Vegetables dehydration

Saravacos, G.D. and Charm, S.E. 1962. A study of the mechanism of fruit and vegetable dehydration. Food Technol. 16, 78-81. 

Products and Uses Used in baked goods, bakery mixes, frozen desserts, fruit juices (dehydrated), fruits (dehydrated), milk or cream substitutes for beverage coffee, pancake mixes, pudding mixes, rice (precooked instant), shortening (liquid), vegetable juices (dehydrated), and vegetables (dehydrated). It is an emulsifier (stabilizes and maintains mixes to aid in suspension of oily liquids). 

In general, it can be said that losses of water-soluble vitamins during conventional drying are less than 20%. For vegetable dehydration, the losses are less than 5% for all vitamins except ascorbic acid. 

The FBA system is satisfactory applied to quantify the amount of MSG in meat and vegetable dehydrated broths. 

Boron. The principal materials used are borax [1303-96-4] sodium pentaborate, sodium tetraborate, partially dehydrated borates, boric acid [10043-35-3] and boron frits. Soil appHcation rates of boron for vegetable crops and alfalfa are usually in the range of 0.5—3 kg/hm. Lower rates are used for more sensitive crops. Both soil and foHar appHcation are practiced but soil appHcations remain effective longer. Boron toxicity is not often observed in field appHcations (see Boron compounds). 

Other examples are glycine — formaldehyde, alanine — acetaldehyde, valine — isobutyraldehyde, phenylalanine — phenylacetaldehyde, and methionine — methional (106). Products such as dried skim milk, dried eggs, and dehydrated vegetables and fmits are particularly susceptible to deteriorative flavor changes ascribed to this reaction (Table 10). 

The American Spice Trade Association (ASTA) (4) accepts spice as any dried plant product used primarily for seasoning purposes. This broad definition was designed so that items labeled only as spice could give adequate protection to proprietary formulas for spice mixtures. However, ASTA recommends that the dehydrated vegetables and the color spices be listed separately by name on all labels. ASTA also has recommended that the capsicums, no matter the species, be delisted as spices and labeled separately. 

Sulfur Dioxide and Sulfites. Sulfur dioxide [7446-09-5], SO2, sodium bisulfite [15181-46-1], NaHSO, and sodium metabisulfite [23134-05-6] ate effective against molds, bacteria, and certain strains of yeast. The wine industry represents the largest user of sulfites, because the compounds do not affect the yeast needed for fermentation. Other appHcations include dehydrated fmits and vegetables, fmit juices, symps and concentrates, and fresh shrimp (79). Sulfites ate destmctive to thiamin, and cannot be used in foods, such as certain baked goods, that ate important sources of this vitamin. 

Ice formation is both beneficial and detrimental. Benefits, which include the strengthening of food stmctures and the removal of free moisture, are often outweighed by deleterious effects that ice crystal formation may have on plant cell walls in fmits and vegetable products preserved by freezing. Ice crystal formation can result in partial dehydration of the tissue surrounding the ice crystal and the freeze concentration of potential reactants. Ice crystals mechanically dismpt cell stmctures and increase the concentration of cell electrolytes which can result in the chemical denaturation of proteins. Other quaHty losses can also occur (12). 

Drying is an operation in which volatile Hquids are separated by vaporization from soHds, slurries, and solutions to yield soHd products. In dehydration, vegetable and animal materials are dried to less than their natural moisture contents, or water of crystallization is removed from hydrates. In freeze drying (lyophilization), wet material is cooled to freeze the Hquid vaporization occurs by sublimation. Gas drying is the separation of condensable vapors from noncondensable gases by cooling, adsorption (qv), or absorption (qv) (see also Adsorption, gas separation). Evaporation (qv) differs from drying in that feed and product are both pumpable fluids. 

It will be seen that (1) the acidity decreases during the maturing of the plant (2) as in all the cases previously considered, oil of geranium becomes ricber in esters during vegetation (3) tbe proportion of total alcohol increases slightly and the quantity of free alcohol decreases, but not to an extent corresponding with the increase of esters, so that in the course of esterification, which takes place in this case without dehydration, a small quantity of alcohol is produced. 

It appears then that the establishment of practicable and accurate reference methods presents one of the major problems in the determination of moisture in foods. The present paper summarizes some of the important factors that govern the accuracy of moisture determinations in general, and reviews some of the recently published attempts to develop methods that might serve as useful reference standards for dehydrated foods, and especially for dehydrated vegetables and fruits. 

Similar information for other foods would be of great value. With dehydrated vegetables and fruits, large errors are not to be expected, because these foods do not normally contain much nonaqueous volatile matter and some of it will have been lost in the process of dehydration. 

The considerations described above for vacuum-oven drying hold equally well when water is removed by distillation with an organic liquid, as exemplified by the Bidwell-Sterling method (3). The time of distillation for various dehydrated vegetables has been shown to depend on particle size and temperature (IS) and is about the same as would be required in vacuum-oven drying under the same conditions (28). 

It is realized that such rigorous assignment of drying times cannot be strictly correct, because the required time should increase with increasing moisture content. The errors thus incurred would, however, be small for most dehydrated vegetables (moisture... 

Kaur, B. and Manjerkar, S.P., Effect of dehydration on the stability of chlorophyll and P-carotene content of green leafy vegetables available in northern India, J. Food Sci. TechnoL (India), 12, 321, 1975. 

Gomez, M.I., Carotene content of some green leafy vegetables of Kenya and effects of dehydration and storage on carotene retention, J. Plant Foods, 3, 231, 1981. 

Vegetables with peroxidase activity Dehydrated samples... 

Ross and Billing, by means of refractive index measurements on spores and vegetative cells of B. cereus, B. cereus var. mycoides, and B. megaterium, found the values to be very high and comparable with that of dehydrated protein. This suggested that they contained much less water than the vegetative cells. 

The process involves placing the solid food (whole or in pieces) into solutions of high sugar or salt concentration. Le Maguer (1988), Raoult-Wack (1994), Fito and Chiralt (1997), Behsnilian and Spiess (1998), Spiess and Behsnilian (1998), Lazarides et al. (1999), and Torreggiani and Bertolo (2002) have reviewed the basic principles, modeling and control, and specific applications of osmotic dehydration on fruit and vegetables. Additionally, the most recent research advances in this field can be obtained from the European-founded network on osmotic treatments (FAIR, 1998). 

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