Production, isolation and characterization of exopolysaccharides produced by Lactococcus lactis subsp. cremoris JFR1 and their interaction with milk proteins: Effect of pH and media composition.

The aim of this work was to study exopolysaccharides (EPS) produced by Lactococcus lactis subsp. cremoris (JFR1), and their interactions with dairy proteins. The highest viscosities were obtained in media (permeate from filtration with polyvinylidene fluoride (PVDF) 0.1@mm) with added protein at pH 5.8 and 5.5. Isolated EPS showed a rheological behaviour different from that of the whole fermented media. The size of the EPS was measured using size exclusion chromatography coupled with light scattering detection. Results suggested that molecules with higher molecular mass and a more compact structure were produced from fermentation at pH 5.5 than molecules produced from fermentation at pH 6.5. Studies using dynamic light scattering demonstrated that EPS molecules are negatively charged and interact with whey proteins at acidic pH. It was concluded that the impact of EPS on textural properties is determined not only by the molecular characteristics but also by the ability to interact with proteins

Temperature desynchronizes sugar and organic acid metabolism in ripening grapevine fruits and remodels their transcriptome

Background: Fruit composition at harvest is strongly dependent on the temperature during the grapevine developmental cycle. This raises serious concerns regarding the sustainability of viticulture and the socio-economic repercussions of global warming for many regions where the most heat-tolerant varieties are already cultivated. Despite recent progress, the direct and indirect effects of temperature on fruit development are far from being understood. Experimental limitations such as fluctuating environmental conditions, intra-cluster heterogeneity and the annual reproductive cycle introduce unquantifiable biases for gene expression and physiological studies with grapevine. In the present study, DRCF grapevine mutants (microvine) were grown under several temperature regimes in duly-controlled environmental conditions. A singly berry selection increased the accuracy of fruit phenotyping and subsequent gene expression analyses. The physiological and transcriptomic responses of five key stages sampled simultaneously at day and nighttime were studied by RNA-seq analysis. Results: A total of 674 millions reads were sequenced from all experiments. Analysis of differential expression yielded in a total of 10 788 transcripts modulated by temperature. An acceleration of green berry development under higher temperature was correlated with the induction of several candidate genes linked to cell expansion. High temperatures impaired tannin synthesis and degree of galloylation at the transcriptomic levels. The timing of malate breakdown was delayed to mid-ripening in transgressively cool conditions, revealing unsuspected plasticity of berry primary metabolism. Specific ATPases and malate transporters displayed development and temperature-dependent expression patterns, besides less marked but significant regulation of other genes in the malate pathway. Conclusion: The present study represents, to our knowledge the first abiotic stress study performed on a fleshy fruits model using RNA-seq for transcriptomic analysis. It confirms that a careful stage selection and a rigorous control of environmental conditions are needed to address the long-term plasticity of berry development with respect to temperature. Original results revealed temperature-dependent regulation of key metabolic processes in the elaboration of berry composition. Malate breakdown no longer appears as an integral part of the veraison program, but as possibly triggered by an imbalance in cytoplasmic sugar, when efficient vacuolar storage is set on with ripening, in usual temperature conditions. Furthermore, variations in heat shock responsive genes that will be very valuable for further research on temperature adaptation of plants have been evidenced