Publication:
Calidad microbiológica de la leche pasteurizada entera (3.25%) y parcialmente descremada (1%) en Puerto Rico y su efecto en el largo de vida útil
Calidad microbiológica de la leche pasteurizada entera (3.25%) y parcialmente descremada (1%) en Puerto Rico y su efecto en el largo de vida útil
Authors
Otero-Franqui, Angel
Embargoed Until
Advisor
Ponce de León-González, Leyda
College
College of Agricultural Sciences
Department
Department of Food Science and Technology
Degree Level
M.S.
Publisher
Date
2020-05-29
Abstract
Se analizaron 20 muestras de leche pasteurizada (10 enteras, 10 parcialmente descremadas) durante un transcurso de 10 semanas, comenzando en noviembre 2018 y terminando en marzo 2019, para determinar el efecto que tiene la población microbiológica y el porcentaje de grasa en la calidad y la vida útil. A las muestras de leche se les determinó la cantidad de bacterias totales, coliformes, hongos y levaduras presentes. Se seleccionaron colonias para realizar tinción Gram. Ademas se realizaron la pruebas TRAM, y “Mosely Keeping Quality”. Se realizaron análisis para determinar el pH, la actividad de agua y la acidez titulable a la leche pasteurizada y también se determinó la población de bacterias termodúricas en leche cruda.
Todas las muestras examinadas de leche pasteurizada cumplen con los requisitos que hay establecidos por el FDA para bacterias totales y coliformes. Sin embargo, la cantidad de bacterias totales presentes en la leche parcialmente descremada fue significativamente mayor que en la leche entera (p< 0.0475). La prueba de Mosely mostró igualmente diferencias significativas entre la leche pasteurizada regular y la parcialmente descremada (p<0.0085) y luego de un periodo de almacenaje de 5 días se observó mayor proliferación de bacterias totales en la leche parcialmente descremada que en la leche entera. Igualmente, el contaje de hongos y levaduras fue mayor para la leche parcialmente descremada que en la entera (p< 0.008). La acidez titulable de la leche parcialmente descremada fue mas elevada que en la leche entera (0.18 versus 0.16) con un valor p <0.010. No se observó diferencias significativas en el pH de la muestras. Por lo tanto, se puede concluir que la cantidad de grasa en la leche potencialmente afecta el largo de vida útil de la misma porque las bacterias pueden propagarse a mayor cantidad en la leche parcialmente descremada.
Twenty samples of milk (10 wholes, 10 low fat) were analyzed for 10 weeks, beginning on November 2018 and concluding on March 2019, to determine the effect of the microbiological population and fat percentage in the quality and shelf life. In this research, analysis such as total aerobic bacteria counts, the Mosely Keeping Quality Test, thermoduric bacteria count, coliform count, yeast and mold counts, gram staining, pH, water activity, and titrable acidity were performed. The total bacteria count for all samples of pasteurized milk meets the criteria established by the FDA. However, the total bacterial count for low-fat milk was significantly higher than whole milk (p<0.0475). The Mosely keeping quality test also was significantly different, low fat had a higher proliferation of bacteria while storage for 5 days at 7C than whole milk (p<0.0085). The yeast and mold counts were also higher in low fat milk than whole milk (p<0.008). Titratable acidity was higher in low-fat milk than whole milk, 0.18 and 0.16, respectively (p< 0.010). There were not significant diferences in the ph values. This study showed that the % fat of milk potentially affects the shelf life of pasteurized milk due to the higher propagation of bacteria.
Twenty samples of milk (10 wholes, 10 low fat) were analyzed for 10 weeks, beginning on November 2018 and concluding on March 2019, to determine the effect of the microbiological population and fat percentage in the quality and shelf life. In this research, analysis such as total aerobic bacteria counts, the Mosely Keeping Quality Test, thermoduric bacteria count, coliform count, yeast and mold counts, gram staining, pH, water activity, and titrable acidity were performed. The total bacteria count for all samples of pasteurized milk meets the criteria established by the FDA. However, the total bacterial count for low-fat milk was significantly higher than whole milk (p<0.0475). The Mosely keeping quality test also was significantly different, low fat had a higher proliferation of bacteria while storage for 5 days at 7C than whole milk (p<0.0085). The yeast and mold counts were also higher in low fat milk than whole milk (p<0.008). Titratable acidity was higher in low-fat milk than whole milk, 0.18 and 0.16, respectively (p< 0.010). There were not significant diferences in the ph values. This study showed that the % fat of milk potentially affects the shelf life of pasteurized milk due to the higher propagation of bacteria.
Keywords
Milk quality,
Dairy microbiology,
Fat content,
Shelf life
Dairy microbiology,
Fat content,
Shelf life
Usage Rights
All Rights Reserved / restricted to Campus
Persistent URL
Cite
Otero-Franqui, A. (2020). Calidad microbiológica de la leche pasteurizada entera (3.25%) y parcialmente descremada (1%) en Puerto Rico y su efecto en el largo de vida útil [Thesis]. Retrieved from https://hdl.handle.net/20.500.11801/2642