Abstract
ABSTRACT The aim was to evaluate the microbiological, chemical- physical, and shelf-life quality of milk samples after pasteurization (HTST) for 10 days or ultra-high temperature (UHT) treatment for 120 days. Raw milk counts of mesophilic aerobic microorganisms, Staphylococcus spp. and thermotolerant coliforms before HTST and UHT processing were 6.73 and 7.77; 2.84 and 4.30, and 4.68 and 4.37log10, respectively. Pseudomonas spp. were found in raw milk samples. No presence of any other microorganisms studied was detected and no microbial inhibitor was found. Processed samples met microbiological legal requirements. However, aerobic mesophilic counts for HTST pasteurized milk samples stored for 5 and 10 days increased to values comparable to those in raw milk. Composition chemical- physical of all samples were within legal limits. These results demonstrate that, although HTST and UHT processed milk comply with the microbiological standards required by Brazilian law, high microbial counts in raw milk are an issue, possibly due to failures in the early stages of the production chain. Increase in casein macropeptide (CMP), probably because of proteases psychrotrophic bacteria. It is concluded that the quality of raw milk directly influences the progressive increase of the CMP values.
Highlights
The refrigerated storage of milk on farms is an important step in reducing the operational costs of production and avoiding loss of raw milk by acidification
The experiments were conducted at the State University of Western Paraná (PR), and casein macropeptide (CMP) levels were quantified at the Federal University of Minas Gerais (MG)
Raw milk samples obtained in this study were noncompliant with the legislation; raw milk for both High Temperature and Short Time (HTST) and Ultra High Temperature (UHT) treatment exceeded maximum limits with bacterial levels of 1.25 and 2.29log10, respectively (Table 1)
Summary
The refrigerated storage of milk on farms is an important step in reducing the operational costs of production and avoiding loss of raw milk by acidification. Longer periods of storage may result in decreased quality of milk derivatives due to the increased counts of psychrotrophic bacteria, such as Pseudomonas, and microbial enzymatic activity (Marchand et al, 2009; Machado et al, 2015). UHT technology offers the advantages of extended shelf-life of milk without need for refrigeration and avoiding significant changes in its essential characteristics and flavor (Walstra et al, 2005). Psychrotrophic bacteria may produce proteolytic and lipolytic enzymes that are directly related to loss of quality and reduced shelf-life of milk even after heat treatment, since such enzymes are highly heatresistant (Marchand et al, 2009; Samaržija et al, 2012; Von Neubeck et al, 2015). The result may be milk that is unstable to heat and undergoes physicochemical changes, such as coagulation during heating, gelation of UHT milk during storage, development of off-flavors and reduced cheese yield (Datta and Deeth, 2003; Svensson et al, 2004)
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