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.

Another way of thinking about it is as follows:

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 Group	Number 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 Pigment	Color	Solubility	Effect of Acid	Effect of Alkali	Prolonged 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.

Q10 and Temperature Range Above Vegetable and Fruit

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.