Table 3.

Analytical methods for yeast determination.

Objective	Method	Observations	Ref.
Viability determination	Methylene Blue dye Reduction Test (MBRT)	Non-viable cells are dyed blue. High variability. Response times of 48 h.	(Bapat et al., 2006; Dale, 1941)
	A commercial kit was reduced by cellular dehydrogenases to an orange formazan product soluble in a buffer.	The amount of formazan produced was directly proportional to the number of living cells. Response time 3 h. Maximum determination 1 × 107 cell mL−1.	Kwolek-mirek & Zadrag-tecza (2014)
	Cell count hemacytometer method	Inexpensive analysis, easy to carry out, but introduces high variability and low reproducibility. Linear ranges de 5.0 × 104–1.0 × 107 cell mL−1. R2 = 0.9992.	(Fiorino et al., 2004; Lawrence, 2002)
	Suspension inoculated on solid YPD medium.	Response time 48 h, possible errors due to dilution and final count.	Kwolek-Mirek & Zadrag-Tecza (2014)
Vitality determination	Acidification power test.	The change in pH caused by the yeast as it degrades a substrate (glucose) is measured. R2 = 0.9430.	Kara et al. (1988)
	The spectrophotometric method is based on the reaction of luciferin with ATP in the presence of luciferase, Mg2+ ions, and oxygen, resulting in the emission of light.	The analysis must be carried out very quickly, since the physiological conditions of the sample change drastically once taken, affecting the reaction.	Kwolek-Mirek & Zadrag-Tecza (2014)
Estimation of microbial biomass	Gravimetric method. Dry weights	The drying process may take time, and the preparation difficult. The presence of adsorbed non-microbial substances can interfere.	Harris & Kell (1985)
	Spectrophotometric method	It determines the turbidity associated with the microorganism's presence. The number and size of cells influences the measure. Response time 7 h. Linear range (0.0–1.0) g L−1. Sensibility 0.63 g L−1. R2 = 0.9994. Error 1.22%.	Hernández & Marín (2002)
Cell count	Flow cytometric method	It analyzes the scattered and fluorescent signals produced by a cell passing through a light beam. It provides automated data but is expensive and requires specialized personnel and high aseptic conditions. It is more directed to the medical field.	(Bochner et al., 1989; Lawrence, 2002; Michelson AL, 1996)
	Electrochemistry, chronoamperometric method (CA). Cell count of S. cerevisiae and Lactobacillus fermentum.	Measurement of the current generated by microorganisms on a platinum anode covered with a cellulose dialysis membrane. A linear relationship between current and cell number, below 4.0 × 108 cells mL−1. Error 5.0%.	(T Matsunaga et al., 1979)
	Electrochemistry, differential pulse voltammetry (DPV).	The current measurement employed a graphite electrode modified with 4,4′-bipyridine. Linear range (0.03–2.00) x 108 cells mL−1.	(Matsunaga and Namba, 1984b)
Measurement of microorganism populations	Electrochemistry cyclic voltammetry (CV).	GCE modified with tetracycline. Linear range (2.0–5.0) x104 cells mL−1.	Han et al. (2000)
	Electrochemistry cyclic voltammetry (CV).	Graphite working electrode vs. SCE. Linear range (0.1–1.9) x108 cell mL−1. Peak currents were reproducible, error of 4%.	(Matsunaga and Namba, 1984a)
	Electrochemistry chronoamperometry method (CA).	GCE modified with 2,3,5 - TBQ. Range lineal (6.4 × 103–1.6 × 106) cells mL−1.	Tsukatani et al. (2003)
	Electrochemistry chronoamperometry method (CA).	Screen-printed electrodes modified with magnetic nanoparticles. Linear range 1.0–1.0 × 104 CFU mL−1. LOD 5.0 UFC mL−1	Villalonga et al. (2019)
Cellular density determination	Electrochemistry chronoamperometry method (CA).	GCE modified with oxidized multi-wall carbon nanotubes dispersed in water – Nafion® (GCE/OMWCNT-N). Range lineal 3.36–6.52 g L−1. LOD 0.98 g L−1, LOQ 3.36 g L−1. R 0.99.	Acevedo Restrepo et al. (2022)
	Electrochemistry chronoamperometry method (CA).	SPCE modified with oxidized multi-wall carbon nanotubes dispersed in water – Nafion® (SPCE/OMWCNT-N). Range lineal 0.61–7.69 g L−1. LOD 0.17 g L−1, LOQ 0.61 g L−1. R 0.99.	This work

¹YPD: Culture medium of yeast extract, peptone, and dextrose.

²2,3,5-TBQ: 2,3,5-trimetil-1,4-benzoquinona. Redox mediator.