G. Font de Valdez

Heterofermentative pattern and exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in response to environmental pH

Aims: The objective of this work was to evaluate the fermentation pattern of and the exopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in milk batch cultures under controlled pH (4·5, 5·0 and 6·2).

A Low-pH-Inducible, Stationary-Phase Acid Tolerance Response in Lactobacillus acidophilus CRL 639

Acidity is an important environmental condition encountered by lactobacilli during food fermentation. In this report we show that triggering the stationary-phase acid tolerance response (ATR) in L. acidophilus CRL 639 depends on the final growth pH. In free-pH fermentation runs (final pH = 4.5), the cells were completely resistant to acid stress, whereas cells from cultures under controlled pH (pH = 6.0) were very sensitive. The relationship between the final pH and the development of cross-resistance to different kinds of environmental stress was also evaluated. The study of protein profiles showed the overexpression of 16 proteins from 6.5 to 70.9 kDa in stationary phase cells. Seven of these proteins (26.3, 41.4, 48.7, 49.3, 54.5, 56.1, and 70.9 kDa) were expressed as result of the stationary phase itself, while nine proteins (14.1, 18.6, 21.5, 26.9, 29.3, 41.9, 42.6, 49.6, and 56.2 kDa) were exclusively induced as a result of the drop in culture pH during free fermentation runs. These results strongly suggest the involvement of these proteins in cell adaptation to environmental changes.

Whey protein coating bead improves the survival of the probiotic Lactobacillus rhamnosus CRL 1505 to low pH

Aims:  To evaluate the efficacy of a novel microencapsulation procedure using whey protein and pectin to improve the survival rate of Lactobacillus rhamnosus CRL 1505 to low pH and bile.

Effect of galactose and glucose on the exopolysaccharide production and the activities of biosynthetic enzymes in Lactobacillus casei CRL 87.

Aims: The objective of this work was to study the influence of the sugar source on exopolysaccharide (EPS) production and the activities of the enzymes involved in the synthesis of sugar nucleotides in Lactobacillus casei CRL 87. The relationship between these enzymes and EPS formation was determined.

Inhibition of Citrus Fungal Pathogens by Using Lactic Acid Bacteria

The effect of lactic acid bacteria (LAB) on pathogenic fungi was evaluated and the metabolites involved in the antifungal effect were characterized. Penicillium digitatum (INTA 1 to INTA 7) and Geotrichum citri-aurantii (INTA 8) isolated from decayed lemon from commercial packinghouses were treated with imazalil and guazatine to obtain strains resistant to these fungicides. The most resistant strains (4 fungal strains) were selected for evaluating the antifungal activity of 33 LAB strains, among which only 8 strains gave positive results. The antifungal activity of these LAB strains was related to the production of lactic acid, acetic acid, and phenyllactic acid (PLA). A central composite design and the response surface methodology were used to evaluate the inhibitory effect of the organic acids produced by the LAB cultures. The antifungal activity of lactic acid was directly related to its concentration; however, acetic acid and PLA showed a peak of activity at 52.5 and 0.8 mM, respectively, with inhibition rates similar to those obtained with Serenade((R)) (3.0 ppm) imazalil (50 ppm) and guazatine (50 ppm). Beyond the peak of activity, a reduction in effectiveness of both acetic acid and PLA was observed. Comparing the inhibition rate of the organic acids, PLA was about 66- and 600-fold more effective than acetic acid and lactic acid, respectively. This study presents evidences on the antifungal effect of selected LAB strains and their end products. Studies are currently being undertaken to evaluate the effectiveness in preventing postharvest diseases on citrus fruits.

Functionality of exopolysaccharides produced by lactic acid bacteria in an in vitro gastric system

Aims:  To evaluate whether slime‐exopolysaccharides (EPS) or capsular‐polysaccharide (CPS) production could protect the polymer‐producing strains Streptococcus thermophilus CRL 1190 and Lactobacillus casei CRL 87 against the harsh conditions of an in vitro gastric system (GS). EPS stability on the GS was studied.

Lactobacillus reuteri CRL 1098 prevents side effects produced by a nutritional vitamin B12 deficiency

Aims:  To evaluate the efficiency of the vitamin B12‐producing Lactobacillus reuteri CRL1098 strain in preventing the symptoms caused by a nutritional cobalamin‐deficient diet in pregnant female mice and their weaned offspring.

Prevention of chronic gastritis by fermented milks made with exopolysaccharide-producing Streptococcus thermophilus strains.

Acetyl-salicylic acid (ASA) is a nonsteroidal antiinflammatory/analgesic drug, which may cause gastritis or stomach ulcers if intensively employed. Exopolysaccharide (EPS)-producing lactic acid bacteria have been claimed to induce immunostimulatory/antiulcer effects in the host. This study investigated the potential preventive effect of fermented milks (FM) with EPS-producing Streptococcus thermophilus strains (CRL 1190 and CRL 804) on an in vivo model of chronic gastritis. Fermented milks (2 EPS(+) and 1 EPS(-), separately) were fed to BALB/c mice for 7 d before inducing gastritis with ASA (400 mg/kg of body weight per day for 10 d; gastritis group, n = 5). Appropriate control groups (ASA administered but not given FM, n = 5; and ASA not administered but given FM) were included in this study. Gastric inflammatory activity was evaluated through the stomachs histology and the number of IFNgamma(+) and IL-10(+) cytokine-producing cells in the gastric mucosa. Only mice preventively treated with the EPS-producing Strep. thermophilus CRL 1190 FM and later administered ASA did not develop gastritis, showing a conserved gastric mucosa structure similar to those of healthy mice. A marked decrease of IFNgamma(+)- and increase of IL-10(+)-producing cells compared with the gastritis group mice were observed. Purified EPS from Strep. thermophilus CRL 1190 resuspended in autoclaved milk was also effective for gastritis prevention. The EPS-protein interaction might be responsible for the observed gastroprotective effect; such interactions may be affected by industrial manufacturing conditions. The results indicate that the FM with Strep. thermophilus CRL 1190 or its EPS could be used in novel functional foods for preventing chronic gastritis.

Growth and exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in an adenine-supplemented chemically defined medium

Aims:  To analyse the exopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in a chemically defined medium (CDM) and the effect of nutrients and stress culture conditions on cell growth and EPS formation.

Hydrolysis of whey proteins by Lactobacillus acidophilus, Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus grown in a chemically defined medium

Aims: To evaluate the ability of themophilic lactic acid bacteria (LAB) to hydrolyse the whey proteins β‐lactoglobulin (BLG) and α‐lactalbumin (ALA) in a chemically defined medium (CDM).