Abstract
Production of protein hydrolysate as nutraceuticals is typically based on the activity of the hydrolysate, which might not yield the optimal activity under physiological condition due to structural modification of peptides upon gastrointestinal (GI) digestion. This study systematically compared the chemical and cellular antioxidant activities of the in vitro digesta of tilapia protein and its hydrolysates prepared with various degree of hydrolysis (DH) by Alcalase. The enzymes used in the in vitro GI digestion analysis significantly contributed to the peptide content, Trolox equivalent antioxidant capacity (TEAC), and oxygen radical absorbance capacity (ORAC). Proteins and all hydrolysates were slightly digested by pepsin but hydrolyzed extensively by pancreatin. Both hydrolysate and digesta predominantly scavenged free radicals via hydrogen atom transfer (HAT). The antioxidant activities of the hydrolysates increased with the increasing DH up to 16 h of hydrolysis. However, the digesta of 10-h hydrolysate displayed the highest chemical and HepG2 cellular antioxidant activities, while the protein digesta displayed the lowest. Principal component analysis (PCA) showed that the TEAC of the digesta was positively correlated with the cellular antioxidant activity (CAA). Therefore, the production of protein hydrolysate should be optimized based on the activity of the hydrolysate digesta rather than that of hydrolysates.
Highlights
Antioxidant peptides derived from food proteins have been widely elucidated and characterized in various food protein sources [1,2,3,4]
When pepsin and pancreatin were prepared as the enzyme blank for the GI digestion process (Pep-Pan-I), the α-amino content and antioxidant activities (TEAC and oxygen radical absorbance capacity (ORAC)) were approximately 15%–40% of those of H10 -gastric-intestinal digesta (GID)#
These results suggested that the peptides derived from pancreatin possessed significant levels of α-amino and antioxidant activities
Summary
Antioxidant peptides derived from food proteins have been widely elucidated and characterized in various food protein sources [1,2,3,4]. They have been considered as a natural antioxidant, which can retard oxidative deterioration of food during storage [4,5,6]. In vitro GI digestion increased the antioxidant activities of hydrolysates derived from fish muscle protein or skin [3,14,15]. The antioxidant activities of the positively charged fraction of casein hydrolysate and synthesized peptide, ATSHH, Foods 2020, 9, 833; doi:10.3390/foods9060833 www.mdpi.com/journal/foods
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