*3.2. Bruise Susceptibility*

Table 1 displays the impact energy associated with each package configuration based on the mass of the package system and the drop height. The impact energies at each of the drop heights were effectively the same, noting the difference being the lighter mass of the EPS tray compared to the MF tray. Although the impact energies of the two package systems were similar, the bruise susceptibility, in terms of the ratio of the bruise volume to the impact energy [7], was greater for apples packaged using MF trays (Figure 8). These results indicate the EPS trays were able to absorb more of the impact energy, reducing the amount of energy transferred to the apple during the impact event. Although the MF tray reduces the lateral movement of the apples, it provides minimal energy absorption during vertical impacts, resulting in the apples being exposed to greater impact energy and subsequent bruising. The apple package system absorbs the energy through stretching of the trays, container sidewall buckling, and compression between the apple contact surfaces [28,32]. The most significant difference in the two package systems evaluated during this study was the compression of the apple contact surfaces. The EPS trays were able to reduce the compression between apples better than the MF trays.

**Figure 8.** Bruise susceptibility of apples by tray location packaged using MF and EPS trays from 30 and 50 cm drop height (mean ± SD, *n* = 2). Different letters indicate statistically significant differences at *p* < 0.05. Bars with no common letters are significantly different (*p* < 0.05).

To compare the protective cushion properties of the two trays, the resultant acceleration was recorded for each free-fall event. Figure 9 displays an example acceleration versus time curve from the individual impacts showing the apples' response to the free-fall impact. The impact accelerations were averaged for comparison for each treatment type (drop height and material type). As shown in Figure 10, the average acceleration of the apples packaged with the EPS tray was significantly less than that of the MF tray for both the 30 cm and 50 cm drops. The impact duration of the apples in the EPS were twice as long on average compared to MF trays. Comparing the trays from the 30 cm drop tests, the acceleration levels experienced by the apples increased by 30% for those packaged with MF trays. Additionally, examining the results from the 50 cm drop tests, the acceleration levels increased by 71% for apples packaged inside the MF as compared to those of the apples packaged inside the EPS trays. These results indicate that the EPS trays could absorb the impact energy from the event, resulting in less bruising as noted in previous sections.
