Author(s):
Malfeito-Ferreira, Manuel 
; Loureiro, Virgilio ; Sancho, T. ; Gimenez-Jurado, G.
Date: 2000
Persistent ID: http://hdl.handle.net/10400.5/491
Origin: Repositório da UTL
Subject(s): zymological indicators; fruit pulp; fruit concentrate; yeast
Description
DOI:10.1006/fmic.2000.0360; available online at http://www.idealibrary.com In a survey of the microbial quality of raw materials used in fruit juice processing, yeast counts in fruit
concentrates and pulps were found to range from51to 2?96103 cfu g71. Ascomycetous yeasts were
representedby 76%of the isolateswhile 24%were basidiomycetes.The identi¢cation of strains isolated
by the simpli¢ed identi¢cation system(SIM) revealed19 yeast species representing12 genera.Themost
frequently isolated yeasts belonged to the genera Saccharomyces, Pichia, Cryptococcus, Kluyvero-
myces and Candida.
Fatty acid yeast composition allowed the separation of contaminating yeasts into one of threemajor
groups. Group I included yeasts without linoleic (C 18:2) and linolenic (C 18:3) fatty acids such as
Saccharomyces cerevisiae. Group II comprised yeasts without C 18:3 fatty acid like Zygosaccharo-
myces rouxii and Torulaspora delbrueckii, and group III included yeasts with C18:2 and C18:3 acids
that belong, among others, to one of the following yeast genera: Pichia, Candida, Kluyveromyces or
Cryptococcus.
Species-speci¢c PCR primers were used for the rapid detection and identi¢cation of the most
dangerous species a¡ecting fruit concentrate stability. The simpli¢ed protocol used consisted of
PCR-ampli¢cation of conserved tracts in the ITS region of the rDNA unit, thus enabling the detection
ofpotentially dangerous £ora such as Zygosaccharomyces species andT. delbrueckii in contaminated
fruit concentrates. Results from PCR-typing were in full agreement with the fatty acid compositions of
these species.
The grouping of contaminant yeasts into threemain groups showed that fatty acid compositionmay
be used to di¡erentiate yeasts according to their technological signi¢cance.Yeasts isolated in thiswork
as being most dangerous to product stability belong to either group II ( Z. rouxii and T. delbrueckii) or
group I (Saccharomyces spp.). Group III was comprised of several species regarded as indicators of
de¢ciencies in `good manufacturing practices'.Thus, each of the groups delineated may be considered
to be a zymological indicator of technological signi¢cance.The conjugation of fatty acid pro¢les with
PCR-typing methods may be used as a rapid detection system for contaminant yeasts. The fatty acid
pro¢les provide a preliminary identi¢cation of yeasts potentially dangerous to product stability present within 48 h. of isolation. Whereas the PCR-typing method is mainly used to confirm isolate identity, when required, after the initial diagnosis has been performed, over a period of 4 h.
