Research report

​Variability of Alkaline Report

1 documents for this subject

Summary

Hannah Research
Banks, J ; Muir, D

The microbiological safety of milk depends on efficient pasteurisation and prevention of recontamination of the finished product. Pasteurisation, a heat treatment equivalent to a minimum holding of milk at no less than 71.8°C for 15 seconds - inactivates almost all potential pathogens found in raw milk. Validation of the effectiveness of the pasteurisation process is based on destruction of a natural milk enzyme-alkaline phosphatase (ALP). The sensitivity of this test hinges on the initial concentration of ALP in raw milk. The higher the initial activity, the more sensitive is the test. In addition, the sensitivity depends on the method of analysis of residual enzyme activity.

The detection limit for the reference test for ALP is equivalent to contamination of properly pasteurised cows milk by 0.1% raw milk. The implications of applying the test to pasteurised goat milk were explored because goat milk was reported to have natural levels of ALP around 10% of the activity found in cows milk. In such circumstances the sensitivity of the reference method for ALP would be reduced ten fold i.e. contamination of pasteurised goat milk by raw milk could reach a level of 1% before it would be detected. Variations in the initial pool of indigenous alkaline phosphatase in milk lead to different amounts of raw milk being allowed in the pasteurised milk product at the statutory pass level.

The research undertaken in this project aimed to reduce the potential threat to public safety associated with consumption of inadequately processed goat milk.

The effectiveness of the ALP test is determined by three factors: (1) The level of ALP in milk and its variability, (2) The sensitivity of the method of measuring ALP (spectrophotmetric, fluoroescence, bioluminescence) and (3) The levels set in legislation as acceptable standards for residual ALP activity.

The work undertaken within this project encompassed: a lactational study of the variability of ALP in a herd of British Saanen goats; a comparison of the effectiveness of bioluminescence, fluorescence and spectrophotometric measurements of ALP; a study of the formation of heat stable ALP; and a limited survey of residual ALP and microbiological quality of pasteurised goat milk retailed in Scotland.

There is little information in the literature regarding the variability levels of ALP in individual goat milks or the influence of lactational effects on secretion of ALP into milk. Seventeen British Saanen goats from the Hannah Research Institute herd were therefore sampled on a weekly basis throughout a full lactation, i.e. April 2001 to early January 2002. Individual morning and evening milking samples were tested for ALP daily during the first eight weeks of lactation Thereafter the morning milk from individual goats was sampled once a week throughout the remaining lactation period. Alkaline phosphatase was determined by the Fluorophos method (IDF Standard 155A:1999). Statistical modelling of the lactational data explored relationships between ALP levels in milk and goat genotype, age, lactation history and milk composition.

ALP levels in milk were lowest in the early stages of lactation and increased as the lactation progressed and milk yields declined. ALP levels were higher in milk samples from evening milk as compared with morning milk. The lowest mean value recorded for ALP in an individual goat for morning milk in May was 5823 mU/L. 15 of the 16 animals producing milk in May had ALP levels under 32000mU/L. The lowest level of ALP in an individual goat milk sample was 3630 mU/L. Values for ALP in goat milk increased as lactation progressed. In November, the minimum mean value for ALP in an individual goat morning milk was 18658 mU/L. The minimum value for an individual goat was 10410 mU/L. Mean vales for ALP in November ranged from 18658 mU/L to 782000mU/L.

The mean value throughout lactation (11 samples) for ALP in bulk herd goat milk was 38880 mU/L. The equivalent value for cows milk (mean of 22 samples) was more than tenfold higher at 560049 mU/L.

Early lactation pasteurised bulk goat milk which was contaminated with raw milk at levels of 1.0% raw milk did not fail the Fluorophos, Bioluminescence or Sanders and Sager ALP test. In mid lactation failures for goat milk were obtained at levels ranging from 0.7 to 0.9% contamination. In cows milk failures for the ALP tests were evident at 0.08 to 0.1% contamination of pasteurised milk with raw milk.

Results indicate that all tests currently available are not suitable for ALP determination in goat milk.

Twenty nine samples of pasteurised goat milk were collected from retail outlets in Ayrshire. All samples had satisfactory residual phosphatase levels but two of the samples had unacceptably high counts for Enterobacteriaceae.

Project Code: S01003

Arrow_Dropdown Created with Sketch. Arrow_leftArrow_Right Icon_AlchoholIcon_Alchohol_RoundalIcon_AppleIcon_Apple_RoundalIcon_BacteriaIcon_Bacteria_Roundal calorie-outlined Created with Sketch. Icon_CardActivityIcon_CardActivity_RoundalIcon_CarrotIcon_Carrot_Roundal Icon/roundal/Allergen/Celery Created with Sketch. Icon_CertificateIcon_Certificate_RoundalIcon_CheeseIcon_Cheese_RoundalIcon_ChocolateIcon_Chocolate_RoundalIcon_ClipboardIcon_Clipboard_Roundal Icon_CloseIcon_CowIcon_Cow_Roundal Shape Created with Sketch. Icon/roundal/Allergen/Crustaceans Created with Sketch. Icon_CursorIcon_Cursor_RoundalIcon_DeerIcon_Deer_RoundalIcon_download Icon/roundal/Allergen/Eggs Created with Sketch. Icon_Facebook_RoundalIcon-FeaturedIcon_Fish Icon/roundal/Allergen/Fish Created with Sketch. Icon_Fish_RoundalIcon_FizzyJuiceIcon_FizzyJuice_RoundalIcon_ForkIcon_Fork_RoundalIcon_FridgeIcon_Fridge_Roundal Icon/roundal/Allergen/Wheat Created with Sketch. Icon_GrainIcon_GrainNoIcon_GrainNo_RoundalIcon_Grain_RoundalIcon_GraphIcon_GraphResourceIcon_Graph_RoundalIcon_HandIcon_Hand_RoundalIcon_HeartIcon_Heart_RoundalIcon_InfoIcon_Info_Roundal instagram Icon_LambIcon_Lamb_RoundalIcon_LetterIcon_Letter_RoundalIcon_LinkExternalIcon_LinkInternal Icon/roundal/Allergen/Lupin Created with Sketch. Icon_MagnifyingGlassIcon_MagnifyingGlass_Roundal Icon/roundal/Allergen/Milk Created with Sketch. Icon/roundal/Allergen/Molluscs Created with Sketch. Icon/roundal/Allergen/Mustrard Created with Sketch. Icon_NewIcon_NewsIcon_News_RoundalIcon_OilIcon_Oil_Roundal Icon/roundal/Allergen/Peanuts Created with Sketch. Icon_PeopleIcon_People_RoundalIcon_PersonIcon_Person_RoundalIcon_PhoneIcon_Phone_RoundalIcon_PigIcon_Pig_RoundalIcon_PlayIcon_PotatoesIcon_Potatoes_RoundalIcon_PrintIcon_Print_RoundalIcon_ResourceIcon_Resource_Roundal Group Created with Sketch. Icon_SaltIcon_Salt_RoundalIcon_SaveIcon_Save_RoundalIcon_ScotlandIcon_Scotland_RoundalIcon_Search Icon/roundal/Allergen/Sesame Seeds Created with Sketch. Icon_ShellfishIcon_Shellfish_Roundal Icon/roundal/Allergen/Soybeans Created with Sketch. Icon-SpiralIcon_SteakIcon_Steak_RoundalIcon_StopwatchIcon_Stopwatch_Roundal Icon/roundal/Allergen/Sulphur dioxide and sulphites Created with Sketch. Icon_TapWaterIcon_TapWater_RoundalIcon_TestTubeIcon_TestTube_RoundalIcon_ThumbsUpIcon_ThumbsUp_RoundalIcon_Tick Shape Created with Sketch. Icon_Tick_1Icon_Tick_Roundal Icon_TomatoIcon_Tomato_RoundalIcon_TractorIcon_Tractor_Roundal Icon/roundal/Allergen/Tree nuts Created with Sketch. Icon_TrollyIcon_Trolly_RoundalIcon_TurkeyIcon_TurkeyCookedIcon_TurkeyCooked_RoundalIcon_Turkey_Roundal Icon_Twitter_RoundalIcon_WarningIcon_Warning_Roundal Icon_Warning_Roundal_WithBG Icon_WaterDropIcon_WaterDrop_RoundalIcon_WineBottleIcon_WineBottle_RoundalIcon_WineGlassIcon_WineGlass_Roundal youtube Icon_snowflakeIcon_snowflake_RoundalLogo_FSS_Gaelic_WhiteLogo_FSS_WhitePagination_LeftArtboard 69