|dc.description.abstract||The “Gold3” cultivar of kiwifruit (Actinidia chinensis Planch. var. chinensis “Gold3”) has proven to be capable of producing high yields, however, growers have also noted an increased risk of small fruit that have high acidity, low dry matter and poor flavour. This thesis investigated how fruit composition and flavour components develop in “Gold3” kiwifruit, and whether altering the carbohydrate supply using common orchard practises would influence the accumulation and partitioning of the flavour components (starch, sugars and acids) in fruit.
Fruit from a “Gold3” orchard were sampled fortnightly, from anthesis through to harvest, from canes receiving five treatment combinations of leaf or fruit thinning and girdling. These treatments increased or decreased carbohydrate supply, either early or late in fruit development.
Overall, the “Gold3” fruit demonstrated similar patterns of starch, sugar and acid accumulation to other A. chinensis cultivars, in particular the gold kiwifruit cultivar “Hort16A”, with slight differences in timings and peak concentrations. An altered carbohydrate supply to developing fruit strongly influenced their composition in unique ways. As expected fresh weight growth and starch accumulation responded positively to a period of high carbohydrate supply. Regulation of organic acids were shown to be more complex, with the concentrations of some acids responding inversely to increased carbohydrate supply. At eating ripe the fruit from lower carbohydrate supply had altered sugar: acid ratios, with increased total acid concentrations, as well as decreased sugar concentrations.
To identify how these compositional changes affected the taste of fruit at eating ripeness, a controlled consumer sensory experiment was carried out with 78 inexperienced consumers. Fruit from the different treatments were all perceived as having acceptable flavours, despite the fruit having significant differences in the standard flavour determinants (DM, rSSC and TA). Consumers were able to detect differences in sugar and acid concentrations between treatments. Low carbohydrate supply treatments had significantly higher TA, citric acid and quinic acid concentrations, combined with lower °Brix, DM and sucrose concentrations at eating ripe. Consumers more closely associated these fruit with being more acidic and having more sour and under-ripe flavours compared to the treatments that received increased carbohydrate supply.
Overall the results of the research support the hypothesis that “Gold3” kiwifruit are vulnerable to changes in composition due to changes in growing conditions, and that these changes influence flavour as perceived by consumers. These effects may be more pronounced in orchards where high crop loads, shading, or variation in leaf to fruit ratio between shoots create populations of even more carbon deficient fruit.||