Postharvest Biology and Technology of Fruits, Vegetables, and Flowers

BIOSENSOR-BASED TECHNOLOGIES 419
20.2 Methods of analyzing quality
There are several standard methods that are currently used to monitor the quality of fruit
and vegetable produce. Basic methods of inspection include the following:
Visual monitoring (color, gloss, firmness, shape, and size of the product, as well as noting
the presence of defects).
Analysis of soluble solid content.
Monitoring of titratable acidity.
Most of these tests can be carried out immediately after harvesting on location at minimal
cost (Mitchum et al., 1996). However, if these tests are not sufficient for providing confirmation
to the consumer that a product satisfies acceptable regulations (mentioned later),
then it is a common practice for samples to be removed and sent to a central laboratory for
comprehensive in situ analysis (Giraudi and Baggiani, 1994). These methods of analysis
include the following:
High-performance liquid chromatography (HPLC) and gas chromatography/mass spectrometry
(GC/MS). These analytical methods are accurate and highly sensitive, but are
also time-consuming and beyond the analytical capacities of smaller operators (such as
“on-site” laboratories) as they require expensive instrumentation, lengthy sample treatment,
and trained personnel to analyze the data (Bäumner and Schmid, 1998).
The detection of indicator molecules that represent product freshness, including
flavonoids (MacLean et al., 2006).
Monitoring of bitterness (Dourtoglou et al., 2006).
Assessing product firmness (the Magness–Taylor test).
A nondestructive test, measuring an acoustic response from fruit with the signal being
interrogated using a fast Fourier transform, to determine elasticity (Shmulevich et al.,
2003).
Near-infrared spectroscopy (in a nondestructive, accurate, and rapid protocol) for the
detection of mycotoxigenic fungi and their toxic metabolites that are commonly found
in fruits and vegetables (Berardo et al., 2005).
The use of scanning electron microscopy. Schirra et al. (2005) developed a method to
inspect the ultrastructural changes of a fruit’s epicuticular layer when the dip treatment
pesticide, fludioxonil, was used to control Penicillium spp. infestations postharvest.
Biosensor-based platforms, such as Biacore
TM
and electrochemical sensors.
20.3 Biosensor technologies
Biosensors have been particularly successful for monitoring the presence of a variety of
analytes in fruit and vegetable produce (including pesticide and herbicide residues) that
may be present in minute quantities. A biosensor (Fig. 20.1) can be defined as an analytical
device that incorporates an immobilized biological element (see Table 20.1), which interacts
with an analyte of interest in “real time” (Scheller and Schubert, 1992). The three main
components of a biosensor are as follows:
A biological recognition component,
A transducer, and
A readout device (such as a computer).