Orange juice freeze concentration

Freeze Crystallization. Freezing may be used to form pure ice crystals, which are then removed from the slurry by screens sized to pass the fine sohds but to catch the crystals and leave behind a more concentrated slurry. The process has been considered mostly for solutions, not suspensions. However, freeze crystallization has been tested for concentrating orange juice where sohds are present (see Fruit juices). Commercial apphcations include fmit juices, coffee, beer, wine (qv), and vinegar (qv). A test on milk was begun in 1989 (123). Freeze crystallization has concentrated pulp and paper black hquor from 6% to 30% dissolved sohds and showed energy savings of over 75% compared with multiple-effect evaporation. Only 35—46 kJ/kg (15—20 Btu/lb) of water removed was consumed in the process (124). 

After concentration, juices are normally held in storage until they are reconstituted. Some concentrated juices, particularly orange, require freezing at below — 10°C for effective preservation. Others, particularly apple, can be held at around 10-15°C without risk of deterioration. The degree of concentration plays an important part in determining storage conditions in the above examples, orange juice is normally concentrated to about 65°Brix and apple to 70°Brix. 

Orange Juice. In a study of some parameters important to freeze concentration of orange juice, horticultural factors related to the fruit, juice handling and the extent of thermal treatment were more important to product quality than the concentration process (30). 

Table III. Quality Parameters of Fresh Orange Juice Which was Freeze Concentrated (FCNP), Then Pasteurized for 6 Sec at 80 (FC80), 97 (FC97) and 111°C (FC111)...

Gil-Izquierdo et al. (2002) found that mild pasteurization, standard pasteurization, concentration, and freezing of orange juices did not affect the total antioxidant capacity of the juice, but they did affect it in pulp, where it was reduced by 47%. In their study, they also found that ascorbic add provided at least 77%o of the antioxidant capacity, whereas the contribution of phenolic compounds was comparatively irrelevant. 

Concentration of juice by freezing is less economical than evaporation. Hence, it is utilized mostly for products containing sensitive aroma constituents, e. g., orange juice. The juice is cooled continuously below its freezing point in a scraper-type cooler. The ice crystals are separated from the resultant ice slurry by pressing or by centrifugation. The obtainable solid content of the end product is 40-50%. This content is a function of freezing temperature, as illustrated with apple juice in Fig. 18.11. 

Freezing— The vitamin contents of eight common frozen fruit products (apples, apricots, blueberries, cherries, orange juice concentrate, peaches, raspberries, and strawberries) were found to be lower than those of their fresh counterparts, but higher than those of canned fruit products.This study showed that the average vitamin losses were as follows vitamin A, 37% vitamin B-1 (thiamin), 29% vitamin B-2 (riboflavin), 17% niacin, 15% and vitamin C, 18%. 

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