It turns out there are some good nutrition benefits inherent in New Zealand sheep milk. Angus Kebbel talks to Amber Milan, a research fellow at the Liggins Institute

Amber Milan is a postdoctoral scientist at agResearch and a research fellow at the Liggins Institute at the University of Auckland. Her primary focus of research is what happens to foods when we eat them. So she is coming at it from a clinical nutrition perspective, or a nutritional biochemist perspective. And what she is really interested in is the compositional or structural differences that are inherent to foods that we eat, and how that impacts how we digest them and how we metabolise them. And ultimately what that means for us in terms of our health. So it’s taking what we know about food science, or different consumer products and giving it a health angle for a consumer.

New Zealand sheep milk contains higher levels of health-beneficial lipids and fatty acids than European sheep milk or cows milk, and microbiological testing shows that sheep milk is safe.

Although differences in milk composition between species have been known for a long time, prior to the start of this research programme there was no data available on the detailed composition of New Zealand sheep milk. We did not know:

• Whether the composition of New Zealand sheep milk was different to that of milk from other countries
• If/how much the composition and flavour changed throughout the milking season
• How much the composition varied between different New Zealand producers
• If the composition and flavour changed upon processing and storage, and if so, how?

Her project looked to determine the effect of processing on nutritional profile, compositional targets and product characteristics. It also looked to characterise compositional targets at an individual level, including effect of breed, lactation stage, age, seasonality, farm of origin and farm practice effects.

So what is the difference in the nutritional profile of sheep milk versus cow milk?

“So we know that in general, sheep milk is more nutrient dense it has more solids per per mil, per volume. So that I guess basically means that you know, for the same quantity we've got much greater proportions of protein and fat. So just as a comparison, you know that the proportion of total protein in cow's milk is 3%. Whereas in sheep, it's four and a half percent. For fat cow's milk would be about three and a half percent, and sheep milk is just over 5%. So those differences mean that on the glass per glass basis, you are getting more of these nutrients, but then on top of that we also have differences in the quantities, or the composition of some of the nutrients that are available.

So there's more of the essential amino acids, so the proteins that are essential for growth, in sheep milk. And also sheep milk has a bit of a different composition particularly in the fatty acids that it's got, so it has quite a lot more of the medium chain fatty acids, such as capric acid, caprylic acid. And these are some of the fatty acids that contribute to the differences that you might notice in the smell between different species of milk. But I think in terms of health, one of the nice things about these fatty acids is that they're very quickly digested as well, so it means that they can be used a little bit more quickly as an energy source. And that they don't necessarily have the same contribution to some of the, I guess the negative effects of a high fat food that we might associate with, you know, increased risk for cardiovascular disease because they don't, they don't elevate blood lipids in the same way.”

The research also found:

• NZ sheep milk generally contains more protein (notably leucine, valine and isoleucine) fat (especially beneficial lipids such as medium-chain triacylglycerols and polyunsaturated fatty acids and phospholipids), carbohydrates, minerals (e.g. Calcium, Potassium and Magnesium) and certain vitamins than New Zealand cows’ milk.
• Microbial analysis demonstrated that our harvesting and storage protocols in New Zealand are providing a safe product for consumers.
• Sheep milk pH remained stable for nine days when stored at 2 or 4⁰C. Using the lower temperature prolonged storage by up to four days. However, storing at 2⁰C is preferable to retain high-quality protein and heat stability.
• Spray drying at low temperatures produces a product more desirable for reconstitution for drinking.
• Pasteurisation can be done quickly at temperatures of 75⁰C, though sheep milk may need to be diluted achieve this.
• Sheep milk powder had lower levels of the compounds associated with strong flavor (volatile fatty acids) and lower odour activity values compared to goat milk powder, suggesting a milder flavour of sheep compared to goat milk. Higher amounts of volatile fatty acids were measured in the spring (start of the lactation season) compared to autumn (end of the season) which may be due to variation in the composition of the pasture between early and late season.

The high total solids of sheep milk offer technological advantages of higher cheese yield and higher density of nutrients in a variety of sheep milk products. These high solids can interfere with processing options such as pasteurisation. Storage conditions are also critical for further processing of sheep milk. New Zealand sheep milk, from pasture-fed systems has a mild flavor. Further heat treatments have provided an extended shelf-life product of high drinking value.

Listen to the podcast to hear the full interview.

Angus Kebbell is the Producer at Tailwind Media. You can contact him here.