食品科学和技术(英文)(ppt 60页)

1、Food Science and Technology,By Gilsonl 10/23/2002,Definition,Food science: Scientific study of food from “farm to fork”. Food technology: Use of the information generated by food science to produce safe, nutritious and wholesome food.,FOOD SCIENCE,Multidisciplinary Engineering Chemistry/Biochemistry

2、 Microbiology Nutrition Foods as edible biochemicals Touches on many other areas Globalization of world food supply,MORE PEOPLE, LESS FOOD,Widespread food shortages will develop over the next 40 years as a population explosion gradually outstrips world food supply. The food supply is the most immedi

3、ate constraint on the Earths population-carrying capacity.,Milestones often this requires additional treatment processes such as microfiltration and deaeration. C. Cleaning of food equipment surfaces Moderately alkaline and neutral detergents find wide application in food industry as they remove soi

4、l and other deposits yet are noncorrosive to food-contact surfaces. Many types and combinations of detergents used.,Separating,Solid from a solid (e.g., shelling nuts; lye peeler for peaches) Solid from a liquid (e.g., filtration; centrifugation; crystallization of sugar crystals from sugar cane jui

5、ce) Liquid from a solid (e.g., extracting juice from a fruit; pressing oil from peanuts and soybeans) Liquid from a liquid (e.g., centrifuging oil from water) Removing a gas from a liquid or solid (e.g., pulling a vacuum) A. Hand sorting and grading still very common (e.g., fruits ultrasonics also u

6、sed to screen internal tissue of whole fruits and vegetables.,Disintegrating,A. Breakdown of large food particles into smaller particles. Examples: Cutting, grinding, pulping, homogenizing. Some cutting now done with high-pressure water jets and laser beams. B. Disintegration often involves heat bui

7、ld-up due to friction and some products require cooling (e.g., meats to avoid protein denaturation and coffee to avoid burned flavors). Grinding of frozen meat is done to avoid this. Or addition of dry ice that dissipates as carbon dioxide. C. Homogenization,Pumping,A. One of the most common operati

8、ons in the food industry (both liquids and solids suspended in liquids) B. Many kinds of pumps - pump selected depends upon nature of food to be moved. Rotary gear pumps have close tolerances among moving parts, chunk-type foods would be reduced to purees, and sometimes this is the intent, so the pu

9、mp serves two purposes. A single-screw pump (with large clearances) best for moving food with large pieces without disintegration (e.g., corn kernels, grapes, small shrimp).,C. It is essential that all food pumps can be easily disassembled for thorough cleaning (stainless steel is the most common ma

10、terial used to make pumps for the food industry).,Mixing,A. Again, very common operation in the food industry; can be solid-solid, liquid-liquid, solid-liquid, gas-liquid, etc. B. Many are “kitchen-style” mixers, just bigger. Most common used to mix solids into liquids to dissolve them is a propelle

11、r-type agitator within a stainless steel vat. C. Mixing usually involves the generation of heat and in foods it is often desirable to minimize this temperature rise by some form of cooling. D. Some mixing requires high rpm Example: Mixer/beater found in ice cream freezers to incorporate air into ice

12、 cream mix to produce desired volume increase (overrun) required to attain desired texture,Heat exchanging,A. Reasons to heat: Cook Pasteurize Preservation (e.g., blanching) Drive off moisture (evaporate) Develop flavors Inactivate natural toxic substances (soybean meal),B. Need to control applicati

13、on of heat (often necessary to heat and rapidly cool the product) Rapid heating and cooling often require maximum contact of the food with the heating/cooling source (e.g., heat exchangers in the pasteurization of milk). Steam-jacketed stainless steel kettle or tank often used for heating liquid foo

14、ds (mixing propeller usually included to prevent scorching and even distribution of temperature). Canning - using a retort (pressure cooker) Roasting - circulating hot air C. Cooling Again, a heat exchanger can be used, but with cold water pumped through the unit. Commercial blast freezers reach -26

15、C Liquid nitrogen: -196C,Evaporation - to concentrate foods 2- to 3-fold,A. To remove water, to recover desirable food volatiles, and to remove undesirable volatiles. B. Can be solar (raisins), heated kettle (water from a sugar syrup). C. Very common in the industry: Vacuum evaporation - reduced pre

16、ssure allows liquids to boil at lower temperatures (the lower temperature causes less damage to food quality).,Drying - to take foods to near total dryness (often 2 to 3% water),Examples Dried milk processed by spray drying (atomized liquid mixed with heated air); liquid foods are easiest to dry. Ma

17、shed potatoes and tomato puree processed by drum drying (drum heated from within, applied layer of food flashes off its moisture on contact with heated drum, and thin film of food scraped off drum with long knives). Peas and diced onions dried by moving through a long tunnel oven (subject of overhea

18、ting and shrinkage), but a preferred method is, vacuum freeze-drying (used for coffee), food frozen, dehydrated under vacuum from the frozen state.,Forming - foods made into specific shapes (e.g., fish sticks),Application of pressure within an appropriate form. Range of pressures used, varies consid

19、erably dependent upon the product. For example: Extrusion Breakfast cereals - Extrusion cooking Formulated dough or mash is extruded under high pressure with heat.,Packaging (food containers),To protect food from microbial contamination, physical dirt, insect invasion, light, moisture pickup or loss

20、, flavor pickup or loss, and physical abuse (damage). Containers include metal cans, glass and plastic bottles, paper and paperboard, plastic and metallic films, and combinations of these. Packaging is automated.,New processes,To increase the range of options within each unit operation, to improve q

21、uality or increase efficiency. Examples include: supercritical fluid extraction, ohmic heating, and high hydrostatic pressure processing.,QUALITY FACTORS IN FOODS,Appearance factors Textural factors Flavor factors Additional quality factors,Appearance factors,A. Size and shape Size: Easily measured

22、(e.g., fruits and vegetables can be sized according to the openings they can pass through; the basis for automated separating and grading machines). Shape: Some of the most difficult food engineering problems are the designing of equipment to pack odd-shaped food pieces.,B. Color and gloss Food colo

23、r: Helps determine quality, ripeness and spoilage. Color and transparency/cloudiness: Can be measured with a spectrophotometer (measures light transmission through a liquid). Solids and liquids: Reflected color can be measured by comparison with defined colored chips. Hunter colorimeter: Color measu

24、rement by division into three components - value, hue and chroma. Value - lightness or darkness of the color. Hue - predominate wavelength reflected (which determines what the perceived color is). Chroma - intensity strength of the color. Instruments available to measure shine or gloss.,C. Consisten

25、cy - viscosity; many types of viscometers to measure consistency. Bostwick Consistometer - time it takes for food to flow down an inclined trough.,Textural factors,A. Food qualities we feel. B. Food texture can be measured by resistance to force. Squeezing (compression). Shear (force applied so that

26、 one part of the food slides past the other). Cutting. Tensile strength (pulling apart). C. Texture changes - do not remain constant in a food. Change in water content plays a major role,Flavor factors,A. Combination of both taste and smell and largely subjective and therefore difficult to measure,

27、very complex. Wide divergence of opinion. B. Color and texture influence flavor. We become educated as to expect certain colors with certain flavors. Greater intensity of color associated with greater flavor; same with greater viscosity to perception of greater flavor. C. Salt, sugar and acid can be

28、 measured using instrumentation.,D. Taste panels Analytical instruments can be used, but the human “test animal” is still the best. Use of groups of people preferred over an individual opinion, as differences of opinion tend to average out.,1. People involved in taste panels. Trained people for spec

29、ific products (e.g., butter and cheese). Consumer preference groups - panels not specifically trained but provide insight as to what consumers prefer. Highly trained people with heightened taste sensitivity and knowledge of what to recognize as attributes and defects,2. Environment for taste panels.

30、 Isolation of tasters to avoid influence by observing other tasters. Tasters unable to see how food was prepared or what its identity is. 3. Hedonic scale (for quality factors) Range from dislike extremely to neutral to like extremely.,4. Approach Preference test: Choosing one sample over another; s

31、amples are coded so that source or identity of food sample is unknown to taster. Most common is the triangle test (a preference test): Selecting the sample that differs from two others (total of 3 samples). Usually no more than 5 samples tested at one sitting; sense of taste becomes dulled. Statisti

32、cal analysis of results is usually employed. 5. In addition to flavor, taste panels judge texture, color, packaging, sample arrangement, etc.,Additional quality factors,A. Nutritional quality Chemical or instrumental analyses for specific nutrient; however, often animal feeding tests must be used, e

33、specially for quality of protein sources (biological value). B. Sanitary quality Analysis for bacteria, yeasts, molds and insect fragments. X-rays to detect physical contaminants (e.g., glass chips, stones, metal fragments). C. Keeping quality (storage stability) Measured under storage and handling

34、conditions to match conditions encountered in normal distribution. Normal storage tests may take a year; extreme conditions may be used to speed things up.,FOOD DETERIORATION AND ITS CONTROL,Food deterioration includes declines in organoleptic desirability/aesthetic appeal, nutritional value, and sa

35、fety (i.e., product quality); occurs under the best of conditions.,Factors adversely affecting food,changes in temperature (heat and cold), light and other radiation, oxygen, changes in moisture content (water loss or uptake), detrimental enzymes of the food, microorganisms and macroorganisms, indus

36、trial contaminants (e.g., packaging materials) and close proximity of other foods, and time.,Some of the most important advances in food technology have occurred as a result of war. Nicolas Appert - developed the technology of canning (1809) as a result of prize money offered by Napoleon for preserv

37、ation of food for the French army and navy.,Shelf-life and dating of foods,A. Definition of shelf-life: The time it takes for a product to deteriorate to an unacceptable level (what is unacceptable is sometimes a matter of opinion). B. A better definition: Length of time a product remains salable. I

38、t is common for a food manufacturer to define a minimum acceptable quality (MAQ) for a product.,Actual length of shelf-life dependent on,Processing method, Packaging, Storage conditions.,Dating system,1. Different code dates: Date of manufacture (pack date), Date the product was displayed (display d

39、ate), Date by which the product should be sold (sell by date), Last date of maximal quality (use by date), Date beyond which the product is no longer acceptable (use by date or expiration date).,2. Use of these code dates requires a need to predict and monitor shelf-life. Models for predicting shelf

40、-life are particularly useful for new products without a distribution history.,V. Major causes of food deterioration,A. Microorganisms (bacteria, yeasts and molds) B. Insects and rodents C. Heat and cold - can cause deterioration of food if not controlled. D. Moisture and dryness E. Oxygen F. Light

41、G. Time,A. Microorganisms (bacteria, yeasts and molds),More types of microorganisms can spoil food than cause foodborne disease. Sources of these microorganisms: soil, water, air, food itself, humans, food equipment environment.,Healthy living tissue (internally) is usually sterile, hence the presen

42、ce of spoilage organisms is mostly the result of contamination. Bacterial endospores are most difficult to inactivate. Heat and moisture will increase growth and activities of microorganisms. Molds as compared to bacteria can generally grow at: lower pH (more acid conditions), lower moisture contents (dryer conditions), higher salt concentrations, and lower temperatures (in re