A steady-flow compressor is used to compress helium from 15 psia and 70°F at the inlet to 200 psia and 600°F at the outlet. The outlet area and velocity are 0.01 ft2 and 100 ft/s, respectively, and the inlet velocity is 50 ft/s. Determine the mass flow rate and the inlet area.
Food poisoning Food-borne illness: illness caused by food Usually causes gastrointestinal symptoms Abdominal pain, nausea, diarrhea, and vomiting Can cause kidney failure, arthritis, paralysis, miscarriage, death Usually caused by microbes (microorganisms), such as bacteria, viruses, fungi, or parasites Microbes that can cause disease are pathogens (they generate pathology) NOTE: only2 cases of food poisoning that can be tied back to the same source are needed before it can be considered an outbreak Food-borne illness: infection vs. intoxication Food-borne infection: caused by pathogens that multiply in the human body Usually from consumption of a large number of pathogens that cause infection or produce toxins in the body Example: Salmonella Food-borne intoxication: caused by consuming food containing toxins produced by pathogens Can be caused byfood containing onlya few pathogens if theyhave produced enough toxin Example staphylococcus aureus Bacterial Food-Borne illness Food poisoning symptoms and severity depends on: Potency of contaminant How much of is consumed How often it is consumed Age, size, nutritional status, chronic diseases Absorption, metabolism, storage in the body Immune function (at risk: young, elderly, pregnant women, people with AIDS or on chemotherapy or immunosuppressant drugs) Federal Agencies Set standards and establish regulations for: safe handling of food and water information included on food labels Regulate use of additives, packaging materials, and agricultural chemicals Inspect food processing and storage facilities Monitor domestic and imported foods Investigate outbreaks of food-borne illness Food Supply Monitoring Agencies Recent Federal Changes National Food Safety Initiative Goal: reduce food-borne illness by improving US food safety practices and policies Targets food safety from farm to table FDA Food Safety Modernization Act Focus: preventing food-borne illness Passed in 2011 in response to the continued threat from our food supply FDA: inspection mandate and new legal powers Hazard Analysis Critical Control Point (HACCP) Food safety system required for food manufacturers, processors, and distributors Analyzes food production, processing, and transport Goal: identify potential sources of contamination and points where measures can be taken to prevent contamination Monitors these critical control points Bacteria In soil, on our skin, on most surfaces in our homes, and in food Most are harmless, some are beneficial, and a few are pathogenic Examples of Bad Bacteria Salmonella Most common cause of US food-borne illness Common sources: Poultry and eggs are the foods most commonly contaminated; Prevention: killed by heat; thoroughly cook foods likely to be contaminated E coli Causes: some strains are harmless; others can cause serious food-borne infection E. coli O157:H7 produces a toxin causing abdominal pain, bloody diarrhea, fatal kidney failure Common sources: fecal contamination of water or food (for example, meats and produce) Listeria Monocytogenes Causes: flulike symptoms; more serious in high-risk groups (pregnant women, children, elderly people, with compromised immunity) During pregnancy: causes spontaneous abortion and stillbirth, fetal meningitis and blood infections Common sources: everywhere in environment Prevention: survives and grows at refrigerator temperatures so infects ready-to-eat foods; heat hot dogs and lunchmeats to steaming point and avoid unpasteurized dairy products NOTE: listeria fatality rate is 21% How Bacteria Contaminate Food Raw & unpasteurized foods Close/Dirty living environments: bacteria & bacteria-related illness is spread through livestock population Uncooked/Unwashed foods: bacteria on the surface are not killed or removed Contamination in factory line: machine parts get covered in bacteria & contaminate all food that passes through it Sick employees: sick food handlers cough or sneeze on food, spreading their germs Ground meat products: bacteria mixed throughout meat in grinding process & may not be killed by cooking if not cooked thoroughlEX: hamburger w/ pink in middle Botulism Clostridium Botulinum bacteria Causes: blocked nerve function, resulting in vomiting, abdominal pain, double vision, and paralysis leading to respiratory failure and death; deadliest of all bacterial food toxins Common sources: in soil, water, and animal intestinal tracts; toxin produced when heat-resistant spores grow in low-oxygen, low-acid conditions; found in improperly canned foods and foods held in large containers NOTE: this is the deadliest of bacteria Infant botulism Most common form of botulism in the US Caused by ingestion of botulism spores (most common is honey) Spores germinate in the infant’s gastrointestinal tract, producing toxin In adults, competing intestinal microflora prevent spores from germinating Some toxin is absorbed into the bloodstream, causing weakness, paralysis, and respiratory problems; infants generally recover Never feed honey to children less than 1 year Viruses Not classified as living or as cells since they cannot reproduce on their own Human viruses reproduce only inside human cells Viruses turn human cells into virus-producing factories Viruses that cause human diseases cannot grow and reproduce in foods Noroviruses Group of viruses Cause: about 50% of all US food-borne gastroenteritis (stomach inflammation), A.K.A. “stomach flu” Common sources: eating food contaminated with virus or touching contaminated surface and then putting fingers in mouth; Shellfish can be contaminated in water polluted with feces Prevention: cooking destroys noroviruses NOTE: noroviruses are the #1 source of food outbreaks, as they can live on surfaces for up to 2 weeks, and some ordinary cleaners don’t kill it Mold & Fungus Many types grow on foods such as bread, cheese, and fruit Under certain conditions, molds produce toxins (>250 different mold toxins) Cooking and freezing stop mold growth but do not destroy toxins already produced If food is moldy, discard it, clean the area where it was stored, and check neighboring foods to see if they are contaminated Mold & Liver Cancer Parasites Organisms that live at the expense of others Some are microscopic single-celled animals; others are worms large enough to be seen with the naked eye Prevention: killed by thorough cooking Giardia lamblia, Cryptosporidum parvum, Trichinella spiralis (Multicellular parasite in raw or undercooked pork Pathogens in Food: Prions Pathogenic protein that causes degenerative brain diseases such as spongiform encephalopathies Short for proteinaceous infectious particle Prion diseases Bovine spongiform encephalopathy (BSE): deadly neurodegenerative disease in cattle Creutzfeldt-Jakob Disease (vCJD): human BSE Causes: eating brain, nervous tissue, intestines, eyes, or tonsils from cow infected with BSE (meat and milk have not been found to transmit prions) Symptoms: mood swings and numbness progressing to dementia and death Prevention: prevent US cattle from contracting BSE (cooking does not destroy prions) Prevent microbial food-borne illnesses Choose food carefully; when in doubt, throw out Prepare food in a clean kitchen to reduce cross-contamination (transfer to another food) NOTE: cross-contamination happens most commonly in home kitchens Store food in refrigerator or freezer Foods served cold should be kept cold until served Thaw frozen foods in refrigerator or microwave (not at room temperature) Heat foods to recommended temperatures Cooked foods should be kept hot until served Safe Grocery Decisions Leftovers Minimize the danger zone Chill quickly (within 2 hours or less) Store in small, shallow containers Wrap well Good in refrigerator 3 to 4 days Reheat to 165 Safe Handling, Storage, & Prep clean separate cook chill Contaminants in the Food Supply Bioaccumulation Pesticides in Food Prevent plant diseases and insect infestations Applied both before and after harvest Produce higher yields and look more appealing from less insect damage Found on treated plants and in meat, poultry, fish, and dairy products since they enter water, soil, and other parts of environment Risks depend on the size, age, and health of the consumer and on the type and amount consumed Pesticides regulation Types of pesticides, how often used, and amount of residue that may remain when foods reach consumers are regulated EPA: approves and registers pesticides used in food production and establishes tolerances (maximum amounts of pesticide residues that may remain in or on a food) FDA and USDA: monitor pesticide residues in foods Organic Foods Produced, processed, and handled according to USDA National Organic Program standards Reduced chemical pesticides and fertilizer use USDA determines substances that can or cannot be used USDA must certify before labeled “Organic” Most conventional pesticides, synthetic fertilizers, sewage sludge, genetically modified ingredients, irradiation, antibiotics, and growth hormones are prohibited Recycling of resources Conservation of soil and water Labeling Organic Foods Industrial Contaminants Polychlorinated Biphenyls (PCBs) Group of carcinogenic compounds Prior to 1970s, PCBs in runoff from manufacturing plants’ contaminated water Still in environment and accumulate in fish from contaminated waters since PCBs do not degrade Prenatal exposure and contaminated breast milk causes nervous system damage and learning deficits Check with local health departments for recommendations regarding fish consumption during pregnancy and lactation Other Manufacturing Contaminants Chlordane (used to control termites) Radioactive substances Cadmium: interferes with mineral absorption, causes kidney damage, impairs brain development Lead Arsenic: increases cancer risk Mercury: damages nerve cells; more damaging during prenatal development Bisphenol A (BPA) Antibiotics in Animals Animals are treated with antibiotics when sick or to prevent disease and promote growth Increases meat production and reduces costs If used improperly, antibiotic residues can remain in meat Creates antibiotic-resistant bacteria Hormones in Animals Used to increase weight gain in sheep and cattle and milk production in dairy cows Some hormones, such as estrogen and testosterone, occur naturally Generally administered in slow-release form, and levels are no higher in treated animals than in untreated animals Must demonstrate that synthetic hormone residues in meat are within safe limits Bovine Somatotropin (bST) Has created public concern Produced naturally by cows and stimulates milk production Genetically-engineered synthetic hormone is produced by bacteria and injected into cows to further increase milk production Milk from cows that have been treated with genetically-engineered bST is indistinguishable from other milk Minimize food contaminants Choose a wide variety of foods Choose organic or locally-grown produce Wash and in some cases peel produce Trim fat from meat and remove poultry skin Choose wisely and consume a variety of fish Remove fish skin, fatty material, and dark meat Broil, poach, boil, and bake fish Factors to Keep Food Safe Food Preservation Older methods: heating, cooling, drying, smoking, adding substances (sugar or salt) Newer methods: irradiation, specialized packaging Risk: substances enter food High & Low Temp Preservation Provide appealing, safe foods Cooking: kills microbes, destroys most toxins Pasteurization: process of heating food products to kill microbes Sterilization and aseptic processing: placement of sterilized food in sterilized package using sterile process Refrigeration or freezing does not kill microbes but slows or stops microbial growth Food Irradiation (cold pasteurization) Used in more than 40 countries and used infrequently in the US because of public suspicion and of lack of irradiation facilities Exposes food to high doses of X-rays, gamma radiation, or high-energy electrons to kill microbes and insects and inactivate enzymes that cause germination and ripening of fruits and vegetables Food additive: produces compounds not present in the original foods (regulated) Modified atmosphere packaging (MAP) Preservation technique to prolong shelf life of processed or fresh food by changing the gases surrounding food in the package Uses packaging materials impermeable to gases Air in package is vacuumed out to remove oxygen Product remains in a vacuum or the package is infused with another gas Lack of oxygen prevents aerobic bacteria growth, slows ripening and oxidation reactions Additives vs. Contaminants Food additive: any substance that can be expected to become part of a food FDA regulates the types and amounts of food additives Accidental contaminants: unexpected substances that enter food Not regulated Regulating Food Additives Prior-sanctioned substances: > 600 additives in use when legislation was passed Generally recognized as safe (GRAS): additives considered safe based on history of use in food before 1958 or on published scientific evidence Can be added only at levels 100 times below highest level shown to have no harmful effects Part of the 1958 Food Additive Amendment states that a substance that induces cancer in either an animal species or humans, at any dosage, may not be added to food If new evidence suggesting additive in either category is unsafe, FDA may require removal Sensitivities to Additives Some individuals are allergic or sensitive to certain food additives Monosodium glutamate (MSG) can cause MSG symptom complex or Chinese restaurant syndrome Sulfites can cause symptoms ranging from stomach ache and hives to severe asthma FD&C yellow no. 5 (listed as tartrazine on medicine labels) may cause itching and hives Carcinogens from cooking meats Polycyclic aromatic hydrocarbons (PAHs): formed when fat drips on a grill and burns then rise with smoke and deposited on food surface use lower-fat meat and a layer of aluminum foil to prevent fat from dripping on coals Heterocyclic amines (HCAs): produced by burning of substances in meats precook meat, marinate meat before cooking, cook at lower temperatures, reduce cooking time with smaller pieces of meat, avoid overcooking Genetically modified (GM) crops Gene (piece of DNA) for desired characteristic (for example disease resistance) is transferred from plant, animal, or bacterial cells into plant cells Creates recombinant DNA - a combination of DNA from two organisms Modified cells divide and differentiate into plant New plant is a transgenic organism Each cell in plant contains transferred gene Most common: soybeans, corn, rapeseed (canola) Growth of GM Crops Biotechnology for malnutrition For protein deficiency: corn, soybean, and sweet potato varieties with enhanced essential amino acids levels For vitamin A deficiency: genes for carotene synthesis enzymes inserted into rice To address multiple nutrient deficiencies: cassava with increased zinc, iron, protein, and vitamin A levels Biotechnology Concerns Nutrient content may be negatively affected Allergen or toxin may be introduced GM crops will be used to the exclusion of other varieties, reducing biodiversity which may reduce ability to adapt to new conditions, diseases, or other hazards GM crops may create “superweeds” GM crops producing pesticides may promote evolution of pesticide-resistant insects Labeling of GM Foods Not required to have special labeling unless: nutritional composition has been altered it contains potentially harmful allergens, toxins, pesticides, or herbicides, or new ingredients it has been changed significantly enough so that its traditional name no longer applies Premarket approval required if new food contains substance not commonly found in foods or without a history of safe use in foods