Cheese ripening process

Details Cheese ripening process Cheese ripening process

2000-12-29

2003-11-18

Wong, Leslie (Department: 1761)

Food or edible material: processes, compositions, and products

Fermentation processes

Of milk or milk product

C426S034000, C426S036000, C426S038000, C426S043000, C426S582000

Reexamination Certificate

active

06649200

ABSTRACT:

The present invention relates to a process for the accelerated ripening of cheese.
Cheese ripening is the term used to describe the process whereby changes occur in the curd, resulting in the development of flavour, texture and aroma in the finished cheese. In commercial cheese production, ripening is initiated by the addition of a bacterial starter culture and rennet to milk. The starter culture bacteria convert lactose into lactic acid, producing an acidic environment in which biochemical reactions occur that are critical for cheese ripening. (Scott, R., ‘Cheesemaking practice’, Chapter 11, pages 145-146, 1986, Publ. Elsevier). Furthermore, enzymes released from the bacteria are also involved in the degradation of proteins into peptides and amino acids, and the breakdown of fatty acids into keto acids, ketones and esters by lipolysis. These breakdown products are important in the development of flavour, aroma and texture (Aston et al., Aust. Journal Dairy Technology, 38:55, 1983). In all, the ripening process can take up to a year or more.
Modern cheesemaking techniques employ a number of different methods in order to speed up the ripening process, so that the resulting cheese requires less storage time before maturation is complete and is available for sale more quickly.
One method for accelerating the rate of cheese maturation is to add purified bacterial proteolytic enzymes to the maturing cheese (Fox et al., Antonie van Leeuwenhock, 70, 271-297, 1996) but this involves expensive enzyme isolation. Moreover, the majority of the enzyme is commonly lost in the whey.
An alternative method for increasing the rate of ripening is to add a proportionally greater number of starter culture bacteria to the maturing cheese, in order to provide a larger pool of bacterial enzymes. However, if the number of bacteria added exceeds a certain threshold, the level of lactic acid that is produced by the bacterial starter culture imparts flavour and texture defects to the cheese. Thus, the maximum size of starter culture is effectively limited.
To increase the number of starter culture bacteria without increasing cheese acidity, modern cheesemaking methods have employed attenuated starter cultures, added at the same time as the primary culture. The primary culture is responsible for establishing the necessary acidity. However, in the attenuated starter culture, a majority of the cells is killed, or at least rendered incapable of growing in the cheese making process, such as by heat- or freeze-shocking, which prevents or suppresses acid production, but leaving proteolytic enzymes undamaged. Pre-treatment to kill a proportion of the cells, thereby preventing the metabolic processes that lead to acid production, is described by Frey et al. (Milchwissenschaft, 41 [11], 1986). The treatment may also lyse some cells, resulting in losses of enzymes to the whey.
One problem with methods that are based upon temperature shock is that bacterial cells and the enzymes they contain have different sensitivity to heat treatment. Some starter culture cells are stable to temperature shock, while the enzymes important in cheese ripening are temperature sensitive. In this case it is difficult to sufficiently attenuate the cell culture whilst still retaining the desired enzyme activity. The end result is only a very moderate increase in flavour intensity. The use of heat shocked cells additionally presents other problems, such as cheese bitterness, off-flavours and acetaldehyde production. Moreover, the mass of cells required for this process may be economically prohibitive. Striking a satisfactory balance between sufficiently and economically attenuating the cell culture whilst retaining adequate enzyme activity has, thus, been described, but is effectively impossible to achieve in practice (Fox et al., supra).
Alternative pre-treatment methods using solvents, such as n-butanol, to accelerate ripening, have also proven commercially impractical (Exterkate F. A., J. Diary Res., 46, 473-484, 1979).
Thus, there is a need for a commercially practical method to attenuate a bacterial culture which both kills sufficient cells to limit the production of lactic acid but which also retains high levels of enzyme activity.
We have now, surprisingly, found that the treatment of bacterial starter cultures with surface active agents attenuates the starter culture in such a manner as to overcome the problems identified above.
Thus, in a first aspect, the present invention provides a method for accelerated cheese ripening using a primary starter culture and an attenuated bacterial starter culture, characterised in that the attenuated starter culture is obtained by treatment with an acceptable surface active agent.
The term ‘starter culture’ relates to any bacterial culture that is suitable for use in cheese ripening, such as Bifidobacteria, Brevibacteria, Lactobacilli, Lactococci, Leuconostocs, Micrococci and Pediococci. We prefer that the culture is a member of the lactic acid bacteria. We particularly prefer that the bacteria that are used in the starter culture are Lactococcus species. It will be appreciated that the term ‘starter culture’ may encompass a culture containing a single strain of bacterium, or more than one bacterial strain. The term ‘starter culture’ may also include genetically modified organisms (GMO's). In any event, the term, ‘starter culture’ is well known in the art, and the invention extends equally to all known starter cultures.
The ripening of cheese relies on the curds being converted into cheese with the desired flavour, texture and aroma. Without being constrained by theory, it is known that a number of different biochemical reactions are involved in the maturation process. Ripening is related to the production of peptides and amino acids from casein, and also to the breakdown of fatty acids into keto acids, ketones and esters by lipolysis. Nevertheless, the development of cheese flavour evidently involves a complex interaction, most likely comprising mainly the breakdown products of proteolysis and lipolysis, and many starter cultures are known to express enzymes implicated in cheese ripening. It is these cultures which it is preferred to attenuate for use in the present invention.
The attenuated starter cultures are selected for their enzyme activity so that, while they will generally be selected within the criteria laid down above, it is preferred that they do not generate lactic acid as this is the function of the primary starter culture. In fact, the primary starter culture (or primary culture) will not generally start to produce lactic acid until after its addition. Accordingly, as this tends to rely on gene expression, the attenuated culture cannot play a large part in acidogenesis. Instead, the attenuated culture essentially serves as a source of ripening enzymes, but saves on the cost of isolating the individual enzymes and loses no activity through thermolability. It is particularly surprising that surface active agents, such as dodecyl sulphate, have no significant effect on enzyme activity, as they are known to be extremely denaturing (Scopes, R. K., Protein Purification, Principles and Practice, 1982, Springer advanced texts in Chemistry, publ. Springer-Verlag).
As used herein, the term “attenuated” relates to a bacterial culture so treated as to render the majority of the cells therein unviable. In the context of the invention, it is preferred that no cells be detectably viable in the mature cheese and, more preferably, that no cells should be detectably viable in the attenuated starter culture (or attenuated culture).
The cells of the attenuated culture are preferably rendered unviable, or dead, without disruption. An homogenised preparation loses enzymes in the whey, as described above. However, a level of disruption is acceptable, provided that it is not too great.
When using a non-attenuated starter culture, variable growth of the starter culture cells is often observed. This frequently leads to variable enzyme activity levels and a degree of inconsistency in the degr

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