Abstract
In an earlier study, an electronic tongue system (e-tongue) has been 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 e-tongue system to the main chemicals in orange juice that impact flavor and health benefits and are also impacted by HLB. 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 (pharmaceutical) and #5 (food) 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.
Highlights
Most of the oranges grown in Florida are used to make juice [1]
Important are the bitter limonoids, limonin and nomilin. These compounds are affected by HLB disease in that the disease can result in lower sugars, sometimes higher acids and higher levels of bitter limonoids and some flavonoids [4,5]
Orange juice was spiked with taste eliciting compounds, or others of similar structure, among which was sucrose, the major sugar in orange juice; citric acid, the major acid in orange juice; potassium chloride, the major salt in orange juice; limonin and nomilin; limonin glucoside; hesperidin the major flavonoid in orange juice; and hesperitin, the aglycone form of hesperidin [22]
Summary
Most of the oranges grown in Florida are used to make juice [1]. Consumer preference for juice largely depends on flavor quality, ensuring consistent flavor quality is of vital importance to juice processors. One of the procedures that processors employ to maintain uniform flavor within batches is the blending of juices with different color and chemical composition resulting in a final product that meets the criteria for acceptable orange juice [3]. The amounts of potassium in HLB-affected and healthy juice were not found to be consistently different, HLB juice was found to be saltier or having more umami flavor [6] (Plotto, unpublished data). This can result in orange juice that is less sweet, more bitter, saltier and more astringent [2]. Electronic tongue (e-tongue) technology has been used to assess the quality of a variety of foods [7,8,9,10,11]
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