Using a laboratory impact tester, impacts were applied to fruits of different varieties of apples and pears. The response to impact was analized, and many parameters were recorded, to be correlated to bruise susceptibility and to ripeness changes. Different methods for the detection and evaluation of the bruised Area and its features were studied, using direct observation and various reactives. Different types of bruises were established

Garcia Alonso, C.

Rodríguez Sinobas, Leonor

Ruiz-Altisent, Margarita

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698 
4 I P D D A & A i , " ) '"It-'malional Conference Hi l v * r r ^ # 4 I V l Physical Properties of ftgrfcuilurui 
^ " ™ Malorials and ineir Influence 
Roslook, G.D.R., September 4-0,10130 on Ti>chm>looical - ProcL>53L>s 
IMPACT BRUISES IN POMACEAE FRUITS: EVALUATION METHODS AND 
STRUCTURAL FEATURES 
MARGARITA RUIZ, Prof. 
CARLOS GARCIA Ph.D.and LEQNQR RODRIGUEZ Ph.D. 
(Former Grad. Students) 
DEPT.RURAL ENGINEERING-.A6RIC.ENGINEERING COLLEGE 
POLITECHNIC UNIVERSITY MADRID (SPAIN) 
SUMMARY 
Using a laboratory impact tester, impacts were applied to fruits of 
different varieties of apples and pears. The response to impact was analized, 
and many parameters were recorded, to be correlated to bruise susceptibility 
and to ripeness changes. Different methods for the detection and evaluation of 
the bruised Area and its features were studied, using direct observation and 
various reactives. Different types of bruises were established. 
Bruising, impact, fruits, apples, pears, detection. 
1.INTRODUCTION 
In recent years, a great effort is being carried out to investigate 
into the relations between the parameters which characterise mechanical impact 
and the appearence and developement of bruises in different fruits. These 
studies are necessary, considering the objective of controlling the important 
problem of fresh produce quality losses ; another objective of these same 
studies is to obtain data on impact resistance of these fruits,in relation to 
the development of mechanical harvesting in the future . Both problems are 
especially critical for apples and pears. 
The most recent publications on impact in fruits (1,2,3,^,5) , try to 
get indepth knowledge on the relations "impact vs. bruise development", once 
there exist? the possibility of using precise instruments to- measure the 
short-time impact history with accuracy. Some of the research results obtained 
formerly by different investigators with various types of impacters are not 
very consistant, and often contradictory; there is an evidence that impact 
tests need to be very broad, using many fruit* and varying the impact 
conditions, as well as the conditions of the fruits themselves, in a very wide 
range. Garcia et al.(M show that the physical phenomenon of an impact on a 
pear or an apple is considerably different for different ripeness stages of the 
fruit, varying from a mainly elastic response, with over 607. of rebound energy 
from the total input energy, to a mainly plastic response (less than 10'/! of 
rebound energy). The resulting bruises are supposed to be very different for 
these different types of impact response. 
The other fundamental aspect of these studies to be solved is to 
develop the appropriate techniques far observation of the bruises in the fruit 
tissues with sufficient accuracy, in parallell to the accuracy obtained with 
the impact testing device. There is the need to evaluate on one side the 
magnitude of the bruise, to be related to the mechanical parameters of the 
impact, and on the other side the structural characteristics of the same bruise 
, which define the specific impact response for different fruit varieties and 
fruit conditions. 
699 
The direct visual aspect of a bruise is easilly detected from the 
wjftening and brown color of the affected tissue. Softening is due to 
Ijradation of the cellular walls and of the middle lamellae by different times. Browning is known to be due to oxidation of poliphenols, in presence , the enzimes poliphenoloxidases (PPO). Oxigen exists primarily in the bercellular spaces. It is not completely cleared yet what is the actual site ire the oxidative reaction takes place. We know that poliphenols are located imarily in the vacuole and the enzime PPQ in the cloroplasts in the toplasm, therefore both inside the cell,wall. As stated by Shohei (6) and lner (7), cited by Rodriguez (8), browning reaction can take place outside as 11 as inside -tttte cell. Therefore, for the development of a bruise, cell-wall ature is not indispensable. On the other hand, other authors (9) have stated ^ at the browning reaction develops in the intercellular spaces, after cell jftipture occurs due to mechanical action. It is therefore suitable to study the 
structure of the bruised tissue in the different types of observed bruises. 
During the last years, researchers (10) have used various fast and 
Simple colorimetric methods, to evaluate bruise severity and to estimate 
drowning potential. 
2.MATERIALS AND METHODS 
The- impact testing device used in the tests has been described 
previously (1,2,*»,5,11>. The impacting device consists basically of a steel 
rod of 50.6 g mass , with a spherical tip (19 mm diameter), with adjustable 
h^eight of fall (2 to 20 cm were used), and connected to a computer. In two 
^different sets of tests, five varieties of fruits were tested; three pear -
limonera (Williams' type), Blanquilla and Decana, and four apple (Golden 
Delicious and Starking) varieties. After harvesting, the fruits were maintained 
Hn cold storage before testing, and other samples were ripened in a 20°C room 
(for 48 and 96 hours, so as to get a wide range of ripening stages in each fruit 
fVariety. The smallest number of fruits impacted for each combination of 
treatments was lO.in all tests, and a total of.over 900 impacts were tested in 
"'each variety. On a second set of tests, Blanquilla pears were ripened and 
Itested until overripe (senescent). The mechanical parameters of the impact were 
•calculated from the one measured (deceleration) and all of them recorded, using 
them later for complete statistical analysis. 
Different techniques were used to evaluate the bruises, which are 
summarized as follows: 
Direct visual appreciation and measurement: with a scale, depth and 
"width of the centered cross-section of the bruise were measured; these two 
narameters were treated independently in the analysis. 
- Stereoscopic^ microscope (NIKON, 9MZ-2T,l-63 XX) with conventional 
^(trough and reflected.light) and glass-fiber cold light illuminators. It was 
used to observe the bruised area, in the fruit and in manual cuts (l-3mm 
tthick), fresh or stained with histology dyes like Saphranine. 
Fast colorimetric techniques: some of the reactives used for 
browning evaluation applied as follows: 
Cathecol: prepared in a 0.1 M sol on, with citric acid buffer (pH 
6.2) (10). When a drop is placed on the su. .ace of the.fruit flesh, bruised 
tissue is stained very dark brown. This technique was applied in two different 
ways:a) whole fruits were dipped into the solution to reveal skin ruptures; b) 
whole-fruit slices were dipped into the solution to reveal bruised areas near 
the surface. 
- Nitrose test: a solution of sodium nitrate, urea, acetic acid and 
sodium hidroxide; it has been used (10) to evaluate phenolic concentration in 
peaches. 
Epinephrine: prepared in a 0.01 M solution, with phosphate buffer 
0.02 M (pH 7) (12). It gives a reddish coloration of bruised tissue. 
Saphranine: It is a very common Histology dye. It dies specifically 
cell walls and nuclei. 
700 
3.RESULTS AND DISCUSSION 
1. Impact parameters. 
Results of the relations between the mechanical impact parameters and 
bruise depth and width for each variety tested have been previously published 
(*t,5,ll). Some parameters ("first group") appear to be closely related to 
impact energy: maximum deformation, permanent deformation, maximum impulse, and 
depth and width of bruise. Same parameters, though,("third group") appear 
independent from impact energy, and closely dependent on ripeness level of the 
fruits: total impact duration, time to maximum force, slope force/deformation, 
apparent dynamic modulus of elasticity. The so-called " second group" of 
parameters are related to both independent parameters i.e.impact energy and 
ripeness level, and those are: maximum impact force, force/time slope, I ebound 
velocity, percentage of elastic (rebound) energy. 
The results of, the second set of tests, on Blanquilla pear, showed 
that the senescent fruits behaved differently than the non-senescent fruits. 
Linear multiple regression models applied to these data showed that depth and 
width of the observed bruises could be explained for all data in each group in 
a 50'/. (onl.y) by linear combinations of following parameters: maximum impact 
force, total impact duration and ripeness level parameters like firmness, 
acidity and sugar content (8,13). 
All these results at the present stage of analysis lead us to the 
conclusion that in the apple and pear varieties tested, bruise size, as 
measured independently by the depth and the diameter (width) of its centered 
cross-section, depends mainly on the impact energy applied; the size of the 
bruise relates also to the ripeness stage of the fruits when ripeness levels 
include a wide range of variation. 
2. Bruise features. 
Appart from these results, based on direct measurement of bruise size, 
closer observation of the bruises showed that different varieties show 
different bruise patterns, and these, in the absence of important variations 
in other relevant parameters (like it might be the radius of curvature of the 
fruits) seem to be related to the structural differences between these fruits, 
which are remarcably different. Table 1 includes the differences in the 
structures of the fruit tissue gathered for both types of fruits. 
Figure 1 shows models of average bruises observed in th varieties 
studied. The differences between them affect: 
a) the relation depth/width, significantly higher in pears than in 
apples. For 12 cm drops (0,06 J ) , the average depth is similar for both apple 
varieties and Decana and Blanquilla pear, 2.5 - 3.5 mm, with no significant 
change for an 11-week period of cold storage. Bruise width, on the other hand, 
is significantly wider (7-8 mm) for both varieties of apples (pears: 3-5 mm) 
b) the size, shape and number of fractures observed inside the 
bruised tissue. The close microscope direct observation of the bruises makes it 
possible to identify the presence of discontinuities, eventually fractures, in 
what may be the maximum stress and/or strain location in the bruised area when 
impacted. They appear always some mm below the skin, and centered in the 
bruise itself. In the case of the apple varieties, somewhat curved, horizontal 
fissures appear (ft), not completelly separated, but rather showing cell walls 
like bridges between both sides; the cells are crushed together, with no 
evidence of having slided so that they may not be considered properly 
fractures. For low-energy impacts, although a bruise appears (of smaller size) 
no discontinuity can be observed. It is remarcable that after some time, the 
totality of the stressed tissue becomes brownish, and not only the ruptured 
spot or surface. Also, the specific reactives for poliphenoloxidase activity 
become active in the total "affected" area, delimitating very clearly the 
tissue that has been damaged. From electron-microscope complementary studies 
published elsewhere (G) we know that after a few hours most of the cells of 
the bruised area are soft, metabolized by the processes that initiate as a 
701 
consequence of subjecting the tissue to stresses: disgregated middle lammellae 
and cell walls; precipitated citoplasm. When using the reactives, it is 
remarkable how the bruised area dyes immediately, showing a very distinct 
frontier between affected and non-affected surrounding tissue; also, this area 
does not increase with time, even after months of cold storage. From this, it 
appears to be clear that a distinct action has been applied to all the cells on 
the tissue affected by mechanical impact, so that it develops the bruising 
processj and not to the surrounding tissue. 
Another conclusion of all these observations is that bruising may 
develop with of? without cell rupture; we are able to affirm that cell 
compression^can cause th$iniciation of metabolic bruising processes inside the 
cell-wall; . at the same time,it is fairly evident that broken cells accelerate 
the bruising metabolic processes in the area close to them. 
The larger intercellular spaces of the apple tissue, which are the 
cause of its lower density (see Table 1) give rise to the formation of 
subsecuent transversal failure surfaces (Fig.3), which are able to absorb much 
of the strain during impacter penetration, dissipating the corresponding 
stresses, and therefore preventing the formation of deep bruises; these rather 
evolve into wi-de bruises. 
In the case of Decana pear, with a much denser type of parenchima, 
real conical and vertical fractures are observed (Figs 1 and 2), starting at a 
point of maximum concentration of stresses, suggesting stress failure as 
described for some fragile materials. 
Figure' l-ev shows a closer modelization of the bruises of Blanquilla 
peari including senescent fruits. The bruises show some interesting features: 
• • >*--=•' ah,. The shape, tends to become wider and flatter as softening increases 
from preclimacteric to-climacteric and to postclimacteric (senescent) fruits. 
b) For the harder fruits, a conical shape including 
discontinuity/fracture appears , but not in riper fruits. 
c)' Differences appear in the browning of different areas, being the 
intermediate (numbered *2') the most affected, when observed right after 
impact. The bruise develops later further to the whole of the affected tissue, 
as stated before. 
3. Fast colorimetric techniques.Cathecol 
This reactive resulted the most appropriate for the different 
applications studied. For delimiting with high contrast the bruised area and 
therefore, measuring it with better accuracy, it is enough to place a drop of 
the prepared solution. > wait 6 minutes and then measure with a scale, and 
observe the shape. Fractures and fissures can be easily observed by cutting a 
thin slice *of ,-.the section of the bruise being studied; the reactive flows 
trough the ffssufe and" shows it very clearly in the cut slices. 
It Can^ .'be used on whole fruits, bruised or not, by dipping fruit 
slices during 1-2 minutes ; wait 6 minutes; cut a thin slice from the (stained) 
surface and measure the bruises, if present (Fig ^ ) . This last procedure may 
be a way to„automatically detect,, bruised fruits in large samples. This extreme 
is being studied right now. 
Epinephrine gave good results in revealing bruises in pears and can be 
used on cut tissues like cathecol. It is not a good reactive for apples. 
Saphranine is a very good reactive for the microscopic observation of 
directly cutT tissue slices; it reveals very clearly the areas where the 
cell-walls are compressed together around the fractures. 
Acknowledgements 
This .Project <was financed by the U.S.A.-Spain Joint Committee for 
Scientific and Tecnoloqical Research. 
702 
of fn 
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Impact bruises in pomaceae fruits: Evaluation methods and structural features.

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