Vegetable blanching

Dark green vegetables Blanch leaves in boiling water. Homogenize with water containing 0.5% ascorbic acid. Extract an aliquot of the resultant mixture with acetone/ petroleum ether (3 2) containing 0.5% BHT by shaking for 10 min. Reextract until colorless (3 extractions). Saponify (ambient) the combined solvent extracts. Vydac 201 TP Clg 5 /zm 250 X 4.6 mm MeOH/CH,C1,/ H,0, 80 15.2 4.8 A ]-trans-, 9-cis-, 13-cis-/3-carotene, all-trans-a-carotene Vis 450 mn 177... 

However, unless the test is applied very soon after blanching, the results obtained may lead to misinterpretation and unnecessary product rejection. Peas and other vegetables yielding negative tests soon after blanching have been observed on subsequent standing and prior to freezing to yield positive reactions. This condition has been observed to carry over in the frozen and stored product. 

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

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. 

Negi, P.S. and Roy, S.K. 2000. Effect of blanching and drying methods on p-carotene, ascorbic acid and chlorophyll retention on leafy vegetables. Lebensm.-Wiss. U.-Technol. 33 295-298. 

Trimming, cutting, juicing, and blanching of fruits and vegetables... 

Peroxidase, in combination with phenolic compounds, utilizes hydrogen peroxide to bring about oxidation. The enzymes do not act in intact fruits because of the physical separation of enzyme and substrate. Mechanical damage, rot, or senescence lead to cellular disorganization and initiate decomposition. Inhibition of the enzymes in vegetables is achieved by blanching with steam or by... 

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