A Tool For Explaining The Differences on Renneting Characteristics of Milks From Different Origins: The Surface Hydrophobicity Approach

The differences between renneting characteristics of raw milk samples from different origins (bovine, ovine, caprine, buffalo) were investigated by protein surface hydrophobicity approach. 8-Anilinonaphthalene-1-sulfonic acid (ANS) binding method was used to evaluate surface hydrophobicity of raw milk samples and rennet precipitates. The following surface hydrophobicity parameters were calculated: number of surface hydrophobic sites (F (max)), dissociation constant of the fluorescent ANS-protein complex (K (d)), binding affinity of ANS to protein surface (1/K (d)), the average tightness of binding of ANS to the protein (F (max)/K (d)), turnover number (k (cat)), and protein surface hydrophobicity index (PSHI). The number of hydrophobic sites on the protein surface was found to be highest in cow milk, whereas ovine milk samples had the lowest number of hydrophobic sites and binding affinity to ANS. Protein content was not found directly related to the number of surface hydrophobic sites. The binding affinity of the proteins to ANS was greater in buffalo milk. PSHI was found to be the highest for bovine milk and the lowest for ovine milk. Renneting period was interpreted in two phases (enzymatic phase and flocculation phase) for each origin via ANS partition curves of rennet precipitates. Same trends between bovine-ovine and caprine-buffalo milks were observed during renneting. Buffalo milk completed both of two phases and total renneting period significantly earlier than the milks from the other origins. The hydrophobic parameters of proteins were found to play a key role on coagulation properties.Wo

Water absorption and bicarbonate secretion in the intestine of the sea bream are regulated by transmembrane and soluble adenylyl cyclase stimulation

In the marine fish intestine luminal, HCO3 - can remove divalent ions (calcium and magnesium) by precipitation in the form of carbonate aggregates. The process of epithelial HCO3 - secretion is under endocrine control, therefore, in this study we aimed to characterize the involvement of transmembrane (tmACs) and soluble (sACs) adenylyl cyclases on the regulation of bicarbonate secretion (BCS) and water absorption in the intestine of the sea bream (Sparus aurata). We observed that all sections of sea bream intestine are able to secrete bicarbonate as measured by pH–Stat in Ussing chambers. In addition, gut sac preparations reveal net water absorption in all segments of the intestine, with significantly higher absorption rates in the anterior intestine that in the rectum. BCS and water absorption are positively correlated in all regions of the sea bream intestinal tract. Furthermore, stimulation of tmACs (10 lM FK? 500 lM IBMX) causes a significant decrease in BCS, bulk water absorption and short circuit current (Isc) in a region dependent manner. In turn, stimulation of sACs with elevated HCO3 - results in a significant increase in BCS, and bulk water absorption in the anterior intestine, an action completely reversed by the sAC inhibitor KH7 (200 lM). Overall, the results reveal a functional relationship between BCS and water absorption in marine fish intestine and modulation by tmACs and sAC. In light of the present observations, it is hypothesized that the endocrine effects on intestinal BCS and water absorption mediated by tmACs are locally and reciprocally modulated by the action of sACs in the fish enterocyte, thus fine-tuning the process of carbonate aggregate production in the intestinal lumen