"Income and spending remain under pressure due to factors including the decline of the rand, slow economic growth, unemployment and a generally challenging economic environment," said index founder Adré Schreuder.
More than 2000 supermarket customers were interviewed over the past two months.
According to Schreuder, satisfaction scores fell from 2014 to 2015 across the board, with every major retailer experiencing a dip.
Woolworths has been leading the pack for the past two years, scoring 80% for customer satisfaction.
But although Woolworths customers remain the most contented, the store's quality rating has dropped by 3.3 index points.
Other supermarkets surveyed include Shoprite and Checkers, which both scored 77.1%, Pick n Pay (76.2%) and Spar (75.7%).
Although Checkers and Shoprite achieved the same overall satisfaction score, Shoprite outperformed Checkers in that customers felt it offered better value for money.
Spar, Pick n Pay and Checkers had the most complaints. Customers cited products being sold past their expiry date, products being out of stock and incorrect pricing.
Responding to the survey's findings, specifically the complaints, Pick n Pay spokesman Jennifer Crocker said: "If people aren't happy, we aren't happy.
"Consumer sovereignty is a core principle so we encourage customers to give us feedback through traditional ways and social media."
Spar customers complained more than any others - but the store received plaudits for dealing with problems effectively.
Shoprite achieved a complaint resolution score of 71%; the industry average is 67%.
Woolworths and Checkers had not responded to The Times's questions at the time of going to press.
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