The electronic nose (e-nose) is designed to crudely mimic the mammalian nose in that most contain sensors that non-selectively interact with odor molecules to produce some sort of signal that is then sent to a computer that uses multivariate statistics to determine patterns in the data. This pattern recognition is used to determine that one sample is similar or different from another based on headspace volatiles. There are different types of e-nose sensors including organic polymers, metal oxides, quartz crystal microbalance and even gas-chromatography (GC) or combined with mass spectroscopy (MS) can be used in a non-selective manner using chemical mass or patterns from a short GC column as an e-nose or “Z” nose. The electronic tongue reacts similarly to non-volatile compounds in a liquid. This review will concentrate on applications of e-nose and e-tongue technology for edible products and pharmaceutical uses.

Huanglongbing (HLB) or citrus greening disease is the most severe citrus disease, devastating the industry worldwide. The presumed causal bacterial agent Candidatus Liberibacter spp. affects tree health as well as fruit development, ripening and quality of citrus fruit and juice. Fruit from infected trees can be either symptomatic or asymptomatic. Symptomatic fruit are small, asymmetrical and greener than healthy fruit. Furthermore, symptomatic fruit show higher titratable acidity and lower soluble solids, solids/acids ratio, total sugars and malic acid levels, lower ethyl butanoate, valencene, decanal and other ethyl esters, straight-chain aldehydes and sesquiterpenes, but higher in many monoterpenes compared to healthy and asymptomatic fruit. The disease also causes an increase in secondary metabolites in the orange peel and pulp, including hydroxycinnamic acids, limonin, nomilin, narirutin and hesperidin. Resulting from these chemical changes, juice made from symptomatic fruit is described as distinctly bitter, sour, salty/umami, metallic, musty, and lacking in sweetness and fruity/orange flavor. Those effects are reported in both Valencia and Hamlin oranges, two cultivars that are commercially processed for juice. The presumed HLB pathogen remains unconfirmed and its management is challenging due to the unpredictable latency times for symptoms after the tree has become infected, and the lack of effective curative treatment methods. When present, disease management depends on incidence rate, and relies on vector control, tree eradication, nutritional programs and use of plant varieties with increased tolerance. Earlier research showed that HLB-induced off-flavor was not detectable in juice made with up to 25% symptomatic fruit. In some production regions, it is increasingly difficult to find fruit not showing HLB symptoms. This review focuses on the effects of HLB on orange juice quality regarding chemical, physicochemical and biochemical characteristics, including levels of sugars, organic acids, secondary metabolites, levels and profiles of amino acids, bioactive amines, volatile compounds and sensory characteristics, as well as future research needs.