Italcementi SpA is interested in five of the 10 cement plants which are being privatised by the Turkish government, a spokeswoman said, confirming earlier reports.   ’The company is potentially interested in five cement plants,’ she said, without specifying if the company will make a bid for all of them.   According to the spokeswoman, the privatisation auction for the plants started yesterday and will end on Monday or Tuesday next week.   Prospects of a further expansion in Turkey are supporting Italcementi shares, which were up 3.33 per cent at Euro 13.93.