Addition Of Cell-free Extracts Research Articles

Effect of Yogurt Addition on the Stability of Anthocyanin during Cold Storage of Strawberry, Raspberry, and Blueberry Smoothies.

The addition of yogurt to fruit smoothies enhances their nutritional value by introducing components not naturally found in fruit products. However, the addition of fermented products can affect the stability of fruit bioactive components in fruits, such as anthocyanins. This study aimed to evaluate the effect of varying yogurt additions (0, 10, 20, and 30%) on the stability of anthocyanins during a 4-week refrigerated storage period. The smoothies were obtained from purees of strawberry, raspberry, and blueberry, combined with apple juice and apple puree. In addition, to elucidate the causes of the observed changes in the smoothies, model studies were conducted using purified anthocyanin extracts obtained from the analyzed fruits. We assessed the effects of pH, hydrogen peroxide concentration, and the addition of cell-free extracts from Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus on changes in anthocyanin content during storage. We found that adding yogurt led to a decrease in anthocyanin stability during the 4-week cold storage period. Specifically, a 30% yogurt addition decreased anthocyanin stability in all tested beverages, while a 20% yogurt addition impacted the strawberry and raspberry smoothies. The degree to which yogurt affected anthocyanin stability was dependent on the source of the raw material. The most notable impact was observed in strawberry smoothies and the least in blueberry smoothies. The variability could be attributed to differences in anthocyanin profiles among the fruits, the chemical composition of the beverages, and the observed difference in the survival rates of lactic acid bacteria. Model studies showed that during the storage of anthocyanin extracts, the addition of hydrogen peroxide and cell-free extract had a significant effect, whereas pH within the examined range (3.0-4.5) did not affect anthocyanin stability.

Biotic factors in induced defence revisited: cell aggregate formation in the toxic cyanobacterium Microcystis aeruginosa PCC 7806 is triggered by spent Daphnia medium and disrupted cells

Bioassays with the toxic cyanobacterium Microcystis aeruginosa PCC 7806, its non-toxic mutant ΔmcyB, and Daphnia magna as grazer were used to evaluate biotic factors in induced defence, in particular cyanobacterial and grazer-released info-chemicals. Three main questions were addressed in this study: Does Daphnia grazing lead to a loss of cyanobaterial biomass? Is the survival time of Daphnia shorter in a culture of the toxic cyanobacterium? Does direct grazing or the presence of spent Daphnia medium or a high number of disrupted toxic Microcystis cells in the assays lead to an increase in the cellular microcystin content in the remaining intact cells? The biovolume (growth) as well as size and abundance of Microcystis aggregates were determined by particle analysis, while the survival time of Daphnia individuals was recorded by daily observation and counting, with the relative concentration of cell-bound microcystin-LR, was measured by HPLC analysis. Compared to some recent studies in the field of induced defence, in this study, evidence was found for a direct grazing effect, i.e. the loss of biovolume in the toxic culture. In addition, Daphnia magna ingested more non-toxic than toxic cells, and survived longer with non-toxic cells. In terms of increased cell-bound toxin concentration as a means of defence reported in some studies, a higher cell-bound microcystin-LR content was not measured in this study in any of the treatments (P > 0.05). Under low light conditions with impaired growth of Microcystis, and the presence of a high number of particles with less than 1-μm diameter (possibly heterotrophic bacteria), Daphnia medium was associated with a strong reduction in cell-bound toxin concentration (P 0.05), but increased aggregation with spent Daphnia medium under high light conditions (P < 0.05). Further, the addition of cell-free extract from disrupted toxic Microcystis cells strongly increased the aggregation of the intact cells under low light (P < 0.05). These findings are discussed with the possible role of microcystin and other infochemicals in the expression of proteins and morphology changes in Microcystis.

Sensory improvement of dry-fermented sausages by the addition of cell-free extracts from Debaryomyces hansenii and Lactobacillus sakei

The effects of the addition of a combined cell-free extract from Lactobacillus sakei and Debaryomyces hansenii (D + L) or just a D. hansenii cell-free extract (D) to the initial formulation of a dry-fermented sausage were evaluated. The differences found among batches in the main microbial populations, pH, moisture content and global proteolytic and lipolytic indexes (total free amino acids, non protein nitrogen, acidity and tiobarbituric acid index) were not significant. Only, the acidity value of batch D was significantly higher ( p < 0.05) than that of batch D + L. Thus, cell-free extract from D. hansenii accelerated the lipolysis. Moreover, there were some significant differences ( p < 0.05) in the amino acid profile and, especially, in the aroma profile. The combination D + L and D promoted the generation of volatile compounds derived from lipid oxidation and carbohydrate fermentation. In batch D, the production of volatile compounds derived from amino acid catabolism and microbial fermentation was also enhanced. The overall quality was improved by both treatments (D + L, D) and also the aroma by addition of the combination of extracts (D + L). It is concluded that the addition of cell-free extracts from D. hansenii and, particularly, D. hansenii plus L. sakei could be useful to improve the final quality of fermented sausages.

Functional Demonstration of Reverse Transsulfuration in the Mycobacterium tuberculosis Complex Reveals That Methionine Is the Preferred Sulfur Source for Pathogenic Mycobacteria

Methionine can be used as the sole sulfur source by the Mycobacterium tuberculosis complex although it is not obvious from examination of the genome annotation how these bacteria utilize methionine. Given that genome annotation is a largely predictive process, key challenges are to validate these predictions and to fill in gaps for known functions for which genes have not been annotated. We have addressed these issues by functional analysis of methionine metabolism. Transport, followed by metabolism of (35)S methionine into the cysteine adduct mycothiol, demonstrated the conversion of exogenous methionine to cysteine. Mutational analysis and cloning of the Rv1079 gene showed it to encode the key enzyme required for this conversion, cystathionine gamma-lyase (CGL). Rv1079, annotated metB, was predicted to encode cystathionine gamma-synthase (CGS), but demonstration of a gamma-elimination reaction with cystathionine as well as the gamma-replacement reaction yielding cystathionine showed it encodes a bifunctional CGL/CGS enzyme. Consistent with this, a Rv1079 mutant could not incorporate sulfur from methionine into cysteine, while a cysA mutant lacking sulfate transport and a methionine auxotroph was hypersensitive to the CGL inhibitor propargylglycine. Thus, reverse transsulfuration alone, without any sulfur recycling reactions, allows M. tuberculosis to use methionine as the sole sulfur source. Intracellular cysteine was undetectable so only the CGL reaction occurs in intact mycobacteria. Cysteine desulfhydrase, an activity we showed to be separable from CGL/CGS, may have a role in removing excess cysteine and could explain the ability of M. tuberculosis to recycle sulfur from cysteine, but not methionine.

Cell-free Synthesis of the Major Storage Protein of the Bean, Phaseolus vulgaris L.

As seeds of the French bean (Phaseolus vulgaris, L. cv. Tendergreen) mature, a single protein, G1 globulin (analogous to legumin), represents the majority of protein synthesized. Washed polysomes extracted from developing cotyledons had little endogenous activity in amino acid incorporation, but on addition of cell-free extracts from wheat germ, active incorporation was obtained, the level being similar to that with viral RNA as messenger. The Mg(2+) optimum for protein synthesis in the presence of bean polysomes was 6 mm compared with 4 mm for synthesis of viral polypeptides in the wheat germ system. Using T-2 toxin as an inhibitor, it was shown that 29% of the incorporation depended on initiation events. Electrophoretic analysis of the total polypeptide products of cell-free synthesis gave a disperse profile. Centrifugation to remove polysome-bound peptides after 60 minutes incubation gave a supernatant having a product with the same electrophoretic mobility as G1 globulin and containing 26% of the radioactivity present in the gel. Protein eluted from this peak was subjected to re-electrophoresis and shown to consist of the three polypeptide subunits characteristic of G1 globulin.