Field of the Invention
The present invention relates to the field of fermented
(or cultured) soy-containing products, especially fermented soy-based beverages.
Background of the invention
Consumers have become more knowledgeable about protein
and its role in a healthy diet. This new understanding has had a profound effect,
stimulating consumer interest and demand for healthier beverages that are fortified
with protein. Because beverages are a convenient way to incorporate protein into
the diet, manufacturers continue to formulate new products in an effort to make
protein more accessible to a wider group of consumers.
The two most popular beverage proteins are whey and soy,
and their various isolate derivatives. According to the U.S. Food and Drug Administration,
the consumption of food products rich in soy protein can reduce cholesterol, enhance
athletic performance, and even aid in the battle against diabetes. In addition,
interest for milk replacement by soy protein has increased in view of, on the one
hand, issues in relation to over-sensitivity and/or intolerance towards milk constituents
experienced by growing numbers of consumers and, on the other hand, elevated milk
protein prices and supply issues that some manufacturers are experiencing relative
to this commodity. Soy proteins have been proposed to replace milk proteins, either
partially or totally, depending on the system, and dairy-like products have been
developed based entirely on soy protein.
In view of soy protein's documented health benefits it
is desirable to incorporate substantial quantities of soy protein in beverages.
However, incorporation of soy protein in beverage formulations often results in
"off-flavours", making it necessary for beverage manufacturers to employ masking
ingredients. Common issues experienced involve heat stability, acid stability, clarity,
dispersability (in dry mix applications) and solubility. Especially in the field
of fermented dairy-like beverages, wherein part or all of the milk protein is replaced
with soy protein, it has proven difficult to mimic the mouthfeel and texture, typically
smoothness and/or creaminess, of the original milk-protein based beverages.
In soy-based beverages the key challenges are flavour,
texture and protein stability. Soy-based acid or fermented beverages usually make
use of a protein stabilizing agent, such as pectin, to prevent protein precipitation.
Nonetheless, despite the use of protein stabilizing agents, stability of soy-based
beverages can easily be adversely affected by e.g. thermal processing.
In order to be accepted by consumers, fermented soy-based
beverages must have a pleasant mouthfeel, especially a creamy mouthfeel that is
typical of their full dairy counterparts. So far, manufacturers have experienced
great difficulty in achieving such a creamy mouthfeel in fermented soy-based beverages.
FMC BioPolymer, has launched Avicel RT 1133 cellulose gel,
which is claimed to provide long-term shelf stability and creamy mouthfeel at reduced
retort-processing time. Inclusion of this product in soy-protein based products,
e.g. yoghurt, is said to offer an excellent flavour profile, as well as a reliable
product consistency without separation or settling.
The Derwent abstract of JP
2007068410 discloses an acidic soybean-milk drink containing fibrous
insoluble cellulose having an average diameter of 0.01-1 micron. The aggregation
and precipitation in acidic condition is suppressed.
describes a ready to consume liquid food drink, comprising a particulated cereal
product, a stabiliser and milk. It is explained in the international patent application
that the term "milk" encompasses liquid milk type products derived from plants,
including soy milk, rice milk, coconut milk. The preferred food stabilizer is micro-crystalline
alpha-cellulose, sold under the trade name Avicel® by the FMC Corporation in
discloses methods of processing soy-derived materials for use in cultured soy products.
According to this document a soy-containing fermented product is provided by fermenting
a mixture of a deflavoured soy milk material and an effective amount of a dairy
culture. It is stated in US 7,108,881
that when a bulky flavouring or sweetener is added to the soy-containing yoghurt
after fermentation the natural consistency of the product is modified and it may
become necessary to add stabilizers of a type and in an amount sufficient to restore
the natural yoghurt-like texture. Natural and synthetic hydrophilic colloids, such
as carboxymethyl cellulose, vegetable/fruit gums, pectin, carrageenans and alginates
are added prior to or after fermentation.
It is an object of the present invention to provide an
improved fermented soy-based beverage, having a texture, especially a creamy mouthfeel,
that does nct noticeably differ from that cf fermented beverages based on milk protein
instead of soy protein. In addition it is an object of the invention to achieve
higher stability of the fermented beverage during storage and/or processing as compared
to prior art soy-based fermented beverages.
Summary of the Invention
The present inventors have surprisingly found that these
objectives can be realized by the incorporation of an effective amount of insoluble
cellulosic fibre in a fermented soy-based beverage prior to, during or after fermentation,
wherein the cellulosic fibres are non-hydrolysed and underivatised and wherein the
cellulose molecules contained within the insoluble cellulosic fibres contain at
least 1000 &bgr;-(1→4)-D-glucopyranose units. In particular, it was found
that soy-based fermented beverages having a pH of 3.5-5.5 and containing 1.5-8.0
wt.% of soy protein and 0.03-0.8 wt.% of insoluble cellulosic fibre have a very
pleasant creamy mouthfeel. In addition it was found that these beverages exhibit
improved emulsion stability, typically reflected by a reduced rate of syneresis
of the composition, as compared to prior art soy-based fermented beverages.
The insoluble cellulosic fibre employed in accordance with
the present invention can be isolated from varies fruit, such as citrus fruit, tomatoes,
peaches, pears, apples and plums. The inventors have achieved excellent results
with insoluble citrus fibres.
The present invention also provides a method of preparing
the aforementioned fermented soy-based beverages. Another aspect of the invention
relates to the use of insoluble cellulosic fibres for improving the texture and/or
mouthfeel of fermented soy-based beverages.
Detailed description of the invention
Thus, a first aspect of the invention concerns a fermented
soy-based beverage having a water content of at least 80 wt.%, a soy protein content
of 0.5-8.0 wt.% and a pH in the range of 3.5-5.5, preferably in the range of 3.5-5.0,
said beverage further containing from 0.03 to 0.8 wt.% of insoluble cellulosic fibres.
As used herein the term "fermented soy-based beverage",
refers to a liquid composition in which the main source of protein is soy protein
and which has been fermented using bacteria, preferably lactic acid bacteria. Typical
examples of such beverages include soy yoghurts and soy yoghurt drinks, i.e. products
fermented with yoghurt culture, which, according to the Codex
Alimetarius, FAO/WHO 1977, include Lactobacillus bulgaricus and Streptococcus thermophilus.
The beverages of the invention preferably have a water
content of at least 85 wt%, most preferably 87 wt%, based on the total weight of
the fermented soy-based beverage. The stabilising effect of the cellulosic fibres
is very pronounced in beverages having a pH within the range of 3.7-5.5, especially
within the range of 4-5.
According to a preferred embodiment, the soy protein content
of the soy-based fermented beverage of the invention is within the range of 2-7
wt%, most preferably 2.5-6.5 wt%, based on the total weight of the fermented soy-based
"Soy protein content", as used herein, refers to the total
amount of soy protein and soy protein derived peptides contained in the fermented
beverage. The fermented beverage may be based on soy protein, on soy protein hydrolysate
or combinations thereof. As will be understood by the skilled person enzymatic as
well as acid hydrolysis of peptide bonds may occur during fermentation.
Cellulose is found in plants as microfibrils, which typically
have a diameter of 2-20 nm and a length of 100-40,000 nm. These form the structurally
strong framework in the cell walls of plant materials. Cellulose is a linear polymer
of &bgr;-(1→4)-D-glucopyranose units. Cellulose molecules typically consist
of between 2,000-14,000 of such units and are completely insoluble in normal aqueous
solutions. When dispersed in an aqueous solution insoluble cellulosic fibres typically
bind considerable amounts of water. Cellulosic fibres may contain other fibrous
components such as hemicelluloses, pectins and lignin. Purified cellulose is used
as a starting material for the manufacture of a number of water-soluble hydrocolloids,
such as carboxymethyl cellulose (CMC). The manufacture of these cellulose derivatives
involves chemical modification of the natural cellulose material. CMC, for instance,
is synthesized by the alkali-catalyzed reaction of cellulose with chloroacetic acid.
The polar (organic acid) carboxyl groups render the cellulose soluble and chemically
The cellulosic fibres of the present invention are completely
underivatised. According to a most preferred embodiment of the invention the insoluble
cellulosic fibres are natural cellulosic fibres which have not been chemically modified.
Unlike, for instance, microcrystalline cellulose, the cellulose
molecules within the present cellulosic fibres are non-hydrolysed. The cellulose
molecules contained within the insoluble cellulosic fibres employed in accordance
with the present invention contain at least 1,000, preferably at least 2,000 &bgr;-(1→4)-D-glucopyranose
It was found that insoluble cellulosic fibres originating
from fruit yield particularly satisfactory results. According to a particularly
preferred embodiment the insoluble cellulosic fibres employed originate from citrus
fruit, tomatoes, peaches, pears, apples, plums or combinations thereof. Even more
preferably, the insoluble cellulosic fibres are insoluble citrus fibres. Most preferably,
the insoluble citrus fibres originate from the albedo and the flavedo of the citrus
The insoluble cellulosic fibres employed in the fermented
soy-based beverages of the present invention typically have a length of 1-200 µm.
Preferably, the cellulosic fibres have an average length of 5-100 µm, most
preferably of 10-80 µm.
In accordance with yet another preferred embodiment of
the invention a soy-based fermented beverage as defined herein before is provided,
wherein the insoluble cellulosic fibres have a water binding capacity of 6-30 wt.%,
more preferably of 7-25 wt.%, most preferably of 8-20 wt.%. The water binding capacity
expressed in wt.% refers to the weight of the water that can be absorbed per weight
unit of the insoluble cellulosic fibres. A suitable method of determining this parameter
in accordance with the invention is provided by the following procedure. The water
binding capacity has been determined by slowly adding water to a fixed mass of the
cellulosic fibres until no more water is taken up.
The beverage obtained by the present method has a rheology
that is quite different from that of e.g. set yogurt. The present beverage preferably
has a relatively low viscosity, e.g. a viscosity at a temperature of 7 °C of
less than 400 mPa.s at 100 s-1, most preferably of less than 300 mPa.s
at 100 s-1. A viscosity of 400 mPa.s at 100 s-1 means that
the product is 400 times more viscous than water and about 200 times more viscous
than milk. Viscosity is suitably measured with the help of a rheometer AR1000 (TA
Instruments, Etten-Leur, the Netherlands), using cone plate geometry. The diameter
of the cone being 40 mm, with an angle of 2% and a gap of 70µm. The viscosity
is recorded during a shear sweep between 0.03-1000s-1. The measuring
temperature is 5 °C and controlled by a Peltier system. The inventors have
observed a positive correlation between the mouthfeel of the present fermented soy-based
beverage and the so called specific storage modulus G', which is a parameter commonly
used in the art of describing rheological behaviour of visco-elastic systems. In
accordance with a preferred embodiment. the fermented soy-based beverage has a storage
modulus G' of at least 8 Pa and G" of at least 2 Pa at a temperature of 5 °C
at an oscillatory stress between 0.01-0.1 Pa. More preferably the beverage has a
storage modulus G' of at least 20 Pa and G" of at least 3 Pa at an oscillatory stress
between 0.01-1 Pa, most preferably a G' of at least 30 Pa and a G" of at least 8
Pa at an oscillatory stress between 0.01-8 Pa, at an oscillatory stress between
0.01-0.1 Pa. Preferably, G' should show a significant decrease over the range of
oscillatory stresses from 0.1 to 10 Pa, more preferably a decrease in this range
of at least one order of magnitude, most preferably a decrease in this range of
at least two orders of magnitude.
The moduli G' and G" as mentioned herein are measured using
a TA AR1000 from TA instruments. The moduli are determined using an oscillatory
stress sweep (the stress ranging from 0.01-100Pa) at a frequency of 1Hz and T=5°C.
The beverages of the present invention offer the advantage that they show little
or no instability. Instability here refers to physical instabilities like creaming,
sedimentation or syneresis. Creaming refers to the build-up of ingredients at the
top of the packaging. An example of this is the lightest ingredients floating to
the top, leaving a more clear solution at the bottom. Sedimentation refers to the
build-up of ingredients at the bottom of the packaging. An example of this is the
heaviest ingredients sinking to the bottom, leaving a more clear solution at the
top. The term "syneresis" refers to the exudation or segregation of (clear) aqueous
liquid from the (opaque) beverage. Syneresis can be expressed as the amount (in
grams) of liquid segregated from a specified amount of the beverage over a specified
period of time.
All instabilities pose a serious consumer issue as they
adversely affect the appearance and hedonic quality of the beverage and because
it is very difficult to undo the undesirable effect of destabilisation, except if
rigorous shaking or intensive stirring is applied. In accordance with a preferred
embodiment of the present invention, the level of instability observed after two
weeks at 7°C is less than 1% of the total product volume. The level of instability
is measured by storing flasks filled with 100 ml of the beverage under the conditions
specified above, followed by measuring the volume of separated liquid (top or bottom)
or sediment (bottom) using a ruler. Advantageously, the beverage of the invention
comprises a significant amount of lactic acid. Preferably, the beverage contains
at least 0.05 wt.% of lactic acid, more preferably at least 0.2 wt.% of lactic acid,
most preferably at least 0.4 wt.% of lactic acid.
Both taste and mouthfeel of the present beverage are favourable
affected by the presence of at least a limited amount of dispersed oil. In accordance
with a preferred embodiment, the fermented beverage contains 0.05-5 wt.%, more preferably
0.08-3 wt%, most preferably 0.1-1.5 wt% of dispersed oil. The dispersed oil is preferably
present as discrete droplets having a mass weighted average diameter of 0.5-7 µm,
preferably of 0.8-5µm. The dispersed oil preferably is a triglyceride oil,
notably a triglyceride oil having an unsaturated fatty acid content of at least
50 wt.%. Most preferably, the dispersed oil is soy oil.
The fermented soy-based beverage of the present invention
has preferably been fermented by lactic acid bacteria and/or Bifidobacterium.
Even more preferably, the present beverage has been fermented by lactic acid bacteria.
The lactic acid bacteria are advantageously selected from strains that belong to
the genus Lactococcus, Streptococcus, Leuconostoc or Lactobacillus.
Advantageously, the lactic acid bacteria strains used in accordance with the present
invention are selected from Lactobacillus helveticus, Lactobacillus acidophilus,
Streptococcus thermophilus, Lactobacillus delbrueckii (including subspecies
bulgaricus and lactis), Lactobacillus casei, Lactobacillus reuteri,
Lactobacillus rhamnosus Lactobacillus fermentum, Lactococcus lactis (including
its subspecies such as cremoris and lactis), Leuconostoc mesenteroides,
Leuconostoc cremoris, Leuconostoc lactis, Lactobacillus brevis, Lactobacillus fermentum,
Lactobacillus sake and combinations of two or more
these strains. The bacteria either survive to live in the end product, or are killed
by heating (pasteurisation, sterilisation), to prolong shelf life.
The present invention enables the manufacture of soy-based
beverages of high stability without using high levels of pectins, notably low methoxy
pectin and/or high methoxy pectin. Consequently, in a preferred embodiment, the
beverage contains less than 1% wt.%, preferably less than 0.75 wt%, most preferably
less than 0.5 wt% of a high methoxy pectin.
The fermented soy-based beverage of the present invention
can contain significant amounts of fruit and/or vegetable constituents, preferably
fruit constituents, such as fruit chunks, fruit juices, fruit concentrates etc.
The fermented soy-based beverage can further contain one
or more additional ingredients selected from the group of sweeteners, flavouring
substances, preservatives, vitamins, minerals, satiety inducing or enhancing agents,
cholesterol lowering agents, etc. Each and every class of these ingredients is well-known
in the art and the skilled person will be able to provide suitable examples and
to determine by routine experimentation the amounts in which they are most advantageously
A second aspect of the invention concerns a method of preparing
a fermented soy-based beverage according to any one of the preceding claims, said
wherein, insoluble cellulosic fibres are added to the liquid, the fermenting liquid
and/or the fermented beverage in an amount of 0.03-0.8% by weight of the fermented
beverage wherein the cellulosic fibres are non-hydrolysed and underivatised and
wherein the cellulose molecules contained within the insoluble cellulosic fibres
contain at least 1000 &bgr;-(1→4)-D-glucopyranose units. The insoluble
cellulosic fibres are added to the liquid before sealing of the containers. Thus,
said insoluble cellulosic fibres may be added before, during or after fermentation.
Naturally, it is also feasible to add the citrus fibres in two or more steps, e.g.
one part prior to fermentation and another part after fermentation. Preferably,
the insoluble cellulosic fibres are added before fermentation, especially in case
a beverage with live lactic acid bacteria is prepared. Thus, the fibres can be pasteurised
or sterilized together with the other beverage constituents prior to, during or
after fermentation. According to a particularly preferred embodiment of the present
method the fermented beverage is pasteurised or sterilised. The fermented beverage
may be pasteurised or sterilised prior to filling, or it may be pasteurised or sterilised
in the container.
- inoculating a pasteurised or sterilised aqueous liquid containing 0.5-6 wt.%
of dissolved soy protein with a starter culture;
- continuing fermentation at temperature in the range of 25-45°C for 2-24
- filling the fermented beverage so obtained into sealable containers; and
- sealing the filled containers;
It is furthermore preferred that the liquid is homogenised
after addition of the insoluble cellulosic fibre. It was found that the stabilising
effect of the cellulosic fibres can be increased significantly by such homogenisation.
Typically the liquid is homogenised at a pressure of at least 50 bar, more preferably
of at least 80 bar and most preferably of at least 130 bar.
According to a particularly preferred embodiment, the present
method comprises homogenisation of the fermented beverage. It was found that in
the absence of cellulosic fibres, homogenisation of the fermented beverage causes
the beverage to destabilise, especially if the fermented beverage is also subjected
to pasteurisation or sterilisation. The aqueous liquid in accordance with the invention
contains water and soy protein in amounts essentially as indicated herein above
for the fermented beverage. More in particular the aqueous liquid comprises 0.75-6
wt%, preferably 2-3.5 wt% of soy protein. The soy protein may suitably be provided
in the form of soy milk, soy milk powders, soy protein isolate, hydrolysed soy protein
isolate or a combination thereof. Suitable soy milk (extracts), soy protein isolates
or hydrolysed soy protein isolates are commercially available, for example from
suppliers such as Solae, Cargill, Kerry Group plc and SunOpta plc. In a particular
preferred embodiment of the invention the soy milk (extract), soy protein isolate
or hydrolyzed soy protein isolate has been de-flavoured using any of the methods
described in the prior art, such as for example in US
The aqueous liquid containing dissolved soy protein should
have been pasteurized or sterilized prior to fermentation in order to avoid microbial
contamination. Sterilisation and pasteurization may be achieved using different
techniques well-known in the art, such as heat treatment, membrane filtration, ultra
high pressure etc.
Typically, the step of inoculating the liquid, involves
applying a starter culture containing a sufficient amount of viable bacteria to
the liquid. Typically, starter culture is added in an amount that is adequate to
yield in the order of 104-109 Cfu/ml right after fermentation.
According to a preferred embodiment, the starter culture delivers at the end of
the fermentation 104.5-108.5, preferably 105-108
per ml of viable cells. The viable strains contained in the starter culture advantageously
include lactic acid bacteria strains belonging to the group consisting of
Streptococcus, Lactobacillus, Leuconostoc, Lactococcus and/or Bifidobacterium.
After inoculation the aqueous liquid is incubated to effect
fermentation. Fermentation advantageously takes place at a temperature of 28-45°C,
most preferably 35-45°C. Fermentation is preferably continued for 3-24 hours,
most preferably for 4-12 hours.
The present method advantageously employs a starter culture
of micro-organisms that generate a food grade acid during fermentation. Examples
of such food grade acids are lactic acid and acetic acid. In accordance with a particularly
preferred embodiment, during fermentation the pH of the aqueous liquid decreases
by at least 1.5 pH units and/or a final pH of maximally not more than 5.5 is reached.
Preferably, during fermentation the pH of the aqueous liquid decreases by at least
2 pH units. Advantageously the final pH reached is less than 5.0.
In accordance with a preferred embodiment of the present
invention, between 0.5 and 20 g/l of carbohydrate substrate is digested during fermentation.
Said carbohydrate substrate is preferably selected from the group of sucrose, glucose
or fructose, most preferably said carbohydrate substrate is a mixture of any of
these, most preferably a mixture of sucrose and glucose. Sugars naturally present
in soy milk (including complex sugars like raffinose and stachyose) or any added
sugars can be digested during fermentation.
In accordance with another particularly preferred embodiment
of the present invention the aqueous liquid is prepared by combining the insoluble
cellulosic fibres with a soy protein and optionally water, preferably followed by
homogenization at a pressure of at least 50 bar.
As mentioned above, the method of the invention further
comprises filling the fermented beverage obtained into sealable containers. Preferably,
the filling is done under aseptic conditions.
A third aspect of the present invention concerns the use
of insoluble cellulosic fibres for improving the mouthfeel and/or texture of a soy-based
fermented beverage, wherein the cellulosic fibres are non-hydrolysed and underivatised
and wherein the cellulose molecules contained within the insoluble cellulosic fibres
contain at least 1000 &bgr;-(1-4)-D-glucopyranose units. Preferred embodiments
of this particular use have been described herein before.
The invention is further illustrated by means of the following
Fermented soy-based beverages were prepared from the following
Concentration in wt.%
Whole bean extract (WBE)
Sunopta Grains and Food Group, Hope, MN, USA
AQplus N (Citrus Fibres, 90% insolubles)
Herbafood GmbH, Germany
The ingredients were mixed at 70°C, pasteurised and
homogenised at 150 bar. Next, the solution was cooled to 43°C and the starter
culture (T-051046 a mixed culture of Streptococcus thermophilus strains,
ex Chr. Hansen, Hørsholm, Denmark) was added. The solution reached a pH of
5 after 3 hours following which the pH was reduced to approximately 4.5 using lactic
acid. After acidification the beverage was pasteurised to kill the bacteria and
homogenised at 150 bar. The beverage was hot filled into containers that were sealed
and subsequently stored at 5°C.
During storage under ambient conditions, the reference
product started to develop 5-10% separation in the form of a transparent layer after
only a few days. Separation was observed in the product according to the present
invention only after the product had been stored for 3 weeks or longer.
At a temperature of 5 °C and at a oscillatory stress
between 0.01 and 0.1 Pa the product containing the citrus fibres had a storage modulus
G' of 40-70 Pa and G" of 8-10 Pa. Under these same conditions, the reference product
exhibited a storage modulus G' and G" of 0.1-0.3 Pa. For these measurements a TA
Instruments AR1000 rheometer was used. The geometry was cone-plate (2° angle,
4 cm diameter, gap 71 µm).
The two products were evaluated by a sensory panel. The
results showed that the product according to the invention scored significantly
higher on the attributes "thickness, sliminess and creaminess". These attributes
are considered to be favourable sensory attributes for yogurt-type drinks.