Low-temperature blanching

Fuchigami, M., Miyazaki, K., and Hyacumoto, N. (1995). Frozen carrots texture and pectic components as affected by low-temperature-blanching and quick freezing. ]. Food Sci. 60, 132-136. 

Abu-Ghannam,N., Crowley, H. (2006). The effect of low temperature blanching on the texture of whole processed new potatoes. J. Food Eng., 74,335-344. 

Canet, W., Alvarez, M. D., Fernandez, C. (2005c). Optimization of low-temperature blanching for retention of potato firmness effect of previous storage on compression properties. Eur. Food Res. Techrwl., 221,423 33. 

Truong, V. D., Walter, W. M., Bett, K. L. (1998). Textural properties and sensory quality of processed sweet potatoes as affected by low temperature blanching. J. FoodScL, 63, 739-743. 

S. Mohamed and R. Hussein, Effect of low temperature blanching, cysteine-HCl, Ai-acetyl-L-cysteine, Na-metabisulphite and drying temperature on the firmness and nutrient content of dried carrot, J. Food Pres. Process., 18(4) 343-348 (1994). 

The structural features of ceU wall polysaccharides of carrots have been studied by Stevens and Selvendran (1984) and Massiot et al.(1988). Plat et al.(1991), Ben Shalom et al.(1992) and Massiot et al.(1992) investigated the changes in pectic substances of carrots after blanching, dehydration and extended heat treatment. Data on the changes in ceU waU polysaccharides of canned carrots are lacking. This study aims to investigate the effect of preheating time at low temperature and the addition of CaCL on texture and on the composition of various pectin fractions of carrots canned by conventional and by a new process. 

Degree of methylation (DM%) of total pectin of carrot alcohol insoluble sohds (AIS) was decreased from 60.73% for fresh carrots to 48.70, 44.62 and 43.83% for canned carrots preheated at 65°C for 15. 30 and 60 min, respectively (Fig. 2). Similar levels of demethylation were also reported in potato (Bartolome and Hoff, 1972), in carrots (Lee et al., 1979) and in snap beans (Adams and Robertson, 1987) when they were blanched at low temperature between 65°C and 70°C. 

The present study indicates that the extracellular enzyme, pepsin, exhibits striking differences from its mammalian homologue with respect to optimum pH, Ea for catalysis, thermal stability, and substrate affinity. These data are interesting from the viewpoint of biological adaption at low temperatures, but they also provide some substance to our contention that enzymes from fish plant wastes can have sufficiently unique properties to justify their use over conventional sources of enzymes used as food-processing aids. The relatively low Eas for protein hydrolysis by fish pepsins indicate they may be especially useful for protein modifications at low temperatures. Alternatively, the poor thermal stability of the fish pepsins studied indicate that the enzymes can be inactivated by relatively mild blanching temperatures. The reality of this concept will have to await studies where the pepsins are used as food-processing aids. Such studies are currently underway in our laboratory. 

The fate mechanisms of GB in soil includes hydrolysis, evaporation and leaching the phos-phonic acid hydrolysis products are subject to biodegradation. Depending on temperature, > 90% of GB added to soil may be lost in 5 days (Small, 1984). As shown by field studies under snow in Norway, low temperatures would increase persistence. In this setting, approximately 55% was removed by evaporation within 5 h and 15% was removed by hydrolysis. Hydrolysis products and several impurities were present up to four weeks later (NMFA, 1982-1983 Johnsen and Blanch, 1984). Hydrolytic half-lives are highly dependent upon pH and temperature. Hydrolytic half-lives are shorter in acidic and basic solutions than at a neutral pH. At 20° C and the pH of natural waters where the half-life is a maximum, estimates of the half-life range from 461 h (pH 6.5) to 46 h (pH 7.5) (Clark, 1989). At 25°C, the half-life ranges from 237 h (pH 6.5) to 24 h (pH 7.5). A half-life of 8300 h at 0°C and a pH of 6.5 was estimated. Durst et al, (1988) have documented a half-life of 3 s at a pH of 12. 

Another reason for the persistence of sulfur mustard is its characteristic freezing at moderate temperatures (13 °-15 °C) (Small 1984). Studies of the persistence of sulfur mustard performed at low temperatures (-1 °C) under actual field conditions in Norway show that small solid particles are formed on the snow surface. The droplets disappeared fairly rapidly, however, primarily by evaporation, and after 2 wk only 0.0001% remained (Johnsen and Blanch 1984 NMFA 1982, 1983). 

L.F. Moreno-Perez, J.H. Gasson-Lara, and E. Ortega-Rivas, Effect of low temperature-long time blanching on quality of dried sweet potato. Drying Technol., 14(7-8) 1839-1857... 

Low-temperature long-time (LTLT) blanching (65-70°C for 15-20 min) was found to improve the... 

Storage at low temperature in the dark. The autoxidation rate is thereby decreased substantially. However, in fruits and vegetables which contain the lipoxygenase enzyme, these precautions are not applicable. Food deterioration is prevented only after in activation of the enzyme by a blanching process (cf. 2.6.4). 

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