A new low temperature, short time (LTST) process reduced the microbial load in pasteurized milk and prolonged the shelf life of cold milk by up to 63 days.
As reported in SpringerPlus by researchers at Purdue University and University of Tennessee, the LTST method disperses pasteurized milk in the form of droplets through a heated, pressurized chamber where the temperature is rapidly increased and lowered about 10 degrees Celsius, but below the 70 degree Celsius threshold needed for pasteurization. Increasing the temperature of the milk by 10 degrees for less than one second eliminated more than 99 percent of the bacteria left behind after pasteurization, the researchers say.
The microbial load in milk exposed to conventional pasteurization treatments with and without the LTST process was analyzed in the study by using model Gram-positive and negative organisms—Lactobacillus fermentum and Pseudomonas fluorescens Migula, respectively. In these tests, the use of the LTST process significantly reduced the microorganisms present in the inoculated milk. Both organisms that were added to the raw milk at high concentrations were below detection limits after LTST treatment, according to the study.
Researcher Bruce Applegate, PhD, associate professor in the department of food science at Purdue, says that “whatever does survive is at such a low level that it takes much longer for it to multiply to a point at which it damages the quality of the milk.” There were no differences detected in the color, aroma, taste, or aftertaste of milk that had been pasteurized compared with the milk that was pasteurized and then run through the LTST process.
Thermal processing, such as pasteurization, uses high temperatures of 70-120 degrees Celsius, which can damage and/or cause structural modification to proteins in the product, resulting in noticeable changes to the taste of the milk, the researchers say. Lowering the heat, as used in the LTST process, was found to increase the overall quality of the product.
“The process extends the shelf life of fresh milk while maintaining its flavor and nutrient value,” Dr. Applegate says. “The extended shelf life has a number of benefits from the farm to the table. The extended shelf life process has potential benefits at the farm as it could provide a raw product of higher quality.
“Transportation also greatly benefits as it increases the effective radius of product delivery as well as allows for potential storage and redistribution, providing better inventory management, an increase in exports, and reductions in waste,” Dr. Applegate says.