Raw milk cheeses: a valuable and diverse treasure with ...

Raw milk cheeses: a valuable and diverse treasure with challenges for the future / 7

Raw milk cheeses: a valuable and diverse treasure with challenges for the future

Extracts of the document: Les fromages au lait cru : un capital précieux et multiforme avec des enjeux pour l’avenir - Recueil de connaissances 2016

Authors: Florence Arnaud - Syndicat du Morbier, du Mont d’Or et du Bleu de Gex Haut-Jura, Pascal Berion – Université de Franche-Comté / UMR CRS 6049 ThéMA, Eric Beuvier – INRA de Poligny, Yvette Bouton – Comité Interprofessionnel de Gestion du Comté, Valérie Michel – Actalia, Eric Notz – Centre Technique des Fromages Comtois, Denise Renard – Comité Interprofessionnel de Gestion du Comté, Dominique-Angèle Vuitton – Université de Franche-Comté / EA 3181


What is raw milk? What is a raw milk cheese?

Raw milk stands for natural untreated, animal milk that has not gone through pasteurization,

sterilization, thermization or micro-filtering. Raw milk is not brought to a temperature higher than

40°C, i.e. a temperature close to the temperature of the animal’s body. Consumption of liquid raw

milk nearly totally ceased in Western urban areas after pasteurization was discovered in 1864, but it

has remained steady in rural territories, especially in the regions where dairy farms are present.

A raw milk-cheese is a cheese prepared from raw milk. For years, and for some cheeses for

centuries, the microbial flora, i.e. the assemblage of microbes proper to raw milk (also called

‘microflora’, and now ‘microbiota’) has been exploited for its acidifying, proteolytic, lipolytic and

aromatic properties through specific regional craftsmanship transmitted from generation to

generation.

Empirically, the organisms present in milk have been used for milk preservation, including cheese

making. Raw milk-cheese making, following a deeply rooted heritage of diversity and complexity,

were and still are in absolute need of science inputs. As time went on, scientific progress has

highlighted the more precise role of the microbiota in cheese fabrication processes. First, it was a

matter of mastering cheese organoleptic quality by using microbial species with precise technological

and aromatic functions. Then, studies have focused into the sanitary level as well, in order to make

cheeses safely and with a constant level of quality. For the last past years, studies have taken interest

into understanding the complex biological phenomena which make possible that highly diverse

cheese production which is a unique heritage of our Western civilization. They have especially well

demonstrated that the final highly praised distinct sensorial properties of traditional raw milk-

cheeses and their associated microbiota came from each step of the milk and cheese producing

chain, from the flowers of the pastures to the environment of the ripening cellars, through the

unique ‘know-how’ of the cheese makers. They have also addressed the possible beneficial effect of

raw milk-cheese on health and diseases.

Raw milk, a factor of diversity for cheeses

Traditional practices used from milk production to ripening allow for particular flavours and

extremely different aromas between cheeses of a same type. This diversity of cheeses is due

especially to important variations in the initial microbial ecosystems of the various milks. These

variations in microbial composition lead cheese makers to technological adjustments. It is generally

accepted that these adjustments affect the general aspect of the cheese; but they also induce an

organoleptic signature specific to the dairy where the cheese was made. Richness and uniqueness of

each Protected Denomination of Origin (PDO) family of cheeses is generated thanks to the subtle and

infinite combinations of animal breed and mode of feeding, season, soil and flora of the pastures

(comprehensively included in the French word ‘terroir’), and fabrication processes. Original microbial

communities thus provide a unique sensorial diversity to raw milk-cheeses, as the outcome of a

complex and interactive process.

Raw milk-associated health benefits

An ability to limit the emergence of antibiotics- resistant strains of bacteria


Results obtained by a consortium of French, Swiss and Italian cheese professionals and researchers

working at the University of Franche-Comté and at the National Institute for Agronomic research

(INRA) in the French Jura mountain area, have strongly supported the ability of raw milk-cheese

microbiota to survive in the intestine and to limit the occurrence of antibiotics-resistant bacteria

after a common antibiotic treatment, amoxicillin associated to clavulanic acid.

Prevention from allergies and from infections of the 1st year of life

An epidemiological study on allergy prevention and immunity by the rural environment, the

‘PASTURE cohort’, has involved a thousand families at the scale of 5 European countries for 16 years,

including Austria, Finland, France, Germany, and Switzerland. Allergy, i.e. asthma, atopic eczema, hay

fever, food allergy, constitutes a major public health issue which rapidly increased within the last 4

decades of the 20th century to reach more than 25% of the population today. As the number of

allergic patients is higher in cities, it was believed for long that urban pollution was at stake, as well

as changes in urban vegetal environment and population feeding habits. Yet, pollution is not but an

aggravating factor to these diseases; it does not increase the number of cases itself. Actually, and

conversely, studies performed in the 1990s highly suggested that the rural way of live, a countryside

living environment and, most importantly, the traditional style of life of dairy farmers, protected

from allergies.

To confirm that hypothesis, the PASTURE cohort has prospectively studied children since before they

were born. The 500 children born and living on a farm were compared to those 500 living in the same

rural areas but not on a farm. An enormous amount of data has been collected from the analysis of

samples of maternal milk and cow milk, of farm, carpet and mattress dust, of parents’ and children’s

blood as well as of the multiple questionnaires on children health and alimentation all along the

study. The study confirms unequivocally that life on dairy farms is an important factor of protection

against allergies. The earlier children are exposed to farming environment, including during their

mother’s pregnancy, the higher the positive influence. The main 2 factors of protection clearly and

consistently identified through the follow-up of this children cohort are the contact with animals (in

stables and barns: farm animals, and also dogs and cats), and regular consumption of raw milk – by

the infant but also by his mother during her pregnancy. Similar results have been obtained in other

studies with other designs, conducted in several other countries. “Drinking raw milk’ is a factor

distinct from ‘living on a farm’, and it applies as well to rural children not living on farms, and even to

children living in cities but sharing the same raw milk consumption. Consumption of dairy products -

like yoghurts, farm cheeses – was associated with protection as well. In addition, the PASTURE study

showed that infants drinking raw milk had less acute respiratory infections during infancy. It also

showed the importance of food diversification during the first year, and the influence of eating a

variety of cheeses during the first 18 months of the infant’s life. Overall, the concept of diversity

appears as a central idea from the results of recent studies, and so the necessity to preserve it comes

out scientifically reinforced.

Scientists keep on searching what raw milk and raw milk-cheeses bring up exactly in terms of

protection against disorders of allergic origin. An early encounter with microbes is important to

educate and train the immune system, and early changes in the immunological profile of the

protected children was demonstrated in the PASTURE study. Non-pathogenic organisms brought by

fermented products, such as cheeses, play a major role in this learning process since they are


determining the quality of the intestinal microbiota (also called collectively ‘intestinal –or gut-

microflora’ or ‘microbiome’). These microbiota are composed of the billions of organisms – bacteria,

yeasts, fungi– present in the intestines and depend on what one breathes and eats

We now know that microbiota have multiple functions: in addition to immunological functions,

production of vitamins and fibre digestion, they have metabolic properties involved in the prevention

of obesity and cardiovascular diseases, and they even influence psyche, stress level and decision-

making… For all these functions, the diversity of microbial strains and species present in the intestine

is essential. Any alimentation favouring this diversity favours a balanced microbiome, and therefore a

balanced health status.

In addition to the role of organism biodiversity, the presence of immunomodulating factors and

distinctive lipids in raw milk, like omega-3 fatty acids in non-heated and/or homogenised milks, has

been associated with protection against asthma and allergies. A number of whey proteins, of

peptides with immunoregulatory properties, and of lipid components found in raw milk are

destroyed or highly modified, at various degrees, by the various modes of thermization. Recent

results from the PASTURE cohort have shown that children with the highest levels of the short chain

fatty acids (SCFAs) butyrate and propionate in faeces at the age of one year had significantly less

allergenic sensitization and were less likely to have asthma between 3 and 6 years; children with the

highest levels of butyrate were also less likely to have a reported diagnosis of food allergy or allergic

rhinitis. Such results are supported by experimental data. Further researches are necessary to assess

a possible responsibility of traditional raw milk-cheese consumption in triggering such effects.

Raw milk effects on inhibition of pathogenic microbes If the possible infection of some raw milk-cheeses by pathogenic microbes can be considered a

disadvantage in the food safety domain – to the point that the USA ban any importation of raw milk

cheese under 60 days of maturation – conversely, the microbial richness of a raw milk-cheese

protects it effectively against those hazards related to re-infection by pathogenic microbes all along

the cheese-making, ripening, and storage processes. Indeed, sterilizing milk before cheese

production can, because of the absence of competition between species/strains, paradoxically leave

the gates open for secondary infection by this type of pathogens, as suggested by the

epidemiological analysis of food-borne infections during the past 15 years which often involved

cheeses produced with heat-treated milk.

There is scientific evidence that the diversity of the microbial ecosystem of raw milk-cheeses such as

the French raw milk-cheeses Saint-Nectaire or Livarot may effectively counter the development of

pathogenic bacteria such as Listeria. Works from the INRA Unit in Aurillac, in the Massif Central area

of France, have shown raw milk potential for inhibiting pathogenic bacteria in semi-hard cheeses.

Other research works have demonstrated that an inhibiting effect towards Listeria monocytogenes

was operating when a complex biofilm was present on ripening shelves of the Reblochon cheese, a

PDO cheese produced in the French Alps. Using raw milk and certain traditional equipment, like

wooden vats or wooden ripening shelves, far from increasing risks of health hazards, guarantee a

lower risk, thanks to the inhibiting effect of certain non-pathogenic organisms. Indigenous microbiota

of very different compositions protect against Listeria monocytogenes inside cheese curd and at the

cheese surface. The inhibition seems to be associated with quantitative and qualitative composition


of these microbial ecosystems rather than to their degree of diversity. Traditional cheese capacity to

limit the development of pathogenic bacteria is thus related to indigenous inhibiting strains or

microbial consortia. However, the mechanisms of inhibition have not yet been figured out exactly.

The mechanism may be biological – synergy, commensalism, or, on the contrary, antagonism or

competition. Natural non-microbial components of the milks play probably also a role in the process

such as temperature, hygrometry, oxygen level, or pH. It may also involve an association of several

factors. Depending on the case, bioprotection may rely on inhibiting elements (fatty acids, peptides),

on nutriments (present or absent), on physical or chemical modifications (acidity) and/or on

biological competitions (colonization).

A promising way towards understanding the inhibiting systems that are observed in practice consists

in isolating and simplifying the microbial ecosystems present in cheeses whenever the existence of a

protecting system is suspected. Then, the goal would be to identify practices that favour the

appearance of the identified ecosystem and/or to offer cocktails of selected strains capable of

reproducing its effects. Recently, the INRA Unit in Aurillac showed that it was possible to protect raw

milk-cheeses against the development of Shiga Toxin-like producing Escherichia coli by using

antagonistic bacteria throughout the development of two serotypes: O157 and most importantly,

O26, the prevalence of which is higher in raw milks.

Prevention of pathogenic hazards can rely on understanding and then application or preservation of

actions or mechanisms that have an inhibiting effect such as the sequential or simultaneous use of

temperature, water activity, pH, production of acetic acid, etc. Then, safety will not rely any longer

on the effectiveness of a single “barrier” but on mastering a succession of barriers. This proposition is

defined in the Codex Alimentarius as ‘the use of a combination of factors to control microbial

development’. However, our understanding of microbiota of technological interest must be explored

in more depth. New research techniques should eventually allow us to better understand the cheese

microbiota and make the link with the composition and properties of the human microbiota, a

domain with unprecedented expansion and fascinating developments. Understanding the

mechanisms behind the construction of cheese intrinsic characteristics, at the milk production and

cheese transformation levels, would make it possible to formalize the role and management

modalities of microbial ecosystems during this construction. Given the number of varieties of

cheeses, there is much to do, and funding such research remains an issue.

Traditional raw milk-cheese making as an asset to preserve

environmental biodiversity with societal added value.

Traditional raw milk-cheese making plays an important part into adding value to the dairy farming

and cheese making professions, into maintaining a lively agriculture in territories with difficulties,

into preserving employment and keeping landscapes open, into preserving the touristic

attractiveness of a variety of regions, and into creating social bonds in our modern society. The

studies conducted to reinforce connections between milk production and cheese transformation

allow all actors of the field involved in the cheese making process, producers, cheese makers and

ripeners, to share the same objective: producing high-quality cheeses, rooted in their territory.


Particularly present in mountains and areas with geographic constraints, activities of production and

transformation of raw milk meet the expectations of a part of consumers which is getting bigger and

bigger, in European countries, in terms of the finished products themselves (the cheeses) and in

terms of their methods of production as well (sustainable agriculture). This change in consumers’

perception of the produces and modes of production includes, paradoxically, countries that were

defenders of pasteurization at any cost in the past, such as the USA. The dynamism and the

adaptation of producers to evolutions, internal just as external, lie in their capacity to offer high-

quality non-standardized products, based at the core on the proper management of microbial

populations all along the process of production and transformation. The microbial ecosystems

present naturally in the fabrication cycle of traditional cheeses are controlled and exploited through

the good practices that all actors at each level of the cheese-processing chain – breeders, cheese

makers, ripeners – have succeeded into maintaining and developing as time went on. Therefore, the

biodiversity naturally present in the various production and transformation environments eventually

finds its achievement in each cheese through the creation of its inimitable sensorial specificities. The

diversity of cheese characteristics, and the subsequent consumer’s pleasure, are thus the outcome of

the diversity of conditions of production and transformation of the milk, which are in turn part of the

consumer’s satisfaction.

Conclusion

Positive aspects of raw milk-cheeses are considerable. The benefits mentioned in this document

show the importance of maintaining a high biodiversity in cheese indigenous microbial communities

but also of maintaining the diversity of cheese fabrication practices which guarantee this microbial

diversity and the cheese quality. A great diversity of microbial metabolic activities, combined with

distinctive cheese fabrication methods, is crucial for the diversification of gustatory characteristics

specific to traditional cheeses; in addition it may be a very attractive leverage for reducing

pathogenic hazards.

The goal of searching for scientifically-based knowledge on raw milk-cheeses, and protecting their

mode of production, is neither to convert the entire cheese industry to using raw milk nor to

encroach on other types of production with their own economical and/or social logics. It is to

maintain and improve the quality of produces with high added-value – which we have seen to have a

lot of different impacts into many sectors of human activity, and that cannot only be accounted for

an alignment on the shelves of a supermarket.

A few questions should first be addressed, e.g.: What is the correlation between soil and cheese

microbiota? What is the health benefit directly related to the consumption of raw milk cheeses?

Studying the relationship between consumption of traditional cheeses and the intestinal microbiota

is likely a new and fruitful way to address the second question. The fast improvements in

metagenomic analysis and their easier and cheaper access should provide new data on the

microbiota of soil, raw milk, cheeses and of human gut. Combined with those on non-microbial

components of cheeses which could act as prebiotics, with measurements of the immunological

response and with the evaluation of the prevalence of diseases, these data should clarify the

relationship between health and consumption of raw milk-cheeses.

Demonstrating the risks associated with the consumption of raw milk-cheeses with a couple of food-

poisoning cases, with its emotional weight conveyed by the media, is relatively easy; estimating how


this consumption has also “saved lives”, however, is far more complex and relies on long-term, less

emotional, evaluations. Isn’t sentencing raw milk cheeses to death with suffocating regulatory

pressure also a risk for public health in the middle- and long-term? It is essential that the weight of

regulation stays proportional to our scientific knowledge of risks, to a sound evaluation of the

risks/benefits ratio, and to the measure of the real pathogenicity of microbes originating from raw

milk and raw milk-cheeses for the populations. Loss of microbial biodiversity is, by definition, less

visible than loss of floral or wildlife biodiversity, but it may be just as serious.

Sanitary pressure from the last decades translated into a general impoverishment of the microbial

flora of raw milks. There are other ways of food processing than the hygienic strategy which consists

in “emptying, then replacing”: cultivating and supporting biodiversity all along the fabrication process

is a sensible alternative. The question of having a different approach to the microbial ecosystems is

worth asking. There is no question of advocating for a “backward step” and fostering permissiveness

when it comes to hygiene and infection. But the microbial ecosystems of milks are complex and their

balance subtle, not only a catalogue of microbes with single functions that can be put indifferently

next to each other. Finally, taking up on complexity will likely be the hallmark of the 21st century

scientific research, after the necessary simplifications that have been ruling over the 19th and 20th

centuries. Didn’t Pasteur himself – whom it would be pretty reductive to assimilate to pasteurization

– spend the best part of his life studying how complex microbial associations were contributing to

the quality of wines and beers? It is fortunate that new technologies of genomic characterization

finally make accessible an approach of microbiota that was still unthinkable until very recently.

Raw milk cheeses: a valuable and diverse treasure with ...

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