M. Ruiz-Altisent

Nondestructive quantification of chemical and physical properties of fruits by time-resolved reflectance spectroscopy in the wavelength range 650–1000 nm

Time-resolved reflectance spectroscopy can be used to assess nondestructively the bulk (rather than the superficial) optical properties of highly diffusive media. A fully automated system for time-resolved reflectance spectroscopy was used to evaluate the absorption and the transport scattering spectra of fruits in the red and the near-infrared regions. In particular, data were collected in the range 650-1000 nm from three varieties of apples and from peaches, kiwifruits, and tomatoes. The absorption spectra were usually dominated by the water peak near 970 nm, whereas chlorophyll was detected at 675 nm. For all species the scattering decreased progressively with increasing wavelength. A best fit to water and chlorophyll absorption line shapes and to Mie theory permitted the estimation of water and chlorophyll content and the average size of scattering centers in the bulk of intact fruits.

Time-Resolved Reflectance Spectroscopy Applied to the Nondestructive Monitoring of the Internal Optical Properties in Apples

Time-resolved reflectance has been used for the nondestructive measurement of optical properties in apples. The technique is based on the detection of the temporal dispersion of a short laser pulse injected into the probed medium. The time distribution of re-emitted photons interpreted with a solution of the diffusion equation yields the mean values of the absorption and reduced scattering coefficients of the medium. The proposed technique proved useful for the measurement of the absorption and scattering spectra of different varieties of apples, revealing the spectral shape of chlorophyll. No major variations were observed in the experimental data when the fruit was peeled, showing that the optical properties measured were those of the pulp. With this technique the change in chlorophyll absorption during storage and ripening could be followed. Finally, a compact prototype working at few selected wavelengths was designed and constructed, demonstrating potentialities of the technique for industrial applications.

Development and implementation of an on-line impact sensor for firmness sensing of fruits

A prototype impact system for firmness sorting of fruits (TOUCHLINE), developed initially by Chen and Ruiz-Altisent (Paper presented at AgEng 96, Madrid, Paper no. 96F-003), has been modified and installed in an experimental fruit packing line. The system consists of a lateral impact sensor with a control electronic circuit, a control software and an ejection system with three outlets regulated by a microcontroller. The lateral impact sensor detects the presence of fruit by means of an optical sensor and impacts it. Impact signal is obtained by an accelerometer and sent to a PC where it is processed by specific software to yield a firmness index. According to this index the software gives an order to the microcontroller of the ejection system and fruit is sent to its corresponding outlet. n nSeveral tests were carried out with spherical balls of cork, tennis and rubber, showing a good performance of the sorting system.

Detection of internal quality in kiwi with time-domain diffuse reflectance spectroscopy

Time-domain diffuse reflectance spectroscopy (TRS), a medical sensing technique, was used to evaluate internal nkiwi fruit quality. The application of this pulsed laser spectroscopic technique was studied as a new, possible non-destructive, nmethod to detect optically different quality parameters: firmness, sugar content, and acidity. The main difference with other nspectroscopic techniques is that TRS estimates separately and at the same time absorbed light and scattering inside the nsample, at each wavelength, allowing simultaneous estimations of firmness and chemical contents. Standard tests (flesh npuncture, compression with ball, .Brix, total acidity, skin color) have been used as references to build estimative models, using na multivariate statistical approach. Classification functions of the fruits into three groups achieved a performance of 75% ncorrectly classified fruits for firmness, 60% for sugar content, and 97% for acidity. Results demonstrate good potential for nthis technique to be used in the development of new sensors for non-destructive quality assessment.

Instrumentation and procedures for commercial non-destructive determination of firmness of various fruits

A high interest in non-destructive instrumentation for firmness sensing of fruits is developing, and commercial laboratory and on-line equipment is already available. Many fruit handling lines offer NIR (plus VIS) systems, claiming that they can estimate firmness, in addition to chemical quality of fruits, as soluble solids. Optical firmness sensing is difficult or not feasible for many fruits, so that mechanical firmness devices are rapidly increasing presence in the market. Mechanical firmness devices, which can be used on-line, as well as table-top in laboratory, are based on either of two principles: deformation by contact or vibration response to contact. Contact is of the fast type, being an impact with low energy, with a duration of a few miliseconds. The vibration response spectrum is analized after transformation into frequency-domain, and characteristic frequency is determined. In both techniques, deformation of fruit is encountered, being this related to structure of fruit flesh, and therefore to firmness. Furthermore, both procedures can be (and are) combined in the same system. A review of the existing commercial equipment is made. Selected results on different fruits, which show experimental comparisons of different non-destructive with respect to destructive instruments are presented, showing the feasibility and better repeatability for non-destructive procedures. The need for standardising non-destructive firmness measurement of fruits is discussed.

Nondestructive measurements of the optical properties of fruits by means of time-resolved reflectance

The non-destructive assessment of the quality of fruits is getting a crucial task. As a possible first step toward the noninvasive evaluation of quality, we propose the measurement of the internal optical properties of fruits and vegetables by means of time-resolved reflectance spectroscopy. Mode-locked dye and Titanium:Sapphire lasers are used as the illumination source. The reflectance signal is processed by an electronic chain for time-correlated single-photon counting. The time-dispersion of re-emitted photons is fitted to the solution of the diffusion equation, with absorption and transport scattering as free parameters. The whole instrumentation is computer-controlled and allows one to perform measurements from 610 to 1000 nm. Absorption and scattering spectra of several species of fruits were acquired, and particular attention was devoted to the optical characterization of apples.

Reduction of Mechanical Damage to Apples in a Packing Line Using Mechanical Devices

Fresh fruits and vegetables experience impacts as they are mechanically handled in commercial packing lines. nImpacts commonly occur when the product is transferred between successive unit operations (transfer point) along the line. nMechanical devices can be used at transfer points to decrease the mechanical damage to fruit. nBruise onset is induced when the failure stress or the maximum deformation for the product tissue are exceeded (depending nupon the damage mechanism). Bruise onset and its magnitude depend on different factors: height of the transfer points, nworking velocity, hardness of the surfaces, curvature of the surfaces, and fruit characteristics (mass, curvature, temperature, nhumidity, and firmness). nTo analyze the effectiveness of mechanical devices (cushioned rollers, powered brush, and padding materials) to reduce nmechanical damage to “Golden” apples, three standard transfer points (transporting belt – rollers transporter; rollers ntransporter – singularizer; and transporting belt – transporting belt) of a experimental packing line were studied using ninstrumented spheres (IS 100). The efficiency of the solutions was analyzed using “Golden” apples and measuring the npresence of external bruises during the handling. nSolutions tested reduced the acceleration values under 50 g, which is commonly a safe level to avoid the mechanical ndamage in apples. Once the transfer points were improved, apples were handled, and values around 100% of fruit were EC nGrade I. nTests carried out showed that mechanical devices are useful to reduce mechanical damage in “Golden” apples, but must nbe correctly regulated to obtain optimum results (fruit without bruises). This regulation can be carried out using instrumented nspheres (IS 100) and fresh fruit.

Decelerator elements for ramp transfer points in fruit packing lines

Abstract Two different decelerator elements used to reduce impacts on fruits on ramp transfer points in fruit packing lines were designed and tested. The performance of these elements, a powered decelerator and a multiple curtain, was compared to commercial decelerators (blankets). A ramp of length 60 cm was placed at an angle of 30° in an experimental fruit packing line between a roller transporter and a conveyor. The decelerators were placed on top of the ramp. Different tests were carried out to study the performance of the decelerators using instrumented spheres (IS 100) of various sizes. Results showed that decelerators can reduce the impact intensity down to safe thresholds. The powered decelerator was the most effective because it reduced the speed of fruits and did not cause retention of the fruit, when correctly regulated.

Evaluation of a Non-Destructive Impact Sensor to Determine On-Line Fruit Firmness

A non-destructive impact sensor to measure on-line fruit firmness was evaluated. This sensor is an adaptation of a static model used in the laboratory to measure fruit quality and was installed in an experimental fruit packing line with a commercial sizer chain. The firmness index is related to the acceleration-time curve supplied by an accelerometer attached to an impacting arm. The main objective of this study was to evaluate sensor performance and sources of variation. We made classification trials on three fruits: peaches ( Prunus persica (L.) Batsch), apples (Malus domestica Borkh.), and pears (Pyrus communis L.), as well as working trials, such as placing the fruit, orientation, and others. The sensor works correctly at a speed of 7 fruits s -1 (0.63 m s -1 ) and allows fruit classification at three levels of firmness using specific software . Good discrimination was obtained only for soft peaches. There were variations in results between different fruits and different parts of the same fruit mainly due to the non-uniformity of fruit shape and lack of ripeness homogeneity of each one.

ANALYSIS OF THE FACTORS IMPLIED IN THE FRUIT-TO-FRUIT IMPACTS ON PACKING LINES

The problem of fruit-to-fruit impacts on packing lines was analysed in an experimental fruit packing line. Different nfactors were considered including fruit susceptibility to damage, fruit flow in the line, and characteristics of the transfer points nbetween elements on the line. Tests were performed using “Golden” apples and IS 100 instrumented spheres. Most of the nfruit-to-fruit impacts occurred at angled transfer points. A powered decelerator was developed and installed in the packing nline that significantly minimized the number and intensity of fruit-to-fruit impacts at transfer points with a 90. angle between ntwo transporting belts.