Consumer demand for high quality products has increased in the last decades, and is still increasing. One such aspect of quality is the detrimental effect of impact damage. This is not restricted to visual aspects, but higher risk of bacterial and fungal contamination, leading to a lower shelf-life, also results from this damage. Other collateral effects include water loss; moisture loss of a single bruised apple may be increased by as much as 400% compared to that of an intact apple
For most fruit types, including apples, bruising is the most common type of postharvest mechanical injury. A survey for 12 years in the New York market (summarized by Knee and Miller, 2002) indicated that 6% of apples were affected by bruising. In this survey, mechanical injury was never the most common defect for most fruit (including apples). Usually one or more kinds of fungal diseases exceeded the mechanical injury, pre- dominantly gray mold (Bortrytis) or blue mold (Penicillium). Like most postharvest pathogens, these organisms cannot infect healthy tissue, and typically enter through dead or wounded tissue before contaminating the rest of the fruit. It is likely that minor mechanical injuries were not counted by the mar- ket inspectors and were only manifested by their consequent fungal infections, and thus mechanical injury could be the most important cause of defects and disease. If mechanical injury could be avoided there would be less need for fungicides to pre- vent disease and there would be much less loss of fruit (Knee and Miller, 2002). Studman (1997) indicated that apple bruis- ing can result in product losses up to 50%, although typically loss levels are in the 10–25% range, depending on consumer awareness.
The economic cost of mechanical damage to apples in Bel- gium has also been estimated. The percentage of degraded apples identified during sorting, in which bruised apples were a major part, was 15 and 8% in 2000 and 2001, respectively. On the Belgian market the auction price for degraded apples (industrial apples, apples not suitable for fresh market) is 1/3 of the normal price. A reduction of only 10% in degraded apples could have led to an income increase for the growers of 892,000 D in 2000 and 595,000 D in 2001 (Van Zeebroeck et al., 2003). Further- more, some (smaller) bruise damage cannot be detected during grading and damage but can become visible later, leading to the presence of bruised apples in the supermarkets and stores and further losses.
The objective of this paper is to give a state-of-the-art review of impact bruising of apples by discussing the causes of impact damage, and by categorizing the research and discussing the most important results of each category.