Sensory and Microbial Quality of Milk Processed for Extended Shelf Life by Direct Steam Injection ^†.

Area of Science:

• Food Science
• Dairy Technology
• Microbiology

Background:

• Extended shelf life (ESL) milk offers longer distribution potential than pasteurized milk.
• Limited data exists on the safety and sensory attributes of ESL milk.
• Commercial processing of ESL milk is expanding fluid milk market reach.

Purpose of the Study:

• To evaluate the safety and sensory qualities of milk processed using direct steam injection.
• To determine the impact of processing temperature and holding time on ESL milk characteristics.
• To assess consumer preference for ESL milk compared to other milk processing methods.

Main Methods:

• Milk was processed via direct steam injection at 100–140°C for 4 or 12 seconds.
• Sensory quality was assessed by a trained taste panel.
• Microbial analysis identified psychrotrophic Bacillus species.
• Consumer preference panels compared ESL milk with UHT and HTST processed milk.

Main Results:

• Higher processing temperatures (≥134°C) eliminated detectable organisms.
• Cooked and off-flavors increased with processing temperature and storage time, but were similar between 132°C and 140°C.
• Lipase activity was less affected by higher temperatures; storage time had no significant effect.
• Consumers preferred milk processed at 134°C for 4s over UHT milk, but slightly preferred HTST milk.

Conclusions:

• Processing milk at 134°C for 4 seconds ensures microbial safety and acceptable sensory qualities for ESL milk.
• Optimal processing parameters balance microbial inactivation, sensory attributes, and enzyme activity.
• ESL milk processed at 134°C for 4s presents a viable alternative to UHT milk, with consumer acceptance.