Use of Electronic Nose for Evaluation of Fruit Harvest Maturity, Variety, and Quality

Electronic nose (enose) crudely mimics the human smell (gas sensors) and their communication with the human brain.  The human olfactory system is by far the most complex and contains thousands of receptors that bind odor molecules and can detect some odors at parts per trillion levels and include between 10 and 100 million receptors.  Apparently some of the receptors in the olfactory mucus can bind more than one odor molecule and, in some cases, one odor molecule can bind more than one receptor.  This results in a mind-boggling amount of combinations that send unique signal patterns to the human brain.  The brain then interprets these signals and makes a judgment and/or classification to identify the substance consumed, based in part, on previous experiences or neural network pattern recognition.  The electronic nose often consists of non-selective sensors that interact with volatile molecules that result in a physical or chemical change that sends a signal to a computer which makes a classification based on a calibration and training process leading to pattern recognition.  The non-selectivity of the sensors results in many possibilities for unique signal combinations, patterns or fingerprints determined with multivariate statistical programs.  For enose sensors, the metal oxide semiconductors (MOS), conducing polymer, surface acoustic wave (piezoelectric sensors) are most common, but the newer Z-nose contain short columns such as are found in gas chromatographs.  It is only upon establishing a relationship to sensory perception that the enose can then be substituted for sensory panels in giving objective classifications for quality control, process monitoring, authenticity, shelf-life stability and differences between samples or products.  As a nondestructive instrument for testing of fruits and vegetables, it has been used to differentiate harvest maturity and storage conditions for tomato,  mango, strawberry, blueberry, and other fresh produce.  It has also been use to differentiate between healthy and diseased citrus leaves infected with citrus canker.