Notes
Evaluation of the Relationship Between Shock and Bruise Area of Apple Fruit
2016 Volume 22 Issue 4 Pages 485-489
Details
2016 Volume 22 Issue 4 Pages 485-489
We evaluated the effect of both the change in velocity (Vc) and the peak acceleration (PAcc) on the bruise area (BA) of apple fruit by shock tests. The results demonstrated that the BA of apple fruit caused by shock changes depends on a combination of Vc and PAcc. We also drew damage boundary curves (DBCs) corresponding to the BAs that were determined from the combination of Vc and PAcc. Moreover, by using a multiple regression analysis, we inferred that an increase in the BA of apple fruit due to shock is caused by an increase in the PAcc, rather than the Vc; the relative contributions of the independent variables in the regression for Vc and PAcc were 0.48 and 0.71, respectively. This finding will contribute to the consideration of measures to counteract the occurrence of bruising of apple fruit during transport.
When a product is delivered a pulsed shock pulse, the extent of damage is determined by two factors of the shock pulse: change in velocity (Vc) and peak acceleration (PAcc). Here, Vc is equal to the area under the time (t)-acceleration curve of the shock pulse (Fig. 1); it is equivalent to the total energy to be given to a product by the shock pulse. PAcc is equal to the height of the t-acceleration curve of the shock pulse; it is equivalent to the maximum power to be given to a product. This is summarized by the damage boundary curve (DBC) theory (i). By drawing the DBC (Fig. 2) from a shock test under several conditions of Vc and PAcc, we can determine whether a product will be damaged. Thus, measures against damage can be reliable.
Image of the relationship between peak acceleration (PAcc) and change in velocity (Vc) for a half-sine shock pulse
Image of a damage boundary curve (DBC) obtained from half-sine shock pulse
The DBC theory has been applied to evaluation of damage to fresh products such as fruits and vegetables. There have been applications to peaches (Maness et al., 1995), potatoes (Mathew and Hyde, 1997), apples (Lu and Wang, 2007), and strawberries (Kitazawa et al., 2014). In these studies, the DBC theory was used to evaluate the relationship between specific shock conditions and the probability of damage.
Consumers primarily judge fresh produce based on its appearance (Jiang et al., 2001; Opara and Pathare, 2014). Therefore, it is important to clarify the relationship between shock stress and the appearance of damage. Considering this point, the effect of shock on damage to fresh produce has been evaluated. For example, for peach fruit, the relationship between shock energy and the width, depth, and volume of the bruised part was evaluated (Schoorl and Holt, 1980). Lu et al. (2010) evaluated the effect of PAcc on the bruise area (BA) of apple fruit. Moreover, Yu et al. (2014) observed the effect of differences in blueberry fruit firmness on the BA. However, there are few reports on the effect of both Vc and PAcc on the BA of fresh produce.
Thus, the aim of this study was to clarify the effect of Vc and PAcc on the BA of apple fruit, and to draw DBCs corresponding to combinations of both factors. Measures against the bruising of the fruit during transport will be optimized by clarifying whether Vc or PAcc is the primary factor in bruise occurrence. Therefore, we also statistically analyzed which was the main factor affecting the size of the BA.
Fruit material We used the yellow-green apple cultivar ‘Orin’ for ease of identifying the bruised area. The mean fruit diameter was 86.9 mm in the vertical direction and 83.8 mm in the horizontal direction, and the weight was 306.9 g. It was reported that the firmness of the ‘Orin’ cultivar immediately after harvest is about 65 N or more (Iwanami et al., 2005; Miller et al., 2004). However, we used more mature samples, which bruise easily due to shock. The firmness of our samples measured by a fruit firmness tester with a 5 mm diameter plunger (KM-5, Fujiwara Scientific, Tokyo, Japan) on the equatorial surface of fruit was 28.3 N; this value was similar to that for fruit stored over one month at 20°C (Tatsuki et al., 2007). Additionally, the fruit color was nearly yellow.
Shock conditions Half-sine shock pulses were generated by a shock tester (SDST-300, Shinyei Testing Machinery, Tsukuba, Japan) with a buffer adjuster (SVS-300, Shinyei Testing Machinery, Tsukuba, Japan) (Fig. 3). Vc of the shock pulse was adjusted to 2.50, 3.00, 3.50, 4.00, 4.50, and 5.00 m/s, while PAcc was set to 392.3, 490.3, 588.4, 686.5, 784.5, 882.9, 980.7, and 1372.9 m/s2 (i.e., 40, 50, 60, 70, 80, 90, 100, and 140 G, respectively). These adjustments were carried out with an accelerometer (2351AW, Showa Sokki, Tokyo, Japan) and shock analysis system consisting of a device (SMH-12, Shinyei Testing Machinery, Tsukuba, Japan) and software (SMS-500, Shinyei Testing Machinery, Tsukuba, Japan). The conditions for Vc = 2.50 m/s + PAcc = 882.9 and 980.7 m/s2, and Vc = 3.00 – 5.00 m/s + PAcc = 1372.9 m/s2 could not be set due to the design of the shock tester and the buffer adjuster. Thus, the total number of shock conditions we tested was 41.
Testing setup. (A) shock tester and (B) buffer adjuster (left image), with right enlarged image showing how apple fruit was arranged and fixed:
(a) shock table, (b) apple fruit, (c) rubber sheet to fix the fruit, (d) steel plates to fix the rubber sheet, and (e) accelerometer
Evaluation of BA of fruit The fruit was placed sideways on the table holding the shock tester, and fixed to the table by two pairs of steel plates and a 5 mm thick rubber sheet (Fig. 3). Then, shock pulses were applied to the equatorial surface of the fruit. Each shock pulse was applied once to a single piece of fruit. One day later, the width of the bruised part (Fig. 4) was measured with a caliper (CD-20CX, Mitsutoyo, Kawasaki, Japan). The BA values [× 10−4 m2] corresponding to each set of shock conditions were calculated by the equation obtained by Lu et al. (2010):
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Example of fruit bruise due to shock
W1 and W2 represent bruise widths along the major and minor axes.
Statistical analysis Multiple regression analysis was performed to see how Vc and PAcc were related to BA. In this case, Vc and PAcc were explanatory variables while BA was the objective variable. The analysis was performed using a linear model function of R statistical software, version 3.0.0 (ii).
The relationship between Vc, PAcc, and BA Fig. 5 shows the relationship between Vc, PAcc, and BA. BA values ranged from 5 to 14 [× 10−4 m2] and monotonically increased with increases in both Vc and PAcc. With a fixed Vc, BA linearly increased with PAcc (Figs. 5–7). On the other hand, with a fixed PAcc, BA linearly increased with Vc. This shows that both Vc and PAcc are factors affecting BA.
The DBCs corresponding to several BA values [× 10−4 m2] of apple fruit due to shock Each number indicates the values of BA.
The solid and dashed lines connect the upper and lower points, which are estimated to have the same value of BA.
Example of shock pulses used in this study
The combination of Vc [m/s] and PAcc [m/s2] for A, B, C, and D were 3.0 + 490.3, 3.5 + 588.4, 3.5 + 980.7, and 4.5 + 980.7, respectively.
The current results also suggest that various combinations of Vc and PAcc corresponding to the same BA were not the same, and we can draw DBCs corresponding to each BA. Although several past studies proposed to clarify the relationship between specific shock conditions and the probability of damage of fresh produce by drawing DBCs (Maness et al., 1995; Mathew and Hyde, 1997; Lu and Wang, 2007; Kitazawa et al., 2014), the current result is an advance in clarifying the relationship between Vc, PAcc, and BA for apple fruit.
Regression equation To perform a quantitative analysis of the relationship between Vc, PAcc, and BA, regression analysis was performed and the following equation was obtained:
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The above regression analysis shows that the coefficients for both Vc and PAcc were significant (i.e., P < 0.01). The multiple R-squared value was 0.7, and the predicted BA and the observed value correlated well (Fig. 8). The standardized partial regression coefficients, which are an index of the relative magnitude of contribution of an independent variable in the regression, for Vc and PAcc were 0.48 and 0.71, respectively; thus, PAcc furnished a greater contribution to the BA. The intercept of the above equation was −1.7 and the difference from 0 was statistically significant. In reality, the bruise area is 0 when both Vc and the PAcc are 0. This may suggest that a shock which gives a BA smaller than 0 does not bruise the fruit, and also suggests that a no-damage boundary obtained from PAcc and Vc exists. However, the regression equation is valid only in the study range, which was a Vc of 2.5 – 5.0 m/s and a PAcc of 392.3 – 980.7 m/s2. Outside that range, the relationship between BA and Vc and PAcc is not clear but may be nonlinear, and Eq. (2) does not predict BA correctly. There are two possibilities: a low Vc and PAcc do not result in a nonzero BA, or a low Vc and PAcc produce a nonzero BA but the regression coefficient is much less than in Eq. 2. In either case, damage to the apple fruit increases quickly through excessive Vc and PAcc.
The relationship between the measured BA and predicted BA, based on the multiple regression equation of Vc and PAcc
The present study demonstrated that BA of apple fruit caused by shock depends on the combination of Vc and PAcc. Moreover, we present the DBCs corresponding to BA values as determined by various combinations of Vc and PAcc. Our results also suggest that the expansion of BA of apple fruit due to shock is caused by an increase in PAcc, rather than Vc. This finding will contribute to the consideration of measures to protect against bruising of apple fruit during transport. Our future works will focus on finding suitable cushioning materials for reducing PAcc. Moreover, we will discuss the bruise boundary as a factor in consumer acceptance.
Acknowledgements This study was supported by a Grant-in-Aid for Young Scientists (B) (No. 26850160) of the Japan Society for the Promotion of Science (JSPS).
Damage Boundary Curve
Bruise area, m2
PAccPeak acceleration, m/s2
πThe ratio of the circumference of a circle to its diameter
tTime of shock, ms
VcVelocity change, m/s
W1Bruise width along major axis, m
W2Bruise width along minor axis, m
