Rheological characterization under shear of a fraction of polymer produced via fermentation of whey-related media by Rahnella aquatilis1Most material reported in this paper was presented in poster form at GLUPORTwO-Second International Meeting of the Portuguese Carbohydrate Chemistry Group, and such communication received the Best Poster Award.1

Elaboration of spin-coated cellulose-xyloglucan multilayered thin films

In the context of developing a biomimetic model of the primary cell wall, our aim was to produce multilayered thin films composed of cellulose nanocrystals (CN) and xyloglucan (XG). We investigated the effect of XG concentrations ranging from 0.5 g/L to 10 g/L. The choice of concentration was based on rheological investigation of the XG solutions which indicated that the two lower concentrations (0.5 and 1 g/L) correspond to a semidilute regime where the polymer chains are not entangled, whereas they are entangled at the highest concentrations (5 and 10 g/L). Several processes of film preparation were tested (dipping or spin-coating, with or without a rinsing step). The film growth profiles obtained for different XG concentrations by mechanical profilometry showed that spin-coating without rinsing was the most efficient process. Results showed that at high XG concentrations (XG = 5 g/L and XG = 10 g/L) plateau values were reached after the formation of 3 or 4 bilayers, whereas growth of the multilayer structure was linear at the lower XG concentrations (XG = 0.5 g/L and XG = 1 g/L). The thickness of one CN/XG bilayer corresponded to a single layer of CN covered by a thin XG layer, despite the absence of a rinsing step between successive coatings. The importance of the XG concentration was confirmed by determining by neutron reflectivity the film architecture obtained from four XG solutions after eight successive paired coatings. The results are discussed in relation to the role of XG in the plant cell wall.

Rheological Behavior and Organoleptic Effects of Ovalbumin Addition in Yogurt Mousse Production

Yogurt mousse is a novel, high added-value dairy product that has been well received by the market. This paper presents a study of the effect of the addition of ovalbumin to the product on its rheological and organoleptic qualities. The ovalbumin was previously separated from egg white with a high grade of purity using an ion exchange resin synthesized by the authors. Diverse rheological tests at different temperatures and corresponding sensorial assessments were conducted to compare samples without and with added ovalbumin. The obtained results confirm that the product is viscoelastic and combines the properties of foams and emulsions; the elastic component is greater than the viscous component. Moreover, at temperatures ranging from 5 to 15 degrees C, a usual interval of consumption, the product behaves rheologically in a similar way. Conversely, the addition of ovalbumin under the assayed conditions also makes the elastic character of the product increase at a given temperature. Finally, the sensorial assessment tests and determinations of stability and volume yield enabled us to verify that the addition of ovalbumin at an amount of 1.3% hardly alters the stability, resistance to shear stress, or the texture and improves the degree of foaming. Therefore, the product with additive is of good commercial quality.

ADSA Foundation Scholar Award. Critical issues affecting the future of dairy industry: individual contributions in the scope of a global approach

Several constraints that have been affecting the dairy industry are identified in a critical fashion, and directions are given with an emphasis on food processing implemented at the postproduction level. The rationale for modifications aimed at enhancing the appeal of condensed dairy products should be consubstantiated in strengthening of organoleptic characteristics, improvement of nutraceutical impact, and reduction of polluting power. This enumeration follows an order of increasing time scale required for consumer perception and increasing size scale associated with expected impact. Pursuance of such streamlines should lead to manufacture of dairy products that resemble nature more closely in terms of milk coagulation, milk fat modification, milk fermentation, whey fermentation, and starter culture addition. Directions for research and development anticipated as useful and effective in this endeavor, and which have been previously and consistently adopted in the development of an individual research program, are characterization and development of alternative rennets from plant sources, development of starter and nonstarter cultures from adventitious microflora, utilization of probiotic strains as starter cultures, upgrading of whey via physical or fermentation routes, and modification of milk fat via lipase-mediated interesterification reactions.