+ Fruits Dr.Fatimah Yousef

Fruit Classifications Fruits are classified according to the type of flower from which they develop into: Simple fruits: Develop from one flower and include drupes, pomes and citrus fruits (oranges, lemon, …..). Aggregate fruits: Develop from several ovaries in one flower, ex., blackberries, strawberries. Multiple fruits: Develop from a cluster of several flowers, ex. Pineapples and figs. Dr.Fatimah Yousef

Fruit Classifications Fruits are divided into groups according to their physical characteristics: Berries Drupes Pomes Citrus fruits Melons Tropical fruits Dr.Fatimah Yousef

Berries Small juicy fruits with a thin skin and fragile cell structure. Ex. include: blackberries, blueberries, raspberries, strawberries, cranberries and grapes. Look for bright texture when purchasing Highly perishable. Dr.Fatimah Yousef

Drupes Outer skin covering a soft, fleshy fruit. Examples include: Apricots, peaches, and plums The fruit surrounds a single hard stone, or pit, which contains the seed Dr.Fatimah Yousef

Pomes Smooth skin with a central seed containing core. Thick layer of flesh. Examples include: Apples and pears Dr.Fatimah Yousef

Citrus fruits Thick rinds and thin membranes separating the flesh into segments Examples include: oranges, limes, lemons, grapefruit Grown in warmer regions Dr.Fatimah Yousef

Melons A part of the gourd family, large and juicy with thick rinds and many seeds. Examples include: cantaloupe and watermelon. Dr.Fatimah Yousef

Tropical fruits Grown in warm climates Considered to be somewhat exotic Different in warm skin composition and seed characteristic Examples include, pineapples and pomegranates. Dr.Fatimah Yousef

+ Nutritional Value Great source of vitamins, minerals and fiber. Pro-vitamin A: found in fruits that are yellow and red. Ex: cantaloupe, apricots and pineapples. Vitamin C: Examples: citrus fruits. Calcium (mineral): Examples oranges, strawberries, cantaloupes and dried fruits Low in fat. Dr.Fatimah Yousef

+ Composition of fruits: The cellular structure and pigments of fruits are similar to those of vegetables. Organic acids, pectic substances and phenolic compounds are more relevance to fruits than vegetables. Organic acids: They are either volatile (vaporize during heating) or nonvolatile (non vaporize during heating, but they are leach cut when fruit is cooked in water). Dr.Fatimah Yousef

+ The common organic acids include: citric acid (citrus fruits), malic acid (apples), oxalic acid (rhubarb) and benzoic acid (cranberries). Acidity varies with the maturity of the plant, usually decreasing as the fruit ripens. tartness of fruits is related in part to their acidic content. The lowest pH values are very tart fruits ( lemons, limes….), and the least acidic fruits are more bland and sweet in flavor. Dr.Fatimah Yousef

+ There are three groups: Protopectin, Pectin (pectinic acids), Pectic acid. Pectin is a general term describing the group of polysaccharids found in fruits acts as a cementing substance between cell walls and is partially responsible for the plant’s firmness and structure. Protopectin: is a larg insoluble molecule found in immature fruit As the fruit ripens, enzymes convert protopectin to the more water-soluble pectin. Pectin (pectinic acids): the stage of ripeness affects pectin concentration, and it is the pectin extracted from rip fruits that is used to gel jams and jellies Pectic substances : Dr.Fatimah Yousef

+  Ripening mechanisms related to the pectinase enzymes, which break down the pectic substances as the fruits ripens.  The degree of fruits softening is related to how many pectic substances were degraded, so the stage of ripeness affects pectin concentration.  Neither protopectin nor pectic acid can contribute to gelling (that is used to gel jams and jellies), only fruit at the height of ripeness should be used for making fruit spreads without added pectin. Pectic substances :

+ Pectic acid:  As fruits continues to ripen and becomes overripe,all the pectin gradually turns to pectic acid When juice is extracted from fruits, pectic substances can sometimes cause it to cloud  Heating also converts pectin to pectic acids by hydrolyzing the chemical bonds holding the molecules together, causing the texture of the fruit to become soft and eventually mushy. Pectic substances :

+ Protopectin PectinPectic acid Immature fruitRipe fruitOverripe fruit (no gel) (gels) (no gel) Chemical breakdown of protopectin

+  Responsible for the browning and bruising that often occurs in ripening fruits, ex., (apples, apricots, bananas…..).  These compounds also known as tannins, are found predominantly in unripe fruits, given them a bitter taste and leaving an astringent feeling in the mouth. Phenolic compounds: Dr.Fatimah Yousef

+  Fruits turn brown from enzymatic browning.  These occur due to presence of three substance: plenolic compounds (found within the cells), polyphenolic oxidase enzymes phenolase (enzyme that oxidize phenolic compounds ), and oxygen (which enters the cells when the food is cut or bruised).  The polyphenolic oxidase enzymes turn the color of the phenolic compounds from clear to brown (called melanins, though unappetizing but are safe to consume) Phenolic compounds and enzymatic browning: Dr.Fatimah Yousef

+ Phenolic compounds and enzymatic browning Dr.Fatimah Yousef

+ Selecting and storing fresh fruit Buy fruits that are in season: Cheaper. More available. Better flavor. Purchase fruit that is not bruised or damaged. Buy what you will use in a short period of time. Look for freshness and ripeness signs. Consider the use you plan for the fruit. Dr.Fatimah Yousef

+ Storing fresh fruit Fruit is very delicate, handle gently to prevent bruising. Let under ripe fruits ripen at room temperature. Refrigerate ripe fruits. Berries are highly perishable, use as soon as possible. Dr.Fatimah Yousef

+ Preparation of fruits: Fruits can be eaten fresh, cooked or preserved. Wash all fruits, removes pesticide residue, dirt and germs. Cut or peel away the thick, inedible skins such as oranges, kiwi and pineapples. Be careful with some fruits, once cut they may turn brown while exposed to the air, such as apples or bananas. Called enzymatic browning Dr.Fatimah Yousef

+ Enzymatic Browning: Certain kinds of fruit, when peeled or sliced are susceptible to enzymatic browning. Inhibiting enzyme activity can be accomplished by the following methods: 1-Denaturing the enzymes: Blanching foods by dipping them briefly in boiling water destroys the enzymes through denaturation. Fruits are not generally blanched, because heating already ripe fruits makes them lose texture and flavor. Dr.Fatimah Yousef

+ Enzymatic Browning: 2-Acid pH: Polyphenol oxidase enzyme activity is inhibited in the presence of acid. High acidic content of some fruits such lemons and limes prevents enzymatic browning. Less acidic fruits such as apples, peaches and bananas can be protected from enzymatic browning by coating them with lemon or orange juices. Dr.Fatimah Yousef

+ Enzymatic Browning: 3-Cold temperatures : It reduces the rate of enzyme activity and thereby slow, but never completely inhibit enzymatic browning. Dr.Fatimah Yousef Coating fruits with sugar or water: By covering cut fruits with a light layer of sugar or syrup. Submerging fruits in water also blocks oxygen from contacting their surface.

+ Enzymatic Browning: 5- Antioxidants: such as ascorbic acid (vitamin C) and sulfur compounds prevent enzymatic browning by using up available oxygen. Dr.Fatimah Yousef

+ Cooking Fruits Fruits cooked in sugar will maintain their shape. Sugar strengthens the cellulose structure. Main goals of fruit cookery: Preservation of nutrients. Change texture, form or consistency. Prolong storage time. Dr.Fatimah Yousef

+ Changes during heating: Dr.Fatimah Yousef I-Color: The pigments coloring fruits are the same as vegetables. II-Texture: Fruits is often served raw because the texture is usually more desirable than that of cooked fruits. During heating several changes occur that contribute to this softens: The conversion of the fruit's protopectin to pectin.

+ Changes during heating: Dr.Fatimah Yousef The degradation of cellulose and hemicellulose. The denaturation of the cell membrane proteins. Osmosis: During heating, the fruit's osmotic system of selective permeability is replaced with simple diffusion, contributing to the loss of shape in heated fruits. Normally, the cell walls of raw fruits have semi- permeable membranes, which allow water, but not solutes such as sugars to pass through the membrane. The water moves from a low solute concentration to a higher one, until the solution concentration is equal on both sides of the membrane.

+ Dr.Fatimah Yousef Sprinkling sugar on fruits produces the opposite effect, causing fruits to become syrupy as water passes out from the cells to surface where the solute concentration is higher (due to sugar). If sugar is left on fruits too long producing a soft, mushy texture. Heating destroys the membrane's ability to prevent the loss through the cell wall. Solutes can then freely pass across the membrane until solute concentrations are equal on both sides.

+ Dr.Fatimah Yousef Sugar may be added to fruits before it is cooked in water to replace the loss sweetness. This also helps the fruits to retain its shape and firmness. If fruits are heated in a syrupy solution greater than 15 % sugar, the sugar enters the cells as the water leaves. Sugar further inhibits loss of texture by interfering with the conversion of protopectin to pectin.

+ Dr.Fatimah Yousef III- Flavor : Flavors are derived from the chemical compounds such as sugars, acids, phenolic acid and aromatic compound and essential oils. The flavor substances and volatile compounds that contribute to aroma can be lost during preparatoin, which explain why fruits are either served raw or heated only for the minimum amount of time.