Probiotic bacteria as adjunct starters: influence of the addition methodology on their survival in a semi-hard Argentinean cheese

Pategrás cheese as a suitable carrier for six probiotic cultures

The viability of five single-strain and one three-strain probiotic cultures was assessed during Pategrás cheese ripening. Probiotics were inoculated into cheese-milk after a pre-incubation step – intended to improve their survival – or directly as a lyophilised culture; control cheeses without probiotics were also obtained. pH of probiotic and control cheeses was similar, except in probiotic cheeses containing the strain Lb. acidophilus B or the mixed culture. In these cases, the probiotic cheeses were more acid than their respective control cheeses. All the probiotics tested maintained counts above 107 cfu/g during the shelf-life settled for the product. Strains of the Lb. casei group: Lb. paracasei, Lb. casei and Lb. rhamnosus reached and kept the highest cell concentration during cheese ripening, followed by Lb. acidophilus and bifidobacteria. The direct addition of the probiotic cultures was more efficient than their inoculation after a pre-incubation step, for all the probiotics assayed. We have provided evidence that support the use of Pategrás cheese as a performing food-based vehicle for probiotic bacteria.

Production of hard-type cheese using free or immobilized freeze-dried kefir cells as a starter culture

This study provides a contribution to hard-type cheese starter culture production through the use of a freeze-dried culture in the ripening of hard-type cheeses. The effect of initial cell concentration, ripening temperature, and cell immobilization of kefir on the degree of openness, mold spoilage, microbial associations, physicochemical characteristics, and aroma-related compounds was studied. Use of kefir starter cultures resulted in cheese with an increased shelf life and resistance to spoilage as compared to control cheeses without kefir inoculants. Furthermore, the freeze-dried kefir culture improved aroma, taste, and texture characteristics while increasing the degree of openness in comparison to traditional hard-type cheese products. The kefir culture resulted in an increase in counts of total aerobic bacteria, yeasts and molds, lactococci, and lactobacilli until the 15th day of ripening. From then on, only lactobacilli counts increased, reaching levels up to 9.17 log CFU/g in cheeses ripened at 5 degrees C using freeze-dried kefir cells immobilized on casein. SPME-GC/MS analysis revealed major differences in volatile composition, especially with regard to alcohols (up to 75%), carbonyl compounds (up to 75%), and esters (up to 64%) between cheeses made with kefir cells and cheeses made without kefir inoculants.

Highlights on new food research

The understanding that probiotic foods can have beneficial effects on health has recently led to an increase in consumer demand for such products, thus enhancing their commercial value. Daily intake of probiotic micro-organisms, such as Lactobacilli and Bifidobacteria, contributes to maintaining and improving the balance of intestinal microbe populations, and their presence in high numbers largely prevents gastro-intestinal disturbances and improves the well-being of the organism by reinforcing its natural defences. In products destined for human consumption, probiotic bacteria are mainly incorporated in fermented milk products whose consumption may be limited by allergies and intolerances, or by low-cholesterol diets. Research is currently aimed at developing probiotic vegetable products which may ensure a regular assumption of beneficial micro-organisms from foods and beverages which are part of a normal diet, thus overcoming the limitations imposed by the use of milk-based products. This paper provides an overview of probiotic products and recently developed technologies, with some details on vegetable carriers used for delivering probiotic species into the human gastro-intestinal tract.

Nonstarter lactobacilli isolated from soft and semihard Argentinean cheeses: genetic characterization and resistance to biological barriers

Nonstarter lactic acid bacteria isolated from Argentinean cheeses were identified and characterized by focusing on their resistance to biological barriers, along with other physiological features of potential interest, in the search for future probiotic organisms. Lactobacilli were enumerated and isolated from semihard and soft cheeses made with multistrain Streptococcus thermophilus starters. Lactobacilli counts in 1-week-old cheeses were between 10(5) and 10(7) CFU/g and then reached 10(7) CFU/ g in all 1-month samples, while streptococci were always above 10(9) CFU/g. A total number of 22 lactobacilli isolates were retained, identified, and characterized by in vitro tests. Species identity was determined by carbohydrate metabolism and species-specific PCR assays. Genetic diversity was explored by random amplified polymorphic DNA (RAPD) PCR analysis. The Lactobacillus strains were assigned to the species L. casei, L. plantarum, L. rhamnosus, L. curvatus, L. fermentum, and L. perolens. All the strains studied tolerated 25 ppm of lysozyme, and most of them showed resistance to 0.3% bile. After incubation in gastric solution (pH 2.0), counts decreased by several log units, ranging from 3.2 to 7.0. The strains were able to grow in the presence of bile salts, but only three isolates were capable of deconjugation. The nonstarter lactobacilli that were assayed fermented the prebiotic substrates (especially lactulose and inulin). Some strains showed high cell hydrophobicity and beta-galactosidase activity, as well as inhibitory activity against pathogenic bacteria. It was concluded that most of the lactobacilli isolated in this study demonstrated resistance to biological barriers and physiological characteristics compatible with probiotic properties, which make them suitable for further research in in vivo studies aimed at identifying new probiotic organisms.