Over the next week and a half we are going to be hearing a lot about Britain’s vote on its European Union membership and its effect on financial markets across the world.

Australian investors are already starting to look nervous, with the S&P/ASX 200 (Index: ^AXJO) (ASX: XJO) dropping 2% on Tuesday following news that current polls are pointing to an exit for Britain. If the performance of key markets around the world overnight are anything to go by, the Australian market could be set to have another day in the red.

During times like these I believe it can pay to have defensive shares with low betas in your portfolio. Beta is a measure of the volatility of a share or a portfolio compared to the market as a whole. A beta above 1 means the share is expected to exhibit higher levels of volatility than the market, and vice versa for shares with betas under 1.

So I have picked out two shares which have low betas and could be solid long-term investments today, in my opinion.

1300 Smiles Limited (ASX: ONT)

The shares of this operator of full-service dental facilities has a low beta of just 0.5. Whilst the majority of the shares on the Australian market were heading lower yesterday, 1300 Smiles’ share price climbed higher by 2.3%.

I believe 1300 Smiles would make a great addition to your portfolio today due to its defensive characteristics and its strong earnings growth. In the last 10 years the company has grown its earnings by a compound annual growth rate of 12.2%, and I believe it is more than capable of continuing to grow at this strong rate for some time to come.

In its half-year results the company produced a stunning rise in net profit after tax of 20% year-on-year. Perhaps what was most impressive was the fact that revenue only rose by 3%. Management has done an excellent job of increasing the company’s profitability during a spell of low growth.

At 22x trailing earnings I believe 1300 Smiles is better value than industry rival Pacific Smiles Group Ltd (ASX: PSQ) which is seeing its shares change hands at 32x trailing earnings.

Cochlear Limited (ASX: COH)

Cochlear survived the market sell-off on Tuesday more or less unscathed, dropping just a fraction of a percent. I believe the manufacturer and distributor of cochlear implantable devices is one of the best shares on the Australian Stock Exchange.

Just like 1300 Smiles, Cochlear delivered a very impressive half year result which saw sales increase 32% year-on-year to $582 million. The bottom line was equally good, with net profit after tax also growing by 32% to $94 million.

Thanks to its market leading position and best-in-class products, I believe that Cochlear can continue to produce strong results like this for some time to come. It does trade on a reasonably high multiple of 36x estimated FY 2016 earnings, but I believe it is worth every cent.

With Cochlear’s shares also having a low beta of just 0.5, I feel they could be a great addition to a balanced portfolio today.

Foolish takeaway

Lowering the beta of your portfolio has been a great way of shielding your portfolio from market volatility in the past. But it isn’t guaranteed, so investors ought to consider this before making any changes to their portfolio.

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Motley Fool contributor James Mickleboro has no position in any stocks mentioned. The Motley Fool Australia has no position in any of the stocks mentioned. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy. This article contains general investment advice only (under AFSL 400691). Authorised by Bruce Jackson.  I contribute to The Motley Fool as a freelance writer and the thoughts and opinions in this post are my own, not that of The Motley Fool’s.