Quality of fruit juices

Faults in pasteurization are the main reason for deficient keeping quality of fruit juices. Simple thermometers can show divergences of up to 4°C. If the temperature out of the pasteurizer falls, these thermometers still indicate the higher temperature. 

High juice content is defined by a content of more than 20% by weight in the final drink. In this category, the turbidity derives from a stable colloidal dispersion of fruit cells. Stability and quality of the final drink are mainly based on the quality of fruit juice concentrates formulated into the product. Additional stabilisers, mainly hydrocolloids, might be added. 

Ghenghesk, K.S., Belhaj, K., El-Amin, W.B., El-Nefathi, S.E., andZalmun, A. 2005. Microbiological quality of fruit juices sold in Tripoli-Libya. Food Control 16, 855-858. 

Since many years, pectolytic enzymes have been widely used in industrial beverage processing to improve either the quality and the yields in fruit juice extraction or the characteristics of the final product [1,2]. To this purpose, complex enzymatic mixtures, containing several pectolytic enzymes and often also cellulose, hemicellulose and ligninolytic activities, are usually employed in the free form. The interactions among enzymes, substrates and other components of fruit juice make the system very difficult to be investigated and only few publications are devoted to the study of enzymatic pools [3-5], An effective alternative way to carry out the depectinisation process is represented by the use of immobilized enzymes. This approach allows for a facile and efficient enzymatic reaction control to be achieved. In fact, it is possible to avoid or at least to reduce the level of extraneous substances originating from the raw pectinases in the final product. In addition, continuous processes can be set up. 

From a number of pilot applications Fig. 1.4-8 shows the quasi-continuous train for the sterilization of fruit juices with pulp contents. The high pressure sterilization offers valuable advantages with respect to the quality of the final product compared to other sterilization procedures, especially if natural fractions of fruit pulp are desired by the consumers. 

Determination of cations is one of the most important analyses for the routine quality control of fruit juices and purees. Weak cation exchangers are in general highly selective with respect to the H+ ion ... 

A Versari, S Biesenbruch, D Barbanti, PJ Famell. Adulteration of fruit juices dihydrochalcones as quality markers for apple juice identification. Lebensm Wiss Technol 30 585 -589, 1997. 

Although a combination of product quality and cost considerations will dictate the methods used for bulk processing of fruit juices, there are instances where the flavour components present in the juice at e vulnerable to any form of heating din ing concentration. Strawberry juice is perhaps the best example of this, being one of the most heat sensitive of fruits, and it works well with alternative processes for concentration such as freeze-concentration and hyperfiltration. 

Good improvements in the concentration of fruit juices have been achieved in recent years. As it is the case that the majority of concentrates are to be reconstituted in application, the quality achievable for the natural strength remake will be an important issue. 

Thirty year s ago there would have been a limited set of equipment in the quality control laboratory of the majority of fruit juice and soft dr inks factories. This would probably have consisted of a reffactometer, a burette, a spectrophotometer, an instrument to measure the level of carbonation and some equipment for checking the microbiological integrity of the product. However, with the move to larger... 

Although there are only a limited number of methods that have been validated specifically for soft drinks, there are around 80 validated methods available for the analysis of fruit juices, most of which would work equally well for soft drinks. These methods are published in the International Fruit Juice Union (IFU) handbook of analytical procedures, which offers the best reference collection of methods for the analysis of fruit juices in the world, with new methods added on a regular basis (Anon, 2004a). The IFU s collection of analytical methods covers most of the main procedures required to assess the quality and authenticity of fruit juices and nectars. The methods are hsted on the IFU s website (http //www.ifu-fruitjuice.com) at the time of writing they cannot be purchased directly from there, but they can be obtained from the Swiss Fruit Union, Zug, and details of how to do this are given on the website. It is possible that at some time the methods will be made available directly from the website. 

In the analysis of fruit juices, it is important to determine the levels of the individual acids to assess authenticity and quality. A range of these acids can be determined using an enzyme-linked assays and these procedures have been collaboratively tested and published in the IFU compendium of methods (citric no. 22, isocitric no. 54, D-malic no. 64, L-malic no. 21 and D-and L-lactic acids no. 53). r-Biopharm now distributes the Boehringer Mannheim kits to assess the levels of these acids. Similar kits are available from other suppliers. 

Vasavada, P.C. (2003) Beverage quality and safety, in Microbiology of Fruit Juice and Beverages (eds T. Foster and P.C. Vasavada), CRC Press, Boca Raton, FL, pp. 95-123. 

It should be pointed out that if extraction conditions are carefully controlled, the quality of the juice will be maintained. No degree of manipulation of extraction conditions can yield a good quality juice if poor quality fruit is used. The important role that fruit variety and maturity play in determining the quality of the final product cannot be overemphasized. 

It was realised that the method of processing fruit juices significantly influences the specific flavom of the fruit and consequently the quality of the juice. When producing concentrate from a high quality fruit juice, the recovery and isolation of the aroma during the concentration process is essential for adding it back to the juice upon reconstitution of the concentrate. 

Many applications of SNIF-NMR to the determination of the origin and quality of non-alcoholic products have been demonstrated.17 These include studies of the origin (natural or synthetic) of aromas and flavours such as vanillin337 338 and anethole,339 of vinegars340 and of possible adulteration of fruit juices and jams. The technique is expected to assume increasing importance in response to the demands of consumers and regulatory authorities for guarantees of food quality. 

Pectinases, cellulases and hemicellulases are used for clarification of fruit juices, juice extraction, improvement of cloud stability of vegetable and fruit juices and nectars, liquefaction and maceration of fruits and vegetables, reduction of cooking time of pulses and improvement of rehydration characteristics of dried vegetables. The chemical basis of these treatments and of the consequential changes in sensory and nutritional quality are discussed. 

NMR-based Multi Parametric Quality Control of Fruit Juices... 

The examples presented here for the screening of fruit juices can also be seen as proof-of-principle for other upcoming applications. The same workflow (preparation, measurement, processing, reporting) and underl)dng mathematical methods can be easily transferred to other quality control applications, such as the screening of milk, wine or beer. 

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