Frozen plant products

Frozen fish fingers and similar products are made from a mixture of different fish that arrive at the processing plant as frozen blocks of the average size 62.7 x 254 x 482 mm (thick x width x length). The frozen blocks are minced and the still frozen minced fish blocks are mixed and pressed into the desired shape, covered with batter and bread crumbs, baked on the outside (still with a frozen core), packed and stored in a deep freezer. 

Food processing firms producing heat-preserved, frozen, dehydrated, or chemically preserved foods may be classified by their finished products. Companies may be further grouped based on whether they process raw materials into ingredients, such as in poultry and meat processing plants, or whether they take these ingredients and convert them to ready-to-eat consumer products. 

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. 2.7.1. Course of processes in a freezing plant, in which the liquid product is frozen dropwise in LN2 (Cryopel Firma Messer Griesheim GmbH, D-47809 Krefeld).

Fig. 2.19. Plots of a test to determine the specific water vapor flow or the water vapor speed in a production freeze drying plant with approx. 30 m2 shelf area. For the tests 300 kg of distilled water were filled into ribbed trays, which were placed on the shelves. Six RTD were placed in different trays and frozen with the water. The RTD temperatures and BTM measurements were practically identical, because the RTD were always immersed in the ice, and during the test only 25 % of the ice was sublimated.

There will be some differences and it is a quantitative question, whether or not they can be tolerated or not. For a final decision, test runs in a pilot plant should be carried out with freshly frozen product and such which has been resting for 5 h before drying. These tests are recommended because the methods mentioned above use different sized samples in different configuration than are used in the production. The amount of product and its geometrical dimension will also influence the structure as well as the number of crystallization nuclei in the product, which can be very different in a normal laboratory and in a clean production area. 

Although LOX activity is important to the plant s defense against pathogens, there are negative aspects of the enzyme in foods. LOX activity and the resulting fatty acid hydroperoxide products initiate free radical chains that modify proteins (particularly residues of Trp, His, Cys, Tyr, Met, and Lys) as well as vitamins or their precursors (e.g., carotene and tocopherol). Evidence of such free radical reactions is often visibly observed as loss of carotenoid/chlorophyll pigments in improperly blanched frozen foods. Another consequence of these free radical reactions is the development of potent off-flavors, many of which originate from decomposition of the fatty acid hydroperoxide products. 

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