Graduate Thesis Or Dissertation

 

The texture and appearance of dual blanched frozen green beans Public Deposited

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  • 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 storage. 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.
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