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Frequently Asked Questions


OBJECTIVES

The learner will be able to --
  • discriminate and list the similarities and differences between a generalized animal cell and a plant cell.
  • determine, analyze and describe the influence of thermal and/or mechanical stress on catalase and peroxidase activity.
  • list, analyze and describe factors affecting the specific components comprising the flavor of selected fruits and vegetables.
  • be able to analyze and discuss the effect of thermal, chemical and mechanical or physical stress on the texture of fruit and/or vegetables.
  • Discuss the discoloration of apples versus potatoes, vs peaches.
  • Compare the suitability of mealy and waxy potatoes for baking versus boiling.
  • Describe the effects of method and time of cooking on the color, flavor, and texture of selected fruits and vegetables.
  • Know how to combine complementary plant proteins
  • know the impact of pH on the rehydration of dried legumes
  • know how to substitute plant protein foods in a diet.

CONTENT

Fruits, vegetables, and other plant tissues either directly or indirectly supply all of man's foods. There are an estimated 270,000 plant species. The number of crops which fit into man's dietary picture is probably between 1,000 and 2,000 species. Some 100 to 200 species are of major importance in world trade,15 species provide the bulk of world food crops, such as rice, wheat, soybean, peanut, coconut, and banana. This site on factors that influence their color, texture and flavor.

There are a number of different types of vegetables. They are classified as bulbs, roots, and tubers. Vegetable fruits, such as okra, or cucumbers, make up another category or classification of vegetables. Of course, there are also flowers, buds, stems and leafy vegetables. Vegetable seeds are those such as the legumes, coconut, or corn.

In discussing the composition of fruits and vegetables, one is interested in both the tissue structure and in the components which make up this structure. One of the major structural components of fruits and vegetables is cellulose. Scanning electron micrograph allows us to view the extracted cellulose in crystalline form. It is a polymer of glucose and is the major structural component. Cellulose is not the only structural material; however, the fundamental type of cells are parenchyma or ground cells. There are several different categories of tissues. All cells have a cell wall . The cell wall consists of very thin primary cell wall and a hydroxyproline-containing membrane. This cell wall contains much of the cellulose. Additionally, there are other polymers, such as the pectic substances, lignin, and sometimes even leucoanthocyanins (pigments).

The understanding of the structure of a particular plant cell is not only important for texture elucidation. It will also assist with a greater awareness of color and of flavor.

Leafy vegetables are generally high in water and low in carbohydrates, proteins and fats. They frequently contain the mechanism for photosynthesis.

  • Spinach: Leaves of Spinacia oleracea.
  • Lettuce: Leaves of the plant Lactuca sativa.
  • Mustard Greens: is the leaves of the mustard plant used in salads or cooked as a vegetable. The mustards are of the CRUICFERAE family which gets its name from the characteristic cross-shaped flowers, and of the genus BRASSICA.
  • Cabbage: The Cabbage is one of the innumerable forms of the species Brassica oleracea (Crucifer Family), these characterized by a more or less compact head formed by the leaves. >
Seeds, a mature ovula, vary in water content and are a source of carbohydrates and proteins. They may be "fresh" and high in water or "dried" and relatively low in water content.
Tubers are generally higher in carbohydrates and lower in water content than stem, flower or leafy vegetables. Tubers are an enlarged underground stems.

  • Potatoes:
  • are a vegetable. The tuber of a plant belonging to the order Solanaceae. The potato (Solanum tuberosum) furnishes a high amount of starch.
    Fruits are the fleshy part of the plant which surrounds the seed. It may be eaten either, botanically or culturally, as a fruit or as a vegetable.
  • Cantaloup: cantaloupes and muskmelons are names used interchangeably to refer to both the netted and smooth type of melon. These melons are oval and approximately 5 inches or more in diameter, with yellow or golden (not green) background color.
  • Eggplant: the eggplant (aubergine) is native to Asia, having been cultivated in China from 600BC.
  • Squash: is an edible fruit of the gourd family, the flesh of which is cooked and eaten as a vegetable.
  • Peas (snow peas): Another name, sugar peas, is more accurately descriptive because these tender pods are as sweet as sugar when young, which is when they should be eaten. Their Cantonese name is a corruptionof Holland (hoh laan), and this may explain their origins. They look similar to green garden peas, except that they are flatter. Snow peas develop a large, fleshy shell long before their peas develop. When they are fully developed, it is necessary to remove the string that runs along the top before cooking.
  • Stems are plant portions generally high in water and fiber. They have relatively little other nutritive value.
  • Asparagus: is called in Britian sometimes "Sparrow-grass" a term with no meaning. The plant is one of the lily tribe, and, although cultivated in gardens for table use, is not unfrequently met with growing wild along the sea-shore.
  • Bulbs are generally higher in carbohydrates and lower in water content than stems, flowers or leafy vegetables. Bulbs are enlargements above the roots.

  • Onion: Belonging to the Liliaceae family, onions are characterized by layered crisp flesh, usually white but in some types a red-purple. When raw they have a pungent odor and strong flavor, which becomes almost sweet when cooked.
  • Garlic: Bulb of Allium sativum (Lily family) with pungent odor when crushed. This is due to diallyl thiosulphinate, ammonia and pyruvic acid liberated from an odorless precursor, alliin (allyl-cysteine sulphoxide) by the enzyme alliinase.
  • Although broccoli, cauliflower and artichokes are generally listed as the edible flowers, naturalists are exploring edible decorative flowers. Flowers are generally high in water and low in carbohydrates.
  • Artichokes: there are two kinds of vegetables known by this name -- the Green or Globe artichoke (Cynara Scolymus), the flower of which resembles that of a thistle, and provides the edible part; and the Jerusalem artichoke, which is a species of sunflower, with edible, tuberous roots (Cynara Scolymus), the flower of which resembles that of a thistle.
  • Broccoli: is a plant of the cabbage family related to the cauliflower, bearing heads of green or purplish flower buds. The flower stalk and head are eaten as a vegetable.
  • Cauliflower: is a plant of the cabbage family that bears a large immature flower head of small creamy-white flower buds.
    -the flower head of this plant eaten as a vegetable.
  • Roots are generally higher in carbohydrates and lower in water content than stem, flower or leafy vegetables. Roots are the part of a plant which grows downward into the soil and furnishes nourishment by absorbing nutrients.

  • Carrot: The Carrot (Daucus Carota) is a native of the warmer parts of Europe and western Asia, but was used as a food crop in such places as China, Japan, and India as early as the thirteenth century.

  • In discussing the parts of the plant, both the tissue structure and components which make up this structure are important to the understanding. One of the major structural components of fruits and vegetables is cellulose. Scanning electron micrograph allows us to view the extracted cellulose in crystalline form. It is a polymer of glucose and is the major structural component. Cellulose is not the only structural material; however, the fundamental type of cells are parenchyma or ground cells. There are several different categories of tissues. All cells have a cell wall . The cell wall consists of very thin primary cell wall and a hydroxyproline-containing membrane. This cell wall contains much of the cellulose. Additionally, there are other polymers, such as the pectic substances, lignin, and sometimes even leucoanthocyanins (pigments).

    The understanding of the structure of a particular plant cell is not only important for texture elucidation. It will also assist with a greater awareness of color and of flavor.
    cell wall
    chloroplasts
    chromoplasts
    cytoplasm This is the living part of the cell. Generally, it is at least immediately inside the cell wall. The plastids, nucleus, and mitochondria are located within this cytoplasm.
    leucoplasts/amyloplasts
    pectic substances
    plasmamembrane
    middle lamella
    nucleus
    vacuole

    As can be seen in the transmission electron micrograph below, within the cell wall there is the cytoplasm which is simply a jelly-like colloid of living matter. In this cytoplasm are plastids, mitochondria, and a nucleus. Plastids consist of chloroplasts, chromoplasts, and leucoplasts. Also, in the cell are the mitochondria and nucleus, which are the predominant metabolic organizing units of the cell. The cell also contains a vacuole which is, essentially, the garbage can of the cell for waste substances containing compounds such as sugars, acids, and soluble pigments and tannins. In addition to parenchyma cells, there are dermal tissues (shown in the cabbage leaf) and vascular tissues. Parenchyma tissue occurs in abundance in the potato.

    Cell
    Plant cell structure depends upon the role and function of the cell. Regardless of the cell's function, there are a number of commonalities between different cells. The cell wall consists of a primary wall and a secondary wall. The primary walls of two cells are joined together by a common layer called the middle lamella. The cell wall and middle lamella's chief components are cellulose, hemicellulose and pectic substances. The pectic substances in the middle lamella are hydrolyzed from an insoluble macromolecule to smaller pectic substances during the maturation and ripening process.

    Pectic substances, large macromolecules primarily of (1->4)-alpha-D-galacturonic acid, are the glue or cementing substances of plant cells. The polymers are located in the cell wall or middle lamella. These polygalacturonic macromolecules are found both between the cells and within the cellulose, hemicellulose, and lignin matrix of the cell wall. During maturation of the plant the largest of the polymers, protopectin, is hydrolyzed by pectinases to smaller polymers. An example of such a change, determined through texture changes, is observed during the ripening of an apple. The unripe apple, which is generally firm and hard, has the pectic cementing substance, protopectin dominate. As the apple ripens, pectinases hydrolyze the protopectin to pectinic substances dominating in a ripe apple and pectic acids dominating in an over ripe apple.

    A vacuole is contained within plant cells. Its size is somewhat dependent upon the cells function. The vacuole is composed of water with soluble substances dissolved within it. These may include sugars, acids, volatile esters, aldehydes, ketones, and water soluble pigments depending upon the particular fruit or vegetable.

    Energy conversion in the cell is carried out by the chloroplasts and mitochondria. The leucoplasts store starch which is used for energy. The mitochondria are small spheres, rods, or filaments that produce energy for the cell through cellular respiration. They contain fats, proteins and enzymes.

    The nucleus of the cell is imbedded within the cytoplasm. This is the nerve center of the cell. It controls reproduction and protein synthesis. Both the nucleus and mitochronria are needed for the continued life of the cell.

    The cell can be diagrammed as follows:


    When we look at plant life in the moderate Oregon climate, we see many different natural plant colorants. This can be seen in the mountains and forests as well as in the grocery display case. The type of pigment is going to influence the plant colorant. Plant colors are not entirely dependent upon the plant pigment alone. Many factors influence pigment color. In addition to pigment interaction and the presence of acids, bases, and salts, the ripeness of the food is an important contributing factor.

    The color of fruits and vegetables are either fat-soluble and water-soluble pigments. However, many of the other constituents in the plant impact the resulting color of the pigments.

    Fat-Soluble Pigments Water-Soluble Pigments
  • Chlorophyll: Green coloring matter of all plant materials, by the aid of which plants manufacture foodstuffs from simple salts and carbon dioxide with energy derived from sunlight, i.e. photosynthesis.
  • Flavonoids - anthocyanins: Intensely colored, water-soluble pigments responsible for nearly all the reds and blues of flowers and other plant parts. Such color, which is dissolved in plant sap, is markedly affected by the acidity and alkalinity of substances: red at low pH and blue at higher pH values. Violet, red and blue water-soluble coloring matter of many fruits, flowers and leaves. Consist of glucose plus anthocyanidins (these consist of two 6-membered carbon rings containing one oxygen atom).
  • Carotenoids: a group of yellow to red pigments occurring widely in plants and animals and structurally related to carotene. Some are converted into retinol in the body - the carotenes, cryptoxanthin, echinenone, torularhodin and apocarotenal; others are not - canthaxanthin, lycopene, zeaxanthin, bixin.
  • Flavonoids - anthoxanthins: are the white to colorless to cream colored pimgent that is relatively water soluble that is a flavonoid.
  • Flavonoids - phenolics or tannins: any polyphenolic substance with molecular weight greater than 500. Classified as hydrolyzable (to yield sugar residue and phenolcarboxylic acid) and condensed or compound tannins, which are polymeric flavonoids (also called catechin tannins).
  • Leucoanthocyanins: these are not thought by some to be true pigments as leucoanthocyanins themselves do not have color. It is only in the presence of heat and acids that a pinkish color appears.
  • Betalains: violet-red pigment in beetroot, related to anthocyanins. Are nitrogen containing ring structures
  • Another way of thinking about it is as follows:

    PIGMENT GROUPSOLUBILITY
    chlorophylls lipid and water
    carotenoids lipid
    anthocyanins water
    anthoxanthins water
    leucoanthocyanins water
    phenolics water
    betalains water

    The chlorophylls and carotenoids are lipid soluble pigments and usually considered as two entirely separate categories. A really broad category of water-soluble pigments are the flavonoids. Flavonoids consist of anthocyanins, anthoxanthins, and then the large class of phenolic compounds sometimes called tannins. These water-soluble pigments are not localized in the plastids, but rather are diffused in the vacuole of the cell.

    In addition to structure of the pigment, there are other factors influencing plant color. Ripeness and color may impact it. However, it is not enough to think of pigments as being either chlorophyll or carotenoids or some other pigment class. These relative complex chemical structures may have a variety of derivatives as shown in the table below.

    Summary Of Characteristics of Natural Pigments

    Pigment GroupNumber of
    Compounds*
    Chlorophylls 25
    Carotenoids 300
    Anthoxanthins 120
    Anthocyanins 120
    Flavonoids 600
    Leucoanthocyanins 20
    Tannins 20
    Betalains 70
    Quinones 200
    Xanthones 20
    *Approximate

    The following table summarizes the affect of heating, acid and alkali on color during the heating of a fruit and/or vegetable. It indicates the stability of each pigment.

    Name of PigmentColorSolubilityEffect of AcidEffect of AlkaliProlonged Heating
    Chlorophylls green slightly changes to olive green(phaeophytin) intensifies green (chlorophyllin) olive green (pheophytin and pyropheophytin)
    Carotenoids yellow and orange; some red or pink slightly less intense color little effect color may be less intense
    Anthocyanins red, purple, and blue very soluble red purple or blue little effect
    Betalains purplish red; some yellow very soluble little effect little effect pale if pigment bleeds from tissue
    Anthoxanthins white or colorless very water soluble White yellow darkens if excessive

    Bennion, p. 303.

    Before the above pigments in the plant are prepared and have these stresses, there are a number of other production affects upon the plant and possible color. The season is one such important determinant. The availability of a variety of quality fresh fruits and vegetables is no longer completely dependent upon the growing season. The current world wide market distribution system has decreased the impact of season availability; however, season still does impact the costs and some select highly perishable produce. Each variety or cultivar not only has the optimum soil and cultivation conditions but does have a genetically prescribed days to maturity,. These days to maturity must coincide with the appropriate temperatures for fruit onset and for fruit ripening and vegetable maturity.

    It is of interest to know the optimum storage temperature for fruits and vegetables. Some fruits store best before ripening at refrigerator temperature others store best at room temperature. Certainly the growing season and days to maturity is important. However, one should be aware that there is a constant horticultural engineering taking place to protect plants against environmental stress. There are a number of plants which have proteins that enable them to tolerate cold weather. There are other plants with proteins to protect them against dehydration and shriveling by filling the space between a plant's cell membrane and its tough cell wall.

    Irrigation and/or the presence of water in food may dramatically affect the quality of a fruit or vegetable. For example, moisture content and respiration of moisture is how a potato plant serves to keep their temperature down. This is critical for those potatoes grown in Eastern Oregon and Washington or Western Idaho. It has been shown that "heat stress" because there is not adequate water available to the potato will cause the developing potato to become deformed and form a type of potato called sugarend potato.

    Sugar-end potato has a high sugar content in the stem end. Often the appearance of the potato itself will indicate this defect. The potato will be misshapen and often tapered toward the stem end. Normally, this would be absorbed and changed into starch; however, with this potato it does not happen.

    Why is this important? If the stem end of the potato has a high sugar content it will French fry unevenly with this stem end being a darker brown. Supposedly the fast food eater will not accept this unevenly fried potato.

    Storage impacts the quality of the food brought to the kitchen for preparation. Storage requirements of crops varies depending upon the vegetable or fruit.

    Q10 and Temperature Range Above Vegetable and Fruit

    Optimum Temperature Range,C Q10 Values
    0-10 2.5-4.0+
    10-20 2.0-2.5
    20-30 1.5-2.0
    30-40 1.0-1.5
    Weichmann, 1987, p. 35

    There are many factors and interactions affecting ripeness as well as maturation influencing ripeness. The effect of ripening on the different fruits and how you adjust either the temperature, time or added gases is of real interest. Each fruit appears to function differently, particularly in reference to color causative factors. Following is a partial listing of changes during ripening of a fruit:

  • development of color
  • chlorophyll breakdown
  • beta-carotene and lycopene accumulation increases in osmiophilic granules in plastids
  • change in "tannins"
  • changes in "soluble" solids
  • changes in "insoluble" solids
  • changes in acidity
  • changes in flavor components
  • changes in texture

  • One aspect of ripening is the production of ethylene (C2H4), which signals and orchestrates the growth stages of fruits and flowers for senescence. The plant actually senses with protein kinase this compound. This in turn activates fruit ripening.


    Flavors and aromas in fruits and vegetables are due to a variety of compounds working together to give unique and distinctive characteristics. Although each fruit or vegetable tasted is unique, many of the compounds likely come from the aldehydes, alcohols, ketones, organic acids, esters, sulfur compounds, and a trace amounts of other chemical structures.

    Astringency in fruits and vegetables is primarily due to the flavonoid pigments classified as tannins or phenolics. These flavor components will make the mouth pucker.
    Fruity flavor is extremely complex and can not be attributed to one specific compound. The fruity flavor can be generally attributable to a combination of esters, alcohols, aldehydes, ketones, and minor compounds. Some specific compounds attributable to fruity flavor in specific fruits is seen in the table below.
    Acid flavor from fruits and vegetables is formed by many different acids. Although malic and citric acid are the most common acids, a number of others can be found in selected plant foods. For example, grapes has considerable tartaric acid and oxalic acid (rhubarb) and benzoic acid (plums, cranberries) is found in a number of fruits. These acids, in turn give a range of pH values.
    The cabbage and onion family give flavors and odors due to a variety of sulfur compounds. In addition to contributing to flavor, one of the sulfur-containing compounds in the cabbage family, sulforaphane, is thought to protect against cancer.

    The cabbage family includes broccoli, Brussels sprouts, cabbage, cauliflower, kale, kohlrabi, mustard, rutabaga, and turnips is sometimes known as the Cruciferae family. Although relatively mild when raw, cooking will develop strong flavors due to hydrogen sulfide and other volatile sulfur compounds. A portion of this strong flavor development during cooking is due to the breakdown of S-methyl-L-cysteine sulfoxide into dimethyl disulfide. Unfortunately, the natural plant acids may accelerate this process. For this reason, the recommended cooking method is to cook similarly to green vegetables.

    Cabbage may develop a strong flavor if shredded or cut. Sinigrin, a sulfur compound present in cabbage, is broken down by myrosinase to produce a mustard oil called allyl isothiocyanate, a sharp, pungent flavor. The process of sinigrin breakdown can be followed in the preparation of cole slaw. As cole slaw stands, it develops an increasingly distinct flavor.

    Onion, garlic and leek (Allium edible species) has its typical flavor primarily due to the degradation of alliin or a derivative by the enzyme, allinase to allicin (or a derivative) and pyruvic acid and ammonia. The cutting across the cytoplasm of the cell will release the enzyme and bring about the reaction. This is noted when one cuts or dices raw onions. During cooking, the onion flavor mildness is maintained by cooking in a large amount of water.

    Sweetness of fruits and vegetables has been the one taste perception that is constantly searched for. Some plants, such as sugar cane and sugar beet are grown for their sweet component, sucrose. Other foods are consumed for a combination of sugars and other flavor component interactions. Glucose, fructose, maltose, xylose, and less common sugars are also found. The types of sugars in plants vary considerable. There are also "non-sugar" types of plant source of sweetness as well. Glycyrrhizing from licorice is one widely used sweetener.


      Texture of plant foods has been difficult to describe in precise terms. For example compare crisp versus wilted lettuce, a crisp tender versus a crisp tough carrot, a plump watery Vs plump standard Vs plump pithy strawberry. All of these comparisons emphasize the dichotomy of texture. The crux is texture of fruits and vegetables is dominantly caused by either the structural components themselves or by the process of osmosis and diffusion.

      Toughness or tenderness of a fruit and vegetable is complex. In the butt end of the asparagus shown above, these are likely tough as they have been in picked for over a week. They are tough as the lignin content has increased. If one is discussing the toughness/firm or tenderness/mealy of an apple, it becomes really complex. The actual "crispness" is also a mitigating factor. In the case of the firm versus tender or mealy apple it likely is the pectic substances in the middle lamella which are most critical.

      The toughness is due primary to the cell wall components, pectins, hemicelluloses and cellulose which change during maturation, storage and processing. There are many factors impacting the toughness including tissue conditions, pH, enzymes, and salt concentrations. Certainly the texture-affecting reactions of pectic materials such as glycosidic hydrolysis, beta-elimination type depolymerization, demethoxylation, and complex formation occurs.

      Crispness/Wiltness

      The crispness of a vegetable is due to the movement of water in the plant. There are a number of factors which impact this. It is critical for the texture.

      CELL TURGIDITY FACTORS

    • concentration of osmotically active substances
    • permeability of the protoplasm
    • elasticity and toughness

    • WATER MOVEMENT

    • capillary action
    • diffusion
    • transpiration
    • osmosis

    • Crispness of fruits and vegetables, particularly leafy green and stem vegetables and fruit, such as apples, is partially due to osmosis and diffusion. In preparing fruits and vegetables, they can be made more crisp by increasing the cell turgidity. This is done by creating an osmotic gradient at the semipermeable membrane within the cell wall.

      Leafy green vegetables, such as lettuce, may be made more crisp by placing them in a bowl of cold water. The solute inside of the vacuole is of a greater concentration than that on the exterior of the leaf. Since there is a natural tendency to equalize concentrations on either side of the semi-permeable membrane, the smaller water molecule rapidly moves into the cell, building up the turgor pressure and enhancing crispness. If a salt or sugar solution is exterior to the cell, water likely will be drawn from the cell and the leafy vegetable will appear wilted.

      The affect of water and sugar solutions becomes more complicated in working with apples and other fruits. Generally, apples become more crisp when raw if placed in water. However, if apples are cooked, the water seems to enhance a mushy texture. This could be partially due to the breakdown of the cell wall structure and components. If an apple is cooked in a medium to heavy sugar solution, before the semipermeable membrane is denatured, water is rapidly pulled from the vacuole and sugar slowly replaces the water. The apple pieces cooked in the syrup will generally hold its shape, be firmer and somewhat translucent.



      Value-addition or increasing the value of the product with processing of fruits and vegetables will change quality expectations. A recent innovation has been value-addition by peeling, cutting, chopping or mixing the fresh produce and then packaging, utilizing advances in packaging technologies. The oldest and/or traditional methods of processing are fermentation, dehydration, heating, and freezing. All these function to minimize quality deterioration due to enzyme action or microbial growth.

      These traditional methods have been modified and combined to maximize quality of the fruits and vegetables. For example, strawberries can be frozen, placed in a vacuum which permits the water to sublimate, and becomes freeze-dried, retaining the original shape and the "fresh" flavor.

      Ionizing radiation is the "new" totally new method of food preservation. Although original work done with the radiation was towards sterilization, the detriment to quality decreased that likelihood of an optimized processing method. Now, ionizing radiation is being used to pasteurize fruits and vegetables. That is, quality is maintained due to the decreased mold and enzyme activity. It is primarily used with potato and other tubers to minimize sprouting. Quality maintenance and increased shelf life with ionizing radiation of strawberries is currently allowed by the FDA.

      Dehydration of plums to prunes is an old method of preparation. It has been up-dated to make intermediate moisture prunes.
      This picture shows freeze-dried slices, fresh, and dehydrated strawberry slices. The freeze-dried slices not only had a brighter color but it had a "fresh" flavor. Freeze-drying was simply done by freezing the strawberry slice, placing it in a vacuum chamber and applying heat of approximately 30C under vacuum. The ice in the strawberry sublimated and left the cell structure intact. The dehydrated slices was placed in a dehydrator in the raw form, a temperature with a fan for area currents of approximately 24F was applied. The fresh strawberries certain was the "fresher" product.



      GLOSSARY

      • aromatic compounds: is a substance with a spicy scent and pungent, pleasing taste.
      • carotenes: C40H56 is a colorant and provitamin, being a hydrocarbon which is a sub group of the carotenoids (yellow, orange, or red pigments) while the other subgroup is xanthophylls. It functions as a colorant with B-Apo 8-carotenal being a red-orange carotenoid and B-carotene being a yellow carotenoid. It is also a viatmin A precursor which is converted by the body to vitamin A.
      • carotenoid pigments: A group of yellow to red pigments occurring widely in plants and animals and structurally related to carotene. Some are converted into retinol in the body - the carotenes, cryptoxanthin, echinenone, torularhodin and apocarotenal; others are not - canthaxanthin, lycopene, zeaxanthin, bixin.
      • catalase: enzyme in plants and animals which splits hydrogen peroxide into water and gaseous oxygen. It is a conjugated protein containing haem (identical with the haem of hemoglobin) as its prosthetic group.
      • controlled atmosphere storage: the monitoring and control of content of gases in the storage warehouse atmosphere; a low oxygen content slows down plant respiration and delays senescence (aging)
      • enzymatic oxidative browning: the browning of cut surfaces certain fruits and vegetables catalyzed by enzymes and phenolic compounds in the presence of oxygen.
      • enzymatic reactions: those that are catalyzed by enzymes, which are special proteins produced by living cells; a catalyst changes the rate of a reaction without itself undergoing permanent change.
      • essential oils: he oily liquid obtained from plants through a variety of processes. The essential oil usually has the taste and smell of the original plant. Essential oils are called volatile because most of them are easily vaporized.
      • ethylene: a gas of the formula CH2CH2, of interest in its use to assist the ripening of fruits: e.g. 0.4% accelerates the ripening of pears; 0.05% will convert green lemons to yellow in one week at 30-40C.
      • fiber: common termed "bulk" - the indigestible carbohydrates including cellulose, hemicellulose, and gums. Used in food to reduce calorie content, as a thickening agent, and a stabilizer. No known toxicity.
      • fiber indigestible substances: including cellulose, hemicelluloses, and pectin (all polysaccharides), and also lignin, which is a noncarbohydrate material found particularly in woody parts of a vegetable
      • flavonoids: Flavonoids divided into flavonols-hydroxyl group replaces H in flavone nucleus; flavonones - one double bond reduced in the 2=3 position; flavanals - hydroxyl group in place of the O and reduction of double bond at 4 and reduction of 2-3 double bond; isoflavones - benzenoid ring attached to C3 instead of C2.
      • flavonoid pigments: phenolic compounds related to flavones. They have hydroxyl, methoxyl, or sugar groups substituted for some of the hydrogen atoms of the flavone; a group of plant pigments with similar chemical structures; they include both anthoxanthins which are white, and anthocyanins, which are red-blue
      • isomerization: a molecular change resulting in a molecule containing the same elements in the same proportions but having a slightly different structure and, hence, different properties; in carotenoids, heat causes a change in the position of the double bonds between carbon atoms
      • isozyme: multiple forms of the same enzyme arising from genetically determined differences in primary amino acid sequences.
      • legume: Members of the Leguminosae family eaten by man and domestic animals. Consumed as dry mature seeds (grain legumes or pulses) or as immature green seeds in pod.
      • lipooxygenase: an enzyme that catalyzes the oxidation of unsaturated fatty acids
      • metabolic: is having to do with any of the chemical changes that occur in living cells.
      • methyl ester of galacturonic acid : the chemical combination of methyl alcohol with an organic acid, such as galacturnoic acid
      • microcrystalline cellulose : is a gum which is the nonfibrous form of cellulose, being an alpha cellulose. It is dispersible in water but not soluble, requiring considerable energy to disperse and hydrate. In this form it is used in dry applications such as tableting, capsules, and shredded cheese where it functions as a nonnutritive filler, binder, flow aid, and anti caking agent.
      • mince: s to cut up or grind food, especially meat, into very small pieces, typically in a machine with revolving blades. Something that is minced is mincemeat. It also is used to indicated a quantity of something minced, for example, a mince of garlic.
      • modified-atmosphere packaging: Storage of fruits and vegetable and pre-packed red meat in a controlled atmosphere in which a proportion of the oxygen is replaced by carbon dioxide, sometimes with the addition of other gases. In modified atmosphere storage (MA) the control is less precise.
      • organic acid : an acid containing carbon atoms, for example, citric acid and acetic acid, generally weak acids characterized by a carboxyl (-COOH) group
      • ovary: part of the seed-bearing organ of a flower; an enlarged hollow part containing ovules that develop into seeds.
      • oxalic acid : an organic acid that forms an insoluble salt with calcium.
      • pectic enzymes: enzymes such as pectinase that hydrolyze the large pectin molecules.
      • pectin: s a gum which is water soluble pectinic acid of varying methyl ester content and degree of neutralization. It is obtained from citrus peel and apple pomace. It forms a gel in systems of low pH (pH 2.8-3.7) and high sugar (55-80%) levels. The gel sets at 55-99C and melts above 70C. Pectins are characterized by rapid and slow set types. the high methoxyl pectins have a degree of methylation (DM) greater than 50% while those of less than 50% degree of methylation are termed low methoxyl pectins. The low methoxyl pectins gel in the presence of calcium ions and do not require a certain level of acid or sugar.
      • pectin esterase : an enzyme that catalyzes the hydrolysis of a methyl ester group from the large pectin molecule, producing pectic acid; pectic acid tends to form insoluble salts with such ions as calcium (ca2+);these insoluble salts cause the cloud in orange juice to become destablized and settle
      • pectinase: an enzyme that hydrolyzes the linkages that hold the small building blocks of galacturonic acid together in the pectic substances, producing smaller molecules
      • peel: is the very thin removal of the skin of fruits and vegetables.
      • pH: A measure of acidity or alkalinity. Values range from 0 to l4. A food is neutral when its pH is 7.0: lower values are increasingly more acid; higher values are increasingly more alkaline.
      • phenolic compounds: an organic compound that includes in its chemical structure an unsaturated ring with -oh groups on it; polyphenols have more than one -oh group; organic compounds that include in their chemical structure an unsaturated ring with -oh groups on it; these compounds are easily oxidized, producing a brownish discoloration
      • plant exudates : materials that ooze out of certain plants; some that ooze from certain tree trunks and branches are gums
      • polymer: a giant molecule formed from smaller molecules that are chemically linked together.
      • polysaccharides: complex carbohydrates formed by the condensation of large numbers of monosaccharide units, e.g. starch, glycogen, cellulose, dextrin's, inulin. On hydrolysis the simple sugar is liberated.
      • precursor: a substance that "comes before"; precursor of vitamin a is a substance out of which the body cells can make vitamin a; something that comes before; in flavor study, it is compound that is nonflavorful but can be changed, usually by heat or enzymes, into a flavorful substance; is a forerunner or predecessor such as a molecule that later develops into a flavor molecule.
      • respiration: is the release of energy, carbon dioxide and water as oxygen is consumed; the opposite of photosynthesis.
      • salt: usually refers to sodium chloride, i.e. common salt or table salt (although any compound of acid and alkali is a salt).
      • senescence: the state of growing old or aging.
        This is important in fruit as senescence means the fruit is becoming "overripe".
      • succulent: having juicy tissues; not dry
      • tannins: are phenolic compounds which have several hydrolyzable groups. They are classified as (a) hydrolyzable, yielding phenols such as gallic acid in the presence of acid and heat; (b) condensed, being obtained from the extract of oak trees and not hydrolyzable.
      • tuber: a short, thickened, fleshy part of an underground stem, such as a potato; new plants develop from the buds or eyes. An enlarged underground stem, for example, the potato
      • vacuum packed:
      • vegetable fruit: botanically, a fruit is the ovary and surrounding tissues, including the seeds, of a plant; a vegetable - fruit is the fruit part of a plant that is not sweet and is usually served with the main course of a meal.
      • vegetable gums: polysaccharide substances that are derived from plants, including seaweed and various shrubs or trees, have the ability to hold water, and often acid as thickeners, stabilizers, or gelling agents in various food products; for example, algin, carrageenan, and gum arabic.
      • vegetable peeler: a kitchen utensil designed to peel away the outer skin of vegetables. Vegetable peelers come in many designs and are made from a variety of materials.



      Updated: Wednesday, May 23, 2012.