INTERRELATIONSHIPS BETWEEN SENSORY AND MECHANICAL CHARACTERISTICS OF CANNED PEACHES

INTERRELATIONSHIPS BETWEEN SENSORY AND MECHANICAL CHARACTERISTICS OF CANNED PEACHES

C . APOSTOLOPOULOS and J.G. BRENNAN

Dept. of Food Science and Technology University of Reading

Reading RG6 2AP, UK

(Manuscript received June 16, 1993; in final form December 13, 1993)

ABSTRACT

The 3 7 sensory characteristics of commercially canned peaches were measured using Quantitative Descriptive Analysis. Some mechanical parameters of the fruit were also measured b>i using both empirical andhndamental instrumental tests. Principal Component Analysis was employed to study the intra- and interrelationships of the sensory and the mechanical characteristics of the canned peaches. The results indicated that most of the characteristics were grouped in four main clusters. These clusters defined two perceptual ares corresponding to the first two principal components which described 76% of the variation. The Jirst component described the viscoelasticity and the second the pleasantness of the sensory characteristics. It was also shown that the mechanical parameters of the fruits were good predictors of the whole range of their textural characteristics.

INTRODUCTION

Canned foods, despite their nonwholesome reputation, retain a great deal of their nutritive value. The only area in which canned fruits always fall short of fresh ones is in their sensory properties. Of these properties, texture is the most severely affected during canning. In order to monitor and control the textural characteristics of a fruit there is a need to measure them as accurately as possible. Numerous attempts have been made to quantify objectively the texture of fruits (Abbott etal. 1968; Bourne 1968; Ahmed and Dennison 1971; Ahmed and

'Centre for Biomimetics. University of Reading, Earley Gate, Reading RG6 2AT. UK.

30urn.d of Texture Studies 25 (1994) 191-206. All Rights Resened. 0 Copyriglit 1994 by Food & Nutrition Press, h c . , Trumbull. Connecticut 191

192 C . APOSTOLOPOLILOS and J .G. B R E N N A N

Fluck 1972: Bourne 1974: Bourne 1979; Lin and Rao 1981: Abbott et al. 1984). Many workers have used empirical tests. where the pattern of forces involved is rather complex. However. they are still popular because they are easy to per- form and often correlate well with sensory measurements. Fundamental tests, where well-defined mechanical properties of the fruits are measured. were reported by a number of researchers (Clevender and Hamann 1968: Fridley et al. 1968; Mittal and Mohsenin 1987: Khan 1989) but the relationships with the sensory measurements was either poor or not reported. Often the textural descriptors used by panels are ill-defined in physical terms. Indirect tests such as sonic, vibration, electromyography etc. have also been used. but probletris such as the background noise. specificitj,. etc. make them less useful than the direct tests.

I n most of these studies the relationships between the sensory and instrumental properties were expressed by a simple correlation coefficient. This does not give an integrated picture of the physical and sensory aspects of texture or any infor- mation about the perception of the textural characteristics and their relationships to the other sensory properties ofthe fruit. This study aims to enlighten this unex- plored area of texture perception in canned fruits and also give an integrated picture of the suitability of a particular instrumental test.

METHODS AND MATERIALS

Sensory Evaluation

Samples from four different commercial canned peaches were used. Particular care was taken to ensure that the samples covered a broad range of the most important characteristics of canned peacheb. The four samples were canned in four different liquids (water ( A ) . syrup (B). pearjuice (C) and peach juice (D)). They were all in the form of slices and all the cans of each sample used were drawn froni the same batch. Panelists were sersed two to three slices with some of the canning syrup. at a temperature of 10 f 1C. For the instrumental tests, slices of fruits from more than three cans were randomly chosen and tested. The panelists were selected from among the students and the staff of the Department of Food Science and Technology. More emphasis has been given to the psychological screening rather than the physiological ability of the panelists. Availability, in- terest and abilitp to verbalize were the three main factors in the final selection of the panel members.

The training of the panelists was done initially with four kinds of commercial canned fruits (peaches. pears. apricots and pineapples). This helped the panelists t o understand better and become more familiar with a wide range of sensory characteristics present in canned fruits. The four samples of commercial canned peaches were then given to the panelists who were instructed to write down any

TEXTURAL CHARACTERISTICS OF PEACHES I93

perceived characteristic from the moment when they first saw the samples until after they swallowed them. The four samples were presented to each panelist all together in random order and the panelists were instructed to complete their evaluation of the first sample before moving on to the next one.

Development of the terminology was achieved by group discussions and individual interviews to avoid the possibility of a biased agreement due to either the panel leader’s instructions or the opinions of some panelists with stronger personalities. Unstructured rating scales were used and the extreme ends of the scales were defined after further discussions with the panel members. A sample of the questionnaire used is shown in Table 1.

Experimental Design

A 6 X 2 balanced incomplete block design was used, and the serving order of the four samples (A, B, C, D) was balanced among the panelists. To balance the serving order in each session, the assessors were divided equally in two groups (I, 11). Each group was served the same pair of samples but in the opposite order. The division of the assessors into the two groups was done randomly at each session, keeping always the same number of assessors in each group.

Instrumental Tests

Extrusion, shear and compression tests were used for the objective measurement of the textural characteristics of fruits.

Extrusion. A rectangular alloy cell (45 X 45 X 125 mm) was used. The cell was placed on the Instron and two types of extrusion test were conducted, both at a crosshead speed of 300 mm min-’.:

Back e.rtrusion. An alloy plunger was used to compress and extrude the sample. The lower travelling limit was set at 10 mm above the bottom of the cell. The square horizontal area of the piston was 16.5 cm2, and the extrusion annulus created from the clearance between the piston’s head and the inner walls of the cell was 2 mm.

Wire extrusion. The settings were the same as with the back extrusion test ex- cept that here the plunger used had a square horizontal area of 18.5 cm2 and a clearance of 0.8 mm. Nine wires were mounted in a separate frame which fitted into a slide, close to the bottom of the cell. The wires were 1.55 mm thick and had an even spacing of 3.0 mm. The cell was filled with fruit cut in slices (preliminary tests showed no significant difference if the fruit was cut in halves).

In both the extrusion tests (back and wire), the recording of the force was started at the time of the first contact of the piston with the sample and the test ended automatically when the piston reached a pre-defined distance from the bottom

C .APOSTOLOPOCLOS and 1 G BRENNAK

TABLE 1 .A PART OF THE QUESTIOSAIRE PRESENTED TO PANELISTS TO ASSESS THE

SENSORY CHARACTERISTICS OF CANNED PEACHES

NAME: ............................................................ DATE: ..........................

Please score. h e following characteristics of the samples provided, marlong with a vertical line on

the scales below. according to the perceived intensity.

O r a l c h a r a c t e r i s t i c s

- T e x m

FIR!dNESS .................................................................... firm

RBROUSMSS not fibrous I ....................... ..................I very fibrous

CRLXCHI1;ESS not crunchy I ............................................................................... 1 very crunchy

SLPPERLUESS not slippery I .................................................................

C H E r n Z S S not chew" I.... ........................................................................... 1 very chewy

VISCOSITY OF w a q I ................................................. ........................ 1 syrupy/viscous LIQLD

DEGRRE OF h@y p-& j ............................................................................... 1 fresh/raw FRESHNFSS

O t h e r c h a r a c t e r i s t i c s :

............................................................................... I I

............................................................................... \ I

C o m m e n t s :

of the cell. The typical force-deformation curve obtained during a back extrusion test is shown in Fig. 1 . The back extrusion curve could be divided in two stages:

(1) The compression stage: This extends from point A to point B on the curve. The main phenomena that are taking place during that stage are: (1) Compres- sion of the sample. ( 2 ) Rearrangement of the fruit pieces inside the cell and (3) SqueeLing of the fruit and excretion of fruit juice.


300

200

100

z

00 s LL

0

FIG. 1. TYPICAL FORCE-DEFORMATION CURVE OBTAINED DURING BACK EXTRUSION TEST ON CANNED PEACHES IN PEAR JUICE

(2) The extrusion stage: Is the stage from point B to point C where the fruit is travelling backwards between the piston and the inner walls of the cell. Phenomena that are taking place during that stage are: (1) Breakdown of the fruit structure, (2) Further juice is excreting from the fruit not only due to compression forces but also to some shearing forces which are predominant during the extrusion period.

The force during this stage fluctuates due to the nonuniform structure of the fruit. The peaks represent tough segments that are forced to pass through the clearance between the piston and the walls of the cell. The shaded area shown in Fig. 1 was measured and used as an index of the firmness of the fruit. The curve obtained during the wire extrusion was similar to the back extrusion curve. However, the force needed to start the extrusion phenomenon was much less than that recorded in back extrusion. In both extrusion tests, the work needed for the extrusion of the sample was calculated from the force/deformation curve (Fig. 1).

Shear. A Kramer shear compression cell with 10 flexible blades, each 3 mm thick, was also used. The blades were mounted on the Instron’s crosshead and were driven into the cell compressing, shearing and finally extruding part of the sample through 10 slots in the bottom of the cell. Only one orientation of the

196 C . APOSTOLOPOULOS and J.G. BRENNAN

cell was used since the readings are affected by the orientation (Voisey and Kloek 1981 1. The cell was filled with 150 g of fruit cut in slices and the forces involved during the shear compression were recorded as a function of traveling distance. The test was terminated manually when the blades protruded through the slots on the bottom of the cell. A typical force-time curve is shown in Fig. 2 . Two distinct stages can be recognized here:

( 1 ) The compression stage: This can be further divided into two other substages, the nonlinear and the linear. The first stage (points A - B) corresponds to the rearrangement of the pieces of the fruit, forced by the blades to fill the empty spaces that were created during the random filling of the cell. The second (linear stage. points B - C ) represents the true compression stage where the fruit is deformed without failure of its structure (excretion of fruit juice is also taking place).

( 2 ) The shear-extrusion stage: This stage starts when a structural failure oc- curs in the fruit (bio-yield point). During this stage (points C - D) the fruit is forced by the thick blades to extrude through the slots in the bottom of the cell. The recorded force increases with time. reaching a peak (point D). which is follow- ed by an abrupt decrease of the force. as the last part of the sample has been pushed through the slots at the bottom of the cell.

Beyond point D. while the blades continue their descent. the force registered is due to the friction of the blades with either the sides of the slots or the remain- ing fruit in the cell. Much care was taken before the actual test with the alignment of the blades and the slots in order to reduce the friction with the sides of the slots. Indeed. due to the very small clearance between the blades and the sides of the slots. the friction forces during the test could be quite significant. This could affect both the absolute and relative recorded forces and distort the profile of the force-deformation curve. For this reason a test with the empty cell was always performed before every test on a fruit sample. Friction forces were recorded during this test. Accepted alignment was considered to be the position where the friction forces recorded did not exceed the level of 3 % of the full scale used during the actual test but in most of the empty-cell tests the recorded force was close to OR. The peak force and the work needed to both shear and extrude the sample was calculated from the forceideformation curve (Fig. 2 ) .

Compression. A two-cycle uniaxial compression was applied on rectangular flat slices of fruit (6 X 13 X 3 mm) which were cut with a special double blade cutter in order to obtain flat, parallel surfaces. Crosshead speed was 10 mm min- and since "failure characteristics" were important. the deformation applied was SO% of the original height. For this reason. the height of the specimen was kept as low as possible to minimize any barrelling or expansion effect.

A typical force-deformation curve obtained by this two-cycle compression test is shown in Fig. 3. The curve can be divided into 3 stages: the nonlinear

TEXTURAL CHARACTERISTICS OF PEACHES

A - s u n o f

B = run of lmc.r compurion sugc

C = bio-yield point

D = shear through point

197

z

0 0

8 L

0

FIG. 2. TYPICAL FORCE-DEFORMATION CURVE O F A KRAMER SHEAR COMPRESSION TEST ON CANNED PEACHES IN SYRUP

viscoelastic stage (A - B), the linear viscoelastic stage (B - C), and the recovery stage (C - D). During the recovery, the applied stress is being withdrawn and the sample is recovering (partially) from its previous deformed state. The 2nd

C. APOSTOLOPOULOS and J.G. RRENNAN

FIG. 3. TYPICAL FORCE-DEFORMATION CURVE OF A TWO- CYCLE UNIAXIAL COMPRESSION TEST ON SAMPLES OF

CANNED PEACHES IN SYRUP

cycle is a repetition of the first, with the only difference that the degree of deformation is lower due to the plastic deformation of the compressed specimen.


The parameters measured from the two-cycle compression tests are the following: (1) the 1st peak force, which corresponds to the maximum force attained in the 1st compression cycle, (2) the 2ndpeakforce, which corresponds to maximum force in the 2nd compression cycle, (3) the ratio of the 2nd lo the Is f peak force. (4) The degree of elasticity, which is the ratio of the elastic deformation to the sum of the elastic and plastic deformation. ( 5 ) The elasric hysreresis, which is the ratio of the energy recovered during the upstroke to the energy introduced into the material during loading. (6) The compression modulus of the first loading cycle, which was calculated as the slope of the initial straight part of the stress- strain curve representing the stiffness of the material. (7) The recovered deformation, which was calculated as the total deformation minus the distance AD (Fig. 3).

RESULTS AND DISCUSSION

Sensory Evaluation

The preliminary tests carried out on the four commercially canned fruits created a vocabulary of 62 terms describing the various sensory characteristics of the fruits from which 2 1 were related to texture. After group discussions and during the structuring of the scales which was done on an individual basis, the list with the 62 terms was reduced to 37.

The values for the sensory tests are the grand means from all the 20 assessors and all the three replicates used in the experimental design. The Analysis of Variance of the results showed that the variance among the assessors was less than that among the samples (at 95% level of significance) and that a slight in- teraction of sample/assessors occurred regarding some attributes but was not significant enough to affect the results.

Table 2 shows the levels of significance of F values for the various samples and the experimental error for each sensory characteristics of the fruits tested. From this it seems that the samples were significantly different in most sensory characteristics. Particularly as far as the textural characteristics were concerned, differences were detected in all the characteristics whereas the experimental error (within samples error effect) was not significant at the 95% level.

Instrumental Measurements

Some preliminary tests were conducted to find out the main factors that in- fluence the instrumental readings and to establish the optimum conditions for the tests. For this the sample's weight (size), the crosshead speed and the degree of deformation of the sample were varied. A crosshead speed of 300 mm min- '

200 C. APOSTOLOPOULOS and J.G. BRENNAN

TABLE 2 . THE SIGNIFICANCE OF F VALUES FOR THE VARIOUS SAMPLES AND THE EXPERIMENTAL ERROR (LEVEL OF SIGNIFICANCE: *- 9576, ** ++ 99%.

CANNED PEACHES * * * - 99.9%. NS ++ < 95%) OBTAINED FROM SENSORY TESTS ON

sample means experimental error Characteristic

VISUAL NS Colour *I*

NS Brightness *** NS Uniformity of colour *** NS Translucency ** NS Firmness ***

smcnrral integrity *** * Fibrousness NS **

NS Smoothness of cut surface *** Stone cavity breakdown *** * Size of stone cavity NS NS

NS Viscosity of juice it*

NS Clarity of juce *I*

Presence of skin NS *** Bruising *** ***

NS Size of h t *** NS Ripeness ***

neeL T e x t u r e

NS Firmness *** NS Dew of disinagmion *** NS Fibrousness *** NS Slipperiness ** NS Crunchiness *I*

NS Chewiness *** NS Viscosity of juice ***

T a s t e NS Sweetness ***

Binmess *I* ** Acidity I** *** Asmgency ** *** Freshness .** ** Strength of flavour *** ** Off-flavour *** ***

NS Fruitiness ***

AFTER EFFECTS &ReInCSS *** ** Acidity *** ***

NS Refreshing *** Mouth coating *** $3

Tongue dryness *** ** Persistance of flavour NS ***

was chosen for all the extrusion tests because at higher speeds both the extrusion force and the extrusion work remained relatively unchanged. For the same reason a sample weight of 150 g was also chosen for all the extrusion tests. Similar tests have been done to study the effect of the crosshead speed on the various parameters

TEXTURAL CHARACTERISTICS OF PEACHES 20 1

in the two-cycle uniaxial compression test. For this four different crosshead speeds were used. The results show that there is a logarithmic relationship between the crosshead speed and the 1st peak force during a uniaxial compression test. Degree of elasticity seems not to be affected by the crosshead speed, whereas the elastic modulus and the elastic hysteresis increase logarithmically as the crosshead speed increases. The effect of the thickness of the sample on the various mechanical parameters was also investigated. There is a linear relationship between the elastic deformation and the specimen thickness. Indeed the elastic deformation increases with the thickness of the sample but the degree of elasticity remains the same. On the other hand, there is a logarithmic relationship between the specimen thickness and compression modulus which decreases as the thickness of the specimen increases. The degree of deformation also seems to affect the parameters in a two-cycle uniaxial compression test. The degree of elasticity this time decreases logarithmically as the level of deformation increases, whereas the elastic hysteresis increases. Detailed results of the preliminary instrumental tests will be published elsewhere.

The means of 10 replicates are shown (Table 3). The variation within the samples was relatively small for most of the tests and the parameters measured. The unex- pected high variation which was noticed in some cases during the uniaxial compression tests was due to the fact that the same samples probably originated from totally different fruits (i.e. different maturity, variety, size, etc.). This was con- firmed with additional tests performed on specimens derived from the same fruit where the variability for all the parameters was significantly lower than that obtained from the mixed specimens (Apostolopoulos 1991). Thus, the apparent variability of the uniaxial compression tests derives mainly from the different origin of the fruit samples.

Relationships

Endo-relationships. The correlation matrix of the sensory and instrumental characteristics of the four fruits showed that the colour did not seem to correlate with any textural property. However, this conclusion does not have a general application since the experiment was dealing with probably more than one un- controlled variable. In spite of this, the colour is highly negatively (-0.99) correlated with the degree of bruising of the fruit which possibly means that the assessors could not discriminate the darker colours from the bruising or that it is less likely for the processed fruits with light color to show bruising phenomena. Colour is also highly correlated with some taste characteristics (i.e. bitterness, astringency, sweetness, acidity) indicating some relationship between colour of the fruit tissue and its taste.

Firmness and structural integrity do not necessarily follow the same path. The viscosity of the canning liquid seems to control the slippery properties of the fruit

202

m -.- 0 c - W

5 E E 2 1 3

3 3 E

C. APOSTOLOPOULOS and J.G. BRENNAN

38) Bsflr EXTRUSION WORK (N m] 39) Wm ECIXUSION WORK M m) &)SHEAR mmprarron WORK ( N r 41) SHEAR mmp. PEAK FORCE (N 42)Um. mmpr. 1srPEAKFORCE (h 43) Urn compr. 2nd PEAK FORCE 4) uN. mmpr. ( ~ 1 s ) P. F. 45)Um. COMPR. MODULUS (Pa) 46)Uru. mmpr. RECOV. DEFO. (nu 47)Uru. 9. DEGREE OF ELAS1 48)Um. mmu. E W T . HYSTERES

TABLE 3. MEANS OF THE SENSORY AND INSTRUMENTAL MEASUREMENTS OF FOUR

COMMERCIALLY CANNED PEACH FRUITS (sensory scores 0-100)

3) UNiK)RMIl-YOFcOLoUR 4) TRANSLUCENCY OF CVT SURFAC S) FIRMNESS 6) SIXUCNRALINIZCRIIY 7) FIBROUSNESS 8) SMOOTHNESS OF CUT SURFACE 9) STON€CAVrnBREAK-WW 10) SIZE OF SrONE C A W 11) VISCOSKY OF NICE. 12) CLARITY OF JUICE 13) PRESENCE OF SKIN 14)BRUISING 15) SIZE OF FRUITS

116) RIPENESS

A m

' e a h juice

624 36.8 63.3 329 21.9 36.5 51.8 a. 1 628 57.2 71.3 8.9

13.1 18.8 67.2 73.8

7.8 88.4 25.9 4.4

63.0 6.4

726

46.0 30.6 37.6 46.8 19.3

53.8 34.8 44.3

. - -_ - -

. - - - - -

29.9 50.1 33.4 55.7

43.0 ._____ LQ.2..

2.64 I .04 1.29 27.8 1.67

1304 0.781

31823 0.41

0 117 0.1 12

- B in

Syrup

8 3 2 69.2 15.7 48.4 745 76.5 4 9 s 73.1 29.6 50.6 64.7 715 145 8.9

423 57.6

69.8 27.4 36.9 61.1 53.6 62.1 68.6

71.0 11.0 30.2 24.6 36.7

64.1 19 5 63.6

8.6 34.4 53.6 52.4

.--.3>2 49.8

-

-

_ - _ -

- - - -

-

25.91 13.86 12.77 356.0 1356 9 .M

0.693 13588.:

0.78 0.211 0.81: -

C in

P u p Jrcicc

63.3 60.1 64.0 47.5 64.1 68.0 52.3 61.7 38.0 46.9 48.6 78.6 11.6 16.1 47.8 54.1

60.7 37.5 40.0 47.9 49.9 54.7 47.3

53.4 20.4 35.1 33.1 39.0

55.9 18.1 56.5

_ - _ - - _

_ - - - - -

18.4 43.9 55.4 34.2

._------ 41 41.9

21.63 13.78 11.66 30x5 10.28 7.06

0.686 13487.1

0.76 0.208

0.79

- D in

WorU - 37.2 42.3 54.4 41.0 56.1 43.9 49.3 45.6 63.1 56.3 48.1 73 5 18.9 28.3 50.7 35.7

65.3 40.4 49.1 56.6 42.6 59.2 45.5

20.7 50.0 46.7 60.4 45.2

41.0 38.8 28.6

48.2 59.5 34.2 35.9

47.1

-

----.

- - - - -

-

.-.-.>u

20.00 16.49 6.99

166.5 7.70 5.88

0.763 9547.0

0.61 0.165 0576 -

TEXTURAL CHARACTERISTICS OF PEACHES 203

much more than the smoothness of the cut surface. This indicates that the slippery properties of the fruit are derived either directly from the coating of the sample’s surface by the liquid or indirectly from the overall softening (solubiliza- tion and migration of some molecules from the tissue to the liquid phase) and consequent smoothing phenomena on the surface of the fruit.

The visually-assessed firmness is a very good predictor of firmness assessed orally. This, of course, is a result of the contribution of several supplementary characteristics (i.e. colour, clarity of the juice, structural integrity) which, according to the previous experience of the assessors, are associated with firmness. Firmness, chewiness and crunchiness appear to follow the same pattern. Assum- ing that these characteristics represent different attributes of the fruit, the mat- ching of these properties is an indication that they show similar variation within the range of texture and the number of samples used in the experiment.

The way that the fruit disintegrates during mastication (degree of disintegration) is highly negatively correlated with the firmness (-0.99***), showing that the predominant factor in the firmness is “how strongly the tissues of the fruit are linked together.” On the other hand, fibrousness is a distinctive property and it is worth looking at the low correlation between visual and oral fibrousness. This low correlation reveals some illusive phenomena that occur, probably because the visual estimation of the fibrousness is based almost exclusively on the colour contrast between the fibres and the other fruit tissue. The oral fibrousness, however, is based on their difference in resistance during mastication. As regards the viscosity of the liquid of the fruits, no conclusion can be made since four different liquids have been used. However, by taking into account only the ex- tremes, a possible negative relationship appears to exist between firmness and the viscosity of the liquid.

Inter-relationships. The work needed for the fruit to be extruded during the back extrusion and the elastic hysteresis during the uniaxial compression test seemed to be the best predictors of the fruit firmness (correlation coefficients 0.98** and 0.94*, respectively). The work in the wire extrusion test and the second peak force during the uniaxial compression test are similarly well correlated (0.97** and 0.92*). Fibrousness on the other hand is predicted well by the work in the wire extrusion test (0.92’).

However, a better and more integrated picture of the whole sensory and instrumental profile of the fruit parameters is needed. For this a Principal Compo- nent Analysis (PCA) of both the sensory and instrumental results was carried out. The distances between the different letters shown in Fig. 4 are indices of the levels of correlation that exist among the 47 parameters (37 sensory and 10 instrumental). The variance accounted for by the first two principal components of the PCA is 76% so the number of variables, and consequently the dimensions, were reduced to two.


0 12 ‘

. undesirable l rh @

C

4 JR I I I I I I I 1 I I

iIJ.3 1136 0 2 4 012 000 012 i l2J 036 048 060 0;2

0

R

flow I st

What is clear from the plot is that there are four groups (clusters) of parameters: In the first group are gathered all the “jlmt~-dependenr” characteristics of the

fruit (viscosity. slipperiness). Ripeness is also included in this group showing that there is a definite relationship between the ripening and the flow characteristics of the fruit. In the second group are those properties that comprise the pleasant characteristics of the fruit (sweetness. fruitiness. strength of flavour). The third group clearly includes the mechanical characteristics of the fruit. Finally in the fourth group are some taste characteristics which could be described as undesirable

TEXTURAL CHARACTERISTICS OF PEACHES 205

A = COLOUR Y = BITTERNESS B =BRIGHTNESS 2 = ASTRINGENCY C = UNIFORMITY OF COLOUR AA = ACIDITY D = TRANSLUCENCY OF CUT SURFACE BB = FRESHNESS E = Visual FIRMNESS CC = STRENGTH O F FLAVOUR F = STRUCTURAL INTEGRITY DD = OFF FLAVOUR G = SMOOTHNESS OF THE CUT EE = FRUITINESS

H = FIBROUSNESS (visually) GG = ACIDITY (after taste) I = STONE CAVITY BREAK-DOWN HH = REFRESHINGNESS J = SIZE OF STONE CAVITY I1 = AMOUNT OF COATING K = VISCOSITY OF JUICE (visually) JJ = TONGUE DRYNESS L = CLARITY O F JUICE KK = PERSISTENCE O F FLAVOUR M = PRESENCE OF SKIN LL = EXTRUSION WORK (back) N = BRUISING MM = EXTRUSION WORK (wire) 0 = SIZE OF FRUIT P = RIPENESS 00 = PEAK FORCE (shear compression) Q = FIRMNESS PP = PEAK FORCE (1st)-uniaxial compr. R = DEGREE OF DISINTEGRATION QQ = PEAK FORCE (2nd)-uniaxial compr. S = FIBROUSNESS RR = RATIO OF fnd/lst PEAK FORCES T = CRUNCHINESS TT = MODULUS (uniaxial compression) U = SLIPPERINESS UU = DEGREE OF ELASTICITY V = CHEWINESS (uniaxial compression) W = VISCOSITY JUICE VV = ELASTIC HYSTERESIS X =SWEETNESS (uniaxial compression)

(astringency, bitterness, bruising, off-flavour). In addition to the above groups there are some (more or less) isolated parameters, most of which represent geometrical characteristics of the samples (i.e., size of the fruit, size of stone cavity).

The instrumental parameters cover and predict satisfactorily most of the textural parameters, mainly the mechanical and instrumental. There is also an isolated instrumental parameter (the ratio of the 2nd to the 1st peak from the uniaxial compression test) related to some physical properties of the fruit (i.e., size of the fruit, thickness of the flesh), giving some evidence that the recoverability and elasticity (sensory) of the tissue is influenced by the size and shape of the fruit.

Thus the plane defined by the first two principal components is better described by two perceptual axis defined from the above mentioned clusters. The first component ranges from viscous to elastic and the other from pleasant to unpleasant. The mechanical parameters, which were determined instrumentally, describe well the textural characteristics of the fruit (3rd cluster).

SURFACE FF = BITTERNESS (after taste)

NN = SHEAR WORK (shear compression)

CONCLUSION

Both empirical and fundamental tests have been used to describe objectively the texture profile of the canned peaches. Principal Component Analysis (PCA)


was used to give an integrated picture of both the physical parameters of the instrumental tests and the multidimensional character of the fruit texture. Two components describe quite accurately the above multivariate data. The data formed four main clusters which characterise and define the first two principal components. The first component described the viscoelasticity and the second, the pleasantness of the sensory characteristics. Most of the mechanical parameters used proved to be good predictors of the textural characteristics of the fruits.

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ABBOTT. J.A.. WATADA. A.E. and MASSIE, D.R. 1984. Sensory and instrumental measurement of apple texture. J . Amer. Soc. Hort. Science 109,

AHMED. E.M. and DENNISON. R.A. 1971. Texture profile of irradiated mangoes and peaches. J . Texture Studies 2. 489-496.

AHMED. E.M. and FLUCK. R.C. 1972. Puncture testing of Tioga strawber- ries. J . Texture Studies 3. 165-172.

APOSTOLOPOULOS, C. 1991. Interrelationships between physical properties, processing variables and sensory characteristics of peach fruit. Ph.D. Thesis. University of Reading, UK.

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BOURNE. M.C. 1974. Textural changes in ripening peaches. J . Can. Inst. Food

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INTERRELATIONSHIPS BETWEEN SENSORY AND MECHANICAL CHARACTERISTICS OF CANNED PEACHES