Fruit juices consistency measurement

Quality can be regarded as a measure of the suitability of a fruit juice, fruit juice concentrate or fruit juice extract for an intended application. In general, whatever the application, it will be the consistency in performance of the product, from batch to batch and season to season, that is the prime concern. In order to meet quality targets, therefore, it becomes critical that processing is carried out in the correct manner using fruit of an optimum level of maturity, and that the product is stored under suitable conditions to limit effects of degradation during a required shelf-life. 

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... 

Similar analyses are now common in the quality control procedures of many consumer products, such as beer and wine, coffee, fruit juice, and infant formula, where consistency is demanded even though the quality of the raw starting materials may vary with source and season. This is chemical analysis at its best, and the above example is emphasized here because it clearly illustrates this type of approach, which in general combines precise measurements with sophisticated numerical analysis to produce practical results. 

The apricot (Prunus armeniaca L.) is one of the most desirable of the temperate tree fruits. It is delectable and versatile, being important for fresh production as well as for the canning, dehydrated and juicing industries (Burgos and Ramming 1993). Exceptional fruit quality consists of a balance of sugar and acidity as well as a strong apricot aroma (Mehlenbacher et al. 1983). Thus it is important to be able to accurately and reproducibly measure fruit quality characteristics. 

Another study employed an ODS column and different mobile phase composition for the measurement of carotenoids in orange juice. Citrus fruits were hand-squeezed and the juice was filtered. Aliquots of 5 ml of juice were extracted with ethyl acetate (3 X 50 ml) containing 0.004 per cent butyl hydroxytoluene (BHT). The organic phase was dried with 50 g of anhydrous sodium sulphate and the aqueous phase was mixed with 50 ml of mehanol and 100 ml of 1 M NaCl, extracted with 75 and 25 ml of ethyl acetate. The ethyl acetate fractions were combined, evaporated to dryness at 40°C and redissolved in the mobile phase. Extracts were analysed in an ODS column (250 X 4.6 mm i.d. particle size 5 jian). The mobile phase consisted of ACN-methanol-l,2-dichloroethane (60 35 5, v/v) containing 0.1 per cent BHT, 0.1 per cent triethylamine and 0.05 M of ammonium acetate. The column was not thermostated and the flow rate was 1 ml/min. Pigments were detected... 

Chapter HI relates to measurement of flow properties of foods that are primarily fluid in nature, unithi.i surveys the nature of viscosity and its relationship to foods. An overview of the various flow behaviors found in different fluid foods is presented. The concept of non-Newtonian foods is developed, along with methods for measurement of the complete flow curve. The quantitative or fundamental measurement of apparent shear viscosity of fluid foods with rotational viscometers or rheometers is described, unithi.2 describes two protocols for the measurement of non-Newtonian fluids. The first is for time-independent fluids, and the second is for time-dependent fluids. Both protocols use rotational rheometers, unit hi.3 describes a protocol for simple Newtonian fluids, which include aqueous solutions or oils. As rotational rheometers are new and expensive, many evaluations of fluid foods have been made with empirical methods. Such methods yield data that are not fundamental but are useful in comparing variations in consistency or texture of a food product, unit hi.4 describes a popular empirical method, the Bostwick Consistometer, which has been used to measure the consistency of tomato paste. It is a well-known method in the food industry and has also been used to evaluate other fruit pastes and juices as well. 

---