Carla Luciana Gerez

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.

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.

A ready-to-use antifungal starter culture improves the shelf life of packaged bread.

Fungal spoilage is the main cause of economic loss in the baking industry. In this study, we developed a ready-to-use biopreserver (slurry [SL]) for nonsliced packed bread by using selected antifungal lactic acid bacteria (LAB) and low-cost ingredients that are compatible with the food matrix. Four LAB strains (Lactobacillus brevis CRL 772, L. brevis CRL 796, L. plantarum CRL 778, and L. reuteri CRL 1100) tested in bread preservation were able to inhibit Penicillium sp. growth and lengthen shelf life twofold with respect to breads prepared using only Saccharomyces cerevisiae (2 days shelf life). The best biopreservation effect (5 days shelf life) was obtained with 40% antifungal slurry SL778 containing L. plantarum CRL 778; this was as effective as 0.2% calcium propionate (PCa). The antifungal effect of SL778 was related to the synthesis of acetic and phenyllactic acid as well as lactic acid, which was produced at a high concentration (31.2 mmol/kg) and lowered the pH of the dough, favoring the undissociated fraction of the organic acids. The combination of the starter SL778 with 0.4% PCa extended the shelf life of packaged bread to 24 days, 2.6-fold longer than breads prepared with only 0.4% PCa.

Gluten breakdown by lactobacilli and pediococci strains isolated from sourdough.

Aims:  To evaluate the growth and metabolic activity of lactobacilli and pediococci strains in a gluten base medium (GBM), formulated for a proper selection of proteolytic strains to be used in sourdough fermentation.

A combination of two lactic acid bacteria improves the hydrolysis of gliadin during wheat dough fermentation

The evaluation of gliadin hydrolysis during dough fermentation by using two lactic acid bacteria, Lactobacillus plantarum CRL 775 and Pediococcus pentosaceus CRL 792, as pooled cell suspension (LAB) or cell free extract (CFE) was undertaken. The CFE pool produced a greater (121%) increase in amino acid concentration than the LAB pool (70-80%). These results were correlated with the decrease (76,100 and 64,300 ppm) in the gliadin concentration of doughs supplemented with CFE and LAB, respectively, compared to control doughs. The use of LAB peptidases seemed to be a viable technologic alternative to reduce the gliadin concentration in wheat dough without using living bacteria as starter.

Lactobacillus reuteri CRL 1100 as starter culture for wheat dough fermentation

The effect of sucrose on the fermentation balance of Lactobacillus reuteri CRL 1100 and the invertase activity of this strain in wheat dough and culture medium (MRSs) was evaluated. The enzyme activity was dependent on the environmental pH releasing glucose and fructose from sucrose hydrolysis. Glucose was used as carbon source, while fructose was mainly used as electron acceptor to produce mannitol up to 10h of fermentation. Thereafter, fructose seemed to be metabolized by the heterofermentative pathway, which determined an increase in the concentration of acetate (6 mmol l(-1)), lactate (2 mmol l(-1)) and ethanol (1 mmol l(-1)) and the lack of mannitol formation after glucose depletion. The fermentation balance of Lb. reuteri CRL 1100 during the dough fermentation resulted in lower (63%) ethanol, higher (75%) acetate production and soluble carbohydrates concentrations, like MRSs cultures. This fermentation profile would be important to obtain an optimal growth of yeast and the optimal bread flavor and taste.

Functionality of lactic acid bacteria peptidase activities in the hydrolysis of gliadin-like fragments

Aims:  To evaluate the role of the peptidase activities from sourdough lactic acid bacteria (LAB) in the degradation of α‐gliadin fragments.

Influence of oregano essential oil on traditional Argentinean cheese elaboration: Effect on lactic starter cultures

The aim of this work is to study the oregano essential oil (OEO) composition from Northwestern Argentinean regions and to evaluate its effect on the lactic starter cultures. The oregano used, Origanum vulgare var hirtum, was obtained from Andalgalá, Catamarca. The essential oil presented high amounts of α-terpinene (10%), γ-terpinene (15.1%), terpinen-4-ol (15.5%) and thymol (13.0%) as the main components. No negative effect on growth or metabolic activity of lactic acid bacteria Streptococcus thermophilus CRL 728 and CRL 813, Lactobacillus delbrueckii subsp. bulgaricus CRL 656 and CRL 468, and Lactococcus lactis subsp. lactis CRL 597 up to the maximum concentration (200μg/g) assayed was observed. No differences in the organoleptic characteristics of semi-hard cheeses flavored with oregano essential oil (200μg/g) and homemade cheeses flavored with oregano leaves were found. With respect to the microbiological quality of the products, neither enterobacteria nor mold and yeast were detected during ripening in essential-oil flavored cheese compared to control cheese (enterobacteria 2×103UFC/g) and cheese flavored with oregano leaves (mold/yeast 4×104CFU/g). Our results showed that the use of oregano essential oil and lactic starter culture considerably improved cheese quality.

Inorganic salts and intracellular polyphosphate inclusions play a role in the thermotolerance of the immunobiotic Lactobacillus rhamnosus CRL 1505

In this work, the thermotolerance of Lactobacillus rhamnosus CRL1505, an immunobiotic strain, was studied as a way to improve the tolerance of the strain to industrial processes involving heat stress. The strain displayed a high intrinsic thermotolerance (55°C, 20 min); however, after 5 min at 60°C in phosphate buffer a two log units decrease in cell viability was observed. Different heat shock media were tested to improve the cell survival. Best results were obtained in the mediumcontaining inorganic salts (KH2PO4, Na2HPO4, MnSO4, and MgSO4) likely as using 10% skim milk. Flow cytometry analysis evinced 25.0% live cells and a large number of injured cells (59.7%) in the inorganic salts medium after heat stress. The morphological changes caused by temperature were visualized by transmission electronic microscopy (TEM). In addition, TEM observations revealed the presence of polyphosphate (polyP) granules in the cells under no-stress conditions. A DAPI-based fluorescence technique, adjusted to Gram-positive bacteria for the first time, was used to determine intracellular polyP levels. Results obtained suggest that the high initial polyP content in L. rhamnosus CRL 1505 together with the presence of inorganic salts in the heat shock medium improve the tolerance of the cells to heat shock. To our knowledge, this is the first report giving evidence of the relationship between polyP and inorganic salts in thermotolerance of lactic acid bacteria.

Lactic Acid Fermentation Improved Textural Behaviour, Phenolic Compounds and Antioxidant Activity of Chia (Salvia hispanica L.) Dough

In this work, autochthonous lactic acid bacteria (LAB) were isolated from chia (Salvia hispanica L.) dough and selected on the basis of the kinetics of acidification and proteolytic activity. Strain no. C8, identified as Lactobacillus plantarum C8, was selected and used as starter to obtain chia sourdough. Lactic acid fermentation increased the organic acid mass fractions (lactic, acetic and phenyl lactic acids to 12.3 g, 1.0 g and 23.8 µg per kg of dough respectively), and antioxidant activities, which increased by approx. 33-40% compared to unfermented chia flour dough. In addition, total phenolic content increased 25% and its composition was strongly modified after 24 h of fermentation by L. plantarum C8. Chlorogenic acid was only found in the fermented dough (2.5 mg/g), while ferulic acid was detected from the beginning of fermentation, being 32% higher in chia sourdough (5.6 mg/g). The use of fermented chia sourdough improved the overall characteristics of white bread, including physical (e.g. reduced hardness and chewiness of the crumb) and antioxidant properties (25% on average), compared to the white bread. These results indicate that the use of chia sourdough could be a promising alternative to improve the technological and antioxidant properties of wheat bread. In addition, this work has shown, for the first time, that lactic acid bacterium is able to ferment chia dough, improving its overall characteristics.