The process of acetaldehyde formation by the yogurt bacterium Streptococcus thermophilus is described in this paper. Attention was focused on one specific reaction for acetaldehyde formation catalyzed by serine hydroxymethyltransferase (SHMT), encoded by the glyA gene. In S. thermophilus, SHMT also possesses threonine aldolase (TA) activity, the interconversion of threonine into glycine and acetaldehyde. In this work, several wild-type S. thermophilus strains were screened for acetaldehyde production in the presence and absence of L-threonine. Supplementation of the growth medium with L-threonine led to an increase in acetaldehyde production. Furthermore, acetaldehyde formation during fermentation could be correlated to the TA activity of SHMT. To study the physiological role of SHMT, a glyA mutant was constructed by gene disruption. Inactivation of glyA resulted in a severe reduction in TA activity and complete loss of acetaldehyde formation during fermentation. Subsequently, an S. thermophilus strain was constructed in which the glyA gene was cloned under the control of a strong promoter (P LacA ). When this strain was used for fermentation, an increase in TA activity and in acetaldehyde and folic acid production was observed. These results show that, in S. thermophilus, SHMT, displaying TA activity, constitutes the main pathway for acetaldehyde formation under our experimental conditions. These findings can be used to control and improve acetaldehyde production in fermented (dairy) products with S. thermophilus as starter culture.Yogurt is a product obtained through milk fermentation with a specific yogurt starter culture consisting of a mixture of two species of lactic acid bacteria (LAB), Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus (23). The main roles of this mixed starter in the production of yogurt are (i) acidification through the conversion of lactose into lactic acid, (ii) creation of the viscous texture by the production of exopolysaccharides, and (iii) development of the typical yogurt flavor (29).The typical yogurt flavor is caused by lactic acid, which imparts an acidic and refreshing taste, and a mixture of various carbonyl compounds like acetone, diacetyl, and acetaldehyde, the latter of which is considered the major flavor component (10,11,21,29). The relatively high concentration of acetaldehyde (in the range of 5 to 21 mg/liter) found in yogurt must be due to a low utilization rate of this metabolite since the yogurt bacteria lack the main enzyme for acetaldehyde conversion into ethanol, alcohol dehydrogenase (12).The production of acetaldehyde by LAB seems to be strain dependent. L. delbrueckii subsp. bulgaricus has been reported by some authors to be a greater acetaldehyde producer than S. thermophilus, whereas other authors have reported the contrary (21, 27). Although it is presently unclear what the major pathway for acetaldehyde production by LAB is, several metabolic pathways have been shown to lead to its formation (5, 24) and it is possible that more th...

-This work focuses on the adsorption of Bromelain in expanded bed conditions, such as the adsorption kinetics parameters. The adsorption kinetics parameters showed that after 40 minutes equilibrium was achieved and maximum adsorption capacity was 6.11 U per resin mL. However, the maximum adsorption capacity was only determined by measuring the adsorption isotherm. Only by the Langmuir model the maximum adsorption capacity, Qm, and dissociation constant, kd, values could be estimated as 9.18 U/mL and 0.591, respectively, at 25 °C and 0.1 mol/L phosphate buffer pH 7.5. A column made of glass with an inner diameter of 1 cm was used for the expanded bed adsorption (EBA). The residence time was reduced 10 fold by increasing the expansion degree 2.5 times; nonetheless, the plate number (N) value was reduced only 2 fold. After adsorption, the bromelain was eluted in packed bed mode, with a downward flow. The purification factor was about 13 fold and the total protein was reduced 4 fold. EBA showed to be feasible for purification of bromelain.

The aim of this research was to evaluate the effect of grape probiotic fermented beverages made of goat milk, with or without added grape pomace on gut microbiota in a Simulator of Human Intestinal Microbial Ecosystem (SHIME®). SHIME® model was used to investigate to assess changes in microbial composition and fermentation metabolites (short- and branched-chain fatty acids and ammonium), as well as under the antioxidant capacity. The results demonstrated that the beverages formulated, with or without grape pomace extract, exhibited high dietary fiber, oleic acid, phenolic compounds content and antioxidant activity. Both beverages also kept L. rhamnosus and S. thermophilus viable during their passage through the intestinal tract and had a positive effect on gut microbiota metabolism, increasing the antioxidant capacity and the production of short-chain fatty acids, and decreasing the ammonium concentration. Therefore, the multifunctional beverages formulated in this study can offer a new perspective for the production of foods with positive potential effects on human health.

Objetivou-se avaliar características do leite cru e do queijo Minas artesanal do Serro, Minas Gerais, produzidos em diferentes meses. Amostras foram coletadas em janeiro, março, maio, julho, setembro e novembro de 2013. No leite cru foi determinada a acidez titulável, densidade, gordura, umidade, massa seca, proteína, lactose, resíduo mineral fixo, coliformes totais e termotolerantes, Staphylococcus spp., Staphylococcus coagulase positiva, bactérias láticas e micro-organismos aeróbios mesófilos. Nos queijos foram realizadas as análises mencionadas, exceto densidade e lactose. Também foi determinado pH, atividade de água, firmeza, adesividade e cor (L*a*b*, croma e matiz). Houve variação (P<0,05) na acidez, lactose, contagens de coliformes termotolerantes e bactérias láticas no leite cru. Dentre estas, ressalta-se a maior acidez e menor teor de lactose em janeiro, março, julho, setembro e novembro, meses que também apresentaram maiores contagens de coliformes termotolerantes e bactérias láticas. Nos queijos houve variação, ao longo dos meses, para pH, acidez, gordura corrigida para a massa seca, massa seca, firmeza, adesividade, intensidade de verde (−a*), intensidade de amarelo (b*), croma (C), atividade de água, contagens de coliformes termotolerantes e Staphylococcus spp. Os resultados sugerem que o teor umidade, massa seca e gordura corrigida para massa seca dos queijos são suscetíveis à umidade relativa do ar e variações nestes parâmetros influenciam a firmeza, adesividade, atividade de água e cor. Assim como no leite, nos queijos foram observadas maiores contagens de coliformes termotolerantes e de Staphylococcus spp. em janeiro e novembro, os quais apresentam maior índice pluviométrico e temperatura mais alta.

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The typical yogurt flavor is caused by acetaldehyde produced through many different pathways by the yogurt starter bacteria L. bulgaricus and S. thermophilus. The attention was focused on one specific reaction for acetaldehyde and folic acid formation catalyzed by serine hydroxymethyltransferase (SHMT), encoded by the glyA gene. In S. thermophilus, this enzyme SHMT also plays the typical role of the enzyme threonine aldolase (TA) that is the interconvertion of threonine into glycine and acetaldehyde. The behavior of engineered S. thermophilus strains in milk fermentation is described, folic acid and acetaldehyde production were measured and pH and counts were followed. The engineered S. thermophilus strains StA2305 and StB2305, have the glyA gene (encoding the enzyme serine hydroxymethyltransferase) overexpressed. These engineered strains showed normal growth in milk when it was supplemented with Casitione. When they were used in milk fermentation it was observed an increase in folic acid and in acetaldehyde production by StA2305 and for StB2305 it was noticed a significative increase in folic acid formation.

Neste trabalho, foi avaliado o impacto da adição de inulina na aceitação sensorial e nas características microbiológicas e físico-químicas de um leite fermentado probiótico concentrado com maçã. Foram desenvolvidas três diferentes formulações com leite UHT: integral [I]; desnatado [D]; e desnatado com 1% de inulina (p/p) [IN]. Para a fermentação, foram utilizadas as bactérias láticas: Streptococcus thermophilus, Bifidobacterium animalis Bb-12 e Lactobacillus acidophilus La-5. Para a concentração do produto (separação de soro), utilizou-se um dessorador com o produto a 4 ºC por 12 horas. Com relação ao índice de aceitabilidade, não foi observada diferença significativa (p < 0,05) entre as formulações I, D e IN, que apresentaram, respectivamente, 82,9%, 78,0% e 75,1%. As três formulações estudadas apresentaram uma boa aceitação sensorial sendo que: 98% dos provadores atribuíram notas variando de 6 (gostei ligeiramente) a 9 (gostei muitíssimo) para a formulação I; 88% para a formulação D; e 82% para a IN. Em relação à contagem de Bifidobacterium, no dia do processamento, o produto apresentou 1,4×10(8) UFC/g, bem superior a 10(6) UFC/g, mínimo exigido pela legislação para que o produto possa ter alegação funcional de alimento probiótico. Após uma semana de armazenagem refrigerada, a formulação IN continha 9,6×10(7) UFC/g. Não foi observada diferença significativa na contagem deste probiótico durante o período de análise. O que determinou o fim da vida útil do produto foi a contagem de bolores e leveduras. Com relação aos sólidos totais e umidade, observou-se diferença significativa apenas entre a formulação D e IN, a I não diferiu das demais. O teor de proteína da I foi de 5,4%, mais baixo que o da D e da IN, que foram de 6,2%. O teor de gordura foi significativamente maior na I, igual a 3,9%, enquanto que para a D e IN não foi observada diferença significativa. Com relação à acidez, observou-se que a da IN foi superior às demais e não foi observada diferença com relação ao teor de cinzas. Esta pesquisa demonstrou ser possível produzir leite fermentado probiótico concentrado de maçã com inulina com boa aceitação sensorial, dentro das especificações da legislação vigente.

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