J. Vet. Med. B 40,727-729 (1993) 0 1993 Paul Parey Scientific Publishers, Berlin and Hamburg ISSN 093 1 - 1793

Short Communication

Faculty of Veterinary, Department of Food Science and Technology, University of Cdrdoba

Microbiological Quality of French Yogurts Commercialized in Spain

CARMEN LOPEZ, VALLE RODRIGUEZ, L. M. MEDINA, MARIA J. BARRIOS and R. JORDANO

Address of authors: Veterinary Faculty, E-14071 Cordoba, Spain

With one table

(Received for publication January 22, 1993)

Summary The microbiological quality has been evaluated in 6 batches of yogurt (plain, flavoured and

fruit-added) produced commercially in France and purchased in Spain. The essential microflora: Streptococcus salivarius subsp. therrnophilus and Lactobacillus delbrueckii subsp. bulgaricus, and contaminants (coliform bacteria, yeasts and molds) were checked. The pH was also measured. The totality of the samples tested fulfilled French and Spanish regulation with respect to the presence of viable yogurt organisms. Likewise, in 100 % of the yogurts, counts of contaminants were under 10 cfu/g. The pH ranged between 3.92 and 4.19.

Introduction France and Spain are amongst the members of the European Community (EC)

which restrict the microorganisms considered as essential to yogurt to Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, only. Furthermore, these countries place under the denomination “yogurt” an abundant presence of viable microorganisms. Thus, whilst the Spanish quality standard establishes (3) that at the time of its sale the product should contain a minimum number of 1 x 10’ per g or rnl streptococci and lactobacilli, French legislation ( 2 ) increases this figure to 1 x 10R/g or ml. The legal situation of yogurt and other fermented milk products, the harmonization of the legal requirements in member states, the relevance of living yogurt bacteria for product quality and the consumer’s health, the checking, everything within the framework of the Common Market, have been revised by GLASER (5).

In ROBINSON’S and TAMIME’S opinion (10) an examination of the microbiological quality of yogurt is usually concerned with two aspects, namely: the protection of the consumer from exposure to any health hazard; and to ensure that the material does not suffer microbial deterioration during its anticipated shelf-life. Both these aims are of importance to consumer and producer alike. The estimation of yogurt microflora is usually done with respect to viable starter bacteria counts and the level of microbial con- tamination (11). R A S I ~ and KURMANN (8) consider that the yogurt may contain a small

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72 8 LOPEZ et al.

number of non-pathogenic contaminants in addition to a large number of lactic acid bacteria.

The objective of this work was the evaluation of the microbiological quality of different types of yogurt (plain, flavoured and fruit-added) produced in France and commercialized in Spain.

Material and Methods Material: A total of 30 samples grouped in six different batches of 5 of commercial yogurt

(2 plain, 2 flavoured and 2 fruit-added) was analyzed for essential microflora: S. salivarius subsp. thermophilus and L. delbrueckii subsp. bulgaricus; and for contaminants: coliforms, yeasts and molds. The storage time of the samples tested ranged from 1 to 24 days. Samples were aseptically removed from containers and diluted by mixing 10 g with 90 ml of 0.1 % bacto-peptone (Difco). Further dilutions were made as required.

Enumeration of essential microflora: The count of streptococci was verified on M17 agar (13) (Oxoid). The inoculated plates were incubated at 37 "C for 2 days. Under these conditions, S. sali- van'us subsp. thermophilus forms lenticular colonies with a diameter of 1-2 mm (1). MRS agar (4) (Difco) was utilized for the counts of lactobacilli. The plates were incubated at 37 "C for 3 days in an anaerobic culture jar (HJCO,). Under these conditions L. delbrueckii subsp. bulgaricus forms lenticular, often starshaped, colonies of 1-3 mm in diameter (1).

Enumeration of contaminant microflora: The count of yeasts and molds was vcrified on potato dextrose agar (PDA, Difco) at 25 "C for 5 days (12). Violet red bile agar (VRBA, Difco) at 32 "C for 1 day (12) was utilized for the counts of coliforms. The results were expressed as colony- forming units (cfu) per g.

p H determination: By potentiornetric methods on a digital pH-meter (Crison, Model 501) with combined electrode.

Results and Discussion A summary of the results obtained is given in Table 1. The highest counts of

streptococci were obtained in fruit-added yogurts whilst in the same variety the lowest counts of lactobacilli were registered. The greatest population of L. delbrueckii subsp. bulgaricus was detected in one of the flavoured batches whereas the smallest of S. sali- varius subsp. thevrnophilus was found in the other. The p H ranged between 3.92 and 4.19.

Table 1. Microbial evaluation of six batches of commercial yogurt: 2 plain (PI, PZ), 2 flavoured (F11, F12) and 2 fruit-added (Frl, Fr2)

Batch Shelf-lifea p H S. salivarius L. delbrueckii Coli- Yeasts + (day) subsp. thermophilus subsp. bulgaricus forms Molds

x 10" cfu/g x 10* cfu/g < 10 cfu/g < 10 cfu/g

P1 18th 3.98+ 0.015" 1.23' 1.79' 1 OOd 1 OOd

(n = 5) P2 1st 4.06 5 0.008 1.82 2.17 100 100 (n = 5) F11 14th 3.92 f 0.004 2.69 2.51 100 100 (n = 5) F12 19th 3.96+ 0.020 1.40 0.38 100 100 (n = 5) Frl 24th 4.19+ 0.010 27.74 0.28 100 100 (n = 5) Fr2 10th 4.13 * 0.016 22.14 0.80 100 100 (n = 5)

a Period of time during which a product will remain acceptable in quality to the5onsumer (7). In Spain 2 tdays of refrigerated storage (3). I, Mean values f Standard deviation (X + SD). Mean values (X). Percentages of samples (%).

Microbiological quality of French yogurts commercialized in Spain 729

The differences found between batches, i. e. in the figures of the essential viable micro- flora and in the p H values, were predictable since the yogurts were of different varieties, came from different batches and, above all, had variable storage times (1 t o 24 days). Furthermore, in the case of fruit-added yogurts the batches belonged to different manu- facturers.

Actually, R A W and KURMANN (9) consider that the possible variations in viable yogurt organisms are related with the p H value and the storage time, amongst other factors. Also, HAMANN and MARTH (6) suggest that manufacturing practices and the variety of culture-starting strains used by different manufacturers have a greater effect o n the survival of essential microflora in yogurt than that exercised by the presence o r absence of fruit.

The number of streptococci and lactobacilli in all the yogurts tested exceeded 10’ cfu/g and therefore fulfilled the corresponding French and Spanish regulations (2,3) with respect to the presence of essential viable microflora.

In all cases the counts of coliform bacteria were below 10 cfu/g. Likewise, the absence of any fungal contamination was confirmed in 100 % of the samples. R A W and KURMANN (8), on examining possible yogurt contaminants, consider that whilst coli- forms can develop during incubation t o a limited extent, yeast and molds which are acid and cold tolerant can develop in the final product. The absence of contaminating micro- flora in the yogurts investigated was interpreted by us as being indicative of a good microbiological quality.

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