Electronic noses and tongues: applications for the food and pharmaceutical industries

Abstract

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.

Keywords: biosensors; chemical sensors; flavor; gas chromatography; liquid chromatography; mass spectroscopy; multivariate statistics; neural networks; pattern recognition; sensory; shelf life.

Figure 1.

PCA plot of citrus juices based on the electronic nose signals. The observations are grouped by juice type, fresh squeezed orange juice (OJ) with high peel oil, processed OJ, processed OJ from Huanglongbing (HLB) infected fruit, and fresh squeezed tangerine juice.

Figure 2.

(A) Trained sensory panel rating of processed juice from Hamlin oranges harvested from healthy or Huanglongbing (HLB) diseased trees (2008) including juice from asymptomatic (normal looking) and symptomatic fruit (symptomatic for the disease: small, green and lopsided). Healthy juice was significantly higher in orange flavor, fresh and sweet tastes, and HLB juice was higher in sour/fermented, musty/earthy and salty/umami tastes. (B) E-tongue (AlphaMOS ASTREE) PCA plot of the same juice.

Figure 3.

(A) Trained sensory panel rating of processed juice from Hamlin oranges harvested from healthy or Huanglongbing (HLB) diseased trees (2009) including juice from asymptomatic (normal looking) and symptomatic fruit (symptomatic for the disease: small, green and lopsided). HLB symptomatic juice was significantly lower in orange flavor, fruity non-citrus, fresh and sweet tastes and higher in sourness and off flavors than asymptomatic or healthy juices, which were not different from each other. (B) E-tongue (AlphaMOS ASTREE) PCA plot of the same juice.

Figure 4.

E-tongue (AlphaMOS ASTREE) PCA plot of Hamlin orange juice processed in 2008 and 2009, from fruit harvested from healthy or from Huanglongbing (HLB) diseased trees including juice from asymptomatic (normal looking) and symptomatic fruit (symptomatic for the disease: small, green and lopsided).