Abstract
An electronic nose is an arrayed gas sensor mimicking the human olfactory system that can analyze and identify a flavour on collecting an odour from an environment. In our experiments, an electronic-nose system based on a surface acoustic wave (SAW) was used to measure the freshness of kiwifruit. 128° YX-LiNbO3 acted as a piezoelectric material; Au was deposited as an electrode and sensing area. With a polymer coating of various types on the sensing area and a connection to an oscillator circuit, a 113-114 MHz SAW was obtained. Depending on the properties of varied polymers, the frequency shift varied due to absorbed volatile organic compounds (VOC). In this way, with four surface-acoustic-wave sensors coated with varied polymers we built a kiwi-flavour database according to results from a TD-GC-MS system. When the concentration of esters increased, the kiwifruit began to ripen, accompanied by increased concentrations and types of VOC. As a result, polystyrene (PS) and fluoropolymer (CYTOP) polymers, which played the role of sensing materials, served as major materials to determine the ester aroma profile. Polyvinyl alcohol (PVA), polyvinyl butyral (PVB) and poly-N-vinylpyrrolidone (PNVP) were used to trap the alcohols and acids during a kiwifruit ripening period. This research proved that discrimination of differences is feasible from an unripe stage to a ripe stage and from a ripe stage to an over-ripe stage.
Highlights
As a valuable fruit crop, kiwifruit is widely appreciated by consumers for its rich nutrition such as vitamin C, amino acids and dietary fibers [1] and for its effective prevention of thrombosis, arteriosclerosis and coronary heart disease
After 80 years, two interdigital transducers on piezoelectric materials simulated a surface acoustic wave (SAW); this structure has been used until the present time [10]
On providing a time-varying electric field to one interdigital transducer, through a reverse piezoelectric effect a piezoelectric substrate transfers an electric signal to a mechanical signal, which is the SAW. Using another interdigital transducer to transfer a SAW to an electric signal, a signal output can be obtained [11], as shown in table 1
Summary
As a valuable fruit crop, kiwifruit is widely appreciated by consumers for its rich nutrition such as vitamin C, amino acids and dietary fibers [1] and for its effective prevention of thrombosis, arteriosclerosis and coronary heart disease. After 80 years, two interdigital transducers on piezoelectric materials simulated a SAW; this structure has been used until the present time [10]. On providing a time-varying electric field to one interdigital transducer, through a reverse piezoelectric effect a piezoelectric substrate transfers an electric signal to a mechanical signal, which is the SAW. Using another interdigital transducer to transfer a SAW to an electric signal, a signal output can be obtained [11], as shown in table 1. On measuring the frequency decrease, the nature of absorbed molecules and the concentration of VOC can be identified
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