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Chapter 2

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University of Guelph
Food Science
FOOD 2010
Massimo Marcone

CHAPTER 2  Food Groups and Categories: o Beverages o Cereals, grains, baked products o Confectionary and chocolate o Fruits and vegetables o Legumes and nuts o Meat, poultry, eggs seafood o Milk  Food composition refers to the substances or components found in a beverage or food - By identifying and quantifying the nutrients in foods, scientists have obtained the data needed to develop tables of food composition.  Raw foods are composed of naturally occurring substances, while processed foods often contain specific, functional additives.  Tables of food composition are printed by the U.S Department of Agriculture (USDA), which provides nutritionists and consumers with information regarding the specific nutrient and calorie (kcal) content of beverages and food.  Commodity is defined as “a useful consumer good, a product of agriculture, produced and delivered for shipment”.  Processed commodities are value-added commodities derived from agricultural commodities that offer convenience, longer shelf life and some added nutrients.  It’s not just what foods we eat but how much of it.  The quantity of food recommended by the Food Guide Pyramid is called servings; product food labels specify serving sizes, tables of food composition employ measures.  The amount of food that counts as one serving depends on the food group.  Serving sizes are now more uniform and reflect the amounts people actually eat.  The Nutrition Labeling and Education Act (NLEA) define serving size as the amount of food customarily eaten at one time.  Serving sizes that appear on food labels are based on the FDA-established lists of “Reference Amounts of Customarily Consumed Per Eating Occasion” which must be expressed in both common household and metric measures grams (g) and milliliters (mL).  A beverage is a drinkable liquid, consumed for a variety of reasons, including thirst quenching, stimulant effect, alcoholic content health value and enjoyment.  Nutrients are substances in foods and beverages that when absorbed into the body, are used for specific functions like growth, maintenance and repair of tissues.  Nutrient density is a concept that applies to beverages and to foods if it supplies a variety of protein, complex carbohydrates, vitamins and minerals without excess fat and calories.  Commonly used beverage sweeteners are sugar (sucrose) and high-fructose corn syrup.  Sucrose is a part of the total soluble solids content of the beverage.  The sucrose concentration of beverages is measured as degrees Brix (°Brix), which is equal to the weight percent of sucrose in solution (grams of sucrose per 100 grams of sample)  Any sweetened beverage formulation using sucrose as the only sweetener, the °Brix reading is directly proportional to the amount of sucrose in solution.  The measurement of °Brix is made by refractometry, using either a refractometer of a hydrometer device calibrated in degrees Brix, with corrections applied according to fruit type and acid context.  Sucrose inversion; in which sucrose molecules in solution come apart and yield the two component sugars, glucose and fructose. Fructose is a sweeter sugar than sucrose or glucose, so sucrose inversion can affect the final sweetness and flavour of the beverage. o Fructose due to inversion = sweetness increase.  Factors promoting sucrose inversion include: o Low storage pH (high acidity) o High storage temperature o Desirable and created by the action of enzyme, invertase o Action of acidulant  Food products analyzed for °Brix include: o Syrups such as honey, maple syrup, and molasses o Jams and jellies o Tomato products  Flavour depends on the °Brix/acid ratio o This ratio varies as the relative proportion of sugar to acid content, and is critical in selecting certain fruit and vegetable types to make juices.  For fruits and vegetables the °Brix/acid ratio can vary according to region example California oranges 8°Brix while Florida oranges 13°Brix  Different °Brix/acid ratios is one reason why consumers prefer one orange variety over another.  Cereal grains, corn, rice, wheat, barley, millet, rye, sorghan and oats are among the world’s major crops. o Are high in carbohydrate content, such as starch, and the sugars glucose, maltose and fructose as well as fibre.  Cereal grains can be consumed directly or milled into flours processed into a wide variety of food products.  Two non-cereal crops, sugarcane and beets, are also processed into sugars and syrups.  Enriched cereal grain products are processed to contain added vitamins and minerals. However, the layer of the kernel used also has an impact on nutrient composition ex. Bran flakes contain significantly more protein and iron than corn flakes  Cereal grains are composed of 3 nutritious parts or structures o Endosperm-which comprises about 83% of the kernel o Bran –layer which is about 15% of the kernel o Germ-which is embryonic or sprouting part 2-2.5%  Energy and nutrient values vary among processed grain products  Average unprocessed cereals are about 75% carbohydrate, 10% protein and up to 2% fat  The protein in cereal grains has a lower bioavailability and biological valve than protein found in animals.  Biological valves refer to the amount of nitrogen derived from food protein that s used in the body to promote growth.  BV is related to the amino acid content of a protein  A food high in BV is said to possess high-quality protein, meaning all the amino acids are present.  Plant protein sources usually lack or are deficient in lysine and methionine and are termed “incomplete proteins”  Bioavailability is the degree to which nutrients are digested and absorbed in the body. Influenced by such factors as source (animal vs. plant) and food processing (certain nutrients, such as the B vitamins, are destroyed by heating)  Leavening refers to the production of gases in dough that contributes to the volume achieved during baking “leavening effect” and the final aerated texture  Typical leavening agents are: yeasts (ex of a biological leavening agent), baking soda (NaHCO , sodium bicarbonate), baking powder and ammonium bicarbonate (NH HCO ) 3 4 3  Leavening agents function to produce carbon dioxide as the specific leavening gas.  Steam (heated water vapour) is also produced during baking and contributes to “oven spring”  A fruit is a fleshy or pulpy plant part commonly eaten as a dessert due to its sweetness. o In botanical terms, fruits are defines as the ripened ovary of a plant, which means it contains seeds.  A vegetable is a plant or plant part or plant part that is served either raw o Botanically a vegetable is an herbaceous plant containing on edible portion such as a leaf, shoot, root, tuber, flower and stem.  A vegetable fruit is the fruit part of the plant that is not sweet, usually served with the main course of a meal like cucumbers, squashes and tomatoes.  Fruits and vegetable shave many similarities in composition, methods of cultivation and harvesting, storage properties and processing.  Most fresh fruit and vegetables are high in water content (up to 90%), low in protein (up to 3.5%) and low in fat (up to 0.5%).  Fruits and vegetables contain various minerals, and are good sources of both digestible carbohydrates (sugars and starches) and indigestible carbohydrates (fibre including cellulose and peptic substances) o Good sources of specific vitamins: the vitamin A precursor beta-carotene (in green leafy vegetables and yellow-orange fruits and vegetables) and Vitamin C (in citrus fruits, green leafy vegetables and tomatoes).  Research is discovering a link between a link between fruit and vegetable consumption and health; foods high in vitamin A, beta-carotene, vitamin C and fibres, such as pectin and these substances may provide a protective effect against heart disease and certain cancers.  Red wine contains resveratrol, a substance that may lower blood cholesterol, prevent heart disease and act as an anticancer substance.  Ripeness is the optimum or peak condition of flavour, colour and texture for a particular fruit.  Maturity is the condition of a fruit when it is picked, the fruit may be at or just before the ripened stage.  Some fruits if picked at peak ripeness will continue to ripen and become overripe.  Harvesting is the collection of fruits and vegetables at a specific time of peak quality in terms of colour, texture and flavour in order to market them.  The decline in the quality of stored, respiring fruits and vegetables that occurs after harvesting is called senescence (example, the sweetness of corn decrease dramatically during storage because up to 50% of the sugars may convert back to starch).  Fruit and vegetable quality depends upon such qualitative characteristics as size, colour, blemishes and bruises, flavour, firmness and presence of extraneous matter of such as unwanted stems, pits and leaves.  Quantifiable data include °Brix, microbiological information, moisture content, pH and viscosity.  In fruit and vegetable juices, Pectin levels, starch levels, pulp and solids content are often measured.  Dried fruits are a processed category of fruits created by dehydration; removes moisture from fruits to prevent microbial and enzymatic deterioration, concentrating the nutrients in a dried fruit product.  Fruits to be dehydrated must be in a very ripened state so they contain the highest possible natural sugar levels.  A process called infusions can also be used to create dehydrated fruit; using heat and pressure, fructose is forced in a fruit piece and this sugar replaces the water inside the fruit. Infusion adds flavour, adds colour and achieve a certain texture (chewy or soft).  Legumes, which are edible seeds and pods (as beans and peas) of certain flowering pants including beans, lentils, soybeans and peas.  Most legumes off good-quality protein compared to other plants that are low in fat  Legumes are becoming more popular due to their low-fat, low-sodium, high fiber, vitamin, mineral and protein content.  Soybeans are legumes with a dual role as an “oilseed” and a “foodbean” because of the fat and protein content.  Lipoxygenase an enzyme present in soybeans was responsible for off tastes in soymilk because it converted soy fatty acids to odorous compounds. This enzyme is deactivated by heat, which eliminates off-flavours.  Some soy foods provide a phytochemical called isoflavones, compounds that might be effective in the prevention and treatment of cancer and certain chronic diseases.  Nuts are well-balanced, nutritious food, providing protein, fiber, vitamins, minerals, unsaturated fatty acids and phytochemicals.  Almonds come in two varieties: sweet and bitter; the bitter almond is poisonous if consumed-it contains a substance called amygdalin that can be broken down to produce hydrogen cyanide.  Popular tree nuts include almonds, hazelnuts, pecans, pistachios, macadamia and walnuts.  Meat can be defined as the edible flesh and organs of animals and fowls. Red meat describes the flesh of cattle, pigs and sheep. The flesh of poultry (chicken, turkey, duck) is concerned white meat.  Processing can include physical methods such as grinding, chemical treatment such as curing and smoking.  Drying strips of meat produces jerky.  Meat by products includes organs and glands such as liver, heart, brain, thymus and intestines.  Meat is a source of high-quality protein and is valued for its cooked flavour and tender texture. It provides various B vitamins, iron, magnesium and other minerals.  The basic unit of muscle tissue is the muscle cell or muscle fibre, which is surrounded by a cytoplasmic substance called sarcoplasm.  The muscle fibre consists of many unit called myofibrils.  These myofibrils contain contractile proteins organized in a specialized array of thick and thin rod-like filaments o The thick filament protein is called myosin o The thin filament protein is called actin o When muscles contract, these filaments form cross-linkages with each other – bonds that produce a new protein called actinomyosin.  Two kinds of connective stromal proteins common in meats: elastin and collagen.  Collagen is known as white connective tissue; the toughness of meat is directly related to the amount of collagen it contains. Older animals tend to have high levels of collagen.  An emulsion is a two-phase system in which one phase is dispersed in the other, in the form of finely divided droplets.  Emulsions in which the main components are lipid (oil or liquid fat) and water can be classified as oil-in-water (o/w). The first term refers to the dispersed phase and the second term to the external or continuous phase. o Emulsions separate into their component phases because they are thermodynamically unstable.  Comminuted meat emulsions contain finely chopped meat mixed with water, fat and sometimes additives such as preservatives and water-binding agents.  Some meat proteins are termed soluble because they remain dispersed with the watery phase, while others are insoluble and can form gels.  Seafood includes clams, oysters, lobsters, scallops and other food animals derived from oceans, lakes and streams.  Fish can be derived into two groups: finfish and shellfish o Finfish are fish with a backbone and fins o Shellfish include crustaceans, which are sea invertebrates with a hand upper shell and a soft under shell and mollusk with two enclosing shells.  The composition of seafood is quite variable, as it depends on species, age and season of capture or “harvest”.  The protein is highly digestible and good source of all the essential amino acids.  Fish fat (example cod liver oil) is rich in unsaturated fatty acids, as well as fat-soluble vitamins A and D  Fish oil is highly perishable.  B vitamins are found in the muscle.  Fish can be rich sources of iodine and some magnesium, calcium and iron are often present.  Fish flesh is more perishable because of 3 basic reasons: fish microbiology, fish physiology and fish fat chemistry.  Fish microorganisms are pyschrotrophic, which means they live and multiply in colder temperatures, even in refrigeration temperature (4-15°C).  When fish are caught in nets and die, bacteria rapidly invade all the tissue constituents.  In fish physiology, fish store more energy in muscle
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