The prevalence and
control of spoilage
yeasts in foods and
beverages
V. Loureiro
Ã
and A. Querol
y
Ã
Departamento de Bota
Ã
nica e Engenharia Biolo
Â
gica,
Instituto Superior de Agronomia, Universidade
Te
Â
cnica de Lisboa, 1349-017 Lisboa Codex, Portugal
(1fax: 351 21 363 50 31; e-mail: vloureiro@isa.utl.pt)
y
Departamento de Biotecnologia, Instituto de
Agroquõ
Â
mica y Tecnologia de Alimentos (CSIC), P.O.
Box 73, 46100 Burjassot, Valencia, Spain (2fax: 34 96
363 63 01; e-mail: aquerol@iata.csic.es)
Consumers in developed countries have a more critical
attitude about what they eat and drink as a consequence of
modern life. Food microbiologists are facing a huge chal-
lenge regarding food `freshness' implicit in the consumer's
demand for more natural products. Food with less severe
processing, that is additive-free, safer, with satisfactory shelf
life and easy to prepare is sought because of higher con-
sciousness about nutrition and health. Besides the develop-
ment of new methods and preservation concepts, great
advances in the ®elds of chemistry, biochemistry, micro-
biology, hygiene and food safety have occurred in recent
decades. But are such developments properly used to
respond to the challenge to food mycology? We will sum-
marize the eects on food of yeast spoilage activity and
we will re¯ect on how this activity can be monitored by
food microbiologists. # 2000 Published by Elsevier Science
Ltd.
The overviews on food spoilage yeasts published
about 30±40 years ago [1,2] reported that food-borne
yeasts had no signi®cance in public health, being regarded
as harmless for the consumers, even when ingested in high
amounts through fermented foods (e.g. lambic beer,
ke®r, kuomiss, some raw milk smear ripened cheeses,
etc.). However, Fleet [3], mentioning works of the
1980s, refers for the ®rst time, to the need to re-evaluate
the impact of food-borne yeasts on public health/safety.
This author cites occasional reports of gastro-enteritis
caused by the ingestion of foods in which the suspected
etiological agents were yeasts. In addition, a report is
cited referring to increasing evidence for the develop-
ment of allergies and negative eects in humans due to
yeasts, which has led to the coming up of lay literature
promoting the virtues of `yeast-free' diets. Thomas [4]
also cites a reference stating that the exposure to anti-
gens from Saccharomyces cerevisiae may contribute to
in¯ammatory bowel disease. In a recent review on new
and emergent yeast pathogens, Hazen [5] states, as well,
that in the medical ®eld, the infections caused by yeasts
are increasingly signi®cant, and the author attributes such
situations to, among other factors, immunosuppressive
therapeutic regimens, long-term catheterization, broad-
spectrum antibiotic use, and longer survival of immuno-
logically compromised individuals. He states that some
yeasts previously thought as innocuous (e.g. Candida
utilis, Saccharomyces cerevisiae and Candida lipolytica)
are capable of damaging the human body. Although the
cases reported are rare and occur in extremely peculiar
situations, we have to admit the possibility that the
presence of yeasts in foods, either spoilers or not, may
assume an increasing protagonism in public health and
should be a growing concern for microbiologists and
food technologists.
The spoilage yeasts of foods and drinks have also
gained, in recent years, an increasing importance in
food technology, being responsible for signi®cant eco-
nomic losses [4]. However, reports on these losses are
still rare. For reasons of commercial con®dentiality, the
incidence and economic cost of industrial outbreaks of
yeast spoilage remain unreported [3]. According to this
author and also based on our experience of outbreak
costs, these are considerably high and involve large legal
disputes involving manufacturers, suppliers of raw
materials and packaging, and, often, retailers.
In broad terms, the comprehensive overviews on
spoilage yeasts published in the second half of the 20th
century were focused, essentially, in the qualitative
description of the main yeast species present in foods
and beverages. Barnett et al. [6], listed nearly 120 yeast
species, belonging to 30 genera, as being associated with
0924-2244/99/$ - see front matter Copyright # 2000 Published by Elsevier Science Ltd.
PII: S0924-2244(00)00021-2
Trends in Food Science & Technology 10 (1999) 356±365
Review