Introduction to Fruits and Vegetables 1122

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Introduction to Fruits and Vegetables1122

• Steven C Seideman, PhD
• Extension Food Processing Specialist
• Cooperative Extension Service
• University of Arkansas

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Introduction to Fruits and Vegetables

• This module covers some of the basic fruits and
  vegetables, their structure and processing.
• It is a brief summary of Chapter 18
  Vegetables and Fruits from the book FOOD
  SCIENCE by Norman N. Potter and Joseph H.
  Hotchkiss. Published by Kluwer Academic/Plenum
  Publishers. New York.

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Fruits and Vegetables
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Vegetables and Fruits

• Fruits and vegetables are cultivated and
  processed similarly.
• Many vegetables are fruits by the truest
  botanical definition.
• Fruits are defined as those portions of a plant
  which houses the seeds- Therefore tomatoes,
  cucumbers, peppers, okra, sweet corn etc are
  considered fruits.

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Vegetables and Fruits

• The important distinction between fruits and
  vegetables is made based on their usage.
• Vegetables are those plant items generally
  eaten with the main course of a meal.
• Fruits are those plant items commonly eaten
  alone or as a dessert.

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Classification of Certain Vegetables

• Generally classified by their location on a plant
  such as roots, leaves, stems, buds, etc..
• Vegetables/fruits can be classified as earth,
  herbage or fruit vegetables.
• The next chart shows the classification system of
  vegetables.

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Fruits

• Fruits are the mature ovaries of plants with
  their seeds.
• The edible portion of most fruits is the fleshy
  part of the pericarp or vessel surrounding the
  seeds.
• Fruits in general are acidic and sugary.
• Fruits can be classified by botanical structure,
  chemical composition and climatic requirements.

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Fruit Classifications

• Berries- usually quite small- grapes, cranberries
• Melons-large and have a tough outer
  rind-watermelons, cantelope
• Drupes-contain single pits- apricots, cherries,
  peaches and plums.
• Pomes-contain many pits- apples, pears.
• Citrus Fruits-high citric acid-oranges,
  grapefruit, lemons
• Tropical fruits-require warm temperatures-
  bananas, dates, figs, pineapple, papayas, mangos

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Composition

• Fruits and vegetables have similar compositions.
• They are very high in water content (70-85),
  relatively high in carbohydrates but low in fat
  (less than 0.5) and protein (less than 3.5) and
  usually contain useful vitamins.
• The carbohydrate portion can be further broken
  down into digestible and indigestible parts
  (sugars and starches vs pectins and cellulose
  material).
• Vitamin A is found in yellow-orange fruits and
  vegetables and leafy, green vegetables.
• Vitamin C is found in citrus fruits, tomatoes and
  green, leafy vegetables.

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Structural Features

• The structural material of the edible portion of
  most fruits and vegetables is the parenchyma
  cell. Although parenchyma cells of different
  fruits and vegetables differ somewhat is gross
  size and appearance, all have essentially the
  same fundamental structure. See diagram on next
  page.

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Structural Features

• Cells- The cells of the edible portion of most
  fruits and vegetables are characterized by a
  large, water filled vacuole. Sugars and other
  water-soluble compounds may also exist in this
  area. Cellulosic material (complex carbohydrates)
  surround the vacuoles and also form the cell
  wall. Protein is also in the cell walls. The next
  table shows the Structure and Chemical Components
  of Plant Cells.

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Texture

• The range of textures encountered in fresh and
  cooked vegetables and fruit is great and, to a
  large extent, can be explained by changes in
  specific cellular components. Since plant tissues
  generally contain more than two-thirds water, the
  relationships between these components and water
  further determine textural differences.

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Textural Features

• Turgor- The rigidity of cells is due to being
  filled with water. The cell membranes are elastic
  and give and take with changes in water
  content. Living plants have a high turgor,
  resulting in crispness. When plant tissues are
  damaged or destroyed by storage, freezing,
  cooking or other causes, turgor pressure is lost,
  leaving the tissue soft and wilted.

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Textural Features

• Cellulose, Hemicellulose and Lignin- Cell walls
  in young plants are very thin and are composed
  largely of cellulose. As the plant ages, cell
  walls tend to thicken and become higher in
  hemicellulose and lignin. These materials are
  fibrous and tough and are not significantly
  softened by cooking.

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Textural Features

• Pectin and related substances are complex
  polymers of sugar-acid derivatives.
• Pectins are the cement-like substance found
  especially in the middle lamella which helps hold
  plant cells together.
• Fruits and vegetables contain a natural occurring
  enzyme, pectin methyl esterase that hydrolyzes
  pectin.

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Textural Features

• It is often desirable to firm the texture of
  fruits and vegetables.
• By adding calcium ions to fruits and vegetables
  before processing, calcium pectates are formed
  from pectins that increase structural integrity.
• Thus it is a common commercial practice to add
  low levels of calcium salts to tomatoes, apples
  and other fruits and vegetables prior to canning
  and freezing.

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Color and Color Changes
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Color and Color Changes

• Much of the appeal of fruits and vegetables in
  our diets is due to their desirable colors.
• The pigments and color precursors found in fruits
  and vegetables occur in the cellular plastid
  inclusions. (e.g. chloroplasts).

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Photo courtesy of USDA
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Chlorophylls

• Chlorophylls are largely contained within the
  chloroplasts and have a primary role in the
  photosynthetic production of carbohydrates from
  carbon dioxide and water.
• The bright green color of leaves is largely due
  to oil-soluble chlorophylls.
• When cells are destroyed by aging, processing or
  cooking, the proteins are denatured and the
  chlorophyll in changed to pheophytin which is
  olive green to brown in color.
• For this reason, peas, beans, spinach and other
  green vegetables lose their bright green upon
  cooking.

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Carotenoids

• Pigments belonging to the carotenoid group are
  fat soluble and range in color from yellow
  through orange to red.
• Important carotenoids include the orange of
  carrot, corn, apricot, peach, citrus fruits and
  squash the red lycopene of tomatoes, watermelon
  and apricot and the yellow-orange xanthophyll of
  corn, peach, paprika and squash.
• In food processing, the carotenoids are fairly
  resistant to heat, changes in pH and water
  leaching since they are oil soluble. However,
  they are very sensitive to oxidation which
  results in both color loss and destruction of
  vitamin A.

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Anthocyanins

• These pigments represent a group known as
  flavonoids that are water soluble and commonly
  present in the juices of fruits and vegetables.
• They range in color from purple, blue to red
  found in grapes, berries, plums and cherries.
• The color expressed is pH dependent (violet to
  blue in alkaline media to become red upon the
  addition of natural occurring or intentionally
  added acid).

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Flavonoids

• The yellow flavonoids are structurally related to
  anthocyanins and comprise a large group of
  chemicals found in plant foods. They are also pH
  dependent tending toward a deeper yellow in
  alkaline media.
• Thus potatoes and apples tend to become somewhat
  yellow when cooked in water with a pH of 8.0 or
  higher. Acidification to pH of 6.0 or lower
  favors a whiter color.

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Tannins

• Tannins are complex mixtures of phenolic
  compounds found in plants.
• Under most circumstances, they are colorless but
  on reaction with metal ions, they form a range of
  dark-colored complexes which range from red,
  brown, green or black.
• Water soluble tannins appear in the juices
  squeezed from grapes, apples and other fruits as
  well as in the brews of tea and coffee.
• If in high enough levels, can contribute an
  astringent flavor note.

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Activities of Living Systems
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Activities in Living Systems

• Fruits and vegetables continue to respire after
  harvest meaning they take in oxygen and give off
  carbon dioxide, water and heat.
• The moisture and heat buildup can cause serious
  damage to fruits and vegetables unless quickly
  controlled.
• Numerous changes occur to starches, sugars,
  pectins etc immediately after harvest.

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Activities in Living Systems

• The quality decline in stored respiring fruits
  and vegetables is termed senescence and results
  from the continued enzymatic activity.
• The two primary factors that influence senescence
  rate are temperature and composition of the
  storage atmosphere.
• Reduced temperatures, lower oxygen rates and
  raised carbon dioxide levels reduce the rate of
  senescence and increase storage times.

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The Harvest and Processing of Vegetables
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Varietal Differences

• Food scientists and food processors appreciate
  the substantial differences that cultivars of a
  given vegetable possess.
• In addition to differences in response to weather
  and pest resistance, cultivars of a given
  vegetable differ in size, shape, time of maturity
  and resistance to physical damage.

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Harvesting and Preprocessing Considerations

• When vegetables are maturing in the field, they
  are changing from day to day. There is a time
  when the vegetables will be at peak quality from
  the standpoint of color, texture and flavor.
• Because the peak quality lasts only briefly,
  harvesting and processing of several vegetables,
  including tomatoes, corn and peas, are rigidly
  scheduled to capture this peak quality.

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Vegetable Processing

• Washing-vegetables are washed not only to remove
  field soil and surface microorganisms but also
  fungicides, insecticides and other pesticides.
• Skin removal-There are numerous methods of
  removing the skins from vegetables ranging from a
  hot alkaline soak that softens the skin to the
  use of steam under pressure.

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Vegetable Processing

• Cutting and Trimming- Many vegetables require
  various kinds of cutting, stemming, pitting or
  coring.

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Vegetable Processing

• Blanching-Most vegetables that do not receive a
  high-temperature heat treatment (as in normal
  canning) must be heated to a minimal temperature
  to inactivate natural enzymes before processing
  or storing even when frozen. This is known as
  blanching.
• Table 18.4 shows minimum blanch times of some
  vegetables.
• Too little blanch time is ineffective and too
  much time damages vegetables by excessive
  cooking.
• If not blanched properly, off-flavors, off-colors
  and poor textures will develop.

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Vegetable Processing

• Canning-Canning refers to the science of placing
  the desired vegetable in a can, evacuating the
  air, sealing it and heating to a temperature to
  totally destroy all living organisms.

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Fruit Processing
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Varietal Differences

• As with vegetables, the diversity of kinds of
  fruit is further enlarged by the numerous
  cultivars of a given fruit.
• For example, there are over 1,000 varieties of
  apples and over 3,000 varieties of pears.
• Although some fruit is marketed fresh, most is
  further processed into a wide range of products.

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Fruit Quality

• Fruit quality depends on tree stock, growing
  practices and weather conditions.
• Most important to quality is the degree of
  maturity and ripeness when picked and the method
  of harvesting.
• Maturity is the condition when the fruit is ready
  to eat or, if picked, will become ready to eat on
  further ripening.
• Ripeness is that optimum condition when color,
  flavor and texture have developed to the peak.
• Some fruits are picked when they are mature but
  not yet ripe (e.g. cherries, peaches).

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Fruit Harvesting and Processing

• Much of the harvesting of most fruits is still
  done by hand. This labor may represent about half
  the cost of growing fruit.
• Washing-fruit is washed to remove soil,
  microorganisms and pesticide residues.
• Sorting- Field fruit must be sorted by size and
  quality which defines the next steps in
  processing.

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Fruit Harvesting and Processing

• Freezing- Large amounts of fruits are frozen each
  year for further use. Freezing is considered far
  superior to canning for firmness.
• Blanching- Fruits are generally not heat blanched
  because the heat causes loss of turgor, resulting
  in sogginess and juice drainage after thawing.
  Instead, chemical antioxidants are used. If
  blanching is to be done, calcium salts are added
  to the blanching water to form calcium pectates.

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Beverages
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Why are Beverages Consumed?

• Nutritive value
• Thirst-quenching properties
• Stimulating effects
• Pleasure

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Major Beverage Consumption

• Beverage
• Carbonated Soft Drinks
• Coffee
• Milk
• Beer
• Bottled Water
• Selected Fruit Juices
• Tea
• Fruit drinks, cocktails
• Wine

• Gallons/person/year
• 48.8
• 24.3
• 23.7
• 22.1
• 16.0
• 14.2
• 8.4
• 7.9
• 1.9

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Juice Processing

• Extraction-Fruit is pressed or ground to yield
  the juice.
• Clarification- Resulting juice may contain small
  particles of pulp and other debris. Typically,
  commercial enzymes are added to the juice to
  digest the suspended particles. Then the juice is
  centrifuged to remove the denser particles.

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Juice Processing- Continued

• Deaeration- Air is removed to prevent oxidation
  and losses in vitamin C.
• Pasteurization- performed to reduce microbial
  counts and inactivate enzymes.

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Fruit Juice Concentrates

• Since most juices have a very low solids content,
  the juice may be concentrated to provide a more
  valuable product for shipping. The water that is
  evaporated contains significant amounts of
  volatile flavor compounds. These are recaptured
  and added back to the juice or used as flavorings
  for other products.

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Organic Foods
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Organic Foods

• Organic is a labeling term that denotes
  products produced under the authority of the
  Organic Foods Production Act. The principle
  guidelines for organic production are to use
  materials and practices that enhance the
  ecological balance of natural systems and that
  integrates the parts of the farming system into
  an ecological whole.

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Organic Foods

• Organic does not refer to the food itself but to
  how it is produced. Organic food production is
  based on a system of farming that maintains and
  replenishes the fertility of the soil. Organic
  foods are produced without the use of synthetic
  pesticides and fertilizers. Organic foods are
  minimally processed to maintain the integrity of
  the food without artificial ingredients,
  preservatives or irradiation.

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Is Organically Grown Produce Healthier than other
Produce?

• Certified organic produce is not essentially
  healthier than produce that has been grown under
  non-organic conditions. The nutritional content
  of a particular vegetable doesnt change. But
  the lack of synthetic pesticide residues on
  organically grown produce may make for a safer
  product. Organic products may also have higher
  incidences of pathogenic bacteria.

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Organic Regulations

• The USDA regulations on the definition, labeling
  and requirements for organic can be found at
  www.ams.usda.gov/nop.

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Biotechnology
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Biotechnology

• Agricultural Biotechnology is a collection of
  scientific techniques, including genetic
  engineering, that are used to create, improve or
  modify plants, animals and microorganisms. Using
  conventional techniques such as selective
  breeding, scientists have been working to improve
  plants and animals for human benefit for hundreds
  of years. Modern techniques now enable scientists
  to move genes (and therefore desirable traits) in
  ways they could not before and with greater ease
  and precision.

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Biotechnology

• Biotechnology is literally the insertion of
  pieces of DNA into a plants DNA. Thus, the
  inheritable and specific properties and traits
  can be incorporated into the plants genetics.
• Desirable traits such as resistance to plant
  diseases and viruses or quality and storage
  attributes can be specifically engineered into
  plants.

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Benefits of Biotechnology

• Crop resistance to disease, pests etc
• Improved shelf life of foods
• Optimization of the enzymes used in food
  processing
• Environmental impacts through lower energy costs
  and less pesticide/ herbicide use.
• Improved health through dietary impacts.

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Negatives of Biotechnology

• Who owns the control of patented genes and
  biotechnology techniques?
• Cross-pollination of adjacent crops.
• Allergenicity of new proteins.

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Crops that have been Genetically Modified

• Soybeans-reduced saturated fat
• Soybeans-resistant to pests
• Soybeans- resistant to herbicides
• Corn-resistant to pests

• Corn-resistant to herbicides
• Tomatoes- resistant to pests
• Tomatoes-delayed ripening
• Golden rice-beta-carotene added to rice

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Conclusions

• In this module, you should have learned about
• 1)The structure, composition and color changes of
  fruits and vegetables.
• 2)The basic operations of fruit, vegetable and
  beverage processing.
• 3)What the terms organic and biotechnology
  refer to.

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