Chapter 7: Vegetables and Fruit
Fiber
-Fiber is the combination of materials in foods that cannot be digested readily -Plant foods are valued in the diet as outstanding sources of fiber
Many maturity indices are used for fruit, including:
-Measuring size, weight or density (mature fruit is larger) -Color -Solids content -Brix-to-acid ratio for citrus fruits, whereas both soluble solids and acidity are used to assess maturity in grapes -Flavor (mature fruit is sweeter)
Factors that Influence Respiration: Stress
-Mechanical stimulation -Wounding: stimulates the respiration
How many servings of fruits and veggies are recommended in the Fruits and Veggies - More Matters campaign?
-Minimum of at least 5 servings of vegetables & fruits -3 vegetables & 2 fruits
Non-climacteric fruits
-No characteristic respiratory rise and ethylene production -Best when ripened before harvesting
Factors that Influence Respiration: O2
-Respiration rate decreases with decreasing oxygen -Fermentation under anaerobic conditions
What happens to spinach and other greens during heat treatment/steaming?
-Spinach and other greens are softened visibly during steaming or other heat treatment -The cell walls become increasingly permeable, causing water loss, and loss of turgor in the cells
Bananas, persimmons ripe: sweetness is due to what change in flavanone levels? what environment reduces flavanones?
-Sweetness increase due to reduction of flavanones -Warm temperature reduces flavanone
Color changes of climacteric fruit
-Synthesis of pigments during ripening, e.g., lycopene, anthocyanins (red color of apple) -In apple: cold nights required for color development on the tree
Where are pectin esterases used in food manufacturing?
-The action of pectinesterases is valued in making apple and grape juices because the increased solubility of the degraded pectic substances, notably pectic acid, promotes a less cloudy beverage and increases the visual appeal of the juices. -Limitation - cannot use this for jelly
Enzymes also can cause detrimental changes in anthocyanin pigments: (4 of them)
-anthocyanase -peroxidases & phenolases -glycosidases
The plant cell wall is mainly composed of two carbohydrates:
-cellulose -hemicellulose
In the plastids, two (three?) types of pigments and starch are formed and stored
-chloroplasts -chromoplasts -leucoplasts
Hemicelluloses
-contain a variety of sugars in their long chains—unlike starch and cellulose -They contain both pentoses and hexoses
What else causes softening? (3 things)
1) Depolymerization 2) Demethylation 3) Loss of calcium
What are the two groups of carotenoids?
1) carotenes 2) xanthophylls
Which anthoxanthins (2) are especially abundant in fruits and veggies?
1) flavones 2) flavonols
Breads & other baked products can be made with bran up to a level of about __% of the flour weight. What are the effects of this?
15% Effects include a decrease in volume; aid to moisture retention during storage
There also is a pigment change when the pH exceeds ____, for the phytyl and methyl groups are eliminated
7
All chlorophyll-related compounds have the same __________ with _______________
All chlorophyll-related compounds have the same basic tetrapyrrole structure, with connecting methyne bridges
What happens to anthoxanthins (and all polyphenolic compounds) when exposed to air for a period of time?
Anthoxanthins—all polyphenolic compounds—may show browning or blackening reactions when bruised, cut, or exposed to air for a period of time
Which enzyme is responsible for the browning or blackening rxns?
Attributed to the action polyphenoloxidases enzymes
Pungency is related to ______________ families
Capsaicinoid
Image of cauliflower
Figure 7.18 Cauliflower exhibits the subtle color change that anthoxanthins exhibit when cooked in acidic (left) and alkaline medium (right).
What is involved in fruit softening?
Fruit softening involves a coordinated series of modifications to the polysaccharide components of the primary cell wall and middle lamella, resulting in a weakening of the structure Protopectin --> pectin (pectinic acid) --> pectin (soft, mushy texture) All products soften after harvest, but climacteric fruit in particular
Postharvest changes in veggies like legumes, potatoes, and carrots
In vegetables like legumes, potatoes & carrots, starch synthesis may continue if the storage temperature is approximately normal room temperature or slightly warmer
How do you restore turgor?
Restore by storing it in high humidity
Rutabagas- pigment changes
Rutabagas naturally contain poly-cis-lycopene as a dominant pigment; however, some of the cis compound is shifted to form some all trans-lycopene, with the result that the orange pigment is intensified in the cooked vegetable
___________, a flavone in asparagus, reacts with iron to form a ferric-rutin complex that produces an unattractive dark color.
Rutinol These compounds oxidize easily—potentially important as antioxidants in processed foods
What happens if salt is in the soaking water for beans?
Salt in the soaking water makes the outer surface of beans more resistant to water penetration - delays the softening process.
Figure 7.5 ______________ contribute to the somewhat granular texture noted in pears.
Sclereids (unique sclerenchyma cells)
_______________ cells are woody cells that contribute a somewhat gritty texture to some plant foods
Sclerenchyma
Preparation of Legumes: Mustard Oil
Sinigrin may interact with an enzyme, myrosinase, released from the cut or bruised cell and produce potent mustard oil.
Why is soaking discouraged?
Soaking discouraged - loss of water-soluble nutrients, pigments
Soluble fibers
Soluble fibers appear to be digested to a limited extent to provide calories to the body May reduce serum cholesterol levels
What medium affects hemicelluloses?
Strongly affected by an alkaline medium—vegetables cooked with soda added become flaccid & mushy
What are anthoxanthins responsible for?
They are responsible not only for color of some vegetables—but also for some flavor overtones—such as cauliflower
Plant Exudates
Sugars & hexuronic acids in plant exudate gums: -Gum arabic—galactose, arabinose, rhamnose, galacturonic acid, and the methyl ester of galacturonic acid -Tragacanth—xylose, arabinose, galactose, fucose, rhamnose, and galacturonic acid
Gums: Seaweed Extracts (3 examples and what they're used for and what they're made of)
Agar forms strong and transparent gels, which are reversible when heated and then re-form when chilled. -β-D- and α-L-galactose; Carrageenan occurs in fractions; some form gels, some do not. Algin is used to form both gels and films. -mannose and guluronic acid are its principal components and with numerous salts
Betacyanins and pH
Betacyanins are sensitive to pH and undergo color changes parallel to those noted for anthocyanins
Chlorophyll a
Blue-green, more abundant form of chlorophyll, broccoli
Sometimes _____ is added to retard deterioration of some fruits and vegetables during storage
CO2
Cooking red cabbage
Caution - red cabbage (4 hydroxyl groups) red cabbage frequently is cooked with the addition of slices of a tart apple to ensure that the pH is acidic. Not so much with strawberries (3 OH group)
Parenchymal cells are polyhedral. What does that mean?
The exact number of faces and the tightness between the cells are specific to a species
What is left after the action of chlorophyllase? How is its solubility affected?
The remainder of the chlorophyll molecule, now termed chlorophyllide, becomes water soluble.
What are the substrates for oxidation in browning/blackening rxns?
Tyrosine, chlorogenic acid, and the various catechins among the many compounds that can serve as substrates for oxidation
Fat content in veggies
Unprocessed vegetables contain little to no fat; the only vegetable foods high in fat are vegetable oils
Array of acids vs. content in veggies vs. fruits
Vegetables contain a greater array of acids than fruits—but the content is not as great
The vascular system (phloem & xylem) in enlarged granules appear in an orderly arrangement of __________
concentric rings Figure 7.2 Cross section of beet. Note the vascular system (phloem and xylem) in enlarged granules appearing in an orderly arrangement in concentric rings.
What is another gum produced by microorganism fermentation?
curdlan
Breakdown of chlorophyll: _____________________
degreening
The sugar in freshly harvested peas also is rapidly ___________ as a result of the rapid respiration rate typical of the various legumes.
depleted
Flavanones & flavanols do not have what?
do not have the middle-ring double bond of quercetin & related compounds
Postharvest, Most bulbs, roots, tubers & seeds become ___________
dormant
Maturation
end of cell division, increase in sweetness, flavor, and color
Cell wall components undergo changes after harvest due to action of various _________
enzymes
Hemicelluloses, matted with pectic substances, serve as a connection between ______________
fibrillar cellulose
Astringency is due to what
flavanones
An alkaline medium ____________ softening
greatly accelerates
Starch synthesis for some vegetables occurs continuously when stored at room temperature, such as ____________
green beans. For these vegetables, in which some sweetness is desired, refrigerator storage is recommended
Microbial Extracts are used to produce ______
gums
Gums of commercial significance
gums from guar & locust bean (carob), both classified as legumes
Locust bean gum requires _____ for maximum hydration
heat
What becomes softer as veggies are heated?
hemicelluloses
As fruits & vegetables mature, they __________ their content of cellulose, hemicelluloses, and lignin
increase
Emphasis on fiber has led the food industry to develop products with _____________ fiber content
increased
Pectin methyl esterase _____________ in tomato, banana during ripening
increases
Chilling __________ are detrimental to the quality of produce
injuries
Both sclereids and the other type of sclerenchyma cells (often simply called fibers) have thick cell walls containing ________, a wood-like compound.
lignin
Other common anthocyanidins
malvidin, peonidin, and petunidin
Composition of guar gum
mannose units linked together by a 1,4-β linkage, with the galactose being linked by a 1,6-α linkage at regular intervals
Reactions also can occur if canned vegetables interact with __________ in the cans.
metal
How are these enzymes inactivated?
mild heat treatment
What is transpiration?
moisture loss
Texture at alkaline pH
mushy
Federal regulations do not permit identification of coloring agents from plants as ___________.
natural Instead, these agents are designated as exempt, accompanied by a statement "color added with ______" or "______ color." This terminology for colors from plant sources is in contrast to the chemical coloring agents that are identified as certified.
Synthesis of ___________________ halts after harvest
organic compounds Numerous physiological changes continue in storage
What is respiration?
oxidative breakdown of organic biomolecules
The principal type of cell in fruits and vegetables is the _________ cell
parenchyma The most abundant type of cell in the ground system
The rate of respiration is directly related to the ________________ of fruits and vegetables
perishable character
Chlorophyll can lose its magnesium and its phytyl group—for a new compound called _______________
pheophorbide
Between the cell wall and the interior of the cell wall is a thin membrane, the ____________
plasmalemma
Peaches results in a lower content of _______________ than is developed when cooler, cloudy weather occurs
polyphenols
Lower acid content of vegetables explains the requirement for _______________ of vegetables
pressure canning
The ____________ is found immediately within the plasmalemma
protoplasm
What is the warming, hot sensation called from "spicy foods"
pungency
When a sugar isn't complexed, the pigment becomes less _______ than it is as an anthocyanin.
red
Respiration rate of highly perishable fresh produce can be retarded appreciably by ________________
refrigeration
How should lettuce be rehydrated?
rehydrate lettuce, not be soaked, but rather placed in only 2 inches or so of warm water. Sprays or dips
Vascular system
responsible for the transport of fluids, nutrients, and waste products.
Fleshy tissues of fruits & vegetables usually ripen after maturation—then continue to _______________
senescence [the condition or process of deterioration with age]
The action of chlorophyllase prior to cooking some fresh green vegetables is responsible for the ______________appearance of the cooking water, as some chlorophyllide is dissolved in the cooking medium
slightly green
Acid ________ these softening changes during cooking
slows
Dried beans have a hard outer covering that needs ______________________ prior to simmering
soaking in unsalted water
Where are protease inhibitors found?
soybeans
Glycosidases
split the sugar from anthocyanin to form anthocyanidin
Leucoplasts produce & store _______________________
starch granules
Many vegetables are considered more palatable when they retain a reasonable _______ level rather than synthesizing starch
sugar
Anthocyanidins are anthocyanins not complexed to a _____________
sugar, such as glucose
Anthocyanidins
the sugar-free counterparts of anthocyanins
Soda also has a destructive effect on ______________
thiamine
The ___________ is the thin membrane that separates the protoplasm from the interior of the cell
tonoplast
Most carotenoids are in the ____________ configuration at the double bonds, as can be seen in the structure of β -carotene.
trans
Harvested vegetable falls apart due to loss of water --> loss of ________
turgor
Variations in green vegetables are from what?
two basic forms of chlorophyll -Varying ratios in which these are found -Combination of chlorophyll with other pigments
Lakes
used with fats and oils because they are insoluble in water
The _________ contains flavor components
vacuole
Carotenoids
very colorful, important compounds in fruits and vegetables
Carotenes (potential _______________ activity)
vitamin A
Dyes
water-soluble chemical coloring agents available as powders, granules, liquid, or other forms
The most prominent of the carotenes is ________________
β-carotene
Anthoxanthin compounds are ___________ or ______________, depending on pH of the medium
colorless or white to yellow
Anthoxanthins
colorless or white—but may change to yellow
The primary cell wall is composed of ____________ carbohydrates
complex Cellulose, hemicelluloses, and pectic substances
What is the breakdown of chlorophyll initiated by?
chlorophyllase
Guar gum hydrates in _____ water
cold
Allin is in what?
garlic
A problem of flavones and flavonols is their propensity to complex with _____________
metal ions
Lignin gives a _________ quality to plant foods
woody
Betaxanthins contribute a somewhat ___________ pigment
yellow
Synthetic Gums: what are they made of? what is the most prominent one?
-Cellulose serves as the starting material for the production of some synthetic gums. -Carboxymethyl cellulose (CMC) (also called cellulose gum) is the most prominent of these. -The structure is cellulose that has undergone a chemical reaction to add a carboxymethyl group.
Inulin: what is it? where is it processed in the body?
-Complex fructooligosaccharide -This soluble fiber is not digested until it reaches the large intestine, where some bacterial digestion occurs.
Concord grape juice
-Concord grape juice with other ingredients. It is pigmented with delphinidin-3-monoglucoside and cyanidin-3-monogluco- side, which contain six and five hydroxyl groups, respectively, in their pigment structures. -This abundance of hydroxyl groups causes the extreme color changes that may occur when Concord grape juice is blended with other ingredients that influence the pH of the mixture.
What is a fruit?
-Defined as the ripened ovary of a plant -Nature's desserts -Available in most every shape & color
What is a vegetable?
-Definition - Any plant whose parts are used for food In practice -The edible part of a plant -Raw or cooked -Accompanying the main course -Impart color & unique flavors & textures to the meal
Various metallic ions can cause undesirable color changes in anthocyanins
-Enamel can linings prevent metallic interactions during storage of anthocyanin-containing fruits & vegetables -Metal knives other than stainless steel knives.
What are the purposes of respiration?
-Energy production to support maintenance processes -Source of important flavor components (malic and citric acid, starting point for biosynthesis of many volatiles) -Oxidation of compounds such as sugars, starch and organic acids to water and carbon dioxide Glucose is main substrate Glucose + 6 O2 → 6 CO2 + 6 H2O + 2870 kJ -Respiratory quotient (RQ) = [CO2] Produced/[O2] Consumed
Climacteric fruits
-Ethylene hastens [speeds up] ripening -Dramatic increase in ethylene production and respiration
Where are saponins found? What do they cause in the body?
-Found in common beans and cowpeas -Can reduce feed intake and cause growth depression -The concentrations are usually too low for significant effects.
Where are lectins found? What do they do in the body?
-Found in soybeans and common beans -Polymeric proteins that bind to monosaccharides in glycoproteins of the cell membranes, causing lesions in the intestinal mucosa and reduced nutrient absorption.
What are flavonoids?
-Group of closely related phenolic compounds -phenyl rings; intermediate 5- or 6-membered ring https://www.youtube.com/watch?v=Y23PATwEVOs
Seed gums (2 examples and what they require to work)
-Locust bean gum requires heat for maximum hydration -Guar gum hydrates in cold water
Factors that Influence Respiration: Temperature
-Low respiration rate at low temperatures -High temperatures: denaturation of enzymes -Every ten degree rise in temperature, respiration rate increases by 2 - 3 fold.
Effects of cooking on non-mealy (waxy) potatoes
-Non-mealy (waxy) types hold their shape well and remain rather compact after being cooked. -Their cells tend to remain tightly associated.
What happens to the parenchyma cell during cooking?
-Once the parenchyma cell is cooking, osmosis ceases and diffusion occurs, -changes the texture, flavor, and shape of fruits.
What happens to pears and white potatoes sometimes on cut surfaces? Why does this happen?
-Pears and white potatoes sometimes develop a pinkish color in their cut surfaces when they stand for awhile after being peeled or sliced. -Color change is caused by the conversion of the proanthocyanin to a pigmented and closely related compound, cyanidin.
Veggies and fruits in USDA's MyPlate. Why are these recommendations made?
-Plant foods occupy half the plate in the USDA's MyPlate logo, with vegetables being recommended in somewhat larger quantities than fruits -These recommendations are made to increase the intake of vitamins (A and C in particular) and minerals, many of which are contained in significant amounts in various kinds of produce.
What is curdlan? How does it work?
-Polysaccharide in which glucose units are joined by 1,3-β-glucosidic linkages. -Curdlan was approved by the FDA in 1996 and is marketed as Pureglucan®. -It does not dissolve in water, but it can be suspended in water and heated to 80°C (176°C) to form a gel that is stable under freezing -Alicaligenes faecalis var. myxogenes produces curdlan, -When a suspension of curdlan is heated to 55-60°C (131-140°F) and then cooled below 40°C (104°F), a gel forms that behaves much like carrageenan.
Recipe for dried legumes that include molasses illustrates what?
-Recipes for dried legumes that include molasses illustrate the effect of calcium ions on texture -Soften the legumes before molasses is added -Calcium ions in molasses form insoluble calcium pectinates & pectates and greatly delay softening
Attention is focused on gums as food additives due to potential nutritional and health benefits:
-The most dramatic calorie savings are afforded when gums are used to replace fats and oils -Gums are used to increase beverage or food fiber content
Charge of the oxygen in the central ring of anthocyanins vs. anthoxanthins
-The oxygen in the central ring of anthocyanins carries a positive charge -in anthoxanthins, the oxygen is uncharged
Anthocyanidins and pH
-These compounds are highly sensitive to the pH of the medium in which they occur -High pH: The positively charged oxygen form changes to the quinone form. The quinone form has a violet color.
Betacyanins and boiling
-They diffuse rather rapidly into the cooking water, resulting in the highly pigmented water associated with boiling beets. -This rapid diffusion is aggravated by cutting into beets prior to cooking, a practice that leads to dull coloration in the boiled product.
Inulin promotes absorption of what? decreases what? stimulates what?
-This prebiotic fiber has been shown to promote absorption of calcium and magnesium and decrease cholesterol and serum lipids. -Inulin stimulates Lactobacilli and Bifidobacteria in the colon, which helps to combat possible harmful microorganisms and to promote health.
What happens to chlorophyll when heated?
-When vegetables containing chlorophyll are heated, a gradual color change occurs -First is an intensification of the bright green of chlorophyll—as air is expelled from the tissues -What follows is a slow transformation to an unattractive olive-drab -Replacement of the central magnesium ion by hydrogen forms pheophytin (a or b) -This conversion is facilitated by the presence of dilute acids released into the cooking water
How is xanthan gum formed?
-Xanthan gum formed when Xanthomonas campestris ferments glucose in the presence of trace elements -glucose units (1,4-β-glucosidic linkage) and a side chain consisting of two mannose and a glucuronic acid unit attached on alternating glucose unit.
Isoflavone
-a soybean anthoxanthin of interest due to a role in reducing LDL & serum lipids -Also responsible for the creamy color of soybeans
Anthocyanins
-highly pigmented, water-soluble pigments that range from red to purple to blue -Contained in plant cell vacuoles -In fruits and vegetables, one or more of these compounds may contribute to the overall color
Which metals must food pigmented with anthocyanins NOT contact to maintain desirable colors?
-iron -aluminum -tin -copper
Toxins/Antinutritive factors of veggies (4 things)
-protease inhibitors -lectins -saponins -cyanide poisoning
What happens during ripening?
-respiration -transpiration -maturation
Allium
-sulfur, different from cruciferous -Eye irritating substance (propenylsulfenic acid,onion), enzymatic breakdown of (+)-S-(prop- 1-enyl)-L-cysteine sulfoxide
Retention of chlorophyll is favored by: (3 things)
1) Boiling vegetables without a cover- remove volatile organic acids 2) Heating the water to boiling before adding vegetables 3) Using a slight excess of water to dilute the acids Breakdown of chlorophyll to pheophytin begins between 5 and 7 minutes after heating begins. By adding the vegetable to boiling water, the actual time required to tenderize the vegetable adequately is reduced, and chlorophyll retention is improved.
Volatile compounds that contribute to aroma and flavor of fruits and vegetables are (6)
1) Esters 2) aldehydes 3) acids 4) alcohols 5) ketones 6) ethers
The tissues in fruits and vegetables are designated in three different systems:
1) The dermal tissue (skin or rind) is the protective covering of each portion of the plant 2) The vascular system is composed of two parts—the xylem and the phloem 3) The remainder, which constitutes much of the edible portion, is the ground system.
What are the two subcategories of flavonoids?
1) anthocyanins 2) anthoxanthins
Subdivisions of fruits (7)
1) berries 2) citrus 3) drupes 4) grapes 5) melons 6) pomes 7) tropical/subtropical fruits
Two groups of betalains. What do they both contain?
1) betacyanins 2) betaxanthins Both contain nitrogen
What are two subgroups of flavanols?
1) catechins 2) leucoanthocyanins
Two types of chlorophyll
1) chlorophyll a 2) chlorophyll b
Collection of fruits and vegetables at a specific time for peak quality of: (3 things)
1) color 2) texture 3) flavor Dependent on species
Classifications of plant foods (5)
1) fruits 2) veggies 3) nuts 4) herbs 5) spices
Examples of organic acids (4)
1) malic 2) citric 3) tartaric 4) oxalic
What are 3 prominent anthocyanidins?
1) pelargonidin 2) cyanidin 3) delphinidin Pelargonidin, cyanidin, and delphinidin do not have a sugar complexed with them
What are the 4 factors that influence respiration?
1) temperature 2) O2 3) CO2 4) stress
There are about ___ different carotenoid pigments
300
What is recommended to inactivate enzymes to avoid possible souring during an overnight soaking?
A 2-minute boiling period prior to soaking beans is recommended to inactivate enzymes to avoid possible souring during an overnight soaking
Scoville organoleptic test - Scoville Heat Units
A measurement of chili pungency that was developed through taste testing of a trained sensory panel. Low heat chillies: 200 - 2500 Shu High heat chillies: upto 70000Shu Limitations - panelist variability, fatigue issues
What is chlorophyllin? How is it formed? What does it result in?
Abnormally green pigment formed when the methyl and phytyl groups are removed from chlorophyll in an alkaline medium, resulting in a mushy texture.
How does the addition of calcium salt affect mushiness?
Addition of a small amount of calcium salt prevents the mushiness by blocking the breakdown of the hemicelluloses.
What can the addition of copper/zinc (in place of Mg) do? What is negative about using these?
Addition of copper/zinc (in place of Mg) can also retain green color These metals are toxic
What happens to plants after soaking?
After soaking, plant pores reclose, hold the absorbed water if it is refrigerated for 6 hours.
Subdivisions of veggies (6)
Divided by part eaten: 1) bulb 2) root 3) tuber 4) leaves/stems 5) fruits 6) seeds
Dopachrome and melanin
Dopachrome (reddish) melanin (grayish - black) Not desirable
What happens to chlorophyll during ripening?
During ripening, chlorophyll diminishes, and other pigments give the characteristic colors of ripe fruit
Rate of respiration in edible stems, roots, or leaves postharvest
Edible stems, roots, or leaves respire at about the same rate as at harvest—or even at a reduced rate
Phosphorylase
Enzyme in potatoes that promotes sugar formation during cold storage.
Storage of potatoes vs. green beans and fresh basil
Figure 7.10 Potatoes (whether white, red, or blue) should be stored at about room temperature to maintain their starch content, but green beans and fresh basil should be in the refrigerator.
Good recipes to use waxy potatoes in and why?
Figure 7.11 Waxy potatoes retain their shape well when boiled, which makes them a good choice for potato salad or other recipes where pieces need to retain their shape.
Image of foods with pigments
Figure 7.4 Chloroplasts in cells contain chlorophyll, the green pigment in lettuce and other green vegetables; chromoplasts are the site of carotenoids, the pigment in carrots and other orange and some red produce; and white flavone pigments are in the vacuole of leeks and other white vegetables.
What is high in hemicelluloses?
Figure 7.7 Many types of legumes are available in markets. They are high in hemicelluloses, as well as in starch and protein.
___________ also contribute to taste sensations
Flavonones
What is the respiratory quotient (RQ)?
From google: the ratio of CO2 produced to O2 consumed while food is being metabolized: RQ = CO2 eliminated/O2 consumed. Most energy sources are food containing carbon, hydrogen, and oxygen.
What is ethylene?
General plant hormone (Sometimes dubbed the "ripening hormone")
What are gums?
Gums are complex hydrophilic carbohydrates found in plants They undergo little digestion in the small intestine
What other enzymes increase softening?
Hemicellulase, cellulase also increase softening.
_________ and ___________, compounds found in the peels of oranges and grapefruit, respectively, become intensely sweet when their molecules are modified slightly by opening the central ring.
Hesperidin and naringin
Fresh veggies are generally high in what? (3 things)
High in carbs (including fiber), vitamins, & minerals
What is now used to measure a chili's "heat"
High performance liquid chromatography is now used to measure a chili's "heat."
In root vegetables like parsnips and carrots, lignin is more likely to be deposited in the ________ of the vascular system than in the __________ region. What does this result in?
In root vegetables like parsnips and carrots, lignin is more likely to be deposited in the xylem of the vascular system than in the phloem region. This causes considerable toughening in these vegetables when they are harvested at maturity.
Factors that Influence Respiration: CO2
Increasing the concentration of CO2 decreases respiration
Insoluble fibers
Insoluble fibers are excreted undigested, providing stool bulk—but not energy Possibly beneficial because they reduce transit time of waste from the body
Coloring Agents in Food Products
Interest in natural foods has led to a rise in food colors made from plants
Relationship between lignin content and age
Lignin content increases with age
What happens to lignin during fruit and veggie prep?
Lignin is removed from fruits and vegetables during their preparation
Cyanide poisoning
Lima beans grown in some tropical countries contain a cyanogenic glycoside that is enzyme-hydrolyzed to release hydrogen cyanide during processing
Fresh veggies are generally low in what? (4 things)
Low in calories, cholesterol, sodium, & fat
What ripeness test can be used? What happens during it?
Lugol Test -Purple color decreases gradually when ripening proceeds -Typical harvest for long term storage at stage 6-8
______________ responsible for red color in tomatoes and watermelon and overtones in apricots and other yellow-orange fruits and vegetables; antioxidant that may help prevent some cancers and coronary heart disease.
Lycopene Acyclic carotene
Cooking mealy (non-waxy) potatoes
Mealy (non-waxy) potatoes slough and seem to become slightly fluffy when cooked.
Starch granules of mealy potatoes
Mealy potatoes have large, numerous starch granules, which swell significantly during cooking.
Do plants contain cholesterol?
NO
When do chilling injuries occur? Examples?
Occur if storage is at a non-freezing temperatures that's below the range for a particular fruit or vegetable. For example, potatoes held at a storage temperature of 4°C (39°F) accumulate sugars at the expense of starch content; apples stored at 3°C (37.9°F) gradually develop an internal browning and soft rot.
What can occur when garlic is crushed
Odorless, --> diallyl sulfide (allinase enzyme), can occur when garlic is crushed.
____________ contribute significantly to sour perceptions on the tongue—and overall flavor
Organic acids
What happens to the pectic substances of mealy potatoes during cooking?
Pectic substances in the middle lamella become more soluble—allowing cells to begin to separate.
How is a methyl ester removed from pectin?
Pectin methyl esterase (pectin methoxylases, pectases, and pectin demethoxylases) remove of methyl ester from pectin
Presence of carotenoids in unripe fruits
Presence may be masked by the intense pigmentation of chlorophyll in unripe fruits
Where is pheophorbide present?
Present in dill pickles & canned green beans
Heat processing of fruits and vegetables containing anthocyanins can present significant problems
Quinonoid↔Flavylium ↔Carbinol base↔Chalcone (colorless)
What is the main postharvest biochemical process?
Respiration
Breakdown of chlorophyll is desired in which fruits?
banana and yellow kiwifruit
All of the flavonoid pigments are derived from the same ______________
basic structure.
The distinctive color of beets is derived largely from the presence of the _____________
betacyanins
Beets contain ____________, closely related to, but not actually categorized as, anthocyanins
betalains
Chromoplasts contain ____________ pigments
carotenoid
Peroxidases and phenolases
catalyze oxidative reactions that result in less desirable colors
Growth phase
cell division, enlargement
Chloroplasts are where ______ is found
chlorophyll
Figure 7.9 Bananas, a _______________ fruit, are harvested when mature, but not fully ripe and carried via an overhead transit system to the packing floor to be shipped to distant ports.
climacteric
What flavors does cruciferous veggies have?
- sulfur Sinigrin --> allyl isothiocyanate (very pungent) hydrogen sulfide is produced, with the production accelerating when cooking extends beyond 5 minutes
What is turgor pressure?
-A plant's turgor pressure is the pressure that water-filled vacuoles exert on the cytoplasm and the partially elastic cell wall. -Crispiness
Two noteworthy characteristics of gums
-A remarkable ability to attract and bind water and act as thickeners -Very limited caloric contribution due to limited digestion and absorption
Another effective way to inhibit enzyme action
-A sodium chloride solution is also effective -Not used often due to excessively salty flavor
What happens if soda is added to the water that the beans are in?
-Addition of soda to the water reduces the softening time for cooking beans by about one-third -Offset by some loss of thiamin
How does blanching influence color?
-Blanching, as a preparation for freezing, enhances color by expelling air from intercellular spaces -The bright color is retained during freezing and the subsequent boiling prior to serving
What does rhodanide do?
-Brassicaceae contain glucosinolates which decompose enzymatically into rhodanides. -For example, in savoy cabbage, the rhodanide content is 30mg/100g fresh weight, while in cauliflower it is 10 mg and in kohlrabi 2 mg. -*Since rhodanide interferes with iodine uptake by the thyroid gland, large amounts of cabbage together with low amounts of iodine in the diet may cause goiter.*
Where are carbohydate gums derived from?
-Carbohydrate gums are derived from seeds, plant exudates, seaweed extracts, and microorganisms -These, as a group, are hydrophilic polysaccharides
Carrageenan: what does it interact with? what is it made of?
-Carrageenan can interact with protein to aid in the stabilization of various milk products, notably ice creams, process cheeses, and chocolate milks -Carrageenan structurally can be characterized as predominantly sulfate esters of galactose.
Anthocyanase
-Catalyze reactions that cause loss of color of anthocyanins -Good in case of white wines
Dermal tissue
Changes during development and maturation Protection function remain constant
Chemical composition of gums
Chemical Composition -All gums are polysaccharides in which glucose usually is absent. -Galactose is common to seed, plant exudate, and seaweed gums (with the exception of algin).
Examples of food with pungency
Chillies, ginger, pepper, horseradish, mustard, garlic, onion.
____________ cells are elongated cells, such as those found in the fibrous strands of celery
Collenchyma
Color ranges of carotenoids
Colors range from yellow, through orange, to some reds
Hydrogen sulfide levels in cauliflower vs. cabbage vs. broccoli vs. rutabagas
Cooked cauliflower (2 times hydrogen sulfide) compared to cooked cabbage. Cooked Broccoli more H2S than cabbage Boiling rutabagas= H2S + methyl sulfide.
How do corn and dried beans change texture during cooking?
Corn & dried beans achieve some texture change in cooking by taking up water as starch gelatinizes
Chlorophyll b
Yellowish-green form of chlorophyll, yellow green stalks
Cellulose
a glucose polymer whose units are joined by 1,4-β-glucosidic linkages
What is lignin?
a noncarbohydrate polymer of aromatic structures linked to form a large, complex molecule.
Other gums
agar and carrageenan (red algae), gum arabic and ghatti (plant fluids)
Senescence
ageing, death of tissues The age-dependent programmed degradation and degeneration process of cells, organs or the entire organism, leading to death
Yellow onions and spinach or other leafy vegetables will cause the cooking water to turn a bit yellow when they are cooked in _____________
aluminum A similar problem is noted with iron when these vegetables are cooked in cast-iron pans.
When the fruit or vegetable has cut surfaces, it is possible to add _________ to inhibit enzyme action
an acid ex: Citric or ascorbic acid are useful
Chlorophyllase
an enzyme that catalyzes the removal of the phytyl group, which is the complex alcohol esterified to the acid radical in the chlorophyll molecule
Breakdown of chlorophyll is undesired in which foods?
apple, broccoli
The __________ surrounding fresh produce also influences respiration rate
atmosphere Lettuce needs at least 1% O2; asparagus at least 5%
