Sequence alterations affect the antidiabetic attributes of hazelnut peptide fractions during the industrial manufacture and simulated digestion of hazelnut paste

Abstract

Press cakes are by-products of cold press oil manufacture and are characterized by significant protein concentrations. Our group has previously demonstrated potential bioactive attributes of hazelnut protein hydrolysates including their antidiabetic activities. Here, an effort was made to utilize DPP-IV (Dipeptidyl peptidase-IV)-inhibitory hazelnut peptides in industrial food manufacture. Hazelnut protein isolates (approx. 95% protein) were obtained via an alkali extraction-isoelectric precipitation method. Papain, bromelain and pepsin were used in the enzymatic hydrolysis and hydrolysates were fractionated via Fast Protein Liquid Chromatography. As a general observation, although fractionation lead to dilution of the samples, fractions were observed to be more bioactive than the total hydrolysates. In vitro antidiabetic activities of the fractions were tested and 3 antidiabetic fractions were added to hazelnut paste. Afterwards simulated gastrointestinal digestion and antidiabetic activity assays were performed. DPP-IV inhibition was the major antidiabetic mechanism in the fractions and digested paste, while some fractions were characterized by comparable IC50 values as the positive controls. Alpha-glucosidase inhibition was limited by digestion trials, whereas alpha-amylase inhibition was only slight in the digested paste (< %6). In silico analyses predicted partial degradation of the peptides, whereas the interactions between DPP-IV or alpha-glucosidase and hazelnut peptides were predicted to be significant (p < 0.05). Consequently hazelnut press cakes were regarded as a potential source of antidiabetic peptides that can be used in industrial manufacture of functional foods, while food processing conditions or gastrointestinal digestion could largely affect peptide bioactivity.