Chapter 16
The effluent exiting the activated sludge unit is much reduced in its total organic carbon (TOC) because much of the organic content of the water that entered the aeration tank is now retained in the settled floc that forms the secondary sludge. The reduction in organic carbon in the effluent is reflected in a reduction in the biochemical oxygen demand_____________________. BOD is the amount of dissolved oxygen required by microorganisms to decompose the organic matter in sewage or water. As you might expect, the BOD of raw sewage entering the treatment plant is relatively high. If treatment is effective, the BOD of the effluent should reflect the lower concentration of organic compounds and be relatively low. Incoming effluent from a slaughterhouse or a dairy could exert significant pressure on a treatment plant designed to handle only domestic sewage
(BOD) or biological oxygen demand
Wastewater, or sewage,
, is water carrying soluble or solid wastes originating from human activities, including farming and manufacturing. Household or domestic wastewater, consists of toilet waste, bathing water, cooking wastes, laundry wastes, and other waste products originating from everyday living. In addition, surface runoff, or storm water, from urban streets is often treated before it is allowed to enter water reservoirs. In urban centers, wastewater treatment plants help to minimize the amounts of contaminating material from urban centers entering the source water.
A wastewater treatment plant is designed to achieve several goals before the outflow, or effluent, of cleaned wastewater exits the plant and is discharged into the receiving water, such as a lake or stream. These goals include:
-A reduction in the total organic carbon (TOC) of the wastewater. -The removal or inactivation of any harmful microbes in the wastewater. -A reduction in the level of inorganic nutrients, which are nitrogen- and phosphorus-containing compounds, such as ammonium (NH4+), nitrate (NO3−), and phosphates.
Typically agents of foodborne illness target the: 1. nervous system 2. gastrointestinal tract 3. respiratory system 4. musculoskeletal system
. gastrointestinal tract
What are three methods to avoid phage infection of starter cultures
1)Good manufacturing practices, such as aseptic technique, are particularly important, especially during starter culture production. Second is the use of media that are not conducive to phage infection. 2)LAB bacteriophages need calcium ions (Ca2+) to adsorb to their hosts; accordingly, low-calcium phage-inhibitory media are used to grow the bacteria. 3)A third method is to employ strain rotation, which takes advantage of the fact that bacteriophages are often strain-specific. Multiple strains of bacteria that can fulfill the same role in starter culture function are rotated into and out of the mix so that an accumulation of phages that can infect a particular bacterial strain does not occur.
How do we treat wastewater? Wastewater treatment is a multistep process:
1. Pre-treatment: Physical removal of large objects 2. Primary treatment: Physical removal of sediments and grease that form primary sludge 3. Secondary treatment: Uses trickling filter/activated sludge unit to form complex biofilms that break down organic compounds over time 4. Tertiary treatment: Not always used; filtration method 5. Disinfection: Chlorination, UV light exposure, or ozonation
The different tastes of fermented products are a result of different metabolic end products. 1. True 2. False
1. True
Modified atmosphere packaging (MAP) helps to preserve food by: 1. removing oxygen from the atmosphere 2. removing water vapor from the atmosphere 3. removing carbon dioxide from the atmosphere 4. all of these choices
1. removing oxygen from the atmosphere
Pasteurized products such as milk are sterile. 1. True 2. False
2. False
Secondary Sludge
A slimy mixture of bacteria-laden solids that settles out from sewage wastewater during secondary treatment.
Hurdle Technology Steps:
A. When used independently, each antimicrobial hurdle must be of sufficient intensity to inhibit microbial growth, represented by the dashed line. Thorough cooking, salting or dehydration, or pickling can each prevent microbial growth but significantly alters the food. B. Reducing the intensity of the hurdle is desirable to maintain food freshness but does not sufficiently inhibit growth when each is used independently. C. When hurdles are used together, they sufficiently inhibit microbial activity enough to allow lowering of the intensity of the preservation treatment and thereby maintain food freshness.
activated sludge system
Activated sludge systems are used for municipal wastewater treatment plants. An activated sludge process relies on the formation of flocs—clumps of biomass consisting of adsorbed material and biofilm microorganisms. Activated sludge is comprised of accumulated flocs, the formation of which is critical to efficient function of the activated sludge unit. The word "activated" refers to the effect that the perfusion of oxygen throughout the otherwise thick and oxygen-free mixture has on the resident microorganisms in the sludge.
Fermentation of milk products
An amazing array of microorganisms, and variants on metabolic pathways, contribute to food fermentations, and the exact biochemistry that is taking place in each of the thousands of fermented products found globally is still not completely known. However, we are aware of some of the main metabolic pathways and groups of microorganisms involved.
Chemical preservatives can also be used to prevent food spoilage (often by reducing pH).:• Artificial preservatives include:
Artificial preservatives include: • Sodium benzoate • Proprionate • Sorbates • Sulfur dioxide • Nitrites
bacteriocins (nisin)
Bacteriocins are small proteins that do not affect the organisms that produce them, but exert a negative effect on other closely related bacteria
Pasteurization of milk
Batch method Flash pasteurization Ultrahigh-temperature pasteurization
Disinfection
Chlorination, UV light exposure, or ozonation
Effluent disinfection
Disinfection is the last step in wastewater treatment. Disinfection of water relies on the addition of chemicals to inactivate infectious agents that may be present. The aim of disinfection is to kill bacteria and viruses that normally reside in the intestinal tract and that can be present in feces-contaminated water, but were not eliminated in previous stages of treatment. A simple method of disinfection is chlorination. The water is dosed with a hypochlorite solution, either Ca(OCl)2 or NaOCl (bleach). Adding hypochlorite to water forms hypochlorous acID
The hurdle technology concept
Each constraint applied is a hurdle the microorganism must overcome in order to proliferate.
Drinking water purification
Ensuring a supply of clean drinking water includes selecting the best available source, such as a river, lake, or aquifer, and protecting that source from contamination. Although microbial numbers can be reduced significantly in a well-operated water treatment plant using conventional wastewater treatment technologies, microbes still remain in the effluent. These microbes are introduced into the receiving water when the effluent is discharged from the plant. Drinking water sources may also be contaminated by wild or domestic animals that discharge potential pathogens into a river, lake, or stream. For these reasons, water is often purified before it is made available to citizens for drinking.
Irradiation of food
Exposing food to radiation, termed irradiation, has been recognized for decades as an effective way to reduce the number of microorganisms on the surface of or, to a limited extent, within fresh food products.
What is the downside for freezing your food?
Extending storage by freezing is possible for some foods, although not all. Ice crystal formation during the freeze-thaw process can damage food tissue, producing a mushy thawed product that bears little resemblance or taste to the original fresh material. -Apples and citrus fruits, for example, undergo this transformation after freezing. A typical home freezer operates at about −20°C, below the temperatures that permit most microbial growth. In addition, aw is reduced by the conversion of liquid water to ice crystals. It is important to monitor how long frozen food has been stored, because the cold, dry atmosphere of the freezer will lead to physical defects such as freezer burn. Moreover, some slow microbial growth may be possible in small pockets of fluid that do not freeze because of their high-solute content. Frozen foods will remain unspoiled for months, but not indefinitely.
Fermenting with mold
Extensively used in Asia • Miso = Fermented soybean paste • Tempeh = Fermented soybean • Soy sauce • Sake
• How are microorganisms used in food production?
Fermentation can be used to produce a number of different types of foods. • Often well-characterized starter cultures of microbes are added to food to begin the fermentation process. • The process is monitored and controlled for a desirable outcome of flavors and textures. • Many foods are produced in this way
Botulism
Foodborne intoxication resulting in flaccid paralysis that occurs when botulinum toxin produced by Clostridium botulinum is ingested
The high-tech method of making vinegar uses a submerged culture technology with a bioreactor called the_______________, a far more efficient semicontinuous operation that produces product in 24-48 hours under highly controlled conditions. depicts the_______________________of vinegar production, a "medium-tech" approach that employs acetic acid bacterial biofilms growing on an inert support material such as beech wood chips or birch twigs.
Frings Acetator Quick or Trickle method
Why do fruits have more mold than veggies?
Fruits are typically more acidic than vegetables. Because of this, mold spoilage is more common on fruit. The slower-growing fungi are generally more tolerant of lower pH and can grow on fruits that are too acidic to support bacterial growth. For example, lemons spoil extremely slowly, but will eventually be covered by mold if abandoned in the refrigerator. Faster-growing bacteria out-compete molds at near neutral pH, as found in many vegetables.
What did Louis Pastur find in his experiments?
He found that mild heating could prevent souring without greatly affecting the flavor of the wine. His success was primarily due to killing the majority of alcohol-metabolizing acetic acid bacteria and other spoilage microorganisms in the wine. Today, pasteurization uses a variety of techniques to destroy microorganisms, without cooking the food product. Pasteurization processes include heating, irradiation, or applying high pressure.
Likelihood of spoilage is related to ________________ (food properties) and __________________(storage environment) factors.
Intrinsic factors Extrinsic factors
_______________________relate to characteristics of the food itself such as its nutrient content or pH. These also include structures that protect the food from microbial invasion, such as rinds or shells. We simulate that protection when we wrap our foods in plastic to protect it from spoilage. __________________ relate to the conditions under which a food is stored. For example, cold temperatures in a refrigerator will slow the growth of human pathogens that grow best in warmer temperatures of the body.
Intrinsic factors Extrinsic factors
_______________is of considerable benefit in the handling of raw meats, especially hamburger and poultry, to eliminate foodborne pathogens such as Escherichia coli O157:H7, Salmonella, and Campylobacter. These have been the cause of several large and infamous outbreaks of illness usually related to undercooking of raw meat
Irradiation
Increase in acidity of food
Microbial spoilage occurs most readily in a pH ranging from 6 to 8, where many microorganisms prefer to grow. Food is preserved from spoilage if the pH can be made more acidic or more alkaline without impairing the food's appeal. Humans ingest very few alkaline foods due to their bitter taste; egg white is one such alkaline food
This strategy is employed in _______________________, or vacuum packaging. MAP is frequently coupled with refrigerated storage. In vacuum-packed foods, microbial respiration and respiratory activity of fresh vegetables and fruits leads to O2 depletion and carbon dioxide (CO2) accumulation within the sealed package. One example of MAP, used for products such as cured luncheon meats or wieners, uses relatively impermeable plastic pouches, which are then evacuated and sealed.
Modified-atmosphere packing (MAP)
4. Tertiary treatment:
Not always used; filtration method
low-temperature hold (LTH)
Pasteurization method that heats a large volume of liquid to a low temperature (at least 62.8°C) for a long period of time (30 minutes or more)
Flash heating
Pasteurization method that heats a small volume of liquid to a very high temperature (at least 72°C) for a short period of time (15 s or less); includes high-temperature-short-time (HTST) and ultra-high-temperature (UHT) processes
Such growth does not necessarily lead to unsafe food, but most consumers consider such food to be unpalatable or unattractive and refer to it as spoiled. ___________________can easily support the growth of microorganisms. These include many fresh foods such as green salad ingredients or fresh meat. ____________________, such as nuts or potatoes are not likely to spoil as quickly. Foods that cannot support microbial growth, often because they lack available water, are called ________________________ and they may remain edible for long periods of time, even years. Examples of these foods include flour, sugar, and dried beans.
Perishable foods Semi-perishable foods non-perishable foods,
Where can you find microbs that spoil fruits and veggies?
Potential spoiler microorganisms must have access to a food item. Microorganisms that spoil fruits and vegetables are often found in soil; such foods are unlikely to be spoiled by intestinal microorganisms. However, fresh produce can sometimes be contaminated with incorrectly treated manure that has been used as fertilizer in the field or untreated rinse water containing intestinal pathogens from sewage. It is not unusual to find intestinal inhabitants on poultry or fresh meats. Their source is typically the carcass from which the tissue has been derived, or other animals nearby in the feedlot, farm, or slaughterhouse. Workers and airborne dust within food-processing plants are additional sources of microorganisms that can contaminate and spoil foods.
Non-ionizing radiation (UV light)
Radiation of wavelength longer than 240 nm that does not possess sufficient energy to produce ions in solution; non-ionizing UV radiation of wavelength 240-280 nm can damage DNA
Reduction of the water activity (aw) of food
Reduction of water activity can be achieved by drying food out or by adding solutes (sugar/salt)
3. Secondary treatment: Uses trickling filter/activated sludge unit to form complex biofilms that break down organic compounds over time
Secondary treatment of wastewater follows primary treatment and makes use of microbial activities to degrade the organic content of the sewage, further improving the quality of the wastewater. The two main strategies for secondary treatment include the "trickling filter" and the "activated sludge" process. A particular plant will likely employ either trickling filters or an activated sludge system, but not both. Trickling filters and activated sludge units contain communities of microorganisms that would be found in natural waters, but these populations are far denser and break down waste much faster under the conditions provided in the treatment plant.
Process Diagram: Steps in cheese making
Starter cultures are added to pasteurized, homogenized milk to induce acid production, but they also impart flavor, aroma, and texture. Acid production coagulates milk protein and forms curds. Addition of citric acid or rennin facilitates coagulation. For loose cheeses, the curds and liquid whey are mixed together, ready for consumption. For creamy and hard cheeses, the curds are separated from whey and pressed. Ripened cheeses are aged by storage, allowing microbial growth to continue. Unripened creamy cheeses are not aged.
Quick or Trickle method of vinegar production
The ethanol-containing liquid is introduced onto a bed of inert support material such as wood twigs or shavings. As the fluid passes through the bed by gravity, the adherent biofilm of acetic acid bacteria metabolizes the ethanol to acetic acid. Air is constantly diffusing up through the bed to ensure the bacteria have sufficient oxygen. The acidic liquid drips through the grate at the bottom and is recirculated as necessary to obtain a 4 percent minimum acetic acid concentration. The process requires approximately 4-5 days.
What is the first stage of soy sauce production? The first stage is called a koji fermentation.
The first stage is called a koji fermentation. Koji refers to various cultivated molds used in making fermentation products, such as soy sauce, miso, and sake or rice wine. The seed koji mold contains a mixture of strains pregrown on a similar substrate to produce enough fungal mass to mix into the soybean-wheat mix. For soy sauce, a mixture of soaked, steamed soybeans and roasted cracked wheat (in a ratio of about 1:1) is inoculated with spores of the aerobic mold Aspergillus oryzae, or Aspergillus sojae, and spread in layers about 5 cm deep. Over 2-3 days, the mold grows throughout the solid substrate, producing the extracellular proteases and amylases it requires to hydrolyze the macromolecular material in the substrate. The distinctive flavor of soy sauce comes from the amino acids that are released from the hydrolyzed soybean proteins.
1. Pre-treatment: Physical removal of large objects
The pretreatment step of wastewater treatment sends incoming material through a series of grates and coarse metal screens to ensure that large objects such as branches, stones, or pieces of metal that might damage or clog plant equipment are removed from the incoming wastewater. Screening of the incoming wastewater also removes much of the gravel and grit that may be present, particularly if the plant is treating waste from combined sewers. Solid debris is collected by periodically scraping the grates and screens and is frequently deposited in landfills.
Process Diagram: General schematic of drinking water purification
Untreated water may be screened to remove large objects before it enters the flocculation tank. A chemical such as alum is added to promote floc formation. The floc-laden water moves to a sedimentation tank where the floc settles as sludge, which is removed and treated, similar to that for a wastewater treatment plant. The clarified water is filtered through thick layers of sand, activated charcoal, or other specific filtration media. Filtered water is disinfected and stored, ready for distribution.
activated sludge system
a process used in secondary sewage treatment in which batches of sewage are held in highly aerated tanks; to ensure the presence of microbes efficient in degrading sewage, each batch is inoculated with portions of sludge from a precious batch
. The starting material is some type of alcoholic solution metabolized by bacteria belonging to a group known as the "____________________," to produce acetic acid. Diluted pure ethanol is used for distilled or white vinegar; wines (from grapes in Europe, rice in Asia), fruit ciders, and malt liquors are other starting materials.
acetic acid bacteria
• Methods vary in efficiency. • Trickle/Quick method uses _______________ growing on inert support material for fermentation.
acetic acid bacteria
A foodborne intoxication
an illness caused by toxins that an organism has produced in a food; toxins may also be produced by chemicals, heavy metals, or other substances
Enterotoxins, mentioned
are secreted microbial toxins that cause or contribute to the intestinal symptoms in affected individuals. This frequently occurs because enterotoxin action stimulates water and electrolyte release from the cells lining the gut, resulting in diarrhea and dehydration. "Oral rehydration therapy" (ORT), which increases fluid intake by mouth as opposed to intravenously, may be an effective means of combating these effects. O
Outbreaks of foodborne or waterborne illness are known as "_______________ as the incidence pattern typically reflects the fact that many people are exposed to the causative agent and become ill at about the same time from the same source (
common source outbreaks"
In __________________, which is also known as _________________ the food is first frozen and then dried under a vacuum, often with subsequent storage in watertight packaging. The process is expensive but efficient and can be useful for special purposes. Freeze-dried foods are compact and lightweight, making them convenient for transport. Campers often carry freeze-dried food in a backpack and add water on site to rehydrate it before consumption.
freeze-drying lyophilization,
Indeed, if MAP technology is used with foods where the presence of C. botulinum is possible, then additional preservative methods must also be applied. This is an example of ____________________ which employs multiple constraints or "hurdles," each of which the microorganism in question must overcome in order to proliferate
hurdle technology,
Before water is released for drinking, it is tested to ensure its purity. Public health drinking water standards state that drinking water should be entirely free from pathogenic microorganisms. However, routine examination of water for the presence of all human pathogens would be a time-consuming, difficult, and expensive task. Microbiologists do not test for every potential pathogen that might remain in the water but instead use a presumptive test for___________________. These are microorganisms whose presence in a water sample indicates the possible presence of fecal matter, and thereby potential pathogens. Because many pathogens associated with drinking water are of fecal origin, having been introduced by sewage, bacteriological tests are designed to detect the indicator organisms called fecal coliforms—a group of bacteria found in the intestinal tract of humans and other animals. ______________________ are a subset of coliforms, which are Gram-negative, non-spore-forming, facultative anaerobic bacilli belonging to family Enterobacteriaceae. The most numerous fecal coliform bacterium in intestines is E. coli, although it only constitutes about 1 percent of microbes present in the human intestine.
indicator organisms Fecal coliforms
Nitrites
inhibits some spoilage microorganisms, as well as C. botulinum and other gas-producing clostridia. Sodium nitrite also stabilizes the red color of cured meats and contributes to flavor development. Nitrite seems to exert its inhibitory effect by interfering with cellular respiration by targeting nonheme iron-sulfur proteins, such as ferredoxin, in susceptible microorganisms
• Food contaminated with microbes can cause illness • Usually referred to as foodborne __________________ • Due to microbial toxins in food • May be due to actual microbes in food (referred to as a foodborne ______________________)
intoxication infection
What is the first stage of soy sauce production? The second stage in the production of soy sauce, known as the moromi fermentation or mash stage
involves addition of salt water (brine) and depletion of available oxygen by sealing the mash in air-tight vats to prevent further mold growth. The mold-derived enzymes continue to hydrolyze proteins, polysaccharides, and nucleic acids in the mash to produce a liquid rich in soluble nutrients. This now enables associated halophilic LAB and osmophilic yeasts to use the released nutrients to carry out lactic acid and ethanol fermentation. Fermentation continues for several months at 35-40°C in the sealed containers. Thereafter, the moromi mash is pressed to collect the liquid phase, which is pasteurized and may be filtered and aged in casks before bottling. The end product contains up to 2 percent ethanol, lactic acid (pH 4.8), and salt (18 percent), all of which inhibit growth of microbial contaminants.
Radiation harmful to microbes includes ___________________ and non-ionizing radiation. Ionizing radiation refers to radiation of short wavelength with sufficient energy to remove electrons from molecules in a medium, producing ions. In cells, ionizing radiation produces oxidative damage and toxic free radical generation, all of which directly or indirectly damage nucleic acid. Ionizing radiation in the form of X-rays or gamma rays can be used to pasteurize or even sterilize foods, particularly in regions where refrigeration is not widely available.
ionizing radiation non-ionizing radiation.
Vinegar is also used in
is also used in the food industry as a pH control agent, as a preservative, and as a flavoring agent
Acetic Acid (Vinegar)
is one of several weak organic acids used as food preservatives. In 1908, sodium benzoate was the first chemical food preservative permitted by the U.S. Food and Drug Administration (FDA). Propionates and sorbates have also been used in some types of food for decades. All of these acids have "generally recognized as safe" (GRAS) status awarded by the FDA, permitting their widespread use
trickling filter
is that it is simple and relatively passive in operation, making it inexpensive to run. Trickling filters are used for municipal and on-site wastewater treatment, such as for farms and industrial plants. It consists of a bed of solid material, such as crushed rock, or special molded plastic units that are contained in a cement tank. Effluent from primary treatment is pumped to a rotary spray boom that sprays the effluent across the filter bed surface. The fluid percolates through the bed by gravity, then collects beneath. As the fluid trickles downward, it serves as a source of substrates for a complex microbial biofilm community growing on the bed matrix. T
The ____________________is extended, and more time will pass before the microorganisms reach exponential phase. Certain preservation methods, such as heat processing, can also reduce or even eliminate the microbial load on foods. Other preservation practices aim to produce conditions that are not optimal for microbial growth by manipulating either intrinsic factors, such as pH, or extrinsic parameters, such as storage temperature
lag phase
The________________ at the beginning of the growth cycle, when organism numbers remain fairly constant, and the exponential phase, during which the number of living organisms doubles in a given time, are most critical to determining microbial spoilage . Often a product is already noticeably spoiled before growth stabilizes in the stationary phase. By extending the lag phase or reducing the rate of microbial growth, a product's shelf life can be extended.
lag phase
trickling filter
like activated sludge process, but slower
The original process of milk pasteurization involved heating milk in batches to a temperature of at least 62.8°C and holding it there for 30 minutes. This is termed the ______________________method . Modern dairies often use ______________________,which forces a small volume of milk between metal plates or pipes heated to very high temperatures (Figure 16.7). Small volumes reach the required temperatures much more quickly and evenly than large volumes.
low-temperature hold (LTH) flash-heating,
2. Primary treatment: Physical removal of sediments and grease that form primary sludge
of wastewater involves the physical removal of particulate matter by sedimentation, and oils by skimming. Pretreated wastewater flows into large tanks where it is typically retained for several hours to separate these materials. Oil and grease and any material less dense than the water float to the surface and are removed by skimmers. Suspended materials that are denser than the water fall to the bottom of the tank and are removed by a raking apparatus that scrapes the material from the tank bottom into a hopper, forming the primary sludge, which is collected and then pumped to the ANAEROBIC SLUDGE DIGESTER. The digester processes this waste under anoxic conditions and will be described later. About 40-60 percent of the suspended solids are removed during sedimentation, along with the microbes that adhere to the particles. However, not all microbes are removed, nor are dissolved organic and inorganic compounds. The effluent derived from the primary treatment step is further subjected to secondary treatment.
Tertiary treatment: Not always used; filtration method
of wastewater, which is rarely used, employs additional biological or physicochemical protocols to effluent water prior to disinfection. Modern technologies exist that will permit the production of very clean effluents, but they are quite costly and not widely implemented. The techniques typically involve some types of physicochemical processes, including filtration, activated carbon adsorption, reverse osmosis or additional disinfection or coagulation protocols. The targets are the same as in the primary and secondary treatments, but tertiary treatment seeks to further reduce pollutant levels. Reduction of one or more waste products may be targeted: the organic content, turbidity, N or P content, metal concentration, or pathogen levels.
Heat can affect the flavor or texture of some food products adversely, making them unsuitable for high-heat processing. Heat processing, or ____________________, was developed by Louis Pasteur to avoid such problems. Pasteur's original goal was to develop a process to prevent wine from souring without causing irreparable damage to the wine from heat.
pasteurization
Some of these chemicals, such as synthetic pesticides and pharmaceutical drugs excreted in urine, are difficult to break down and are referred to by the acronym POP, which stands for__________________. If present in wastewater, certain of these organics may be found in effluents exiting the plant. They may also be detected in natural waters. The concentrations are typically very low, and the significance of POPs in natural waters is uncertain. Evidence is becoming clear that even vanishingly small quantities of some POPs may affect reproduction and development of fish and mammals because they tend to accumulate in tissues.
persistent organic pollutant
We don't seem to mind acidity, however, and perceive it as tartness. However, too much acid in a food can be perceived as sour. In a process known as _____________, the pH of a food can be reduced by storing or marinating it in a chemical such as dilute acetic acid (vinegar), or by allowing lactic or acetic acid production to occur naturally through microbial fermentation.
pickling
foodborne intoxication
refers to illness caused by ingestion of microbial exotoxins as is the case with S. aureus food poisoning. Toxins produced by microorganisms may be present in food even though the organisms that produced them are no longer present when the contaminated food is eaten. Generally in foodborne intoxication, the microorganisms themselves may be harmless, and ingestion of the cells alone may be safe; it is the toxin that they produce that causes illness.
ionizing radiation
refers to radiation of short wavelength with sufficient energy to remove electrons from molecules in a medium, producing ions. In cells, ionizing radiation produces oxidative damage and toxic free radical generation, all of which directly or indirectly damage nucleic acid. Ionizing radiation in the form of X-rays or gamma rays can be used to pasteurize or even sterilize foods, particularly in regions where refrigeration is not widely available.
foodborne infection
requires consumption of the organisms themselves. When these living pathogens are ingested, they actively multiply within the body, typically in the small or large intestine. In the body, these organisms may also produce a toxin that initiates symptoms when the level becomes high enough. Symptoms of food infections typically do not appear immediately as the organisms will enter a lag phase of growth before showing the exponential increase causing illness.
After being held for a suitable time in the aeration tank, the floc-laden____________________Is pumped to the settling tank, where a rapid settling of floc is desirable to separate the sludge from clarified effluent. The clarified effluent is next sent to the disinfection process to kill remaining microbes. Part of the settled floc is used as a starter culture and is recycled to inoculate the next volume of incoming effluent in the aeration tank.
secondary sludge
The concept of a ___________________was established in these early societies. Starter cultures are preparations of microorganisms that are added to food to aid in the production of fermented products. For example, taking leftover dough from a previous bread-making session and adding it to a new dough ensures that bread will rise. In today's industrialized age we have numerous other food preservation strategies from which to choose, yet fermented foods continue to be very popular worldwide because their diverse sensory properties add variety to the diet.
starter culture or inoculum
Chemical preservatives can also be used to prevent food spoilage (often by reducing pH).Natural antimicrobial preservatives include:
• Bacteriocins (nisin) • Lactic acid • Acetic acid (vinegar)
Control of temperature
• Cooling or heating can be used (pasteurization) • Usually cheap and highly effective • May be combined with pressure to eliminate endospores (canning) • May alter taste or texture of food, though
Secondary treatment: activated sludge systems
• Depends on formation of flocs: • Clumps of biomass of adsorbed material and biofilm microbes • Aeration tank mechanically mixes sludge. • Settling tank/clarifier collects sludge to remove it from the effluent.
Semi-perishable foods
• Don't spoil as quickly • Nuts, potatoes
Perishable foods
• Easily support microbe growth • Green salad items, fresh meat
Fermentation of milk products
• Lactic acid bacteria (LAB) are used to produce: • Cheese • Yogurt
Secondary treatment: anaerobic sludge digester
• Last step in secondary treatment. • Digests remaining organic wastes in anaerobic processes by microbes: -Can take 2 to 4 weeks to break down sludge -Can operate in mesophilic mode (35 to 37° C) or thermophilic mode (50° C, speeding up reactions) • Biosolid material (undigestible) is dehydrated/incinerated or used as fertilizer.
Irradiation of food o This does not cause food to become radioactive itself. o Strength of microbe elimination depends on type of radiation (but all cause damage to microbe DNA).
• Non-ionizing radiation (UV): Surface level only, not strong • Ionizing radiation (gamma/X-rays): Stronger, more penetrating
What about water quality? • Water covers much of the Earth, but.....
• Only about 3% is freshwater. • Not all of that 3% is in a form ready to be consumed. • Waste can build up and run off into water (sewage).
Increasing the acidity
• Pickling places foods in vinegar or allows fermentation to naturally drop the pH over time. • Many microbes cannot grow (or die) in a low-pH environment.
Vinegar manufacture
• Produced by fermentation of ethanol by acetic acid bacteria into acetic acid: • The source of the ethanol can imbue different flavors to different vinegars
Goals for treating wastewater (sewage)
• Reducing total organic carbon (TOC) • Removal or inactivation of harmful microbes in wastewater • Reduction of inorganic compounds (especially ammonium, nitrogen, and phosphorus levels) to prevent eutrophication of natural waters • A newer goal is to reduce persistent organic pollutant (POP) levels. - These compounds, even in low levels, may affect fish and mammal reproduction and development
How can we minimize food spoilage?
• Reduction of water activity (aw) of food • Control of temperature • Increase in acidity of food • Addition of chemical preservatives • Irradiation of food • Use of modified-atmosphere packaging (MAP) • Hurdle technology
non-perishable foods
• Remain edible for long periods • Flour, sugar, dried beans
Drinking water purification
• Screening removes large objects. • Flocculation, sedimentation, and sludge treatment are similar to wastewater treatment steps. • Filtration removes many microbes from the water. • Disinfection steps destroy remaining microbes. • Water is usually tested for indicator organisms (likely to cause disease) such as fecal coliforms prior to release. - May be tested through the most probable number (MPN) or biochemical identification methodologies
Secondary treatment: trickling filter
• These are simple, passive, and inexpensive. • Crushed material is used as a base support for a growing biofilm of microbes. • As the material trickles across the surface of the support, the biofilm uses it as a food source.
What is hurdle technology?
• Using multiple levels of antimicrobial control in food. • The levels often work synergistically, giving better overall protection than a single method alone
Modified-atmosphere packing (MAP)
• Vacuum packing takes oxygen out of the package. • Many microbes need oxygen to survive and multiply. -Sometimes, packaging is also flooded with CO2 to achieve the same effect. • Red meat may be packed in a high-oxygen environment to reduce growth of harmful anaerobic microbes and keep the meat a desirable red color.