Electronic tongue response to chemicals in orange juice that change concentration in relation to harvest maturity and citrus greening or Huanglongbing (HLB) disease

Authors: Raithore, Smita; Bai, Jinhe; Plotto, Anne; Manthey, John; IREY, MIKE - Us Sugar Corporation; Baldwin, Elizabeth - Liz

Submitted to: Sensors
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2015
Publication Date: 12/2/2015
Citation: Raithore, S., Bai, J., Plotto, A., Manthey, J.A., Irey, M., Baldwin, E.A. 2015. Electronic tongue response to chemicals in orange juice that change concentration in relation to harvest maturity and citrus greening or Huanglongbing (HLB) disease. Sensors. 15(12):30062-30075.

Interpretive Summary: The electronic tongue (etongue) crudely mimics the human taste system. The human tongue has sensors that react to sugars, acids, salts, limonoids and flavonoids sending signals to the brain that does pattern recognition for perceived sweetness, sourness, saltiness, bitterness and astringency. The etongue has sensors that react to a food or juice and send signals to a computer, which through software, does pattern recognition and determines that one sample is different from another. The citrus industry is undergoing a major challenge due to citrus greening or Huanglongbing (HLB) disease that is killing trees and causing off-flavor in the juice due to lower sugars, sometimes higher acids and higher levels of bitter limonoids and astringent flavonoids. These compounds also change during the orange harvest season. In this study, the etongue was able to distinguish between orange juices from healthy or HLB-affected trees as well as juices from fruit harvested at different times during the harvest season. This research further showed that the etongue sensors reacted to different levels of sugars, acids, limonids and some flavonoids spiked into orange juice, in the range at which they change due to HLB or over the harvest season. Thus, it was demonstrated that the etongue could be used as a quality control tool by orange juice processors.

Technical Abstract: In an earlier study, the electronic tongue system (etongue) was used to differentiate between orange juice made from healthy fruit and from fruit affected by the citrus greening or Huanglongbing (HLB) disease. This study investigated the reaction of an etongue system to the main chemicals in orange juice that impact flavor and health benefits and are also are impacted by HLB. To this end, orange juice was spiked with sucrose (0.2,-5.0 g/100 mL), citric acid (0.1-3.0 % g/100 mL) and potassium chloride (0.1- 3.0 g/100 mL) as well as the secondary metabolites nomilin (1- 30 µg/mL), limonin (1-30 µg/mL), limonin glucoside (30-200 µg/mL), hesperidin (30- 400 µg/mL) and hesperetin (30-400 µg/mL). Performance of Alpha MOS sensor sets #1 and #5 were compared for the same samples, with sensor set #1 generally giving better separation than sensor set #5 for sucrose, sensor set #5 giving better separation for nomilin and limonin, both sets being efficient at separating citric acid, potassium chloride, hesperitin and limonin glucoside, and neither set discriminating hesperidin efficiently. Orange juice made from fruit over the harvest season and from fruit harvested from healthy or HLB-affected trees were separated by harvest maturity, disease state and disease severity.