This review covers developments in non-invasive techniques for quality analysis and inspection of specialty crops, mainly fresh fruits and vegetables, over the past decade up to the year 2010. Presented and discussed in this review are advanced sensing technologies including computer vision, spectroscopy, X-rays, magnetic resonance, mechanical contact, chemical sensing, wireless sensor networks and radio-frequency identification sensors. The current status of different sensing systems is described in the context of commercial application. The review also discusses future research needs and potentials of these sensing technologies. Emphases are placed on those technologies that have been proven effective or have shown great potential for agro-food applications. Despite significant progress in the development of non-invasive techniques for quality assessment of fruits and vegetables, the pace for adoption of these technologies by the specialty crop industry has been slow.

Here, we review different methods for non-destructive horticultural produce size determination, focusing on electronic technologies capable of measuring fruit volume. The usefulness of produce size estimation is justified and a comprehensive classification system of the existing electronic techniques to determine dimensional size is proposed. The different systems identified are compared in terms of their versatility, precision and throughput. There is general agreement in considering that online measurement of axes, perimeter and projected area has now been achieved. Nevertheless, rapid and accurate volume determination of irregular-shaped produce, as needed for density sorting, has only become available in the past few years. An important application of density measurement is soluble solids content (SSC) sorting. If the range of SSC in the batch is narrow and a large number of classes are desired, accurate volume determination becomes important. A good alternative for fruit three-dimensional surface reconstruction, from which volume and surface area can be computed, is the combination of height profiles from a range sensor with a two-dimensional object image boundary from a solid-state camera (brightness image) or from the range sensor itself (intensity image). However, one of the most promising technologies in this field is 3-D multispectral scanning, which combines multispectral data with 3-D surface reconstructio

The flow of air generated by a new design of air assisted sprayer equipped with two axial fans of reversed rotation was analyzed. For this goal, a 3D sonic anemometer has been used (accuracy: 1.5%; measurement range: 0 to 45 m/s). The study was divided into a static test and a dynamic test. During the static test, the air velocity in the working vicinity of the sprayer was measured considering the following machine configurations: (1) one activated fan regulated at three air flows (machine working as a traditional sprayer); (2) two activated fans regulated at three air flows for each fan. In the static test 72 measurement points were considered. The location of the measurement points was as follow: left and right sides of the sprayer; three sections of measurement (A, B and C); three measurement distances from the shaft of the machine (1.5 m, 2.5 m and 3.5 m); and four measurement heights (1 m, 2 m, 3 m and 4 m). The static test results have shown significant differences in the module and the vertical angle of the air velocity vector in function of the regulations of the sprayer. In the dynamic test, the air velocity was measured at 2.5 m from the axis of the sprayer considering four measurement heights (1 m, 2 m, 3 m and 4 m). In this test, the sprayer regulations were: one or two activated fans; one air flow for each fan; forward speed of 2.8 km/h. The use of one fan (back) or two fans (back and front) produced significant differences on the duration of the presence of wind in the measurement point and on the direction of the air velocity vector. The module of the air velocity vector was not affected by the number of activated fans.

Firmness is a very important quality property in peach. The storage of peach affects its subsequent softening process and shelf life. The temperature and duration of storage mainly influence the firmness of stored fruit, and monitoring the evolution of fruits enables producers to manage its commercial life. The objective of the present study was to use non-destructive acoustic and impact tests to estimate firmness of peaches and to elucidate the influence of storage temperature and of time on the softening process of peach. Continuous and classification models based on variables obtained from non-destructive methods were developed. Parameters obtained from non-destructive methods were compared to destructive reference tests. The maximum force in ball compression correlated well with the maximum acceleration from impact test ( r 2 = 0.75), and with a band magnitude parameter from acoustic test ( r 2 = −0.71). Combining impact and acoustic parameters, the multiple correlation coefficient increases up to 0.91 (adjusted R 2 = 0.82) in the prediction of the maximum force in ball compression. Classification models based on both non-destructive parameters and sorting peaches into two classes of firmness, showed scores of well classified higher than 90%. Keywords Non-destructive methods Fruit quality Firmness Peach Acoustic technique Impact technique 1 Introduction Firmness is a very important quality property in peach. Determination of the storage time effect on the evolution of this quality is a desirable objective for producers, distributors and market agents, who need reliable firmness measuring instruments for commercial purpose. Previous studies carried out by different researchers show that impact techniques can be used to evaluate firmness of fruits successfully ( Chen & Ruiz-Altisent, 1993; Delwiche, Arévalo, & Mechlschau, 1996; Jarén, Ruiz-Altisent, & Pérez de Rueda, 1992 ). The force response of an elastic sphere impacting a rigid surface is governed by the impacting velocity, mass, radius of curvature, elastic modulus, and Poisson’s ratio of the sphere. It had being found that the impact of a fruit on a rigid surface can be closely modelled by the impact of an elastic sphere and that the firmness of a fruit has a direct effect on the impact force response. A problem inherent to the technique of dropping the fruit on a force sensor is that the impact force is also a function of the mass and radius of curvature of the fruit. A different approach has been to impact the fruit with a small spherical impactor of known mass and radius of curvature and measure the acceleration of the impactor. The advantage of this method is that the measured impact-acceleration response is independent of the fruit mass and is less sensitive to the variation of the radius of curvature of the fruit. An impact device for firmness testing of fruits was developed by Chen and Ruiz-Altisent (1996) . It consisted of a semi-spherical impacting tip attached to the end of a pivoting arm. Impact is done by swinging the impactor to collide laterally with the tested object. A small accelerometer is mounted behind the impacting tip. Further versions have been developed at the Physical Properties Laboratory (LPF) to obtain systems with better data resolution, signal-noise ratio and precision ( Diezma et al., 2000 ): “LPF-Lateral Impact Sensor 2.0”. This lateral impact sensor has been modified and installed in an experimental fruit packing line ( García-Ramos et al., 2003; Homer, 2003 ). An on-line impactor, based on a spherical tip impacting vertically on fruit using aerodynamic impulse is commercially available ( Valero, García-Ramos, De Merlo, Ruiz-Altisent, & Howarth, 2004 ). In biological tissues, vibrational behaviour of fruits has been used as an indicator of maturity and post-harvest ripeness based on the elastic properties of the tissue. Non-destructive techniques using sonic characteristics of the fruit tissue have been applied for measuring firmness and for detecting internal disorders in several products such as apples, pears, avocados and melons. Determination of the natural frequencies of fruits and vegetables as a mean of measuring firmness has been suggested by several authors ( Armstrong, Stone, & Brusewitz, 1997; De Baerdemaeker, Lemaitre, & Meire, 1982; De Belie, Schotte, Coucke, & De Baerdemaeker, 2000; Farabee & Stone, 1991 ). According to theory, resonant frequencies of a specimen are also proportional to its dimensions, density and Poisson’s ratio. Several authors have used mass to approximate the combination of density and dimensions in order to avoid these influences in the estimation of firmness by vibrational methods, different stiffness coefficients have been applied. A first stiffness coefficient was proposed from experimental results, which include resonant frequency and mass, f 2 (m) ( Abbott, Bachman, Childers, & Fitzgerald, 1968 ). Based on the spherical resonator model other stiffness coefficient has been calculated as f 2 (m 2/3 ) ( Cooke, 1972 ). A device developed at the Katholieke Universiteit Leuven (Belgium) is being developed into an on-line sensor ( De Ketelaere, Ruiz-Altisent, Correa, De Baerdemaeker, & Barreiro, 2001 ). At LPF a device, composed mainly by a microphone, a signal conditioning amplifier, a data acquisition card, structural elements, and a component to produce the mechanical impact was designed and tested in order to detect internal discontinuities in watermelon ( Diezma, Ruiz-Altisent, & Orihuel, 2002; Diezma, 2003 ). Firmness in peaches can be an indicator of immaturity or overmaturity. Excessive firmness indicates an immature peach with little free juice. An overmature, soft peach can be excessively juicy and prone to bruises. Previous investigations of non-destructive firmness measurement for peaches utilized impact parameters of a fruit that was bounced onto a load cell ( Delwiche, MacDonald, &...