COMPARATIVE ANALYSIS OF TRYPAN BLUE AGAR AND CONGO RED AGAR FOR THE ENUMERATION OF YEAST AND MOLD USING THE HGMF SYSTEM1

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Abstract
Enumeration of yeast and molds from 39 food samples, including 6 dairy products, 2 meat products, 5 cereal products, 9 fruits, 4 vegetables, 6 beverages, 4 spices, and 3 condiments on Trypan blue (at 1: 10,000 dilution) in potato dextrose agar (Trypan blue agar) was compared with Congo red (at 25:1,000,000 dilution) in potato dextrose agar (Congo red agar) using the hydrophobic grid‐membrane filter (HGMF) technique of the ISO‐GRID system. Yeast and mold grew well on both Trypan blue agar and Congo red agar, producing blue and red colonies, respectively, in the ISO‐GRID system, when examined in incan‐descent light. However, not all yeast and mold colonies grown on Congo red agar fluoresced under ultraviolet (UV) light (a recommended observation procedure). Thus, results indicated that Trypan blue agar observed in incandescent light is more convenient to use for enumerating yeast and mold in food samples.