Abstract
The psychrotrophic bacteria growth in refrigerated milk is responsible for the production of heat resistant enzymes, including those which have lipolytic capacity. Lipases can cause rancidity and off-flavor in pasteurized and UHT milk, milk powder and cheese. Pseudomonas spp. is the major genera responsible by lipases synthesis, mainly Pseudomonas fluorescens. The lipolytic capacity of Pseudomonas spp. (1182 strains) and P. fluorescens (158 strains) isolated from cooling tank and bulk milk transportation were tested. Pseudomonas spp. strains were isolated by Pseudomonas Agar Base, adding the supplement cephalotin, fusidic acid, cetrimide- CFC (30o C/48 h) and Pseudomonas Cetrimide Agar with 10% of glicerol (21o C/ 48 h) to determine P. fluorescens. The strains lipolytic capacity were tested with Tributyrin Agar (21 o C/72 h). Lipolytic indexes of Pseudomonas spp. were 51.4% and 67.2% in cooling tank and bulk milk transportation (p< 0.05), respectively. P. fluorescens lipolytic capacity indexes were 26.4% from strains isolated from cooling tank and 41% (p < 0.05) from strains isolated from bulk milk transportation. High lipolytic indexes had been found in the strains isolated from refrigerated raw milk sent to manufacturing. Refrigeration temperature and storage time may contribute to the difference observed between two points of collection evaluated in this study.
Highlights
High counts of psychrotrophic bacteria in raw milk are directly related to poor hygienic conditions during production and milking, and to the time and temperature of milk storage (ARCURI et al, 2008)
The result of Chi-square test is to reject the null hypothesis, that is, the lipolityc strains frequency isolated from cooling tanks (CT) was different from that of bulk milk transportation (BMT)
Difference (p
Summary
High counts of psychrotrophic bacteria in raw milk are directly related to poor hygienic conditions during production and milking, and to the time and temperature of milk storage (ARCURI et al, 2008). Low psychrotrophic bacteria counts are essential to maintain milk quality, once the metabolic activity of these microorganisms modify milk biochemical constituents (ARCURI et al, 2008), such as lipid, protein and carbohydrate degradation (COUSIN, 1982), limiting the shelf life of fluid milk and its products (SANTOS et al 2009; ARCURI et al, 2008). Lipolysis involves the enzymatic hydrolysis of milk lipids, producing free fatty acids and glycerol. Bacterial lipases are not inactivated by heating, and cause rancidity and off-flavor in pasteurized and UHT milk, milk powder and cheese (JONGHE et al, 2011; COUSIN, 1982). Pseudomonas spp. is the major genera responsible by lipases synthesis, mainly Pseudomonas fluorescens (MU et al, 2008; DEETH; FITZ-GERALD, 2006; SHAH, 1994)
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