-Addition of CaCl 2 to skim milk, from 0 to 13.5 mmol·kg -1 , leads to significant physicochemical changes in milk salts equilibrium. Indeed, acidification, insolubilizations of calcium, inorganic phosphate and citrate are observed. Calculation of ion equilibria in the resulting milk ultrafiltrates indicates that the observed ion migrations, controlled by solubilities of calciumphosphate and calcium-citrate, do not cause change in ion activity products of dicalcium-phosphate (calculated as CaHPO 4 ·2H 2 O and Ca(HPO 4 ) 0.7 (PO 4 ) 0.2 ). In the same way, the acidification of calcium-supplemented milks in the range of pH 6.7-3.5 shows a solubilization of calciumphosphate similar to non-enriched milk. So whatever the added calcium concentration, the behaviour of colloidal calcium-phosphate seems to be unchanged. However, at room temperature, addition of calcium to milk originates a decrease in soluble casein concentration and tightly bound water of ultracentrifuged pellets. The consequences are (i) an increase in milk protein hydrophobicity; (ii) a decrease in zeta potential of casein micelles, without modification of their hydrodynamic diameter; and (iii) an increase in milk lightness and turbidity. Furthermore, calcium supplementation of milk seems to lead to a proteinic reorganization of micellar casein, responsible for an increase in micellar density. Milk / calcium / physicochemical characterization / calcium phosphate / acidification / supplementationRésumé -Caractérisation physicochimique d'un lait écrémé enrichi en calcium. L'addition de CaCl 2 à du lait écrémé, pour des concentrations allant de 0 à 13,5 mmol·kg -1 , induit d'importants changements physicochimiques du lait. En effet, une acidification, une insolubilisation du calcium, du phosphate inorganique et du citrate sont observées. Le calcul des équilibres ioniques dans les ultrafiltrats des différents laits montre que les flux ioniques observés, contrôlés principalement par les solubilités du phosphate et du citrate de calcium, ne modifient pas les produits d'activité ionique du phosphate dicalcique (calculés pour CaHPO 4 ,2H 2 O et Ca(HPO 4 ) 0,7 (PO 4 ) 0,2 ). De la même manière, l'acidification de ces laits supplémentés en calcium entre pH 6,7 et 3,5 montre une solubilisation du phosphate de calcium similaire à celle d'un lait non enrichi. Quelle que soit la concentration en calcium ajouté, le comportement du phosphate de calcium colloïdal semble donc inchangé. Par ailleurs, l'addition de calcium à du lait écrémé est responsable, à température ambiante, d'une diminution de la concentration en caséines ultracentrifugeables et de l'eau

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Kiwifruit (Actinidia spp.) is a recently domesticated fruit crop with several novel‐coloured cultivars being developed. Achieving uniform fruit flesh pigmentation in red genotypes is challenging. To investigate the cause of colour variation between fruits, we focused on a red‐fleshed Actinidia chinensis var. chinensis genotype. It was hypothesized that carbohydrate supply could be responsible for this variation. Early in fruit development, we imposed high or low (carbon starvation) carbohydrate supplies treatments; carbohydrate import or redistribution was controlled by applying a girdle at the shoot base. Carbon starvation affected fruit development as well as anthocyanin and carbohydrate metabolite concentrations, including the signalling molecule trehalose 6‐phosphate. RNA‐Seq analysis showed down‐regulation of both gene‐encoding enzymes in the anthocyanin and carbohydrate biosynthetic pathways. The catalytic trehalose 6‐phosphate synthase gene TPS1.1a was down‐regulated, whereas putative regulatory TPS7 and TPS11 were strongly up‐regulated. Unexpectedly, under carbon starvation MYB10, the anthocyanin pathway regulatory activator was slightly up‐regulated, whereas MYB27 was also up‐regulated and acts as a repressor. To link these two metabolic pathways, we propose a model where trehalose 6‐phosphate and the active repressor MYB27 are involved in sensing the carbon starvation status. This signals the plant to save resources and reduce the production of anthocyanin in fruits.

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