Milk thermal treatment
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1. The document discusses different thermal treatments for milk including pasteurization, sterilization, and boiling. 2. Pasteurization involves heating milk to temperatures between 63-85°C for short periods of time to minimize pathogens while preserving chemical and physical properties. Common pasteurization methods are listed. 3. Sterilization or long-life milk involves higher temperatures over longer periods to destroy all microorganisms allowing milk to be stored at room temperature for several months. Methods of in-bottle and UHT sterilization are described.
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Milk thermal treatment
- 1. Dr. Dina A. B. Awad Lecturer food hygiene and control , faculty of veterinary medicine Benha university, Egypt
- 2. Milk thermal treatments 1- Pasteurization 2- Sterilization 3- Boiling Chemical, organoleptic properties of milk ???????????????????????????????????
- 3. 1- Pasteurization processes Raw milk Certain temperature Certain time Sudden cooling Minimizing pathogenic organisms Aim Associated Minimal chemical, physical changes 63°C/30 min 72°C/15sec 85°C/2-4 sec 4-10° C
- 4. Receiving of raw milk at 4 °C Organoleptic examination Acidity determination (C.O.B,A.P.T) Dirt & sediment examination Antibiotic residues & T.B.C & MBRT Filtration 35-50 °C OR clarification 4.5 °C Standardization Homogenization Pearson square (add cream or skim milk) (LTLT) 63C/30min Kill 98% bacteria Not affect chemical properties 1- avoid cream line 2-mouth feel 3- improve color Pasteurization process (HTST) 72C/ 15 sec. Kill 99% bacteria Slightly affect chemical properties (Flash method) 85C/ 2-4 sec. Kill 99.5% bacteria Slightly affect chemical properties Pasteurization flow chart Cooling less 7°C (inhibit thermoduric bacteria)&packaging (7 days) Coxiella burnteii
- 8. clarification 4.5 °C Milk mechanical clarifier Filtration 35-50 °C Applied under centrifugation (ppt dirt) Producing clarifier slime Remove dust, somatic cell,some bacteria Using disc wool or synthetic filters Remove visible dirt and sediment, coarse particles But not the bacterial cells
- 10. 10 1st stage 2nd stage Advantages: 1- Smaller fat globules --no cream-line formation 2-Whiter and more appetizing colour. 3-More better mouthfeel. 4-Better stability of cultured milk products. Disadvantages: 1-May increased sensitivity to light – sunlight can result in “sunlight flavour” . 2-More susceptible for rancid flavour. April /2020 Dr.Dina A. B.Awad Homogenization
- 11. Factors affecting keeping quality of pasteurized milk Initial bacterial count Efficiency of pasteurization Process Sudden cooling at 5-7 C Post pasteurization contamination Time –temperature factor (accurate) (phosphatase enz.) To stop the action of bacteria that resist pasteurized temperature. Insufficient clean piplines,tanks,filling machine, contamination water supply, poor personal hygiene To avoid that?????????????????????????????????????????????????????????????????????????????? - Thermophilic bacteria-- resist holding method but HTST destroy it. St. coccus thermophilus Thermoduric bacteria– resist pasteurization (spore former) as bacillus cereus,bacillus subtilus. (bactofugation) Pschrophilic bacteria –as pseudomoans bacteria produce heat resistant enzymespoilage in pasteurized milk.(thermisation)
- 12. Spoilage of pasteurized milk When stored at high temperature or at room temperature or kept opened – shelf life Growth thermophilc bacteria 5.5pH Growth of lactobacilli 4 or less pH N.B Survive thermoduric bacteria, bacillus (Sweet curdling) (Rennin like enz.) Mould &yeast pH --Their presence indicate post pasteurization contamination Extend shelf life (ESL)--- means extended shelf life of the product With maintaining its nutritional value (ultra-pasteurization ) 125-130°C –2-4 sec
- 13. Milk sterilization (long life milk) A process in which milk is heated to a certain time that all microorganisms are destroyed Producing high quality milk could stored for long time at room temperature (tropical areas). Methods of sterilization In –bottle (container) UHT(uprization) Sterilization for both milk &bottle
- 14. Flow chart for in -bottle sterilization APT Test negative Remove debris(brown sediment??) Avoid cream line formation Initial removal bacterial spores Pre-serilization of milk at 80 C Bottling in pre-wormed bottles Milk in bottle sterilization Cooling gradual within 1 hr At 115-120/15-20 min in steam Kept at room temp. 6 months Page 132
- 15. Flow chart UHT sterilization APT Test negative Remove debris(brown sediment??) Direct heating type Inject milk in steam Fearing from unsterile packaging UHT process 140 – 150° C/1-4 sec. Homogenization (avoid aggregates) Packaging under O3 Page 132 Tubular heating using Plate heat exchanger Steam instead of hot water
- 16. Advantage and disadvantages UHT sterilization Milk is effectively sterilized Gelation, ppt protein, loss vit.,cooked Spoilage of UHT sterilization Page 130 Rare:::::::::but,,,,,,,,,,,,,,,,,,heat resistant spores --- survived Post- heat treatment contamination Psychrotrophic organisms Dual heat treatment 140C/5 sec 60 C/5 min Bactofugation