Reference
Potato Fruit Juice (PFJ)
**Potato Fruit Juice (PFJ)** is the protein-rich liquid that remains after starch is separated from potatoes during starch manufacture — the raw material from which potato protein is extracted. It is also referred to as potato fruit water (PFW), the term used when the same stream is treated as production waste.
Where PFJ comes from
When potatoes are processed for their starch, the tubers are ground and the starch granules are washed out. The liquid left behind carries the soluble proteins, peptides, and other compounds that do not bind to starch. Potato proteins are extracted from potato fruit juice (PFJ) or potato fruit water (PFW), a byproduct of starch production (Food and Bioprocess Technology, 2012). The same material is also recovered from potato peels alongside PFJ.
Historically this stream was discarded. A patent assigned to Cooperative Avebe UA describes potato fruit water as a waste stream from the production of potato starch or from the processing of consumption potatoes (Patent WO2014011042A1, 2014). Recovering protein from it converts what was an effluent burden into a marketable food ingredient — an upcycling step that gives potato protein a smaller production footprint than crops grown specifically for protein.
From PFJ to protein
The proteins suspended in PFJ are dilute and heat-sensitive, so extraction methods aim to concentrate them without destroying their structure. One documented approach precipitates protein concentrates from potato fruit juice using ethanol or ferric chloride; the resulting concentrates were characterized for chemical composition and amino acid profile and found to have high nutritional value (PMID:19739640). Other routes rely on isoelectric precipitation or membrane filtration to recover the same fraction.
The dominant protein recovered from PFJ is patatin, accompanied by a family of protease inhibitors. After concentration and drying, a finished potato protein isolate can contain 80–95% protein on a dry basis. The DIAAS for potato protein isolates has been reported as high as 100 (Food Science & Nutrition, Herreman et al., 2020, PMID:33133540), placing the protein recovered from this byproduct on par with high-quality animal proteins.
Why it matters
PFJ is the origin point for every potato protein product. Understanding it clarifies why potato protein is a single-ingredient material derived from a food crop rather than a synthesized additive. For a broader overview of the ingredient and how it is used, see what is potato protein. The byproduct origin also underpins the environmental case made for the category: the protein is recovered from a stream that already exists wherever potato starch is produced.
Related terms