Process for the production of dried fruits

Dried fruits are treated by contacting and incubating them with a glycerol solution containing a carbohydrase enzyme in an amount of 0.05 to 0.5 parts enzyme by weight per 100 parts fruit at a temperature of from 40.degree. C. to 60.degree. C. for a time sufficient so that the fruit absorbs at least 10% by weight glycerol. The carbohydrase enzyme is inactivated and the incubated fruit is dried so that the fruit has a water activity of from 0.25 to 0.40.

BACKGROUND OF THE INVENTION 
This invention relates to a process for the production of dried fruits. 
Certain food products of the ready-to-serve type, more particularly 
intended for breakfast, consist essentially of a mixture of cereals in the 
form of flakes and dried fruits either whole or in the form of cubes. The 
cereals used are generally wheat, corn and oats while the dried fruits may 
be apples, apricots, bananas, figs and grapes, for example. 
One of the main characteristics of these food products is the crispy 
texture of the cereal flakes and the tenderness of the dried fruits. 
Accordingly, it is important that each of the constituents of the end 
product retain its own organoleptic qualities in storage up to the moment 
it is consumed. 
Now, the crispiness of the cereal flakes and the tenderness of the dried 
fruits depend mainly on their water activity value (Aw). Thus, the cereal 
flakes have a crispy texture when their water activity is of the order of 
0.15-0.25. When the water activity exceeds 0.35, the flakes lose their 
crispiness and become soft. Similarly, the dried fruits have a pleasant 
tenderness when their water activity is of the order of 0.50 to 0.55. When 
the water activity falls below 0.40, the dried fruits become hard. 
When the end food product is produced and stored by mixing the cereal 
flakes and the dried fruits, a transfer of moisture can take place so that 
the dried fruits lose water to the cereal flakes. A balance is generally 
obtained around a water activity value of the end product of 0.25-0.40, at 
which the flakes are soft and the dried fruits are hard. 
Now, it has already been proposed to treat the fruits with a humectant, 
such as glycerol, so that they retain a pleasant and tender texture for a 
water activity value below 0.50. To obtain good absorption of the 
humectant in the fruits, it is preferable to increase the permeability of 
their skin by pretreatment before they are steeped in the humectant. 
Thus, it is known, for example from Canadian Patent No. 981,523, that the 
fruits can be subjected to a hot pretreatment with a weak acid and then to 
treatment with a humectant, such as a solution of sorbitol or glycerol, 
for about 15-24 hours so that the fruits absorb at least 3% humectant. The 
fruits thus treated are then dried to a dry matter content of 80to 88%. 
SUMMARY OF THE INVENTION 
The problem addressed by the present invention was to provide a process for 
the production of dried fruits in which the step of pretreatment with a 
weak acid would be avoided. 
Accordingly, the present invention provides a process in which dried fruits 
are contacted with a solution of glycerol containing 0.05-0.5 part 
carbohydrase enzymes per 100 parts fruits, the fruits are incubated in 
contact with the glycerol solution at a temperature of 40.degree. to 
60.degree. C. until the fruits have absorbed at least 10% glycerol, the 
enzymes are inactivated and the fruits obtained are dried to a water 
activity of 0.25-0.40. 
The use of a solution of glycerol containing carbohydrase enzymes enables 
the time required to prepare the dried fruits to be significantly reduced 
on the one hand, by eliminating the pretreatment step and, on the other 
hand, by reducing the incubation time of the fruits in the presence of the 
glycerol. This is because it appears that the use of a solution of 
glycerol containing carbohydrase enzymes enables the permeability of the 
skin of the treated fruits to be improved and hence, facilitates 
absorption of the glycerol by the fruits. 
DETAILED DESCRIPTION OF THE INVENTION 
In the rest of the present specification, parts and percentages are by 
weight unless otherwise stated. 
In the process according to the invention, the dried fruits, for example 
either whole or precut into cubes and having a dry matter content of 85 to 
88%, are contacted with a glycerol solution containing 0.05-0.5 part 
carbohydrase enzymes per 100 parts fruits to be treated. The glycerol 
solution may consist-either of pure glycerol or of an aqueous solution 
containing 80-90% glycerol. It preferably contains 0.1-0.4% carbohydrase 
enzymes. Any enzyme which allows correct diffusion of the glycerol into 
the fruits may be used as the source of carbohydrase enzymes. The enzyme 
used may be, for example, a cellulase, a mixed carbohydrase, a pectinase, 
a galactomannanase, a hemicellulase, or a mixture of these various 
enzymes. The glycerol solution containing the enzymes and the fruits are 
then contacted. 
In a preferred embodiment, one part fruits is contacted with 1 to 2 parts 
glycerol solution. This may be done, for example, by steeping the fruits 
in the solution, preferably preheated to 40.degree.-60.degree. C., for 2 
to 5 hours and preferably for 3 hours. In one preferred embodiment, the 
glycerol solution containing the enzymes may also be sprayed onto the 
fruits at a temperature of 40.degree.-60.degree. C. Spraying may also be 
carried out several times or in several steps. This embodiment provides 
for the use of a smaller quantity of glycerol (of the order of 70-80 ml 
per 100 g fruits) while promoting its absorption in the fruits. 
The fruits are then incubated in contact with the glycerol solution at a 
temperature of 40.degree.-60.degree. C. until the fruits have absorbed at 
least 10% glycerol. For example, the fruits may be incubated in an oven 
for 2-5 hours at 40.degree.-60.degree. C. 
The incubation time may be shortened by subjecting the fruits to a 
pretreatment before they are contacted with the glycerol solution. Thus, 
if the fruits are pretreated by immersion in water at 
90.degree.-100.degree. C. for 2-4 minutes before they are contacted with 
the glycerol solution containing the enzymes, the incubation time at 
40.degree.-60.degree. C. required to obtain a glycerol content of at least 
10% is reduced to 1.5 h-2.5 h. 
When the fruits have acquired the desired glycerol content, the enzymes are 
inactivated. This may be done, for example, by steeping the fruits in a 
glycerol solution at 75.degree.-95.degree. C. for 20-40 minutes. 
Inactivation in the glycerol reduces the migration of the sugars present 
in the fruits to the outside. The fruits thus obtained may be rapidly 
rinsed, for example in water, and are then dried, for example with hot air 
at 50.degree.-70.degree. C., for about 10-20 hours until a water activity 
of 0.25-0.40 and a dry matter content of the order of 88-92% are obtained.

EXAMPLES 
The invention is illustrated in more detail by the following Examples. 
Example 1 
An 87% glycerol solution containing 0.1% of a carbohydrase is prepared. 100 
g dried grapes having a dry matter content of 88% are steeped in 100 g of 
this solution heated beforehand to 50.degree. C. The mixture is stirred to 
eliminate the air trapped at the surface of the grapes and is then 
incubated for 3 hours at 50.degree. C. 
After the incubation period, the grapes are steeped for 30 minutes in an 
87% glycerol solution heated beforehand to 95.degree. C. to inactivate the 
enzymes and are then rapidly rinsed with water to remove the glycerol 
present at their surface in order to facilitate their subsequent handling 
by minimizing the risks of adhesion and agglomeration. The grapes thus 
treated are then dried in a ventilated oven at 40.degree. C. for about 15 
hours with occasional turning. The dry grapes thus obtained have a dry 
matter content of 88-90%, a water activity of 0.29-0.32 and a glycerol 
content of 21.5%. 
Example 2 
An 87% glycerol solution containing 0.5% carbohydrase is prepared and 
heated to 50.degree. C. This solution is sprayed onto dried grapes to 
moisten them as thoroughly as possible. The grapes are then spread over an 
aluminium foil and placed in an oven at 50.degree. C. where they are left 
to incubate for 3 hours. During this 3 hour incubation period, the 
spraying step is repeated twice. After the incubation period, the grapes 
are steeped for 30 minutes in an 87% glycerol solution heated beforehand 
to 95.degree. C. to inactivate the enzymes and are then rapidly rinsed 
with water to remove the glycerol present at their surface in order to 
facilitate their subsequent handling by minimizing the risks of adhesion 
and agglomeration. The grapes thus treated are then dried in a ventilated 
oven at 40.degree. C. for about 15 hours with occasional turning. The dry 
grapes thus obtained have a dry matter content of 88-90%, a water activity 
of 0.29-0.32 and a glycerol content of 18.2%. 
Example 3 
Dried grapes having a dry matter content of 88% are steeped in hot water at 
90.degree.-100.degree. C. for 3 minutes to tenderize their skin and are 
then left to cool to 50.degree. C. 
An 87% glycerol solution containing 0.5% carbohydrase heated beforehand to 
50.degree. C. is then sprayed onto the grapes thus pretreated. The grapes 
are then spread over an aluminium foil and placed in an oven at 50.degree. 
C. where they are left to incubate for 3 hours. During this 3 hour 
incubation period, the spraying step is repeated twice. After the 
incubation period, the grapes are steeped for 30 minutes in an 87% 
glycerol solution heated beforehand to 95.degree. C. to inactivate the 
enzymes and are then rapidly rinsed with water to remove the glycerol 
present at their surface in order to facilitate their subsequent handling 
by minimizing the risks of adhesion and agglomeration. The grapes thus 
treated are then dried in a ventilated oven at 40.degree. C. for about 15 
hours with occasional turning. The dry grapes thus obtained have a dry 
matter content of 88-90%, a water activity of 0.29-0.32 and a glycerol 
content of 18.5%. 
Example 4 
Two batches of a product of the muesli type are prepared by mixing 90% base 
consisting of cereal flakes (wheat, corn, . . . ) and 10% dry grapes. The 
first batch A contains standard commercially available grapes while the 
second batch B contains grapes prepared in accordance with Example 3 
containing 15.3% glycerol. 
The two batches are stored at 30.degree. C. 
Samples are taken after storage for 1 month and 3 months. The base and the 
grapes are separated and the dry matter content (DM), the water activity 
value (Aw) and the hardness of the base and the grapes are determined. 
Hardness is evaluated by sampling and awarding marks on a scale of 1 (very 
hard) to 5 (very tender). 
The following results are obtained: 
______________________________________ 
Batch A Batch B 
Storage time Base Grapes Base Grapes 
______________________________________ 
t = 0 
DM (%) 4.4 15.5 4.4 17.2 
Aw 0.22 0.59 0.22 0.46 
t = 1 month 
DM (%) 5.5 7.4 4.8 12.1 
Aw 0.32 0.34 0.30 0.30 
Hardness -- 1.3 -- 4.0 
t = 3 months 
DM (%) 5.0 7.2 5.0 8.3 
Aw 0.36 0.36 0.31 0.31 
Hardness -- 2.3 -- 3.8 
______________________________________ 
It can be seen that, after storage for 1 month or 3 months at 30.degree. 
C., the grapes according to the invention have retained their tender 
character while the standard commercially available grapes are hard and 
considered unacceptable for consumption. 
Example 5 
Dry grapes are pretreated, treated and dried in exactly the same way as 
described in Example 3 except that the carbohydrase is replaced by other 
enzymes: pectinase, cellulase and galactomannanase. The following results 
are obtained: 
______________________________________ 
Final glycerol content 
Enzyme used (% based on dry matter) 
______________________________________ 
Carbohydrase 18.5 
Pectinase 16.0 
Cellulase 14.7 
Galactomannanase 
18.7 
______________________________________ 
Accordingly, various enzymes may be used to carry out the invention. 
Example 6 
Dry grapes are pretreated, treated and dried in exactly the same way as 
described in Example 3 except that the incubation time is varied. For 
comparison, the same treatment is applied to a control batch using a 
glycerol solution containing no enzymes. The following results are 
obtained: 
______________________________________ 
Glycerol content 
Incubation (% based on dry matter) 
______________________________________ 
Batch with enzyme 
. 3 hours, 50.degree. C. 
24.5 
. 6 hours, 50.degree. C. 
26.7 
. 15 hours, 50.degree. C. 
27.6 
Control batch without enzyme 
. 3 hours, 50.degree. C. 
19.1 
. 6 hours, 50.degree. C. 
23.2 
. 15 hours, 50.degree. C. 
16.7 
______________________________________ 
It can be seen that the use of enzymes considerably improves the absorption 
of glycerol by the grapes. It can also be seen that the final glycerol 
content of the grapes can be influenced through the incubation time.