Mean Ice Crystal Size Research Articles

Modeling ice recrystallization in frozen carrot tissue during storage under dynamic temperature conditions

Ice recrystallization occurring in vegetables during frozen storage causes changes in crystal morphology, and, thus, may affect product microstructure and quality. A mathematical model to describe the evolution of the crystal number density in frozen carrot tissue during dynamically changing temperatures was introduced to get a more comprehensive insight into microstructural changes. The model was based on a population balance equation that incorporated the ice crystal size distribution and a lumped heat transfer model, which assumed ice recrystallization via Ostwald ripening. Ice recrystallization was governed first by the dissolution of small crystals and then by redeposition at the surface of large crystals. This was observed mainly at the beginning of storage and gradually decreased as storage time proceeded. Sensitivity analysis showed that the activation energy is the most important model parameter, followed by the growth and dissolution coefficients. The model was validated based on measurements of the ice crystal size distribution and mean ice crystal size of carrot tissue to describe ice recrystallization during a two-month storage period under dynamically changing temperature condition. The PBE model was then applied to simulate ice recrystallization in carrots under industrial relevant conditions. The simulation results indicate that PBE model may be used to improve storage of frozen vegetables with respect to microstructure and quality.

The microstructural, melting, rheological, and sensorial properties of high-overrun frozen desserts.

Air incorporated during dynamic freezing influences the development of the microstructure and the final texture of frozen desserts. Frozen desserts were manufactured with 100-175% overrun from a constant ice cream mix formulation. Microstructural elements (fat, air, and ice phases) of the frozen desserts were then investigated and related to the melting, rheological, and sensory properties of the product. Mean ice crystal and air cell size were found to decrease with increasing overrun, and the extent of fat destabilization increased. Frozen desserts manufactured with higher overrun had slower drip-through rate and better shape retention after melting at ambient conditions, demonstrating that fat destabilization and the interplay of fat, air, and serum phases affect the melting behavior. Structural elements also influenced the rheological behavior, as measured by oscillatory thermo-rheometry. Frozen desserts had similar rheological properties at temperatures below the freezing point due to the presence of ice, and the values of G' and G″ (solid-like and viscous-like character, respectively) increased with increasing overrun above the freezing point, corresponding to a more solid-like structure. Slight differences in sensory denseness and breakdown were detected, but sensory texture was not significantly different for the frozen desserts studied. This study provided insights into the role of air in ice cream and frozen desserts, and its influence on product texture.

Single-step purification and characterization of antifreeze proteins from leaf and berry of a freeze-tolerant shrub seabuckthorn (Hippophae rhamnoides).

Seabuckthorn is a freeze-tolerant Himalayan shrub, capable of withstanding temperatures below -40°C. Antifreeze proteins prevent freezing associated damage by restricting ice crystals growth. In the present study, homogenous purification of two antifreeze proteins (41 and 39kDa) from Hippophae rhamnoides leaf and one (41kDa) from berry was performed using ice-affinity chromatography. MS identification and Basic Local Alignment Search Tool search showed homology of berry antifreeze proteins with disease resistance protein while leaf antifreeze proteins showed similarity with transmembrane protein (39kDa) and low temperature induced protein (41kDa) suggesting their role in cold stress signalling. Hexagon shaped ice crystals (Nanoliter osmometer) and ice recrystallization inhibition assay (Splat assay) confirmed higher ice recrystallization inhibition activity of purified leaf (2.5 fold decrease in mean ice crystal size) and berry (2.1 fold decrease) antifreeze proteins. String interactome analysis showed interaction of antifreeze proteins with cold stress modulated targets including pathogenesis related proteins. This probably is the first report of antifreeze proteins purification from naturally growing seabuckthorn. Further validation of these targets may open gates for commercial utilization of this plant growing abundantly in Himalayan regions of India, for crop improvement of freeze susceptible crops or biomedical applications like cryopreservation of tissues and cells.

Industrial Applications of Selected JFS Articles

Industrial Applications of Selected <i>JFS</i> Articles

Characterization of ice recrystallization in ice cream during storage using the focused beam reflectance measurement

Ice recrystallization was investigated in two commercial and differently stabilized ice creams using an original and real time particles counting and sizing method: the focused beam reflectance measurement (FBRM). Ice cream A (with locust bean gum – LBG – as primary stabilizer) and ice cream B (with carrageenan as primary stabilizer) were stored for 154days at four different temperatures (−5, −8, −12 and −18°C) and three amplitudes of temperature fluctuations (±0.1°C, ±0.75°C, ±2.5°C). Crystal’s size distributions were assessed at various time and recrystallization kinetic data were derived by fitting the experimental results to the asymptotic Ostwald ripening model. As expected, recrystallization rates increase with mean storage temperature and amplitude of temperatures fluctuations. Carrageenan seems to be more effective than LBG in slowing down ice crystal growth during storage. Mean ice crystal size increased as a function of time1/3 for both ice creams. The temperature dependence of recrystallization rate fitted Arrhenius well, with activation energies fairly similar for ice creams A and B.

Structural, compositional, and sensorial properties of United States commercial ice cream products.

Commercial vanilla ice cream products from the United States (full fat, low fat, and nonfat) were analyzed for their structural, behavioral (i.e., melt rate and drip-through), compositional, and sensorial attributes. Mean size distributions of ice crystals and air cells, drip-through rates, percent partially coalesced fat, percent overrun and total fat, and density were determined. A trained panel carried out sensory analyses in order to determine correlations between ice cream microstructure attributes and sensory properties using a Spectrum(TM) descriptive analysis. Analyses included melt rate, breakdown, size of ice particulates (iciness), denseness, greasiness, and overall creaminess. To determine relationships and interactions, principle component analysis and multivariate pairwise correlation were performed within and between the instrumental and sensorial data. Greasiness and creaminess negatively correlated with drip-through rate and creaminess correlated with percent total fat and percent fat destabilization. Percent fat did not determine the melt rate on a sensorial level. However, drip-through rate at ambient temperatures was predicted by total fat content of the samples. Based on sensory analysis, high-fat products were noted to be creamier than low and nonfat products. Iciness did not correlate with mean ice crystal size and drip-through rate did not predict sensory melt rate. Furthermore, on a sensorial level, greasiness positively correlated with total percent fat destabilization and mean air cell size positively correlated with denseness. These results indicate that commercial ice cream products vary widely in composition, structure, behavior, and sensory properties. There is a wide range of commercial ice creams in the United States market, ranging from full fat to nonfat. In this research we showed that these ice creams vary greatly in their microstructures, behaviors (the melt/drip-though, collapse, and/or stand up properties of ice cream products at ambient temperatures), and sensory properties.

Blends of delactosed permeate and pro-cream in ice cream: Effects on physical, textural and sensory attributes

Various blends of delactosed whey permeate (DLP) and pro-cream, a by-product of microfiltration during whey protein isolate production, were made and assessed for application in ice creams as a source of protein and fat. These blends were compared with control ice cream containing nonfat dried milk (NFDM) as the primary source of protein. Textural properties of ice creams were influenced by partial replacement of NFDM with DLP-pro-cream blends. Compared with control ice cream, those containing DLP-pro-cream blends showed similar mean ice crystal size, relatively higher melt rate, and reduced fat destabilization. Melt rate (based on linear portion of melting curve) correlated well with the fat globule size distribution or extent of fat destabilization. In sensory analysis, ice creams containing the DLP-pro-cream blends (30:70 and 50:50) were slightly less accepted by panelists than the control ice cream for most of the attributes, with an off-flavor more noticeable with increasing DLP content.

Addition of ice-nucleation active bacteria: Pseudomonas syringae pv. panici on freezing of solid model food

Ice-nucleation active bacteria (INAB), Pseudomonas syringae pv. panici, were cultured at 26 °C in a nutrient broth and harvested at late log phase. The ice-nucleation activity unit per unit volume of the bacterial culture measured by the droplet-freezing assay developed by Vali was 3.29 × 10 4 INA/mL. A differential scanning calorimetry (DSC) analysis of 77 g/100 g Tylose samples showed that the addition of bacteria had no obvious effect on the glass transition temperature and heat of fusion of the samples. Freezing operations carried out at −20 °C showed that the addition of INAB produced no obvious change in the freezing time. The scanning electronic microscope (SEM) observation of microstructure of the model food indicated that the mean ice crystal size was reduced from 25.7 μm to approximately 15 μm by the addition of INAB.

Ice Slurry Formation in a Cocurrent Liquid-Liquid Flow

A new technique for ice slurry production was explored. Multiple small water-drops were formed in another immiscible chilled liquid by a single-nozzled atomizer and frozen in the fluidized bed by direct contact heat transfer. Experiments were conducted to investigate the dynamic behaviors of the ice crystal making system. The results demonstrate that the ice crystals could be produced continuously and stably in the vertical bed with the circulating coolant of initial temperature below −5°C. The size distribution of the ice crystals appears non-uniform, but is more similar and more uniform at lower oil flow rate. The mean ice crystal size rests seriously with the jet velocity and the oil flow rate. It decreases with decreasing the oil flow rate, and reaches the maximum at an intermediate jet velocity at about 16.5 m·s −1. The ice crystal size is also closely related to the phenomenon of drop-coalescing, which can be alleviated considerably by reducing the flow rate or lowering the temperature of the carrier oil. However, optimization of liquid-liquid atomization is a more effective approach to produce fine ice crystals of desired size.

Ice crystallization in a scraped surface freezer

Ice crystal size plays an important role in determining the quality of ice cream, with small ice crystal sizes desired to enhance consumer acceptance. During freezing, nuclei formation must be promoted and ice crystal growth and recrystallization minimized to create many small ice crystals. The effects of sweetener type, draw temperature, dasher speed, and throughput rate on ice crystal size distributions during freezing of ice cream were investigated. These operating variables affect the mechanisms by which ice crystals form and ripen into the disc-shaped crystals observed exiting the freezer. Increasing the throughput rate, reducing the residence time, in the freezer allows less time at warmer temperatures where recrystallization occurs rapidly, which leads to smaller ice crystals at the freezer exit. Smaller ice crystals were also found at lower draw temperatures, since coolant temperatures were reduced, increasing the driving force for nucleation. Increased ice crystal size at draw occurred when faster dasher speeds were utilized due to the addition of frictional heat into the system causing melting of small crystals. Residence time was found to have the most pronounced effect on mean ice crystal size followed by draw temperature and dasher speed, whereas type of sweetener had no significant effect.

Analysis of Ice Structure Formed in Frozen Agar Gel

Ice crystal structure was analyzed for frozen agar gel under unidirectional freezing in various operating conditions to elucidate the mechanism of the process of ice crystal growth. A linear relationship was obtained between the mean ice crystal size and the inverse of the moving speed of the freezing front. The slope of the correlation was in the same order as the diffusion coefficient of water, suggesting the important role of the molecular diffusion in this growth process. No meaningful effect of the agar concentration was observed on the ice structure showing that the agar matrix structure does not affect the ice structure in an agar concentration ranging from 1.5 to 5%.

An Investigation into the Relationship Between Freezing Rate and Mean Ice Crystal Size for Coffee Extracts

Coffee extracts—10, 20 and 40% solids content—were uni-directionally frozen. The parameters characterizing freezing kinetics, such as the rate of fall of temperature and the velocity of ice front, were determined experimentally and compared with the predictions of Neumann's model. Freeze dried samples were subsequently observed under a fluorescence microscope and the mean size of ice crystals were determined from the mean hydraulic radius of the pores. A model linking the mean hydraulic radius with freezing kinetics was developed, and the following equation was obtained: r H = n exp(– mX so )[2δ 2 α 1 / s i ] [( T m — T p )s i −1 ] −0.5 . Here, X s is solid content, δ is Neumann's dimensionless constant, t is time, T m is the initial freezing point of the extract, T p is the freezing temperature, α 1 is the thermal diffusivity of the frozen region, s i is the position of the ice front and finally n and m are material related constants. Experimental data and model predictions were found to be in satisfactory agreement.

Effect of Double Homogenization and Whey Protein Concentrate on the Texture of Ice Cream

Ice cream samples were made with a mix composition of 11% milk fat, 11% milk solids-not-fat, 13% sucrose, 3% corn syrup solids (36 dextrose equivalent), 0.28% stabilizer blend, or 0.10% emulsifier and vanilla extract. Mixes were high temperature short time pasteurized at 80°C for 25s, homogenized at 141kg/cm2 pressure on the first stage and 35kg/cm2 pressure on the second, and cooled to 3°C. The study included six treatments from four batches of mix. Mix from batch one contained 0.10% emulsifier. Half of this batch (treatment 1), was subsequently frozen and the other half (upon exiting the pasteurizer) was reheated to 60°C, rehomogenized at 141kg/cm2 pressure on the first stage and 35kg/cm2 pressure on the second (treatment 2), and cooled to 3°C. Mix from batch two contained 0.28% stabilizer blend. Half of this batch was used as the control (treatment 3), the other half upon exiting the pasteurizer was reheated to 60°C, rehomogenized at 141kg/cm2 pressure on the first stage and 35kg/cm2 pressure on the second (treatment 4), and cooled to 3°C. Batch three, containing 0.10% emulsifier and 1% whey protein concentrate substituted for 1% nonfat dry milk, upon exiting the pasteurizer was reheated to 60°C, rehomogenized at 141kg/cm2 pressure on the first stage and 35kg/cm2 pressure on the second (treatment 5), and cooled to 3°C. Batch four, containing 0.28% stabilizer blend and 1% whey protein concentrate substituted for 1% nonfat dry milk, upon exiting the pasteurizer was reheated to 60°C, rehomogenized at 141kg/cm2 pressure on the first stage and 35kg/cm2 pressure on the second (treatment 6), and cooled to 3°C. Consistency was measured by flow time through a pipette. Flow time of treatment 3 was greater than all treatments, and the flow times of treatments 4 and 6 were greater than treatments 1, 2, and 5. Flow time was increased in ice cream mix by the addition of stabilizer. Double homogenization lowered ice cream mix flow time in the presence of stabilizer, but no difference in flow time was observed without stabilizer addition. Treatment 4 had a lower mean ice crystal size at 10 d postmanufacture compared with treatment 3; however, overall texture acceptability between treatments 3 and 4 was similar. Mean ice crystal size of treatment 6 was less at 18wk postmanufacture compared with treatment 3; however, overall texture acceptability for treatments 3, 4, and 6 was similar. Mean ice crystal sizes of treatments 1, 2, and 5 were greater at 10 d and 18wk compared with treatment 3. Sensory evaluation indicated that treatments 3, 4, and 6 had higher mean scores for icy, coldness intensity, and creaminess than treatments 1, 2, and 5 at 10 d and 18wk postmanufacture.

Experimental study and modelling of the ice crystal morphology of model standard ice cream. Part I: Direct characterization method and experimental data

A standard commercial dairy ice cream was used to study the ice crystal texture by a direct method namely by optical microscopy with episcopic coaxial lighting and with image analysis software (IPS). The exactness, precision and reproducibility of the method was checked. A mean ice crystal size at different locations inside the food samples was determined for different freezing conditions (initial temperature, freezing rate) and different compositions with and without stabilizers. This relatively new method for foodstuffs was compared with the freeze-drying method (indirect method) previously used in our laboratory and some discrepancies were observed. Because it preserved at best the frozen original texture, we think that this direct optical microscopic method is more reliable and more precise than the other methods previously used. We observed that the mean crystal size increased with the distance to the cooling plate and, on the other hand, decreased with the cooling rate or the cooling temperature. Due to its numerous advantages – i.e., low cost, rapidity, reliability and precision – we forecast, that the use of this direct method, quite unknown to the frozen food technologist, will increase in the near future.

Freezing and ice crystals formed in a cylindrical food model: part II. Comparison between freezing at atmospheric pressure and pressure-shift freezing

Cylindrical gelatin gels were pressure-shift frozen at different pressure levels (100, 150 and 200 MPa). Temperature and pressure profiles were compared and the maximum supercooling obtained after pressure release was evaluated. A comparison between the freezing steps at atmospheric pressure and those of pressure-shift freezing was carried out to compare the time steps during the processes. The degree of supercooling increased with the level of pressure. For pressure-shift freezing, the size of ice crystals appeared to be more homogeneous in the whole sample and independent of the location. The mean representative ice crystal diameter decreased as the pressure level increased. This may be due to the degree of supercooling achieved during pressure-shift freezing. The ice crystal size for pressure-shift frozen sample was smaller than those obtained with classical freezing methods. A regression between the supercooling level and the mean ice crystal size was proposed.

Effect of Emulsifiers and Food Gum on Nonfat Ice Cream

Nonfat ice cream was made with a mix composition of 12% milk SNF, 12% sucrose, 5% corn syrup solids, 3.5% maltodextrin, and 0.25% stabilizer blend. Two emulsifiers at three levels each and one gum at three levels were evaluated in nonfat ice creams. Emulsifiers were 52% α-monoglyceride and 72% α-monoglyceride, and the gum was hydroxypropylmethyl cellulose. A portion of the mix was retained as the control, which contained no emulsifier or additional food gum, and was evaluated in addition to the nine treatments. Mean fat content of the mix was 0.14%, and total solids content was 34.16%. Results indicated differences between treatments in whipability and stability to heat shock; however, there were no differences in meltdown. There was about a 10-μm increase in mean ice crystal size for treatments when compared after 1 and 12 wk of storage. Addition of either emulsifier to nonfat ice cream reduced the mean ice crystal size when compared with the control or gum, which is a major factor in improvement of the texture of nonfat ice cream. The sensory panel preferred the nonfat ice cream with 0.25% added monoglyceride and diglyceride with 72% α-monoglyceride content stabilizer over the control with respect to coarseness and iciness, coldness intensity, and overall body and texture scores.

Measurements of wave‐cloud microphysical properties with two new aircraft probes

Measurements of ice water content (IWC) and mean ice‐crystal size and concentration made by two in‐situ probes, CVI and PVM, were compared on the DC‐8 aircraft during SUCCESS flights in orographic ice clouds. The comparison of IWC in these wave clouds, that formed at temperatures of about −38 °C on April 30 and −62 °C on May 2, 1996, showed good agreement. The comparison of ice crystal concentrations agreed better for the April‐30 clouds than for the May‐2 clouds; and the effective radius compared for both probes and for remote retrievals from aircraft and satellite for a segment of the Berthoud wave cloud (May 2) agreed within 30%. The measured parameters of the ice crystals were similar to earlier measurements and recent modeling of cold wave clouds.

Experimental and theoretical study of model food freezing. Part II. Characterization and modelling of the ice crystal size

Frozen gelatin gels were freeze-dried, then sliced, microphotographed and analyzed with image analysis software. A mean ice crystal size was determined at different locations inside the gel for many operating conditions and different gelatin concentrations with or without ionic solute (sodium chloride). It was observed that the mean ice crystal size grew proportionally with the distance from the cold plate. Ionic solute addition had a great influence on the mean ice crystal size. A model based on the principle of the supercooling resulting from the maximum concentration difference in the interdendritic zone was able to justify the experimental relationship and to interpret quantitatively these data.

Recrystallization of ice during bulk storage of ice cream

Abstract Ice recrystallization was studied in 1.9 L containers of ice cream stored so that surface temperature of ice cream was controlled with fluctuations of ±1.0 °C. Core and surface samples were taken at regular intervals and analyzed for ice crystal size by cold-stage microscopy and image analysis. Mean ice crystal size plotted vs. time0.33 resulted in a straight line, with a slope equal to recrystallization rate (μm day−0.33). Storage temperatures between −15 and −5 °C were studied. Recrystallization rate increased with storage temperature and extent of temperature fluctuations. Within a single container, mean ice crystal size grew significantly larger in ice cream at the outside wall than near the core of the package. Recrystallization rates determined in this study were compared to those found at identical temperature conditions, but in an accelerated storage study. Recrystallization was more rapid in the accelerated study for fluctuating temperature, but slower for constant temperature.

Recrystallization of ice in ice cream during controlled accelerated storage

Abstract Accelerated ice recrystallization in a thin film of vanilla ice cream was studied on a cold stage microscope, housed in a refrigerated glove box. Sample temperature was held constant (within ±0.01 °C) or sinusoidally oscillated for 5 days. Changes in ice crystal size distribution were monitored using an image analysis technique. Several recrystallization mechanisms were observed. Melt-refreeze recrystallization was important for oscillating-temperature conditions, while rounding was particularly apparent at a constant temperature. Accretion was evident for all conditions studied, but migratory recrystallization was observed only rarely. Mean ice crystal size increased as a function of approximately time −0.33 . Recrystallization rates increased with mean storage temperature (−20 to −5 °C) and amplitude of temperature fluctuations (0.01 to 2 °C). However, recrystallization still occurred at very low amplitudes (±0.01 °C), with a recrystallization rate about half as large as for recrystallization with temperature fluctuations of ± 1 °C. Slower temperature fluctuations (2 h cycle) resulted in an initial lag in recrystallization rate that was not observed for more rapid fluctuations (10-min cycle).