Introduction to Fruits and Vegetables 1122

1. Introduction to Fruits and Vegetables1122 Steven C Seideman, PhD Extension Food Processing Specialist Cooperative Extension Service University of Arkansas

2. 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.

5. Fruits and Vegetables

6. 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.

7. 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.

8. 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.

10. 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.

11. 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

12. 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.

14. 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.

16. 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.

18. 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.

19. 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.

20. 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.

21. 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.

22. 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.

23. Color and Color Changes

24. 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).

26. Photo courtesy of USDA

27. 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.

28. 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.

29. 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).

30. 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.

31. 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.

32. Activities of Living Systems

33. 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.

34. 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.

35. The Harvest and Processing of Vegetables

36. 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.

37. 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.

38. 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.

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

40. 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.

42. 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.

44. Fruit Processing

45. 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.

46. 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).

47. 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.

48. 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.

49. Beverages

50. Why are Beverages Consumed? • Nutritive value • Thirst-quenching properties • Stimulating effects • Pleasure