Freeze-dried Carrots Research Articles

The impact of freeze-drying on microstructure and rehydration properties of carrot

The impact of freeze-drying, blanching and freezing rate pre-treatments on the microstructure and on the rehydration properties of winter carrots were studied by μCT, SEM, MRI and NMR techniques. The freezing rate determines the size of ice crystals being formed that leave pores upon drying. Their average size (determined by μCT) can be predicted in a quantitative manner by considering dendritic growth and freezing rates. Blanching as a pre-treatment, however, did not affect pore size distribution induced by freeze-drying. Upon rehydration of the freeze-dried carrots, PFG NMR and MRI show that cellular compartments were not restored and instead a porous network with permeable barriers is formed. Blanching pre-treatment introduced a less connected and more anisotropic porous network if followed by fast freezing, indicating that more of the native cell wall morphology is preserved.

Modeling rehydration of porous food materials: II. The dual porosity approach

Following the foundation for physical modeling of rehydration ( Troygot et al., 2011), the Richards equation together with the independently evaluated characteristic curve yielded a close approximation for the early stage (1000 s) of rehydration data. It was revealed that the porosity of wheat groats (WG) and freeze-dried carrots consists of inter- and intra-particles porosities playing a distinct role on the rehydration kinetics. A dual porosity mobile–immobile model was suggested for modeling water flow by capillarity in the inter porosity and by water-content difference (diffusion-type) in the intra porosity. The model fits the overall rehydration process well. A double Weibull distribution model predicted also well the experimental rehydration data for freeze-dried carrots verified the above, demonstrating the roles for both diffusion and relaxation in a dual-porosity structure. The physically-based model combined with the characteristic curve, hydraulic conductivity function, and a transfer coefficient for rate-limited exchange between inter- and intra-particles porosities was adequate for modeling the rehydration process of porous food.

Chemical and Physicochemical Quality Parameters in Carrots Dehydrated by Power Ultrasound

Preservation of the quality and bioactivity of carrots dehydrated by power ultrasound (US) under different experimental conditions including prior blanching has been evaluated for the first time by measuring the evolution of the Maillard reaction and the changes in soluble sugars, proteins, total polyphenols, antioxidant activity, and rehydration ability. This study also includes a comparison with a freeze-dried sample and data of commercial dehydrated carrots. The synergic effect of US and temperature (60 degrees C) increased the dehydration rate of carrots (90% moisture loss in only 75 min) while still providing carrots with a level of 2-furoylmethyl-amino acids significantly lower than that of dehydrated commercial samples. Whereas a decrease in the content of reducing soluble sugars was observed with processing temperature, minor carbohydrates (scyllo- and myo-inositol and sedoheptulose) were rather stable, irrespective of the US dehydration parameters. Blanching significantly improved the rehydration ability of US-dehydrated carrots without increasing the loss of soluble sugars by leaching. As supported by the similarity of most quality indicators studied in both US-treated and freeze-dried carrots, the mild processing conditions employed in US dehydration gave rise to premium quality dehydrated carrots.

Studies on the Carotenoid Pigments in Freeze-dried Carrot

Studies on the Carotenoid Pigments in Freeze-dried Carrot

Evaporation influences on the crystallization of an aqueous dihydrate cupric chloride solution with additives

The overall structure of the crystallization results of dihydrate cupric chloride with additives in a petri dish is affected by the duration between the beginning of the evaporation and the start of the crystallization. Experiments done with polyvinylpyrrolidone and freeze-dried carrot as additive are compared with those of the additive free case. The dependency of dewetting on the dihydrate cupric chloride amount is discussed in terms of depletion of the solution and the surface tension properties of the system. The possible influence of the depletion is depending on the moment the crystallization starts. This is defined by the size of the evaporated area on the dish.

Studies on Drying of Purple Carrot Roots

The article compares kinetics of drying and properties of dried roots of purple carrot cultivars: Deep Purple F1 and Purple Haze F1 Bejo Zaden B.V., which differ in coloring of the core section of roots. Sliced carrots were dried by convective drying (CD), microwave-convective drying (MCD), infrared-convective drying (IRCD), and freeze drying (FD). An enhancement of convective drying due to the application of infrared or microwave radiation considerably reduced drying time. The lowest values of apparent density were recorded for freeze-dried carrots, whereas these values for carrots dried by other methods were approximately four times higher. Roots of carrot cv. Deep Purple dried markedly faster than those of cv. Purple Haze. Rehydration of freeze-dried carrots was higher than that dried by other methods. This was clearly manifested particularly in the initial stage of rehydration. Kinetics of rehydration were comparable for carrot dried by other methods. Cultivars did not have a noticeable effect on the analyzed physical properties apparent density and reconstitution properties. Dried carrots of cv. Deep Purple were characterized by an approximately 2.5 times higher antioxidant capacity and higher contents of anthocyanins and polyphenols than dried carrots of cv. Purple Haze.

Combined Microwave-Vacuum and Freeze Drying of Carrot and Apple Chips

A combination of microwave-vacuum (MWV) drying and freeze drying was investigated as potential means for drying carrot and apple chips. The sample was first dried by microwave-vacuum to dehydrate some amount of internal free water and then by freeze drying to a final moisture content of less than 7% (wet basis). Chemical properties (carotene and vitamin C retention) and physical properties (shrinkage, color, texture, and rehydration ratio) of carrot and apple slices dried by this method were evaluated and compared with those dried by freeze drying alone, MWV drying alone, and conventional hot air drying, respectively. The comparison showed that the carotene retention of carrot slices and the vitamin C retention of apple slices dried by the current method were close to those of freeze-dried carrot and apple slices and much better than those of conventional hot air–dried ones. The samples prepared by the current method exhibited very close rehydration capacity, color retention, and texture with those of the freeze-dried ones but with a little higher shrinkage. However, the samples still showed the attractive external appearance without marked warp.

Biofortified Carrot Intake Enhances Liver Antioxidant Capacity and Vitamin A Status in Mongolian Gerbils1,

Biofortification efforts have increased concentrations of bioactive compounds in carrots. We measured the antioxidant potential and vitamin A bioefficacy of 4 biofortified carrot varieties [purple/orange, purple/orange/red, orange/red, and orange] in Mongolian gerbils (n = 73). Following a 4-wk vitamin A depletion period and baseline kill (n = 7), freeze-dried carrot powders were mixed into purified feeds and fed to 6 groups (n = 11/group) for 4 wk. White carrot-fed control and vitamin A-supplemented groups were used to calculate carrot provitamin A bioefficacy. Antioxidant capacities of carrot powders, sera, and livers were determined using the 2, 2´-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) radical cation decolorization assay and carotenoid and retinol concentrations were determined by HPLC. Antioxidant capacity of liver extracts from the 4 colored carrot-fed groups [10.1 ± 1.2 μmol Trolox equivalent antioxidant capacity (TEAC)/g] was significantly higher than the white carrot-fed control group (9.3 ± 0.9 μmol TEAC/g) and vitamin A-supplemented group (8.8 ± 1.4 μmol TEAC/g) (P < 0.05). Liver retinol stores in the colored carrot-fed groups (0.62 ± 0.13 to 0.67 ± 0.08 μmol retinol/liver) did not differ and were higher than the white carrot-fed control group (0.32 ± 0.08 μmol retinol/g) (P < 0.0001). Serum antioxidant capacity and retinol did not differ among treatment groups. Liver antioxidant capacity and vitamin A stores were higher in gerbils fed colored carrots than in those fed white carrots. Antioxidant activity is one of several proposed mechanisms by which plant foods, like biofortified carrots, may provide additional health benefits beyond maintenance of vitamin A status.

Bioactive compounds with high antioxidant potential in biofortified carrots do not influence provitamin A carotenoid bioefficacy in gerbils

Dietary Guidelines for Americans recommend a diet rich in fruits and vegetables of a variety of colors. Colored carrots contain several groups of phytochemicals. Provitamin A carotenoid bioefficacy was measured in four carrot varieties (purple/orange, purple/orange/red, orange/red and orange) using gerbils. Freeze‐dried carrot powders were mixed into diets to achieve 6 nmol beta‐carotene equivalents/g diet and fed to 4 groups (n = 11/group) for 4 wk. Diets were equalized for carrot powder using carotenoid‐free white carrot powder. Diets containing carrot varieties rich in lycopene and/or anthocyanins were formulated to have equal concentrations of these compounds. Antioxidant capacities of the carrot powder, diets, serum and livers were determined with the ABTS+ free radical scavenging decolorization assay. All four colored carrot‐fed groups had higher liver retinol stores (0.230 + 0.029 to 0.259 + 0.047 μmol/g) compared to the white carrot‐fed control group (0.124 + 0.036 μmol/g), but did not differ from each other. Hydrophilic antioxidant capacities of the anthocyanin‐rich purple varieties were 5 and 10‐fold higher than white carrot. Lipophilic antioxidant capacities were 10 to 20‐fold higher in the carotenoid‐rich colored carrots compared to white carrot. Provitamin A carotenoids in biofortified carrots maintained vitamin A status with no discernable influence of lycopene or anthocyanins on bioefficacy at the levels fed in this study. Supported by Hatch WIS04975; Standard Process, Inc., Palmyra, WI; and IEDR UW‐Graduate School 118–0617.

Arsenic Speciation and Identification of Monomethylarsonous Acid and Monomethylthioarsonic Acid in a Complex Matrix

Anion-exchange chromatography was utilized for speciation of arsenite (As(III)), arsenate (As(V)), dimethylarsinic acid (DMA(V)), monomethylarsonic acid (MMA(V)), monomethylarsonous acid (MMA(III)), and the new As species monomethylthioarsonic acid (MMTA), using inductively coupled plasma mass spectrometric (ICPMS) detection. MMA(III) and MMTA were identified for the first time in freeze-dried carrot samples that were collected over 25 years ago as part of a joint U.S. EPA, U.S. FDA, and USDA study on trace elements in agricultural crops. The discovery of MMA(III) and MMTA in terrestrial foods necessitated the analytical characterization of synthetic standards of both species, which were used for standard addition in carrot extracts. The negative ion mode, high-resolution electrospray mass spectrometry (HR-ESI-MS) data produced molecular ions of m/z 122.9418 and 154.9152 for MMA(III) and MMTA, respectively. However, ESI-MS was not sensitive enough to directly identify MMA(III) and MMTA in the carrot extracts. Therefore, to further substantiate the identification of MMA(III) and MMTA, two additional separations using an Ion-120 column were developed using the more sensitive ICPMS detection. The first separation used 20 mM tetramethylammonium hydroxide at pH 12.2 with MMA(III) eluting in less than 7 min. In the second separation, MMTA eluted at 11.2 min by utilizing 40 mM ammonium carbonate at pH 9.0. Oxidation of MMA(III) and MMTA to MMA(V) with hydrogen peroxide was observed for standards and carrot extracts alike. Several samples of carrots collected from local markets in 2006 were also analyzed and found to contain low levels of inorganic arsenic species.

P‐Nitro‐N‐propylaniline/silica: Synthesis, characterization, and its application in matrix solid phase dispersion for multiresidue analysis of pesticides in carrots

A new material for matrix solid phase dispersion (MSPD) was synthesized -- p-nitro-N-propylaniline/silica (pNNPASi) by grafting reactions, characterized by elemental analysis and N(2)-adsorption-desorption isotherms, and tested for multiclass multiresidue analysis of pesticides in wet and freeze-dried carrots. Results obtained applying this new solid phase sorbent to MSPD extraction of ten pesticides (trichlorphon, trifluralin, dicloran, chlorothalonil, prometryn, linuron, captan, procymidone, prochloraz, and deltametrin) in wet carrots showed better results than the ones obtained for freeze-dried samples. Recoveries were in the range of 48-106% and precisions varied from 6 to 20% when wet samples were employed. Comparison between pNNPASi sorbent and C(18) showed better performance of pNNPASi for eight out of ten pesticides tested. The LOQs show that the developed method can be used to detect the pesticides investigated in carrots at concentrations below the maximum residue levels (MRL) established by EU, USEPA, and National Sanitary Surveillance Agency (ANVISA). Linuron, captan, prochloraz, and deltamethrin were found in at least one of the two commercial samples studied in concentrations above the LOQ of this method. Concentrations of the last three pesticides were above the European MRL in one of the commercial samples.

Effect of water activity on carotenoid degradation in dehydrated carrots

The effect of water activity on the stability of carotenoids in dehydrated carrots was studied. Freeze-dried carrots from blanched and unblanched batches were placed in air-tight glass jars containing saturated salt solutions with water activity ranging from 0.052 to 0.75, at 40 °C. The equilibrium moisture, water activity, α- and β-carotene, and lutein contents were analysed at different storage times. The Guggenheim–Anderson–de Boer (GAB) equation was applied to model experimental data for moisture content as a function of water activity, and to calculate the monolayer water activity, where the oxidative reactions are expected to be at minimum. Estimated monolayer water activity was 0.33 (confidential limits at 95%: 0.26 and 0.38). α- and β-carotene, and lutein degradation followed pseudo-first-order kinetics in all dehydrated carrots, with rate constants ranging from 0.031 to 0.374 days −1. Similar rate constants were found between α- and β-carotene, whereas lutein degraded faster. In both blanched and unblanched batches the rate of carotenoid degradation was at a minimum over the water activity range 0.31–0.54. Blanching resulted in a higher initial carotenoid content, but it accelerated carotenoid decrease during storage of dehydrated carrots.

Comparison of the solubility of β-carotene in supercritical CO 2 based on a binary and a multicomponent complex system

Carotenoids such as β-carotene are gaining interest in the food industry due to their nutritional and antioxidant properties. Understanding the solubility behavior of carotenoids in supercritical CO 2 (SC CO 2) is fundamental for any industrial supercritical process application and design. Solubility of β-carotene was measured in both a binary and a multicomponent complex system. Solubility of β-carotene in the binary system was measured using a quartz crystal microbalance technique at temperatures of 40 and 50 °C and pressures ranging from 120 to 200 bar. Solubility of β-carotene in the multicomponent complex system was determined from dynamic extraction experiments using a laboratory-scale supercritical extraction system. Carotenoids were extracted from freeze-dried carrots with SC CO 2 at temperatures of 40 and 50 °C and pressures ranging from 120 to 327 bar. β-Carotene solubility values for the binary system measured herein and reported in the literature are of the order of 10 −7 mole fraction while the solubility values for the multicomponent complex system (β-carotene extracted from carrots with SC CO 2) under the same conditions are 5–10 times smaller. Solubility in both systems increased with temperature and pressure. The difference in the solubility values obtained using both systems is mainly due to the matrix effects of the multicomponent complex system such as the cell structure and the interactions of β-carotene with other components such as carbohydrates in the carrot matrix.

Inhibitory Effects of Feeding with Carrots or (−)-Falcarinol on Development of Azoxymethane-Induced Preneoplastic Lesions in the Rat Colon

The effects of intake of dietary amounts of carrot or corresponding amounts of (-)-(3R)-falcarinol from carrots on development of azoxymethane (AOM)-induced colon preneoplastic lesions were examined in male BDIX rats. Three groups of eight AOM-treated rats were fed the standard rat feed Altromin supplemented with either 10% (w/w) freeze-dried carrots with a natural content of 35 mug falcarinol/g, 10% maize starch to which was added 35 mug falcarinol/g purified from carrots, or 10% maize starch (control). After 18 weeks, the animals were euthanized and the colon was examined for tumors and aberrant crypt foci (ACF), which were classified into four size classes. Although the number of small ACF was unaffected by the feeding treatments, the numbers of lesions as a function of increasing size class decreased significantly in the rats that received one of the two experimental treatments, as compared with the control treatment. This indicates that the dietary treatments with carrot and falcarinol delayed or retarded the development of large ACF and tumors. The present study provides a new perspective on the known epidemiological associations between high intake of carrots and reduced incidence of cancers.

Liquid imbibition during rehydration of dry porous foods

Water imbibition theory has been shown to have a multidisciplinary validity. To demonstrate its applicability to the rehydration of dried porous food, kinetics of water uptake of freeze-dried (FD) carrots was studied. Water imbibition followed the general Lucas–Washburn equation. Utilizing different liquid media highlighted the need for model improvement overcoming several discrepancies mainly related to the utilization of a single “effective” cylindrical capillary and a constant contact angle. A significant swelling of the carrot samples was observed and quantified. The rate of lateral one-dimensional expansion of the samples was modeled assuming two first-order independent kinetic processes. These results indicated that dry foods could be treated as a composite “porous media”, for which pertinent processes and variables should be taken into consideration. Industrial relevance Dry food particulates are an integrative part of many soups and ready-to-eat products. The increased consumers demand for convenience foods makes fast rehydration a significant quality consideration. Better understanding of the transport phenomena occurring in dried foods containing particulates is paramount to facilitate product reconstitution and improving consumer acceptance. This study highlights the complexity encountered in modeling of the rehydration process of freeze-dried (FD) carrots. The commonly assumed Fick's diffusion law was replaced with a physical model describing the capillary imbibition into a porous media. This approach offers to analyze the complex phenomena occurring during rehydration. Viscosity of the rehydration medium was found not to be the sole factor responsible for the decrease in the rehydration. Due to the encountered complexity in modeling, the need for further research on physical properties usually disregarded (e.g., tortuosity, roundness of pores, contact angle, swelling) is suggested. This could open new avenues for the optimization of the process. As the drying process affects significantly some of the physical properties and the rehydration of the food particulates, a system approach is recommended.

Effect of mixing and viscosity on rehydration of dry food particulates

Rehydration of dry food particulates is a rate-limiting step related to the nature and the history of the particulates and of utmost consumer importance. Developing the appropriate methodologies for studying the kinetics of water uptake during a short time, and identifying the pertinent variables affecting the process were the overall objectives. Water uptake of air- and freeze-dried carrots was monitored continuously. Open porosity increased water uptake significantly only when no starch was added to the medium. Water uptake was slightly affected by mixing speed and became significant with the increased viscosity of a 3% starch solution. The rehydration rate increased linearly with sample surface area.

Arsenic extraction and speciation in carrots using accelerated solvent extraction, liquid chromatography and plasma mass spectrometry.

Arsenic present in freeze-dried carrots was extracted using accelerated solvent extraction (ASE). Several parameters, including selection of the dispersing agent, extraction time, number of extraction cycles, particle size and extraction temperature, were evaluated to optimize the ASE method. Filtering and treatment with C-18 SPE cartridges were also evaluated as part of the sample preparation procedure before speciation analysis. The method was validated by spiking single arsenical and mixed arsenical standards on the dispersing agent and on portions of freeze-dried carrot prior to extraction. LC-ICP-MS was used to determine individual arsenic species in the carrot extracts. A weak anion-exchange column was used for the separation of As(III), As(v), monomethylarsonic acid (MMA), dimethylarsinic acid and arsenobetaine. Optimized sample preparation conditions were applied to the extraction of arsenic in nine freeze-dried carrot samples. Total arsenic concentration in the carrot samples ranged from less than 20 ng g(-1) to 18.7 microg g(-1), dry mass. Extraction efficiency, defined as the ratio of the sum of individual arsenic species concentrations to total arsenic, ranged from 80 to 102% for freeze-dried carrots with arsenic concentrations greater than the limit of quantitation. Inorganic As(III) and As(v) were the only species found in samples that contained less than 400 ng g(-1) total arsenic. MMA and an unidentified arsenic compound were present in some of the samples with higher total arsenic content.

Thermal transitions in freeze-dried carrot and its cell wall components

Differential scanning calorimetry (DSC) was used to measure the glass transition temperature, T g and a sub- T g event in freeze-dried carrot material and different carrot cell wall components, at moistures ranging from 0% to 20% (w.w.b.). Two glass transition temperatures were detected in the freeze-dried carrot material associated with two phases: a sugar-rich phase and a cell wall-rich phase. The water distribution in the different phases is also important and sorption isotherms of freeze-dried carrot and different cell wall components were determined and compared with published results produced on sugar, pectins and cellulose. For the insoluble carrot cell wall materials, a single T g was detected which increased in the order: a Ca 2+ bound pectin-free residue, an esterified pectin-free residue and a cellulose-rich residue. In all cases T g increased with decreasing moisture. Additionally, a sub- T g endothermic event was observed in all the materials which disappeared on rescanning, consistent with results published on ageing of other biopolymers. The T g of the different cell wall residues was modelled, using the Gordon–Taylor and Kwei equations. The latter showed that water–biopolymers interactions are less prominent in the cellulose-rich cell wall residue, shown by a negative value of q.

The thermomechanical properties of carrot cell wall material

The effect of temperature and moisture on the fabrication of pressed carrot cell wall specimens for Dynamic Mechanical Thermal Analysis was assessed. Results obtained from the water extractability of the material showed that more cell wall material became solubilised when moisture and temperature of the different treatments were increased. Chemical analysis revealed that this involved an increase in the water-soluble uronic acid components. Furthermore, more water-soluble neutral monosaccharides were observed, represented principally by galactose, rhamnose, arabinose and glucose. Pectic polysaccharides became more water soluble when isolated carrot cell wall was pressed at 100°C with a water content 800 g kg−1 (wet weight basis). A molecular weight fraction centred at 100000 Da was observed in the severely pressed material (100°C, 800 g kg−1 water) but was barely present in the mildly pressed (30°C, 500 g kg−1 water) and unpressed specimens, consistent with depolymerisation and solubilisation. In contrast to the chemical modifications, the bending modulus, E′, of the pressed carrot cell wall material remained unchanged for the cell wall specimens moulded under different conditions, consistent with small changes in molecular weight. Pressed cell wall material was stiffer than pressed freeze-dried carrot which could be due to the plasticising role of the intracellular components. The stiffness of both cell wall and freeze-dried carrot specimens decreased with plasticisation by water in the range 10–500 g kg−1. © 1998 Society of Chemical Industry.

Extraction of β-carotene with supercritical fluids: Experiments and modelling

This work investigates extraction of β-carotene by supercritical carbon dioxide and nitrous oxide from impregnated beds and from freeze-dried carrots. Extraction rate was measured as a function of temperature, flow rate and particle size. Based on results from spiked beds, mathematical models were proposed to analyze the dynamic behavior of extraction from carrots. The validity of a diffusion model or a mass balance model was discussed through results on particle size. Although the diffusion model and the experimental results were in good agreement, provided that two stages of diffusion were considered for larger particle size, we further analyzed all data regarding a differential mass balance model. This model, accounting for external mass transfer, diffusion within the matrix and dissolution at the solid/fluid interface, described the time-dependent process satisfactorily despite assumptions on the matrix description. Results showed that both external mass transfer and desorption of solute from the matrix were the limiting steps.