Abstract
Pasteurized milk foam has become a quality issue in some applications, such as cappuccino-style drinks, as it should be stable and high-capacity. The extended shelf life of pasteurized milk is also a challenge. Some factors affect the foam capacity and stability; among them, the increasing amount of free fatty acids in raw milk is critical. The psychrotrophic bacteria can produce a lipase-like enzyme, which is responsible for increasing the level of free fatty acids in raw milk. Therefore, this work aims to utilize the cell-free supernatant of a bacteriocin-producing culture as a natural preservative against psychrotrophic and spore-forming bacteria to enhance the foaming capacity and stability and improve the final product's quality and shelf life. Milk samples from 15 dairy farms were assessed for free fatty acids, microbiological quality, and foaming capacity. Raw milk was divided into four portions: a control without any additive and cell-free supernatant (CFS) treatments, with CFS added at concentrations of 5, 10, and 15 mL/L in each portion. Raw milk was stored for 5 days before heat treatment at 75 °C/30 s, then cooled at 5 °C. All samples were examined for microbiological, free fatty acid, and foaming properties immediately after heat treatment and during storage up to 14 days. The results of this study reveal that there is a negative impact of free fatty acids on the capacity and stability of foaming. The cell-free supernatant (15 mL/L) of the traditional dairy isolate Pediococcus acidilactici inhibits the psychrotrophic bacteria in raw milk during storage for 5 days, a phenomenon which has a direct impact on reducing the free fatty acids, improving the foaming capacity and stability, as well as reducing the bitterness at the end of the shelf life of pasteurized milk up to 14 days compared to the detection of bitterness after 8 days in the control pasteurized milk. It is concluded that, to produce pasteurized milk with a high foaming capacity and extended shelf life, raw milk with low amounts of free fatty acids should be used and fast pasteurized or treated with a bacteriocin of lactic acid bacteria.