Soy whey is the clear liquid obtained after curdling the proteins in
soy milk
Soy milk (or soymilk), also known as soya milk, is a plant-based milk produced by soaking and grinding soybeans, boiling the mixture, and filtering out remaining particulates. It is a stable emulsion of oil, water, and protein. Its original ...
to form
tofu
or bean curd is a food prepared by Coagulation (milk), coagulating soy milk and then pressing the resulting curds into solid white blocks of varying softness: ''silken'', ''soft'', ''firm'', and ''extra (or super) firm''. It originated in Chin ...
(tofu whey), or after curdling out the proteins in a soy extract to make
soy protein isolate (SPI whey). It is named in analogy to the clear liquid
by-product
A by-product or byproduct is a secondary product derived from a production process, manufacturing process or chemical reaction; it is not the primary product or service being produced.
A by-product can be useful and marketable or it can be cons ...
from
cheese
Cheese is a type of dairy product produced in a range of flavors, textures, and forms by coagulation of the milk protein casein. It comprises proteins and fat from milk (usually the milk of cows, buffalo, goats or sheep). During prod ...
production,
whey
Whey is the liquid remaining after milk has been curdled and strained. It is a byproduct of the manufacturing of cheese or casein and has several commercial uses. Sweet whey is a byproduct resulting from the manufacture of rennet types of hard c ...
. It is traditionally treated as
wastewater
Wastewater (or waste water) is water generated after the use of freshwater, raw water, drinking water or saline water in a variety of deliberate applications or processes. Another definition of wastewater is "Used water from any combination of do ...
, though some work has been done to try and produce more valuable products out of it.
Composition
Tofu whey may contain components of the soy milk as well as the coagulant used, which could be either acid-based or mineral-based. It contains 0.85% carbohydrates (largely
stachyose
Stachyose is a tetrasaccharide consisting of two α--galactose units, one α--glucose unit, and one β--fructose unit sequentially linked as Gal(α1→6)Gal(α1→6)Glc(α1↔2β)Fruf. Together with related oligosaccharides such as raffinose, st ...
,
raffinose
Raffinose is a trisaccharide composed of galactose, glucose, and fructose. It can be found in beans, cabbage, brussels sprouts, broccoli, asparagus, other vegetables, and whole grains. Raffinose can be hydrolyzed to D-galactose and sucrose by th ...
, and
sucrose
Sucrose, a disaccharide, is a sugar composed of glucose and fructose subunits. It is produced naturally in plants and is the main constituent of white sugar. It has the molecular formula .
For human consumption, sucrose is extracted and refined ...
; no lactose), 0.13–0.82% protein, 0.4–1% fat, and about 0.4% minerals (as
ash).
Soy protein isolate is made by curdling proteins out of a weakly alkaline, aqueous extract of defatted soy using an acid. SPI whey contains 0.95% carbohydrates, 0.03–0.3% protein, no fat (because defatted soy is used to make the extract), and about 0.2% minerals (as ash).
Besides these components, soy whey also contains
isoflavones
Isoflavones are a type of naturally-occurring isoflavonoids, many of which act as phytoestrogens in mammals. Isoflavones occur in many plant species, but are especially high in soybeans.
Although isoflavones and closely-related phytoestrogens are ...
, which are potentially valuable.
Applications
Very little has been done commercially in transforming soy whey into more valuable products.
The minerals in tofu whey can be recovered for reuse as tofu coagulant. The carbohydrates in soy whey, especially the oligosacchides, are functional food ingredients. The proteins have good emulsifying properties.
A number of different organisms can be used to ferment soy whey to produce a drink. Soy whey with added sugar can be fermented with yeast into a wine similar to
sake
Sake, , or saki, also referred to as Japanese rice wine, is an alcoholic beverage of Japanese origin made by fermenting rice that has been polished to remove the bran. Despite the name ''Japanese rice wine'', sake, and indeed any East Asi ...
.
Soy whey can be fermented with
lactic acid bacteria
Lactobacillales are an order of gram-positive, low-GC, acid-tolerant, generally nonsporulating, nonrespiring, either rod-shaped (bacilli) or spherical ( cocci) bacteria that share common metabolic and physiological characteristics. These bact ...
to obtain a sour drink, or to obtain a
sauerkraut
Sauerkraut (; , ) is finely cut raw cabbage that has been fermented by various lactic acid bacteria. It has a long shelf life and a distinctive sour flavor, both of which result from the lactic acid formed when the bacteria ferment the sugar ...
starter. This liquid can also support the growth of fungi (including mushrooms and yeasts) and microalgae.
See also
*
References
{{reflist
Soy-based foods
Tofu