|Abstract or Summary
- A quality problem that frequently occurs with frozen green beans
is the sloughing of the skin (epidermal tissues) of the cooked, ready-to-
serve bean pods. It was found that by giving the beans a pre-blanch
(relatively mild heat treatment) prior to the blanch treatment normally
used for frozen green beans, on cooking, sloughing was markedly
reduced, and furthermore, the bean pods were firmer.
As an additional heat treatment was involved, over and above what
is now used for commercial packs of frozen green beans, it was of
interest to know the extent to which the color of the beans was affected.
Also of interest was the effect of storage at 0°F for four months on
the color of the beans.
The color changes in the dual and single blanched green beans
were evaluated by two methods: (1) a physical analysis of the light
reflected from the beans (Hunter Color and Color Difference Meter) and, (2) a physical analysis of the light absorbing properties of the
pigments extracted from the beans and subsequent calculation of the
per cent conversion of chlorophyll to pheophytin. Texture (firmness),
as indicated by resistance to shear, was measured by a modified
Kramer Shear Press. A mechanical device was used to determine the
amount of sloughing of the skins of the bean pods.
After a statistical analysis of the data collected in the experiment,
the following conclusions were drawn:
1. The firmness of the cooked, dual and single blanched, frozen
green beans, as measured by the shear press, was found to be highly
significantly negatively correlated with sloughing of the skins.
2. There was no change in lightness or darkness of the color of
single or dual blanched beans over storage at 0°F for four months.
The Hunter "-a [subscript L]/b [subscript L]" index of color noted a significant change in hue
from green towards yellow of the single and dual blanched beans. The
conversion of chlorophyll to pheophytin was not significant over
3. The color of those beans receiving the 200°F - 150 second
final blanch (single blanch) was the same as the color of those beans
receiving the 210°F - 105 second final blanch (single blanch).
4. As the time and temperature of the pre-blanch increased,
there was a corresponding increase in the amount of chlorophyll
converted to pheophytin, and a change in the visual color of the beans from green towards yellow. The effect of variations of time of preblanch
was much greater on the color of the dual blanched beans than
the effect of variations of temperature of pre-blanch.
5. As the time and temperature of the pre-blanch increased, the
texture (firmness) of the cooked dual blanched beans increased. The
200°F - 150 second final blanch resulted in beans that were firmer
than beans receiving the 210°F - 105 second final blanch,
6. A pre-blanch at 170°F for 30 seconds followed by a final
blanch at 200°F for 150 seconds was found to result in beans that
were similar in color, yet firmer in texture (less sloughing of the
skins) than the single blanched beans.