Pasteurisation

Water Boiling, pasteurisation, sterilisation, blanching, evaporation, extrusion cooking... 

Another important food processing technology is pasteurisation. It consists of rapid heating to temperatures between 60 and 65°C in order to destroy microorganisms. Oxidoreductases are inactivated at the same time. As the heating is short, the destruction of antioxidants is only moderate. Losses of ascorbic acid are a good indicator of the destructive changes. Losses of ascorbic acid and carotenes are minimised by deaeration. 

Commercial sterilisation is a more severe process than pasteurisation as the temperature is higher (70-90°C). The process is used to protect food during long-term storage. The oxygen residue should be minimised before heating to reduce deterioration of antioxidants or, in some cases, antioxidants... 

Apples (Red Belle de Boskoop, Jonagold or Mutzu) were cut and milled (1.5 mm) and 5% (w/w) of a 2% ascorbic acid solution was added immediately. Enzyme preparations (25 mg enzyme protein / kg mash) were added and the mash was incubated for 2 hours at 20°C whereafter it was pressed. The resulting apple juice was pasteurised at 85°C to discontinue further enzyme degradation. The cloud was measured as turbidity in EF/F units [15]. The cloud stability was determined by a centrifugation test as the amount of turbidity remaining after centrifugation at 4,200 x g for 15 minutes [15]. 

Figure 3. Oligouronides evolution in a reactor without cross-flow ultrafiltration membrane, (a) Native Rh. nigricans endoPG. (b) Pasteurised Rh. nigricans endoPG.

In the nonchemical field cooking, drying, sterilisation and pasteurisation are areas where microwave heating is applied on a large scale. 

The restricted shelf life of liquid milk continues to be a problem that is often more influenced by the type of milk being sold rather than the pasteurisation technique. The shelf life of processed milk is determined primarily by the quality of the raw milk from the dairy herd. Increasing cell counts in the milk and a higher concentration of free fatty acids, contribute to rancidity in both liquid milk and milk products. Janzen (1972) reported that the 0-14 day shelf life of pasteurised milk is influenced by the somatic cell concentration in the raw milk and found that after 14 days any observed changes in the flavour and stability of the milk were attributable to microbial activity during storage. 

Lewis M J (2003), Improvements in the pasteurisation and sterilisation of milk , in Dairy Processing - Improving quality, Gerrit Smith, Woodhead Publishing, Cambridge, UK 81-103. 

Ensure maximal hygiene (pasteurisation, filling and storage). 

Sample preservation by pasteurisation has been applied to the preservation of nitrite and nitrate in seawater [152], Samples can be stored for several months before analysis. 

The French site http //www.calixo.net/braun/conserve/pasteurisation.htm and the Canadian site http //www.foodsci.uoguelph.ca/dairyedu/pasteurization.html both cite pertinent details. 

Thermal treatment, applied to honey, may destroy vitamins and bionutrients, and produce a simultaneous decrease in diastase activity and an increase in HMF content. Honey treatment temperature and time must be limited when pasteurising and stabilising it both diastase activity and HMF content are national and international parameters used as controls so as to limit thermal treatment application. HMF can be formed by hexose dehydration in acid media or by the Maillaid reaction [11,12]. According to Ibarz et al., HMF formation can be described by a second order kinetics (auto-catalytic), with the following equation as expression model [13] ... 

M. Lewis and N. Heppell, Continuous Thermal Processing of Foods — Pasteurisation and UHT Sterilisation, Aspen Publishers, New York, 2000. 

Non-carbonated RTD beverages have shown some considerable growth in recent years mainly because of the availability of aseptic packaging forms. Still drinks that rely on chemical preservation or hot-pack/in-pack pasteurisation suffer from a number of potential problems, including rapid flavour and colour deterioration. 

Some manufacturers produce RTD products at drinking strength but this is wasteful of plant and requires large-volume production tanks. The usual approach is to manufacture a syrup or concentrated form of the beverage that is then diluted with carbonated water. The syrup, which can be flash-pasteurised, can be dosed into bottles that are then topped up with carbonated water. This is known as the post-mix method. Where the alternative, pre-mix , method is employed, syrup and water are mixed in the correct proportions in special equipment prior to bottle filling. 

Most concentrated beverages contain fruit juice or whole fruit , a term that refers to a comminuted form of citius that includes components of juice, essential oil, peel (flavedo) and pith (albedo). Concentrated soft drinks are usually flash-pasteurised and chemically preserved. Their dilutable form means that they are often held in partially filled bottles for significant lengths of time (often many weeks or even months) and are extremely vulnerable to spoilage by micro-organisms. 

Some manufacturers do produce unpreserved concentrates, but such products are invariably pasteurised in the bottle and carry a warning that the contents should be refrigerated after opening and consumed within a short time-span (typically 2 weeks). 

Concentrates are normally produced at their packed strength, flash-pasteurised and transferred immediately to their final packaging. 

If juice is to be sold as not from concentrate it is usually screened and pasteurised immediately after pressing - an operation with two main objectives. The first is to control the growth of spoilage micro-organisms that live on the fruit surface (mainly yeasts and moulds). The second is to destroy the pectolytic enzymes that occur naturally in fruit that would otherwise break down the cloudy nature of the juice. If, however, a clear juice is required (e.g. apple or raspberry), enzymes can be added to accelerate this natural process. 

Perhaps the most exciting developments are yet to feature in fruit juice packaging. PET can be laminated with other plastics, such as nylon and ethylene vinyl alcohol (EVOH), to give extremely good barrier properties, and polyethylene naphthalate (PEN) may enable production of a plastic bottle that can be pasteurised at high temperatures. 

The expressed juice is subjected to screening before being further processed. A rotary brash sieve, followed by a centrifugal separator, may be used to bring the suspended particles into the stability range of below 1 pm diameter, at which point the juice can be pasteurised and aseptically packed for direct consumption as single-strength juice or concentrated as required. 

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