Fruit freeze-drying

Increasingly, freeze drying is used for dehydrating foods otherwise difficult to dry, such as coffee, onions, soups, and certain seafoods and fruits. Freeze drying is also increasingly employed in the drying of pharmaceutical products. Many pharmaceutical products when they are in solution deactivate over a period of time such pharmaceuticals can preserve their bioactivity by lyophilization soon after their production so that their molecules are stabilized. 

Freeze-dried tomato powders obtained from whole tomato fruits and from their pulp after centrifugation, containing 474 and 5399 pg/g dry weight, respectively, were developed for use as additives for food fortification. Cis isomers of lycopene were determined in only a few smdies. The 5-cis-, 9-cis-, and 13-d5 --El5-d5 -lycopene were the isomers found in commercial tomato products. The structures of lycopene cis isomers are shown in Figure 4.2.1 and the structure of the dll-trans isomer is displayed in Figure 6.2.1 in Chapter 6. 

In order to preserve, as much as possible, the phenolic content in fruit and vegetable samples, the literature proposed the application of cold temperatures, even reaching to freezing, when lyophilization is the objective. These procedures also could inactivate the enzymes. The freeze-drying is largely the main preservation technique used in the studies related to the identification and quantification of the phenolic compounds of fruit... 

Figure 2.3 illustrates a process in which the outer layer of a product is quickly frozen as a congealed crust. These CRUSToFREEZE plants have a capacity between 1500 and 5000 kg/h and require 0.5 to 0.8 kg LN2 pro kg of product, which has to be frozen totally on a conveyor belt. Figure 2.4 shows the product exit of the plant in Fig. 2.3. The freeze drying of coffee and tea extracts, fruit pulps or small pieces of meat require a multi- stage pretreatment. The granulated end product from coffee and tea extracts should have a defined grain size, a desired color, and a predetermined density. Fruit pulps should become granulated, with the appearance of fruit pieces, while meat pieces should not stick together like a small meat ball, but be recognized as single pieces when presented in a meal.

Fig. 4.3. Survey of freeze dried vegetables and fruits. Blanching time between 2 and 4 minutes (part of Table 1 from [4.11]).

Fig. 4.4. Influence of fruit and vegetable type on color, taste and consistency of freeze dried products.

Sauvageot, F., Simatose, D. Some experimental data on the behavior of fruit juice of volatile components during freeze-drying. International Institute of Refrigeration (Comm. X, Paris, 1969)... 

Soil (L, F, H, and A layers), mosses and fungal fruiting bodies were each collected from the same spots at the three locations. The L, F, H samples were ground to pass a 1 cm sieve the mineral soil was sieved to retain its fine-earth 2mm fraction mosses were separated into green versus dead tissues the fruiting bodies were separated by stalk and cap. Subsamples were freeze-dried prior to... 

Citrus pectin ( Polygalacturonic Acid Methyl Ester from Citrus Fruits, Grade I ) was obtained from the Sigma Chemical Company. It had a galacturonic acid content of 89% and a degree of esterification of 57. Separate aqueous solutions of citrus pectin were freeze-dried and air-dried in deionized water. These samples were replicated with 9.8A Pt/C and backed with 148A of carbon. The replicas for these samples were picked up without a carbon support film (38). 

Transgenic tomato fruit expressing taxadiene synthase were able to reroute the production of taxadiene, allowing extraction of large amounts of highly purified taxadiene from freeze-dried tomato (Kovacs et al, 2007). 

Tomato Tomato is also popular for the expression of biophamaceuti-cals due to the relative ease of processing of the fruit, and the fact that the fruit can be consumed fresh, thus providing stability of the recombinant protein at room temperatures. Tomato fruit has a short shelf life but, alternatively, can be freeze-dried, an inexpensive and well-established technology. Freeze-drying results in concentration of the protein and maintenance of batch consistency. 

Frozen materials should be stored at —20°C, fruits and salad vegetables at around 4°C, and canned foods at room temperature. Powdered and freeze-dried materials should be stored in the dark in their original containers. Storage of fresh materials should preferably not exceed 3 days. After the initial preparation (see below), fresh or cooked materials can be conveniently stored at -20°C for a short time prior to extraction. 

For other plant food samples, appropriate sample sizes will depend on chlorophyll content and water content. Samples with low chlorophyll content may require 100 to 200 mg per replicate. For samples with low chlorophyll content and high water content (e.g., in florescences, fruit tissues, fruit juices), it is necessary to start with 2 to 3 g fresh weight sample and freeze dry it before extraction. Frozen food samples should also be freeze dried before extraction. 

Water-containing plant materials need to be extracted with polar solvents such as acetone, methanol, or ethanol that can take up water. Freeze-dried plant tissues and freeze-dried juices can be directly extracted with diethyl ether, which contains traces of water and is more polar than light petrol or hexane. Pure light petrol or hexane are less suitable, because more polar pigments, such as Chi b or xantho-phylls, are only partially extracted from freeze-dried plant samples. A few drops of acetone or ethanol added to light petrol or hexane will, however, guarantee a complete extraction. This mixture will extract Chi a, Chi b, and all carotenoids—including xanthophyll esters and secondary carotenoids that are present in many fruits and juices—from the freeze-dried plant material. 

The ultrasound-assisted extraction of freeze-dried plant-based materials normally takes 2 hr. If the extract is evaporated to dryness, a total of 3 hr is necessary. As an additional sample preparation step, 2 to 4 days should be allotted for freeze-drying fresh plant materials, depending on the quantity of the material. Homogenizer-assisted extraction of fresh fruit takes <4 hr. 

Vegetables, fruits Extract freeze dried material with THF/MeOH (1 1) + MgC03 + internal standard (/3-apo-8 -carotenoate) at 0°C. Homogenize, centrifuge. Saponify if /3-cryptoxanthin needs to be determined. Add 10% NaCl (w/v) to either saponified or unsaponified solution and extract with petroleum ether. Vydac 201 TP C,g 5 /zm (Hastalloy frits replaced with PAT (Peek alloyed with Teflon frits) 250 X 4.6 mm... 

Hertog et al. (119) developed a fast HPLC method for the identification and quantification of five major flavonoid aglycones (quercetin, kaempferol, myricetin, luteolin, and apigenin) in freeze-dried vegetable and fruits. However, due to the inadequate resolution of quercetin and luteolin on RP-HPLC on Nova-Pak C]8, two different eluents of different solvent strength and viscosity were utilized. The conditions for hydrolysis and extraction were tested based on different conditions of hydrochloric acid concentration (1.2-2.0 M), reaction period (0.5-6 h), and meth-... 

Moy and Speilmann (90) recently reported on the economic feasibility of vacuum puff freeze drying of tropical fruit juices and nectars. They considered the process economically feasible if production rates were 250,000 or 1,000,000kg of dried nectar base per year (two plant sizes) with an assumed level of 35% sucrose (wet weight basis) blended with the juice or puree before dehydration. One assumption made in their study was that a marketing share equivalent to 0.5% of the annual orange juice volume in the U.S. was attainable. 

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