Fruit juice clarification

Details Fruit juice clarification Fruit juice clarification

1999-12-28

2002-03-12

Hendricks, Keith (Department: 1761)

Food or edible material: processes, compositions, and products

Fermentation processes

Of plant or plant derived material

C426S050000, C426S489000

Reexamination Certificate

active

06355284

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to substantially clear fruit juices and to a process to prepare these clear fruit juices.
BACKGROUND OF THE INVENTION
The manufacturing of fruit juices typically involves fruit squeezing, followed by depulping and centrifugation. The depulped juice is pasteurized as soon as possible after depulping in order to prevent oxidation. The juice thus obtained can be clarified with sulfur dioxide (SO
2
), fining agents or enzymes before pasteurization, solid removal and concentration.
Fruit juices in general and citrus fruit juices in particular are very difficult to clarify because of their high acidity. After juice extraction and pasteurization, the cloudy citrus juices are usually stored at 2-15° C. for months so that they can clarify slowly, before further processing. The temperature must be kept low to prevent oxidation reactions in the juice. Two other factors that complicate clarification of citrus fruit juice are the presence of protein and pectin.
One conventional method of clarifying juice is adding SO
2
as a clarification agent. However, this may result in high concentrations of SO
2
in the juice which is undesired. Although this can be solved by desulfitation, some SO
2
will remain in the juice. In addition, juice manufacturers must invest in large storage capacities since the juice has to be stored for quite a long time.
Another conventional method for clarifying juice is adding pectinases after squeezing, depulping and pasteurisation. The dosage used is usually rather high and the clarification takes several hours, sometimes even days, depending on the temperature. Then the juice may be fined with bentonite or silica sol and filtered on an earth filter and/or an ultrafilter. This process is also time-consuming and may result in a rather high waste production.
U.S. Pat. No. 4,624,980 discloses a process for the continuous clarification of fruit juices comprising the addition of coagulants that form a floc with the solid particles in the juice. The latter are then separated by introducing a non-deleterious gas in the form of micro-bubbles which causes the floc particles to float to the surface of the juice.
Le Quere et al. (Industries Alimentaires et Agricoles, 105, 137-139, 1988) disclose a method for clarifying specifically cider apple must prior to fermentation involving a pectin demethylation step by pectin esterase for 66-72 hours, subsequent addition of a CaCl
2
solution and nitrogen gas and flotation of the pectic gel thus formed.
G.B. patent 1,535,983 discloses a method to clarify lemon juices and comprises the addition of a combination of polygalacturonase and pectin esterase in order to eliminate the pectin completely in combination with colloidal silica.
Similarly, U.S. Pat. No. 4,211,799 discloses a method of making citrus juice resistant to flocculation on storage by treating the naturally turbid citrus juice having a pH below 2.5 with a pectinase of the polygalacturonase/pectin esterase type at a temperature below 30° C. until the alcohol test for pectin is negative and then decanting the flocculation resistant supernatant juice after settling.
Therefore, there is still a need for a fast process for the clarification of fruit juices in general, in particular for the clarification of citrus fruit juices. Surprisingly we have found that fast clarification of fruit juices could be obtained by applying a pectin esterase treatment during 0.5-48 hours in combination with a flotation technique.
SUMMARY OF THE INVENTION
The present invention relates to a process for the production of substantially clear fruit juices with a turbidity less than 300 NTUs from the corresponding fruit comprising the following steps
i. extract the fluid part from the fruit and depulping and optionally pasteurizing the fluid part;
ii. incubate this fluid part of the juice with an enzyme preparation containing pectin esterase and optionally calcium ions between 0.5 and 48 hours;
iii. transfer the enzyme treated fluid part of the fruit to a flotation tank followed by pressurization;
iv. release the pressure and allow the solid particles in the enzyme treated fluid part of the fruit to float to the surface, followed by removal of the insoluble particles and
v. recover the substantially clear fruit juice.
In another aspect, the invention relates to clear fruit juices with a turbidity of less than 300 NTUs.
In a further aspect, the invention relates to the use of pectin esterase in combination with a flotation technique for the production of substantially clear fruit juices.
DETAILED DESCRIPTION OF THE INVENTION
The present invention solves the problem of how to clarify fruit juices, more particularly, how to clarify citrus fruit juices. According to the present invention this problem can be solved by a simple process which includes the use of a pectin esterase treatment and flotation. This process is faster than conventional processes.
The process involves releasing the fluid part from the fruit, mechanically, enzymatically or by a combination of both. Then, after depulping and optionally pasteurization, pectin esterase is added to the fluid part of the fruit. The pectin esterase used is preferably free of pectin depolymerising activities such as pectin lyase (PL) and polygalacturonase (PG), resistant to high acidity (pH lower than 2) and active at low temperatures (10°-50° C.). The pectin esterase treatment takes only a relatively short time compared with conventional fruit juice clarification processes. The pectin esterase treatment lasts 0.5-48 hours, preferably 0.5-24 hours and more preferably 1-5 hours. Treatment times vary depending on the amount of pectin esterase and temperature used. Pectin esterase dosage may vary from 100-100,000, more preferably from 1,000-50,000 and more preferably from 1,000-15,000 pectin esterase units per hectoliter. The temperature may be chosen between 0 and 45° C., preferably between 0 and 35° C. and more preferably between 2 and 200° C.
Subsequently, the enzyme treated fluid part of the fruit is subjected to flotation in order to get a substantially clear juice. Then, the juice is introduced in the flotation tank in a pressurized state. Pressure conditions are 2-10 bars, preferably 2-7 bars and more preferably 4-7 bars and are applied for 1-120 minutes, preferably 2-120 minutes and more preferably for 2-60 minutes. After this time, the pressure is released causing the juice particles to float and separate out from the juice.
Optionally, calcium may be added during flotation, for instance as calcium chloride. Preferred calcium chloride concentrations range from 1-500, more preferably from 10-500 and more preferably from 10-200 grams per hectoliter.
The turbidity of the substantially clear fruit juices obtained by the present invention can be determined by several methods. The most common method is to express the turbidity in Nephelometry Turbidity Units (NTUs). The substantially clear fruit juices obtained by the present invention have a turbidity less than 300 NTU, preferably less than 200 NTU and more preferably less than 100 NTU.
With another method the filterability of the substantially clear fruit juices is determined by filtering these juices through paper filters and measuring the amount of the filtrate as a function of time. The less turbid the substantially clear fruit juice, the larger the amount of the filtrate per unit of time.
Similarly, the ultrafiltration (UF) capacity of the substantially clear fruit juices can be determined by filtering these juices through ultrafilters and measuring the amount of the ultrafiltrate as a function of time. The less turbid the substantially clear fruit juice, the larger the amount of the filtrate per unit of time.
Materials & Methods
The pectin esterase can originate from any source, such as from microorganisms or plants. The pectin esterase suitable for the use according to the present invention is stable in fruit juice medium and retains its activity during the juice processing. Due to the desired enzyme characteristics, the pectin esterase preferably o

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