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Page last updated
29 Oct 2010
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Apples get bruised by static or impact forces that exceed the strength of the apple tissue. Most of the bruises that occur during harvesting and postharvest handling are caused by impact forces, so that's where we are concentrating our research efforts. The amount of impact bruising that occurs depends upon the number and severity of impacts that the apples experience and upon the bruise susceptibility of the fruit. Another article discusses number and severity of impacts in packing lines (Hyde and Zhang 1992). This article deals with apple bruise susceptibility.

We ran experiments to measure bruise susceptibility (bruise volume divided by impact energy absorbed, milliliter/Joule) versus storage humidity, temperature and cultivar (Red and Golden Delicious). We also measured both firmness and susceptibility over time.

Figure 1 shows humidity effects on the bruise susceptibility of Red and Golden Delicious apples.¹ The 50% relative humidity resulted in significantly lower bruise susceptibility than in the other humidities for both cultivars in this experiment

Figure 2 shows temperature effects on bruise susceptibility. Warming both cultivars to at least 60°F significantly reduced bruise susceptibility. In Figures 1 and 2 Reds were more bruise susceptible than Goldens. This was true also when the data were pooled across the whole experiment (Figure 3) and agrees with bruise threshold results from Michigan State University (Schulte et al. 1992).

This was true also when the data were pooled across the whole experiment (Figure 3) and agrees with bruise threshold results from Michigan State University (Schulte et al. 1993).

Figure 4 shows the change in apple firmness over the 5 weeks of the experiment for all of the apples stored at 100% relative humidity. While the Magness-Taylor firmness decreased significantly, the bruise susceptibility did not. So the bruise susceptibility was independent of the apple firmness, at least in this experiment.

These results show that temperature and storage humidity just before handling are very important in reducing the bruise susceptibility of both Red and Golden Delicious apples. The apples should be warmed to about 60°F before handling. Optimum combinations of temperature, humidity, and conditioning time for each cultivar are still unknown, but we will learn more about these factors if research funding becomes available.

Schulte, N. L., G. K. Brown and E. J. Timm. 1992. Apple Impact Damage Thresholds. Applied Engineering in Agriculture 8(l):55-60.

See Apple Bruising Research Update: Packingline Impact Evaluations, p. 12

This research was funded by the Washington State IMPACT Center at Washington State University.

¹In the graphs, the vertical lines are 95% confidence intervals. Generally, if an average value lies within the confidence interval of another, then those two averages are not significantly different.