# Application of an Electronic Nose as a New Technology for Rapid Detection of Adulteration in Honey
## 1 Introduction  
Honey is a natural sweet substance produced by honeybees (_Apis mellifera_) from plants' nectar or secretions of their living parts. This animal product is used in various applications, such as in _natura_; in sweeteners, phytotherapeutics [1], medicines [2], and cosmetics (for improving moisture, cleansing, miscibility, and spreadability) [3]; and as a food industry additive (antioxidant, enzymatic inhibitor, clarifying, and anti-browning agent) [4, 5], among others [6]. In general, honey's composition and physicochemical and organoileptic properties vary according to its botanical origin (the types of flowers used by the bees), geography and climate, processing, and storage [7]. Regarding chemical composition, honey is a mixture of sugars (mainly fructose, followed by glucose and sucrose), amino acids, proteins, enzymes, organic acids, carotenoids, vitamins, antioxidants, phenolic, minerals, trace elements, and volatile organic compounds (VOCs) [7, 8]. Focusing on the latter group, hundreds of different compounds have been identified in the volatile fraction of honey, among them being aldehydes, ketones, carboxylic acids, alcohols, hydrocarbons, terpenes, benzene, pyran, and derivatives [9, 10]. Due to its natural scarcity, increased demand, high production cost, and commercial value, honey has been one of the most adulterated products worldwide. Nowadays, the decrease in the global honeybee population due to environmental pollution and the spreadof insect diseases have further reduced honey availability, encouraging some producers to adulterate their products to obtain a more significant income [11]. Several types of adulteration are possible, such as direct incorporation of foreign substances into honey, blending with lower-cost honey types, or indirect adulteration of honey through bee feeding with industrial sugars [12]. In this sense, to reduce deliberate adulteration and incentivize good practice standards, the quality control of honey is a fundamental step. However, due to the heterogeneity of samples, with parameters varying considerably among honey types, and the addition of adulterants with physical-chemical properties similar to authentic honey, the quality control of this product involves several tests and a series of steps, which can take from hours to days and add substantial costs to the production chain [13]. Analytical methods used in food adulteration studies are often based on identifying and quantifying specific markers, such as some classes of compounds (carbohydrates, polyphenols, fatty acids). Usually, the techniques to unravel adulteration, such as chromatographic analysis, electrophoretic methods, spectroscopic methods, immunoassay assays, and isotope ratio mass spectrometry, require complex sample pretreatments, laborious, and time-consuming procedures; expensive analytical instrumentation; and specialized professionals [11; 12; 14; 15; 16]. According to the Codex Standard for Honey, for adequate honey quality control, the main parameters to be evaluated are sugars (fructose, glucose, and the ratio between them), moisture and water activity, free acidity and pH, ash and electrical conductivity, color, and 5-hydroxymethylfurral (5-HMF) content [13; 17]. E-noses are a device that mimics the human nose, recognizing gas patterns (smell) and relating to a known sample. In this equipment, gases or vapors interact with sensors, leading to variations in the system's physical properties according to the atmosphere's composition to which the sensor is exposed. By studying the variations in these properties through mathematical/statistical tools, it is possible to evaluate the sensor's performance in identifying or distinguishing VOCs and even in quantifying certain species present in the given sample. Among the advantages of using an e-nose, the low cost of manufacture and operation, easy handling, and low response time have been highlighted [18].