Microbial Changes in Sweet Sorghum (Sorghum bicolor) Juices

Area of Science:

• Food Microbiology
• Agricultural Science
• Biotechnology

Background:

• Sweet sorghum (Sorghum bicolor) juice is a raw material for syrup production.
• Microbial contamination of juice can lead to spoilage and affect product quality.

Purpose of the Study:

• To identify microorganisms in freshly expressed sweet sorghum juice.
• To determine the primary microbial agents responsible for juice spoilage.
• To assess the impact of temperature on spoilage and identify optimal storage conditions.

Main Methods:

• Microbial enumeration and identification of bacteria and yeasts in fresh juice.
• Incubation of juice at ambient temperatures (20°C and 32°C) to observe spoilage.
• Pure culture studies to confirm the role of specific bacteria (L. mesenteroides, L. plantarum) in spoilage.
• Refrigeration studies at 4°C to evaluate long-term storage.

Main Results:

• Fresh juice contained approximately 10 microorganisms/ml, dominated by Leuconostoc mesenteroides and gram-negative rods.
• Spoilage (odor, discoloration, foaming) occurred within 5-12 hours at ambient temperatures, correlated with a pH drop from 4.9 to 4.5.
• L. mesenteroides was the main spoilage agent at 20°C, while L. plantarum dominated at 32°C.
• Prompt refrigeration at 4°C allowed for juice storage up to 14 days.

Conclusions:

• Microbial spoilage of sweet sorghum juice is rapid at ambient temperatures.
• Specific lactic acid bacteria, L. mesenteroides and L. plantarum, are key spoilage agents.
• Refrigeration is crucial for preserving sweet sorghum juice quality and extending its shelf life.