Determination of Shelf Life of Concentrated Yogurt (Labneh) Produced by In-Bag Straining of Set Yogurt using Hazard Analysis

¹ Department of Nutrition and Food Science, Faculty of Agricultural and Food Sciences, Beirut, Lebanon
² Department of Biology, Faculty of Arts and Sciences, American University of Beirut, Lebanon
³ Department of Plant Sciences, American University of Beirut, Lebanon
⁴ Department of Environmental Health, Faculty of Health Sciences, American University of Beirut, Lebanon
⁵ Computer Center, Faculty of Agricultural and Food Sciences, American University of Beirut, Lebanon

Strained yogurt, labneh, produced by straining cow's milk set yogurt in cloth bags, was stored at 5, 15, and 25°C, and changes in microbial counts, pH, titratable acidity, percentage of free whey, and sensory attributes were monitored during storage. Counts of total aerobes, psychrotrophic yeasts, yeasts and molds, and lactic acid bacteria, except in samples stored at 25°C, increased irrespective of storage temperature. The pH of samples decreased, titratable acidity and percentage of free whey increased, and texture defects were detected at a later stage than flavor changes during storage. Shelf-life data of labneh was adequately described by the Weibull distribution. The nominal shelf life determined using sensory changes and yeast counts as failure criteria ranged from 8.5 to 10.5, 4.7 to 5.8 and 2.3 to 2.7 d at 5, 15 and 25°C, respectively. Q₁₀ (shelf life at T°C/shelf life at T+10°C) for flavor quality loss was 1.98 at 5°C, and the corresponding activation energy was 11.3 kcal/ mol.

Key Words: shelf life • sensory • concentrated yogurt • labneh

Submitted on October 3, 2001
Accepted on December 11, 2001