Personal hygiene and hand washing for food production and foodservice personnel. Each day, a few people coming to work are potential spreaders of pathogenic microorganisms, even though they seemingly have no illness symptoms.
The main threat of transfer of these pathogens is in salad / cold food preparation. This problem exists because these menu items are composed of many ingredients that are not cooked or heated sufficiently to inactivate pathogenic microorganisms and are not held at temperatures that prevent the multiplication of pathogens (62, 123).
To prevent transfer of pathogenic bacteria and viruses, employees should be banned from carrying all forms of nose wipes in order to prevent inadvertent contamination of hands. If employees must blow their noses, they must be trained to go to the hand washing sink, get a facial tissue, and use it to wipe or blow the nose. After discarding the facial tissue, employees should then wash their hands using the single hand wash method. If employees need to sneeze or cough, they should step back from the food preparation area and sneeze into their shoulder.
When employees have cuts or infections on their hands, the cut or infection must be cleaned; bandaged, if necessary; and covered with a glove. The glove is used to keep the bandage on the hand and prevent it from falling into food, not to control the infection, since the cut will have been verified by the supervisor as not infected. The glove must be changed as often as hand washing is necessary for safe food preparation. The use of the glove should be discontinued as soon as a scab is formed and the cut does not bleed, since the glove provides no added safety, just protection of the scab.
Food handlers should stay home when they are ill, especially with diarrhea, but they do not. It is the responsibility of the supervisor to watch for people who are using the toilet frequently. If these individuals seem ill, they should be asked if they are sick and if so, sent home.
The only real control for safe hands is to assume that every employee is ill and require that all employees use adequate methods for washing fingertips and hands in order to control the hazard of pathogen (viruses, bacteria, and parasites) transfer.
Hand washing. There are as many as 109 Salmonella per gram in the feces of people carrying this pathogen (141). If the toilet paper slips just a little, infected individuals may easily get 0.001 gram feces or 106 pathogens on their fingertips. Without reduction of these pathogens to a safe level on hands and fingertips, the food, particularly salads, handled by food preparers can become hazardous and make consumers ill. The following double hand / fingertip wash procedure has been shown in a laboratory study by Snyder (173) to reduce pathogens 10-6.
0.98 aw and above: Fresh meats and fish; Fresh
fruits and vegetables; Milk and other beverages; Canned vegetables in brine;
Canned fruit in light syrup
These are very moist foods, including those containing less than 3.5% sodium chloride or 26% sucrose in the aqueous (water) phase. Foodborne pathogenic bacteria and common spoilage microorganisms (bacteria, yeasts, and molds), with the exception of extreme xerophiles and halophiles, grow almost unimpeded at levels of aw within this range.
Below 0.98 to 0.93 aw: Evaporated milk; Tomato
paste; Lightly salted fish, pork, beef products; Canned cured meats; Fermented
sausages (not dried); Cooked sausages; Processed cheese; Gouda cheese;
Canned fruits in heavy syrup; Bread; High moisture prunes
Maximum concentration of salt or sugar in the aqueous phase of the foods will be near 10% and 50% respectively. All known foodborne pathogenic bacteria can grow in the upper part of this range.
Below 0.93 to 0.85 aw: Dry or fermented sausage
(Hungarian, Italian types); Dried beef; Raw ham; Aged cheddar cheese; Sweetened
This group includes foods up to 17% salt or saturated sucrose in the aqueous phase. Only one bacterial pathogen, Staphylococcus aureus, can grow in this aw range. However, many molds that produce mycotoxins can grow in this range.
Below 0.85 to 60 aw: Intermediate moisture food;
Dried fruit; flour; Cereals; Jams and jellies; Molasses; Heavily salted
fish; Meat extracts; Some aged cheeses; Nuts
No pathogenic bacteria grow within this range. However, spoilage can occur from growth of xerophilic, osmophilic, or halophilic yeasts and molds.
Below 0.60 aw: Confectionery; Chocolate; Honey;
Noodles; Biscuits; Crackers; Potato chips; Dried eggs, milk, and vegetables
Microorganisms do not multiply below 0.60 aw, but can remain viable for long periods of time.
It is much more difficult
to inactivate these surviving microorganisms in lower-water-activity foods,
starch-thickened sauces, and desserts containing substantial amounts of
sugar. Higher temperatures for longer periods of time are required
to ensure destruction. A practical application of this knowledge
is to add sugar and salt to a food product only when it has reached the
pasteurization temperature of 165°F (73.9°C), because the salt
and sugar will reduce the water activity (aw) and make it more
difficult to inactivate microorganisms, depending on how much salt or sugar
Nutrients and acids (pH). When the supply of nutrients is low or not optimum, the multiplication of microorganisms is slower, and the population declines.
The incorporation of common food ingredients such as lemon juice, vinegar, or wine, which lower the pH of food products, also contributes to the destruction of microorganisms. If the pH is less than 4.6, the food will be safe from C. botulinum multiplication. However, Salmonella will multiply down to 4.1 pH. It is assumed in the preparation of salad dressing and mayonnaise that ingredients such as the egg yolks are contaminated with Salmonella spp.; therefore, they are normally to be manufactured with a pH of 3.8 or less. This is an acetic acid concentration of less than 1.4%. At this pH, the salmonellae not only do not multiply, they actually die in a period of 5 minutes to a few hours at room temperature (167). Tomatoes, raw or cut up at a pH of 4.2 to 4.4, may be contaminated with Salmonella and must be maintained at a temperature of less than 50°F (10.0°C) to assure that the Salmonella does not multiply (9, 201). Snyder (206) has found that in common fat sauces such as mayonnaise, Hollandaise, and Béarnaise, which include egg yolks for emulsion, incorporating 1 tablespoon of vinegar or lemon juice per egg yolk gives a safe pH below 4.1.
Preservatives. Some retail food operations make their own products such as sausage, which entails the addition of preservatives such as nitrite. This should be done in accordance with USDA regulations. Chemical compounds added to food as preservatives in the United States must be added at levels that are GRAS (Generally Recognized As Safe) (29, 30, 31). Common preservatives include nitrites used to prevent growth of C. botulinum in meat, butylated hydroxyanisol (BHA) and butylated hydroxytoluene (BHT) used to prevent oxidation of lipids, and sulfites to preserve color in dried fruits and vegetables. Used in correct amounts, these compounds can be safely added to food. Excessive addition can lead to illness (97). If preservatives are added to foods, food preparers must be taught to use acceptable amounts according to the Code of Federal Regulations (29, 30, 31).
Oxidation-Reduction. Redox potential is known to be an important selective factor in all environments, including food, and influences the types of microorganisms found in the food and their metabolism (90). The main application of this control is to inhibit or prevent the growth of C. botulinum in foods (specifically, to prevent growth of non-proteolytic types in fish, and proteolytic types in fruits and vegetables). If vegetables, some fruits, and pasteurized smoked fish are packaged anaerobically (at less than 2% oxygen concentration) and left at room temperature for 1 to 2 days, it has been shown that there is the likelihood of C. botulinum toxin production (25, 174). The control is to raise the oxygen level to more than 4% in the package by means of holes in the plastic package, or keep the food at less than 50°F (10.0°C) to prevent growth of proteolytic C. botulinum. It is important to realize that meat and fish can bind oxygen after the package is sealed, and vegetables (e.g., mushrooms) can metabolically convert O2 to CO2 to create anaerobic conditions. To prevent growth of nonproteolytic strains of C. botulinum, a temperature below 38°C must be maintained. Controlled atmosphere packaging lengthens shelf life by inhibiting the growth of anaerobic spoilage microorganisms.
Time and Temperature
Control - Safe Food Holding Times at Specified Temperatures
Pathogen growth during processing and food handling. Since the hazardous temperatures are 30ºF to 127.5ºF (-1.1ºC to 53.1ºC) [Phoenix phenomenon], and there is very little refrigerated food in the retail food sector stored below 41ºF (5.0ºC), time must be introduced to control the acceptable limits of growth during storage and processing in retail operations, or most refrigeration will need to be replaced.
A review of infective bacterial pathogen growth data shows that Y. enterocolitica and L. monocytogenes should be used as the low-temperature process design control organisms. They begin to multiply at 29.3ºF (-1.5ºC), as does Aeromonas hydrophila (88). They are the "organisms of choice" for control up to approximately 70°F (21.1°C) because of the severity of illness and speed of multiplication. Disease or illness caused by L. monocytogenes is estimated to be fatal about 27 to 28% of the time (93). The 1999 FDA Food Code (204) allows a 7-day holding at 41°F (5.0°C) and 4 days at 45°F (7.2°C). This time falls in between the growth rates of Y. enterocolitica and L. monocytogenes and will allow approximately 10 multiplications (1 microorganism becomes 1,024).
For temperatures ranging from 70 to 112°F (21.1 to 44.4°C), Salmonella spp. is the control choice pathogen, because it is commonly present in many foods and can cause serious illness. It multiplies about once every 25 minutes at 104°F (40.0°C) in Chinese barbecued chicken (145).
If the FDA's 4-hour food holding standard is applied at 112°F (44.4°C), this will allow the same 10 multiplications of a pathogen. From 112 to 126.1°F (44.4 to 52.3°C), the control microorganism of choice is C. perfringens. It multiplies every 8 to 15 minutes in the temperature range of 105 to 120°F (40.6 to 48.9°C) and is the pathogen that grows at the highest temperature, 126.1°F (52.3°C) (141). This sets the upper temperature growth limit at slightly less than 130°F (54.4°C). While vegetative cells of C. perfringens multiply rapidly, there is about a 2-hour lag for outgrowth of the spores. Two hours of lag and 10 multiplications again is compatible with allowing a 4-hour period of holding at the most dangerous temperature of about 110°F (43.3°C). Therefore, it seems prudent to establish the upper limit growth temperature based on the common pathogen C. perfringens as the high-temperature limit for controlling the growth of pathogenic foodborne illness bacteria.
Snyder (169, 171) has accumulated extensive data from scientific literature concerning the growth rates of pathogenic bacteria in food. Using this information, the growth rates of pathogenic bacteria can be predicted over the entire temperature range by using the formula of Ratkowsky et al. (147).
y = 0.032 (temp-(-2.924)) (1-Exp (0.444 (temp-52.553))).
Figure 5-1. Generation Time - FDA Food Code (Centigrade)
It will be noted that the
spoilage microorganisms multiply almost twice as fast as the predicted
FDA hazard control times over the range of 30 to 126.1°F (0 to 52.3°C).
The predicted Y. enterocolitica growth is slightly faster than the
FDA hazard control standard below 50°F (10°C). There is a
safety factor, because the infective dose for Y. enterocolitica
is quite high. Clostridium perfringens is controlled when
the lag is factored in. The FDA temperatures and times very safely
control all other pathogens, including C. botulinum.
In an actual kitchen or food production area, food does not remain at any one temperature for long. Therefore, the question becomes, "How long can food be left at other equivalent growth temperatures between 30 and 126.1°F (0 and 52.3°C)?" The formula can be used to calculate the times at specified temperatures. The results are shown in Table 5-1.
Utilizing the set of guidelines given in Table 5-1 allows the use of refrigeration units that exist in most retail food operations today. Most existing refrigeration units hold food between 40 and 55°F (4.4 and 12.8°C) during normal operations, because the doors are opened so often. Thus, the temperatures of many cold foods, such as those items found in salad bars, are at 50 to 55ºF (10 to 12.8ºC) (61, 123). Using the equivalent growth generation time calculated from the FDA data, for example, if freshly prepared food is placed on a salad bar at 10:00 a.m., held at 55°F (12.8°C) until 10:00 p.m. there would be less than the allowed 10 multiplications of pathogens, and the food will be safe for consumption during this time period. The food should be discarded at the end of this 12-hour holding period, because with overnight storage, there would not be enough "safe time" remaining for another day. This also points out the hazard of combining leftover cold, ready-to-eat foods with fresh products.
Similarly, within the rapid growth temperature range of 90 to 115ºF (32.2 to 46.1ºC), for which the generation time of pathogenic bacteria such as Salmonella spp. and S. aureus is once approximately every 24 minutes, there are about 4 hours of safe time. All buffet leftovers should be discarded at the end of 4-hour uncontrolled holding at 90 to 115°F (32.2 to 46.1°C).
What should be done about customer hot take-out food, when the food will often cool to 80 to 100°F (26.7 to 37.8°C) in less than 20 minutes after it is given to the customer? If the customer does not plan to eat the food for a couple of days, and if the food is refrigerated in less than 2 hours, at a depth no greater than 2 inches, the food will cool rapidly enough in a home refrigerator and will be safe to eat after a couple of days of 40°F (4.4°C) refrigerated holding. However, there is essentially no information in the research literature on this problem. More research must be done to define hazard controls more precisely for take-out food.
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