Field of the invention
The present invention relates to a food product fermented
with lactic acid bacteria comprising soy protein. The invention further relates
to use of such food products as a health food and a process for the preparation
of the food products.
Background to the invention
According to the Codex Alimentarius (FAO/WHO 1977), yogurt
is milk fermented with Lactobacillus bulgaricus and Streptococcus thermophilus
and the microorganisms in the final product must be "viable and abundant". Other
food products fermented with S. thermophilus, which may not be called yogurt according
to the above definition exist. For instance "Bifidus yogurt" is made using selected
cultures of B. bifidum, B. longum, S. thermophilus, and L. delbrueckii, which
results in a yogurt-like product having a milder taste than yogurt.
Also known are so-called "soy yogurts", in which the main
source of protein is not milk, but soy protein and which are fermented with yogurt
culture. These soy yogurts are herein also described as yogurts. Examples of commercially
available soy yogurts are Yofy produced by Van der Moortele and Sojasun produced
by Triballat. Though the preparation of these commercial food products is not always
known, most of these soy yogurts are prepared from soy beans and have a soy protein
content that is relatively low.
describes isoflavone rich soy protein isolates and their application in
food products. Column 8, Formulation 4, shows the preparation of a soy yogurt with
SPI containing about 8 grams of soy protein per 170 gram serving.
XS 002200893 discloses a lactic acid fermented pudding
comprising hydrolysed soy protein.
We have found that a food product prepared with soy protein
isolate (SPI) as sole protein source is very thick and gives a non-dairy yogurt
characteristic dry mouthfeel.
We have found that the use of hydrolysed SPI in yogurt
applications results in improved product stability at low pH, but the products have
no yogurt texture. The texture/firmness in these products may be improved by addition
of thickeners, such as starch or pectin. However, addition of these thickeners still
does not create a dairy-like yogurt texture. Further for fruit yogurt applications
additional problem is that the shear required to mix the fruit preparation into
the yogurt further breaks down the texture.
Summary of the invention
It is therefore an object of the invention to provide a
food product fermented with one or more lactic acid bacteria comprising soy protein
that has a high level of soy protein and a good taste and texture resembling that
of yogurt. It is a further object of the invention to provide such food products
in which the presence of thickeners or gums is not required. Still a further object
is to provide a food product that is a stirred-type food product, preferably spoonable
as defined herein, in which flavouring such as fruit can be easily mixed without
disrupting the texture of the product.
One or more of these objects are attained according to
the invention in that the food product comprises at least 0.2 wt.% hydrolysed protein.
According to the invention dairy-like spoonable yogurt texture may be obtained even
without the need of thickeners.
Detailed description of the invention
Lactic-acid Bacteria herein are gram-positive, rod- or
sphere-shaped bacteria that produce lactic acid as the principal or sole end product
of carbohydrate fermentation.
The amount of soy protein in the food product according
to the invention is 4-10 wt.%, preferaby 4-7 wt.%.
The amount of hydrolysed protein in the food product according
to the invention is at least 0.2 wt., preferably, at least 0.5 wt.% more preferably
at least 1 wt.% and most preferably at least 1.5 wt.%. Amounts of hydrolysed soy
protein present are included in the amounts of soy protein.
The presence and amounts of proteins (non-hydrolysed and
hydrolysed) present in the food product may be determined by the skilled person
using common analysis techniques e.g. mass spectroscopy and liquid chromatography.
The production of the fermented soy according to the invention
may include the following steps:
- 1) Standardizing of soy starting material
- 2) Thermal treatment and homogenisation
- 3) Addition of starter culture
- 4) Fermentation at 40-45°C
- 5) Cooling to about 10°C and packaging
- 6) Mixing in fruit other flavouring components
The characteristic flavor of yogurt is largely due to carbonyl
compounds, particularly acetaldehyde (25 - 50 mg/kg), volatile fatty acids, and
to some extent, due to acetone and acetoin.
The typical pH of soy yogurt varies from 4.0 - 5.0, according
to type of yogurt, fat content, and specific starter cultures used.
Low-acidity yogurts have a pH above 4.6, while normal acidity
yogurt has a pH of 4.0-5.0.
The soy yogurt according to the invention may be set-style
yogurt with a firm gelled texture, or may be stirred-style yogurt, with a spoonable
or fluid texture. Fruit yogurts are preferably stirred type.
Preferably the fermentation for the set-style soy yogurt
takes place in the package of the yogurt after packaging.
Stirred-type soy yogurt is preferably fermented in fermentation
tanks. After fermentation, the product may be stirred at a low speed prior to its
transport by pumping and filling. A moderate to low shear rate is critical to achieve
the desired viscous properties of stirred-style yogurt.
The food products according to the invention may be frozen
like ice cream or it may be dehydrated to give yogurt powder.
Non-hydrolysed soy protein isolate, when used alone in
the food products results in very firm and dry textures at soy protein levels above
4 wt.%. Such food products also have a taste that is less preferred, in particular
they give a dry mouthfeel.
Further texture improvement can be achieved by addition
of some milk protein, e.g. skim milk powder (SMP) buttermilk powder (BMP) and/or
whey powder (such as sweet whey powder), which will result in a smoothier texture
and better taste,in which case the soy protein isolate ratio still largely determines
Although firmness of the food products according to the
invention is lower for all products after application of shear for instance for
mixing in fruit preps, still spoonable textures may be achieved.
Preferably vegetable oil and/or may be added to the food
products. The addition of oil leads to an improvement in terms of smoothness and
Although the addition of thickeners is not needed in food
products according to the invention, thickeners may be added, e.g. for further improving
syneresis (e.g. pectin, carrageenans, locust bean gum).
The food product is fermented with any lactic acid bacteria
or any combinations of lactic acid bacteria. Preferably the food product is fermented
with Streptococcus thermophilus and Lactobacillus bulgaricus. The
combination of these lactic acid bacteria gives a characteristic yogurt taste.
The hydrolysed protein is hydrolysed soy protein.
Preferably the food product has a Stevens value of 50 to
300 g, more preferably 50 to 250 g, even more preferably 120 to 200 g. Preferably
the food product is spoonable.
Preferably the food product has a viscosity of 10000 to
800000 mPa.s, more preferably 50000 to 200000, most preferably 50000 to 100000 mPa.s.
Preferably the food product comprises 0.1-3 wt.% milk protein.
The presence of oil and/or fat is advantageous in the products
according to the invention. Oil and/or fat has a positive effect on mouthfeel, the
products become more creamy, smoother and less watery. Additionally, the preferred
addition of oil or fat make it easier to control foaming of the protein during preparation
of the food product. Therefore preferably, the food product comprises 0,2-10 wt.%,
more preferably 0,5-5, even more preferably 0,5-2 wt.% oil or fat.
The invention further relates to a process for the preparation
of a fermented food product, wherein a starting material comprising soy protein
is fermented with on or more lactic acid bacteria and wherein 40-95wt.% relative
to the total amount of soy protein is hydrolysed soy protein.
The starting material comprises a mixture of non-hydrolysed
and hydrolyseed protein.
Preferably, the mixture comprises 50-95 wt.% of hydrolysed
soy protein relative to the total amount of soy protein.
Preferably the mixture is prepared from hydrolysed soy
protein isolate (herein also designated as SPI) and non-hydrolysed soy protein isolate.
Stevens values give an indication about the firmness (spoonability)
of a product. The firmness of all products at 5°C (after storage at 5°C
for 24 hours) was measured using a Stevens Texture Analyser (1 mm/sec, 25 mm depth,
mayonnaise grid (mesh 7, thread thickness 0.8 mm, mesh width 2.8 mm) and is quoted
herein as the Stevens value (in g). The accuracy of this measurement in all cases
is ± 10 g.
Stevens values of above 120 and well below 300 g are typical
for a spoonable product.
Viscosity of the food products is measured using a Brookfield
viscometer, spindle 6, at 5 rotations per minute (herein abbreviated rpm).
Syneresis was measured by after storing flasks with the
food product for 24 hours at 25°C and subsequently 24 hours at 5°C. The
weight of the flasks before (wi) and after (wd) decantation
of supernatant water and syneresis values were expressed as (wi- wd)
The Bostwick equipment consists of a 125 ml reservoir provided
with a outlet near the bottom of a horizontally placed rectangular tub and closed
with a vertical barrier. The tub's bottom is provided with a 25 cm measuring scale,
extending from the outlet of the reservoir. When equipment and sample both have
a temperature of 5°C, the reservoir is filled with 125 ml of the sample after
it has been shaken by hand ten times up and down. When the closure of the reservoir
is removed the sample flows from the reservoir and spreads over the tub bottom.
The path length of the flow is measured after 30 seconds. The value, expressed as
cm per 30 seconds is the Bostwick ratio.
A fermented food product (yogurt) was prepared as follows.
Soy protein isolate Supro Plus™ 651 and hydrolysed soy protein
isolate FXP H220D, both containing about 80 wt.% soy protein and originating from
Protein Technology International, skimmed milk powder and salt in amounts as given
in table 1 were mixed with hot demi water at 70°C using a Silverston mixer
at a speed of 2500 rpm until a homogeneous mixture is obtained. The mixture was
sterilized in an Ultra High Temperature (UHT) apparatus at 170-200 bar, with heating
bath temperature 85°C and holding bath temperature 75°C. The sterilized
product was filled into 125 ml flasks and 0.2 wt.% yogurt culture YF202 (ex Rhodia)
suspended in tripton solution was added to the flasks. The flasks were incubated
at 43°C for 12 hours and thereafter cooled to 10°C and stored at 5°C.
Viscosity, hardness and syneresis of the prepared yogurt-type
food compositions were measured according to the above described test methods. The
results are given in table 2.
Examples 2 & 3 and comparative experiments A, B and C
The food products in these experiments were prepared as
in example 1, however with different amounts of non-hydrolysed and hydrolysed soy
protein isolates as indicated in table 1.
The results are given in table 1.
Examples 1-3 and the comparative experiments A, B & C show
that when only non-hydrolysed soy protein isolate is used, too thick products are
prepared that have a less preferable taste (mouthdry). When only hydrolysed soy
protein isolate is used no spoonable yogurt texture may be obtained.
The yogurts of examples 1-3 had a clean, fresh yogurt tase
with no or little residual soy taste
Fruit yogurts may be made by adding fruit or fruit puree
to the yogurts of examples 1-3.
Table 1: Composition of milk starting material
Comp. Ex. C
Comp. Ex. A
Comp. Ex. B
Ratio hydrolysed/ non-hydrolysed soy
Hydrolysed SPI FXP H0220D
Non-hydrolysed SPI Supro 651
Sweet milk powder
Table 2: Properties of fermented food products, Bostwick values "-" means
too low to be measured.
Stevens value (g)
Syneresis after 24 hr
Viscosity after shear (mPa.s)
Stevens value after shear (g)
Bostwick value after shear