pH Measurement in Acidification of Fermented Sausages

Lowering pH or increasing acidity of meat has become main hurdle against pathogenic bacteria in sausage making. pH is used in the course of fermentation process in order to produce microbiologically stable product that has a pH value of 5.3 or less.

Introduction

The process of fermenting and drying is believed to be one of the oldest techniques for preserving meat. This results in a characteristic flavoured sausage with a lowered pH and a reduced water activity that makes the final sausage stable with long shelf life, even if not being subjected to heat treatment.

Fermented sausages are a class of chopped or ground meat products that, as a result of microbial fermentation of a sugar have reached a pH of 5.3 or lower and have undergone a drying/aging process to remove 15-25% moisture. They are classified according to moisture content—dry (e.g., Pepperoni, Salami) or semi-dry (e.g., Summer sausage, Thuringer, Cervelat, Landjaegar).

After mixing the ingredients and stuffing into casings, sausages are placed in an environment with controlled temperature and humidity. At this fermentation stage, the pH of the sausages decreases due to lactic acid bacteria that produce lactic acid from metabolizing sugar.  Lactic acid bacteria such as Lactobacillus or Pediococcus are either naturally present or added as starter cultures. Aside from bacteria, chemical acidulants such as glucono-delta-lactone and citric acid can also be added to rapidly increase acidity and create an extra margin for safety.  The pH drop causes the proteins to give up water, resulting in a drying effect that creates an environment unfavorable to spoilage organisms. Drying continues after the fermentation stage and more moisture is removed from the sausage.

Fermented sausages should attain a pH of 5.3 or lower within the proper time frame in order to control the growth of pathogenic bacteria such as E. coli 0157:H and Staphylococcus aureus. During the fermentation of sausages to a pH 5.3, it is necessary to limit the time during which the sausage is exposed to temperatures exceeding 15.6°C, otherwise the product will spoil, even though the recommended pH was attained. This time frame is temperature dependent and these are the criteria (tables shown are guidelines in developing fermentation process):

The pH of every batch of sausages should be periodically checked and recorded during fermentation to ensure that the pH reaches 5.3 or lower within the required period. The LAQUAtwin pH meter can be used by home sausage-makers or meat processing plants for monitoring the pH of their sausages.

Method

Test the meter’s accuracy regularly and if necessary, calibrate the LAQUAtwin pH meter using 4.01 and 7.00 pH buffers according to manufacturer’s instructions.

Sample Measurement

This method is based on the Australia New Zealand Food Standards Code - Standard 1.6.2.

  1. Mince a representative portion of the sausage and place that portion in a stoppered bottle with twice its weight of water then shake.
  2. Place a portion of the liquid into the sensor. Record the pH and temperature once stabilized.
  3. Clean the sensor with soap and warm water to remove oily residues and/or protein cleaning solution to remove proteins. Rinse the sensor with water and blot dry with soft tissue.

To obtain accurate results, a uniform temperature should be maintained for the standard buffer solutions and  samples. The test should be made at a temperature between 20-30°C, the optimum is 25°C.

Results and Benefits

Fermented sausages such as salamis have been associated with food-poisoning outbreaks globally due to pathogenic microorganisms. In light of this, it is of utmost importance to be in strict compliance with the regulatory guidelines for fermented sausages. In the USA, the Food Safety and Inspection Service requires that the shelf-stable dry sausages be nitrite cured, fermented, smoked, reached a final pH of 5 or less and have a moisture/protein ratio of 1.9:1 or less. The two main factors contributing to the safety and stability of these products are low pH and reduced water activity. The product must reach pH 5.3 or below (or other validated pH) within a specified period to control the growth of pathogenic microorganisms including Staphylococcus aureus and pathogenic E. coli.

References and Suggested Reading
  1. Marianski, Adam and Marianski, Stanley. The Art of Making Fermented Sausages. 2nd ed. USA: Book Magic, 2009.
  2. New Zealand Food Safety Authority.Guidelines for the Production of Uncooked Comminuted Fermented Meat (UCFM) Products. July 2009
  3. Good Manufacturing Processes for  Fermented Dry & Semi-Dry Sausage Products. The American Institute Foundation. October 1997

REV 0, 30 JULY 2015

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