Freezing of vegetables

Arthey, D., Freezing of vegetables and fruits, in Mallett, C.P., (ed.), Frozen food technology, Blackie, Glasgow, 1993. 

Pala, M. (1983). Stepwise blanching and its importance in freezing of vegetables. Refrigeration in the Service of Man. In Proceedings XVIth International Congress of Refrigeration , Vol. 3, pp. 631-638. Paris. 

CRiVELLi G and polesello A (1973), Research on quick-freezing of vegetables. Ill Suitability of carrot varieties , Freddo, 27, 29-30. 

In 1991, a group of Freezing of Vegetable Products Department, Spanish Council for Scientific Research, Ciudad University, Madrid, Spain examined the carotenoids in four best known kiwifruit cultivars in Spain of Hayward, Abbott, Bruno and Monty by the retention times and absorption spectra of high performance liquid chromatography (HPLC) on a C-18 reversed-phase column (Table 6) (Figure 16a) (Figure 16b). 

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

Other applications of liquid-solid fluidized beds that have been suggested or put into practice include the leaching of vegetable oils from seeds (Epsfein, 2003), fhe freeze concentration of solutions (Rios et al., 1985) and osmotic drying (Marouze et al., 2001). Fluidization is also the basis of fhe hydraulic fransport of vegetables (McKay et al., 1987). Three-phase fluidized beds have been employed for the fermentation of cocoa beans (Jacquef et al, 1981 Rios et al, 1985). 

Looking back also over the historical development of quality requirements for processed foods, freezing when properly carried out is undoubtedly the most satisfactory method for the longterm preservation of vegetable produce. The low temperatures commonly prescribed for frozen foods (—18°C) can maintain initial quality and nutritional value practically unchanged, so that frozen and fresh vegetable products differ only in texture (Canet, 1989), which is however a particularly important quality attribute in potato products. 

Alvarez, M. D., Canet, W. (2001c). Influence of cooking and freeze-thaw cycles on viscoelastic properties of vegetable purees. Lebensm. Wiss. Technol., 34, 549-555. 

Manzini, A., Crivelli, G., Bassi, M. and Buonocore, C. (1965). Structure of vegetables and modifications due to freezing (Istituto Sperimentale per la Valorizzazione Tecnologica dei Prodotti Agricoli Ed.), pp. 1-267, Milano. 

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-... 

The initial moisture content of B is X, and after equilibration with A, the moisture content is X2. The substances A and B will reach a mean relative humidity of about 40 percent, but not a mean moisture content. If this were a dry soup mix and the sensitive component was a freeze-dried vegetable with a moisture content of 2 percent and the other component, a starch or flour with a moisture content of 13 percent, the vegetable would be moistened to up to 9 percent. This would result in rapid quality deterioration due to nonenzymic browning reactions. In this case, the starch would have to be postdried. 

Freezing of tissues (vegetable or animal) generally causes some damage. At temperatures above — 10°C, ice crystals only form outside the cells. This causes freeze concentration of the extracellular liquid, hence to an osmotic pressure difference between intra- and extracellular liquid and hence to osmotic dehydration of the cells (plasmolysis). At lower temperatures, ice crystals tend to penetrate the cells, whereby intracellular crystallization occurs. This reduces plasmolysis but tends to increase mechanical damage, possibly leading to a soft texture of the tissue after thawing. 

WILLIAMS D C, LIM M H, CHEN A O, PANGBORN R M and WHITAKER J R (1986), Blanching of vegetables for freezing - which indicator enzyme to choose . Food Techn, 40, 130-140. 

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