Storage of green fruits

There is much demand for fresh, green, pungent and sweet peppers as they are a major ingredient of spicy foods, especially of Indian food items. Demand for fresh pungent peppers has greatly increased in the United States as south-western foods have become the most popular ethnic food (Lownds et al., 1994). Freshly harvested bell peppers have a shelf-life of only a few days since they lose water rapidly after being harvested (Anandaswamy et al., 1959; Ryall and Lipton, 1972; Showalter, 1973; Watada et al., 1987). Extending post-harvest longevity to meet the demand for fresh peppers, therefore, requires special attention.

Research on extending the shelf-life of fresh peppers is rather sparse. Loss of water content, flaccidity, changes in colour and development of diseases are some of the physical changes that occur during storage and which have a direct impact on the loss of fruit quality. The rate of water loss, flaccidity and colour development increase with an increased temperature (Lownds et al., 1994). Placing pepper fruits in perforated polythene pouches at 14-20°C reduced water loss rates 20 times or even more, eliminated flaccidity and reduced colour development. The development of diseases in packed fruits, however, results in a reduction of post-harvest quality (Lownds et al., 1994; Miller et al., 1984; Maiero and Waddell, 1991). In contrast,

Ben Yehoshua et al. (1998) reported that bell peppers packaged in perforated film lost less weight during storage and maintained a higher quality than fruits stored in open boxes. They also demonstrated that lower decay levels occurred in the fruits stored in perforated films compared to the non-perforated packing.

Post-harvest water loss of fruits is the major factor influencing the quality of the fresh fruits of peppers. Water loss was found to be positively correlated with the initial water content, ratio of surface area and volume and the cuticular thickness of the fruits and negatively correlated with surface area and epicuticular wax content and hence, is cultivar dependent (Lownds et al., 1993).

Shelf-life of fruits with thick exocarp is more compared to fruits with thin exocarp. However, the fruits with thick exocarp are tough, difficult to digest and, if processed, the exocarp peels off from flesh, and not preferred. On the other hand, fruits with very thin exocarp which are preferred by consumers and processing industry, are tender and readily bruised, cracked and crushed during post-harvest operations (Fischer, 1992, 1993). These mechanical injuries affect pepper quality and subsequent shelf-life which ultimately reduce the market grade. To reduce the damage during post-harvest operations all locations should be cushioned where peppers impact a hard surface and drop height should be limited to 8 cm on hard surface and 20 cm on a cushioned surface (Marshall and Brook, 1999).

Storage of fruits under controlled conditions was found to enhance their longevity (Yuen and Hoffman, 1993; Lownds et al., 1994; Ahmed et al., 1996; Mencimcopschi and Popa, 1999). Fruits can be stored for longer periods (14-28 days) at 8°C and more than 75% RH (relative humidity) with minimum change in chemical composition and market acceptability (Lownds et al., 1994; Ahmed et al., 1996). Further, storage can be extended for another six to eight months at freezing temperature with or without blanching (Lisiewska et al., 1994; Mencinicopschi and Popa, 1999). However, Sundstrom (1992) reports that bell peppers are subject to chilling injury, characterized by pitting of the fruits, if stored in temperatures less than 7°C. At storage temperatures above 10°C, however, further fruit ripening and the development of anthocyanin and red carotenoid pigments will occur. At these warmer temperatures, bacterial soft rot also becomes a major problem. Hence, the temperature range of 7—10°C at 90—95% RH is ideal for the storage of bell peppers for up to three weeks.

From these studies it is observed that water loss is no longer a limiting factor of fresh fruit longevity if the fruits are stored in a modified atmosphere or in perforated polythene film. However, the limiting factor under these conditions is the incidence of diseases. Bell peppers, after harvest, are graded and frequently run through a hot (53°C) water bath containing 500ppm chlorine to control bacterial rots. Following this process, most bell pepper fruits are sprayed with a wax emulsion to reduce moisture loss prior to being packed in cardboard cartons (Sundstrom, 1992). In another study, Fallik et al. (1996) found that dipping naturally infected fruits in water at 50°C for three minutes completely inhibited or significantly reduced the fruit decay caused by Botrytis cinera and Alternaria alternata without any adverse effect on fruit quality.

Since these studies are independent of storage conditions and specific to only a few pathogens, further studies are required to develop suitable storage practices in order to protect fruits from storage decay.

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