6
Ultrasonics 38 (2000) 717–722 www.elsevier.nl/locate/ultras Determination of avocado and mango fruit properties by ultrasonic technique Amos Mizrach * Institute of Agricultural Engineering, A.R.O., The Volcani Center, P.O.Box 6, Bet Dagan, 50250, Israel Abstract A nondestructive ultrasonic measurement system was developed for the assessment of some transmission parameters which might have quantitative relations with the maturity, firmness and other quality-related properties of avocado and mango fruits. The system utilizes a set of low-frequency probes arranged to measure the ultrasonic signal transmitted and received over a short distance across the peel. The attenuation of the ultrasonic waves, transmitted through the peel and the attached fruit tissue, changes as a result of the progressive ripening and softening of the fruit during the fruiting season and in the course of storage. The present study quantitatively addressed the linkage between the ultrasonic attenuation and the physiological parameters of the flesh of the fruits. Results were obtained in the time and frequency domain, and the data set was analyzed statistically to identify the relations between the major physiological indices and the ultrasonic parameters. Quantitative relations were developed to describe the linkage between ultrasonic parameters and the maturity, firmness and other quality-related properties in mango and avocado fruits. © 2000 Elsevier Science B.V. All rights reserved. Keywords: Fruits; Nondestructive testing; Quality; Spectral analysis; Ultrasonic 1. Introduction are the most acceptable method for measuring firmness, but they are destructive and time-consuming methods; a nondestructive method for determination of avocado Maturity determination of fruits before picking, and and mango maturity would be of considerable economic subsequent quality evaluation are important issues that interest to the food industry. a ect the agricultural industry. The demand for high Mizrach et al. [4] built and evaluated an experimental quality calls for a reliable, rapid, nondestructive, nonin- system for determination of the basic acoustic properties vasive technique for measuring some of the physical of some fruits and vegetables, i.e. wave propagation properties of the fruit, which develop as it matures and velocity and attenuation, and suggested the application which are indicative of its quality. In avocado fruits, of this technique to the nondestructive quality evaluation firmness, and oil and dry matter content (DW ) of the of fruits and vegetables. In addition, Mizrach et al. [5,6 ] flesh are the subjects of the most acceptable methods found a strong interdependence between ultrasonic for a reliable test of maturity, according to which the properties and post-harvest ripening parameters of the date of fruit harvest is determined [1]. Maturity indica- fruit tissue, which indicated the potential usefulness of tors in mango are softening of the flesh, decreasing this ultrasonic method for determination of firmness acidity and increasing contents of sugars, soluble solids properties of fruit tissue. Mizrach et al. [7] patented a and total solids. One of the main indices of maturity in nondestructive quality-determining device based on the fruit is firmness: this changes during the ripening and use of ultrasonic waves transmitted through the peel softening process, which starts on the tree, and continues and the flesh of a whole fruit by means of probes in during harvesting, handling and storage [2]. Chemical contact with the peel. This method was used by Mizrach tests are also important factors in determination of the et al. in several studies: they measured ultrasonic wave maturity of fruits, but firmness is the factor most closely attenuation in avocado fruit [8–10] and mango fruit related to the stage of maturity [3]. Penetration tests [11] in the time domain and in mango in the frequency domain [12] to assess fruit properties and to relate them * Tel.: +972-3-9683451. fax: +972-3-9604704. E-mail address: [email protected] ( A. Mizrach) to shelf life. In all of these studies, the attenuation 0041-624X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved. PII: S0041-624X(99)00154-7

Determination of avocado and mango fruit properties by ultrasonic technique

Embed Size (px)

Citation preview

Page 1: Determination of avocado and mango fruit properties by ultrasonic technique

Ultrasonics 38 (2000) 717–722www.elsevier.nl/locate/ultras

Determination of avocado and mango fruit propertiesby ultrasonic technique

Amos Mizrach *Institute of Agricultural Engineering, A.R.O., The Volcani Center, P.O.Box 6, Bet Dagan, 50250, Israel

Abstract

A nondestructive ultrasonic measurement system was developed for the assessment of some transmission parameters whichmight have quantitative relations with the maturity, firmness and other quality-related properties of avocado and mango fruits.The system utilizes a set of low-frequency probes arranged to measure the ultrasonic signal transmitted and received over a shortdistance across the peel. The attenuation of the ultrasonic waves, transmitted through the peel and the attached fruit tissue,changes as a result of the progressive ripening and softening of the fruit during the fruiting season and in the course of storage.The present study quantitatively addressed the linkage between the ultrasonic attenuation and the physiological parameters of theflesh of the fruits. Results were obtained in the time and frequency domain, and the data set was analyzed statistically to identifythe relations between the major physiological indices and the ultrasonic parameters. Quantitative relations were developed todescribe the linkage between ultrasonic parameters and the maturity, firmness and other quality-related properties in mango andavocado fruits. © 2000 Elsevier Science B.V. All rights reserved.

Keywords: Fruits; Nondestructive testing; Quality; Spectral analysis; Ultrasonic

1. Introduction are the most acceptable method for measuring firmness,but they are destructive and time-consuming methods;a nondestructive method for determination of avocadoMaturity determination of fruits before picking, andand mango maturity would be of considerable economicsubsequent quality evaluation are important issues thatinterest to the food industry.affect the agricultural industry. The demand for high

Mizrach et al. [4] built and evaluated an experimentalquality calls for a reliable, rapid, nondestructive, nonin-system for determination of the basic acoustic propertiesvasive technique for measuring some of the physicalof some fruits and vegetables, i.e. wave propagationproperties of the fruit, which develop as it matures andvelocity and attenuation, and suggested the applicationwhich are indicative of its quality. In avocado fruits,of this technique to the nondestructive quality evaluationfirmness, and oil and dry matter content (DW ) of theof fruits and vegetables. In addition, Mizrach et al. [5,6 ]flesh are the subjects of the most acceptable methodsfound a strong interdependence between ultrasonicfor a reliable test of maturity, according to which theproperties and post-harvest ripening parameters of thedate of fruit harvest is determined [1]. Maturity indica-fruit tissue, which indicated the potential usefulness oftors in mango are softening of the flesh, decreasingthis ultrasonic method for determination of firmnessacidity and increasing contents of sugars, soluble solidsproperties of fruit tissue. Mizrach et al. [7] patented aand total solids. One of the main indices of maturity innondestructive quality-determining device based on thefruit is firmness: this changes during the ripening anduse of ultrasonic waves transmitted through the peelsoftening process, which starts on the tree, and continuesand the flesh of a whole fruit by means of probes induring harvesting, handling and storage [2]. Chemicalcontact with the peel. This method was used by Mizrachtests are also important factors in determination of theet al. in several studies: they measured ultrasonic wavematurity of fruits, but firmness is the factor most closelyattenuation in avocado fruit [8–10] and mango fruitrelated to the stage of maturity [3]. Penetration tests[11] in the time domain and in mango in the frequencydomain [12] to assess fruit properties and to relate them* Tel.: +972-3-9683451. fax: +972-3-9604704.

E-mail address: [email protected] (A. Mizrach) to shelf life. In all of these studies, the attenuation

0041-624X/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0041-624X ( 99 ) 00154-7

Page 2: Determination of avocado and mango fruit properties by ultrasonic technique

718 A. Mizrach / Ultrasonics 38 (2000) 727–722

measurements were correlated with the results of transmission mode was selected, with one transduceracting as a transmitter, and the other as a receiver. Thedestructive penetration measurements of firmness and

of physiological tests of the fruit tissue, in the course of transmitted pulses passed over the peel and through thefruit tissue, and were then sensed by the receiver.storage. The objective of the present paper is to review

all the studies mentioned above, the technologies, meth-ods and results, and to derive conclusions concerning 2.1.1. Time domain measurement system

The arrangement for this system allowed relativethe nondestructive determination of quality indices inavocado and mango fruits. motion of the ultrasonic probes, to adjust the gap

between them while applying a controlled contact forceon the fruit peel (Fig. 1). Narrow-band 50 kHz ultra-sonic transducers were chosen to provide the best com-2. Material and methodspromise in performances, between penetration andresolution [4]. The distance between the tips of the2.1. Instrumentationbeam-focusing elements was adjustable from 5 to 18 mmfor measurements at different spacings. The output pulseThe experimental arrangement for mango and avo-

cado fruit testing included an ultrasonic head structure was displayed on a cathode ray tube monitor, on whichthe pulse amplitude and transit time could be visuallywith a transmitter–receiver system that provided trans-

mission and reception of ultrasonic signals, which passed evaluated. In parallel, a built-in peak detector andmicroprocessor-controlled serial interface captured thethrough the peel and the fruit tissue next to the peel

(Fig. 1). The basic arrangement included a high-power, signal amplitude and the transit time, and sent a digitizedread-out to an external microcomputer. The stored datalow-frequency ultrasonic pulser–receiver (Krautkramer

Model USL33), a pair of ultrasonic transducers for were used to calculate the attenuation coefficient of thefruit, on the basis of standard formulations described inavocado and mango testing and a microcomputer system

for data acquisition and analysis. Exponential Plexiglas the following section.beam-focusing elements were used to reduce the diame-ter of the beam emitted by each transducer to match 2.1.2. Frequency domain measurement system

The entire structure that held the ultrasonic probesthe desired contact area with the fruit. Two kinds ofultrasonic wave attenuation measurement systems were could be moved only up and down, keeping a fixed

distance of about 3 mm between the tips of the beam-developed: one based on measurements in the timedomain [8–11] and the other for measurements in the focusing elements, and applied a controlled contact force

to the fruit peel. Wide-band, 100 kHz ultrasonic trans-frequency domain [12]. The transducers were mountedin a structure that allowed movement as required by ducers were chosen to provide the best measurements

in the frequency domain. The waveform signals and theeach system (Fig. 1). The angle between the axes of thetransducers was set to about 120° for both systems. The transit time were captured and collected by a LeCroy

9410-50A digital storage oscilloscope as machine datatransmitter–receiver assemblage was capable oftransmitting and receiving an ultrasonic signal over a files. By using the 94TRAN Translation Software (fur-

nished by LeCroy Corporation), the data were convertedshort distance of the peel of the fruit. The through-into ASCII output and then transferred to an externalmicrocomputer for further analysis.

2.2. Fruit selection and test procedures

Several different studies were performed for avocado:immature fruit picked directly from the tree, freshlyharvested fruit received from the packinghouse andstored at a controlled room temperature, and avocadofruits stored at low temperatures. Mizrach et al. [10]performed a study to follow the changes in avocadofruits nondestructively during maturation on the tree.The fruits were taken from a plot containing 400 trees.Ten trees per cultivar, distant from the plot edge orlane, were randomly tagged. 20 fruits per month werepicked and sampled from the trees, for 6 months. Afterpicking, the fruits were equilibrated at room conditions,for ultrasonic and DW content tests on the day ofFig. 1. Schematic diagram of the setup for ultrasonic testing of avo-

cado fruit. picking. Several studies followed the shelf life of avocado

Page 3: Determination of avocado and mango fruit properties by ultrasonic technique

719A. Mizrach / Ultrasonics 38 (2000) 727–722

fruits stored at room temperature, and established rela- into the frequency domain. The frequency spectrumanalysis was implemented in Matlab software [15],tionships based on ultrasonic parameters for nondestruc-

tive assessment of their physiological properties. Models which included data processing, with the stored analogsignal as input. The frequency amplitude spectra wereof these relationships for acoustic, mechanical, oil

content and DW parameters were suggested for avocado obtained by means of fast Fourier transform (FFT)techniques with a window of 350 ms starting from thefruits cv. ‘Ettinger’ [9] and cv. ‘Fuerte’ [8]. An analytical

study of the effects of the temperature and storage time leading edge of the transmitter signals. The frequencyrange was divided into 32 spectral bands, from 0 toon the softening process of avocado was performed by

Mizrach et al. [13]. Mature avocado fruits (cv. 75 683 Hz in 2441 Hz intervals and the amplitude foreach band was collected into a spectrum data file. The‘Ettinger’) were stored in a well ventilated rooms at 2,

4, 6 and 8°C. At weekly intervals for 4 weeks, 15 fruits ultrasonic measurements of the pulse amplitude anddetermination of the frequency spectrum of each pulsewere removed from each temperature regime and

allowed to reach room temperature (20°C), for non- were performed daily, on each particular sample, untilfull ripening of fruit was detected.destructive ultrasonic tests and destructive penetration

tests. Controls were assessed daily. Destructive testswere conducted immediately after the ultrasonic tests to 2.4. Determination of physiological parametersdetermine the firmness of the avocado fruit. Otherstudies were performed for mango fruit stored in a Quality and maturity indicators in fruits are the

firmness, and the oil and DW content of the flesh in thecontrolled-temperature room [11,12]. Mizrach et al. [11]developed a procedure and performed a study to evalu- case of avocado fruits, and the softening of the flesh,

decreased acidity and increased contents of sugars, solu-ate physiological changes nondestructively during stor-age. 80 mango fruits (cv. ‘Tommy Atkins’) were taken ble solids and total solids in the case of mango fruits.

The firmness tests were performed on unpeeled fruits,from a packinghouse, 5 h after they had been harvested,all from the same orchard. The fruits had been cooled with a durometer (John Chatillon & Sons, New York,

USA) fitted with a cone head [5]. The test was performedand sized by weight. The fruits were stored in an air-conditioned laboratory at 20°C and about 85% humidity in the radial direction near the application point of the

ultrasonic test [9]. Each fruit was subjected to thefor 0–360 h. Each fruit was marked for ultrasonic nonde-structive testing. 10 fruits were taken and measured after penetration test; control fruits were tested daily, until

they reached eating ripeness (5–8 N). The fruits wereeach time interval. Each of the selected fruits wassubjected to ultrasonic nondestructive testing, penetra- ultrasonically measured daily and firmness tests were

performed every other day, usually up to four times,tion firmness tests and physiological (physio-chemical )tests after each of eight time intervals, up to a total until full ripening was detected. The measured forces

were averaged and stored for further analysis. The drystorage time of 360 h.weight (DW ) of avocado was determined according toLee et al. [16 ]. A sample of about 10 g of avocado2.3. Ultrasonic teststissue was taken from the location at which ultrasonicnondestructive testing had been performed earlier, andThe ultrasonic test procedures in the time domain

were generally performed as follows. Each fruit was was weighed and dried in a 105°C forced-air oven for3 mm before being reweighed for DW percentage calcu-subjected to ultrasonic nondestructive tests, applied to

the marked points. The pulse amplitude of the transmit- lation. The oil content of the fruit was determined bymeans of the refractive index technique [17,18], whichted ultrasonic signal was measured at five different

spacing (5, 12, 14, 16 and 18 mm) between the two has been described in detail by Lee [19]. Acid assess-ments in mango were done by extraction procedureprobes, along the equator of the fruit, as described

above. The attenuation of the ultrasonic signal was described the in detail by Fuchs et al. [20].calculated from these measurements according to theexponential expression [14]:

3. Results and discussionA=A

0exp(−al ), (1)

where l is the distance between the input and collection These studies monitored the progress of the changesin fruit tissue properties, starting on the tree for avoca-probes, A0 and A, respectively, are the ultrasonic signal

amplitudes at the beginning and the end of the propaga- dos, and in the course of storage under various condi-tions, for both avocado and mango fruits. These studiestion path of the ultrasonic wave, and a is the apparent

attenuation coefficient of the signal. The ultrasonic test used statistical, correlation and modeling procedures toprocess the data. The results showed the changes in theprocedures in the frequency domain were performed in

a single touch of the probes. The received signals, as ultrasonic characteristics to be strongly related to growthand storage time. The velocity of the ultrasonic wave ineffected by the properties of the fruits, were transformed

Page 4: Determination of avocado and mango fruit properties by ultrasonic technique

720 A. Mizrach / Ultrasonics 38 (2000) 727–722

avocado tissue showed a non-monotonic complex rela- ultrasonic wave attenuation increased with diminishingfirmness at all storage temperatures (Fig. 3) but withtionship and was found to be not sensitive enough to

physiological changes in the fruit tissue; it was, therefore, slight difference in the slopes. This suggests that, for agiven storage temperature, the ultrasonic method canignored in the subsequent studies [9]. However, the

attenuation of the ultrasonic signal in avocado fruit was be used as a nondestructive firmness monitoring tech-nique during low-temperature storage. Changes in thefound to decrease as the fruit grew [10] and to increase

during the post-harvest softening and ripening process, physiological and chemical parameters of the fruits werelinked to the changes in ultrasonic attenuation. By theiruntil the fruit became very soft [8,9]. The reasons for

the inversion of the tendencies of the attenuation physiological nature, the oil and DW percentages ofavocado fruits increase during growth and do not changechanges during time probably resulted from differing

physiological processes, and it needs further investiga- after harvest. Dry weight is an acceptable and convenientindicator for evaluation of oil content in avocado, whention. The attenuation of the ultrasonic wave in mango

fruit also increased with storage time [10]. Nonlinear physiological tests are performed. In previous study[16], the authors indicated a close correlation betweenregression procedures were used to relate variations in

ultrasound wave attenuation and velocity with growth oil content and dry weight during maturation. A nonlin-ear regression procedure related variations in ultrasoundand storage time. A simple curve-fitting program was

used to express the experimental results as a function of attenuation and DW to growth time. An exponentialexpression was selected as the curve of ‘‘best fit’’ betweentime, to determine the curve shapes, and the equations

and the constants of these curves. Quadratic and cubic ultrasonic attenuation and the DW percentage of cv.‘Ettinger’ fruits during growth [10] (Fig. 4). The ultra-equations were chosen for attenuation and velocity

versus time, respectively, in both avocado [4,8,9] (Fig. 2) sonic attenuation asymptotically approaches a constantvalue. The DW content is then approaching the mini-and mango fruits [12]. During low-temperature storage

of avocado fruit, the attenuation initially decreased, and mum standard for maturity and indicates that the fruithas reached the appropriate harvest conditions. Thisthen increased during the 4 weeks of storage. The differ-

ences among the fruits stored at different temperatureswere found to be quite significant [13]. Diminution offirmness during storage is a natural physiological processin avocado and mango fruits. Both avocado and mangofruit firmness diminished monotonically during storageat room temperature, from a hard fruit with a firmnessvalue of about 90–120 N on the first day after harvestto a very soft fruit with a firmness of about 12 N at theend of up to 360 h of the softening process. At thatstage, the fruit was considered to be too soft for furthermeasurements [9,11]. Since the firmness and attenuationwere both time dependent, a direct relationship betweenthese two parameters was defined. A linear expression

Fig. 3. Attenuation versus firmness and linear regressions at severalwas selected as the curve of ‘best fit’ to describe thisstorage temperatures, for avocado fruit cv. ‘Ettinger’: &, 2°C; $, 4°C;relationship for avocado cv. ‘Ettinger’ [9] and parabolic+, 6°C; (, 8°C; %, 20°C (control ). Source Mizrach et al. [13].

expressions for avocado cv. ‘Fuerte’ [4,8] and mango[12]. For avocado fruits stored at low temperatures, the

Fig. 4. Attenuation versus DW during growth time, for avocado fruitFig. 2. The means of firmness, wave attenuation, and velocity versus cv. ‘Ettinger’. Vertical and horizontal lines represent confidence

intervals for attenuation and DW, respectively (confidence prob-storage time, and the suggested model curves, for avocado fruit cv.‘Ettinger’. Source Mizrach et al. [8]. ability=95%). Source Mizrach et al. [10].

Page 5: Determination of avocado and mango fruit properties by ultrasonic technique

721A. Mizrach / Ultrasonics 38 (2000) 727–722

suggests that the DW percentage in avocado could be tion [11]. Partial least squares regressions were used todevelop models relating the FFT spectra in the frequencyevaluated by ultrasonic attenuation measurement during

fruit growth and that the harvest time could be deter- domain with storage time, firmness, sugar content andacidity for each tested fruit [12]. The error associatedmined thereby. The DW and oil contents do not change

after harvesting, however; consequently, because of with the results of such a model was defined by thestandard error of calibration, which represents the sensi-differences in fruit maturity at harvest, there were differ-

ences in attenuation values. The measured attenuation tivity of prediction. The FFT values obtained for eachfruit were analyzed by means of Spectra Matrix andcorresponded to the oil and DW contents of the fruit.

Fig. 5 relates the attenuation and oil content measure- Light Cal software packages [21] using multi-linearregression and partial least squares regression analysis.ments made on the first day: the measured attenuation

was found to be greater at high than at low oil content The inputs for this program were the frequency ampli-tude spectrum, taken from the spectrum data file and[8]. The results of measurements of the chemical changes

in harvested mango fruits confirmed that the sugar the measured value for each of the quality parameters.The output of the program yielded calibrating modelscontents and acidity followed expected trends with stor-

age time: the sugar contents increased while the acidity and standard error of calibration values between 12 and18% of the total range [12].decreased. The variations in ultrasound attenuation and

in the chemical changes were related to one another bymeans of a nonlinear regression procedure [11] (Fig. 6).Both of these physiological parameters reflect internal 4. Conclusionschanges in the mango fruit during ripening, and thederived equations enable us to determine the sugar The ultrasonic method successfully utilized the meas-content and acidity in a batch of mango fruits directly, urement of ultrasonic wave attenuation in the fruit fleshby nondestructively measuring their ultrasonic attenua- by means of ultrasonic probes in contact with the

fruit peel.$ The attenuation was found to be strongly influenced

by the oil content at harvest and by the DW percen-tage at full ripening in avocado fruits.

$ Quantitative relations were satisfactorily devisedbetween ultrasonic parameters, firmness and matu-rity-related factors.

$ Changes in DW content during avocado fruit growthcorrelated well with ultrasonic attenuation measure-ments. The relation may be usable in the nondestruc-tive determination of the DW percentage of avocadofruit and the precise determination of the harvesttime, and for the nondestructive assessment of avo-

Fig. 5. The ultrasonic attenuation in avocado fruits cv, ‘Ettinger’ versus cado firmness, by ultrasonic measurement in place oftheir oil content on the first day. Source Mizrach et al. [8].

the commonly used destructive penetration method.$ The correlation between firmness of avocado fruits

and the measured ultrasonic attenuation during low-temperature storage suggested that the ultrasonicmethod could be used as a nondestructive firmnessmonitoring technique.

$ It was suggested that, by using the nondestructiveultrasonic measurement system in the frequencydomain, it was possible to estimate the maturity ofthe mango fruit.

References

Fig. 6. Polynomial expression of the averaged sugar contents, S (#), [1] C.E. Lewis, The maturity of avocados: a general review, J. Sci.Food Agric. 29 (1978) 866–875.in % TSS, and acidity H (6), in %, values of 80 mango fruits cv.

‘Tommy Atkins’ versus nondestructive testing ultrasonic attenuation [2] S. Lakshminarayana, in: S. Magy, P.E. Shaw (Eds.), Tropical andSubtropical Fruits: Compositions, Properties and Uses, Avi, West-A, in dB mm−1, at 20°C and 60% humidity (each point represents the

means for 10 fruits). Vertical lines are confidence interval bars. Source port, CT, 1980.[3] B.C. Peacock, C. Murray, S. Kosiyachinda, M. Kosittrakul, S.Mizrach et al. [11].

Page 6: Determination of avocado and mango fruit properties by ultrasonic technique

722 A. Mizrach / Ultrasonics 38 (2000) 727–722

Tansiriyakul, Influence of harvest maturity of mangoes on storage method for measuring maturity of mango fruit, Trans. ASAE 40(1997) 1107–1111.potential and ripe fruit quality, ASEAN Food J. 2 (1986) 99.

[12] A. Mizrach, U. Flitsanov, Z. Schmilovitch, Y. Fuchs, Determina-[4] A. Mizrach, N. Galili, G. Rosenhouse, Determination of fruit andtion of mango physiological indices by mechanical wave analysis,vegetable properties by ultrasonic excitation, Trans. ASAE 32Postharv. Biol. Technol 16 (1999) 179–186.(1989) 2053–2058.

[13] A. Mizrach, U. Flitsanov, M. Akerman, G. Zauberman, Monitor-[5] A. Mizrach, N. Galili, G. Rosenhouse, D.C. Teitel, Acoustical,ing avocado softening in low temperature storage using ultrasonicmechanical and quality parameters of winter grown melon tissue,measurements, Comput. Electron. Agric. (1999) in press.Trans. ASAE 34 (1991) 2135–2138.

[14] J. Krautkramer, H. Krautkramer, Ultrasonic Testing of Materials,[6 ] A. Mizrach, N. Galili, G. Rosenhouse, Half-cut fruit response toSpringer, Heidelberg, 1990.ultrasonic excitation, ASAE Paper No. 923017, Am. Soc. Agric.

[15] Matlab, The Mathworks Inc., South Natrick, MA 01760, USA,Eng., St. Joseph, MI, 19921995.[7] A. Mizrach, N. Galili, G. Rosenhouse, Method and a system for

[16 ] S.K. Lee, R.E. Young, P.M. Schiffman, C.W. Coggins Jr., Matu-non-destructive determination of quality parameters in fresh pro-

rity studies of avocado fruit based on picking dates and dryduce, Israel Patent 109 406; USA Patent 5 589 209; French Patent weight, J. Amer. Soc. Hort. Sci. 108 (1983) 390–394..95 04869, 1994 [17] A.F. Shannon, Refractive index and other extraction methods for

[8] A. Mizrach, U. Flitsanov, Nondestructive ultrasonic determina- oil in avocados, Bull. Calif. Dept. Agric. 38 (1949) 127–132.tion of avocado softening process, J. Food Eng. 40 (1999) [18] R.W. Harkness, Chemical and physical tests of avocado maturity,139–144. Proc. Florida State Horti. Soc. 67 (1954) 248–250.

[9] A. Mizrach, N. Galili, S. Gan-mor, U. Flitsanov, I. Prigozin, [19] S.K. Lee, Method for percent oil analysis of avocado fruit, Year-Models of ultrasonic parameters to assess avocado properties and book (California Avocado Society) 65 (1981) 133–141.shelf life, J. Agric. Eng. Res. 65 (1996) 261–267. [20] Y. Fuchs, E. Pasis, G. Zauberman, Changes in amylase activity,

[10] A. Mizrach, U. Flitsanov, R. El-Batsri, H. Degani, Determination starch and sugars contents in mango pulp, Sci. Horti. 13 (1980)of avocado maturity by ultrasonic attenuation measurements, Sci. 155.Horti. 80 (1999) 173–180. [21] Spectra-Metrix 1.8 software, LT Industries Inc., Rockville, MD,

USA, 1989.[11] A. Mizrach, U. Flitsanov, Y. Fuchs, An ultrasonic nondestructive