Dr Valentina Ting

PhD
Food Science

Contact

Ext
Email valentina.ting@otago.ac.nz
Location

Monitoring volatile organic compound (VOC) release in relation to microstructure and texture characteristics in apples.

Supervised by Dr Franco Biasioli (Fondazione Edmund Mach, Italy), Associate Professor Pat Silcock and Professor Phil Bremer.

About

Valentina who is originally from Malaysia recently completed a PhD project on apple flavour and texture, jointly supervised by researchers in Italy (Fondazione Edmund Mach) and New Zealand (University of Otago). To complete her project Valentina spent 6 months a year in each country and  studied apples from two seasons a year. Valentina completed a Bachelor of Science (Honours) degree in 2010 from the University of Otago, Dunedin, New Zealand. Her interests include food, music and travel.

Project Outline

Investigating, in different apple cultivars, the relationship between volatile organic compounds (VOC) and texture.  This project used a quick and easy direct injection mass spectrometry technique known as a proton transfer reaction mass spectrometer (PTR-MS) and in-vivo nose space sampling to quantify VOC release, in real-time, during the consumption of an apple.  Preliminary results showed that firm cultivars such as Fuji took longer to consume and released less ester VOCs compared to softer Golden Delicious apples which emitted more VOCs and were consumed faster. Although Fuji apples took longer to consume, panellists had a shorter time to first swallow compared to when eating Golden Delicious apples, suggesting that as Fuji is a juicier cultivar it induces swallowing faster as more juice is released during mastication. This observation led to the next research question which was on the influence an apple’s mechanical properties have on the breakdown pattern of its flesh.

Apples are climacteric fruits that continue to ripen after harvest. During prolonged storage, ripening leads to an increase of VOCs and the slow dissolution of cell walls. Here, juice that was once held within a cellular matrix permeates through the cells. In some cases, apples can “dry out” due to an excessive loss of moisture. Cell wall breakdown and moisture loss (flaccid tissue) can result in the increased formation of intercellular spaces and the undesirable mealy, floury or grainy texture experienced by consumers when eating soft apples. To investigate the relationship between the morphological properties (porosity, intercellular space size) in an apple microstructure and texture, a visual microscopy technique known as the X-ray microcomputer tomographic, µ-CT scanner was used. Images from the µ-CT scanner generate 3-D structures showing the apple microstructures. In general, results showed firm apples contained a low porosity and a higher dry matter (%), while the opposite was true for soft apples. However, this trend was not visible for all cultivars. Specific differences from the microstructural organization appear to influence the mechanical strength of the parenchyma tissue. This in turn, impacts perceived firmness. For example, a firm Fuji apple may be similar in porosity compared to a softer Golden Delicious. When the µ-CT images were visualized, Fuji apples appeared to contain a lot of smaller and more compact intercellular spaces, compared to Golden Delicious which contained larger interconnected intercellular spaces. It is hoped that these findings will contribute to understanding eating quality in apples.