Probiotic bacteria: safety, functional and technological properties.

During the past two decades probiotic (health promoting) micro-organisms have been increasingly included in various types of food products, especially in fermented milks. Several aspects, including safety, functional and technological characteristics, have to be taken into consideration in the selection process of probiotic micro-organisms. Safety aspects include specifications such as origin (healthy human GI-tract), non-pathogenicity and antibiotic resistance characteristics. Functional aspects include viability and persistence in the GI-tract, immunomodulation, antagonistic and antimutagenic properties. Before probiotic strains, chosen on the basis of their good safety and functional characteristics, can benefit the consumer, they must first be able to be manufactured under industrial conditions. Furthermore, they have to survive and retain their functionality during storage, and also in the foods into which they are incorporated without producing off-flavours. Factors related to the technological and sensory aspects of probiotic food production are of utmost importance since only by satisfying the demands of the consumer can the food industry succeed in promoting the consumption of functional probiotic products in the future.

Demonstration of safety of probiotics -- a review.

Probiotics are commonly defined as viable microorganisms (bacteria or yeasts) that exhibit a beneficial effect on the health of the host when they are ingested. They are used in foods, especially in fermented dairy products, but also in pharmaceutical preparations. The development of new probiotic strains aims at more active beneficial organisms. In the case of novel microorganisms and modified organisms the question of their safety and the risk to benefit ratio have to be assessed. Lactic acid bacteria (LAB) in foods have a long history of safe use. Members of the genera Lactococcus and Lactobacillus are most commonly given generally-recognised-as-safe (GRAS) status whilst members of the genera Streptococcus and Enterococcus and some other genera of LAB contain some opportunistic pathogens. Lactic acid bacteria are intrinsically resistant to many antibiotics. In many cases resistances are not, however, transmissible, and the species are also sensitive to many clinically used antibiotics even in the case of a lactic acid bacteria- associated opportunistic infection. Therefore no particular safety concern is associated with intrinsic type of resistance. Plasmid-associated antibiotic resistance, which occasionally occurs, is another matter because of the possibility of the resistance spreading to other, more harmful species and genera. The transmissible enterococcal resistance against glycopeptide antibiotics (vancomycin and teicoplanin) is particularly noteworthy, as vancomycin is one of the last effective antibiotics left in the treatment of certain multidrug-resistant pathogens. New species and more specific strains of probiotic bacteria are constantly identified. Prior to incorporating new strains into products their efficacy should be carefully assessed, and a case by case evaluation as to whether they share the safety status of traditional food-grade organisms should be made. The current documentation of adverse effects in the literature is reviewed. Future recommendations for the safety of already existing and new probiotics will be given.

Production of conjugated linoleic acid by dairy starter cultures.

Nineteen different strains of lactobacilli, lactococci, streptococci and propionibacteria commonly used as dairy starter cultures were tested for their ability to produce conjugated linoleic acid (CLA) from free linoleic acid in vitro. Two strains of Propionibacterium freudenreichii ssp. freudenreichii and one strain of P. freudenreichii ssp. sheramnii were found to be capable of converting free linoleic acid to extracellular CLA. The highest level of CLA formed in the media was 265 micrograms ml-1. Of the different isomers, cis- and trans-9,11-octadecadienoic acid represented more than 70% of the total CLA formed. The inhibitory effect of linoleic acid on the growth of the bacteria and its conversion to CLA in different media by propionibacteria are discussed.

[Salmonella bacteria in double cream (author's transl)]. / Salmonella i vispgrädde

In June 1974 a serious outbreak salmonellosis was reported from the southeast of Sweden. The epidemic was caused by Salmonella typhimurium and spread by infected cream, packed in one-way paper-plastic containers. Ordinary pasteurization of cream purposely infected with the strain in question at 60 degrees for 38 sec or 67 degrees C for 4,5 sec, resulted in a reduction by more than 7 decimal logs (Table I). The decimal reduction time at 60 degrees in cream was estimated to roughly 1.3 sec. The cream, which caused the outbreak, was pasteurized at 90 degrees C for 2-3 sec, which should destroy all salmonella in raw cream. In Sweden pasteurized cream has to be stored at a temperature not higher than 8 degrees C. The isolated salmonella strain was not able to grow at + 8 degrees or at + 10 degrees C during 17 days in pasteurized or UHT-treated cream. During this storage the viable counts were reduced by 79% at 8 degrees and 54% at 10 degrees C. Minimum growth temperature of the strain was 11-12 degrees C. The mean generation time in pasteurized cream at 12 degrees was 9.4 hours and at 15 degrees C 3.4 hours (Fig. 1 and 2). The salmonella strain was able to grow in competition with other bacteria in pasteurized cream even at low levels of infection (Table II). An exposure to a higher temperature, followed by storage at + 8 degrees C did not cause a further growth of salmonella at the low temperature (Fig 3). To avoid a recurrence, the possibility of reinfection of the cream with salmonella has to be further decreased and the cream has to be stored at a low temperature during all the storage period.

Occurrence of conjugated cis-9,trans-11-octadecadienoic acid in bovine milk: effects of feed and dietary regimen.

Twenty-eight lactating cows were used to study the effects of different diets and different dietary regimens on the variation of cis-9,trans-11-octadecadienoic acid in milk. Cows were divided into three groups and assigned to dietary treatments differing in the ratio of forage to concentrate. The control group was fed a diet with an average ratio of forage to concentrate of 50:50. The two trial groups were fed a trial diet either in restricted or nonrestricted amounts. Variation of cis-9,trans-11-octadecadienoic acid in milk was substantial (2.5 to 17.7 mg/g of fat). Cows fed restricted amounts of the trial diet, which contained a lower forage to concentrate ratio than did the control diet, exhibited, on average, the highest concentration (11.28 mg/g of fat). For cows fed for ad libitum consumption, the trial diet did not differ significantly from the control diet (6.6 vs. 5.0 mg/g of fat). The concentration of cis-9,trans-11-octadecadienoic acid and trans-11-C18:1 was positively correlated. Therefore, conjugated linoleic acid in bovine milk, if considered to be beneficial, could be increased through a suitable dietary regimen.

The protein tolerance of very low birth weight infants fed human milk protein enriched mother's milk.

Pooled breast milk was ultra-filtrated and freeze-dried to give a product with a protein content of 60 g/100 g powder. More than half of the secretory IgA activity against E. coli O antigen was preserved. This concentrated protein was added to the mother's fresh milk providing a protein supply of 3.0-3.5 g/kg/24 hours in four VLBW infants, at a calorie supply of 110 kcal/kg/24 hours. Growth followed the intrauterine rate. Free amino acid levels, acid-base balance and urea concentrations of peripheral whole blood indicated tolerance of the increased supply of human milk protein.