M. Le Meste

Understanding the texture of low moisture cereal products: mechanical and sensory measurements of crispness

The texture of extruded starch products has been measured sensorially and instrumentally. The instrumental data were analyzed using different approaches such as fractal analysis and peak analysis. The data showed useful correlations between sensory crispness and crackliness and a parameter obtained from the application of a newly developed fractal method to analyze the force deformation curve obtained from a penetration test of the cereal samples. This suggests that fractal analysis of the force-deformation plots could be used instead of sensory analysis. n n n nMoreover, it was observed that an increase in water content altered the texture of starch based samples from crispy to crackly, whereas the texture of starch-sucrose samples remained unchanged in the same hydration range. n n n n© 2000 Society of Chemical Industry

Structural changes in oil-in-water emulsions during the manufacture of ice cream

Abstract Ice cream was manufactured on a pilot plant and the product was analysed in terms of droplet size distribution and protein composition of the aqueous phase at three stages of the process: after homogenization, after aging and after freezing-aeration-hardening stages. The components (fat 8% wt, skim milk powder 8% wt, glucose syrup 40 DE 6% wt, sucrose 16.75% wt, stabilizer 0.45% wt) and water were homogenized using a two stage high pressure homogenizer (19 MPa + 3 MPa, 70°C). The fat used was either butteroil or fresh unhomogenized milk cream. After an aging period (4°C, 18 h), ice cream mixes were frozen and aerated using a continuous ice cream freezer (overrun = 100%, outlet temperature = − 4°C), hardened in a blast air hardening tunnel (−40°C, 20 min) and stored (−30°C). Droplet size measurements in homogenized and aged mixes did not show any influence of the type of fat used: fat globule distributions were monomodal with an average surface/volume diameter d 32 ≃ 0.50 μm. For both fats, the aging stage did not affect the initial droplet size distribution. The freezing-aeration-hardening stage led to a partial flocculation of aged mix, the effect being more pronounced in butteroil ice cream than in cream ice cream. Protein analysis carried out on the aqueous phase of butteroil ice cream showed a preferential adsorption of caseins over whey proteins during the homogenization stage. Aging and freezing-aeration-hardening stages gave rise to a partial desorption of the proteins from the surface of fat globules, especially during the freezing-aeration-hardening stage.

Thermomechanical properties of glassy cereal foods

The main objective of this paper is to discuss the relationship between physical state, fracture mechanism, and texture for low moisture cereal-based foods. Experiments were also carried out to get a better understanding of the role of water. At room temperature, extruded bread and white bread (previously) dehydrated, then rehydrated in atmospheres with controlled humidities) exhibited a brittle behavior up to around 9% moisture. At 13.7% moisture, they were ductile. A significant loss in the crispness of extruded bread was observed between 8.5 and 10% moisture. The glass transition temperature (Tg) was measured, using dynamic mechanical thermal analysis (DMTA), for samples with up to 40% moisture. The resultingTg curve showed that the important changes in fracture mechanisms and crispness occurred while the samples were still in the glassy state. The viscoelastic behavior of both extruded and white breads suggested that a secondary relaxation occurred around 10‡C. Another event was observed around 70‡C for low moisture sample, using DMTA. This event was attributed to disruption of low energy interactions.

Thermomechanical Behavior of Concentrated Starch-Water Preparations

ABSTRACT The rheological behavior of concentrated starch preparations from various origins was studied by dynamic mechanical thermal analysis (DMTA). Four types of starch were used: wheat, potato, normal, and waxy corn adjusted to moisture contents in the 42–49% (w/w) range. The thermal treatments of the starch-water mixtures consisted of heating to 85°C and cooling to room temperature, both at a rate of 1°C/min. During heating, the storage modulus (E′) appearance was first characterized by an increase with a maximum at ≈70°C (or potato starch at 63°C) followed by a decrease to 85°C. During cooling, storage modulus increased steadily down to room temperature. The magnitude of these variations depended on the starch type. Despite some differences, all the loss tangent curves showed a decrease during heating from 60–70°C to 85°C, followed by a plateau during cooling. To propose an interpretation for the DMTA results, we measured, by laser-light diffraction, the influence of heating (up to the maximum E′ pea...

Interactions between food components in ice cream. Part 1: unfrozen emulsions

Abstract Ice cream was manufactured on a pilot plant and the structure of the emulsion was estimated in terms of droplet size distribution and protein composition of the aqueous phase after homogenization (two stages: 19 MPa + 3 MPa, 70°C) and after ageing ( 18 h, 4°C). Four different factors were studied: the nature of the milk protein [skim milk powder (SMP), skim milk replacer (SMR) or whey protein concentrate ( WPC) ], the nature of the emulsifier (saturated monoglycerides or Sugin Fl50, which is apolysorbate 80-based emulsifier) and its concentration (0.17–0.67% w/w for Sugin F150; 0.20–0.54% wlw for saturated monoglycerides), and the amount of butter oil (8–12% wlw). Freshly homogenized mixes containing either SMP or an SMR were stable during the ageing stage, irrespective of the nature and the concentration of the emulsifier. WPC-based mixes, however, were destabilized after homogenization: this destabilization was found to be flocculation only, which shows that whey proteins are efficient against coalescence. The quantity of adsorbed protein per surface unit was systematically higher for SMP mix than for both SMR and WPC. After the ageing stage, the structure of the mixes containing monoglycerides or WPC + polysorbate 80 remained unchanged. However, polysorbate 80 used in combination with both SMP and SMR led to a destabilization of the mix during the ageing stage: this destabilization was found to depend upon the mass/surface ratio of polysorbate 80 to butteroil.

Influence of Water on the Mobility of Small Molecules Dispersed in a Polymeric System

The rotational mobility of paramagnetic solutes dispersed in partially hydrated macromolecules (proteins, polysaccharides, synthetic polymers) was measured using Electron Spin Resonance. A critical minimum amount of water was observed to be necessary for these molecules to reach a level of mobility of the same order as in dilute solutions. This amount of water depended on the size of the diffusing solute and on the microporosity of the macromolecule. Above this critical moisture range, a progressive increase of the proportion of mobile solute occurred over a hydration range determined by the size of the diffusing solute. At the same time, the rotational diffusivity of the mobile solute increased linearly with water content. The mobilization pattern of spin-labelled side chains of caseinates was observed to be similar to that of the solute. Results are discussed with reference to free volume theory.

Factors influencing changes in moisture content during storage of freeze-dried vaccines in vials

Previous studies have demonstrated that the water content of freeze-dried vaccines increases during storage. The reasons for these variations in water content are discussed in this paper. Different possible mechanisms have been considered: microleakages at the closure sealing point, water vapour transfer through the closure (permeation, loss and uptake of water by the stopper). Several types of vials and closures were studied, under different conditions of storage. Regardless of the vial form selected, the probability of microleakages was low. The stopper would seem to play an important role in the water transfer mechanisms. The moisture content of the stopper determines its equilibrium relative humidity (ERH) and whether there will be moisture transfer between the stopper and the vial contents and between the stopper and the storage atmosphere.

An Electron Spin Resonance Study of the Interactions Between Proteins and Lipids

Despite the large using of milk proteins by the food industry, the mechanism of their action for emulsion stabilisation remains partially understood. Among the factors which are presumed to play a role in the mechanism, we selected to study both of them: 1) the affinity of milk proteins for lipids: neither its real importance, nor the nature of the lipids — proteins interactions are known. 2) the flexibility of protein which seems to have an essential function in the etablishment of the interactions with small solutes or polymers.