Temperature fruit juice production

The OMD process provides the great advantage of working at both constant (and low) temperature and atmospheric pressure, with a consequent reduction in both thermal and mechanical damage. These gentle operating conditions are very important, especially in the concentration of heat sensitive materials in biomolecules, in natural colours, or in food processing (fruit juice production, for example). 

Tables have been published relating Baume, Brix and specific gravity. As density is temperature dependent it is necessary to either bring the syrup to a fixed temperature or, as is more common in practice, to use temperature correction factors or tables. The relationship between density and concentration is slightly different for invert sugar or glucose syrups. The Brix scale is sometimes applied to products that are not sucrose syrups, such as concentrated fruit juice. Recipes are certainly in use that state boil to x Brix . In practice these instructions mean that the material should give the same reading as a sugar syrup of that concentration. As often happens in confectionery these practices have been proved to work empirically.

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. 

Fruit juices and nectars are highly susceptible to fermentation and other forms of microbial spoilage and with few exceptions it is essential that some form of pasteurisation is employed when these products are packaged. The exceptions that are seen usually relate to freshly squeezed orange (or other) juices that are processed directly from fresh fruit and packaged immediately. These products have a very short shelf life, usually a few days, and are maintained by storage at temperatures between 0 and 5°C. 

Typical flash pasteurisation operations for fruit juices and nectars will employ a plate pasteuriser with heat recovery and final product cooling. Typical flash pasteurisation conditions will use temperatures between 85 and 95°C with holding times varying between 15 and 60 s. Selection of the appropriate conditions will depend on the product, including the level of microbial load pre-pasteurising. If enzyme deactivation is required as well as microbial removal then a temperature between 90 and 95°C will normally be used. At these temperatures, holding times are normally reduced to around 15 s. 

Claims have been made for the successful high-pressure pasteurisation of fruit juice in containers. The equipment required is expensive and the process is carried out as a batch operation, which tends to be both slow and ineffective. It may, in future, provide a very interesting means of low-temperature pasteurising of fresh juices, thus retaining all the flavour characteristics of the product. 

The RO potentialities as a concentration technique to remove water from fruit juices for the production of high-quality fruit-juice concentrate are well known [24], The most relevant advantages of the RO process over traditional evaporation are in the reduced thermal damage of the product, increase of aroma retention, and lower energy consumption, since the process is carried out at low temperature. 

All parts of the tamarind tree are useful in one way or another. Tamarind is valued mostly for its fruit and pulp, which is used for a wide variety of domestic and industrial purposes (Kulkarni et al., 1993), in particular to prepare juice, jam, syrup and sweets. Tamarind juice concentrate (TJC) is a convenient product due to the ease with which it can be dissolved and reconstituted in warm water. The specific heat of TJC increases with temperature and the glass transition temperature of the product is -70.74°C (Ahmed etah, 2007). Tamarind intake appears to... 

To maintain cloud stability in fruit juices, high-temperature-short-time (HTST) pasteurization is used to deactivate pectolytic enzymes. Pectin is a protective colloid that helps to keep insoluble particles in suspension. Cloudiness is required in commercial products to provide a desirable appearance. The destruction of the high levels of pectin-esterase during the production of tomato juice and puree is of vital importance. The pectinesterase will act quite rapidly once the tomato is broken. In the so-called hot-break method, the tomatoes are broken up at high temperature so that the pectic enzymes are destroyed instantaneously. 

Pectin, a waste product of the fruit juice industry, has many applications in the food ingredients sector. It forms gels in the presence of Ca ions and its solubility is determined by its molecular weight and degree of esterification as well as solution pH and temperature. Pectin can be incorporated into jams, jellies, low calorie foods as a fat or sugar replacer, and frozen foods [85]. Found in the cell wall of all plants, concentrations are higher in the fruits rather than the rest of the plant. Some fruits contain higher amounts of pectin than others for... 

Low Temperature Treatment. Many commercial frozen food products are high in ascorbic acid. Refrigeration is used for various fresh fruit juices and for holding many fruits and vegetables prior to retail sale or further processing. 

In order to produce clear juice the cloudy product is treated with pectolytic enzymes to degrade the pectic substances which are responsible for the cloud stability of the cloudy juice. The treatment time depends on the activity of the enzymes and the temperature respectively. Several years ago the industry had no enzymes which were able to work in very acid juice environments (e.g. lemon juice). However, in the meantime new types were developed which are capable of treating acid juices satisfactorily. Some fruit juices contain substances which cannot be removed with pectolytic enzymes and which require other specific enzymatic products to eliminate turbidity, e.g. starch in apple juice requires a suitable amylase. 

The capacity can be increased further by reducing the viscosity of the liquid to be filtered. This can be achieved by treating fruit juices enzymatically and also by increasing the filtration temperature. The ideal temperature is determined by the temperature resistance of the membrane material and on the other hand by the fact that it must not impair the quality of the product. 

Hsin-Yu, C. and Chou, C.-C. 2001. Acid adaptation and temperature effect on the survival of E. coli 0157 H7 in acidic fruit juice and lactic fermented milk product. International Journal of Food Microbiology 70 189-195. 

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