Marisa S. Garro

Aglycone production by Lactobacillus rhamnosus CRL981 during soymilk fermentation.

Lactobacillus rhamnosus CRL981 showed the highest levels of beta-glucosidase and was selected to characterize this enzyme system, among 63 strains of different Lactobacillus species. The maximum activity was obtained at pH 6.4 and 42 degrees C. The enzyme showed weak resistance to thermal inactivation maintaining only 20% of the initial activity when it was exposed at 50 degrees C for 5 min. It also, showed stability when stored at 4 degrees C for 60 days. Afterwards, L. rhamnosus was evaluated for hydrolysis of isoflavones to aglycones, cell population, residual sugars and organic acid produced during fermentation on soymilk (37 degrees C for 24 h). Higher viable counts were obtained after 12 h of fermentation (8.85 log CFUml(-1)) followed by a drop of pH and an increase of acidity during fermentation due the production of organic acids. L. rhamnosus CRL981 was able to proliferate in soymilk and produce a high beta-glucosidase activity achieving a complete hydrolysis of glucoside isoflavones after 12 h of fermentation. The present study indicates that L. rhamnosus CRL981 could be used in the development of different aglycone-rich functional soy beverages.

Starter culture activity in refrigerated fermented soymilk.

The refrigerated shelf life of soymilk fermented with single cultures of Lactobacillus fermentum, L. casei, Streptococcus salivarius subsp. thermophilus, and Bifidobacterium longum was evaluated. During storage at 4 degrees C for 28 days, the stability of the microflora differed markedly among the starter cultures. After 28 days, the average numbers of S. salivarius subsp. thermophilus decreased by two log cycles to 6.0 x 10(7) CFU/ml, whereas those of L. casei increased gradually by more than two log cycles to 4.6 x 10(9) CFU/ml. Numbers of B. longum and L. fermentum remained moderately high (8.7 x 10(8) CFU/ml and 3.7 x 10(8) CFU/ml, respectively) even after 28 days of storage. S. salivarius subsp. thermophilus and L. casei continued to metabolize sucrose during the storage period, but the pattern of consumption was different among the strains. The other starter cultures did not seem to have significant activity (P > 0.05) on the residual sugars. In most cases, L(+)-lactate predominated.

Reduction of α‐galactooligosaccharides in soyamilk by Lactobacillus fermentum CRL 722: in vitro and in vivo evaluation of fermented soyamilk

Aims:  Consumption of soya‐derived products has been hampered by the presence of α‐galactooligosaccharides (α‐GOS) because mammals lack pancreatic α‐galactosidase (α‐Gal) which is necessary for their hydrolysis. These sugars thus reach the large intestine causing gastrointestinal disorders in sensitive individuals. The use of lactic acid bacteria (LAB) expressing α‐Gal is a promising solution for the degradation of α‐GOS in soyamilk.

α-D-Galactosidase (EC 3.2.1.22) from Bifidobacterium longum

α‐Galactosidase activity in Bifidobacterium longum was maximal in a range of 40–45°C and at pH of 5.8. At temperatures above 60°C the enzyme was completely inactivated, but it maintained a 100% activity during storage at low temperatures (4, ‐ 30, ‐ 70°C) for 3 months. The addition of Hg2+ to the reaction buffer produced a strong inhibitory effect while Mn2+ exerted a slight positive effect upon activity. The addition of EDTA, inhibitors and other metal ions had no effect on the enzyme α‐galactosidase.

Influence of Carbohydrates on the α-Galactosidase Activity of Lactobacillus fermentum

Abstract. The influence of soybean galactosaccharides (stachyose, raffinose, melibiose) as well as galactose and glucose on the synthesis and activity of α-galactosidase (α-gal) from Lactobacillus fermentum CRL 251 was studied. Stachyose was the most effective inducer, followed by melibiose, raffinose, and galactose; scarce activity was detected with glucose. Exogenously supplied glucose inhibited the synthesis of the enzyme in cultures of L. fermentum growing on galactose. This effect was reversed by the addition of cyclic adenosine-3′,5′ monophosphate (cAMP), which suggests that this compound could be involved in the regulation of α-gal synthesis.

Optimization of fermentation parameters to study the behavior of selected lactic cultures on soy solid state fermentation.

The use of solid fermentation substrate (SSF) has been appreciated by the demand for natural and healthy products. Lactic acid bacteria and bifidobacteria play a leading role in the production of novel functional foods and their behavior is practically unknown in these systems. Soy is an excellent substrate for the production of functional foods for their low cost and nutritional value. The aim of this work was to optimize different parameters involved in solid state fermentation (SSF) using selected lactic cultures to improve soybean substrate as a possible strategy for the elaboration of new soy food with enhanced functional and nutritional properties. Soy flour and selected lactic cultures were used under different conditions to optimize the soy SSF. The measured responses were bacterial growth, free amino acids and β-glucosidase activity, which were analyzed by applying response surface methodology. Based on the proposed statistical model, different fermentation conditions were raised by varying the moisture content (50-80%) of the soy substrate and temperature of incubation (31-43°C). The effect of inoculum amount was also investigated. These studies demonstrated the ability of selected strains (Lactobacillus paracasei subsp. paracasei and Bifidobacterium longum) to grow with strain-dependent behavior on the SSF system. β-Glucosidase activity was evident in both strains and L. paracasei subsp. paracasei was able to increase the free amino acids at the end of fermentation under assayed conditions. The used statistical model has allowed the optimization of fermentation parameters on soy SSF by selected lactic strains. Besides, the possibility to work with lower initial bacterial amounts to obtain results with significant technological impact was demonstrated.

Soymilk fermentation by Enterococcus faecalis VB43 leads to reduction in the immunoreactivity of allergenic proteins β-conglycinin (7S) and glycinin (11S)

Food allergies represent a serious problem affecting human health and soy proteins rank among the most allergenic proteins from food origin. The proteolytic enzymes produced by lactic acid bacteria (LAB) can hydrolyse the major allergens present in soybean, reducing their immunoreactivity. Many studies have reported the ability of LAB to ferment soy-based products; while the majority of them focus on the improvement of the sensory characteristics and functionality of soy proteins, a lack of information about the role of lactic fermentation in the reduction of immunoreactivity of these proteins exists. The aim of the present study was to evaluate the capability of the proteolytic strain Enterococcus faecalis VB43 to hydrolyse the main allergenic proteins present in soymilk and to determine the immunoreactivity of the obtained hydrolysates. Sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) results of fermented soymilk demonstrated complete hydrolysis of the β-subunit from β-conglycinin and the acidic polypeptide from glycinin. Reversed phase high performance liquid chromatography (RP-HPLC) analysis of the peptides released after hydrolysis revealed the appearance of new peptides and the disappearance of non-hydrolysed proteins, indicating extensive hydrolysis of the substrate. Results from competitive enzyme-linked immunosorbent assay (ELISA) tests clearly indicated a reduction in the immunoreactivity (more than one logarithmic unit) in the fermented sample as compared to the non-fermented control. Our results suggest that the soymilk fermented by E. faecalis VB43 may induce lower allergic responses in sensitive individuals. The strain E. faecalis VB43 may be considered as an excellent candidate to efficiently reduce the immunoreactivity of soymilk proteins.