Effect of Freezing/Thawing Temperature on the Viscoelastic and Nutritional Qualities of Carrots

This study evaluated and correlated the viscoelastic and nutritional properties of carrots after freezing (–20, –70, and –196^oC) and thawing (4 and 18^oC) treatments. Results showed that all samples exhibited a solid behavior (storage modulus G′ > loss modulus G″) dominating the viscoelastic response. After treatments, G′, G″, hardness, fracturability, springiness, and chewiness of carrots significantly decreased, whereas loss tangent (Tanδ) increased. Compared with other treatments, fast freezing (–196^oC) and thawing (18^oC) better maintained G′, G″, hardness, and fracturability of carrots, and intermediate freezing (–70^oC) better retained springiness, cohesiveness, and chewiness. For nutritional parameters, fast freezing and thawing conditions also contributed to preserving the contents of carotenoids of carrots. Partial least squares regression analysis revealed that β- and α-carotene, lycopene, and soluble sugars were positively correlated with hardness, fracturability, G′, and G″, and negatively with Tanδ in carrots. The variation of viscoelastic parameters could well predict the changes at nutritional levels.     

Effects of different osmo‐dehydrofreezing treatments on the volatile compounds,phenolic compounds and physicochemical properties in mango (Mangifera indica L.)

The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with concentration of 45%) on the volatile compounds, phenolic compounds and other physicochemical parameters in frozen mangoes were studied. Volatile and phenolic compounds were measured using SPME/GC‐MS and HPLC method, respectively. The results revealed that compared with untreated frozen mango, some volatile compounds (e.g. alcohols, aldehydes and some terpenes and esters) increased significantly and there were more compounds identified in osmo‐dehydrofrozen samples. These changes positively affected mango aroma and resulted in higher sensory scores for osmo‐dehydrofrozen samples. In addition, data on phenolic compounds showed that dehydrofrozen samples pretreated in glucose and sucrose had higher ρ‐hydroxybenzoic acid and quercetin contents, respectively, while samples pretreated in maltose showed higher ρ‐coumaric acid and sinapic acid contents compared with untreated frozen samples. The current work indicates that osmo‐dehydrofreezing can improve the retention of phenolic and aromatic compounds in frozen mango.     

Predicting the properties of petroleum blends

The aim of this study was to find new correlations to predict the properties of petroleum fractions blends. Several correlations for viscosity, smoke point, freezing point, Reid vapor pressure, aniline point, and cloud point were developed. These new correlations were assessed for their ability to predict the properties by comparing the estimated values with the experimental data as well as other correlations in literature. The developed correlations gave an absolute average deviation of 2.6 mm²/s for viscosity, 0.015 mm for smoke point, 0.05 K for freezing point, 6.47 kPa for RVP, 0.32 K for aniline point, and 0.9 K for cloud point.     

Experimental study on freezing of liquids under static magnetic field

Freezing processes of several liquids under static magnetic field (SMF) less than 50 mT were investigated.Central temperature of liquid samples held in glass test tubes immersed in a liquid bath was measured and collected.Nucleation temperature and phase transition time were obtained from freezing curves.Normality tests were performed for nucleation temperature of these liquids with/without magnetic field and normality distributions were justified.Analysis of variances was carried out for nucleation temperature of these liquids with magnetic field flux density as the influencing factor.Results showed that no significant difference was found for deionized water with or without SMF.However,differences exist in 0.9％ NaCl solution and 5％ ethylene glycol solution with and without SMF.Nucleation temperature of 0.9％ NaCl with SMF is lower than that without SMF,while its phase transition time is shorter than that without SMF.Nucleation temperature of 5％ ethylene glycol with SMF is higher than that without SMF,while its phase transition time is not modified with SMF.     

Effect of ultrasound irradiation on some freezing parameters of ultrasound-assisted immersion freezing of strawberries

In this study, the effect of ultrasound irradiation temperature and ultrasound intensity on the freezing and nucleation in strawberry samples was studied. The application of ultrasound irradiation at different temperatures was able to induce nucleation at lower degree of supercooling compared to the control samples. The achieved degree of supercooling in the ultrasound irradiated strawberries was linearly correlated to the ultrasound irradiation temperature. At the ultrasound irradiation temperature of −1.6 °C, the characteristic freezing time (CFT) was significantly shorter than that in the control sample (p < 0.05). The application of ultrasound at higher intensities was found to effectively shorten the CFT. The degree of supercooling in ultrasound irradiated samples was not linearly correlated to ultrasound intensity. In conclusion, the combination of ultrasound irradiation temperature and intensity can be effective in controlling nucleation and freezing processes of perishable fruits such as strawberry.     

Temperature dependency of linear viscoelastic properties of a commercial low-fat soft cheese after frozen storage

The temperature dependency of linear viscoelastic properties of a commercial low-fat soft cheese containing microparticulated whey protein as fat replacer was studied considering the effect of freezing. After thawing, cheeses were held at 6 °C during 48 days for ripening. Refrigerated cheeses (stored at 6 °C for 48 days) were used as control samples. Frequency sweeps (0.01-10 Hz) in the linear viscoelastic region at 10, 20, 30, 40, and 50 °C were performed. Activation energies for complex viscosity at 1 Hz were obtained from an Arrhenius-type equation. Also, the time-temperature superposition method, the modified Cole-Cole analysis and the weak gel model for foods were used to compare the behavior of frozen and refrigerated cheeses. The results obtained in this work indicated that the viscoelastic properties of the studied cheeses obtained at different temperatures were influenced by freezing.     

Osmotic dehydration pretreatment for improving the quality attributes of frozen mango: effects of different osmotic solutes and concentrations on the samples

The effect of osmotic dehydration pretreatment on the quality attributes (e.g. colour, hardness, drip loss, vitamin C content and pH) of frozen mango cuboids in different osmotic solutions (sucrose, glucose and maltose) and concentrations (30, 45 and 60% (wt/wt)) was investigated. Results revealed that melting temperature of mango cuboids was affected by both solute type and solid mass fraction. In addition, the dehydrofrozen samples pretreated in maltose had higher quality in vitamin C content (increasing by 23.5–73.0%), colour (colour change reducing by 2.6–39.2%) and drip loss (reducing by 0.7–9.7%) than those pretreated in other osmotic solutions. The cuboids pretreated in glucose displayed higher hardness (increasing by 16.4–36.2%). Based on principal component analysis and group distance, osmotic dehydration in 45% maltose was proposed as the most favourable freezing conditions with the highest sensory score (6.8). The current work indicates osmotic dehydration significantly improves frozen mango quality.     

Effect of freezing on the viscoelastic behaviour of whey protein concentrate suspensions

The effect of freezing on viscoelastic behaviour of whey protein concentrate (WPC) suspensions was studied. Suspensions with total protein content of 5% and 9% w/v were prepared from a commercial WPC (unheated suspensions). A group of unheated suspensions was treated at two temperatures (72.5 and 77.5 °C) during selected times to obtain 60% of soluble protein aggregates (heat-treated suspensions). Unheated suspensions and heat-treated suspensions were frozen at −25 °C (frozen unheated and frozen heat-treated suspensions). Frequency sweeps (0.01–10 Hz) were performed in the region of linear viscoelasticity at 10, 20, 30, 40, and 50 °C. Mechanical spectra of all studied suspensions at 20 °C were similar to viscoelastic fluids and complex viscosity increased with the frequency (ω). Elastic (G′) and viscous (G″) moduli were modelled using power law equations (G′ = aω^x, G″ = bω^y), using fitted parameters a, x, b, and y for statistical analysis. Exponent y was the most influenced by freezing, indicating the existence of a higher degree of arrangement in frozen unheated suspensions and a lower degree of arrangement in frozen heat-treated suspensions. Only characteristic relaxation times (inverse of the crossover frequency) of suspensions with 5% w/v of total protein content were significantly influenced by freezing. Time–temperature superposition was satisfactory applied in unheated whey protein concentrate suspensions only in the range of high temperatures (30–50 °C). However, this principle failed over the complete temperature range in most of the frozen suspensions. It is possible that freezing produced an increase in the susceptibility to morphological changes with temperature during the rheological measurements.     

Freeze concentration of whey in a falling-film based pilot plant: Process and characterization

Falling-film freeze concentration is a technique for concentration of liquids by freezing the available water in the form of a layer of ice on a refrigerated surface. Processing at low temperatures keeps the organoleptic properties of the initial product. In this study the freeze concentration of whey was investigated as an technological alternative for the use of this byproduct of the dairy industry. Freeze concentration tests were carried out in pilot-scale equipment and the increase in soluble solids content of the whey and the amount and purity of the ice formed were analysed. Electrical conductivity, viscosity and freezing point of the concentrated whey were determined. The concentrate obtained had a solid concentration of up to 21.8 °Brix. The ice formed in the last stage of the freeze-concentration process had a lactose content of 11.3 g/L and protein content of 3.45%. The electrical conductivity of the ice formed increased exponentially to a value of 29.40 mS/cm. Freeze-concentrated whey of 10, 15, and 20 °Brix behaves as a Newtonian fluid in the temperature range of −4 °C-4 °C.     

Effect of freezing treatments and yeast amount on sensory and physical properties of sweet bakery products

The frozen bakery market has grown significantly in developed countries over the past decade.