Flavor of cheeses and the role of animal feed

172
Caciocavalli Palermitani

 Roberto Rubino ex director Crea, Via S. Oronzo, 169, 85100 Potenza, Italy. roberto@robertorubino.eu

Summary

In dairy products, the aromatic complexity (in flavor and taste) and color can show strong variability, even within the same type of product. To some extent, we know the molecules and compounds responsible for flavor, taste and color. We also know the factors that determine their concentration. Conversely, the consumer probably does not have the knowledge to making targeted choices. This article reviews the state of research and the role of ruminant diet on flavor, taste and color of dairy products. The color of cheese depends on the presence of carotenoids, the concentration of which is linked to the physiological stage of the plant and to the environment. The smell and aroma depend on volatile molecules, some of which come from the grass, others develop as a result of technological processes and rumen fermentations. Little is known about the taste, the factors that determine its complexity are not well understood. The hypothesis put forward is that the diet of animals matters much more than what is reported and that polyphenols may be among the factors responsible for taste.

Keywords: cheese, aroma, taste, diet, pasture, polyphenols

Introduction

In almost all regions of the world, the price of milk is sometimes set by commodity stock markets, but above all by the processors. The variations in price used by these organizations are generally linked to local and commercial aspects and, to a lesser extent, to the quality of the product. For these reasons, the price varies little from one ‘milk’ to another. Yet, if we walk into a neighborhood creamery or cheese factory, even an inexperienced consumer realizes that the offer is wide and diverse. In his 1983 novel, Palomar, the Italian writer Italo Calvino (1923-1985), who visited France a lot and whose father, an agronomist, had been director of a research institute in Sanremo, had the right key to reading when he wrote: “Behind each cheese, there is a pasture of a different green under a different sky: meadows salted by the deposits of the Norman tides; meadows flavored with the sunny winds of Provence; there are different herds with different stables and with their specific transhumance; there are secret processes which are passed on from century to century”.

Literature often knows how to offer us interpretations of reality, but seldom allows us to understand its complexity and details that could make the difference for consumers. Dairy products are very different from each other depending on the technologies used, especially ripening and aging, and also depending on the quality of the milk. The first two factors have been studied extensively, not least because over the past forty years the industry of the sector has had to perfect its production processes to ensure safe, traceable and standardized products for the market and demand of consumers. The same cannot be said about milk, except for studies on its safety, because of the obvious consequences of contaminations (in particular those due to Listeria, Staphylococcus aureus, etc.). The consumer certainly wants a healthy cheese, but their choice is affected on the one hand by their memories, and on the other hand by the color and flavor (aroma and taste) and the attractiveness of the product. But today, the consumer also uses other criteria, in particular there is a concern about animal welfare and environmental impact, which importance is increasing on a daily basis.

However, the nature of the raw material is the one that most affects the quality level of the processed product and, in particular, that of the cheeses. In fact, if we take as an example the milk of ruminant females who go to the mountain pastures, we see that its aromatic and nutritional complexity (aroma and taste) changes enormously when the animals switch from feeding to the stable, based on of hay and concentrated feed to that of the pasture. While if we do a comparative tasting between cheeses produced with the same milk but with different manufacturing techniques: raw or pasteurized milk, with or without a starter (of course with well-mastered manufacturing), it is difficult to find the differences, you have to be good experts and in any case the differences tend to be very limited.

And it is no coincidence that in France almost all Protected Designation of Origin (PDOs) limit the amount of concentrates (grains) per head and per year, bringing it to 1,800 kg, or less than 5 kg per day. This implies that those in charge of these organizations consider that large amounts of concentrates fed increases the risks of damaging the quality of the final product. The large amount of concentrate in cow rations is simply explained by the fact that concentrates cause an increase in milk production. However, the research concerning the effect of the diet of cows on the quality of the milk, itself having repercussions on the quality of the cheese is still far too partial because the consumer guides their choices not as much on knowledge of product quality but only by taking into account the experiences accumulated personally on that type of cheese. At least in Italy, the consumer does not enter a business selling quality gourmet products by asking, like in Palomar, for an alpine cheese rather than a pasture cheese. Indeed, very often when the cheese appears yellow, the consumer rejects it, thinking it is oxidized (photo 1). Therefore, it is important to know first which molecules or compounds are involved in determining flavor and secondly which factors determine their concentration. Only then will we be able to say that we have mastered the factors that allow us to define the quality level of cheese at the table and, also, of all other foods.

The subject is complex. Some aspects have been studied, others very probably have in my opinion been systematically neglected. For example, there is little research on the topic of taste. When researchers set out to treat it, they often do so in an unconvincing way. This is a difficult subject for research because the flavor of a cheese is influenced by multiple factors that often interact with each other. Therefore, to clarify my ideas on the subject, I analyzed research work carried out with very different objectives and different experimental conditions. I have tried to get as much information out of it, but important areas of the subject have not been researched or the work appears unreliable. In this case, I was forced to form an opinion which I submit to the reader, trying to reason as objectively as possible.

Consequently, the objective of this article is to report scientific achievements when they exist and when they do not, to reason in the most objective way. I feel able to provide useful reflection on this theme because, during my career, I have worked on different themes concerning the taste, aroma and color of cheeses made from the milk of female ruminants receiving a wide variety of diets.

This article deals only with the dietary factors of the animals which secrete the milk used to make cheese, because these are factors that can be acted on and with which we can observe results quite easily. In addition, they relate to the issues raised by the consumers who increasingly ask to know how the animals whose milk is used in making cheese are treated.

At the end of this introduction to avoid ambiguities, I’ll give some details about cow feed systems, especially pasture-based systems.

There are two dominant food systems in the world: stable and pasture systems. In the first case, the animals consume the same ration often for a long time. On pasture, the ration actually changes every day.

Pastures are a living world. In the upper part there can also be a hundred different plants whose vegetative stage is still evolving, each plant has a different set of scents and a floral variability that attracts thousands of insects including bees. In the hypogeum part, each plant has a different type of root, and the fact that in a square meter there can be up to 7000 plants (Carena et al. 1984) means that this tangle of roots helps to maintain a good structure. of the land and a sufficient level of fertility. But natural and permanent pastures represent above all the ideal basis for the daily diet of ruminants. Thus, each day, the animal can constitute its food by always choosing and selecting different plants. For this reason, during the grazing season, the cheese flavor and color is expected to change almost daily.

Color and carotenoids

The first thing that attracts us to a cheese is the appearance and in particular the color.

If we walk through a blooming meadow and we look around, we will notice how colorful everything is and we continuously smell different odors that come out when touching or walking on the different grasses with our feet. Why are herbs colorful? Because plants have developed defense mechanisms against UV-B rays and, among them, there are carotenoids and polyphenols, a part of which is called UAC, products that are present in the different tissues of the plant, for example in the epidermal layer, lignin, leaves and pollen. Their function is to prevent UV-B rays from penetrating inside the mesophyll of the leaves.

The easiest substances to identify which give valuable information on the quality level of cheeses are carotenoids, which play an important role in human health and nutrition due to their provitamin A function and their antioxidant properties. Despite their low content in milk, carotenoids (β-carotene and lutein) are involved in the sensory properties of dairy products via their coloring and antioxidant properties (Agabriel et al., 2007). The color is less evident in goat and buffalo cheeses because beta-carotene is directly converted into vitamin A, so that their cheeses, if the animal eats a lot of grass, take on different shades of white. However, since the color of the cheese is a very good indicator of its specific aspects such as the aroma or the antioxidant potential and as the physiological characteristics of the grass constantly change according to the latitude and the altitude. It would be important to know what to expect during the grazing season and what the variation in color of the cheese means. Unfortunately, there are no specific studies on the differences in cheeses from pasture-raised animals, but I was able to find some data that allowed us to speculate on this topic.

Maxin et al. (2020) studied the evolution of carotenoids in the initial phase of the vegetative stage and at the flowering stage. 10 carotenoids have been identified in plants. In general, their composition does not vary much between species or during the vegetative phase. What is interesting and will help us understanding the reasons for the variation in the color of a cheese, is the fact that the concentration of total carotenoids decreases significantly when passing from the vegetative stage to the floral stage. The reduction between the two vegetative stages was significant (65%). The composition of the carotenoids is virtually identical as the plant grows, and the percentage of each carotenoid varies little between the initial stage and the flowering stage.

The decrease in carotenoids is believed to be due to the reduction in the leaf to stamen ratio between the vegetative phase and the flowering phase, since the carotenoids are mainly located in the leaves, associated with the chloroplasts.

These data, although limited to only two stages, allow us to hypothesize that the carotenoid content is maximum at the beginning of the vegetative phase, slowly decreases until flowering and then it seems very likely that it decreases faster when the grass turns yellow, because carotenoids are bound to chloroplasts. This hypothesis is always confirmed by the color of cow’s and sheep’s cheese: at the start of grazing period they are very yellow and then the intensity of the color always decreases until it becomes almost white, ivory white. And then the herbaceous varieties present on the pasture also play a role. Legumes, which have a high leaf to stem ratio, add more color to the milk.

Aroma and volatile components

There is a well-stocked bibliography on the aroma of milk and cheese. Almost all authors agree that it is the volatile components that are responsible for the odor and that their content depends in part on animal feed and in part also on microbial fermentation in the rumen. In a long study, Kilkawley et al. (2018) argue that many groups of volatile non-terpenoids are responsible for the aroma of milk: esters, acids, lactones, alcohols, phenols, sulfur compounds, aldehydes and alcohols. A large part of these compounds is formed as a result of chemical transformations (oxidation, breakdown of the carbon chain, etc.) of unsaturated fatty acids, the content of which in milk is anyway determined by the feeding system: the more the animals are on pasture, the more the animal eats grass and the higher the content of unsaturated fatty acids. Therefore, the precursors are all there for the rumen microbes to turn them into volatile and fragrant molecules. For example, with regard to aldehydes, which develop very pleasantly perceptible odors (the classic smell of grass), the authors state that “a significant number of aldehydes can be transferred from plants to milk and cheese”. Alcohols pass into milk especially when they come from silage. For acids, there is not only the influence of diet but also the mode of distribution and the conditions of ingestion. A distribution of a large quantity of concentrates ingested quickly, especially during milking, further lowers the rumen pH, so it can change the direction of rumen fermentations. Volatile sulphides have a lot of importance on the aroma because of their intense smell. The content of di-methyl-sulfone in cheeses is closely related to grazing and, for this reason, it is an obvious indicator or biomarker of grazing. Esters are derived from esterification and alcoholysis processes, so their formation has different origins, but it is always linked to feed. The answer is not unequivocal, because only the components which come from the food are numerous and different. Lactones, on the other hand, are more sensitive to heat treatments than to diet.

As for volatile terpenoids, this is a group of secondary metabolites that derive directly from plants. Therefore, the more grass the animal eats, the more the content of terpenes increases.

Therefore, to what extent, the presence and the concentration of all these substances can vary according to the situation of the pasture? Is there an impact of pasture’s altitude and latitude? Bugaud et al. (2001) found that the level of terpenes is higher in mountain pasture milk than in plain pasture milk. In their research, they found that the more terpenes there were in the herb (limonene, beta-phellandrene, cymene, beta-pinene, and alpha-pinene), the more they were found in milk.

In short, there is agreement that terpenes come from grass and, for this reason, in many places it is proposed to use them as markers of a territory and even a “Cru”, inspired by the use of the term “cru” resulting from the analysis of wine.

It would also be interesting to know how all these substances evolve during the vegetative phase. Tornambè et al. (2006) compared two grazing systems: open grassland and strip grazing. In the open meadow the animals had an area large enough to graze for a period of about 10 days, in the grazing strip they were forced to use a much smaller area (about 5 times smaller) for two days only. In the first case, the trend of terpenes was quite similar during the grazing season, in the second case there was a 5-fold increase from start to finish in the total terpene content. The reason for this large increase is attributed, by the authors, to the fact that the intensively grazed grass is always kept low and green. This condition allows both dicotyledons, plants with more leaves, to take over and always have young leaves and young shoots. Conversely, if the animals had had the choice, they would also have used adult plants, less rich in terpenes.

Borge et al. (2005) analyzed the presence of terpenes in the milk of Norwegian alpine cows reared in three different feeding systems. In winter, an “indoor” diet was adopted, carried out with preserved green fodder and concentrate, while in summer the animals were fed on pasture and more precisely by early grazing at the start of the season and by late grazing at the end of the season. Results over a three-year period showed that the total terpene content tripled during the first pasture feeding period (early grazing) and increased by 5 times during the second pasture feeding period (pasture late), compared to feeding indoors. Four of all the terpenes found in the milk samples were only detected in pasture milk. Therefore, large difference were found between the start and the end of grazing period, but we had no information on the type of grazing and the vegetative state of the grass during this experiment.

Similar results were found by Chion et al. (2010) comparing animals reared in stalls in winter and on pasture in summer. Milk samples obtained during the summer period showed higher levels of terpenes (presence of monoterpenes) in pasture milk compared to milk produced in winter.

From Noni et al. (2008) followed cows in pastures at different altitudes. The monoterpene profile of milk from highland pastures was strictly comparable to that from lower pastures. However, the highest levels of monoterpenes were found in the milk of cows that grazed early in the season at an elevation of 1,400 m.

Two things to consider First, terpenes decrease as we advance towards flowering. Second, the dicotyledons are richer in terpenes because the leaf apparatus is more developed.

Thus, we could explain why spring cheeses, when the grass is low, are yellower and have a stronger aroma.

We can therefore say that the volatile component of cheeses has been widely studied, the several hundred molecules found are known and the causes which determine this aromatic complexity are also known. Though, still see one problem: in front of a very high number of odorous substances, even the trained consumer fails to grasp such complexity. In addition, the relationship between the number of scent notes and the level of quality is not linear: an ordinary cheese can have a proportionately higher number of fragrant notes than a cheese with very high aromatic complexity.

Taste

Let’s go back to tasting cheese. Let’s say we are just chewing a chunk of cheese but we immediately end up with a clean mouth (due to the immediate intervention of saliva) with or without a palate intensely stimulated by different sensations. In practice, the taste can be short and banal or else intense, varied and persistent. This is not the place to go deeper into the scientific aspects of taste, but it does not seem secondary to better clarify the approach and the method of tasting, because everything that comes below is a consequence of the how our taste was formed. It is known that there are five basic tastes (Hartley et al., 2019): sour, bitter, sweet, salty and umami. Then there are the so called “perceptions”, some of which are already defined as kokumi, astringency, metallic, spicy, carbohydrates, calcium, lipids, etc. and others that are waiting for someone to name them. In summary, it is commonly accepted that proteins, or at least some fragments, are responsible for bitterness, amino acids for sweetness, glutamate for umami, acids for acidity and salts for salty. On this aspect, I will limit myself to mentioning a study, which I find interesting, by Engel et al. (2000). Here, the researchers tried to build a model by bringing together the molecules indicated as responsible for taste. The tests carried out allowed us to specify the relative impact of these components on taste, highlighting complex interactions between compounds: the additive effect of salts on salinity, strengthening of the effect of sodium chloride on the acidity, a balance between phosphate and lactate with respect to pH and the masking effect of sodium chloride on bitterness, mainly due to calcium chloride and magnesium chloride. The authors conclude that mineral salts and lactic acid are the main active compounds of taste, while lipids, volatile fraction, lactose, amino acids and peptides do not have a significant impact. More precisely, it has been shown that calcium chloride and magnesium chloride explain, more than peptides, the bitter taste of cheese.

We are still in the realm of the five basic tastes and perceptions that do not allow us to tell and measure the taste sensations we feel when we taste a cheese or an apple or bread. I’m talking about the intensity, variability and persistence of taste. In a cheese made from milk from an intensive system, the classic taste will tell us that it is slightly sour, a little sweet, with a hint of acidity and not very salty. But persistence, intensity and variability are hardly mentioned. On the other hand, in the case of a cheese made from pasture milk, the toasted or herbaceous sensation never washes away in the mount but continues to change, especially if there were many herbaceous species in the pasture. What changes from a stable to a pasture? If the same cow goes from pasture to barn, the proteins in her milk will be the same, so they are not responsible for this long taste; the total fat will undergo slight changes, while its composition changes strongly: the unsaturated ones increase and their oxidation will give more aldehydes and therefore more aroma, but they have no influence on the taste; minerals change little with the feeding system (Arunima et al., 2017) and therefore cannot significantly affect taste. The chemical bodies that change a lot, as we will see in the next chapter, are the polyphenols. It is true that much of the world of science says that they can at most affect astringency and bitterness, but I believe they can play an important role in this little considered part of taste, to namely: intensity, variability and persistence. This is a topic that deserves further study, but it should be studied by comparing cheeses of different taste groups and then tracing the molecules and analyzing the factors that influence their concentration.

Polyphenols and the role of herbs

Forages contain large amounts of aromatic compounds, both in the insoluble cell wall and in the cell contents, including polyphenols soluble in ethanol. These compounds are partially degraded in the rumen to form different aromatic compounds. Certain other components of the diet are also fermented in the rumen to form aromatic or heterocyclic products containing nitrogen and sulfur and, occasionally, some aromatic hydrocarbons. All these compounds are partially absorbed, transformed in animal tissues then excreted in a pool of UV absorbing compounds (UAC) and finally secreted by the udder or deposited in the meat.

Therefore, the main task of polyphenols is to defend plant tissues against the action of UV-B rays. Being antioxidants, they also play an important role in the nutrition of animals and humans and, last but not least, they can influence the taste and color of cheese.

Polyphenols from pasture vegetation

How does the content of polyphenols change during the vegetative life of the plant? Is it different between the start of flowering and the hay-making? Is it different between pastures that are continuously or intermittently grazed? In pasture, this grass, especially if it is perennial, grows under the impulse of the cut, renews itself and is always short, until it dries up with the onset of summer. Thus, the evolution of the phenolic composition will be different depending on whether the grass is grazed or used to make hay.

Fraisse et al. (2007) carried out a study on a natural pasture in Auvergne (altitude 1100 m) at three different periods, May 30, June 13 and July 26. At the botanical level, 43 species have been identified, of which 31 are dicotyledons. Across the pasture, 170 different polyphenolic compounds were detected, of which about 30 were present during the three periods. However, some polyphenols were specific to certain plants while others were ubiquitous in many plants. The total of the polyphenols, in the three successive periods, was 31, 32 and 19 g / kg of dry matter. So there was a very slight increase at the end of June, while at the end of July when the grasses were dry there was a big reduction.

It all depends on the great variation in botanical composition over time. The phenolic acid content was very high in stage 2 (double that of flavonoids), while flavonoids steadily decreased from stages 1 to 3. In general, some compounds increased and others decreased from stage 1 to 2 while ‘a general downward trend has been observed during the last period’. The polyphenolic composition of the main prairie plants harvested individually at the second stage of growth showed that each species had a well-defined polyphenolic composition. All taller plants contain flavonoids in their aerial parts. The main takeaway from this study is that some of the flavonoids are ubiquitous in most grazing plants while others are species specific.

With aging, the content of the main components of the most frequent plants decreases steadily. As the polyphenol content is known to be higher in the leaves than in the stems, the variation with age for a given plant is mainly due to the decrease in the leaf to stem ratio. Environmental conditions are also involved: for example, higher temperatures have a positive effect on polyphenolic content.

The authors conclude that the role of polyphenols is important because a grazing animal can ingest up to 500 g of polyphenols per day, an amount that can affect its well-being and the quality of its production.

Maxin et al. (2020), compared 7 species of herbs, 5 vegetables and 2 grasses at two physiological stages: vegetative and floral. A total of 115 peaks were detected in the analysis, of which only 28 were identified. Almost all the peaks belonged to the classes: simple phenols, benzoic or cinnamic, flavonoids. Therefore, unlike natural pastures, where 170 peaks were detected, here we reached a maximum of 115, demonstrating that the more different the herbaceous species in the pasture, the greater the aromatic complexity will be. Because if each grass provides a different polyphenolic profile, it is clear that the more plants there are in the pasture, the greater the polyphenolic complexity and its consequences.

The result for individual plants is also interesting. Twelve peaks were found in alfalfa, 40 in Alexandrian clover, 35 in sainfoin. However, the number of peaks detected did not differ significantly between phases and comparison of chromatographic profiles showed that there was no common peak for all plant species. In each species, the combination of two or three main peaks represented more than 70% of the total.

The phenolic compounds were mainly made up of flavonoids which made up on average 83% of the total. The distribution of phenolic compounds by class varied among plant species.

Polyphenols in milk

Do the polyphenols in the herbs pass into the milk? There is a fairly comprehensive bibliography on this aspect. We had published a work on goats to which we had given branches of hawthorn and borage (De Feo et al., 2006). In plants and in milk, we had found flavonoids such as quercetin, rutin and beta-sitosterol. Besle et al. (2010) compared six forage systems: 1) intensive with concentrates at 66% of the ration and cocksfoot hay, 2) corn silage 86%, 3) olium silage 85%, 4) olium hay, 5) 87% meadow hay, 6) natural pasture with 0.5 kg of concentrates per head / day. In forages, the number of polyphenols was lower in the corn silage group (57) and higher in the pasture group (85). The amount of phenols in the feed was low in the silage groups (less than 5 g / kg of dry matter ingested). In contrast, in the grazing group, the animals ingested about 35 g / kg of dry matter. The difference between pasture and a diet based on corn silage therefore concerns not only the number of polyphenols, +28, but also the total content, which was 7 times higher.

A total of 230 different peaks were identified in the milk. The groups with the fewest polyphenols were those that remained in the stable receiving silage (87 peaks), while the group whose diet was mainly grazing had only 127 peaks. Among the identified polyphenols we find hippuric acid, phenylacetic acid, benzoic acid, 4-ideoxybenzoic acid and small amounts of ferulic acid and among the flavonoids, quercetin, luteolin and apigenin.

Taste and polyphenols

There is a sufficient bibliography to suggest that the presence of polyphenols can be important in milk and cheese and that it depends on the herb and its physiological stage. On the other hand, there has been no research, at least to my knowledge, relating to the role of polyphenols on taste. However, we know from studies carried out on wine and oil that polyphenols are responsible for astringency. Duizera and Langfried (2016) obtained the same result on wheat: low molecular weight phenolic acids such as vanillic and ferulic acid are responsible for bitterness and astringency when tasting wheat.

We are always on studies of basic tastes or certain perceptions. But there is no information on the factors influencing the variability, intensity and persistence of taste. Can polyphenols be heavier than phenolic acids? It should also be remembered that polyphenols bind to proteins, carbohydrates and fats. We have seen (Buitimea-Cantua et al., 2017) that high molecular weight polyphenols tend to interact closely with proteins and that this interaction produces aggregates that affect their solubility. This interaction influences the functional and nutritional characteristics of raw materials and, in particular, it is responsible for astringency, protein digestibility, absorption and bioavailability of antioxidants. It appears difficult to go beyond basic taste categories. Yet cheeses made with milk from pasture-raised ruminants have an intense taste, and the only molecules that experience a significant increase are polyphenols.

Of course, this is not unequivocable evidence. This only allows us to formulate the following hypothesis: we can assume that the taste depends if not totally but largely on polyphenols and especially on those of high molecular weight?

Conclusions

Except for protein and fat content, the price of milk does not consider its characteristics or components that influence the quality and in particular the taste of the cheese. For this same reason, the price of cheese gives more emphasis to the type or technique of cheese than the quality and flavors of the milk used. Consequently, the price charged to the consumer is somewhat the same. Instead, the differences between wines can be enormous, depending on the source and quality of the grapes. The consumer does not have the tools and keys to make targeted choices, because the messages from the research world are neither clear nor precise. In fact, the rule that determines the level of quality is not known. We still don’t know what the qualitative gradient might be, the difference between the cheese with the lowest quality level and the one with the highest.

Let’s try to summarize the current situation of the problem and see what remains to be done.

The consumer is drawn to the color and flavor of the cheese. The color of cow’s and partly sheep’s cheese has been studied extensively. Very little is known about those of the goat and the buffalo. The molecules responsible are known, we speak of carotenoids, while almost nothing is known about the role of polyphenols, in particular flavonoids, which are normally responsible for the color of plant tissues as well as their contribution to the antioxidant action. Carotenoids come from grass and therefore the relationship between the grass-based diet and the color of cow and sheep cheeses is very clear. The same is valid for goat and buffalo cheeses, although to a lesser extent. But if an animal eats a lot of grass, it will also ingest many volatile compounds and many polyphenols which are also present in herbaceous plants. Therefore, the color could be a very good indicator of the level of aromatic and taste complexity. According to the data in the bibliography, the content of carotenoids can undergo variations in a ratio ranging from 1 to 500. Thus, we have data tending to show that cheeses can be very different. Instead, the message to the consumer is unclear as research continues to say that the factors that affect quality are many and very complicated. And, therefore, in some countries for many consumers the yellow color is a defect. Following this message, goat and buffalo cheeses are supposed to be white and the whiter the cheese, the better (photo 2).

The approach to aroma is not much different. The volatile molecules responsible are known, we know that most of them derive from the feed, that the differences can be important between the content of volatile substances of a milk produced in the stable compared to a milk produced on the pasture. It is also known that their content changes depending on the vegetative stage of the herb but, ultimately, the aroma is largely attributed to microbial rumen fermentations, lipolysis and proteolysis and, to a more limited extent, to the diet of the rumen. animals. However, if we compare a cheese produced with silage and concentrate and a cheese made with milk produced on natural pastures even using the same cows. It is true that the digestion in the rumen will be different, that the lipolysis and proteolysis will be different, but many elements affecting the aroma depend on the herbaceous plants present and chosen by the animal, and in particular the volatile molecules which derive from them. Without them, it would be an ordinary cheese to be produced.

And here we come to the taste of cheese. From what I have read on cheeses but also on other foods, taste is a subject little explored in research, in particular because expensive equipment is necessary and difficult to manage at least until there is a few years. In addition, the discussion is very often blocked on the five basic flavors (sour, salty, sweet, bitter and umami), parameters which do not allow an appropriate measurement of the taste of a food (this is in any case, my personal opinion). Everyone writes that the responsible molecules are the classic components; it can be acids, salts, certain polyphenols at least responsible for bitterness and astringency. However, studies on polyphenols are important in almost all foods because they have a strong impact on health due to their antioxidant properties. This research also teaches us that their concentration, within the same raw material, can be very different, varying in a proportion of a hundred and sometimes a thousand times (as in the case of onions), depending on the production technique for plants, and the diet of animals producing milk or meat.

But it seems obvious to me, if I’m tasting a pasture cheese also produced on the same day of milking, so without the action of proteolysis and lipolysis, I feel an intense and persistent taste. All this can essentially only come from the grass. It is probable that the molecules in question are polyphenols, whether or not they are linked to other compounds and in particular to proteins.

I therefore believe that the role of diet and polyphenols is underestimated while great importance is given to other factors: microbial fermentations in the rumen, proteolysis, lipolysis, fats and proteins. This situation has obvious consequences for consumers and producers. The former does not have the keys to understanding what factors affect the quality of the products they consume and under what conditions they operate. On the other hand, producers are not paid for the quality of the milk they produce and therefore receive a price that does not encourage distributing a diet that respects animal welfare.

List of bibliographic references

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Arunima G., Galvin N., Lewis E., Hennessy D., O’Donovan M., McManus J. J., Fenelon M. A., Guinee T. P. (2017). Outdoor grazing of dairy cows on pasture versus indoor feeding on total mixed ration: Effects on gross composition and mineral content milk during lactation. J. Dairy Sci. 100 :1–14.

Besle M., Viala D., Martin B., Pradel P., Meunier B., Berdagué J. L., Fraisse D., Lamaison J. L., Coulon J. B.  (2010). Ultraviolet-absorbing compounds in milk are related to forage polyphenols. J. Dairy Sci.  93 :2846–2856.

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Bugaud C., Buchin S., Hauwuy, A., Coulon J.-B. (2001). Relationships between flavour and chemical composition of Abondance cheese derived from different types of pastures. Le Lait, 81, 757–773.

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