BS 4285-5 3-1987 Microbiological examination for dairy purposes - Ancillary methods - Test for inhibitory substances《乳品微生物检验 第5部分 辅助方法 第3节 抑制物质试验》.pdf
《BS 4285-5 3-1987 Microbiological examination for dairy purposes - Ancillary methods - Test for inhibitory substances《乳品微生物检验 第5部分 辅助方法 第3节 抑制物质试验》.pdf》由会员分享,可在线阅读,更多相关《BS 4285-5 3-1987 Microbiological examination for dairy purposes - Ancillary methods - Test for inhibitory substances《乳品微生物检验 第5部分 辅助方法 第3节 抑制物质试验》.pdf(10页珍藏版)》请在麦多课文档分享上搜索。
1、BRITISH STANDARD BS 4285-5.3: 1987 Microbiological examination for dairy purposes Part 5: Ancillary methods Section 5.3 Test for inhibitory substances UDC 637.1.055.07:57.042.2BS4285-5.3:1987 This British Standard, having been prepared under the directionof the Dairying Standards Committee, was publ
2、ished under the authority ofthe Board of BSI and comes intoeffect on 30June1987 BSI 08-1999 BS4285 first published March1968 Supplement No. 1 to BS4285:1968 first published April1970 First revision Section5.3 June1987 The Committees responsible forthis British Standard are shown in Part0 The followi
3、ng BSI references relate to the work on this standard: Committee reference DAC/4 Draft for comment 85/55315 DC ISBN 0 580 15844 6 Foreword This Section of BS4285 has been prepared under the direction of the Dairying Standards Committee. It supersedes B.5 of BS4285:1968, which is deleted by amendment
4、. A British Standard does not purport to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprise
5、s a front cover, an inside front cover, pagesi andii, pages1 to4, an inside back cover and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publ
6、ication Amd. No. Date of issue CommentsBS4285-5.3:1987 BSI 08-1999 i Contents Page Foreword Inside front cover 1 Scope 1 2 Definitions 1 3 Principle 1 4 Test organism and culture media 1 5 Apparatus 2 6 Sampling 2 7 Preparation of test sample 2 8 Test culture, test plates and controls 2 9 Procedure
7、3 10 Expression of results 3 11 Interpretation of results 3 12 Confirmation of results for raw milks 4 13 Test report 4 Publications referred to Inside back coverii blankBS4285-5.3:1987 BSI 08-1999 1 NOTEIt is essential that Parts0 and 1, which are published separately, be read in conjunction with t
8、his Section. 1 Scope This Section of BS4285 describes a method for testing for penicillin and other inhibitory substances in milk and milk powders. NOTEThe titles of the publications referred to in this standard are listed on the inside back cover. 2 Definitions For the purposes of this Section of B
9、S4285 the following definitions apply. 2.1 inhibitory substances materials that inhibit the growth of a test organism 2.2 penicillin an antibiotic containing a beta-lactam ring in the molecule and which is inactivated by the enzyme penicillinase NOTESome synthetic penicillin-type antibiotics may not
10、 be inactivated by penicillinase under the conditions of the test and will therefore be classified with inhibitors other than penicillin. 3 Principle A disc of absorbent paper impregnated with sample is placed on the surface of an agar medium inoculated with Bacillus stearothermophilus. After incuba
11、tion, a clear zone around the disc in the otherwise cloudy medium indicates an inhibitory substance. 4 Test organism and culture media 4.1 Test organism The test organism shall be Bacillus stearothermophilus var. calidolactis: NCDO 1780 or NCIB 11780 1) . 4.2 Medium for agar slopes 4.2.1 Composition
12、. The composition of the medium for the agar slopes shall be as follows: 4.2.2 Preparation. Dissolve the components in the water with heat. Adjust the pH so that after sterilization it is7.4 0.1 at 25 C. Dispense8mL to10mL volumes into screw-capped test-tubes. Plug with cotton wool. Sterilize at121
13、1 C for15min and allow to set in sloped position. NOTEThe quantity of agar should be varied according to the manufacturers instructions to give a firm gel. 4.3 Culture broth 4.3.1 Composition. The composition of the culture broth shall be as follows: 4.3.2 Preparation. Dissolve the components in the
14、 water. Adjust the pH so that after sterilization it is8.0 0.1 at25 C. Sterilize at121 1 C for15min. 4.4 Plate count agar 4.4.1 Composition. The composition of the plate count agar shall be as follows: 4.4.2 Preparation. Dissolve the components in the water with heat. Adjust the pH so that after ste
15、rilization it is8.0 0.1at25 C. Sterilize at121 1 C for15min. NOTEThe quantity of agar should be varied according to the manufacturers instructions to give a firm gel. 4.5 Standard penicillin solution Prepare a standard solution of penicillin of100i.u./mL by dissolving sodium or potassium benzyl peni
16、cillin in water in a stoppered bottle (see5.2). Use on the day of preparation and maintain at2 C to5 C. 4.6 Penicillinase solution Prepare a penicillinase solution of1000i.u./mL by dissolving penicillinase in water. Store at2 C to 5 C for not more than2weeks. 1) Obtainable from the National Collecti
17、on of Food Bacteria, AFRC Food Research Institute, Shinfield, Reading RG2 9AT or the National Collection of Industrial and Marine Bacteria, Torry Research Station, PO Box 31, Aberdeen AB9 8DG respectively. yeast extract 2 g peptone 5 g meat extract 1 g sodium chloride 5 g agar 15 g water 1000 m L ye
18、ast extract 10 g tryptone 20 g glucose 0.5 g water 1000 mL yeast extract 2.5 g tryptone 5 g glucose 1 g agar 15 g water 1000 mLBS4285-5.3:1987 2 BSI 08-1999 4.7 Milk free from inhibitory substances Prepare a 100g/L solution of inhibitor-free milk by the reconstitution in water of skimmed milk powder
19、 previously tested and found to be free from inhibitory substances. Alternatively, dispense in bottles of sufficient capacity a quantity of fresh bulk milk tested and found to be free from inhibitory substances. In either case heat for1h at 100 C. Store at2 C to5 C for not more than1week. Carry out
20、a test on nine discs from each batch of paper discs using water to verify that the discs do not give a clear zone when controlled at55 1 C for2.5h to5h on the test plates (see7.3.4) in the incubator (5.5). 5 Apparatus NOTEFor details of apparatus including its preparation and sterilization seeBS4285
21、-1.2. 5.1 Ordinary microbiological laboratory apparatus 5.2 Sample bottles, with closures which do not contain inhibitors. NOTERubber stoppers are not suitable. 5.3 Petri dishes. NOTE 1To ensure an even depth of agar medium, which is essential for accuracy, care should be taken to select a good qual
22、ity flat-bottomed brand. NOTE 2Sterile disposable plastics Petri dishes complying with BS611-2 are recommended. 5.4 Forceps, clean, dry, with fine points. 5.5 Incubator, capable of being controlled at55 1 C. 5.6 Waterbaths, capable of being controlled at37 1 C and80 1 C. 5.7 Antibiotic assay paper d
23、iscs, 12mm to13mm in diameter. 6 Sampling Take the laboratory sample in accordance with BS4285-1.1. 7 Preparation of test sample 7.1 Prepare the test sample from the laboratory sample in accordance with BS4285-1.1. Keep the test sample in a sample bottle(5.2). 7.2 Test raw and heat processed milks u
24、ndiluted. Either test them on the day the sample is taken, or store them at 20 C for as short a time as possible. 7.3 Reconstitute milk powder by adding to sterile distilled water to give a100g/L solution. 8 Test culture, test plates and controls 8.1 Maintenance of test culture Keep the test organis
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