Shelf Life of Plain Liquid Yogurt Manufactured in Saudi Arabia

The shelf life of plain liquid yogurt under local conditions of manufacture and handling has been investigated. Initial coliform counts of <1 cfu/ml in the product remained constant throughout 14 d of storage at 7, 10 or 15°C. With initial counts of mold and yeast not exceeding 1 cfu/ml, growth of these microorganisms was nominal (22 cfu/ml) after 14 d of storage at 7°C. At 10 and 15°C storage, however mold and yeast increased substantially from initial levels not exceeding 1 cfu/ml to 2 × 10³ cfu/ml and 3 × 10³ cfu/ml after 5 and 10 d of storage respectively. The high initial quality of the product, with ⩽10 cfu/ml coliform, ⩽10 cfu/ml mold and yeast and a hedonic score of 8 (like very much), was maintained for 5 d at 7°C storage. After 5 d of storage at 7°C, the mold and yeast count and organoleptic property of the product became unacceptable. The organoleptic quality deteriorated irrespective of the microbial contamination of the product. Quality assessment of the product before expiration (4 d) and under prevailing commercial conditions of manufacture, handling and storage revealed acceptable sensory and microbial quality. The possible causes of product sensory deterioration irrespective of growth of mold and yeast are discussed.