2.4: Effect of pH and Heat on Color and Other Attributes of Fruits and Vegetables; Osmosis; Enzymatic Browning
- Page ID
- 29362
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)- To identify the major categories of pigments found in fruits, vegetables, and other plant foods.
- To observe the effects of heat and pH of cooking medium on plant pigments.
- To observe the effects of acid or basic cooking medium on the texture of vegetables.
- To observe enzymatic browning.
- To identify some methods of controlling enzymatic browning.
- Identify the major categories of plant pigments.
- Boil vegetables representing each of the pigment categories in water, in acidic solution, and in basic solution.
- Prepare raw fruits in a variety of ways designed to control enzymatic browning.
Terms
- Vegetable Pigments: Chlorophyll, Carotenoids, Anthocyanin, & Anthoxanthin
- Flavor Categories: Mild, Brassica, Allium
- Texture: Cellulose, Pectin, & Hemicellulose
- Enzymatic Browning
- Osmosis
Identify the pigments in each of the vegetables listed below:
Pigment categories: carotenoids, chlorophyll, anthoxanthin, anthocyanin
| Vegetable | Major Pigment | Other Pigment Present |
|---|---|---|
| Red Cabbage | ||
| Cauliflower | ||
| Carrot | ||
| Broccoli |
Prepare assigned vegetable according to specific directions for added ingredients and for covering pan.
Raw vegetable preparation:
Cabbage (red or green): Remove outer leaves and wash remaining head. It is not necessary to remove the entire core. Shred cabbage into bite-size pieces with a chefs’ knife.
Cauliflower: Break small flowerets from the head. Wash.
Carrots: Peel, wash and slice into ¼-inch slices. If the carrot is large, quarter lengthwise before slicing crosswise.
Broccoli: Cut thin spears about 2 inches long. Wash.
Onions: Remove outer skin by peeling or by blanching. Cut off root end. Cut onions into bite size pieces. Cook until the flavor is mild.
Lid On and Lid Off Directions:
- Prepare ¼ cup assigned vegetable for each part.
- Boil 1 cup of distilled water for each vegetable. Add vegetable to boiling water; begin timing after water returns to boil.
- Boil until crisp-tender when tested with fork. Record cooking time.
- Reserve a small amount of cooking water for display in custard cup.
- Display vegetable in a custard cup with the sample of cooking water in separate custard cup.
- Record color and texture observations. Do not taste.
Acid/Base Directions:
- Prepare ¼ cup assigned vegetable for each part.
- Boil 1 cup of tap water for each vegetable. Add vegetable to boiling water; begin timing after water returns to boil. Add 1 tsp. vinegar (acid) or ½ tsp. baking soda (base).
- Boil until crisp-tender when tested with fork. Record cooking time.
- Reserve a small amount of cooking water for display in custard cup.
- Display vegetable in a custard cup with the sample of cooking water in separate custard cup.
- Record color and texture observations. Do not taste.
Evaluation
| Major Pigment Vegetable | Lid on | Lid off |
Acid Add 1 tsp vinegar to cooking water |
Base Add ½ tsp baking soda to cooking water |
|---|---|---|---|---|
| Anthocyanin
_________________ |
_________ min | _________ min | _________ min | _________ min |
| Anthoxanthin
_________________ |
_________ min | _________ min | _________ min | _________ min |
| Carotenoid
_________________ |
_________ min | _________ min | _________ min | _________ min |
| Chlorophyll
_________________ |
_________ min | _________ min | _________ min | _________ min |
Observe Osmosis
- To observe the effect of osmosis on the characteristics of raw fruits and vegetables in storage and in preparation.
- Store fresh raw vegetables in a variety of osmotic conditions.
Observe the effect of salt on the appearance and texture of cucumbers:
Cut a small cucumber into 1/8″ slices, divide into three bowls, and treat each sample as directed below. Observe after one hour.
| Method | Appearance | Texture |
|---|---|---|
| Soak in 1 cup cold water only | ||
| Soak in salt/water solution (2 tbsp salt to 1 cup cold water) | ||
| Sprinkle with 2 tbsp salt only |
Explanation:
Demonstrate enzymatic browning and methods of control:
- With a stainless steel knife, slice an apple or banana onto separate dishes.
- Apply assigned treatment.
- Allow to stand uncovered for one hour.
- Record observations.
| Treatment | Appearance | Flavor |
|---|---|---|
| None | ||
| Diluted lemon juice (1 part to 3 parts water) | ||
| Commercial anti-darkening agent |