Plate 2-2 Air-tight plastic jars (500rnl capacity) fitted with a rubber septum, used fo r measurements of kiwifiuit ethylene production and respiration rate 40 Plate 2-3 The prototype II softness meter, developed by Massey University, measures deformation of the fiuit surface non-destructively 44 Plate 2-4 Kiwifi rm developed by Industrial Research Limited, Auckland, measures fiuit firmness non-destructively 45 Plate 6-1 Application of gas including ethylene and I-MCP into plastic containers (24L capacity) that contained 18 fiuit and one sachet (20g) of soda lime 127 CHAPTERONE INTROD UCTION CHAPTER ONE CHAPTER ONE INTROD UCTIONEthylene gas is known to be a potent promoter of fruit softening. It is produced naturally by ripening fruit and induces unripe fruit to ripen rapidly (Abeles et ai., 1992; Puig et ai., 1996). Kiwifruit are very sensitive to ethylene; concentrations as low as 0.01 Jll/1 reduced storage potential by 46 % at OCC and thus very low ethylene levels have the potential to cause the majority of loss of storage life of fruit . Although the minimum threshold limit of kiwifruit sensitivity to ethylene has not been determined (Harris, 1981), scrubbing ethylene levels to near zero should delay kiwifruit softening rate ( McDonald and Harman, 1982; Banks et aI., 1991).The overall objective of the research presented in this thesis was to investigate factors that initiate the postharvest production of ethylene in kiwifruit and to attempt to elucidate the relationship ethylene production and softening in this important fruit.
Softening in kiwifruitKiwifruit softening occurs non-uniformly as the fruit has several distinctly different fruit tissue types (Hallett et aI., 1992� MacRae, 1988) (Fig. 1-1): core, seed area (inner pericarp) and flesh (outer pericarp). Shape of individual cells, and the way in which they are put together, differ in each tissue type. The core consists of small regularly shaped cells (dimensions between 0.1-0.2mm, 2.4 Jlm wall thickness) packed closely together with very fe w air spaces between them. Cells (inner pericarp) from the seed cavity are of two types, locule and locule wall. The locule area contains both seeds and radially elongated thin-walled cells (dimensions 0.2-0.4mm and up to >lmm, 2Jlm wall thickness). The locule walls consist of smaller thicker-walled radially elongated cells (0.05-0.1mm x 0.2-0.4mm, 2.9Jlm wall thickness) fitted closely together. Cells of the outer pericarp are irregular in shape and size (cross-sectional diameter 0.S-0.8mm and 0. 1-0.2 mm for large and smaller cells respectively, mean thickness of cell walls 2.5Jlm) and are loosely arranged together. There are relatively large air spaces between them. These different tissue types in kiwifruit have different effects on tissue firmness; cell wall breakdown, triggered by ethylene, was more pronounced in the outer pericarp and locule wall area of the inner pericarp than in the locule area of the inner pericarp and core tissues (Hallett et aI., 1992; Redgwell et aI. , 1990). When a penetrometer is used to
