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Abstract Soy protein hydrolysates have demonstrated moderate ice recrystallization inhibition (IRI) activity, but the properties of the unhydrolyzed protein contributing to this activity are not well known. The objective of this research was to identify the main protein processing factors important to the varying IRI activities observed. Three possible modification reactions were applied to soy protein isolate (SPI): the Maillard reaction that can occur in soy flour before protein isolation, heat denaturation of the fully defatted protein, and heat denaturation of the protein with the presence of residual lipid, mainly polar phospholipids. These modified proteins were hydrolyzed by Alcalase protease (for 2 min) to produce hydrolysates, which were characterized by HPLC and FTIR to investigate how molecular weight (MW) and changes in secondary structure relate to IRI activity. A multilinear regression with the parameters of modification type, surface hydrophobicity, secondary structure profile, and average MW of the hydrolysates was used to investigate their roles in reducing ice crystal size. It was discovered that polar lipids present in the soy hydrolysate samples and MW were the only significant factors (p < 0.05) for IRI activity of SPI hydrolysates which had an ice crystal size reduction from 22.0% to 36.7%. This study demonstrates for the first time a protein hydrolysate‐phospholipid interaction can produce IRI active molecules.