Trypsin inhibitor activity, phenolic content and antioxidant capacity of soymilk as affected by grinding temperatures, heating methods and soybean varieties

Authors: SHANG, SAM - Mississippi State University; ZHANG, YAN - Mississippi State University

Submitted to: LWT - Food Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/3/2021
Publication Date: 9/5/2021
Citation: Shang, S., Zhang, Y. 2021. Trypsin inhibitor activity, phenolic content and antioxidant capacity of soymilk as affected by grinding temperatures, heating methods and soybean varieties. LWT - Food Science and Technology. 153:112424. https://doi.org/10.1016/j.lwt.2021.112424.
DOI: https://doi.org/10.1016/j.lwt.2021.112424

Interpretive Summary: Soybean is the number 1 food crop in Mississippi. It has a high protein nutritional value. However, raw soybean contain undesirable protease inhibitors, which could cause low protein efficiency and pancreatic hypertrophy. On the other hand, soybean has desirable health promoting factors such as antioxidant phenolic compounds, which in large part contribute to the well recognized health benefits. Our research objective is to retain the most desirable health factors while eliminating undesirable inhibitors through optimizing processing conditions. Among soy food products, soymilk is becoming popular in the Western countries. In the present study, soymilk was prepared from two soybean varieties (yellow and black) by three processing temperature regimes (cold, ambient and hot) and then the raw soymilk underwent three thermal treatments (traditional stove cooking, one-phase ultrahigh temperature, and two-phase ultrahigh temperature). Soybean variety, grinding methods and thermal treatments all had a significant effects on the protease inhibitor activity, phenolic content and antioxidant activity. Hot grinding yielded substantially higher antioxidant capacity in the soymilk. The current study, for the first time, from a different angle, revealed the influence of grinding temperature on the quality of soymilk, especially when it was combined with various heating methods. The results can serve as a foundation for the soy industry to retain the highest health benefits while eliminating undesirable protease inhibitors to benefit the consumers.

Technical Abstract: Two soybean varieties (yellow and black) were ground under three temperature regimes (cold, ambient and hot) and then the raw soymilk underwent three thermal treatments (traditional stove cooking, one-phase UHT, and two-phase UHT). Trypsin inhibitor activity (TIA), chymotrypsin inhibitor activity (CIA), total phenolic content (TPC), total flavonoid content (TFC), condensed tannin content (CTC), DPPH free radical scavenging activity, and oxygen radical absorbing capacity (ORAC) were significantly affected by the above factors and their interactions. For raw yellow soymilk, hot grinding generated 64 and 69% lower TIA than cold and ambient grinding, respectively. For raw black soymilk, hot grinding generated 40 and 43% lower TIA than cold and ambient grinding, respectively. After heating process, the advantage of hot grinding was reduced. By suppression of the development of lipoxygenase-induced hydroperoxides, hot grinding preserved the most sulfhydryl and disulfide groups. Stove cooking following ambient grinding resulted in the lowest CIA. Except TFC, hot grinding recovered the highest phenolic content and antioxidant capacity. CTC from hot grinding was about twice that from ambient grinding. Black soymilk contained significantly higher antioxidant capacity than yellow soymilk and UHT treatments showed advantage over traditional stove cooking in the preservation of phenolics.