Needle-based sampling for fruit flesh

19 May 2016 NUS scientists have developed a simple sampling method for soft fruit flesh using a conventional syringe needle for mapping the three-dimensional (3D) distribution of vitamin C.

A team led by Prof LEE Hian Kee from the Department of Chemistry in NUS, together with his Ph.D. student, Mr TANG Sheng, has developed a syringe needle-based microsampling approach for vitamin C determination in multiple locations in a single fruit. This was demonstrated on apples. Only a small amount (ca. 10 mg) of apple flesh was sampled, held at the needle tip, and then transferred to a glass insert for liquid extraction using <80 μL of a suitable solution, which is then directly analysed. The procedure is simple, convenient, organic solvent minimised, and causes minimal damage to the fruit, allowing many samplings.This novel way to represent the results, specifically, vitamin C distribution, using 3D modelling technology, may be useful as a tool in fruit breeding programmes and production.

Conventional processesto determine beneficial native compounds in fruits are normally laborious, and consume a lot of solvents and fruit. Theseprocesses include collecting, cutting, mashing, and the homogenisation of multiple fruits (ca. 100-1000) for each study. Existing work involves these conventional processes: (1) fruits are harvested, cut and mashed first, and then the flesh is homogenised and extracted using moderate to large volumes of solvent (or the juice is obtained using a juice extractor); and (2) the aqueous solution from the homogenised sample (or juice) is extracted further by additional methods.

This is a destructive approach, where the sampling and processing are for a single analysis only. A fruit cannot be sampled more than once, and multiple locations in an individual fruit cannot be individually studied. These disadvantages prevent the continuous temporal measurement of fruit constituents. Thus, a more accurate distribution of a constituent in a fruit, which is helpful to determine the development of the fruit, cannot be obtained.

The procedure is applied to determine vitamin C (L-ascorbic acid) levels at different sampling locations in a single apple so as to reveal the spatial distribution of the compound in a 3D model. This interesting extraction technique and modelling approach can be used to measure and monitor a wide range of other compounds in various parts of different single-specimen soft-flesh fruits and vegetables. It should also be possible to remove flesh samples from individual fruits and vegetables directly in the field without harvesting them. A lot of wastage is therefore prevented.

If a single fruit can be left on the tree and sampled onsite using this procedure, it can be sampled many times at different points over a prolonged time for temporal analysis of the constituent of interest if suitable protection of the fruit is undertaken. This allows the long-term monitoring of the fruit’s development, possibly indicated by the changes in concentrations of that constituent. The practical application of this procedure can be investigated in future work.

Figure shows the needle-based sampling and the 3D distribution of L-ascorbic acid in an apple (top), and the analytical process shows the needle-based sampling; Liquid-phase extraction;Chromatographic analysis; 3D modelling and demonstration (bottom). [Image credit: TANG Sheng]

Reference

Tang S, Lee HK. “Syringe needle-based sampling coupled with liquid-phase extraction for determination of the three-dimensional distribution of L-ascorbic acid in apples.” Food Chemistry 199 (2016) 533.