Ice Cream and Pathogenic bacterias (2)

Foodborne microbial diseases originate in various ways, depending on the pathogen in question:

Infection: The food acts as a vehicle to introduce the microorganism into the human body. Once there, the germs begin to multiply. The human organism, then, responds to the presence of the germ or to the metabolites that it produces. The minimum dose of microorganisms needed to cause such an infection is very low.

Intoxication: Pathogenic germs multiply in the food and form toxins in it. Toxins are harmful substances that cause damage even in small concentrations. The disease occurs when the food is consumed without the need for the multiplication of microorganisms within man.

The main cause of cases of illness related to the consumption of ice cream contaminated with microorganisms or their toxins are: mainly Salmonellas, causing infections; Staphylococcus aureus, toxin-forming and sporadically shigella and enteropathogenic strains of Escherichia coli.

There are recent data of withdrawals from the market in the United States of almost 1,000 liters of chocolate ice cream because it contains a high contamination with Listeria monocytogenes.

It is important to note that foods contaminated by pathogenic germs usually do not present perceptible manifestations, so it is necessary to carry out the corresponding controls in order to ensure the microbiological quality of the product.

Decomposition: Altered foods microbiologically tend to manifest themselves as such due to their appearance or smell. They are not usually dangerous to health despite being considered unfit for normal consumption.

In ice cream the various ingredients used as raw material and additives are, before freezing, susceptible to decomposition.

The main decomposition problems are related to the raw materials milk and eggs. The alterations that these can suffer are, among others, unfolding of proteins giving malodorous products, fermentation with production of acids and lipolysis that is manifested generally with the rancidity of the products.

Hygiene: The number of microorganisms present and the coliform rate are considered hygienic indicators. That is, if the results obtained from the counts show high values, they indicate hygienic deficiencies. This represents critical points that must be corrected or eliminated.

The main causes of microbial contamination in ice cream are, among others, people who are carriers of germs (sick or injured), insufficient refrigeration of the product, absence or deficiency of heating of the mixture, prolonged periods of rest of the mixture (not immediate cooling) , contaminated raw materials.

In order to obtain the food in suitable hygienic conditions, a series of hygienic standards must be followed that commit the personnel, establishment, facilities, machinery and utensils. The common international standards implemented for the hygienic manufacture of food are known as BMP or GMP ("good manufacturing practices"). These were first published by the Food and Drug Administration of the United States for various food groups.

The remains of ice cream are an excellent means for the development of microorganisms, especially if the optimal conditions of temperature for the development of them are given. Therefore, it is important to avoid the accumulation of these in the machinery and installations throughout the process, especially in the area of work at higher temperatures. To prevent the formation of germ nests in accumulated product remains, it is necessary to perform regular disinfection in the facilities that come into direct contact with the product during its manufacture.

It is necessary to perform microbiological controls of the raw materials and to ensure a subsequent adequate storage until the moment of its use.

During the pasteurization, 99.6-99.9% of the germs are eliminated. Sporagen microorganisms survive pasteurization since their spores are heat-resistant. To prevent these microorganisms and other possible survivors from developing, it is necessary to cool the mixture immediately after pasteurization. Ice creams are very sensitive to fluctuations in temperature and cross-contamination with all the utensils used to handle them

A common problem of importance is the cleaning cloths used to clean work places, machines or utensils. If these cloths are not disinfected after each use, the only thing that is achieved, using them, is to distribute germs uniformly. In these cloths have been found about 200 million microbes per cm2. If they are only washed with hot water and twisted vigorously, a considerable decrease in the number of microorganisms is not achieved.

Another point to consider is that of the ice cream serving spoons. The optimum would be to have a spoon for each ice cream to avoid keeping it in water, since, if that water is not renewed continuously, you can reach microorganism counts of the order of 107 per milliliter.

The levels of contamination in the vending machine nozzle also deserve a special mention. In what are called soft ice cream machines are usually outside or in hot places, where some consumers can touch the nozzle where the ice cream comes out, leaving it unprotected from low temperatures. In these nozzles, the number of bacteria can exceed 10 million per gram, with Enterobacteria growing particularly easily, including Salmonella.

Microbiological analysis: To determine the microorganisms present in a sample of ice cream different culture methods are performed. These can be in growth plates of colonies or in liquid medium, in which the growth is detected by turbidity of the solution. Both methods use nutritious media whose composition will depend on the microorganism that is interesting to detect. In addition to said composition there are other parameters to be considered to achieve the selectivity of the medium, such as: incubation temperature (optimum growth temperature), incubation time and necessary oxygen tension.

Microbiological reports indicate the method by which they were determined. The results thus obtained are then confronted with the established legal limits.

In ice cream samples it is important to revivify the altered microorganisms, but not dead, by the effect of freezing. This is done in some cases of suspicion of pathogenic germs such as enteropathogenic strains of Escherichia coli or Yersinia enterocolitic.

Microbiology in ice cream: Freezing  : As the temperature drops in the freezing process, the microbial activity decreases. The formation of ice crystals of pure water causes a decrease in available water, thus a decrease in water activity (for example at -10 ° C the aw is 0.907). In addition to the decrease in microbial activity, some of the microorganisms also die. In ice creams, colloids, milk salts (mainly phosphates), lactose and casein protect microorganisms from the damage of freezing.

It is important to note the influence of the cooling rate on the destruction of microorganisms: a higher freezing speed causes less damage to the bacteria than a slower freezing. Microorganisms also die during storage in a frozen environment.

It should be borne in mind that microbial toxins and their toxicity are not altered by freezing, as well as bacterial spores.

The physical effects of freezing are of great importance. There is an expansion in the volume of frozen food due to the formation of ice crystals and the increase in their size. The damages suffered by microorganisms during freezing and maintenance at low temperatures will depend on the cooling speed in the following way:

Low speed (extracellular crystallization): When ice is formed in the food, the concentration of solutes in the food increases, causing, due to the difference of osmotic pressures in the interior and exterior of the microbial cell, the exit of the intracellular water. This loss of water leads to intracellular changes (pH, ionic strength) that produce the inactivation of enzymes, denaturation of proteins thus altering cell function and causing reversible and irreversible damage.

Medium-High Speed: Decreases the exposure time of microorganisms to osmotic effects, and, therefore, causes minor damage.

Very high speed (intracellular crystallization): The crystallization occurs inside the cell causing mechanical damage to it (cell breakdown).

Although the freezing considerably reduces the count of viable microorganisms, it SHOULD NOT BE CONSIDERED A STERILIZATION PROCESS. After prolonged storage at low temperatures (-28 ° C) it is found that a considerable percentage of microorganisms survive, including pathogens.

The consequences of a contaminated food will depend on the type of microorganism in question. If they are pathogens, they will cause infection when they are ingested next to the contaminated food or they can generate toxins or other harmful substances, causing health damage. If, on the other hand, microorganisms responsible for decomposition are involved, the main consequence will be the premature alteration of the food by enzymatic cleavage and metabolic products that these originate. This alteration may occur during the manufacture and storage of the product.