Marvin J. Pitts

Development and validation of a finite element model of an apple fruit cell

Abstract A three-dimensional finite element model of an apple parenchyma cell was developed based on measured cell geometry. The cell wall was modelled using thin shell finite elements. Turgor pressure was represented by a distributed force on the cell wall internal surface, resulting in cell wall stresses prior to the application of external loads. Simulation results agreed closely with experimental measurement of volumetric elastic modulus and with results from geometrically simple analytical models. Because the model’s results agree with published data from multiple sources, we believe this validated model is a useful tool in the investigation of apple cell properties.

Modeling Potato Tuber Mass with Tuber Dimensions

ABSTRACT THIRTEEN models for predicting potato tuber mass from tuber dimensions were identified and used to evaluate theoretical limits of performance for mechanical and electronic potato tuber sorting devices. The models were divided into three classes based on: (1) single and multiple variable regression of the tuber length, width and height, (2) approximation of tuber shape by an ellipsoid, and (3) approximation of tuber shape by summation of thin disks. Tuber silhouettes were recorded and analyzed using digital imaging equipment and techniques. Class 3 models were most accurate, followed by Class 2 and Class 1 models. Class 1 models were the most simple, Class 3 most complex. Class 3 models could predict tuber mass within 25 g only 70% of the time, Class 2 models, 90% of the time and Class 1 models over 99% of the time..

Cold Atmospheric-Pressure Plasmas Applied to Active Packaging of Apples

Active packaging of fruits and vegetables uses films that absorb molecules from or contribute molecules to the produce. The pilot application developed in this paper has resulted in the deposition of film to apples. A prospective application relates to replacing hot wax that is expensive and that lowers the textural quality of the apple. This was the early motivation of this paper. Moreover, the focus of this paper will be mostly on the reactor design and film evaluation. The cold-plasma zone was obtained by increasing the voltage on a needle-to-needle electrode structure until the electric field in the feed material (argon + monomer) was sufficiently high to yield electron avalanches and self-propagating streamers. The ¿corona onset criterion¿ was used to design the cold-plasma reactor. The apple was placed in a treatment chamber downstream from the activation zone (cold-plasma zone). Selected physical properties of the film were measured. Environmental scanning electron microscopy and Fourier transform infrared studies of samples were also performed to determine the presence of the film. Electromagnetic modeling was applied to the design of the cold-plasma reactor, and those results are presented in this paper.

Compressive Strength of Wheat Endosperm: Comparison of Endosperm Bricks to the Single Kernel Characterization System

ABSTRACT The three major classes of endosperm texture (grain hardness) of soft and hard common, and durum wheat represent and define one of the leading determinants of the milling and end-use quality of wheat. Although these three genetic classes are directly related to the Hardness locus and puroindoline gene function, much less is known about the kernel-to-kernel variation within pure varietal grain lots. Measurement of this variation is of considerable interest. The objective of this research was to compare kernel texture as determined by compression failure testing using endosperm bricks with results of whole-kernel hardness obtained with the Single Kernel Characterization System 4100 hardness index (SKCS HI). In general terms, the variation obtained with the SKCS HI was of similar magnitude to that obtained using failure strain and failure energy of endosperm brick compression. Objective comparisons included frequency distribution plots, normalized frequency distribution plots, ANOVA model R2, and co...

Compressive Strength of Wheat Endosperm : Analysis of Endosperm Bricks

ABSTRACT The material properties of wheat grain endosperm are central to its processing and end-use quality. The preparation of geometrically-defined endosperm specimens free of bran, germ, and pigment strand can facilitate the objective study of endosperm material properties. This study was conducted to characterize the material properties of wheat endosperm from two soft, two hard, and one durum wheat varietal samples. Additionally, each varietal sample was sorted according to vitreous or mealy kernel type. Endosperm ‘bricks’ approximately 0.76 × 2.08 × 1.06 mm were prepared using an abrading (Kernel Sanders, KS) device. Bricks were tested in compression using a texture analyzer (TA.XTPlus). Stress-strain curves were used to calculate failure strain, failure stress, failure energy, and Youngs modulus. Additionally, the effect of brick aging up to one month, and changes in moisture content (freeze drying, oven drying, and equilibration to ≈10.5–11% mc) were studied. Intrakernel variation was assessed by...

ESTIMATION OF GRAPEVINE CROP MASS AND YIELD VIA AUTOMATED MEASUREMENTS OF TRELLIS TENSION

A novel approach was devised to estimate vegetative growth and fruit mass (i.e., yield) in grapevines by continuously measuring the tension in the horizontal (cordon) support wire of the trellis. Load cells installed in-line with the cordon wire were connected to an automated data acquisition system, a major departure from the viticulture industry’s standard method of collecting fruit samples by hand two or three times per growing season. Each experimental row in the vineyard was calibrated to determine the change in tension in that row in response to an increase in known mass on the cordon wire. The effects of temperature on wire tension were removed by post-processing with a regression-based empirical protocol, which corrected the raw data to a standard temperature. Because data were averaged over 15 min, wind gusts appeared to have little measurable effect on the tension measurement. A smoothing algorithm removed remaining transient disturbances in the data without masking significant events like crop thinning or harvest. Results to date suggest a linear relationship between wire tension and fruit mass that varies among rows, but not within a row, during a single season. Yields were between 4.5 and 20.2 t ha-1 (2 to 9 t acre-1).

FACTORS INFLUENCING DYNAMIC MECHANICAL PROPERTIES OF RED ‘DELICIOUS’APPLE TISSUE

This research measured tissue failure stress, failure strain, and shock wave speed in dynamic axial compression tests to assess, with respect to these properties: (1) the homogeneity of Red ‘Delicious’ apple tissue samples (10 mm dia., 15.2 mm long) taken around the apple equator; (2) the isotropy between tissue samples taken radially and parallel to the stem-calyx axis; and (3) the effects of strain rate and fruit size on dynamic (impact) properties. Results were compared with Magness-Taylor penetrometer measurements. At strain rates from 20 to 150 s –1 (equivalent to drop heights of 5 to 265 mm, respectively), the measured tissue properties were homogeneous around the periphery of the apple, but not isotropic for radial versus parallel sample orientation. Radial samples had lower failure strain but slightly higher failure stress than parallel samples. Smaller apple tissue had lower failure strain, higher failure stress, higher elastic modulus, and higher shock wave speed than that of larger apples. Failure stress and strain both increased as strain rate increased from 20 to 150 s –1 . However, the failure strain was largest at the quasi-static strain rate (0.027 s –1 ), likely due to a bio-yield occurring at the quasi-static strain rate, but not at dynamic strain rates. As expected, very poor linear correlations occurred between the Magness-Taylor penetrometer force and dynamic failure properties. Generally, correlations were better at the lower than at the higher strain rates, which is logical considering the viscoelastic nature of apples and the quasi-static loading rates used in Magness-Taylor measurements. Important conclusions are that measurement of dynamic failure properties must take into consideration fruit size and strain rate, and that Magness -Taylor tests cannot predict such properties, at least in the apples we measured.

Block-Surface Staining for Differentiation of Starch and Cell Walls in Wheat Endosperm

A staining technique for differentiating starch granules and cell walls was developed for computer-assisted studies of starch granule distribution in cells of wheat (Triticum aestivum L.) caryopses. Blocks of embedded caryopses were sectioned, exposing the endosperm tissue, and stained with iodine potassium iodide (IKI) and Calcofluor White. Excessive tissue hydration during staining was avoided by using stains prepared in 80% ethanol and using short staining times. The IKI quenched background fluorescence which facilitated the use of higher concentrations of Calcofluor White. Cell wall definition was improved with the IKI-Calcofluor staining combination compared to Calcofluor alone. The high contrast between darkly stained starch granules and fluorescent cell walls permitted computer assisted analysis of data from selected hard and soft wheat varieties. The ratio of starch granule area to cell area was similar for both wheat classes. The starch granule sizes ranged from 2.1 microns 3 to 22,000 microns 3 with approximately 90% of the granules measuring less than 752 microns 3 (ca. 11 microns in diameter). Hard wheat samples had a greater number of small starch granules and a lower mean starch granule area compared to the soft wheat varieties tested. The starch size distribution curve was bimodal for both the hard and soft wheat varieties. Three-dimensional starch size distribution was measured for four cells near the central cheek region of a single caryopsis. The percentage of small granules was higher at the ends than at the mid-section of the cells.

Objective Assessment of Apple Maturity Based on Starch Location

ABSTRACT PHYSIOLOGICAL maturity is a critical criterion in determining the suitability of an apple for long term storage. A test based on the location of starch in the apple is commonly used as one measure of maturity. In an effort to remove operator subjectivity and errors in grading, a computer based image processing system was developed to determine starch location and estimate maturity grade. Three algorithms were tested. One related the starch maturity index (SMI) to the ratio of starch-cleared to starch-filled cross-sectional areas in the apple. A second algorithm estimated the SMI based on the amount of starch-cleared area with respect to the apple core line and vascular bundles. A third algorithm graded the maturity of the apple with respect to SMI predicted storability. Although the first two algorithms did not predict the starch maturity index, the storability algorithm was able to classify Red Delicious, Golden Delicious and Granny Smith cultivars as to the suitability for long term storage.

Collaborative Analysis of Wheat Endosperm Compressive Material Properties

ABSTRACT The objective measurement of cereal endosperm texture, for wheat (Triticum spp. L.) in particular, is relevant to the milling, processing, and utilization of grain. The objective of this study was to evaluate the interlaboratory results of compression failure testing of wheat endosperm specimens of defined geometry. Parallelepipeds (bricks) and cylinders were prepared from individual soft and hard near-isogenic wheat kernels and compressed in two orientations (parallel and perpendicular to the long brush-to-germ axis). Compression curves were used to derive failure stress, failure strain, work density (area under the curve), and Youngs modulus. In all five laboratories, the ability to delineate hard from soft wheat endosperm material properties was quite high. Four laboratories compressed endosperm bricks in the same orientation, on edge; texture class (soft vs. hard) was consistently the greatest source of variation in analysis of variance models (F-values from 417 to 1401, Youngs modulus and ...