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Sheep milk: Characteristics, unique features and problems of a one-of-a-kind product

Sheep milk means Mediterranean basin, the geographical area in which this food’s history unfolded. A robust milk, ideal for cheese-making, used to make some of world’s most flavorsome cheeses. And Italy is no exception: the nation’s gastronomical tradition sees a sensibly higher incidence of sheep milk dairy products compared to dairy made with buffalo, donkey and goat milk. However, first place is always occupied by cow milk products.

Partly also due to its history, sheep milk to this day is still used especially as raw material for cheese-making, while its consumption as milk is limited to a much narrower, niche user base. This might be one of the reasons why, despite being a complete food, full of health benefits, scientific studies regarding its nutritional composition are not widely available.

Sheep milk VS cow milk

What are the major differences between the two main protagonists, cow milk and sheep milk? If we evaluate sheep milk’s nutritional composition and we compare it to “whole, pasteurized” cow’s milk, most significant differences arise in distribution of lipids, proteins and carbohydrates percentage. Besides, sheep milk has more calories than cow milk (+39 kcal / 100ml) due to a higher fat content (+3,3g / 100ml), protein content (+2g / 100ml) and glucose content (+0,3g / 100ml), in relation to water content. On the other hand, fat content in sheep milk is substantially the same as cow milk.

For what concerns micro-nutrients, we can see that, due to its higher fat content, sheep milk provides a higher dose of retinol (+0,07mg / 100ml) and a higher dose of calcium (+61mg / 100ml).

Therefore, if we take a look at the two foods’ chemical composition, there is a major difference in terms of energy value, which is sensibly higher in sheep milk compared to cow milk and, considering that sheep milk is mainly used for producing hard cheeses, where water percentage drops from 82% all the way down to 30 – 35%, this difference in composition is amplified and translates in a higher nutritional value.
lk sheep and sheep dairy products as functional food?

Milk sheep rhymes with health

Milk sheep and, subsequently, flavorful sheep cheese are among the pillars of Mediterranean diet and are known to prevent not only certain kinds of heart diseases, but also certain specific types of cancer, especially colon cancer and breast cancer. This has been showed years ago, by Professor Mauro Antongiovanni, full professor of Animal Nutrition and Feeding at Zootechnical Science Department of University of Florence, author of a research paper which results had been presented in the United States at the World Meeting of Animal Science and Dairy Science, organized by American Society of Animal Science and American Society of Dairy Science.

The study showed that, by analyzing fat content in milk produced by a herd of Sardinian sheep that had been fed with fresh grass instead of dry forage, it was possible to drastically reduce (40% on average) harmful acids (myristic and palmitic acid) concentration and to likewise increase healthy acids, such as butyric acid (+15%) and especially CLA (conjugated linoleic acid or rumenic acid) of a whopping +500%.

What are these two acids and what is their role? Myristic acid and palmitic acid are saturated fats, some of the worst enemies of our health, because, among other things, they pose a risk factor for hearth and coronary disease. Butyric acid, on the contrary, is a powerful stabilizer of gut’s micro-flora, it prevents colon cancer and acts as anti-diabetic. As for CLA, it is an acid known for its exceptional health benefits: it helps preventing bad cholesterol build-up while promoting good cholesterol, therefore helping with prevention of heart diseases. It also has anti-inflammatory properties and it stimulates immune system with an antitumor function (breast carcinoma, colon cancer).

The above-mentioned research took inspiration from similar studies on cow’s milk, which is still vastly more popular all over the world compared to sheep’s milk, including its dairy derivatives (butter, cheese, yoghurt), and therefore more economically relevant. In fact, sheep milk and sheep cheese are basically niche products or products with limited, ‘marginal’ diffusion, and are mostly consumed in Tuscany, Lazio, Sardinia and, outside of Italy, in Greece (with Feta), and to a limited extent in Spain, Portugal and France. The latter, as a great consumer of goat milk, promotes this product a lot as an alternative to cow milk.

Sheep’s milk: features of a unique product

Let’s analyze in more detail the intrinsic characteristics of sheep’s milk. Let’s start from fat; this component is the most subject to variations during lactation period: right after birth, its levels are quite high, then values go down during the first 50-60 days of lactation, inversely proportional to production. As lactation continues, fat amount can vary greatly, and difference between minimum and maximum values can be as high as 30%; moreover, milk produced by afternoon milking is richer in fat compared to milk produced in the morning. These variations have of course major influence on how milk ‘behaves’ with regards to cheese-making and especially in terms of fats percentage in cheese and yield of cheese factories.

A really interesting study has been conducted by Bologna branch of Istituto Zooprofilattico Sperimentale (Experimental Institute of Veterinary Epidemiology), in collaboration with technicians from Associazioni Provinciali Allevatori (Province Breeders Associations). Researchers took samples of milk from 95 breeding farms of Sardinian and Massese sheep breeds. Here are some results from the analysis: Sardinian breed has fat levels ranging from 6,01% to 8,38%, while Massese breed ranges between 6,52% and 8,23%. Mean value is equal to 7,13%. Other studies found values ranging between 6,20% and 10,60% for Comisana breed and between 6,13% and 7,97% for the Langhe breed.

As for the comparison with cow’s milk we mentioned above, we must highlight that sheep milk contains a higher number of fat globules, but these are smaller and constituted for the most part of medium-chain fatty acids. This makes them easier to digest. As for composition, fats are made up of triglycerides for 98% and phospholipids for 0,8% plus smaller quantities of free fatty acids. Most prominent fatty acids are palmitic and oleic acids (25% and 20%), but we can also find medium-short chain fatty acids like caprinic acid and caprylic acid that are present in higher quantities compared to cow milk and they are responsible for cheese’s pronounced flavor.

Protein content is also subject to variations during lactation, although these variations are smaller than those we can find in fats content. Analyses conducted by Bologna’s Istituto Profilattico showed a general average value for all breeds of 5,91%, with percentages ranging between 5,47% and 6,22% for Sardinian breed and between5,25% and 6,23% for Massese breed.
Data from other studies show protein values ranging between 5,55% and 5,82% for the Comisana breed and ranging between 4,77% and 5,81% for the Langhe breed. In sheep’s milk, ratio of protein and nitrogen-matter is really high (equal to 95%) and indicates a very low content of non-protein nitrogen, with a clear advantage for the cheese’ organic value.

Overall, as lactation continues, milk tend to get richer in casein and soluble proteins, while content of non-protein nitrogen decreases.

Electrophoresis and protein content

Given the main purpose of sheep’s milk, studies regarding composition of various casein fractions are very relevant; besides, thanks to their different electrophoretic mobility (S, S2, beta and K) it is possible to differentiate sheep milk from goat milk and cow milk.

Electrophoresis method is based on differential of electric charges of different protein fractions, which move on dedicated support systems with different speeds: the higher the speed, the greater the electric charge. Analysis of composition shows that S and S2 in sheep milk are lower compared to cow milk, while beta-casein is higher in sheep milk, as an additional proof of this milk’s cheese-making properties. These differences in casein composition are reflected both in the micelle’s structure and in the milk’s behavior in the boiler. In fact, sheep milk takes less time to coagulate and has a thicker texture compared to cow milk. In sheep milk there is a higher percentage of serum proteins and this are involved in Ricotta cheese production.

Fortunately, over the last few years, thanks to a better awareness and maturity in the consumer base, even within huge markets which are crucial to the economic growth of operators and for developing applied research, such as the Chinese market, more and more attention is payed to this product, which is wrongly considered by most as just raw material for its by-product, although we are talking about a first-class by-product such as sheep cheese, a meaningful presence in the nations of the Mediterranean basin with its numerous variants, a kaleidoscope of flavors and knowledge, those of the deepest and most authentic part of the Mediterranean.