Food or edible material: processes – compositions – and products – Fermentation processes – Of milk or milk product
Reexamination Certificate
1998-09-30
2002-01-01
Bhat, Nina (Department: 1761)
Food or edible material: processes, compositions, and products
Fermentation processes
Of milk or milk product
C426S042000, C426S043000, C426S061000, C426S580000
Reexamination Certificate
active
06335040
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of manufacturing dairy products by the use of starter cultures and it provides a safe and convenient system for delivery of such starter cultures directly into the dairy process line.
TECHNICAL BACKGROUND AND PRIOR ART
Microorganisms are involved in the manufacture of most dairy products. Bacterial cultures, in particular bacteria which are generally classified as lactic acid bacteria are essential in the making of all fermented milk products, cheese and butter. Cultures of such harmless bacteria are called dairy starters and they impart specific features to various dairy products by performing a number of functions.
Thus, as an example, the starter cultures ferment lactose to lactic acid, and since the coagulation time by milk clotting enzymes is decreased by the increase in milk acidity, starter cultures aid the enzymatic coagulation of milk in cheese making.
A further example is that the rapid lactic acid development throughout the production process caused by the starter cultures restricts the growth of contaminating micro-organisms. In cheese making, the starter culture promotes the exudation of whey from the curd. The lactic acid-producing bacteria also produce proteolytic enzymes, which aid the degradation of cheese proteins which makes an important contribution to the ripening of cheese. Additionally, lactic acid bacterial cultures ferment lactose and citric acid to aromatic compounds, such as diacetyl and acetaldehyde which confer a desired aroma and taste to the fermented milk products.
Commercial dairy starter cultures are generally composed of lactic acid-producing and citric acid-fermenting lactic acid bacteria. In the present context, the expression “lactic acid bacteria” designates a group of gram positive, microaerophilic or anaerobic bacteria which ferment sugar with the production of acids including lactic acid as the predominantly produced acid, acetic acid, formic acid and propionic acid. The industrially most useful lactic acid bacteria are found among Lactococcus species, Streptococcus species, Lactobacillus species, Leuconostoc species, Pediococcus species and Brevibacterium species.
Commonly used dairy starter culture strains of lactic acid bacteria are generally divided into mesophilic organisms having an optimum growth temperature at about 30° C. and thermophilic organisms having optimum growth temperature in the range of about 40 to about 45° C. Typical organisms belonging to the mesophilic group include
Lactococcus lactis
subsp. lactis,
Lactococcus lactis
subsp. cremoris,
Leuconostoc cremoris, Lactobacillus delbrueckii
subsp. bulgaricus,
Lactococcus lactis
subsp.
lactis biovar
. diacetylactis,
Lactobacillus casei, Streptococcus durans
and
Streptococcus faecalis
. Thermophilic lactic acid bacterial species include as examples
Streptococcus thermophilus, Lactobacillus lactis, Lactobacillus helveticus, Lactobacillus bulgaricus
and
Lactobacillus acidophilus.
Also the strict anaerobic bacteria belonging to the genus Bifidobacterium including
Bifidobacterium bifidum
and
Bifidobacterium longum
are commonly used as dairy starter cultures and are generally included in the group of lactic acid bacteria. Additionally, species of Propionibacterium are used as dairy starter cultures, in particular in the manufacture of cheese.
Another group of microbial starter cultures are fungal cultures, including yeast cultures and cultures of filamentous fungi, which are particularly used in the manufacture of certain types of cheese. Examples of currently used cultures of fungi include
Penicillium roqueforti, Penicillium candidum, Geotrichum candidum, Torula kefir
and
Saccharomyces kefir.
Presently, commercial starter cultures are distributed as frozen concentrates in a medium of milk components, nutrients and growth stimulating compounds. Under these conditions, the viability of the cultures is preserved for extended periods of time, and after thawing the cultures can be inoculated directly into milk without intermediate transfer. Such cultures are commonly referred to as direct vat set (DVS)-cultures. Another presentation of commercial DVS-starter cultures is as freeze-dried or lyophilized cultures in the form of a powder. In this form, the starter can be shipped without refrigeration, but storage below freezing temperature is recommended.
Although commercial dairy starters thus are available as cultures which can be added directly to milk without any intermediate transfer or propagation, it is not uncommon that dairies produce in-house bulk starters at regular intervals depending on the requirement. A bulk starter is defined as a starter culture propagated at the dairy plant for inoculation into milk. Such bulk starters are generally made by inoculating heat treated milk with a volume of a previous bulk starter or with a freeze-dried or frozen starter culture preparation, followed by incubating the thus inoculated milk under conditions permitting the starter culture strain(s) to propagate for a sufficient period of time to provide a desired cell number. The incubation period is typically in the range of 18 to 24 hours.
However, these currently used methods of applying dairy starters involve several problems in modern dairy plants where process lines including reservoirs, vessels, containers, vats, centrifuges, heat treatment equipment, filling equipment and pipelines connecting the elements of the process line are essentially completely closed systems. Any process step which involves that the closed system be opened to the environment evidently involves a serious risk of contaminating the process line with undesired organisms such as milk spoilage bacteria, e.g. Bacillus species or gram negative bacteria or bacteriophages which attack the starter culture organisms resulting in fermentation failures.
In addition to the risk of contaminating the process line, use of bulk starters propagated at the dairy involves the following problems: (i) the preparation of the bulk starter is very labour intensive and it occupies much space and equipment, (ii) there is a considerable risk of contamination with spoilage bacteria and/or phages during the step of propagation and (iii) by passing a mixed population of starter bacteria from one bulk starter to the next, a selection of strains will occur over time whereby the initial desired characteristics of the culture may deteriorate. Similar to the use of bulk starters, the use of DVS-starter cultures also involves a risk of contamination and implies a high degree of manual handling.
In the dairy industry there is a clear trend towards increasingly larger production units. It is therefore evident that the above problems associated with the current use of starter cultures have become more prominent and enlarged.
It is therefore an important objective of the present invention to provide an improved method of delivering dairy starter cultures to the process line which method is not only adapted to the increasing demand for stricter control of contamination of closed dairy process lines but which also implies that the above problems associated with in-plant bulk starter propagation can be reduced or eliminated. Additionally, the starter culture delivery system which is provided herein implies a high degree of convenience for the user.
SUMMARY OF THE INVENTION
Accordingly, it is the primary objectives of the invention to provide a method whereby milk which is processed in a closed dairy process line can be inoculated with the appropriate starter culture directly into the process line, and a starter culture delivery system which is useful in such a method.
Thus, in a first aspect, the invention pertains to a method of preparing a dairy product, the method comprising the steps of (i) providing a microbial starter culture as a culture concentrate in a sealed enclosure which is provided with outlet means for connecting the enclosure to a dairy process line, (ii) combining the microbial starter culture with an aqueous medium to obtain an aqueous suspension o
Elsborg Kristian
Hoier Erik
Laulund Esben
Bhat Nina
CHR. Hansen A/S
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