FAT RICH DAIRY PRODUCTS

Module 5. Quality and preservation of cream

Lesson 14
QUALITY OF CREAM

14.1 Introduction

The keeping quality of retail cream is more critical than that of milk for although cream usually receives a more severe heat treatment than milk but the distribution system is different. Thus, milk is usually pasteurized one day, delivered the next, and consumed a day or two later, while cream has to be separated, standardized, cartoned and distributed, often through a retail dairy organization, and then sold through super markets or shops. There may be no temperature control during this procedure, and as cream sales tend to be concentrated at weekends and on special occasions, and the carton may be opened and used more than once, the keeping quality requirements are severe. Some dairies now achieve, or at least aim at a keeping quality of 14 days with the cream held at temperature not exceeding 5°C

14.2 Factors Effecting the Production of Good Quality Cream

1. Production of clean milk from the animals will have better keeping quality; as well the procurement of good quality milk is also most important. Poor quality raw milk, particularly with high spore and thermoduric counts leads to cream of short shelf life.

2. The milk procured from the farmers needs immediate cooling to prevent the growth of psychotropic bacteria that are responsible for the production of various taints in cream during storage.

3. Separation and processing the milk under hygienic conditions is another factor that affects the quality of cream. Cream separators are the important source of bacteria if not properly cleaned.

4. Wrong choice of temperature for heat treatment.

5. Prompt cooling of cream and its storage at lower temperature.

6. Transport of cream to the dairy under lower temperature.

Of these factors the quality of the raw milk and storage temperature of the end product are perhaps the most important.

14.3 Microbiological Quality of Cream

The micro environment of cream and milk are the same except the difference in the proportion of various constituents like fat, protein, lactose etc. as a result the initial microbiological quality of cream is almost parallel to that of milk, but later stages cream presents more problems than milk because of longer storage and erratic distribution pattern.

The micro flora of cream processed in an unclean plant may include a very high number of psychrotrophs. If cream is not cooled rapidly to less than 5°Cthe organisms like Staphylococci, Lactobacilli and Bacillus cereus have generally been found to predominate. On the other hand, the prolonged storage of cream at low temperature leads to the predominance of psychrotrophs and psychrophilies usually of Protelytic and Lipolytic , mainly ‘pseudomonads’ a gram negative, non spore forming, oxidase positive, catalase positive rods which enter the product as contaminants from dirty water. Holding cream at 5°C results in the predominance of microflora like Pseudomonas, Alcaligenes, Acinetobacter, Aeromonas and Achromobacter where as at 30°C Corynebacterium, Bacillus, Micrococcus, Lactobacillus and Staphylococcus predominate. The coliforms in refrigerated cream multiply slowly at 3 to 5°C and may increase 100 to 1000 folds in few days.

14.4 Relationship Between Microbiological Quality and Condition of Cream

The quality of cream can be interpreted on the basis of microbiological counts like total count, coliform count, yeast count, mould count and spore count as follows:

Results	Interpretation
High count and high Coliforms	Inadequate heat treatment and or Unhygienic manufacture and or storage at high temperature.
High count but low Coliforms	Good hygiene but storage at high temperature
Low count but high Coliforms	Poor hygiene in manufacture but storage at low temperature less than 5°C
Low count and low Coliforms but high Moulds	Good hygiene except aerial contamination in dairy
Low count and low Coliforms but high yeasts	Good hygiene except contamination from fruits, directly or indirectly
Low count and low coliforms but high aerobic spores	Cream made from milk having a high spore count

14.4.1 Microbial defects

The following are some of the common causes that are responsible for the entry and for proliferation of spoilage causing microorganisms in cream.

1. Unhealthy udder of the milch animal which gives rise to infected milk and ultimately an unsafe cream.

2. Unhygienic production of milk leading to high microbial population in milk or cream.\

3. Separation of cream in improperly clean cream-separator

4. Storage of milk or cream in unhygienic containers.

5. High temperature storage or in other words, lack of proper cooling of milk or cream, at various stage especially before heat processing.

6. Inadequate heat treatment during the pasteurization or sterilization

7. Unhygienic personnel handling the cream after heat processing.

8. Faulty filling/packing/ canning of the product.

9. Delayed distribution of market cream coupled with storage under ambient conditions.

The commonly occurring microbial taints in cream include: sour or high/coarse acid cream, bitterness, rancidity, fruity taint, cheesy or putrid flavor, yeasty flavor and discolouration. The organisms responsible for one or more of such defects belong to different categories, namely pseudomonads, aerobic sporeformers, Gram-negative rods, lactic acid producers, yeasts and molds,. etc. Cold storage of pasteurized cream at 7.2°C to 10°C results in rapid multiplication of psychrotrophs like pseudomonas, other Gram-negative bacteria including coliforms and certain yeasts and molds, unlike that at 3.3°C . Some mesophilic lactic streptococci, micrococci and aerogenes-cloacae strains of coliforms, which are derived from post-pasteurization contamination, can multiply relatively rapidly in cream held at 10°C-12°C or above.

14.5 Defects in Cream, their Causes and Prevention

Defects in cream may arise from low grade milk and faulty methods of production, processing and storage. The common defects in both table and manufacturing creams, their causes and prevention, are given in the following Table.

(A). Table cream

Flavour Defects

Name of Defect	Causes	Prevention
Flavour Cooked	Excessive heating of cream during pasteurization.	Proper heating of cream during pasteurization
Highly acid/sour	i. Using sour milk for separation ii. Acid development in cream	(i). Using fresh, sweet milk for preparation (ii). Neutralization of cream.
Oxidized/oily/Metallic/Tallowy	Fat oxidation due to direct contact of milk with copper or iron, exposure of milk or cream to sunlight, etc.	i. Proper tinning of milk or cream holding vessels, or using aluminium alloy or stainless steel as contact surface ii. Vacuum pasteurization of cream
Rancid	Fat hydrolysis due to lipase action in milk or cream	Inactivating lipase by proper pasteurization of milk and cream

(b). Miscellaneous

Name of defect	Causes	Prevention
Feathering in hot coffee	i. Excessive homogenization pressure ii. Using sour cream iii. Addition of salts	(i). Proper homogenization pressure (ii). Using sweet cream (iii). Avoiding addition of salts

(B). Manufacturing cream
(a). Flavour Defects

Name of defect	Causes	Prevention
Barny	(i). Poor ventilation of milking byre/barn (ii). Not keeping milk properly covered during production	(i). Proper ventilation of milking byre/barn (ii). Keeping milk properly covered during production
Bitter	(i). Intake of bitter weeds by milch animals (ii). Lipase activity during (raw) cream separation (iii). Growth of Proteolytic bacteria in cream	(i). Eradication of off ending weeds. (ii). Checking lipase activity by avoiding the ‘danger zone(38-490C) in cream separation. (iii). Storage of cream at 50C(400F) or below to check bacterial growth.
Cheesy	Growth of Proteolytic bacteria leading to casein break down.	Storage of cream at 50C(400F) or below to check bacterial growth.
Coarse-acid/sour	Uncontrolled acid development in cream	Storage of cream at 50C(400F) or below to check acid development
Cooked , Feed and weed Rancid Oxidized etc.	Feeding of milk tainting feeds and weeds within 3 hours before milking.	(i). Avoid Feeding of milk tainting feeds and weeds soon milking (ii). Eradication of milk tainting weeds. (iii). Vacuum pasteurization of cream
Fruity	Development of by-products of growth of certain un-desirable micro-organisms	Storage of cream at 50C(400F) or below to check microbial growth.
Utensil	Using dirty utensils	Using well cleaned utensils
Yeasty	Growth of lactose fermenting yeasts	Storage of cream at 50C(400F) or below to check yeast growth