Children's physiological and behavioural response evoked by the observation, olfaction, manipulation, and consumption of food textures. Part 1: Liquid products.

Children are thought to prefer homogeneous and simple textures that are easy to manipulate in the mouth. Although scientific research has been done on children's acceptance for food textures, there is a lack of knowledge regarding the emotional response elicited by textures in this group of population. Physiological and behavioural methods could be an appropriate approach to measure food-evoked emotions in children since they require a low cognitive effort and allow a real-time measure. In this regard, a study that combined the measure of skin conductance response (SCR) and facial expressions was conducted: (i) to provide a first insight into food-evoked emotions induced by liquid food products that only vary in texture, (ii) to capture the emotional response evoked by the observation, olfaction, manipulation, and consumption of the products, and (iii) to overcome methodological drawbacks that are frequently associated to these methods. To achieve these goals, 50 children (5-12 yrs old) evaluated three liquids designed to only vary in texture (from slightly thick to extremely thick), following four sensory tasks: observation, olfaction, manipulation, and consumption. After each sample was tasted, children rated liking with a 7-pt hedonic scale. Facial expressions and SCR were monitored during the test, and they were analysed as action units (AUs) and basic emotions as well as changes in SCR. Results showed that the extremely thick liquid was less liked by the children and induced a more negative emotional response, whereas the slightly thick liquid was more liked and evoked a more positive emotional response. The combined method used in this study showed good discrimination ability among the three samples tested, obtaining the best discrimination during the manipulation task. The codification of the AUs located in the upper side of the face allowed us to measure the emotional response evoked by the consumption of the liquids, without the artifacts caused by the oral processing of the products. This study provides a child-friendly approach to be used during the sensory evaluation of food products in a broad range of sensory tasks minimising the methodological drawbacks.

Impact of Oscillating Magnetic Field Assisted Freezing on Lactobacillus plantarum Viability: Effects of Frozen Storage Time and Freeze-thaw Repetitions.

BACKGROUND: Oscillating magnetic field (OMF) assisted freezing has been proposed for improving the frozen preservation of biological materials. However, contradictory results have been reported on foods, tissues and cells, and so doubts exist in its actual benefit. OBJECTIVE: To study the effect of OMF-assisted freezing on the viability of fermentation starter Lactobacillus plantarum. MATERIALS AND METHODS: L. plantarum bacteria were frozen in a batch air blast freezer (-20ºC, 5 m s-1) by OMF-assisted freezing (0.57 mT). Bacterial viability was examined after 60 days of frozen storage and 5 freeze-thaw cycles. RESULTS: OMF showed no statistically significant effects (P > 0.05) in key freezing curve characteristics, refuting Cell Alive System (CAS) technology claims. OMF-assisted freezing did not improve bacterial preservation. CONCLUSION: There was no effect of the application of the maximum OMF (0.57 mT) on cell viability independently of the frozen storage time (up to 60 days) and freeze-thaw repetitions (up to 5 cycles).

Involvement of osmotic cell shrinkage on the proton extrusion rate in Saccharomyces cerevisiae.

Saccharomyces cerevisiae has been subjected to hyperosmotic shocks by using permeating (sorbitol, xylitol, glycerol, NaCl) and nonpermeating (PEG 600) solutes. The proton extrusion rate decreased as the osmotic pressure increased, whichever solute was used. However, the total inhibition of the cellular H+ extrusion depended on the solute used. A total inhibition was observed at about 20 MPa with glycerol, xylitol and sorbitol. With PEG 600, a total inhibition of extracellular acidification was obtained at 8.5 MPa. NaCl, with an extracellular pressure of 37.8 MPa (near saturation), did not completely inhibit the extracellular acidification. These results showed that the total inhibition of proton extrusion, involving probably the membrane H+-ATPase. was not correlated to the hydric state of the external medium but was strictly linked to the degree of permeation of solutes across the plasma membrane. The extracellular acidification was totally inhibited by a critical final cell volume reached after the osmotic shrinkage, whichever solute was used. This critical final cell volume represented 50% of the initial cell volume. This result suggests that the final cell volume reached after an osmotic stress represents a key thermodynamic parameter for cell osmoregulation in which H+-ATPase would be implicated.

Influence of thermal and osmotic stresses on the viability of the yeast Saccharomyces cerevisiae.

This work studies the effect of thermal and dehydration kinetics on the viability of Saccharomyces cerevisiae. The influence of the rate of temperature (T) and osmotic pressure (pi) increases are first investigated. Results showed that yeast viability is preserved by slow variations of temperature or osmotic pressure in a precise range of T or pi. The influence of a previous thermal stress on the resistance to a hyperosmotic stress is also studied. Temperatures equal to or lower than 10 degrees C allowed the preservation of viability after an osmotic stress whereas temperatures above 10 degrees C did not preserve yeast survival.

Slow heat rate increases yeast thermotolerance by maintaining plasma membrane integrity.

Thermal resistance of Saccharomyces cerevisiae was found to be drastically dependent on the kinetics of heat perturbation. Yeasts were found to be more resistant to a plateau of 1 h at 50 degrees C after a slope of temperature increase (slow and linear temperature increments) than after a shock (sudden temperature change). Thermotolerance was mainly acquired between 40-50 degrees C during a heat slope, i.e., above the maximal temperature of growth. The death of the yeasts subjected to a heat shock might be related to the loss of membrane integrity: intracellular contents extrusion, i.e., membrane permeabilization, was found to precede cell death. However, the permeabilization did not precede cell death during a heat slope and, therefore, membrane permeabilization was a consequence rather than a cause of cell death. During a slow temperature increase, yeasts which remain viable may have time to adapt their plasma membrane and thus maintain membrane integrity.

Passive response of Saccharomyces cerevisiae to osmotic shifts: cell volume variations depending on the physiological state.

The passive osmoregulation phase of S. cerevisiae has been characterized for different physiological states. The relative cell volume decrease of exponential cells was found to be greater than the volume decrease of stationary ones during the hyperosmotic shock. The application of a slow and linear increase in osmotic pressure has allowed the distinguishing of two phases in the passive osmoregulatory response of cells and to calculate the turgor pressure of S. cerevisiae. Cells in the exponential phase have a weak turgor pressure (0.05 MPa) compared to the turgor pressure of stationary phase cells (0.2 MPa). Nevertheless, the turgor pressure and the relative decrease in volume were found to be independent of the size of cells for the same physiological state.

Effect of the kinetics of temperature variation on Saccharomyces cerevisiae viability and permeability.

The variation rate of the temperature increase was found to have a great effect on the viability of Saccharomyces cerevisiae subjected to heat perturbations between 25 degrees C and 50 degrees C. A low intensity of the increase rate of temperature could maintain an important viability of the cells (about 34% of the initial population) with regard to the corresponding viability (about 1%) observed after a sudden step change for the same final temperature level of 50 degrees C. A cell volume reduction more important (22% of the initial volume) has been observed in cells submitted to a heat shock than for the cells which have been submitted to a slow kinetic of temperature increase (9%). Such an observation allowed to propose a relation between the membrane permeability and the kinetics of temperature variation.