Nutrients

Some loss of nutrients occurs in all cases of blanching, but water blanching may promote excessive losses, typically

Hydrogen Loss Time
Figure 3. Percentage loss of tissue weight, solutes, and water (by difference) from whole pea samples after the given blanch time at 85°C (means of two duplicated replicates). Source: Ref. 25.

up to 40% for minerals and certain vitamins, 35% for sugars, and 20% for protein (1). The most commonly measured nutrient is ascorbic acid because of its high water solubility, susceptibility to oxidation, and ease of analysis. Loss of vitamin C from spinach has been reported as being greater than 70% after 3-5-min blanching (27). Spinach blanched for a range of times at different temperatures was found to lose vitamin C and thiamin following firstorder reaction kinetics (28). The decimal reduction times decreased as temperature increased, and Z values (temperature range over which the decimal reduction time changes tenfold) were about 65°C for both these vitamins.

Losses of vitamin C from peas during water blanching have been studied extensively. Temperatures of 35-97°C for times of 15 s to 25 min were used, and the changes in ascorbic acid and dehydroascorbic acid levels were measured (7,29). It was also found that vitamin C concentration was higher in the seed coat (30). A typical 1-min blanch at 97°C resulted in 28% loss of ascorbic acid from Dark Skinned Perfection peas. A broader study showed that at 94-99°C the K1 blanch-cool system (see also Table 3) had a profound effect on ascorbic acid content of some vegetables but not others. For example, large losses were observed for peas and broccoli but not green beans. An analysis of the beans showed that ascorbic acid was concentrated in the seeds (38 mg/100 g fresh wt), which are protected by the pod (8.4 mg/100 g fresh wt) (31). This highlights the need to study the location and distribution of nutrients within various tissues and to study how the concentrations vary with maturity and variety.

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