Method of heating and freezing a texturized mycelial fungal mass

A process of steaming followed by freezing a texturized mycelial fungal mass having a solids content of about 20 to 40% by weight to toughen the texture and increase the succulence of the mass.

BACKGROUND OF THE INVENTION 
This invention relates to a method of texturizing a proteinaceous 
substance, particularly a mycelial fungal mass. 
Mycelial fungi produced under controlled conditions can be suitable for use 
as a foodstuff for humans and may be desirably texturized so as to 
resemble the appearance of natural meat to make it more acceptable as a 
foodstuff. Texturizing techniques are disclosed in co-pending British 
Patent Applications Nos. 25385/75 and 25387/75. 
A portion of British Patent Application No. 25385/75 now British Pat. No. 
1,508,635 reads as follows: 
"According to the present invention there is provided a method of 
texturizing a mycelial fungal mass having reduced turgor and a solids 
content of between 20% and 35% by weight, which includes passing the mass 
under pressure through at least one apertured member whereby the mass is 
filamented and compacting said filaments to form a textured structure. 
Preferably the mass is passed in succession through a plurality of meshes 
each having a different mesh size. 
The invention also includes apparatus for texturizing a mycelial fungal 
mass having reduced turgor and a solids content of between 20% and 35% by 
weight, which includes means for feeding the mass to a die, at least one 
mesh size within the range of 0.3 to 2.0 mm within the die through which 
the mass is passed to effect filamenting of the mass and compacting means 
for reducing the cross-sectional size of the filamented mass to produce a 
textured structure. 
Conveniently, the feeding means may include a screw-type positive 
displacement pump located within a housing attached to a die and operated 
at ambient temperature. The die may incorporate two mesh structures, the 
first mesh structure being of a fine nature and the second mesh structure 
being of a more coarse nature and a compacting head, having an internal 
taper, attached near to the outlet from the second mesh structure." 
A portion of British Patent Application No. 25387/75 now British Pat. No. 
1,502,455 reads as follows: 
"According to the present invention there is provided a method of 
texturizing a mycelial fungal mass having reduced turgor and a solids 
content of between 20% and 40% by weight, which includes rolling the mass 
between two relatively moving surfaces to elongate the mass into a 
cylinder in which groups of hyphae are attenuated and entangled to a 
substantial extent to give a textured structure. 
The invention also includes a method of texturizing a mycelial fungal mass 
having reduced turgor and a solids content of between 20% and 40% by 
weight, which includes rolling of the mass between two relatively moving 
surfaces to form an elongate cylinder, juxtaposing at least two sections 
of the cylinder to form a tiered mass, repeat rolling the tiered mass to 
form a further elongate cylinder, juxtaposing at least two sections of the 
further cylinder and successively repeating the procedure finishing with a 
rolling step to give a textured structure. 
The invention also includes apparatus for texturizing a mycelial fungal 
mass having reduced turgor and a solids content of between 20% and 40% by 
weight, which includes a stationary base and a movable endless belt spaced 
therefrom defining two relatively movable surfaces, said surfaces 
converging in the direction of movement such that the said mass is moved 
in when placed in contact with both said surfaces so as to form an 
elongate cylinder of said mass, and means located at the downstream end of 
said surfaces for manipulating said cylinder to form a tiered mass for 
further elongation into a textured structure." 
If texturized in accordance with Application No. 25385/75, the mass will 
have a solids content of beteen 20% and 35% by weight and if texturized in 
accordance with Application No. 25387/75 the mass will have a solids 
content of between 20% and 40% by weight. In either case, the average 
solids content will be approximately 30% by weight and the average water 
content will be approximately 70% by weight. The free water in the mass 
may range from 30% by 57% and the bound water from 3% to 25% depending on 
the condition of the mycelial fungi. On average, the free water will be 
approximately 54% by weight and the bound water approximately 16% by 
weight. 
In this Specification, "free water" is defined as the percent of the total 
wet sample which is freezable as measured by differential scanning 
calorimetry and "bound water" is defined as the difference between the 
total water and the free water. 
U.S. Pat. No. 4,056,638 issued to Huang et al discloses a process for 
heating and drying a fungal material comprising treating the same by rapid 
dielectric heating to reduce the moisture content from 8 to 40 weight 
percent to give a produce with a solids level of 30 to 70 weight percent. 
The patent discloses that dielectric heating puffs and heat sets the 
material which can then be further dried at a much slower rate by 
conventional means such as hot air. The resulting product can be 
rehydrated to absorb from 1 to 5 times its weight of water. The patent 
stresses the difference between its dielectric heating step and 
conventional drying means. 
U.S. Pat. No. 4,001,459 issued to Kim et al discloses a method of preparing 
a texturized protein material comprising freezing an aqueous mixture of a 
heat coagulable protein by cooling the mixture in a manner and at a rate 
effective to produce elongated ice crystals generally aligned 
perpendicular to the surface of cooling, freeze-drying the frozen mass, 
and heat-setting the resulting dried protein material. The list of usable 
protein materials given in the patent includes single-cell protein. The 
heat-setting can be done by the use of moist heat. 
It is an object of the present invention to progress further in the 
texturization process of the mycelial fungal mass starting from a 
texturization technique disclosed as the above-mentioned British Patent 
Applications, although it should be appreciated that other initial 
texturization techniques may be employed. 
SUMMARY OF THE INVENTION 
According to the present invention there is provided a method of improving 
the toughness and increasing the succulence of a texturized mycelial 
fungal mass having a macrofiber structure similar to the fibers of natural 
meat and having a solids content of from about 20 to about 40% by weight, 
the solids content of which consists essentially of fungal mycelia, 
comprises carrying out the following steps in the order specified: 
(a) heating the texturized mass in an atmosphere of substantially saturated 
steam for a period of from 1 minute to 21/2 hours so that the entire mass 
is at a temperature of at least 90.degree. C. to reduce bound water by 
about 4% by weight and increase free water of the mass by about 4%; and 
(b) freezing the texturized mass slowly at a rate of about 0.5.degree. C. 
per minute to a temperature between -10.degree. C. and -40.degree. C.; 
said method being conducted so as to maintain the solids content of the 
fungal mass at its initial level of from about 20 to about 40% by weight.

DETAILED DESCRIPTION OF THE INVENTION 
A mycelial fungal mass is blended with suitable additives such as egg 
albumen, gluten, soya isolate, soya concentrate, whole egg, cellulose, 
starch, fats, emulsifiers, foaming agents and gums, and texturized to 
impart to the mass a macrofiber structure in the order of the fibers of 
natural meat. This initial texturizing step may be carried out by using 
one or both of the methods disclosed in the above-mentioned British Patent 
Applications or any other suitable method. The mass, after the initial 
texturization step, will consist of a plurality of substanitally parallel 
macrofibers, each consisting of a mass of hyphae aligned substantially in 
the direction of the macrofibers. 
During the mixing and the initial mechanical texturizing step, the 
additives absorb water in the cold. Bound water in the mass increases from 
about 12% by 17% and free water falls from about 55% to 50% without a 
change in solids. Thus, the bound water content of the mass increases 
about 5% while the free water content of the mass falls about 5% during 
the heating step. 
The material, after having been initially texturized, can then be cut into 
chunks directly or alternatively slabs can be formed by placing several 
texturized blocks, cut to 2 to 6 inch lengths, side by side and pressing 
these into slabs using a suitable press giving a pressure in the order of 
10 to 30 psi although pressures up to 100 psi can be suitable. When the 
blocks are placed side by side they should be orientated with the 
macrofibers lying substantially parallel. 
The mass is then heated in a saturated steam atmosphere at 0 to 15 psi from 
one minute to 150 minutes depending on the thickness of the slabs. The 
heating must be such that the temperature of the entire mass is at least 
90.degree. C. The mass is preferably heated in a saturated stream 
atmosphere at atmospheric pressure for 10 to 90 minutes, this being 
suitable for products of half an inch to one inch thickness. Alternatively 
the heating can be carried out for 90 minutes at a pressure of 5 psi. 
The steam heating has the effect of imparting a resilient meat like texture 
to the mass and significantly reduces the bound water and increases the 
free water of the mass. 
On steaming, the gel forming substances, e.g., the egg albumen and the 
globulin proteins present in the mycelial fungal mass, gel and continue to 
absorb water. Free water is thought to be taken up preferentially from 
areas around the hyphae. Water is also thought to pass through holes in 
the cell walls into the interstices, thus allowing the cell walls to gain 
close proximity with each other and associate by chemical bonding. This 
bonding probably occurs via active groups in the glucan and chitin of the 
cell walls and results in stiffening of the structure and increased 
textural strength. 
If egg albumen or other gel forming substances are not added, the hypahae 
are still thought to loss water to the interstices and become less turgid, 
but to a lesser extent. 
With increasing time of steaming, globulin proteins of the hyphae and egg 
albumen begin to denature and the gel binds water less strongly. This is 
reflected to the progressive change from bound to free water with 
increased steaming time. For example, between 1 minute and 10 minutes 
steaming, increases the free water from 46% to 50 % and the bound water 
falls from 19% to 15%. The change in water state is accompanied by an 
increase in succulence. Free water is not thought to be reabsorbed by the 
hyphae and the chemical association of the cell walls and associated 
stiffening are not reversed. It is to be understood that the steaming does 
not significantly alter the total water content of the fungal mass, i.e., 
the solids content of the fungal mass remains at its initial level of from 
about 20 to about 40% by weight. 
Ten to 90 minutes is considered optimum heating times but acceptable 
texture is obtained up to 21/2 hours. At times in excess of 21/2 hours, 
the protein present begins to degrade and denature. Charged groups are 
released and Maillard sugar protein reactions occur resulting in brown 
products of pasty texture. The free water content falls rapidly at this 
point. 
The mass formed during heating is then frozen using a plate or a blast 
freezer to a temperature between -10.degree. C. and -40.degree. C. and 
preferably to a temperature in the order of -20.degree. C. The freezing 
must be carried out slowly and a temperature drop of 0.5.degree. C. per 
minute has proved to be successful. On freezing, there is a further small 
change in water from the bound state to the free state. This change is of 
the order of 3% to 8% and occurs gradually over a period of approximately 
28 days resulting in a product having a bound water content of between 3% 
and 25% and more specifically between 7% and 12% by weight. In conjunction 
with this further decrease in bound water resulting in an increase of free 
water, there are associated increases in toughening of the texture and 
also an increase in the succulence of the product. These changes are 
related to the growth and migration of large ice crystals during freezing 
and frozen storage, drawing water out of the fibers thus again bringing 
the hyphae into closer proximity with each other and increasing toughness. 
At the same time, the increase in free water which has migrated into the 
interstices, improves the succulence of the product when cooked. 
In the process of the invention the heating and freezing steps cause an 
alteration in the amount of bound and free water but not significantly 
affect the total amount of water, i.e., the solids content of the fungal 
mass remains at its initial level of from about 20 to about 40% by weight. 
Dependent on the product being simulated, coloring and flavoring may be 
added prior to the initial texturization step. 
One particular example of texturizing in accordance with the invention is 
as follows. 
The following ingredients were mixed for 10 minutes in a standard Hobart 
mixer. 
______________________________________ 
Mycelial fungal mass 
2,000 grams (30% 
(IMI No. 145425) solids content in water) 
Egg albumen 150 grams 
Flavoring 1121/2 grams 
______________________________________ 
After mixing, the resultant mass was texturized by the method described in 
British Patent Application No. 25387/75. 
After the initial texturizing step, the product was steamed in a saturated 
steam atmosphere at atmospheric pressure for 90 minutes. 
The product was then frozen in a blast freezer operating at -20.degree. C. 
The resultant frozen product was subsequently coated in batter and crumb 
and cooked by frying.