Module 8. Quality of butter

Lesson 27

MICROBIOLOGICAL ASPECTS OF BUTTER

27.1 Introduction

Microbiology of Butter reflects the micro flora present in pasteurization cream from which it is made, water added at the time of salting of butter, Sanitary Condition of process of equipment, manufacturing environment and conditions under which the product is stored. Intrinsic properties of butter for e.g., pH salt content, uniformity of moisture distribution and droplet size, all impact microbiological stability.

27.2 Micro-Environment of Butter

Micro-environment of Butter is unfavorable for growth of Microorganisms compared because of the following compositional and structural differences.

27.2.1.  Compositional differences

a)      Fat content in butter is relatively resistant to microbial decomposition is present in greater butter in butter (about 80%) compared to cream (except for high fat plastic cream)

b)     Lactose which is readily utilizable by many of the microorganisms is present in lower quantities.

c)      Moisture content which is essential for microbial growth is present lower quantities (<16%) in butter.

d)     Salt in butter make its micro environment unfavorable for microbial growth.

27.2.2.  Structural differences

The nature of distribution of water and fat in cream and butter makes their microenvironment different. In cream water is in continuous phase and fat is in discontinuous phase, where are the reverse in case of butter where water is discontinuous phase present as drops dispersed in fat. A large number of water droplets are more than the number of Microorganisms in butter. Moreover, unlike that in cream, Microorganisms cannot proliferate easily and spread in butter because of the following reasons.

a)      Water phase is separated by relatively resistant fat phase in butter. Molds and Psuedomycelia forming yeast are able to grow and penetrate through the fat phase of butter.

b)     Limited supply of nutrients in the H2O droplet in butter while in cream microorganisms can grow in the continuous H2O phase having dissolved nutrients and migrate one portion to the other.

27.3 Microflora of Butter

 In spite of unfavorable conditions in butter for microbiological growth; since cream utilized for butter making is pasteurized, the bulk of Microbial population in the final packet is contributed by post pasteurization contamination during butter making. Microorganisms of the post pasteurization contamination from utensils, H2O, air etc and belong to different groups of bacteria such as psychrophilic/psychrotropic (proteolytic/Lipolytic), Mesophilic (Lactic and non lactic acid) and spore forming bacteria. In case of yeast and molds, they may enter through aerial route. The microflora of butter which belongs to above groups are summarized in the Table 1.

27.3.1  Sources of microorganisms in butter

Microorganisms which are present in Butter are derived from a variety of sources are explained below.

27.3.1.1 Raw Material (Milk or Cream)

The quality of milk/cream utilized for production of Butter has a direct impact on microbiological quality of the final product. Butter made from cream separated from EOD (Every other day) collected farm bulk tank milk or bulk collected milk (refrigerated) was slightly inferior quality with respect to flavor to butter made from daily collected can milk (cooled at 12°C). This is due to higher microbial number and activity in the EOD or bulk collected milk. Highly heat resistant extracellular lipases which one secreted by Psychrotropic bacteria in such milk may resettled in high free fatty acid content and also affect final composition and flavor of cream and butter manufactured from it. This type of cream exhibited slow acid developed during ripening due to possible adverse effects of liberated free fatty acids.

 

Both sour and sweet creams are generally used for manufacture of butter. Sweet cream contains fewer nor organisms predominantly bacteria compared to yeast and molds. On the other side sour cream contains larger nor of microorganisms sometimes up to a humdrum million per ml. Sometimes the cream may be accumulated before churning into butter. During this period microbial growth may occur. In some cases, because of the high initial population, a large number of bacteria may survive in the pasteurized cream. Since the quality of cream has a direct bearing on the microbiological quality of butter, these are a need for adopting the following measures to maintain the quality standards of butter.

1) Hygiene production of milk and cream.

2) Proper quality control of cream before butter making.

3) Avoiding accumulation and high temperature (75°C)

Storage of cream before butter making

The following test may be carried out for quality control of cream for butter making:-

a)   Organoleptic test

b)  Acidity

c)   Sediment test

d)  MBR test

e)   TBG

f)    YGM count

As per the procedure laid down by APHA for milk and cream, the following standards as given in Table 2 have been suggested for grading of cream on the basis of various microbiological tests.

In India, no separate standard have been suggested for recommended for cream for butter making, though the prescribed ISI standards are available market cream.

27.3.1.2 Equipments

The sanitary condition of various equipments used during butter manufacture determines to a great extent the degree of contamination. Among these equipments, butter churn is microorganisms’ important source of contamination particularly in regard to psychrotrophic organisms and yeast & molds, metals churns are advantageous from sanitary point of view but still in many places, the wooden churns continue to be in use. These wooden churns are difficult clean and sanitize since the wood surface is irregular which takes up water and subsequently cracks, thereby, making the removal of solid particle difficult molds penetrates deep inside pores and crevices of the wood and serve as a potential entry for contamination. The parts of pasteurizers and allied units like pipelines, pumps, valves and coolers may be the other sources of contamination.

27.3.1.3 Water supplies

 During manufacturing of butter, water may be used for different purposes like to flush residual cream form holding values into churns, for dilution of cream as break water, as chilled wash water, for wet salting and for adjusting the moisture content of butter. In case of continuous butter making process, water is used for washing of butter granules. The contaminated water used one or more of those points lead to important sources for the entry of microorganisms. The psychrotrophic bacteria known to cause spoilage in butter known to cause spoilage in butter may gain entry into butter through such water supplies. The bacteria which are causing spoilage into the final product through such water supplies are shown in Table 3.

Psychrotropic bacteria can grow extensively H2O in dairy tanks, when particularly when water contains some organic matter and has not been efficiently chlorinated Coliforms and some heat resistant Psychrotropic strains of bacilli and clostridia have been found to occur in natural water.

Psychrotropic counts of >100/ml & lipolytic counts of >10/ml are indicator of faulty chlorination of H2O supplies. Total colony counts of >250/ml (determined at 21 or 25°C) & Most probable number (MPN) of > 10/ml (at 30°C) for Coliforms are indicator of unsatisfactorily quality of H2O supplies. The effective measures to check contamination through water is chlorination of H2O supply by adding suitable concentration of chlorine (1-5 ppm).

27.3.1.4 Air

Air is comparatively important source of contamination a butter plant than any other during product plant. All plants don’t have a separate packing room or don’t maintain a high standard of hygiene in butter packing room or don’t maintain a high standard of hygiene in butter packing and printing room. Thus butter often gets exposed to air for long periods prior to or during packing and get contaminated bacteria are the most predominant sources of aerial contamination followed by yeast and molds. Suggested standard reported Bacterial counts of air ranging from 11-132/ft3 & yeast & mold count of 4-26/ft3 during butter packing and printing operations. Psychrotrophs are also encountered in the air of dairy plants. Molds spores remain suspended in air and contaminant walls or wooden structures in the packing room, which can serve as growth centres for molds. The main sources of aerial contamination in dairy plant appear to be announcement of workers, fans, drains and dust from the surrounding areas.

Personnel

The persons involved in the manufacture and handling butter may introduce Microorganisms to butter through contaminated hands, clothing, mouth, nasal discharge, sneezing etc particularly doing packaging stage unhealthy persons, particularly those suffering from respiratory disorders should not be allowed to handle butter. The personnel engaged in the packaging room should follow the hygiene measures.

Butter color

The color used for incorporation into butter is particularly free from micro organisms. However, if it is kept in open containers or is mixed with water in a unclean measuring containers, there are chances of contamination of butter through butter color.

Packaging material

Normally, parchment paper is used for packing butter. This paper is usually received in a satisfactory condition from the manufacturer but it may get contaminated especially with molds. Subsequently during transportation or storage use of dry parchment and or air treatment of parchment with hot brine or antifungal chemicals like sorbic acid/ potassium sorbate, Propionic acid/ calcium or sodium propionate or benzoic acid/ Sodium benzoate may reduce the mold contamination. Normally, a combined treatment of hot brine and sorbic acid (0.5%) for 24 hrs is recommended.

27.3.2 Effect of processing on the microflora of butter

A number of factors like processing of cream, method of manufacture, working and salting and conditions of storage affect the microflora of final product.

27.3.2.1 Effect of cream processing

The processing of sweet or sour cream like neutralization, pasteurization and cooling have a pronounced effect on the microbiological quality of butter.

a) Neutralization of cream

The sour cream is neutralized before heat processing. The neutralization step may affect the microbiological quality in the following manner.

The contaminated neutralization solution as a result of poor quality water used for dissolving neutralizers may add microorganisms in cream. However, the contaminants entering at this step may get killed during subsequent pasteurization of the neutralized cream.

(ii) Pasteurization

Cream is pasteurized at 71.1oC for 30 min (LTLT) or 90oC for 16 sec (HTST), which is more severe treatment than that required for fluid milk. This leads to nearly 99% destruction of microorganisms in cream. However, some of the cream borne Microorganisms are still carried over to the butter due to the following reasons:

a)      Resistance of certain microorganisms to survive pasteurization enables some of these organisms like psychotropic heat resistant bacteria to cause spoilage in butter.

b)     Improper pasteurization may results the survival of some spoilage causing Microorganisms. Hence, a proper time-temperature combinatory for pasteurization should be meticulously followed.

c)      The practice of mixing raw cream with the pasteurized cream into the vat may also be responsible for the subsequent transfer of microorganisms to the butter.

(iii) Ripening of cream

This step is applicable for making ripened cream butter. Ripening of cream affects the microbiological quality of butter in the following ways.

a)    There is considerable increase in the total bacterial count in butter involves direct addition and multiplication of the added organism.

b)   If the cultures used are contaminated, the considerable organism can also enter the product.

c)    In general, the acid production by butter cultures during ripening suppresses the growth of spoilage causing organisms. (Eg. proteolytic  and lipolytic pseudomonades)

Cooling /ageing of cream

After pasteurization, the cream is cooled to low temperature and it is help at this temp for ageing (which helps in getting butter fat recovery in during churning). The temperature of cooling and ageing generally followed under Indian conditions varies from 5-10oC for 2-4 hrs or overnight. However, minimum holding is desirable in modern processing practices. If the cream properly cooling/ageing conditions from satisfactory, there is little significance of such cooling/ageing conditions from microbiological point of view. Bacterial numbers in pasteurized cream is relatively lower and mainly thermophilic organisms are present which by and large appears to be harmless in butter.

27.3.2.2 Effect of butter making

(i) Churning

Churning during conventional batch method of butter making involves vigorous agitation of cream at 10°C. This step affects the microbiological quality butter in the following ways.

a)      This process causes quantitative changes in microflora by breaking the bacterial clumps and consequently increasing the total bacterial count.

b)     Contamination of butter churn from extraneous sources may further add to the microbial load in butter.

c)      Major part of bacterial population goes to butter milk instead of butter during churning, whereas rivers are true for molts due to this bigger size.

27.3.2.3 Effect of process for moisture distribution (working, printing and reworking)

The distribution of moisture droplet in butter is directly affected by working; printing and reworking process the working of butter breaks the bigger droplets and brings about a uniform distribution of tiny droplets, printing of butter, however, leads to aggregators of water into bigger droplets and loss of free water from butter. Reworking of butter needed where moisture content of lot of more and needs removal or when two or more lots of butter are to be mined. This is preserved to have the same effect as the ‘Working’ process on moisture distribution.

The nature of moisture distribution in turn affects the microflora of butter. The microbial growth is restricted only infected droplets and a large number of tiny droplets in properly worked butter remain sterile since migrations of bacteria through the resistant fat mass is difficult the proliferation of organism in the infected droplet is restricted due to limited availability of nutrients. On the other hand, in under worked or unworked butter, the bigger water droplets support greater proliferation of microorganisms, thereby leading to butter spoilage. Based on this mechanism, working of butter discourages microbial growth due to fines and uniform moisture distribution whereas printing encourages microbial multiplication by creating bigger droplets. Reworking has been observed to cause rapid deterioration of butter samples stores for long time probably by renewed microbial activity.

27.3.2.4 Effect of salting

Salt, generally added to butter, is inhibitory to the growth of microorganisms. However, its action is influenced by its concentration and its uniform distribution in water droplet which in turn in dependent if butter is worked efficiently. The salted tiny droplets will contain high concentration (>15% salt and hence prevent bacterial growth). If salt is not is uniformly distributed, the bacteria will grow in regions where the salt concentration in moisture is low or absent. Therefore, microbial growth is checked in the infected droplet in droplets in salted butter and as a result microorganisms are more active in can worked or under worked salted butter than in properly salted butter.

However some salt tolerant organisms for example particularly fluorescent pseudomonades can grow in 3% salt concentration very few can grow in 5% salt and none can grow in 6% salt concentration certain molds can also tolerate high slat concentration and grow on the butter surface.

27.3.2.5 Effect of packaging

The addition of contaminating microorganisms in butter, at packaging stage mainly occur through air and packaging materials, although the role of unhygienic packaging equipment surfaces of personnel cannot be excluded.

27.3.2.6 Effect of storage

The temperature and time of storage have a definite effect on the microbiological quality of butter. There is a wide range of temperature over and Microorganisms grow in butter. In tropical countries like India, butter is stored at room temperature and conditions are congenial for the microbial multiplication.

At low temperature storage, particularly in cold stores, the rate of growth of Microorganisms decreases and only Psychrotropic organisms can multiply at such temperature. Coliform bacteria die out during cold storage. Slight growth will occur in butter held at temperature below 0°C and none is expected at -15°C. At this, temperature the total bacterial would be expected to decrease slightly especially unsalted butter. Hence the ideal temperature for storage of butter for keeping quality (12-18 months) is -12 to 18°C. Since the cooling rate of butter is slow due to its high fat content, the bacterial counts will often increase especially in unsalted butter during the initial stage of storage.

27.3.3 Microbial deterioration/spoilage of butter

Growth of micro organisms in butter causes a variety of color and flavor defects. Most of the microorgansims in cream gets killed during pasteurization, the spoilage organisms mainly come through post pasteurization steps and butter making. The defects in butter mainly attributed to the presence of psychotropic bacteria (lipolytic & proteolytic), yeast and molds. The psychotropic bacteria which are entering the product through unhygienic equipment grow during low temperature storage. However, molds create problems and relatively high temperature as prevalent India.

A.   Color defects (Discoloration)

Discoloration of butter may be caused by bacteria, yeasts and molds. However major color defect in butter are caused by yeast and molds.

Bacterial Discoloration

a)   Black discoloration (like grease smudge) causative organisms: Pseudomonas nigrificans. Due to butter stored at low temperature (optimum for pigmentation is 4°C i.e. 15-20% salt concentration in the moisture droplets.

b)   Fungal Discoloration: Butter gets discolored due to surface growth of molds and the defect is also described as ‘moldy butter’. This is a major defect commonly occurred in India since the ambient temperature storage condition encourages the growth of Fungi in butter. Fungi growth also favored by higher moisture content and acidity. Some psychotropic molds like Alternaria, Harmodendrum, phoma and stamphylium have been appear to grow in butter ( unsalted) at low temperature (5°C) slightly growth @ -4 to -6°C but not @ -7 to -9°C. Some common fungal discoloration frequently occurred in butter areas follows

               Discoloration          Causative agent

a. Mold discoloration

i.    Black Cladosporium Eg. C. harbarum,  Aspergillus, Hasmodendrum,Alternaria, Mucor, Rhizopus,  and Stamphylium

ii.   Brown Aspergillus spp, and Phoma spp (muddy brown)

iii.   Green & blue green Penicillium spp and Aspergillus app

iv.    Orange & yellow Geotrichum candidum

v.    Reddish pink Fusarium

            b.  Yeast

i.    Black Torula spp

ii.    Pink Rhodotorula spp

B.    Flavor defects: - Rancid & putrid or cheesy odor is the most common flavor defects in butter. The other defects like malty, Shunk-like flavor yeasty may also occur in butter.

            a. Rancid flavor: - Butter gets rancid due to microbial, enzymatic or chemical degradation of fat constituents. The fat hydrolysis in butter mainly due to the activity of microbial lipases. Many of the lipolytic microorganisms are psychotropic and are able to grow @ temperature slightly under 0°C and survive cold storage @ -10°C. Some of the lipase producing organisms which can grow on butter is as follows.

Bacteria                                          Mold                                         Yeast

Ps. fragi                                           Geotrichism Candidum            Candida lypolitica

P. fluorescence                                  Cladosporium butyri                Torulopsis spp

P. putida                                          Penicillium spp                         Rhodotorula spp

Achromobacter lipolyticum            Aspergillus spp                         Saccharomyces fragilis                                                                                          

            b. Putrefactive taint: - Defect is due to breakdown of proteins by various Putrifactor organisms like Pseudomonas putrefacien, coliform, Flavobacterium maloloris. The chemical compound which produced during the breakdown of protein is closely related to isovaleric acid responsible for off-flavor. The causative organism enter butter through unchlorinated water supplies and equipments (butter churns, Creat vats)

        c.       Cheese taints: - Cheese like flavors in butter is due to association action of different gram negative rods shaped bacteria due to butter stored above 10°C.

        d.      Other flavor taints: -

i.  Malty flavor: - is due to presence and growth of streptococcus Lactsis variable maltigenes in cream. The formation of 3-methyl butanol in butter mainly responsible for malty flavor.

ii.  Shunk-like flavor: - Pseudomonas mephitica

iii.  Fishy taint: Pseudomonas ichthyosmia, Geotrichum candidum and Yeasts due to decomposition of lecithin to Trimethyl amine by microbes.

27.4 Public Health Importance

Butter is not an ideal medium for the growth of pathogenic or food poisoning organisms due to high fat content, yet it may carry certain pathogen if contaminated during production, handling and packaging. Certain pathogens have been found to remain viable for long periods in butter the possible sources of pathogens in butter may be the cream itself (improperly pasteurized) or the post-pasteurization contamination. Handler in the butter plant is usually the major sources of such organisms in butter. Very few outbreaks of diseases or food poisoning have been reported so far from butter. Staphylococcus aureus and salmonella have been encountered in butter. Butter may, however, serves as a good medium for the growth molds including aflatoxins and other Mycotoxins producers. Such toxins may cause serious health hazards in consumers. The necessity of checking mold contamination and growth in butter.        

 27.5. Legal Microbiological Specifications for Cream and Butter

Consumer safety is paramount criteria for any food manufacturer or producer. To ensure the safety to the consumer Food Safety and Standards Authority of India (FSSAI) introduce the Act to monitor the food safety. It assigns the responsibility of food safety to the producer and provides the necessary guideline, some chemical and microbial standards for the products like butter are compulsory and every food manufacturing or dairy product manufacturing organization need to follow these mandatory standards.

27.5.1 BIS standards for cream & butter

Beuro of Indian standards (BIS) has given the following standards for raw and pasteurized cream

i.        Raw cream

Plate count/ ml (or g)

Grade

< 4 X 105

Very good

4 X 105 – 20X 105

good

20X 105 - 1X 106

fair

>1X 106

poor

 

Coliform count /ml (or g) : Not more than 100 Satisfactory

ii.      Pasteurized cream

      The plate count/mL (or g) should not be exceeding 60,000 and coliform count/mL (or g) should not be more than 10.

iii.    BIS Standard for Butter

Standards and recommendations of Indian standards Institution for butter as follows

i)     SPC. No standards have been suggested

ii)   Coliform. The presence of more than 10cfu/mL butter is an index of insufficient pasteurization or contamination of butter from external source like wash water, equipment and other sources during manufacturing and packaging.

iii)       Yeast & Molds (Y&M)

Y&M counts/ml

Quality

Less than 20

Good

21-50

Fair

51-100

poor

More than 100

Very poor

USDA Specifications for Light Butter

Microbial determinations shall be made in accordance with the methods described in the latest edition of Standards Methods for the Examination of Dairy Products, published by the American Public Health Association.  Samples shall be taken as often as necessary to insure microbial control.

27.4.1 Sampling plans for cream and butter

The FSS regulations for microbiological criteria for the acceptance or rejection of sample are lots. It sets out (FSSR, 2011):

v  the food which must comply with the microbiological limits set in relation to that food;

v  the micro-organism or group of micro-organisms of concern;

v  the number of sample units to be taken and tested;

v  the level of micro-organisms considered acceptable, marginally acceptable or critical(depending on the sampling plan specified); and

v  The number of samples that should conform to these limits.

The following terms, as used by the International Commission on Microbiological Specifications for Foods (ICMSF), are defined and used in Standard 1.6.1.

n = the number of sample units which must be examined from a lot* of food. Most sampling plans specify taking five sample units. However, when the risk has been assessed as relatively

high, a greater number of sample units is specified.

c = the maximum allowable number of defective sample units. This is the number of sample units, which may exceed the microbiological limit specified by ‘m’. These are considered marginal results, but are acceptable providing they do not exceed the limit specified by ‘M’.

m = the acceptable microbiological level in a sample unit. Sampling plans in which m=0 and c=0 are equivalent to ‘absent’ or ‘not detected’ reporting for the stated analytical unit size. In most cases this is 25 g (e.g. not detected in 25 g).

M = the level which, when exceeded in one or more samples, would cause the lot to be rejected.

*A lot means a quantity of food, which is prepared or packed under essentially the same conditions, usually:

• From a particular preparation or packing unit; and

• During a particular time ordinarily not exceeding 24 hours.

A lot of food does not comply with the standard if the number of defective sampled units is greater than c, or the level of a micro-organism in a food in any one of the sample units Exceeds M.

 

SI. No.

Requirements

Sampling Plan

Pasteurized cream

Pasteurized Butter

1

Total plate count

m

30,000/g

10,000/g

M

50,000/g

50,000/g

2

Coliform Count2

m

< 10 /g

10/g

M

50/g

3

E.coli3

M

Absent/ g

Absent/g

4

Salmonella4

M

Absent/ 25g

Absent /25g

5

 

Staphylococcus aureus5

(coagulase positive)

m

< 10/ g

10/g

M

50/g

6

 

Yeast and mould count6

m

-

20/g

M

-

50/g

7

Spore Count:

 

m

-

-

(a)  Aerobic7a

(B. cereus )

-

M

-

-

(b) Anaerobic7b

(Clostridium Perfringens)

m

-

-

M

-

Absent/g

8

Listeria  monocytogenes8

M

Absent/g

Absent/g

Sampling Guidelines9

n 1-8

5

5

c

2 1-2, 5

2 1-2, 5-6

03,4, 8

03,4, 8

Storage & transport

0 to 4°C

-18°C

Sample size

100ml or g

100ml or g