Carrots, dehydration

A three level four factor three response design of RSM was employed to optimize the carrot dehydration process. The four factors were drying temperature in HTST fluidized bed dryer, exposure time in HTST fluidized bed dryer, concentration of biopolymers and blanching time. The three responses were rehydration ratio, bulk density and carotenoid loss during the process. Second degree polynomial equations and Statistical Analysis System were used to fit the data for RSM. 

P.P. Lewicki, A. Lenart, and M. Malkowska, Diffusive movement of substance in the carrot dehydrated osmotically in the sodium chloride solution, Ann. Warsaw Agric. Univ., Food TechnoL Nutr., 77 45 (1987). 

Soria, A. C., Corzo-Martinez, M., Montilla, A., Riera, E., Gamboa-Santos, J., Villamiel, M., 2010. Chemical and physicochemical quality parameters in carrots dehydrated by power ultrasound./. Agric. Food Chem. 58(13) 7715-7722. 

An application of this instrument is illustrated in the study of color change in dehydrated carrots with storage at different temperatures. Typical results are given in Table IY. The measurements were made on the dry material packed level in a tray designed to fit at a specific level in the instrument. The instrument is mounted so that the tray rests horizontally and no cover glass is then necessary to hold the sample in place. 

Table IV. Effects of Storage Temperature on Color of Dehydrated Carrots...

Table I. Variation of Apparent Moisture Content of Dehydrated Carrots with Particle Size and Time of Drying in Vacuum Oven at 70° C.a...

Distributions prepared from single lot of diced dehydrated carrots by grinding through food chopper and separating ground material into fractions by sieves. 

As an illustration, the effects of varying the particle size distribution, and of temperature, on the course of water removal from dehydrated carrots in a vacuum oven are shown, respectively, in Table I and Figure 3. 

Falconer, M.E. et ah. Carotene oxidation and off-flavor development in dehydrated carrot, J. Sci. Food Agric., 15, 857, 1964. 

The structural features of ceU wall polysaccharides of carrots have been studied by Stevens and Selvendran (1984) and Massiot et al.(1988). Plat et al.(1991), Ben Shalom et al.(1992) and Massiot et al.(1992) investigated the changes in pectic substances of carrots after blanching, dehydration and extended heat treatment. Data on the changes in ceU waU polysaccharides of canned carrots are lacking. This study aims to investigate the effect of preheating time at low temperature and the addition of CaCL on texture and on the composition of various pectin fractions of carrots canned by conventional and by a new process. 

During osmotic dehydration of apple, pumpkin, and carrot in sugar solution at 30 °C, the rate of water loss was 5-10 times higher than the rate of solid gain and depended on advancement of the dewatering process (Kowalska and Lenart, 2001). Under the same dewatering conditions, pumpkin and carrot reached smaller water contents than apple (Figure 3). 

FIG. 3 Water loss (WL) and solid gain (SG) expressed on initial dry matter (idm) of strawberry (ST) slices (Brambilla et al., 2000) and apple (AP), carrot (CA), and pumpkin (PU) cubes (Kowalska and Lenart, 2001) after 60 min osmotic dehydration in a 60% (w/w) sucrose solution at 30 °C at atmospheric pressure. 

FIG. 4 Effects of varying raw material treatments prior to osmotic dehydration on moisture (MC) and solid (SC) content expressed on initial dry matter (idm). Potato slices, high hydrostatic pressure (Rastogi et al., 2001) carrot slices, PFE (Rastogi et al., 1999) bell pepper disks, PFE (Ade-Omowaye et al., 2002b) and apple slices, edible coatings (Lenart and Dabrowska, 1998). 

Mazza, G. 1983. Dehydration of carrots Effects of pre-drying treatments on moisture transport and product quality. J. Food Technol. 18, 113-123. 

Rastogi, N.K., Eshtiagi, M.N., and Knorr, D. 1999. Accelerated mass transfer during osmotic dehydration of high intensity electrical field pulse pretreated carrots. J. Food Sci. 64, 1020-1023. 

Rastogi, N.K. and Raghavarao, K.S.M.S. 1997. Water and solute diffusion coefficients of carrot as a function of temperature and concentration during osmotic dehydration. J. Food Engineer. 34, 429-440. 

Preliminary experiments, using a container with reflective surfaces, employed light from eight fluorescent bulbs that produced a preponderance of radiation at 310 nm. Myristicin increased in samples that were irradiated 1 h and then kept for a 24-h induction period. However, heat produced by this system and the resulting dehydration of carrot roots may have affected results. Later experiments, employing a Chromato-Vue box used for ultraviolet examination of TLC plates, avoided these problems. One-hour light... 

Common unit operations of food processing are reported to have only minor effects on the carotenoids (Borenstein and Bunnell 1967). The carotenoid-protein complexes are generally more stable than the free carotenoids. Because carotenoids are highly unsaturated, oxygen and light are major factors in their breakdown. Blanching destroys enzymes that cause carotenoid destruction. Carotenoids in frozen or heat-sterilized foods are quite stable. The stability of carotenoids in dehydrated foods is poor, unless the food is packaged in inert gas. A notable exception is dried apricots, which keep their color well. Dehydrated carrots fade rapidly. 

A cell placed in a solution more concentrated than itself (a hypertonic solution) will shrink due to loss of water, and may die of dehydration. A familiar example is a carrot placed in salty water. Within a few hours the carrot will become limp and soft because its cells have shrivelled. A cell placed in a solution more dilute than itself (a hypotonic solution) will expand as water enters it. Under such conditions the cell may burst. 

The following procedure calls for dehydration of tomato or carrot paste with ethanol and extraction with dichloromethane, an efficient solvent for lipids. 

In a small mortar grind 2 g of green or brightly colored fall leaves (don t use ivy or waxy leaves) with 10 mL of ethanol, pour off the ethanol, which serves to break up and dehydrate the plant cells, and grind the leaves successively with three 1-mL portions of dichloromethane that are decanted or withdrawn with a Pasteur pipette and placed in a test tube. The pigments of interest cU e extracted by the dichloromethane. Alternatively, place 0.5 g of carrot paste (baby food) or tomato paste in a test tube, stir and shake the paste with 3 mL of ethanol until the paste has a somewhat dry or fluffy appecu-ance, remove the ethanol, and extract the dehydrated paste with three 1-mL portions of dichloromethane. Stir and shake the plant material with the solvent in order to extract as much of the pigments as possible. 

These principles formed the basis for producing high quality carrots and potatoes by a process of biopolymer infusion followed by high temperature short time fluidized bed dehydration. Infused biopolymers was shown to penetrate intracellular spaces and cell walls and may contribute to reduced cell collapse in the dehydration process. Deposition of infused biopolymer within the cells was elucidated using a convalently bound complex of biopolymer and colored dye which was visible upon histochemical examinations under a microscope. The dehydration process was optimized with response surface methodology. The resulting products have excellent quality, high rehydration ratio and a puffed structure. 

One problem with high porosity in dehydrated foods, in addition to increased packaging requirements, is the possibility of rapid oxidation because of increased surface area of exposure to oxygen if air is present within the pores. An approach which could be used to solve the problem was first suggested by Sinnam et al. (20) when they compressed explosion puffed carrots after dehydration and found that there were no differences in the rehydration rate or rehydration ratio compared to the original explosion puffed dehydrated carrots. This concept has been extensively exploited by the U.S. Army Natick Laboratories (21) in the development of... 

Literature reports showed that pretreated dehydrated carrots can have rehydration ratio (RR, total mass of rehydrated carrots per unit weight of dry matter) in the range of 5 to- 7 (28, 29). 

The RR was calculated after boiling a known weight of dried carrots in 100 ml distilled water for 30 minutes. Currently commercially available samples tested in our laboratory possessed RR<6.0. In the new process developed in our laboratory and pilot plant, the dehydrated diced carrots consistently attained RR of 9.5 or above. In addition, these high quality dehydrated carrots have low bulk density and minimum carotenoid loss (Mudahar, G. S. et al., J. Food Sci., In Press). 

For dehydration of diced potatoes, a three level four factor four responses design was used. The four factors stayed the same as in the carrot study. The four responses were rehydration ratio, bulk density, non-enzymatic browning and water holding capacity. Optimal conditions were determined to be 1450C arid 10 min in HTST fluidized bed dryer with blanching time of 4.5 min and biopolymer... 

The dye-biopolymer complexes were seen at intracellular spaces in intact carrot cells (Fig. 3a) and adhered to cell walls in broken cells (Fig. 3b). These pictures provided some evidence for our hypothesis that the biopolymers migrate on and around cell walls and their presence may have assisted in preventing or reducing cell collapse during dehydration. Much work needs to be done to elucidate the role of biopolymers on quality improvement of dehydrated vegetable pieces, and to define the proper size of molecules that would accomplish the desired texture. 

Figure 3. Microscopic pictures of (a) intact and (b) broken carrot cells after biopolymer-dye complex treatment, dehydration and rehydration. Bar in picture shows one micrometer in length.

Basic principles in physio-chemical changes occurring during dehydration provided an effective approach to improve quality of dehydrated products. Carrot and potato dices infused with biopolymers before dehydration and processed under optimal conditions had good texture, high rehydration properties, good color and puffed appearance. Infused biopolymers were deposited on cell walls and intracellular spaces and may contribute to prevent cell collapse. 

Sinnam, H. L. Eskew, R. K. Cording, J. Dehydrated Explosion Puffed Carrots with High Density, U.S. Department of Agriculture, ARS 73-50, 1965. 

Exposure to oxygen is deleterious, particularly in dried food such as dehydrated carrot slices in which carotenoid oxidation and bleaching occur rapidly because of the formation of activated oxygen species (Coultate, 1996). 

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