FDA食品微生物检验抽样与制样.docx

1、FDA食品微生物检验抽样与制样Bacteriological Analytical Manual Online April 2003 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 colle

2、cted and mishandled or are not representative of the sampled lot, the 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 sampl

3、e is essential when pathogens or toxins are sparsely distributed within 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 b

4、e statistically significant. The composition and nature of each lot 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 sa

5、mpling by using the Investigations Operation Manual (5). Sampling and 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

6、 representative portions to sterile containers under aseptic conditions. 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 propan

7、e torch or dipping the instrument in alcohol and igniting is dangerous 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 lea

8、k-proof may be hermetically sealed. Whenever possible, avoid glass 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 u

9、seful containers for line samples. Take care not to overfill bags or 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 l

10、east 100 g for each sample unit. Submit open and closed controls of 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

11、. Check the temperature of the control sample at the time of collection 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 no

12、t be refrigerated. Transport frozen or refrigerated products in approved 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

13、samples solidly frozen at all times. Cool refrigerated samples, except 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 other

14、wise specified, refrigerated samples should not be analyzed more than 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 analyz

15、ed; keep shell stock above freezing but below 10C. Examine refrigerated 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 Proced

16、ures Manual (3). The Investigations Operation Manual (5) contains sampling 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 o

17、rganisms have received the attention of committees of national and 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 sa

18、mpling or food category depends on 1) the sensitivity of the consumer 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 s

19、ampling plan depends mainly on the first 2 criteria cited. The history 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. - Food

20、s that would not normally be subjected to a process lethal to Salmonella 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 ti

21、me of sampling and consumption. Food Category III. - Foods that would 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 ascerta

22、in whether or not Salmonella is present in the suspect food. Therefore, 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 Cat

23、egory III foods. Individual 25 g analytical units may be combined into 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 shoul

24、d be mixed to ensure homogeneity before withdrawing a 25 g analytical 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 sampl

25、e units is correct, but several of the sample units have been damaged 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 shou

26、ld be mixed to ensure homogeneity before the analytical units are withdrawn. 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 samp

27、le-to-broth ratio (375 g sample/3375 ml preenrichment) as directed 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 a

28、rrived for testing. Since cheese is a Category II food, thirty 25 g 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 co

29、mposites are analyzed rather than a single 25 g analytical unit, as 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 arr

30、ived for testing. Almonds are a Category II food. Category II foods 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 samp

31、le/2041 ml preenrichment medium).If, in the above example, the total 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 random

32、ly from a wide variety of locations in the lot of almonds. Both composites, should be preenriched at a 1:9 sample-to-broth ratio.This sampling plan applies to the collection of finished products under surveillance and/or for determination of compliance for regulatory consideration. It also applies t

33、o 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