Treatment of an edible product with humectants

A method of reducing an equilibrium relative humidity level in an edible product comprising: applying a solution, incorporating a first humectant in a liquid form to the product whereby at least a part of the first humectant is absorbed into the edible product; applying a second humectant in a solid form to the product so as the second humectant absorbs residual moisture and is itself absorbed into the product; and wherein both the first and second humectants are effective in reducing the equilibrium relative humidity of the product to a predetermined level.

This invention relates to treatment of an edible product and in particular 
to the lowering of the equilibrium relative humidity of a dried edible 
product such as fruit whilst retaining some degree of aesthetically 
pleasing appearance, texture and/or flavour. 
Edible products such as dried fruit, in particular sultanas, currants, or 
raisins, are frequently incorporated into breakfast products, such as 
muesli, which contain cereal or cereal products such as bran or oats. 
Sultanas when dried so as to still have a plump, juicy appearance usually 
have an equilibrium relative humidity (E.R.H.) of about 60%. The E.R.H. of 
cereal or bran is usually much lower than this; typically 25-30%. When 
sultanas are mixed with such cereal products and stored, as occurs with 
mass produced breakfast products, in a relatively airtight enclosure, the 
cereal product absorbs water from the sultanas as the E.R.H. values of all 
the ingredients tend to wards equilibrium. Consequently the sultanas 
become shrivelled, hard and less pleasing to the consumer. 
It is known that by infusing a humectant into the dried fruit which lowers 
the E.R.H. value, the tendency for the fruit to dry out further is 
reduced. One known process of adding a humectant to a fruit comprises 
covering the fruit in a liquid humectant and leaving the fruit to stand 
while the humectant is gradually absorbed into the fruit. However, such a 
process can in some instances take up to a couple of weeks before a 
suitable E.R.H. is reached. 
The present invention aims to provide an alternative method of reducing the 
E.R.H. value of an edible product, and in one broad form the invention 
comprises the following steps: 
applying a solution, incorporating a first humectant in a liquid form, to 
the product whereby at least a part of the first humectant is absorbed 
into the edible product; 
applying a second humectant, in a solid form, to the product so that the 
second humectant absorbs residual moisture and is itself absorbed into the 
product; 
wherein both the first and second humectants are effective in reducing the 
equilibrium relative humidity to a predetermined level. 
The two-fold effect of the solid humectant absorbing excess moisture left 
on or in the edible product whilst increasing the humectant levels in the 
product results in the equilibrium relative humidity being reduced to the 
predetermined level at a greater rate than with application of the 
solution alone. 
The solution preferably includes water, since it has been found that 
including water in the solution increases the rate of absorption of the 
first humectant into the product. 
Preferably, the solution is applied to the product in a first tumbling 
operation, whereby to maximise the absorption of the first humectant. 
Preferably, the solid humectant is in the form of a powder that is 
preferably applied to the product prior to or during a second tumbling 
operation. 
Preferably, the edible product comprises a fruit or vegetable and the 
method includes a step of softening a cuticle of the fruit or vegetable by 
washing the fruit or vegetable in water prior to application of the 
solution. The water is preferably at a temperature between 5.degree. C. 
and 40.degree. C. 
Preferably the liquid humectant comprises one or more compounds selected 
from glycerine, or other polyhydric alcohols and sugars. 
Preferably the solution is a glycerine/water mixture that comprises 75% to 
85% glycerine by volume and preferably is applied to the fruit in the 
amount of 10-50 ml per kilogram of fruit. 
Preferably the solid humectant composition comprises one or more compounds 
selected from the group comprising polyhydric alcohols and sugars. In any 
event, the selection of the first and second humectants should be such 
that the relative absorption properties result in the humectants being 
subjected to osmotic pressure toward the interior of the product. 
The invention will now be described with reference to a non-limiting 
embodiment and examples. 
Dried fruit and vegetables, whether it be sultanas, raisins, prunes, 
apricots or other fruit tends to stick together. Accordingly prior to 
packaging the fruit is sprayed with a food grade edible oil which reduces 
the sticking together of the fruit. 
The initial stage of the preferred process is to wash the oil from the 
fruit and simultaneously soften the fruit's cuticle. However, if the fruit 
is oil free this washing step is still preferred for the purpose of 
softening the cuticle, but not essential. Accordingly the fruit is passed 
through a conventional washing plant which washes/delumps the fruit. The 
fruit is processed at the rate of about 1500 kg per hour and is vigorously 
agitated while in contact with room temperature water. 
The washed fruit is then passed into a tumbler where it is sprayed with a 
75-85% by volume glycerine, 25-15% water mixture at the rate of 10-50 ml 
per kilogram of washed fruit. The tumbler is of a continuous flow type and 
the fruit has a residence time of about 5 to 20 seconds within the 
tumbler. 
The fruit exits the tumbler and is transported by an auger to a dusting 
station. The auger agitates the fruit during transportation and thus 
promotes absorption of a substantial amount of the humectant mixture. 
However this stage is not essential since the humectant is basically 
absorbed on contact with the fruit. The residence time is within the range 
of 3 to 5 minutes but greater or lesser residence times are acceptable 
depending on the humectant composition used. 
The fruit is transported to the dusting station where a dusting of about 15 
g per kilogram fruit of a sugar such as dextrose or a polyhydric alcohol 
such as sorbitol, is applied in a second tumbler. As an alternative the 
fruit may be dusted and then tumbled in an auger rather than a tumbler per 
se. Preferably if an auger is used it will have bars running parallel to 
its axis to promote tumbling of the fruit. On discharge from the second 
tumbler the fruit has a reduced E.R.H. whilst substantially retaining its 
pre-process appearance and texture. Typically the reduction of E.R.H. is 
about 4%. 
The following is an example of the process.

EXAMPLE 1 
Dried Australian sultanas were obtained having an E.R.H. of 60%. The 
sultanas were washed/delumped in a conventional washing plant using water 
at 20.degree.-25.degree. C. at the rate of 2500 kg/hour. The residence 
time of the sultanas in the water was about 30 seconds. 
The washed and drained sultanas were supplied to a tumbler and a 
glycerine/water mixture at 25.degree.-25.degree. C. having 85% glycerine 
by volume applied by a spray bar at a rate of 30 ml/kg sultanas (24 g 
glycerine/kg sultanas). The residence time of the sultanas in the tumbler 
was 10 seconds. 
The sultanas were then transported by an auger to a dusting station where a 
dusting of dextrose monohydrate was applied at a rate of 15 g of dextrose 
monohydrate per kilogram sultanas. The residence time of the sultanas in 
the auger was 3 minutes and in the tumbler 10 seconds. 
After about 48 hours, sultanas so processed had an E.R.H. of 57% and were 
substantially comparable in appearance/touch to the unprocessed sultanas. 
Whilst the invention has been described with reference to the use of a 
glycerine/water mixture, it will be appreciated that any appropriate 
humectant or mixtures of humectants may be used. For example a 
glycerine/sorbitol/water mixture may be used. Similarly the dusting stage 
may utilise other sugars or alcohols other than sorbitol or dextrose. 
Further the temperatures at the various stages or of the compounds used 
are not essential to the working of the invention. 
From the above description it will be appreciated that the method of the 
present invention allows for a considerable amount of sultanas or raisins 
having a commercially useful E.R.H. to be produced in a relatively short 
time and as such the present invention has a substantial economic 
advantage over the first described known process. 
It will also be appreciated that the process is not limited to sultanas or 
raisins and may be used on any fruit, vegetables or any other edible 
product, whether dried or fresh. 
It will be apparent that many modifications and variations may be made by 
those skilled in the art to the embodiments described herein without 
departing from the spirit or scope of the invention.