Feasibility of Lactobacilli Concentration
Detection in Beer by Automated Impedance Technique
MBAA TQ http://dx.doi.org/10.1094/TQ-49-1-0315-01 |
VIEW ARTICLE
A. Pompei (1), M. Grossi (2), M.
Lanzoni (2), G. Perretti (3), R. Lazzarini (4), B. Ricc� (2), and D.
Matteuzzi (1). 1. Department of Pharmaceutical Sciences, Via S. Donato
19/2, University of Bologna, CAP 40126, Bologna, Italy. 2. Department
of Electronic Engineering (D.E.I.S.), Viale Risorgimento 2, University
of Bologna, CAP 40136, Bologna, Italy. 3. Italian Brewing Research
Centre (CERB), Via S. Costanzo, University of Perugia, CAP 06126,
Perugia, Italy. 4. Carpigiani Group, Via Emilia 45, Anzola Emilia, CAP
40011, Bologna, Italy.
Abstract
Product quality is a primary concern in the
brewing industry because the presence of high concentrations of bacteria
can alter important organoleptic characteristics of the product (such as
flavor and aroma defects and turbidity problems). Microbial concentration
is usually measured by the standard plate count (SPC) technique, which
produces accurate results but is slow and must be performed by laboratory
tests with the aid of qualified personnel. This precludes the possibility
of on-line monitoring of bacterial concentration at different steps of the
production line. This study shows an alternative method based on impedance
measurements, which proves to be competitive with SPC since it can detect
the microbial concentration of 10(^4) cfu/mL with measurement times as low as
10�12 hours against the 24�72 hours needed by SPC. It also features the
possibility of industrial automation, thus making it very attractive for
microbial screening on brewery production lines. Different media have been
tested to obtain the highest bacterial growth rate (i.e., minimizing
response time) and accuracy in lactobacilli concentration measured by
electrical parameters. The need of selective determination of
lactobacilli concentration has been achieved by adding cycloheximide to
the samples and using filters of gradual size diameters to separate yeast
cells from lactobacilli.
Keywords: beer spoilage, food quality, impedance, industrial
biosensors, lactobacilli
S�ntesis
La presencia de altas concentraciones de
bacterias puede afectar seriamente las caracter�sticas del producto (tal
como defectos de sabor y aroma o problemas con la turbidez), por lo que
esta es una seria preocupaci�n para la industria cervecera. La
concentraci�n bacteriana normalmente es medida por el conteo de unidades
formadores de colonias (ufc) en platos Petri; esto da resultados buenos
pero dura mucho tiempo y debe ser realizado por personal de laboratorio
bien calificado, adem�s de que el m�todo no se presta a mediciones �en
l�nea� para monitorear la concentraci�n en diferentes etapas de
producci�n. Aqu� presentamos un m�todo alterno basado en mediciones de
impedancia capaz de medir concentraciones de hasta 104 ufc/mL en unas
10�12 horas, comparado con las 24�72 horas necesarias con el m�todo
normal. Tambi�n cabe la posibilidad de automatizar el proceso, lo que
ser�a una gran ayuda para el control microbiol�gico de la planta. Se han
testado diferentes medios para obtener la mayor velocidad de crecimiento
(minimizando el tiempo de respuesta) y la mayor exactitud en la
determinaci�n de la concentraci�n de lactobacilos medido por par�metros
el�ctricos. La medici�n selectiva de la concentraci�n de lactobacilos se
consigui� mediante la adici�n de ciclohexamida a las muestras y con el uso
de filtros de diferentes di�metros de poro para separar c�lulas de
levadura de los lactobacilos.
Palabras claves: biosensores
industriales, calidad de alimentos, deterioro de cerveza, impedancia,
lactobacilos
