Fruit Preservation by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9781493933112
Publisher: Springer New York

9.2.1 Database on Fresh Fruits

Data required for fresh fruits concern their optimal conditions of storage and their physiology, and more precisely parameters that permit to evaluate consumption and production of gases (i.e. oxygen and carbon dioxide) and vapours (i.e. moisture and ethylene) through respiration, transpiration and ripening pathways that can be described according to mathematical equations for some of them (presented hereinafter in Sect. 9.3). Once harvested, fresh fruits have to draw on their own reserves to maintain their cellular integrity. During respiration, stored carbohydrates are broken down into glucose, which is oxidized into CO2, water and energy (adenosine triphosphate, ATP) according to several enzymatic steps but limited by the activity of the cytochrome oxidase. As soon as these substrates become unavailable, other carbonated resources that are essential (constitutive protein or membrane lipids) are consumed, leading to the death of the produce. Thus the potential shelf life of fruits is closely related to their carbohydrates content and their respiration rate, expressed as the quantity of O2 consumed (or in a minor extend CO2 released) per time and per mass of produce: the lower is the respiration rate, the longer is the potential shelf life (Marcellin 1975; Paull 1993). Water production during respiration, i.e. transpiration, can also affect the shelf life of the produce depending on the temperature and most of all the surrounding humidity. If it is too low—threshold relative humidity (RH) commonly admitted is of 85 % (Roy et al. 1996; Varoquaux and Ozdemir 2005)—dehydration quickly occurs leading to wilting symptoms until depression of the commercial value of the commodity as soon as water loss reaches 5–6 % (w/w) of fresh weight. Then assessment of weight loss in controlled condition of temperature and RH give information on the potential shelf life of the produce. Along respiration and transpiration, ripening also contributes to the evolution of fresh fruits. Whether ripening is expected to bring optimal organoleptic qualities to the fruits, it is one of the major causes of their premature senescence and need to be delayed as much as possible during distribution and retailing. Since ripening pathway in climacteric fruits (based on the autocatalysis of ethylene) is now quite well understood compared to non-climacteric ones, it will be the only one discussed within this chapter. It can be characterized by ethylene production rate, expressed as the quantity of C2H4 produced per time and per mass of produce.

To develop powerful decision aid tools, database must be as large as possible; but acquisition of data that characterize those physiological pathways is a heavy work because of biological variability, possible contamination of fruits (e.g. microorganisms also contribute to O2 consumption and CO2 production and might affect the results on fruits respiration), absence of globally harmonized methodology of measurements (Fonseca et al. 2002), and dependence on temperature and RH. Some of these points are illustrated in Fig. 9.2 that presents oxygen consumption and ethylene production rates in two varieties of apricot during storage at different temperatures: Ravicille, a new variety with high blush, known

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