Consumer acceptance and sensory drivers of liking for high plant protein snacks.

BACKGROUND: Consumers are being encouraged to increase the proportion of plant protein in their diet to tend to a sustainable food system. Solutions could include developing a food rich in plant protein. However, these new products have an interest only if they are in accordance with expectation and the liking of consumers. In this context, extruded snack balls were developed to explore the sensory drivers of liking and barriers to consumption of formulated products with a high level of plant proteins. Eight different products varying in the type of cereal flour (rice or wheat) and pea flour content (from 60% to 90%) were developed following a factorial design. Eighty omnivore and 72 flexitarian consumers were recruited to evaluate the liking of these products. In addition, their sensory properties were described by a trained panel according to a profile method. RESULTS: The cereal type had globally more influence on liking than the percentage of pea. However, liking was inversely correlated with pea flour content, regardless of the cereal type. The main drivers of liking are texture criteria (in particular crispy and puffy), whereas flavor perception (pea, green) constitutes a barrier to acceptance. Interestingly, very few differences of liking were observed depending on the diet of consumers even though the attitudes of flexitarian'towards such type of products differed from those of omnivores. We identified three clusters of consumers based on their preferences. Pea flavor acceptance or rejection could explain these clusters. Although most consumers rejected pea flavor, approximately 40% of the participants preferred the products with highest pea content. CONCLUSION: The results of the present study will help provide guidance for innovative plant food design and formulation. © 2019 Society of Chemical Industry.

The single molecule probe: nanoscale vectorial mapping of photonic mode density in a metal nanocavity.

We use superresolution single-molecule polarization and lifetime imaging to probe the local density of states (LDOS) in a metal nanocavity. Determination of the orientation of the molecular transition dipole allows us to retrieve the different LDOS behavior for parallel and perpendicular orientations with respect to the metal interfaces. For the perpendicular orientation, a strong lifetime reduction is observed for distances up to 150 nm from the cavity edge due to coupling to surface plasmon polariton modes in the metal. Contrarily, for the parallel orientation we observe lifetime variations resulting from coupling to characteristic lambda/2 cavity modes. Our results are in good agreement with calculations of the nanoscale variations of the projected LDOS, which demonstrates the potential of single molecules as nonperturbative, nanoscale vectorial point probes in photonic and biological nanostructures.

Measurements of thickness dispersion in biolayers by scanning force microscopy and comparison with spectroscopic ellipsometry analysis.

Measuring the thickness of biological films remains a difficult task when using differential measurements by atomic force microscopy (AFM). The use of microstructured substrates combined with a selective adsorption constitutes an alternative to tribological measurements. The statistical thickness analysis of biological layers, especially via the dispersion measurements, can provide a way to quantify the molecular orientation. AFM thicknesses were then compared with those obtained optically by spectroscopic ellipsometry (SE) and surface plasmon resonance enhanced ellipsometry (SPREE). The biolayers could then be modeled using a vertical gradient of optical index, which reflects height dispersions. Thiol-modified DNA strands of various lengths account for a good biological model for the study of the strand motion in air and in liquid.

DNA nanofilm thickness measurement on microarray in air and in liquid using an atomic force microscope.

The measurement of the thickness of DNA films on microarray as a function of the medium (liquid, air) is gaining importance for understanding the signal response of biosensors. Thiol group has been used to attach DNA strands to gold micropads deposited on silicon surface. Atomic force microscopy (AFM) was employed in its height mode to measure the change in the pad thickness and in its force mode to measure the indentation depth of the nanofilm. A good coherence between the height and force modes is observed for the film thickness in air. The adhesion force was found to be an alternative way to measure the surface coverage of the biolayer at nanoscopic scale. However the force analysis (compression, steric and electrostatic) provides baseline information necessary to interpret the AFM height image in liquid. Analysis of the film thickness distribution shows that the height of the DNA strands depends on both the DNA strand length (15-35 base pairs) and the environment (air, liquid). In air, longer strands lay down onto gold surface whereas the charge reversal of gold in liquid causes a repulsion of longer strands, which stand up.

Surface plasmon near-field imaging of very thin microstructured polymer layers.

We report on the near-field imaging of microstructured polymer layers deposited on an homogeneous metal thin film on which a surface plasmon mode is excited. The microstructures in the polymer layers are designed by electron beam lithography, and the near-field imaging is performed with a photon scanning tunneling microscope (PSTM). We show that, despite their very small height, the microstructures can be conveniently imaged with a PSTM thanks to the field enhancement at the surface of the metal thin film supporting the surface plasmon. The influence of the illumination conditions on the contrast of the PSTM images is discussed. In particular, we show that both the field enhancement and the near-field intensity distribution around the microstructures depend dramatically upon the illumination conditions, leading to the conclusion that the PSTM is well suited for spatially resolved near-field surface plasmon sensing purposes.

Direct measurement of the melting temperature of supported DNA by electrochemical method.

The development of biosensors based on DNA hybridization requires a more precise knowledge of the thermodynamics of the hybridization at a solid interface. In particular, the selectivity of hybridization can be affected by a lot of parameters such as the single-strand (ss)DNA density, the pH, the ionic strength or the temperature. The melting temperature, T(m), is in part a function of the ionic strength and of the temperature and therefore provides a useful variable in the control of the selectivity and sensitivity of a DNA chip. The electrochemical technique has been used to determine the T(m) values when the probe is tethered by a DNA self-assembled monolayer (SAM). We have built a special thin layer cell, which allows the recording of the cyclic voltammogram under controlled temperature conditions. T(m) has been determined by recording the thermogram (current versus temperature) of a redox indicator on a double-stranded hybrid (dsDNA) modified electrode and comparison with the corresponding ssDNA response. T(m) of supported DNA varies linearly with the ionic strength. The stability of the SAMs has been considered and comparison between T(m) in solution and on a solid support has been discussed.

Performance of interdigitated nanoelectrodes for electrochemical DNA biosensor.

An electrochemical methodology for bio-molecule sensing using an array of well-defined nanostructures is presented. We describe the fabrication by e-beam lithography of nanoelectrodes consisting of a 100 micro m x 50 micro m area containing interdigitated electrodes of 100 nm in width and interelectrode distance of 200 nm. Sensitivity and response time of the nanoelectrodes are compared to the responses of macro- and microelectrodes. The specificity of the sensor is studied by modifying the gold electrodes with DNA. The technique enables to characterize both single and double-stranded DNA of 15 nucleotides. A special electrochemical cell is adapted to control the temperature and measure the DNA concentration by UV analysis. The electrochemical method requires no label on the DNA, only redox mediators were used.