FDA食品微生物检验抽样与制样文档格式.docx

1、Chapter 1 Food Sampling and Preparationof Sample Homogenate Authors （Return to Table of Contents）The adequacy and condition of the sample or specimen received for examination are of primary importance. If samples are improperly collected and mishandled or are not representative of the sampled lot, t

2、he laboratory results will be meaningless. Because interpretations about a large consignment of food are based on a relatively small sample of the lot, established sampling procedures must be applied uniformly. A representative sample is essential when pathogens or toxins are sparsely distributed wi

3、thin the food or when disposal of a food shipment depends on the demonstrated bacterial content in relation to a legal standard. The number of units that comprise a representative sample from a designated lot of a food product must be statistically significant. The composition and nature of each lot

4、 affects the homogeneity and uniformity of the total sample mass. The proper statistical sampling procedure, according to whether the food is solid, semisolid, viscous, or liquid, must be determined by the collector at the time of sampling by using the Investigations Operation Manual （5）. Sampling a

5、nd sample plans are discussed in detail in ref. 6. Whenever possible, submit samples to the laboratory in the original unopened containers. If products are in bulk or in containers too large for submission to the laboratory, transfer representative portions to sterile containers under aseptic condit

6、ions. There can be no compromise in the use of sterile sampling equipment and the use of aseptic technique. Sterilize one-piece stainless steel spoons, forceps, spatulas, and scissors in an autoclave or dry-heat oven. Use of a propane torch or dipping the instrument in alcohol and igniting is danger

7、ous and may be inadequate for sterilizing equipment. Use containers that are clean, dry, leak-proof, wide-mouthed, sterile, and of a size suitable for samples of the product. Containers such as plastic jars or metal cans that are leak-proof may be hermetically sealed. Whenever possible, avoid glass

8、containers, which may break and contaminate the food product. For dry materials, use sterile metal boxes, cans, bags, or packets with suitable closures. Sterile plastic bags （for dry, unfrozen materials only） or plastic bottles are useful containers for line samples. Take care not to overfill bags o

9、r permit puncture by wire closure. Identify each sample unit （defined later） with a properly marked strip of masking tape. Do not use a felt pen on plastic because the ink might penetrate the container. Whenever possible, obtain at least 100 g for each sample unit. Submit open and closed controls of

10、 sterile containers with the sample. Deliver samples to the laboratory promptly with the original storage conditions maintained as nearly as possible. When collecting liquid samples, take an additional sample as a temperature control. Check the temperature of the control sample at the time of collec

11、tion and on receipt at the laboratory. Make a record for all samples of the times and dates of collection and of arrival at the laboratory. Dry or canned foods that are not perishable and are collected at ambient temperatures need not be refrigerated. Transport frozen or refrigerated products in app

12、roved insulated containers of rigid construction so that they will arrive at the laboratory unchanged. Collect frozen samples in pre-chilled containers. Place containers in a freezer long enough to chill them thoroughly. Keep frozen samples solidly frozen at all times. Cool refrigerated samples, exc

13、ept shellfish and shell stock, in ice at 0-4C and transport them in a sample chest with suitable refrigerant capable of maintaining the sample at 0-4C until arrival at the laboratory. Do not freeze refrigerated products. Unless otherwise specified, refrigerated samples should not be analyzed more th

14、an 36 h after collection. Special conditions apply to the collection and storage of shucked, unfrozen shellfish and shell stock （1）. Pack samples of shucked shellfish immediately in crushed ice （no temperature specified） until analyzed; keep shell stock above freezing but below 10C. Examine refriger

15、ated shellfish and shell stock within 6 h of collection but in no case more than 24 h after collection. Further details on sample handling and shipment may be found in the Investigations Operation Manual （5） and the Laboratory Procedures Manual （3）. The Investigations Operation Manual （5） contains s

16、ampling plans for various microorganisms. Some of those commonly used are presented here. A. Sampling plans1.Salmonella speciesa.Sample collectionBecause of the continuing occurrence of Salmonella in foods, sampling plans for these organisms have received the attention of committees of national and

17、international organizations （6,7）. Each of these committees has recommended varying the number of samples from a particular lot of food according to the sampling category to which a food is assigned. Generally, the assignment to a sampling or food category depends on 1） the sensitivity of the consum

18、er group （e.g., the aged, the infirm, and infants）; 2） the possibility that the food may have undergone a step lethal to Salmonella during the manufacturing process or in the home; and 3） the history of the food. The selection of a sampling plan depends mainly on the first 2 criteria cited. The hist

19、ory of the food would be important in deciding whether to sample, i.e., whether there was a past history of contamination. For the Salmonella sampling plan discussed here, 3 categories of foods are identified. Food Category I. - Foods that would not normally be subjected to a process lethal to Salmo

20、nella between the time of sampling and consumption and are intended for consumption by the aged, the infirm, and infants. Food Category II. - Foods that would not normally be subjected to a process lethal to Salmonella between the time of sampling and consumption. Food Category III. - Foods that wou

21、ld normally be subjected to a process lethal to Salmonella between the time of sampling and consumption. In certain instances, it may not be possible to fully conform to the sampling plan. Nonetheless it is still important to ascertain whether or not Salmonella is present in the suspect food. Theref

22、ore, the analyst should still try to analyze as many analytical units as is required for the food of interest, i.e., 60 analytical units for Category I foods, 30 analytical units for Category II foods, and 15 analytical units for Category III foods. Individual 25 g analytical units may be combined i

23、nto 375 g composites as described above unless otherwise indicated in Chapter 5 or the OMA. Below are examples of situations that might confront the analyst.1.1） The number and weights of the sample units is correct.Each sample should be mixed to ensure homogeneity before withdrawing a 25 g analytic

24、al unit. The analytical units can be composited （fifteen 25 g units into a 375 g composite）, unless otherwise indicated in Chapter 5 or in the OMA. Samples should be preenriched at a 1:9 sample-to-broth ratio.1.2） The number of sample units is correct, but several of the sample units have been damag

25、ed and are unusable.For example, fifteen 1 lb bags of pasta have arrived for testing, but 5 of the bags are torn and unusable. In this case, the analyst should only sample from the 10 intact bags. The contents of each intact bag should be mixed to ensure homogeneity before the analytical units are w

26、ithdrawn. Since the analyst needs one 375 g composite, ten 37.5 g analytical units, from the remaining 10 intact bags, should be used to form the composite. The composite should be combined with its preenrichment medium at a 1:9 sample-to-broth ratio （375 g sample/3375 ml preenrichment） as directed

27、in Chapter 5 or the OMA.1.3） The number of sample units is incorrect, but the total weight of the sample unit（s） is greater than what would be necessary to perform the sample analysis.For example, a single 10 lb wheel of cheese has arrived for testing. Since cheese is a Category II food, thirty 25 g

28、 analytical units must be analyzed. These analytical units should be taken randomly from a wide variety of locations around the wheel. If Salmonella is present in a food, then the odds of detecting it will be enhanced if two 375 g composites are analyzed rather than a single 25 g analytical unit, as

29、 would be the case if the analyst were to treat the entire wheel as a single sample.1.4） There is less sample available than is necessary to form the required number of composites.For example, an 8 oz （226.8 g） bag of almonds has arrived for testing. Almonds are a Category II food. Category II foods

30、 require thirty 25 g analytical units （750g）, so it is impossible to analyze the amount of almonds required by the sampling plan. In this case, the analyst should analyze all of the almonds at a 1:9 sample-to-broth ratio （226.8g sample/2041 ml preenrichment medium）.If, in the above example, the tota

31、l weight of the almonds had been less than 2 composites （750 g）, but more than 1 composite, then the analyst should analyze both a whole and a partial composite. The analytical units comprising these composites should be taken randomly from a wide variety of locations in the lot of almonds. Both com

32、posites, should be preenriched at a 1:This sampling plan applies to the collection of finished products under surveillance and/or for determination of compliance for regulatory consideration. It also applies to the collection of factory samples of raw materials in identifiable lots of processed units and/or finished products where regulatory action is possible. It does not apply to the collection of in-line process sample units at various stages of manufacture since those samples do not necessarily represent the entire lot of food