness

Figures & data

Figure 1 Typical stress-strain data and their standard deviations for the skin of a CA stored Red Delicious apple.

Table 1 Values of breaking strength and apparent modulus of apples. ^a

Apples	Breaking strength, MPa	Apparent modulus, MPa
McIntosh, cold temperature, ^b n = 10	2.03 ± 0.65^c	34.1 ± 7.7^d
McIntosh, CA, n = 4	2.51 ± 0.17^c	26.2 ± 6.3^e
Red Delicious, CA, n = 4	1.74 ± 0.15^c	25.1 ± 5.9^e
Empire, CA, n = 5	2.66 ± 0.52^c	27.1 ± 5.9^e
Honey Crisp, light crop, n = 9	1.48 ± 0.26^c	19.8 ± 2.2^f
Honey Crisp, heavy crop, n = 9	1.44 ± 0.25^c	18.2 ± 2.1^f
Crimson Gala, light crop, n = 8	1.90 ± 0.31^c	24.3 ± 3.3^f
Crimson Gala, heavy crop, n = 8	1.85 ± 0.31^c	19.4 ± 2.5^f
^a n refers to number of tests. In each column, values with the same letter are not significantly (P ≥ 0.05) different.
^bCold temperature: storage without control of atmosphere; these apples were not used in puncture tests. CA: controlled atmosphere storage.

Figure 2 Stress-strain data of skins of CA stored Empire and McIntosh apples.

Figure 3 Puncture force vs. penetration distance plots of CA stored McIntosh, Red Delicious, and Empire apples with and without skin. Also shown are: the peak puncture force with skin, A, an assumed peak value without skin, b, at the same penetration distance at which with-skin sample's peak force occurred, and the apparent elastic limit of the apple flesh without skin, a.

Figure 4 Puncture force vs. penetration distance plots of Honey Crisp heavy and light crop apples.

Figure 5 Puncture force vs. penetration distance plots of Crimson Gala heavy and light crop apples.

Table 2 Peak puncture force, N, values with a rounded end cylindrical probe, 7.9 mm diameter

	Puncture force, N
Apples	With skin	Without skin ^a	Skin contribution, %
McIntosh, CA	42.8 ± 6.8^b	25.1 ± 4.2^d	41.4^f
Red Delicious, CA	40.7 ± 2.8^b	27.3 ± 4.2^d	29.2^f
Empire, CA	49.5 ± 3.5^b	30.5 ± 3.3^d	38.4^f
Honey Crisp-light crop	89.4 ± 16.6^c	70.0 ± 10.1^e	21.7^g
Honey Crisp-heavy crop	96.4 ± 19.3^c	76.7 ± 9.6^e	20.4^g
Crimson Gala-light crop	95.3 ± 24.6^c	60.4 ± 11.8^e	36.6^f
Crimson Gala-heavy crop	113.6 ± 11.3^c	68.7 ± 11.4^e	39.5^f
^aValues taken at the penetration distance at which peak force occurred in the with-skin samples.
In each column, values with the same letter are not significantly (P ≥ 0.05) different.