A pioneering technique for producing cheese from the milk of horses and donkeys has been developed by an Italian researcher.
Milk from horses and donkey has long been considered unsuitable for cheese production because, unlike other milk, no curd is formed with the addition of common rennet.
Preliminary investigations showed that donkey milk under the action of common bovine-based rennet formed a very weak gel compared to the gel formed from bovine milk. Mare’s milk showed no gel formation at all.
Now, food technologist Dr Giuseppe Iannella has discovered that camel chymosin – the enzyme found in camel rennet – is able to effectively clot equid milk if performed through what he describes as an appropriate technological process. It has been named the Nativity-Equid cheese-making method.
Iannella’s findings have the potential to open the way for the commercial production of cheese using donkey or horse milk.
Estimates suggest that more than 30 million people worldwide drink equine milk regularly, with that figure increasing significantly annually.
The nutritional and therapeutic properties of equid milk were well known, he said. Reviews pointed to donkey milk being used successfully as a substitute for human milk in some parts of the world. It had low levels of protein and fat but was high in lactose, which aided palatibility and mineral absorption.
Horse milk and donkey milk also have been used as an alternative food for infants with food allergies, most often a moderate cows’ milk protein allergy, but tolerability must be tested first. However, results to date on equid milk tolerability cannot be considered conclusive, he said.
Equine milk formed a weak coagulum under acidic conditions and this was exploited in the production of yoghurt-type products, especially in the Netherlands, where it was generally flavoured with concentrated fruit extract.
Traditional fermented horse milk beverages, known as airag and koumiss, are popular in Eurasian steppe areas. Koumiss is used in Russia and Mongolia for the management of digestive and cardiovascular diseases, he added.
He noted that although horses were of minor importance for milk production in comparison with cows, buffalo, sheep and goats, they have traditionally been important dairy animals in Mongolia and in the southern states of the former Soviet Union, such as Kazakhstan, Kyrgyzstan and Tajikistan.
Iannella, in his study, “Equid milk renneting through pure camel chymosin and cheese manufacturing”, said sales of equid milk have increased considerably during recent years.
Research was now focused on the development of new products or new methods for extending shelf-life, while maintaining some of the unique components of equid milk.
Cheese-making, an important method for preserving milk, represented one of the earliest biotechnological applications of enzymes, previously referred to as rennet.
The active ingredients in this process are the enzymes pepsin and chymosin. Chymosin is prevalent in the stomach of newborn mammals, unlike pepsin, which predominates in adult mammals. Chymosin is the preferred enzyme in cheese-making, especially bovine chymosin.
He reported in preliminary research in 2011 that horse milk did not form a gel during renneting with bovine-sourced chymosin. Donkey milk formed a very weak gel, but it was unsuited to cheese production.
However, Iannella found in his research, started in 2014, that camel chymosin was able to effectively curdle raw donkey milk and, in further research this year, mare’s milk.
Iannella hypothesizes that the superior clotting activity of camel chymosin could be attributed to variations on the surface charge, at the binding sites, that facilitate the association between camel chymosin and equid casein, and to the improved flexibility of camel chymosin in the ability to accommodate the substrate as happens in camel milk, according to previous work by other authors.
In addition, he found a found a peculiarity with donkey and horse milk: Heat treatment beforehand resulted in no clot formation when the camel chymosin was added.
This was most likely a result of protein changes arising from the heating process that inhibitrf the interaction between camel chymosin and the casein, he said
Iannella described his findings as a decisive step toward the possibility of using equid milk in the dairy sector for cheese production.
“The processing of equid milk into cheese is technically more difficult than milk from other domestic dairy animals,” he said.
“This is mainly due to its low total solids content, and casein content of donkey and mare’s milk.”
He says that the heating of equid milk, at coagulation temperature, is the most critical point in cheese manufacture. For this reason, the process must take place in a “soft way” – in a water bath at temperatures below 43 degrees Celsius.
The elastic coagulum obtained in this process developed about 6 hours after the addition of commercial camel chymosin in a sub-acid environment, he said. The long clotting time is due to the different enzymatic reaction in equid milk.
Cheese curds obtained in the process can be treated in different ways to produce different styles of cheese or used as an ingredient in other foods.
Iannella continued: “The average cheese yield obtained from equid milk, around 4% from mare’ milk and 3.2% for donkey milk was lower than that reported in literature for cow milks (around 10-12%).”
Iannella said that the use of starter cultures was necessary in equid cheesemaking because they were responsible for lactic acid production, which improved curd firmness and suppressed the growth of undesirable bacteria in the curd.
Cheese made with raw milk must be seasoned at least two months, by which time most of the pathogenic bacteria present will be dead.
He said more research was needed to study the mechanism of enzymatic coagulation in equid species to improve cheese yield.
More uses also needed to be examined for the nutritious whey produced from the cheese-making process, in addition to “ricotta” production.
But, in particular, he considered research was needed to assess if cheese and dairy product produced from equid milk can be used as alternatives for people suffering from food allergies.
The full study, “Equid milk renneting through pure camel chymosin and cheese manufacturing” can be read here.
Dr Giuseppe Iannella, of Food Science and Technology Research, in Benevento, Italy, can be reached at firstname.lastname@example.org