The effect of calcium palmitate on bacteria associated with infant gut microbiota.

Gut microbiota development in formula-fed and breast-fed infants is known to differ. This could relate to the usage of unmodified vegetable oil instead of mammalian fat in infant formula (IF), causing the enhanced formation of the poorly soluble soap calcium palmitate (CP) in the infant's gut. Here we investigate in vitro the possible influence of CP on the infant gut bacteria. The growth of several bacterial species dominant in the infant's gut was analyzed by culturing in media with CP. Faecalibacterium prausnitzii as a sensitive representative was analyzed in detail by scanning transmission electron microscopy, membrane staining, gas chromatography, and microbial fuel cell experiments. Of all bacteria tested, the growth of several bifidobacteria and F. prausnitzii was reduced at 0.01 mg/ml CP, Bifidobacterium infantis stopped growing completely. CP reduced the cell envelope thickness of F. prausnitzii, disturbed the cell membrane fatty acids and function of membrane proteins involved in electron transport. CP inhibited the growth of bifidobacteria and faecalibacteria. This suggests that modification of fat in IF may benefit the development of the gut microbiota in formula-fed infants by supporting the colonization of important beneficial bacteria in early life. Future clinical studies are needed to confirm this.

Heat-induced gelation of pea legumin: comparison with soybean glycinin.

Gel network formation of pea legumin (8.4% on a protein basis, pH 7.6) was monitored via dynamic rheological measurements. Gelation was performed in the absence and presence of the thiol-blocking reagent N-ethylmaleimide, at different rates of heating and cooling. Overall, it was shown that pea legumin gel formation was not effected by changes in the heating rate, and the two differently heated samples were unaffected by the addition of 20 mM NEM, which indicated that disulfide bonds were not essential within the network strands of these legumin gels. However, slowly cooling the legumin samples caused disulfide bonds to become involved within the network; this was observed by a large increase in gel strength that was then substantially reduced when repeating the sample in the presence of NEM. These experiments were repeated with soybean glycinin in order to determine whether a common model for gel formation of legumin-like proteins could be built, based upon molecular reasoning. The two proteins were affected in the same way by changes in the conditions used, but when applying a procedure of reheating and recooling the gel networks responded differently. Pea legumin gel networks were susceptible to rearrangements that caused the gels to become stronger after reheating/recooling, yet glycinin gel networks were not. It was concluded that the same physical and chemical forces drove the processes of denaturation, aggregation, and network formation. Each process can therefore be readily targeted for modification based upon molecular reasoning. Pea legumin and soybean glycinin gel networks had structurally different building blocks, however. A model of gelation aimed at texture control therefore requires additional information.

Characterization of pea vicilin. 1. Denoting convicilin as the alpha-subunit of the Pisum vicilin family.

Vicilin, a major globulin protein of pea that has been described as "extremely heterogeneous in terms of its polypeptide composition", was extracted from pea flour under alkaline conditions and subsequently fractionated by salt under acid conditions. This procedure induced the separation of vicilin into two fractions, which, after purification, were called vicilin 1 degrees and vicilin 2 degrees. Vicilin 2 degrees was seen on SDS-PAGE to contain the third globulin protein of pea, convicilin (a band at approximately 70 kDa). Vicilin fractions were thus characterized using gel electrophoresis, differential scanning calorimetry, circular dichroism, and pH-dependent solubility in order to determine whether the convicilin should in fact be considered as a third separate globulin protein of pea. On the basis of the results obtained it was concluded that this distinct polypeptide of the Pisum vicilin gene family should be further denoted as a subunit of the salt extractable protein vicilin. The definition of vicilin heterogeneity should therefore be extended to acknowledge the possible oligomeric inclusion of the 70 kDa polypeptide that is here denoted as the alpha-subunit.

Characterization of pea vicilin. 2. Consequences of compositional heterogeneity on heat-induced gelation behavior.

The gelling characteristics of two vicilin fractions from pea (Pisum sativum L.) were compared over a range of pH and salt conditions after preliminary results showed that despite having equal opportunity to unfold, and expose hydrophobic residues, they had different minimum gelling concentrations (at pH 7.6). Furthermore, at this pH one fraction formed turbid gels and the other formed transparent gels. The fraction that formed transparent gels contained a substantial amount of the 70 kDa alpha-subunits of vicilin, and thus it was hypothesized that the highly charged N-terminal extension region on these 70 kDa subunits hinders gelation of this vicilin fraction at pH 7.6 and I = 0.2 due to repulsion of the net negative charge. The experiments designed to test this hypothesis are presented and discussed in this paper and prove that the hypothesis was true, which offers the possibility to control or modify the gelation behavior of vicilin on the basis of information of its subunit composition.