Skin properties have an important influence on impact parameters and bruising. Skin deformation at puncture (a measure of the turgidity of the fruit skin) is negatively correlated with bruise volume in Golden apples after cold storage

Garcia, J.L.

Ruiz-Altisent, Margarita

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Effects of skin characteristics on impact response and bruising of apples and pears

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EFFECTS OF SKIN CHARACTERISTICS ON IMPACT RESPONSE AND 
BRUISING OF APPLES AND PEARS 
J.L. Garcia 
M. Ruiz Altisent 
Departamento de Ingenieria Rural, E.T.S.I. Agronomos, 
Avda. Complutense s/n, 28040 Madrid, Spain 
ABSTRACT 
Skin propert ies have an impor tan t inf luence on impact parameters and 
bruising. Skin deformation at puncture (a measure of the turgidi ty of the frui t 
skin) is negatively correlated w i t h bruise volume in Golden apples after cold 
storage. 
1. INTRODUCTION 
Bruise damage is a major cause of quality loss for fresh market apples and 
pears. Numerous studies have been undertaken to relate bruise damage w i t h 
physical characteristics of the fruits as firmness, weight, or f ru i t density (Klein, 
1987; Siyami etal., 1988). 
Skin characteristics are not usually taken into account. The first model used to 
analyse the impact problem applies the Hertz contact theory considering the 
f ru i t as an elastic homogeneous body. The most usual procedure to measure 
firmness (Magness-Taylor force) is performed removing the skin. 
However, skin strength probably has an influence on impact response and 
bru is ing . Rodr iguez et al. (1991) suggested t h a t i m p a c t response in 
postclimacteric pears may be explained by the role played by the skin rather than 
by the flesh. 
The objective of our present work is part of a research aimed at studing 
changes happening in impact response and bruising when the characteristics of 
skin in apples and pears are modif ied. 
2. MATERIALS AND METHODS 
"Golden Delicious" apples and "Conference" pears were harvested f rom 
several orchards in Lerida, the main exporter area of Spain, before and during 
the commercial harvest period. Part of the frui ts were tested the day after 
harvest (440 apples, 240 pears). The rest (277 apples, 40 pears) were held in 
conventional cold storage at 1°C and 80% RH for approximately five months. 
Then, fruits were removed from storage and tested along 10 days. Tests were the 
fo l lowing: 
69 
- Penetration test. Performed using an Instron Universal Testing Machine 
w i th a standard Magness-Taylor 8-mm-diameter rod at 20 mm/min. Two 
tests were made at two opposed locations along the equator of each frui t ; 
the skin was previously removed. 
- Skin puncture. Performed using the same Instron Machine w i th a 0.5-mm-
diameter puncture rod at 20 mm/min. Two tests were made at two opposed 
locations along the equator of each fruit. 
- Impact test. Used impact t€:ster has been described previously (Garcia et ai, 
1988). The test was conducted using an instrumented free fall ing mass (50.6 
g) wi th 15-mm-diameter spherical head. The head was previously smeared 
w i th ink to know the contact point on the frui t . Two impact tests were 
made, w i th drop heights of 8 cm (0.039 J), at opposed locations along the 
equator of each fruit . Impact variables were calculated and recorded on a 
computer disk fi le. 
- Bruise size measurement. Bruises produced by the impact test were allowed 
to develop for over 2 h. Then, bruise maximum w id th and depth were 
measured w i th a stereoscopic microscope cutt ing through the center of the 
bruised region. Bruise volume (BV) was estimated by the fol lowing relation 
(Chen and Sun, 1981): 
1
 2 
BV=-nhi r 
6 
in which h and D are the depth and width of bruise (mm), respectively. 
Addit ional impact tests (8-cm-height, 0.039 J) were carried out on fruits held in 
cold storage. Each frui t suffered impacts wi th intact skin (control) and in one of 
the fo l lowing conditions: 
- 1) Without skin, removing an area of 1 cm2. Conference pears, n = 25. 
- 2) With a rigid layer over intact skin (adhesive tape). Granny Smith apples, 
n= 15. 
- 3) Wi th an elastic layer over intact skin (rubberized paint). Granny Smith 
apples, n = 15. 
3. RESULTS 
Skin characteristics changed in a d i f fe ren t way in Golden apples and 
Conference pears (Table 1). 
Skin resistance (measured by maximum force at skin puncture, SMF) decreased 
after storage in pears, but remained fair ly constant in apples. However, 
maximum deformation at skin puncture (SMD) increased after storage in both 
apples and pears, a l though the increment was lower in pears, since skin 
resistance decreased (Figures 1-2). SMD seems to be a measure of skin tension; a 
turgid frui t shows low values of SMD while a wrinkly one shows high values. 
70 
after harvest 
SMD (mm) 
+ after itoroge 
.y. i ^rviri properuev iviaAniium lorce di iKin puncture v-nvir; vb maximum 
deformat ion (SMD) for Conference pears, before and after cold storage 
Maximum force (SMF) decreases after storage. 
3.6 
3.5 
3.4 
3.3 
3.2 
3.1 
3 
2.9 
2.8 
2.7 
2.6 
2.5 
2.4 
2.3 
2.2 
2.1 
2 
1.9 H , r -
0.2 0.6 
d after harvest 
2.2 
SMD (mm) 
+ after storage 
Fig. 2. Skin properties. Maximum force at skin puncture (SMF) vs max imum 
deformation (SMD) for Golden apples, before and after cold storage. 
Maximum deformation (SMD) increases after storage. 
71 
TABLE 1 
Physical properties of tested f r u i t s before and a f te r cold s to rage 
W MT SMF SMD 8MF 8 M D BV 
Golden after 
harvest CV% 
Golden after 
storage CV% 
Conference after 
harvest CV% 
Conference after 
storage CV% 
211.0 
11.8 
202.0 
11.5 
/ 
/ 
/ 
/ 
32.9 
15.1 
17.1 
18.7 
58.3 
11.2 
18.2 
65.1 
2.76 
9.5 
2.70 
9.4 
3.16 
13.9 
1.06 
35.9 
0.5 
10.9 
1.3 
28.1 
0.5 
23.9 
0.6 
31.5 
42.46 
6.3 
32.35 
8.1 
54.88 
5.5 
35.37 
16 8 
1.80 
5.0 
2.32 
9.7 
1.43 
6.7 
2.09 
13.4 
141 5 
15.0 
99 1 
23.8 
/ 
/ 
/ 
/ 
W : W e i g h t (g) 
MT : M a x i m u m force at Magness-Taylor (N) 
SMF: M a x i m u m force at skin punc tu re (N) 
SMD: M a x i m u m d e f o r m a t i o n at skin punc tu re (mm) 
8MF: M a x i m u m force at 8 -cm-he igh t impac t (N) 
8 M D : M a x i m u m d e f o r m a t i o n at 8 -cm-he ight impac t (ms) 
BV : Bruise v o l u m e (mrr>3) 
Bo th f lesh and skin characterist ics i n f l uenced impact parameters (Tables 2-3). 
In pears, f lesh and skin so f tened at t he same t i m e ; i m p a c t p a r a m e t e r s w e r e 
h igh ly c o r r e l a t e d w i t h Magness -Tay lo r f i rmness (F igure 3). In app les , f l esh 
so f tened w h i l e skin resistance r e m a i n e d cons tan t . Impac t response w a s less 
re la ted w i t h Magness-Taylor f i rmness (Figure 4) and seemed to depend m a i n l y 
on skin d e f o r m a t i o n (Figure 5). Bruised v o l u m e was only measured in apples It 
was re la ted t o skin d e f o r m a t i o n , in a simi lar w a y as impact force (Figure 6) 
As for t h e add i t i ona l tests, impacts w i t h o u t skin produced lower impac t forces 
and h igher d e f o r m a t i o n s t han impacts w i t h intact, skin, w h i c h were more elastic 
(Table 4). A d d i t i o n a l layers (adhesive tape , rubber ized paint ) increased impac t 
forces and decreased de fo rma t i ons 
TABLE 2 
Correlation coefficients of Golden apples before and after cold storage 
A) Golden apples after harvest (n = 440). 
MT SMF SMD BV 8MF 8MD W 
MT 
SMF 
SMD 
BV 
8MF 
8MD 
W 
1.00 
0.14 
-0.13 
-0.18 
0.33 
-0.48 
-0.33 
1.00 
0.25 
0.03 
-0.04 
-0.05 
-0.09 
1.00 
0.04 
-0.10 
0.05 
-0.09 
1.00 
-0.21 
0.22 
0.10 
1.00 
-0.60 
0.07 
1.00 
0.13 1.00 
B) Golden apples after storage (n = 277). 
MT SMF SMD BV 8MF 8MD W 
MT 
SMF 
SMD 
BV 
8MF 
8MD 
W 
1.00 
0.05 
0.14 
-0.27 
-0.14 
0.08 
-0.26 
1.00 
0.05 
-0.06 
0.18 
-0.12 
0.05 
1.00 
-0.63 
-0.85 
0.80 
-0.27 
1.00 
0.55 
-0.52 
0.26 
1.00 
-0.89 
0.26 
1.00 
-0.23 1 00 
73 
bb 
60 
55 
50 
45 
40 
35 
3 0 
25 
2 0 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ + + + 
+ + 
+ , 
+ 
+ 
+ 
+ 
+ 
1 
nq_njjj 
D o§||j 
+ D 
4-
+ 
+ 
D 
° ° 
a
 D D Q 
D
 n ~j a DD 
™ a D 
; 
: i 
after harvest 
MT (N) 
after storage 
F ig . 3. Maximum impact force (8MF) vs Magness-Taylor firmness (MT) for 
Conference pears, before and af ter cold storage ( c o r r e l a t i o n 
coefficient: 0.93). 
5* 
52 
50 
48 
42 
40 
38 
36 
34 
32 
30 
28 
26 
24 
22 
rP 
DfiVe if 
MT (N) 
D after harvest +• after storage 
Fig 4 Maximum impact force (8MF) vs Magness-Taylor firmness (MT) for 
Golden apples, before and after cold storage (correlation coefficient: 
0.81). Impact forces are higher before storage even for the same 
firmness values 
74 
aft«r harvest 
F ig . 5. Maximum impact force (8MF) vs maximum deformation at puncture 
(SMD) for Golden apples, before and after cold storage. After storage, 
impact forces seem to be highly related to maximum deformat ion at 
Duncture. 
230 
220 
210 
200 
190 
180 
170 
160 
150 
1*0 
130 
120 
110 
100 
90 
80 
70 
60 
50 
•40 
30 
"0 
+f+±T44± T ±+ 
SUD (mm) 
• aft«r harvast + aft«r storage 
Fig 6. Bruise volume (BV) vs maximum deformation at puncture (SMD) for 
Golden apples, before and after cold storage. SMD increase seems to 
have an influence in the BV decrease after storage. 
75 
TABLE 3 
Correlation coefficients of Conference pears before and after cold storage. 
C) Conference pears after harvest (n = 240). 
MT SMF SMD 8MF 8MD 
MT 
SMF 
SMD 
8MF 
8MD 
1.00 
0.56 
-0.12 
0.56 
-0.46 
1.00 
-0.12 
0.45 
-0.34 
1.00 
-0.26 
0.06 
1.00 
-0.59 1 00 
D) Conference pears after storage (n = 40). 
t 
MT SMF SMD 8MF 8MD 
MT 
SMF 
SMD 
8MF 
8MD 
1.00 
0.79 
0.52 
0.84 
-0.73 
1.00 
0.62 
0.67 
-0.59 
1.00 
0.32 
-0.27 
1.00 
-0.93 1.00 
TABLE 4 
Impact parameters in additional tests, w i t h different modifications of the skin. 
8MF 8MD 8AE 8T 
Without skin 
Control 
Adhesive tape 
Control 
Rubberized paint 
Control 
3043 
35.19 
** 
41.70 
38.98 
* * 
38.99 
38.20 
* * 
2.33 
2.11 
* * 
1.80 
1.90 
* * 
1.90 
1.95 
* * 
37.3 
34.9 
* * 
30.1 
30.9 
* * 
31.5 
29.9 
* * 
58 
5.1 
* * 
4 8 
5.3 
* * 
5.2 
54 
ns 
8MF: Maximum force at 8-cm-height impact (N) 
8MD: Maximum deformation at 8-cm-height impact (ms) 
8AE: Absorbed energy at 8-cm-height impact (mj) 
8T : Impact t ime at 8-cm-height impact (m J) 
** : Significant at 0.01 ns: Not significant 
76 
4. DISCUSSION 
Several researchers have shown that bruise susceptibility can decrease w i th 
moisture loss (Klein, 1987) even wi thout a decrease in firmness (Johnson, 1990). It 
may be explained by the higher susceptibil ity of vegetat ive tissues as cell 
turgid i ty increases. 
However, skin characteristics may have an additional influence in this process. 
When a f ru i t loses water, its volume decreases and the skin gets " loose", even 
forming small folds. Loose skin allows higher deformat ions in the flesh-skin 
ensemble, and as a result, impact forces are lower. Besides, a part of the 
deformat ion energy may be absorbed wi thout damage in the small folds of the 
skin. Therefore bruises should be smaller. The results in this paper suggest this 
kind of relationship between skin and bruising. 
Further experiments are needed varying skin properties w i thou t changing 
firmness. Moisture losses should be tested controlling skin characteristics 
5. REFERENCES 
Chen, P., Z. Sun, 1981, Impact Parameters Related to Bruise Injury in Apples, ASAE 
paper 81-3041. 
Garcia, C, M. Ruiz, P. Chen, 1988, Impact Parameters Related to Bruising in 
Selected Fruits, ASAE paper 88-6027. 
Johnson, D. S., C. J. Dover, 1990, Factors Influencing the Bruise Susceptibility of 
Bramley's Seedling apples, Seminario Internacional sobre Danos por Impacto en 
Frutas y Hortalizas, FIMA 90, Zaragoza, Spain. 
Klein, J. D., 1987, Relationship of Harvest Date, Storage Conditions, and Fruit 
Characteristics to Bruise Susceptibi l i ty of Apple, J. Amer Soc Hort Sci 
112(1): 113-118. 
Rodriguez, L, M. Ruiz, J. L. de la Plaza, 1991, Bruise Development and Fruit 
Response of Pear (cv. "Blanquilla) under Impact Condit ions, Journal of Food 
Engineering 14(1991)289-301. 
Siyami, S., G. K. Brown, G. J. Burgess, J. B. Gerrish, B. R. Tennes, C L Burton, R H 
Zapp, 1988, Apple Impact Bruise Prediction Models, Transactions of the ASAE 
31(41):1038-1046. 
77 


Effects of skin characteristics on impact response and bruising of apples and pears

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