The effect of pectin surface density (ρ s ) on the engineering properties of high methoxyl (HM) pectin-based edible films was determined in order to explore the role of ρ s on structure and functional properties. Films at different ρ s values (2.5, 3.2, 3.8, 4.5, 5.1, 5.8 mg cm −2 ) were analyzed by means of microscopy, thermal, mechanical, and barrier (water vapor permeability WVP, oxygen permeability kP O 2 , carbon dioxide permeability kP CO 2 ) properties. Microscopy, thermal, and mechanical results showed that by increasing ρ s from 2.5 to 5.8 mg cm −2 , the film structure does not change. HM pectin-based film has a tensile strength of 20±7 MPa and an elastic modulus (E) equal to 2,400±200 MPa. However, it is quite brittle as the elongation to break (e) is close to 1%. Although the film structure was unaffected by ρ s , WVP increased with the rise in ρ s while kP O 2 and kP CO 2 decreased. On the whole, HM pectin-based film showed barrier properties comparable to biodegradable commercial film and low selectivity.
Eight trained assessors evaluated one visual, eight texture and four gustative attributes of 15 commercial spreads. In addition, 100 consumers evaluated the acceptability of the spreads. Rheological behavior of the samples was evaluated in transient (stress-relaxation test) and dynamic (strain and frequency sweep test) shear mode. Thermal measurements were also performed. Finally, the microstructure of the samples was analyzed by scanning electron microscopy. Partial least squares regression was used to predict acceptability from sensory attributes and texture from instrumental data. Scanning electron micrographs indicated that spreads differed in morphology, size and distribution of hazelnut particles. Overall liking of the spreads was found to be related to hazelnut flavor and texture attributes. Prediction of the most important texture properties from instrumental measurements was quite successful, especially for spreadability which was found negatively related to the consistency and flow indices and, secondly, for meltability which was found to be strongly dependent on measured thermal parameters.
PRACTICAL APPLICATIONSThis study contributes to knowledge development in the research area of acceptability, sensory and instrumental correlation for semi-solid foods. The results confirm that texture properties of spreadable foods play a most important role in consumer acceptability. The research also allows better understanding as to why no single measurement is able to predict all texture attributes 1 Corresponding
In this work, the effect of the weight ratio (Y E/C ) between transglutaminase (TGase) and sodium caseinate on the main engineering properties and microstructure of maltodextrin/caseinate/glycerol-based films, as well as crosslinking kinetics of the corresponding film-forming mixtures, was assessed. In the absence of TGase, the film forming solution did not jelly at all even after a 20-h gel cure experiment at 30°C. As Y E/C was increased from 0.5 to 8.3 mg/g, the gel point time exhibited quite a hyperbolic dependence on Y E/C , whereas the pseudo-first order reversible kinetic constant rate of casein reticulation linearly increased with the enzyme concentration. Despite a certain data scattering, the initial and equilibrium complex shear moduli appeared to be practically constant and independent of Y E/C . This finding was also extended to the mechanical and water barrier properties of the films under study. This was also indirectly confirmed by scanning electron microscopy, the film structure being quite compact, dense, and about free of air bubbles. In particular, their complex tensile modulus (E*) resulted to be not only independent of the cross-linking agent dosage but also interconvertible with the elastic modulus (E) determined in the quasi-static mode at an initial strain rate equal to the angular frequency. The water vapor permeability (WVP) for all the films examined was found to be extremely dependent on the water, desiccant, or Permatran-W standard methods used as well as on the difference in water activity (a W ) at the inside (a Wi =1.0 or 0) and outside (a Woi =0 or ∼0.5) of the test cup. By maintaining a Wi =0 and a Woi =0.5, the Permatran-W method yielded practically constant WVP values (30±4 pg m −1 s −1 Pa −1 ) whatever the enzyme/ caseinate ratio used. Nevertheless, TGase appeared to decrease the water vapor permeability of not cross-linked maltodextrin-caseinate films.
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