The use of ultrasonics as an analytical technique for providing information about the physicochemical properties of foods is becoming increasingly popular in the food industry. Ultrasound can be used to rapidly and nondestructively measure properties such as food composition, structure, flow rate, physical state, and molecular properties. As well as being used as an analytical instrument in the laboratory, ultrasound can also be used for continuous monitoring of food properties on-line during processing. This article critically reviews the current status of ultrasound in the food industry, presents the basic principles of ultrasonic testing of foods, and highlights areas where ultrasound will prove to be most useful in the future.

Ultrasonic characterization of foods and drinks: Principles, methods, and applications

Here we investigate the solute-medium interaction and solute-centered dynamics in (RCONH2 + LiX) deep eutectics (DEs) via carrying out time-resolved fluorescence measurements and all-atom molecular dynamics simulations at various temperatures. Alkylamides (RCONH2) considered are acetamide (CH3CONH2), propionamide (CH3CH2CONH2), and butyramide (CH3CH2CH2CONH2); the electrolytes (LiX) are lithium perchlorate (LiClO4), lithium bromide (LiBr), and lithium nitrate (LiNO3). Differential scanning calorimetric measurements reveal glass transition temperatures (Tg) of these DEs are ∼195 K and show a very weak dependence on alkyl chain-length and electrolyte identity. Time-resolved and steady state fluorescence measurements with these DEs have been carried out at six-to-nine different temperatures that are ∼100–150 K above their individual Tgs. Four different solute probes providing a good spread of fluorescence lifetimes have been employed in steady state measurements, revealing strong excitation wavelength dependence of probe fluorescence emission peak frequencies. Extent of this dependence, which shows sensitivity to anion identity, has been found to increase with increase of amide chain-length and decrease of probe lifetime. Time-resolved measurements reveal strong fractional power dependence of average rates for solute solvation and rotation with fraction power being relatively smaller (stronger viscosity decoupling) for DEs containing longer amide and larger (weaker decoupling) for DEs containing perchlorate anion. Representative all-atom molecular dynamics simulations of (CH3CONH2 + LiX) DEs at different temperatures reveal strongly stretched exponential relaxation of wavevector dependent acetamide self dynamic structure factor with time constants dependent both on ion identity and temperature, providing justification for explaining the fluorescence results in terms of temporal heterogeneity and amide clustering in these multi-component melts.

Interaction and dynamics of (alkylamide + electrolyte) deep eutectics: dependence on alkyl chain-length, temperature, and anion identity.

Steady state and time-resolved fluorescence spectroscopic techniques have been used to explore the Stokes’ shift dynamics and rotational relaxation of a dipolar solute probe in molten mixtures of acetamide (CH3CONH2) with sodium and potassium thiocyanates (Na /KSCN) at T ∼ 318 K and several other higher temperatures The dipolar solute probe employed for this study is coumarin 153 (C153) Six different fractions (f) of KSCN of the following ternary mixture composition, 075CH3CONH2 + 025[(1 − f)NaSCN + fKSCN], have been considered The estimated experimental dynamic Stokes’ shift for these systems ranges between 1800 and 2200 cm−1 (±250 cm−1), which is similar to what has been observed with the same solute probe in several imidazolium cation based room temperature ionic liquids (RTIL) and in pure amide solvents Interestingly, this range of estimated Stokes’ shift, even though not corresponding to the megavalue of static dielectric constant reported in the literature for a binary mixture of molten CH3CON

Fluorescence spectroscopic studies of (acetamide + sodium/potassium thiocyanates) molten mixtures: composition and temperature dependence.

Summary
The use of ultrasound to determine the sugar content of fruit juices and drinks has been assessed. The velocity of ultrasound and the density were measured in solutions of D-glucose, D-fructose, and sucrose at various concentrations (0–40% w/v) and temperatures (10–30°C). The velocity of ultrasound was measured in 50:50wt:wt mixed solutions of sucrose and D-glucose over the same range of concentrations and temperatures. Measurements of the velocity of ultrasound, the density and the refractive index were made on various fruit juices and drinks at 20°C. The sugar content of the juices and drinks was determined by enzymatic assay. Ultrasonic measurements are shown to predict sugar contents in pure sugar solutions to within 0.2% w/v and in mixed sugar solutions to within 0.5% w/v. The ultrasonic measurements were sensitive to sugar species. It is shown that ultrasound compares well with other techniques for sugar content determination in fruit juices and drinks, and has the advantage that the equipment can be used for on-line process control. Applications for this ultrasonic technique are proposed.

Analysis of the sugar content of fruit juices and drinks using ultrasonic velocity measurements

Dielectric relaxation (DR) measurements in the frequency range 0.2 ≤ ν/GHz ≤ 50 have been carried out for neat molten acetamide and six different (acetamide + electrolyte) deep eutectic solvents (DESs) for investigating ion effects on DR dynamics in these ionic DESs. Electrolytes used are lithium salts of bromide (LiBr), nitrate (LiNO3), and perchlorate (LiClO4); sodium salts of perchlorate (NaClO4) and thiocyante (NaSCN); and potassium thiocyanate (KSCN). With these electrolytes acetamide forms DESs approximately at an 80:20 mol ratio. Simultaneous fits to the measured permittivity (e′) and loss (e″) spectra of these DESs at ∼293 K require a sum of four Debye (4-D) processes with relaxation times spread over picosecond to nanosecond regime. In contrast, DR spectra for neat molten acetamide (∼354 K) depict 2-D relaxation with time constants ∼50 ps and ∼5 ps. For both the neat and ionic systems, the undetected dispersion, e∞ – n(D)2, remains to be ∼3–4. Upon comparison, measured DR dynamics reveal pronounced anion and cation effects. Estimated static dielectric constants (e0) from fits for these DESs cover the range 12 < e0 < 30 and are remarkably lower than that (e0 ∼ 64) measured for molten acetamide at ∼354 K. Hydrodynamic effective rotation volumes (Veff) estimated from the slowest DR relaxation time constants vary with ion identity and are much smaller than the molecular volume of acetamide. This decrease of e0 and Veff is attributed respectively to the pinning of acetamide molecules by ions and orientation jumps and undetected portion to the limited frequency coverage employed in these measurements

Dielectric Relaxations of (Acetamide + Electrolyte) Deep Eutectic Solvents in the Frequency Window, 0.2 ≤ ν/GHz ≤ 50: Anion and Cation Dependence.

Supercooling phenomena in binary mixtures of acetamide and inorganic salts

The shear impedance, density and viscosity of the eutectic mixture NaCNS + CH3CONH2 have been measured in the temperature range 253–313 K and at the frequencies 31 and 87 MHz. The real parts of the complex impedance and of the rigidity modulus have been obtained. The relaxation region is shifted in comparison with that of the Maxwell model and is interpreted using the modified B.E.L. model. Irregularities in the real part of the mechanical impedance (around 283 K) and in the Arrhenius plot of the viscosity (around 293 K) may be attributed to changes in the liquid structure.

Viscoelastic relaxation in the acetamide + sodium thiocyanate binary system

Electrolyte-acetamide molten mixtures

The behavior of the molten system acetamide-electrolyte, including the peculiarity of the structure and the consequent relevant properties, such as the megavalue of the dielectric constant, was reported earlier. The probable structure is a micellar system composed of salt micelles dispersed in an amorphous solvent. The present paper reports measurements in a related system: fluoroacetamide-sodium trifluoroacetate. The phase diagram, the ultrasonic absorption of both longitudinal and shear waves, and the longitudinal relaxation time of the nuclear magnetic momentum were measured at different temperatures. The most importnat result was thatT 1 (NMR relaxation time) on the19F nucleus shows that the amide and salt participate in different environments. The amide environment is less rigid; this proves that the system must be considered microheterogeneous. Moreover, the present system exhibited: 1) a less extended concentration area where supercooling phenomena occur; 2) a much broader curve of the re...

Cryoscopic and dynamic study of the molten system fluoroacetamide-sodium trifluoroacetate

Ultrasonic and viscoelastic relaxation spectra were determined for a mixture of acetamide and calcium nitrate [X (acetamide)= 0.7644]. Retardation phenomena are present in the viscoelastic relaxation spectrum and they seem to be affected by the type of container used; the ultrasonic spectrum is due to a chemical equilibrium. There was no evident structural phenomenon.

G. Vitali

Papers

Supercooling phenomena in binary mixtures of acetamide and inorganic salts

Viscoelastic relaxation in the acetamide + sodium thiocyanate binary system

Electrolyte-acetamide molten mixtures

Cryoscopic and dynamic study of the molten system fluoroacetamide-sodium trifluoroacetate

Viscoelastic and ultrasonic relaxation in molten mixture of acetamide and calcium nitrate