SAO PAULO, Aug 24 (Reuters) - Brazilian financial technology firm Pagbank said on Thursday its second-quarter net profit grew 5% from a year ago, landeding slightly below analysts' expectations though executives said earnings should improve in coming months.

The firm, which operates as a digital bank and as a payment processor, posted net profit of 385 million reais ($79 million), while analysts polled by Refinitiv expected 399 million reais.

Total payment volume (TPV) for its payments arm totaled 92.7 billion reais in the second quarter, up 4% from a year earlier.

The quarter ending in June was a weak period for the payment processing industry, Pagbank CEO Alexandre Magnani told Reuters, but stressed its TPV for the start of the third quarter is showing improvements.

Revenue fell 2% from the previous year to 3.83 billion reais, also missing analysts' estimate of 3.99 billion reais, as the firm's financial services business took a hit from a new cap for prepaid cards' interchange fees introduced in April.

Chief Financial Artur Schunck, however, said the drop in revenue was a one-off and should be reversed in the coming quarters.

The firm's credit portfolio slightly dropped from the previous quarter to 2.6 billion reais ($533 million), reflecting a write-off made in the period and its increasing focus on secured low-risk products.

Pagbank said that at the end of June about 52% of its portfolio was made up of secured credit products, compared to 44% in the previous quarter.

($1 = 4.8762 reais) (Reporting by Peter Frontini; Editing by Isabel Woodford)