Simple Method for Apples' Bruise Area Prediction

Abstract

From the producers' point of view, there is no universal and quick method to predict bruise area when dropping an apple from a certain height onto a certain type of substrate. In this study the authors presented a very simple method to estimate bruise volume based on drop height and substrate material. Three varieties of apples were selected for the study: Idared, Golden Delicious, and Jonagold. Their weight, turgor, moisture, and sugar content were measured to determine morphological differences. In the next step, fruit bruise volumes were determined after a free fall test from a height of 10 to 150 mm in 10 mm increments. Based on the results of the research, linear regression models were performed to predict bruise volume on the basis of the drop height and type of substrate on which the fruit was dropped. Wood and concrete represented the stiffest substrates and it was expected that wood would respond more subtly during the free fall test. Meanwhile, wood appeared to react almost identically to concrete. Corrugated cardboard minimized bruising at the lowest discharge heights, but as the drop height increased, the cardboard degraded and the apple bruising level reached the results as for wood and concrete. Contrary to cardboard, the foam protected apples from bruising up to a drop height of 50 mm and absorbed kinetic energy up to the highest drop heights. Idared proved to be the most resistant to damage, while Golden Delicious was medium and Jonagold was least resistant to damage. Numerical models are a practical tool to quickly estimate bruise volume with an accuracy of about 75% for collective models (including all cultivars dropped on each of the given substrate) and 93% for separate models (including single cultivar dropped on each of the given substrate).

Keywords: apple; bruise volume; drop test; free fall test; nonlinear estimation; numerical model.

Figure 1

Scheme of free fall test procedure.

Figure 2

Procedure for image processing and determination of a bruise surface area: (a) peel removed; (b) bruise perimeters determination; (c) bruise area determination.

Figure 3

Method of slope, intercept, limit value indicator, and model angle determination.

Figure 4

Distribution of apple bruise size in relation to drop height for different apple varieties.

Figure 5

Distribution of apple bruise size as a function of drop height for different substrates.

Figure 6

Determination of substrates models based on averaged test results of apple bruise area as a function of drop height.

Figure 7

Substrates combined models.

Figure 8

Quantitative analysis of fruit bruise volume for different substrates.