## 2 Instrumental Measurement of Red Meat Sensory Quality
### Flavour  
Flavour is generally defined as the sensation resulting from the combinations of signals generated by the senses of smell, taste and irritating stimuli from a food or beverage [57]. Meat flavour develops through thermal processes, as uncooked meat has minimal aroma and only a flavour reminiscent of blood [58]. Although the flavour of cooked meat is shaped by a variety of compounds, the volatile compounds formed during cooking, primarily due to the Maillard reaction and the degradation of lipids [59], contribute the most to its aroma and unique flavour characteristics [58]. The Maillard reaction is typically divided into three stages [60]. The initial stage involves a condensation between an amino group and a reducing sugar, forming an N-glycosamine, which rearranges into the Amadori product in the case of an aldose sugar (or the Heyns product if the reducing sugar is a ketose) [61]. The intermediate stage begins with the Amadori/Heyns product, leading to sugar fragmentation products and the release of the amino group [62]. The final stage involves various dehydration fragmentation, cyclization, and polymerization reaction with the involvement of amino groups [62]. The Strecker degradation, in which amino acids are broken down by dicarbonyls generated in the Maillard reaction, is essential for flavour development [63]. However, the presence of an amino group in the Maillard reaction acts as catalyst, leading to faster reactions and higher amounts of reactive intermediate products [64]. Fat, especially intramuscular fat (IMF), acts as a flavour carrier and positively impacts tenderness and juiciness, which are closely linked to meat flavour [65]. During heating, unsaturated fatty acids seem to be more important compared with saturated, since they break down and produce a variety of flavour compounds [66]. When combined with the Maillard reaction compounds, they can create flavours with a stronger impact on taste [66]. Most of these flavour compounds come from phospholipids [67]. This is also shown by the fact that defatted meat without triglycerides has a similar flavour to regular meat, but defatted meat without triglycerides and phospholipids has a noticeable difference in flavour [68]. Analytical instrumental methods for the analysis of flavour in meat involve the separation and analysis of volatile (VOC) and semi-volatile (SVOC) flavour compounds in meat using gas chromatography (GC) techniques [69]. Sample preparation, including the extraction and the pre-concentration of the volatile compounds, which is considered the main limitation of this method, is the primary step before the analysis of the volatile composition of the sample [70]. Following VOC and SVOC extraction, GC analysis with a suitable detector is performed. Although flame ionization detectors (FIDs), electron capture detectors (ECDs), and thermal conductivity detectors (TCDs) are compatible with GC, mass spectrometry detectors are the most popular approach [71]. Developing predictive models for sensory data based on volatiles requires selecting either aroma or flavour data. There are studies indicating that both flavour and aroma data led to stable models [72; 73; 74]. GC's limitations emphasise the urgent necessity for a quick and affordable meat testing method. The electronic nose (E-nose) is an innovative detection technology that mimics biological olfaction, enabling it to detect, analyse, and identify a variety of categories of gases and odours [75]. The term E-nose applies to an array of chemical gas sensors, with broad and often overlapping selectivity, used to analyse volatile compounds combined with multivariate data analysis [76]. These sensors have several limitations, including the need for high-temperature operation (up to 400 \({}^{\circ}\)C) and the strict control of experimental conditions such as the humidity, pressure, temperature and gas flow [77].