Bacterias mesófilas

D iffere n t researchers have reported that apple hruises do not reach their m,Lximum discolouration until 3-4 h ( Hyde and I ngle, 1 968; Sami m and Banks,

1 993a), 1 2 h (Klein, 1 987) or 1 2 weeks (Prussia et al. 1 986) after i mpact. I ngle and H yde ( 1 968) ohserved that 50% of hrowning occurred within 30 m i nutes of bruising with no further change after ahout 3 h. The rate of discolouration was roughly l inear for the first 60 minutes and t hen decreased s harply. I n a s tudy of hruise colour changes with time, Samim and Banks ( 1 993a) found that to assess bru ises at their most intense degree of discolouration, they s houl d he allowed to develop for a period of 4- 1 4 h hefore sectioning and m easuring. Depending on thc ohjcctive of measuring hruise colour, it appears that measurements cou l d he made at any time provided intervals hetween bruising and measuring arc

accurately replicated.

There arc considerabl e varietal, as wel l as within-fruit, differences i n the concentration of compounds responsible for hruise colou r ( Nadudvari-Markus and Vam os-Vigyazo, 1 984).

2.4 B ruise severity

B ruise diameter, area and volume are a l l m easures of hruise severity. Bruise d i mensions arc hest measured ahout 4- 1 4 h after hruising, hy which time the hruised tissue has hrowned and is c learly distinguish ah l e from undamaged tissue ( I ngle and Hyde, 1 968; Sami m and Banks, 1 993a).

2.4. 1 Bruise size

Variation in hruise size for a given i mpact energy occurs he twee n cult ivar, orchard, season, stage of maturity and storage conditions (Jo hnson and D over,

1 990) . Bruise size can he represented hy l i near dimension, area or volume.

2.4. 1 . 1 Linear dimensions

Bruise diameter (d) and depth (h) are primary m easurements that arc made to evaluate hruise size. Bruise diam eter is easily m easured with m icro-call ipers and has heen used hy a numher of researchers ( Hyde and I ngle, 1 968; Sekse and Opedal, 1 993) to represent hruise severity. With red skinned eul t ivars it m ay he difficu l t to determ ine the hruise perimeter and there is m erit in b isecting the hruise on the intact frui t and measuring diamete r on exposed h al ves ( F igs. 2.2 and 2.3).

2.4. 1 .2 Area

Bruise surface area (A ) i s the m easure which i s most c losely rel ated to that used hy industry and consumers to determine if an appl e satisfies required standards.

ENZA ( 1 994) stipulates an export appl e shou l d not h ave m ore than 1 00 m m2 of accumulated hruise area whilst consumers may differ in w hat they consider is acceptahle ( Opara et

al.

1 99 1 ).

Pang ('l al. ( 1 992) considered that, when two apples c o l lided, the resul tant b ruise was e l l ipsoidal i n shape and calculated hruise area using the fol lowing formula:

w h e re d 1 and d2 w e re t h e m ajor and m i nor diam eters.

Zhang ef al. ( 1 992) used su rface a rea of the i n ne r hru ise houndary ( )f the hru ise (S ) in a n a t t e m p t to reduce the m u l t ip l ication of e rrors assoc iatcd w i t h t h e calc u l at i o n of bruise vol u mc.

. ... 2.2

For defi nition of terms see Fig. 2.2.

2--'. 1 .3 Volume

M any researchers deter m i ne bru ise vol u m e ( V) to lj ua n t i f)1 bru ise severi ty. Kl e i n ( 1 9R7) excavated bruise d t issue and m easur e d i ts m ass. I { oweve f, t h i s m e thod cou l d be ve ry t i m e cons u m i ng.

Fig. 2.2

d

h

A c ross sec t i o n of a n ideal ised b ru ise s h ow i ng t h e sy mbols used by Mohse n i n ( \ 970).

Calculation of bruise vo l u m e req u ires a m easure of bru i se w id t h and d e p t h a n d a s i m p l e proccdurc of m easur e m e n t a n d calcu l a t io n o f bru isc vol u m e was

devc loped by Mohse n i n ( 1 970). A c u t was made l ongi t u d i na l ly to t he c alyx and s t e m of the apple t h ro ugh the eentrc of a b r u i se t o expuse e q u a l h a lves ( Fig. 2.2), and m easure ments taken of

d

and h. H e assu med t he s hape ()f a bru i se was spherical and utilised thc fol lowing vol u m c e q u a t i o n :

... 2.3

H o l t a n d Schoorl ( 1 977) ass u m e d that the shape o f the hru ise WdS s p h e rical above and below the co n tact plane ( Fig 2.3 ). In add i t ion to

d

and II the fol l ow i ng m easurcmcnts wcre takc n :

hcight o f bruise above the cont ac t p l a n e (x ) total bruise depth (II + x)

radi us of thc apple

(R)

on cac h half of thc bruisc ( Fig. 2.3).

The height x of thc bru i si ng abovc thc contact p lane cou l d be calcu l a t e d fro m :

F ig. 2.3

bruise d iame ter d (measured )

a pple radius

R ( measured )

... 2.-4

x (derive d ) bru ise depth

h (measu r e d )

Cross-s ce t i o n of a n i d e a l ised b r u i se s lmw i ng d i m e nsions u s e d i n b r u i se vo l u m e calcu l at ions by H o l t and Sehoorl ( I ) .

Holt and SchoOfl ( 1 977) then used the fol lowi ng formu l ae to calculate hruise vol umes hoth helow ( Va) and ahove the contact plan e (V,,):

... 2.5

... 2.6

Total hruise vol u me was given by:

... 2.7

D iener t't

lIl.

( 1 979) considered that the hruise was a partial sphere and used the fol lowing volume formula:

... , 2.8

Chen and Sun ( 1 98 1 ) assumed that hruise shape was a semi-oh late spheroid and cut through the centre of the hruise region and measured m aximum hruise width and depth with a scale.

• • • • • • 1(1 • • • 2.9

There arc several prohlems with utilising volume as an indicator of bruise severity:

• Bruise s hape varies depending o n tissue type, i m pactor type, e nergy of impact and maturity of the app l c and therefore care is needed i n selection of the appropriate vol um e formula.

• Bruise diameter, depth and height are squared and/or multiplied i n suhsequent volume calculations. Any experim en tal errors associated with their measurement are compounded in the calculations t hereby i ncreasing statistical errors and reducing the accuracy of comparisons hetween treatment means.

I t is clear that if a comparative statistical evaluation of the errors associated with eac h method of representing bruise severity was completed, then i t m ay be possihle to identify a suitable method of representation.

2.4.2 Influence of colour on bru i se visibi lity

Visual cues, particularly colour, aid in the identification of colour- linked,

perceived flavours (Christensen, 1 983). As consumers primarily judge apples o n their appearance (Opara e t

al.

1 99 1 ), even a m oderate amount o f bruising o n appl es can reduce consumer acceptance. The degree o f brown discolouration and the extent to w h ic h the brown colour is masked by apple skin colour are

particularly important in this respect. For i nstance, 'Red D e licious' apples are more susceptible to bruising than ' De l icious' alt hough industry perceives the l attcr to be m ore eas i ly damaged (Zhang e t

al.

1 992). Similar ly, Johnson and D over ( 1 990) found 'Braml ey's Seedling' l ess susceptible to bruising than other cultivars but, because of its l ighter skin colour, it was perceived to be very hruise susceptible.

M anipulation of fac tors may reduce bruise size and m ake them l ess visihle. There m ay bc opportunities to manipulate hruise colour in an analogous way to reduce visibil ity further.

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