Gary M. Hyde

Commodity conditioning to reduce impact bruising

This paper proposes tools for managing bruise threshold in apples, pears, and potatoes by controlling temperature, relative turgor, and strain rate. It includes information on the effects of these three factors on tissue failure stress and failure strain; and an equation for estimating bruise threshold based on these failure properties, Poissons ratio, and specimen mass and radius of curvature. In general, higher temperature and/or lower relative turgor (within limits) in potato tubers and some pear cultivars resulted in improved bruise threshold, while in apples, lower relative turgor improved bruise threshold but temperature had little effect. While some of this information has been available qualitatively or quantitatively for quasi-static loading, this work quantifies the relationships among these variables for impact loading. The theory of elasticity-based equation predicts that impact bruise threshold is directly proportional to tissue failure stress, to the 4th power of tissue failure strain, the 3rd power of radius of curvature, and inversely proportional to specimen mass. Preliminary validation work predicted apple and potato bruise thresholds within 23% of experimental values or better for assumed values of Poissons ratio. The relationship is already proving valuable in screening of new cultivars.

Non-contact bruise detection in apples by thermal imaging

Abstract Thermal imaging is a non-destructive and non-contact infrared sensing technique. Such imaging creates a bit-map called a thermogram by detecting infrared radiation emitted from an object. Up to 100% of apple bruises were detected using thermal imaging during warming of the fruits by discriminating surface temperature between bruised and sound tissues. Apples were bruised by dropping them from 0.46 m onto a smooth concrete floor and then were held at 26 °C and 50% RH for 48 h. They were then thermally imaged using a ThermaCam™ PM390 (FLIR Systems, Inc., Portland, OR) during heating and cooling treatments. Thermal images of bruised tissue showed at least 1–2 °C difference from sound tissue within 30–180 s. The temperature differences between bruised and sound tissues were possibly due to the differences in thermal diffusivity. Under steady-state temperature, thermal imaging did not detect bruises, indicating that the temperature differences were not due to emissivity differences. The technique could provide a basis for automatic bruise sorting, and possibly a better understanding of bruised tissue.

Specific gravity and cultivar effects on potato tuber impact sensitivity

This work investigated the influence of specific gravity on the impact sensitivity of individual potato tubers from three cultivars (Russet Burbank, Snowden and Atlantic). Specific gravity and impact sensitivity are both important quality measures in the potato industry. The two impact sensitivity measures used were: constant-height multiple-impacting (CHMI) of whole tubers to determine bruise volume, bruise energy, and bruise resistance; dynamic axial compression (DAC) of tuber tissue samples to determine failure stress, failure strain, shockwave speed, and predicted bruise threshold using a static prediction equation. The experiment was repeated the following year using only Russet Burbank tubers, with similar but less definitive results. That specific gravity variation in these experiments was natural and not achieved through dehydration. The results show that higher specific gravity tubers were more sensitive to impacts in the Russet Burbank and Atlantic cultivars, which showed lower bruise resistance and lower bruise thresholds with increasing specific gravity. Snowden showed higher bruise threshold, but lower bruise resistance with increasing specific gravity. A recently developed mathematical model was used to predict bruise threshold from tissue failure properties, tuber size, and tuber radius of curvature at the impact point.

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..

TURGOR AND TEMPERATURE EFFECTS ON DYNAMIC FAILURE PROPERTIES OF POTATO TUBER TISSUE

Both turgor and temperature affect the dynamic failure properties of potato tuber tissue and hence its impact sensitivity (bruise susceptibility). Russet Burbank and Atlantic cultivars of potato tuber tissue samples were loaded to failure under dynamic axial compression at 5, 10, and 15°C and 4 turgor levels corresponding to relative mass losses of 0-1.5%, 1.5-3%, 3-4.5%, and > 4.5% that resulted from air drying. Strain rate was constant at 80/s. Measurements were failure stress, failure strain, and shock wave propagation speed. Results showed that shock wave speed is an excellent measure of relative turgor within cultivar, with pronounced increases in wave speed with increased turgor. For both cultivars, increasing turgor resulted in significantly decreasing failure strain and tissue toughness, increasing secant modulus, and a slight decrease in failure stress. Turgor and temperature had very similar effects on the dynamic failure properties, suggesting that both variables alter the failure point through the same mechanism. The overall effect of temperature and turgor on failure stress, strain and toughness were very similar for both cultivars, implying that adjustments in either turgor or temperature, within these tested ranges, might have similar effects on the impact sensitivity of many potato cultivars. The effects of both temperature and turgor were large enough to affect tissue failure significantly. However, though Atlantic had consistently weaker tissue, Russet Burbank tissue strength was more sensitive to the changes in temperature and turgor. This difference implies that managing turgor and temperature to reduce bruising would be more successful with Russet Burbank.

A classification system for impact-related defects in potato tubers

The type of tuber bruise that occurs for a given severity of impact indicates the condition of that tuber in relation to its impact sensitivity. This article describes a system for classifying such bruises. Such information is important because sensitive tubers can be re-conditioned (e.g., temperature and/or hydration can be adjusted) to reduce risk of bruising during harvesting and handling. Each class of bruise is described, illustrated, and related to tuber condition. The literature review illustrates the inadequacies of previous bruise evaluation systems in relating bruise type to tuber condition. Growers, processors, storage operators and fresh packers can use this system to make informed decisions on adjusting modifiable factors such as temperature, hydration level, and impact velocity to reduce impact-related defects during harvesting and handling of potatoes.

TEMPERATURE AND STRAIN RATE EFFECTS ON THE DYNAMIC FAILURE PROPERTIES OF POTATO TUBER TISSUE

We measured effects of temperature and strain rate on the impact properties of potato tubers with the ultimate goal of managing temperature to reduce bruising during mechanical harvesting and handling. Tissue samples from the bud and stem ends of Solanum tuberosum cv. Russet Burbank and Atlantic tubers were loaded to failure under axial compression at 5, 10, 15, and 20°C and strain rates of 20, 50, 80, 110, and 150s–1, using instrumentation developed by the authors. Measurements included failure stress, failure strain, secant elastic modulus, last 50% elastic modulus, toughness (area under the stress-strain curve), impulse load, and shock wave speed. Temperature and strain rate dramatically affected the failure properties of both Russet Burbank and Atlantic tubers. Lower temperature and higher strain rate reduced tissue toughness. The stem end was tougher than the bud end. These results agreed well with impact sensitivity results for whole tubers under similar conditions as reported in the literature. The greater failure strength of Russet Burbank compared to Atlantic agreed with the potato industry observations that Atlantic is more impact sensitive than Russet Burbank.

The Effect of Potassium Deficiency on Chemical, Biochemical and Physical Factors Commonly Associated with Blackspot Development in Potato Tubers

Blackspot bruise is a physiological disorder of potato tubers resulting from mechanical damage to tissues during handling. This study examined the effect of potassium nutrition on biochemical and physical changes normally associated with blackspot bruise in potato tubers. Four potato (Solanum tuberosum L.) genotypes (TXA 763-5 [very resistant], Ranger Russet [very susceptible], Russet Burbank [susceptible], and Lemhi Russet [very susceptible]) differing in susceptibility to blackspot bruise were grown at three potassium nutrition levels (100%, 10% and 0% of the potassium in full strength Hoagland’s solution). Tubers from the three treatments were tested for their chemical, biochemical and physical characteristics commonly related to blackspot bruise susceptibility. The potential to develop malanin pigments was measured as total oxidative potential (optical density, OD475) of clarified tuber homogenates. Tuber tissue extracts were assayed for polyphenol oxidase (PPO) activity with catechol, measured as increase in OD410 over time. Specific gravity of tubers was determined with a brine solution series. Physical property measurements were made by impacting cores of tuber tissue in a specially designed instrumented pendulum. Shock wave speed, Young’s modulus, failure stress, and failure strain were all measured dynamically during impact. Tubers produced under both the 10% and 0% potassium regimens had almost 2x the free tyrosine of control tubers. The 0% potassium tubers had significantly higher PPO activity than the control. Both of these factors likely contributed to the significantly higher total oxidative potential that was observed in tubers from both the 10% and 0% potassium treatments. Tubers from both the 0% and 10% potassium treatments had a significantly lower Young’s modulus (a measure of stiffness), significantly lower failure stress and the shock wave of impact propagated through both of them significantly slower. Although the cultivars were significantly different in their susceptibility to black pigment development, they all responded similarly to the treatment with regards to the variables measured. The TXA-763-5 clone was much more susceptible to developing black pigments in these tests than expected. The other three cultivars performed as they do in commerce.

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.

Effects of mannitol on turgor and on failure stress and strain in potato tuber tissue

Abstract Discrepancies between preliminary results and published literature prompted an investigation into the effects of mannitol manipulation of turgor on failure stress and strain in potato tuber tissue. Tissue samples from two potato tuber cultivars ( Solanum tuberosum cv. Russet Burbank and Atlantic) were treated in 0.15 M (hypotonic) and 0.35 M (hypertonic) mannitol (C 6 H 14 O 6 ) solutions to determine whether mannitol changes fundamental tissue failure properties beyond the effects of turgor change. The use of mannitol for turgor pressure adjustment either above or below the isotonic concentration resulted in distortion of tuber tissue failure properties under dynamic axial loading conditions for potato tissue samples 10 mm in diameter by 15 mm long for both the Russet Burbank and Atlantic cultivars. Sample length did change and shock wave speed (a small strain property) behaved similarly to samples naturally dehydrated. However, the failure stress and strain tended to increase with time regardless of the mannitol treatment, even when these variables should have decreased. Results of this work confirm that mannitol solutions alter both turgor and the potato tuber tissue failure properties under dynamic loading and therefor should not be used to adjust turgor pressure in experiments investigating failure properties.