Browsing by Author "Davie, Ivan John"
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- ItemInfluence of handling at harvest on the softening behaviour of kiwifruit : a thesis presented in partial fulfilment of the requirements for the degree of Master in Horticultural Science at Massey University, New Zealand(Massey University, 1992) Davie, Ivan JohnThe New Zealand Kiwifruit industry in 1991 lost an estimated $54 million due to premature softening of kiwifruit during postharvest storage. The present study sought to determine if premature softening might be associated with the physical damage resulting from handling at harvest. The influence of physical damage on fruit was investigated on fruit from eleven kiwifruit properties from the Bay of Plenty region in New Zealand. Fruit were harvested and stored at 0°C and 20°C; firmness was destructively assessed. Softening behaviour of fruit sampled immediately after harvest from the vine (no physical damage) were compared with fruit from the same orchard block handled through the normal postharvest handling chain and packed in a packhouse. Analysis of variance and nonlinear regression using two, three and four parameter models were used to help in describing any differences in firmness values for fruit held in cool storage (0°C). The advantages and disadvantages of using analysis of variance and nonlinear regression to describe differences in firmness values between treatments are discussed. Analysis of variance determined that the packhouse and vine fruit on average were of a similar firmness. Nonlinear three parameter model: Firmness = a exp-bt + c (starting values: a = 6, b = 0.01 and c = 0.5) where: a = difference between initial and final asymptotic firmness b = exponent describing rate of decline in firmness c = final asymptotic value for fitted firmness was found to best characterise changing fruit firmness values over time. An analysis of variance was then performed on the resulting parameter values a, b and c which found that vine fruit on average had a slightly faster rate of softening than packhouse fruit. Packhouse fruit were not expected on average to have a similar firmness to vine fruit, as packhouse fruit were thought to have been exposed to potentially damaging impacts during handling. This may have been due to vine fruit being of a smaller size, position of fruit trays in cool storage or the rewarming of fruit during transportation. A non-destructive measure of firmness would help to identify the factors leading to premature softening and help to quantify fruit to fruit variability. A second part of this study therefore involved development and evaluation of a non-destructive instrument for measuring kiwifruit firmness (softness meter) compared with a penetrometer and its ability to repeatedly measure an individual fruit's firmness over time. The non-destructive softness meter characterised fruit firmness by measuring changes in deformation over time. Plots of deformation versus the natural log of time were linear and the gradient of the line was used as the measure of firmness (softness coefficient). Fruit with a range of firmness values were assessed using the softness meter, then penetrometer readings were obtained on the same location of each fruit and the relationship between the two instruments established. Within-fruit variation for both softness coefficients and penetrometer data was strongly related to fruit firmness, with coefficients of variation remaining approximately constant at about 10% for each variable. The softness meter will help to identify how localised treatments applied to fruit affect firmness and help to identify premature softening causes in individual fruit.
- ItemRole of calcium and mechanical damage in the development of localised premature softening in coolstored kiwifruit : a dissertation presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Plant Science at Massey University(Massey University, 1997) Davie, Ivan JohnPreharvest, harvest, and postharvest factor(s) were examined to identify the causes of premature quality loss during long term coolstorage of kiwifruit (Actinidia deliciosa). Investigation centred around the role of mechanical damage and calcium in the development of softening disorders, including soft patches (localised soft areas on fruit surface), premature softening, and low temperature breakdown (LTB) during storage. Kiwifruit were vulnerable to compression and impact from harvest onwards, with damage usually being expressed after a period of coolstorage. Physical damage normally just affected the fruit tissue in direct contact with the applied force. Impact damage, and to a lesser extent compression damage, depended on the size of the force and firmness of fruit when damaged. As kiwifruit softened, their susceptibility to soft patch development as a result of physical damage increased whereas the likelihood of flesh fracture in response to impact declined. These changes are attributed to the change in nature of the flesh, which is 'brittle' at harvest and 'viscoelastic' after softening. Physical damage to coolstored kiwifruit caused a slight drop in final firmness whereas there was no effect on firmness if it occurred at harvest. Fruit with softening disorders consistently had lower calcium contents (about 12% less) than equivalent healthy fruit. Fruit with soft patches had a high phosphate content, low dry matter, and at harvest, a low soluble solids content. A causative role for calcium in soft patch development was demonstrated by preharvest calcium treatments that elevated calcium content of the harvested fruit. Other orchard factor(s) were probably the cause of a weaker relationship between calcium content at harvest and storage behaviour of fruit. Although firmness at harvest declined with later picking, after coolstorage, fruit harvested more mature had a higher firmness and lower incidence of LTB. Symptoms for LTB were consistent with chilling injury whereas soft patches appeared to be due to localised premature senescence and not low temperature. A conceptual model of key factor(s) which cause the initiation and development of softening disorders in kiwifruit is proposed. Implications of this model for further investigation of these phenomena and for commercial handling of fruit are discussed. Further development of this model to produce a predictive model of fruit storage potential would require further characterisation of other important influences in storage behaviour