Influence of storage temperature on the population of microorganisms in raw sheep milk and its physical-chemical profile

Samera Rafaela Bruzaroski,Rafael Fagnani,Pamela Da Silva Pasquim,Raquel Pinheiro De Souza,Elsa Helena Walter De Santana

doi:10.33448/rsd-v9i12.10796

Samera Rafaela Bruzaroski, Rafael Fagnani + Show 3 more

Open Access

https://doi.org/10.33448/rsd-v9i12.10796

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Abstract

The aim of the present study was to evaluate the physical-chemical profile of raw sheep milk and the influence of storage temperature on the population of microorganisms. Sheep milk samples were collected from the milk cans (500 mL/sample) and were evaluated the physical-chemical composition: fat, protein, lactose, ash content, total dry matter (TDM), cryoscopy index (°H), titratable acidity, and somatic cell count (SCC). After the samples were stored at 4°C and 9°C (72 h) and the titratable acidity, the population of the deteriorating microorganisms and quality indicators were determined. PetrifilmTM (3M do Brasil Ltda) were used for the mesophilic aerobic count (37°C/48 h), total coliforms (37°C/24 h), Escherichia coli (37°C/48 h), and enterobacteria (37°C/24 h). For psychrotrophic bacteria, was used Plate Count Agar (7ºC/10 days) and for Pseudomonas spp., CFC-supplemented Pseudomonas agar base (25ºC/48 h). Average values for raw milk were 6.28% fat, 83.46% moisture, 16.52% TDM, 0.92% ash, 5.30% protein, 4.43% lactose, a cryoscopy index of -0.575°H, and SCC of 3.38 x 106 cells/mL. Milk acidity values were higher (0.24 g lactic acid/100 ml) with 72 hours of storage. The higher the temperature and/or storage time, the higher the counts of psychrotrophic, Pseudomonas spp., and enterobacteria, for mesophilic aerobic only the storage time. Refrigeration at 4ºC and a reduction of storage time are important to control the microorganism’s population that compromise the quality, shelf life, and food safety of sheep milk and dairy products.

Highlights

Sheep milk is a functionally active dairy food composed of fatty acids, immunoglobulins, and non-immune proteins (Mohapatraa et al, 2019)
Sheep milk samples were collected from the milk cans (500 mL/sample) and were evaluated the physicalchemical composition: fat, protein, lactose, ash content, total dry matter (TDM), cryoscopy index (°H), titratable acidity, and somatic cell count (SCC)
Refrigeration of raw milk limits the proliferation of saccharolytic mesophiles, which are responsible for acidification and thermal instability through hydrolysis of lactose and the production of lactic acid (Mcauley et al, 2016)

Summary

Introduction

Sheep milk is a functionally active dairy food composed of fatty acids, immunoglobulins, and non-immune proteins (Mohapatraa et al, 2019). Refrigeration of raw milk limits the proliferation of saccharolytic mesophiles, which are responsible for acidification and thermal instability through hydrolysis of lactose and the production of lactic acid (Mcauley et al, 2016). Psychrotrophic microorganisms synthesize thermo-resistant proteolytic and lipolytic enzymes that compromise the quality of milk and its derivatives by reducing the shelf-life, turning the taste bitter and rancid, and decreasing cheese yield (Molineri et al, 2012). The most common genus found in refrigerated raw milk are Pseudomonas spp., which rapidly increase and result in intense lipolytic and proteolytic activity. Few of the other contaminants, such as coliforms, Escherichia coli, and enterobacteria, are indicators of food hygiene quality, and their presence can compromise the shelf-life and food safety of milk and dairy products (Franco & Landgraf, 2008)

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