Consumers favor high-quality fruits, which are evaluated on their taste and appearance. For this reason, the fruits supplied to markets should meet the international quality standards for firmness, freshness, and certain other quality parameters (Lubes and Goodarzi, 2017). During the postharvest process, horticultural products are subjected to various external forces. When these forces surpass the critical value for tissue damage, they induce mechanical damage. Therefore, fruits can be damaged during handling, harvesting, transportation, and processing, and this damage has been described as a main source of decreased fruit quality, causing lower sale prices and losses to the grower or orchardist (Menesatti et al., 1999). Postharvest physical damage is common in tomatoes, even when the fruit is treated with care. Compared with other fruits, such as apples, tomatoes have lower storability, and they are susceptible to inappropriate conditions during harvesting, reloading, and transport (Abedi and Ahmadi, 2014; Tran et al., 2017).
Objective methods such as the use of data loggers and environmental factor sensors for monitoring the handling of vegetables and fruits are available. Monitoring the damage that occurs during the handling process is critical to understanding the causes of losses and to developing ways to overcome them. Information on the susceptibility of tomatoes to bruising is helpful for preventing and reducing bruise damage. Tomato bruises are not immediately visible, but they become apparent after handling and a certain amount of time on the shelf. Many studies have focused on the results of the mechanization of fruit grading and harvesting regarding different kinds of mechanical damage, and Allende et al. (2004) characterized factors that result in puncture damage during handling. Bruises develop in the flesh of the damaged fruit as an internal browning region resulting from the oxidation of phenolic compounds and tissue breakdown (Opara and Pathare, 2014). Currently, external bruising of tomatoes has not been clearly described in relation to internal bruising. Most researchers who have studied the influence of impact damage have studied externally visible damage instantly after harvesting or grading. These researchers often classify damage as visible permanent deformations (Sargent et al., 1989) or externally visible skin cracking and rupture (Geyer et al., 2002). Techniques to analyze damaged fruits with a nondestructive method have used thermal imaging devices (Cui et al., 2017a; Kheiralipour et al., 2013). Doosti-Irani et al. (2016) used a thermal imaging camera to assess the relationship between the deep internal temperatures of tested fruit and the external temperatures at the point where bruising appeared using thermal maps and thermal bruise depth. By multiple regression analysis, the results of analysis of variance showed that impact energy and impact region had a significant effect on temperature, which provided the basis of nondestructive fruit bruise detection. Despite the various types of damage studies, no such information is available on the combination of factors determining bruise susceptibility and actual impact-related bruise damage, and the assessment of drop–impact bruising associated with dropping tomatoes is lacking.
The bruise susceptibility of vegetables and fruits is a gauge for reactions to external forces and relies on some factors such as texture, variety, maturity, firmness, temperature, water status, shape, and size; as well as multiple internal factors, such as cell shape, cell wall strength, elasticity, and internal structure (Scheerlinck et al., 2006). Fruit texture is regarded as a primary contributing factor to bruise susceptibility and may differ significantly among fruits (Kerstens et al., 2000). Harker et al. (2010) performed a broad review of the different aspects of fruit texture and listed the factors that strongly affect fruit texture in general. The texture of tomatoes is basically reflected by the mechanical properties of pericarp tissue. Variations in the texture of a fruit change the mechanical properties of the fruit, thus influencing the bruise susceptibility of the fruit. An experiment involving a well-designed model of bruising is required to determine the factors that influence bruising susceptibility in tomato fruit. In the current study, impact force was monitored by an accelerometer at a farm. Then, bruising and changes in quality were observed by performing an experiment in the laboratory according to the analysis of the results from the farm. The current findings could help to determine threshold values for the extent of bruising that does not lead to further tissue damage and to evaluate of tomato bruising.
The objectives of the current study were to monitor the postharvest process at the farm and to develop multivariate analysis models using weight loss, firmness loss, and an assessment of bruising, together with fruit properties, impact force level, storage environment, and storage period as independent variables to determine the bruise susceptibility of red, ripe tomatoes.
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