Physicochemical and functional characteristics of protein co-precipitates from tempeh and egg white flours

Abstract

Recent developments in Indonesia have seen a growing interest in tempeh, with new activities emerging that combine animal and plant proteins through innovative processing technologies. This study examined the blending of egg white and tempeh flour (TF) using a co-precipitation method. The process involved solubilizing the proteins at pH 12, followed by precipitation at the isoelectric point around pH 4.4. Four types of precipitates were produced based on the protein source: co-precipitate of mixed tempeh flour (FMP), egg white protein co-precipitate (EMP), tempeh flour precipitate (TFP), and egg white precipitate (EFP). Among these, FMP demonstrated superior qualities, containing 79.68% protein and achieving 89.80% in vitro digestibility. Notably, the protein was enriched with essential amino acids such as lysine, leucine, and methionine compared to single-source proteins. Functionally, FMP exhibited excellent water and oil holding capacities, measuring 512.82% and 233.82%, respectively. Supporting analyses confirmed these findings: FTIR indicated minor shifts in amide bands, primarily secondary structures; SEM revealed porous, water-stable structures capable of absorption; SDS-PAGE showed minimal fragmentation, with protein bands characteristic of soybean and egg white proteins (15-75 kDa). The bioactive profile of FMP included antioxidant activity (9.45% RSA via DPPH), moderate antioxidant capacity, phenolic content of 4.44 mg gallic acid equivalents per gram, and detectable isoflavones such as daidzein (17.77 mg/100 g) and genistein (3.16 mg/100 g). These results support the potential of locally co-precipitated proteins to contribute to functional food innovation and development.