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PICHIA ANOMALA in the bread and pastry sector

PICHIA ANOMALA: SUMMARY

The yeast found in surface samples of the installations and equipment within our Client's factory (Bread and Viennese pastry production) was found to be :  Pichia anomala. In terms of nomenclature and taxonomy, this yeast was first described in 1894 by Hansen (Hansen, 1894), has undergone numerous taxonomic evolutions and can be found in bibliographies under the name Hansenula anomala, Wickerhamomyces anomalus or Candida pelliculosa (NCBI international database).

Survival and growth

They are asporogenous yeasts capable of growing under drastic environmental conditions such as low or high pH, very low humidity, high osmotic pressure and even under anaerobic conditions (Fredlund et al., 2002). Due to this broad survival and growth capacity, Pichia anomala is a spoilage flora in dairy products, alcoholic beverages and bakery products (Bonjean and Guillaume, 2003).

Bread and pastry making

This yeast will therefore be responsible, in the bread and pastry sector, for altering finished products by producing different types of metabolites such as ethyl acetate in very large quantities, but also ethyl propanoate, phenyl ethanol, 2-phenyl ethyl acetate, etc. These metabolites will cause the emanation of strong solvent-like odours which can modify the organoleptic qualities of the food and lead to dissatisfaction of the end customer with a product recall by the manufacturers concerned. This microorganism is classified as an alteration germ in bread products.

Good hygiene practices

The Agence Nationale de Sécurité Sanitaire de l'Alimentation, de l'Environnement et du Travail recently published an opinion (ANSES, Saisine n°2012-SA-0003, July 2012) on the development and implementation of a "guide to good hygiene practices and the application of HACCP principles for the biscuit and cake manufacturing industries and the crisp and fluffy bakery industries intended for direct consumption".

In this opinion, the yeast Pichia anomala is clearly identified as an indicator of process hygiene. This yeast must therefore be taken seriously and its presence in high concentration may be a sign of a failure or malfunction in the cleaning and disinfection protocol of equipment or surfaces in contact with food products. It should also be noted that no toxicological data currently exist on the molecules produced by this yeast. Toxicological evaluations are currently being carried out following the recommendations of the ANSES and will make it possible to evaluate the real danger of the metabolites linked to this yeast. It is therefore essential to control the contamination of surfaces by this yeast and thus avoid the presence of metabolites in consumer products.

Cleaning

In order to review the resistance and sensitivity of this yeast to the various disinfection processes (chemical, thermal, etc.), we will briefly discuss the existing data, knowing that during the technical demonstration in your premises, steam showed a more than significant effectiveness. It should be noted that few scientific studies have dealt with the disinfection of this yeast, since Pichia anomala is reputed to be antifungal and to inhibit the growth of undesirable fungi such as Penicillium (Druvefors et al., 2005). In view of its growth capacity, any type of cleaning with a very or excessively high water input should be avoided, as this will contribute to the survival and persistence of Pichia Anomala on the surfaces.

Disinfection

For oxidising disinfectants such as hydrogen peroxide and peracetic acid, studies have shown the effectiveness of a hydrogen peroxide/peracetic acid mixture at low concentrations (in the order of 6-8%) in less than 15 min (APABIOmanual spraying of surfaces after cleaning by Industrial dry steam) and allowing a log reduction greater than 4 (minimum reduction to be achieved for yeast-killing efficacy) to be reached in clean or "dirty" conditions (Brougham, 1993). This type of oxidising molecule is also used in aerial surface disinfection by generating a hydrogen peroxide mist that allows disinfection of all surfaces in contact with the air. With this type of process, it has been demonstrated that it is yeast-killing, achieving log reductions of more than 4 logs in less than 10 min at 20°C and less than 2 min at 40°C (APABIO/AIRBIO).

Dry steam

Another equally effective choice is the thermal destruction of microbiological contaminants through the use of Industrial dry steam. It is true that Pichia anomala shows a high thermoresistance compared to other Candida or yeast species, especially in liquid medium (Tchango et al., 1997). Above 60°C, Pichia anomala will not resist heat and will be destroyed by denaturation of the plasma membrane and the cell wall. The thermal mechanisms of yeast destruction are little studied, but this sensitivity to high temperature in conditions of low water content may be a method of choice to replace ethanol (very often used) and without leaving chemical residues on surfaces coming into contact with food (safety of finished products). The first trials carried out "under field conditions" show a significant decrease in the number of Pichia anomala present on contaminated surfaces.

About the author

Président Directeur Général chez IBL SERVICE ET DISTRIBUTION, il conçoit et distribue les produits et appareils de nettoyage et désinfection d'IBL Specifik.