Effects of preheat treatment and syringic acid binding on the physicochemical, antioxidant, and antibacterial properties of black soybean protein isolate before and after in vitro digestion

Abstract This study investigated the effects of preheat treatment (70–100 °C) and syringic acid (SA) grafting on the antioxidant, antibacterial, and physicochemical properties of black soybean protein isolate (BSPI) before and after in vitro digestion. The results revealed that both preheat treatment and SA grafting increased the digestibility and the absolute zeta potential value of BSPI. However, as the preheating temperature increased, the antioxidant ability of BSPI decreased, which was improved by SA grafting. During in vitro digestion, the absolute zeta potential and antioxidant activities of preheated BSPI and preheated BSPI–SA complex followed the order: intestine > gastric > before digestion. Compared with before digestion, preheated BSPI with its SA complex after in vitro digestion exhibited excellent antibacterial activities. Importantly, the preheated BSPI–SA complex enhanced the SA recovery rate during digestion and SA stability, with the highest recovery rate observed for the SA‐grafted BSPI with preheat treatment at 100°C (BSPI100–SA). The principal component analysis sufficiently distinguished preheated BSPI and preheated BSPI–SA complexes. There were partitions between BSPI and BSPI–SA treated at different preheating temperatures. This study contributes to expanding the potential applications of BSPI with its SA complex in food products and offers guidance for designing SA delivery systems. Practical Application Preheated BSPI–SA complexes could serve as functional ingredients in food or health products. Besides, preheated BSPI has application potential as a carrier for SA delivery.