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- Author or Editor: Judith A. Abbott x
A rapid nondestructive method for measuring apple texture using sonic vibrational characteristics of intact apples was tested on freshly harvested `Delicious' apples from major U.S. production areas. Sonic transmission spectra and Magness-Taylor (MT) firmness were measured on whole apples and compression measurements were made on excised tissue. Two experienced Agricultural Marketing Service apple inspectors assessed each apple and assigned a ripeness score according to U.S. Dept. of Agriculture grades and standards inspection procedures (based primarily on texture). Sonic functions correlated significantly with ripeness scores, MT firmness, and forces to rupture or crush the tissue in compression. Ripeness scores were more closely correlated with the destructive firmness measurements than with sonic functions. However, sonic measurement has the advantage of being nondestructive, whereas MT and tissue compression are inherently destructive. Further research is needed to modify the Instrumentation and Sensing Laboratory`s sonic technique to improve the prediction of apple firmness before it can be adapted for on-line sorting.
Demand for fresh fruits and vegetables is increasing worldwide in response to health concerns, wealth, and the desire for variety in the diet. However, consumption of produce is contingent on the ability of the industry to provide high quality fresh produce and on its convenience, as well as on consumer education and economics. Texture measurement is accepted by horticultural industries as a critical indicator of quality of fruits and vegetables. The fresh produce industry and, indirectly, consumers need methods for measuring produce texture to ensure the quality within a grade, and scientists need measurements to quantify the results of their treatments, whether treatments are genetic, chemical, or physical. The variety of attributes required to fully describe textural properties can only be fully measured by sensory evaluation by a panel of trained assessors. However, instrumental measurements are preferred over sensory evaluations for both commercial and research applications because instruments are more convenient, less expensive, and tend to provide consistent values when used by different people. Thus, instrumental measurements need to be developed that predict sensory evaluations of texture. Such instrumental measurements can then provide a common language among researchers, producers, packers, regulatory agencies, and customers. We compare sensory evaluations of specific critical textural attributes to instrumental force/deformation measurements on a wide variety of fruits and vegetables with relatively uniform bulk tissues, such as apples, bananas, carrots, jicama, melons, pears, potatoes, rutabagas, and several others.
Sonic vibrational characteristics of intact apples are related to flesh elasticity which is, in turn, related to firmness. Firmness changes in Golden Delicious and Delicious apples were followed during accelerated ripening and under storage conditions. Firmness was measured by Magness-Taylor puncture force and by compression of tissue cylinders (modulus of elasticity and rupture strength) for comparison with sonic vibrational characteristics of intact apples. Influences of apple temperature, size, shape, and skin on sonic spectra were investigated. Sonic resonant frequencies were significantly correlated with destructive firmness measurements and decreased as storage time increased. Sonic amplitudes were not closely related to firmness. Regression equations incorporating sonic data and size were developed to predict Magness-Taylor force. Use of sonic vibrational characteristics is proposed as a rapid nondestructive method for firmness sorting of apples.
Firmness is a critical quality attribute for kiwifruit, as it is for most commodities. Firmness is related to flesh elasticity and rigidity which, along with geometry and density, determine vibrational behavior. Firmness changes in kiwifruit were followed during storage at 0C by three methods: sonic vibrational spectra from 0 to 2000 Hz, dynamic force/deformation (F/D) in the range 40 to 440 Hz, and Magness-Taylor puncture (MT) on an Instron. Frequencies of sonic resonances and dynamic F/D peaks, as well as MT maximum force, decreased as storage time increased. Sonic resonance frequencies were highly correlated with MT maximum force and apparent elasticity (r=0.79 and 0.88). Frequencies of peaks in the dynamic F/D traces were correlated with MT maximum force and apparent elasticity (r=0.68 and 0.72) and with resonance frequency (r=0.81). Further data processing improves the ability of the nondestructive vibrational measurements to estimate the destructive MT test values.
Refreshed (repetitively stimulated) delayed light emission (DLE) of cucumber and bell pepper fruit was strongly related to temperature and duration of exposure to chilling temperatures. At the 10th measurement cycle (about 150 ms), DLE of cucumbers exposed to 2.5°C for ≥12 hr or 5.0° for ≥24 hr was greater than that of cucumbers held at higher temperatures (7.5° to 12.5°) for 12 to 264 hr. Similarly, DLE of bell peppers exposed to 2.5° for ≥48 hr was greater than that of peppers held at higher temperatures. For both cucumbers and peppers, however, there was a greater difference in DLE between fruit held at 2.5° or 5.0° and those held at higher temperatures around measurement cycles 400 to 500 (at 6.0–7.5 sec) and this difference increased with increasing duration of exposure. Amount of refreshed DLE around measurement cycles 400 to 500 or the rate of change in DLE around cycles 180 to 300 is proposed as an indicator of chilling exposure for cucumber and bell pepper fruit.
Firmness is a critical quality characteristic in kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson] marketing. The industry seeks a nondestructive method for firmness sorting. We measured sonic vibrational responses of 149 kiwifruit over the range 0 to 2000 Hz and compared them with Magness-Taylor (MT) penetrometer values. Sonic resonant frequencies and mass were combined to calculate a sonic stiffness coefficient. Coefficients of determination (r2 ) for sonic stiffness coefficients versus MT slope and log of MT maximum force were 0.88 and 0.86, respectively. Sonic stiffness coefficients provided good to excellent classification of kiwifruit into two or three firmness categories based on MT maximum force values. A combination of amplitudes at several specific sonic frequencies selected by stepwise discriminant analysis or regression tree analysis also provided successful sorting algorithms. Identification of soft kiwifruit was 89% to 96% accurate and of firm kiwifruit 83% to 91%. These conclusions are based on a rather small sampling of kiwifruit of a single source and size, but the results clearly indicate the potential of a nondestructive firmness measurement based on sonic frequency vibrations.
Treatments to inhibit browning and maintain quality of fresh-cut `Anjou', `Bartlett', and `Bosc' pears (Pyrus communis L.) were developed. Slices of `Anjou', `Bartlett', and `Bosc' pears (firmness 22, 36, and 22 N, respectively) were dipped in solutions of 4-hexylresorcinol, isoascorbic acid, N-acetylcysteine, and potassium sorbate prior to storage in air for up to 14 days at 5 °C. Inhibition of browning without loss of firmness and with no microbial growth was achieved for the three cultivars for 14 d. Inhibition of browning during 14 d storage at 5 °C was not affected by initial firmness (21-52 N) of `Anjou' pear slices.
A treatment to inhibit browning and maintain quality of fresh-cut `Anjou' and `Bartlett' pears (Pyrus communis L.) was developed. Slices of ŒAnjou, and ŒBartlett, pears with a range of initial firmness values were dipped in mixtures of 4-hexylresorcinol, isoascorbic acid, potassium sorbate, and N-acetylcysteine before refrigerated storage. Browning, as indicated by visual observation and by colorimeter readings, was inhibited for 14 d. Pears receiving the antibrowning treatment maintained firmness as well or better than the control slices.
We compared the firmness and force relaxation characteristics of tomato flesh harvested at six maturity stages and stored intact or as 7-mm slices for 0 to 20 days. Three measurements were made on outer pericarp and columella tissue. A 4-mm cylindrical probe provided more consistent firmness measurements (lower percent CV) than a 6.4-mm spherical probe at harvest, and distances of 3 mm were more consistent than 1 mm. Following loading, stress relaxation was recorded for 10 s. Stored tomato samples were tested only with the 4-mm cylindrical probe and distance of 3 mm. Firmness was taken as the maximum force (Fmax) in the loading portion, usually occurring at 3 mm. Fmax of freshly harvested tomatoes ranged from 15 to 2 N for mature green and red tomatoes, respectively. Fmax was closely correlated to area, slope, and force at first peak, i.e., all four parameters measured the same physical property, and was moderately correlated (R > 0.9) to forces at specific relaxation times. Tomatoes stored intact generally had lower CVs than that of those sliced before storage, although there was little difference in average firmness (Fmax) between the two at a given storage time. A three-parameter model was developed to fit the relaxation curves. There was little correlation between Fmax and the three relaxation characteristics (R = 0.6 to 0.0), i.e., the relaxation characteristcs measured different physical properties than did Fmax. The responses of the relaxation characteristcs over storage time were dependent on the initial maturity of the tomatoes, but their values usually differed significantly between tomatoes stored intact or sliced, with tomatoes sliced before storage generally having higher values.
Fruit of apple (Malus domestica Bork) stored in air for 3 to 4 months at 0°C before being placed in CA (delayed-CA) generally were of intermediate quality between apples stored in CA soon after harvest and those stored in air. Apples from CA had lower respiration rates, higher acidities, and were rated harder and juicier by taste panelists than apples stored in air. Four cultivars responded similarly to these storage conditions.