There is an increased interest in extending the market life of fresh cranberries as a result of the growing demand for fresh, healthful fruits. To supply this growing demand, fruit quality must be maintained and postharvest losses reduced during extended storage and marketing periods. However, for a variety of known and unknown reasons, successful storage of fresh cranberries has been variable and fruit loss is often excessive.
Unlike most fruit, the optimum conditions for the storage of fresh cranberry fruit are not clearly defined. In various handbooks published in the past 20 years, recommended storage temperatures range from 2 to 7 °C (Hardenburg et al., 1986; Kader, 1997; Kasmire and Thompson, 1992; Lidster et al., 1988; Prange, 2004; Spayd et al., 1990). Similarly, the relative humidity (RH) for storage recommended in these handbooks ranges from 80% to 95%. These recommendations are based on a limited number of studies, most being conducted over 60 years ago (Levine et al., 1941; Wright et al., 1937). These variable recommendations reflect the lack of clear differences reported in these studies, which may reflect inherent fruit properties that are influenced by cultural conditions, cultivars, harvest method, postharvest handling, and storage environment.
Postharvest loss of cranberry fruit is primarily the result of physiological breakdown and decay (Forney, 2003). Physiological breakdown is associated with overmature fruit (Doughty et al., 1968), bruising (Patterson et al., 1967), chilling injury (CI) (Hruschka, 1970), freezing (Bristow and Patten, 1995), extended water immersion (Ceponis and Stretch, 1983), and anoxia (Stark et al., 1974) and is characterized by a dull appearance, rubbery texture, and diffusion of red pigment throughout the fruit flesh (Bristow and Patten, 1995). Decay is caused by a complex of fungal organisms, including Allantophomopsis lycopodina (Hohn.) Carris (black rot), Allantophomopsis cytisporea (Fr.:Fr.) Petr. (black rot), Strasseria geniculata (Berk.& Br.) Höhnel (black rot), Coleophoma empetri (Rostr.) Petr. (ripe rot), Fusicoccum putrefaciens Shear. (end rot), Phyllosticta elongata G.J. Weidemann (berry speckle), Physalospora vaccinii (Shear) Arx & E. Müller (blotch rot), and Botrytis spp. (yellow rot) (Boone, 1995a, 1995b; Carris, 1995; Caruso, 1995; Oudemans et al., 1998; Pepin and Boone, 1995). Infection of the fruit may occur during bloom or wet harvest in the case of fungi causing black rot. Decay is characterized by external lesions and often only part of the internal flesh is red, whereas the unaffected flesh remains white. Unlike most postharvest decays in other crops, there is little spread of disease from infected to healthy fruit in storage (Oudemans et al., 1998).
Contributing to the uncertainty of optimum storage temperature is the fact that cranberries are reported to be chilling-sensitive and may develop physiological breakdown (CI) when stored at temperatures less than 2.2 °C (Levine et al., 1941; Wright et al., 1937). Chilling sensitivity of fruit may be affected by environmental, cultural, or genetic factors, which can alter their response to storage temperature (Patterson and Reid, 1990). In addition, fungal species and races causing fruit decay may vary depending on growing location (Caruso and Ramsdell, 1995). Therefore, decay development may be different in similar storage environments depending on the pathogens present (Bristow and Patten, 1995).
Most berry crops benefit from RH in storage of 95% or greater, which is effective in reducing water loss that would result in shriveling and physiological stress. However, reports indicate that cranberries store better in lower RH with suggested optimum storage RH being 65% to 70% (Stark et al., 1974) or 70% to 75% (Wright et al., 1937). However, in storage handbooks, recommendations are 80% to 90% (Lidster et al., 1988) and 90% to 95% RH (Hardenburg et al., 1986; Kader, 1997; Spayd et al., 1990). These higher recommended RHs are most likely influenced by the positive response of other fruit to high RH.
To clarify storage recommendations, a study was conducted to reassess the effects of temperature and RH on cranberry storage life. The objectives of this study were to determine the relationship among storage temperature, RH, and cranberry fruit storage life and assess the chilling sensitivity of cranberry fruit.
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