An agricultural economics expert says Fonterra's change in strategy has come as a surprise.   The dairy giant has signalled its intent to divest brands including Anchor and Mainland, and overseas operations Fonterra Oceania and Fonterra Sri Lanka.   It wants to focus on producing ingredients and selling those to consumers and other businesses.  Lincoln University agricultural economics professor Alan Renwick told Mike Hosking that the brands are likely to be bought by offshore companies.   He says the main competitor in New Zealand —Goodman Fielder— is based in Singapore, and if they're looking to buy more they could go to Singapore.  LISTEN ABOVE  See omnystudio.com/listener for privacy information.