Innovation in the pasteurization process

Apertura_portaleOne of the main difficulties related to wine-making processes is the possibility of unwanted microbiological contaminations, which can occur at different stages of the production cycle. In order to avoid damaging the production, wine-making industry uses sulfitation, with the well known problems related to the effects of sulphites on health and the need to indicate on the label the caption Contains sulphites for levels of sulphites above 10 mg/L.
A valid alternative to sulfitation is constituted by the pasteurization process.

Traditional process: heat treatment

The pasteurisation heat treatment is applied to young wines, intended for short-term consumption, while aged wines are preferably not pasteurized in order to keep them alive. This process aims at minimizing the health risks caused by pathogenic microorganisms sensitive to heat, such as bacteria in the vegetative form, fungi, and yeasts.
This treatment, applied to the wine in order to stabilize it from both bacterial and enzymatic point of views, consists in bringing the product at high temperatures in a few minutes. The effect of pasteurization, as well as on the combination of time/temperature, also depends on the degree of pollution of the product and resistance by microorganisms to the treatment. It was noted that yeasts are destroyed with a pasteurisation carried out at 60°C for 10 minutes, bacteria are eliminated at 60°C for 45 seconds, enzymes are destroyed at 70°C for 2 minutes. Obviously, it is possible to use higher or lower temperatures by changing the treatment time. It was also noted that the effect of pasteurisation depends on the characteristics of the wine, too, in particular on its alcohol degree, pH, presence of carbon dioxide, and content in sulphur dioxide.

Industrial pasteurizers

The choice of pasteurization units to use is made based on the verification that, with a given pasteurization cycle, the destruction of all microorganisms present in the product to be treated is obtained. The classic industrial pasteurizers try to achieve a certain pasteurization effect trying at the same time to preserve the organoleptic characteristics of the product. To date, the systems adopted mainly provide equipment in order to operate:
– on bulk wine, by using plate pasteurizers;
– on bottled wine, by means of tunnel pasteurizers.

Important innovation: cold pasteurization

Several studies published in scientific newspapers have showed the limits of the heat treatment of pasteurization, because, although it guarantees sanitary safety, it compromises the sensory, qualitative, and nutritional characteristics of the products themselves. For this reason, for some decades innovative techniques have been developed. They do not use heat as the driving force of the process but, for example, pulsed electric fields, ultrasound, microwaves, hydrostatic pressure, carbon dioxide at high pressures.
Scientific researches define these alimentary processes mild technologies, as they can eliminate the microbial forms which are potentially harmful to human health, slowing down their proliferation, without recourse to the action of the temperature, which affects the organoleptic and nutritional characteristics of foods.

High hydrostatic pressures

It is a decontamination athermal process (inactivation of bacteria and yeasts) in which the food, previously sealed in flexible water-resistant containers, is subjected to pressures ranging from 400 to 600 MPa and temperatures slightly above the room one, for a treatment time ranging from 1 to 15 minutes. The technology is based on Pascal’s principle according to which “a pressure exerted on an incompressible liquid is evenly distributed in all directions and with the same intensity at all points of the liquid (isostatic pressure) and also on the surface of a body (food) immersed in that liquid“. Since 2000, several companies worldwide have specialized in the production of plants that apply the technology of high pressure to a wide variety of products (juices, meat- or fish-based foods, milk and its derivatives). They are able to provide an innovative process and offer the consumers many products with organoleptic characteristics similar to fresh foods, but at the same time safe from a microbiological point of view.
Scientific studies that prove the potential of this process for the pasteurization of wine were published. It was demonstrated that the treatments carried out at 200-500 MPa are sufficient to inactivate the microbial flora in both red and white wines, without significantly affecting their sensory characteristics. However, some Authors have found that in red wines high pressures reduce their antioxidant capacity and alter the total content in phenols and anthocyanins, giving a product with deep red colour and characteristics similar to an aged wine.

Carbon dioxide at high pressures

The use of carbon dioxide at high pressures seems one of the most promising opportunities for future development of the process on an industrial scale. This process consists in the direct contact of foods with carbon dioxide at high pressures (lower than 40 MPa) and low temperatures (below 50°C) for a given treatment time. The nature of carbon dioxide, defined as Gras, that is to say Generally Recognized as Safe by FDA (Food and Drug Administration), allows its use and direct contact with foods. In addition, it is inert, cheap, non-toxic, non-flammable, recyclable substance, available at high purities and does not leave any residue when it is removed from the food after the process.
Despite the scientific evidence, to date there are no industrial applications able to effectively use this technology, because of the lack of knowledge about the inactivation mechanism of microbial forms induced by CO2. The understanding of this mechanism might accelerate the optimization of the process and its industrial applications.
The treatment has been successfully applied for the first time in 2006 by a group of researchers of the Department of Food Science and Human Nutrition at the University of Florida (USA), who have subjected a Moscato wine to this process with a continuous system on a laboratory scale. The product, treated with carbon dioxide at 34.5 MPa, 30°C, for 6.25 minutes, had higher content in anthocyanins, soluble phenols, and higher antioxidant capacity in comparison with the same wine treated with the thermal pasteurization process (75°C for 15 seconds). In addition, the product, analyzed after 5 weeks, did not show any microbial contamination and any change of its sensory characteristics (colour, aroma, and flavour).

 

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Minimally processed foods and drinks

Beyond the technical issues related to the introduction into the production cycle of machines with process characteristics completely different from the present ones, the interest food industries have for mild technologies has grown in response to consumers’ needs, which require food with excellent organoleptic/nutritional characteristics and safe from the sanitary point of view. These products are also called minimally processed foods by researchers.

(article by Giovanna Ferrentino – Department of Industrial Engineering – University of Trento)

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