Electronic Sensing of Fruit Ripeness Based on Volatile Gas Emissions

An electronic sensory system for the evaluation of headspace volatiles was developed to determine fruit ripeness and quality. Two prototype systems were designed, constructed, and later modified. The first is an improved version of our original prototype electronic sniffer using a single head sensing unit for use as a single or paired unit placed on an individual fruit surface for applications in the field, lab, or industry. The second electronic sniffer utilizes a matrix of gas sensors, each selected for differential sensitivity to a range of volatile compounds. This system is more sophisticated as it uses multiple gas sensors, but was found to enhance the ability of the sniffer to classify fruit ripeness and quality relative to a single gas sensor. This second sniffer was designed and constructed for the sampling of fresh-cut or whole packs of fruits such as packaged strawberries and blueberries, and can serve as a prototype for research or commercial applications. Results demonstrate that electronic sensing of fruit ripeness based on aromatic volatile gas emissions can be used successfully with fresh frits. Aroma sensing was successful for classifying ripeness in muskmelons, including different cultivars, apples, blueberries, strawberries, and in a complimentary BARD project on tomatoes. This system compared favorably to the physicochemical measurements traditionally employed to assess fruit maturity. This nondestructive sensory system can detect the presence of physically damaged fruits and shows excellent application for use in quality assessment. Electronic sensors of the tin oxide type were evaluated for specificity toward a wide range of volatiles associated with fruit ripeness. Sensors were identified that detected a broad range of alcohols, aldehydes, esters, hydrocarbons, and volatile sulfur compounds, as well as individual volatiles associated with fruit ripening across a wide concentration range. Sensors are not compound specific, thus, the matrix of sensors coupled with discrimination analysis provides a fingerprint to identify the presence of compounds and to assess alterations in fresh products due to alterations in volatile emissions. Engineering developments led to the development of a system to compensate for temperature and relative humidity relative to on-line aroma sensing with melons for ripeness determination and to reduce response time, thus permitting the electronic sniffer to be used for monitoring both fresh and processed food products. The sniffer provides a fast, reliable and nondestructive tool to assess fruit ripeness and quality. We hope that our work will foster the introduction and utilization of this emerging technology into the agricultural and horticultural