The kiwifruit enzyme actinidin enhances the hydrolysis of gluten proteins during simulated gastrointestinal digestion.

This study investigated the effect of actinidin, a cysteine protease in kiwifruit, on the hydrolysis of gluten proteins and digestion-resistant gluten peptides (synthetic 33-mer peptide and pentapeptide epitopes) under static simulated gastrointestinal conditions. Actinidin efficacy in hydrolysing gliadin was compared with that of other gluten-degrading enzymes. Actinidin hydrolysed usually resistant peptide bonds adjacent to proline residues in the 33-mer peptide. The gastric degree of hydrolysis of gluten proteins was influenced by an interaction between pH and actinidin concentration (P < 0.05), whereas the pentapeptide epitopes hydrolysis was influenced only by the actinidin concentration (P < 0.05). The rate of gastric degree of hydrolysis of gliadin was greater (P < 0.05) by actinidin (0.8%/min) when compared to papain, bromelain, and one commercial enzyme (on average 0.4%/min), while all exogenous enzymes were able to hydrolyse the pentapeptide epitopes effectively. Actinidin is able to hydrolyse gluten proteins under simulated gastric conditions.

The Rate at Which Digested Protein Enters the Small Intestine Modulates the Rate of Amino Acid Digestibility throughout the Small Intestine of Growing Pigs.

Background: Actinidin, a cysteine protease in kiwifruit (KF), increases both the gastric digestion and gastric-emptying rate of beef muscle protein. Objective: This study aimed to determine the relation between the rate of digested nitrogen entering the small intestine (SI; a function of the extent of gastric digestion and gastric-emptying rate) and the disappearance of amino acids (AAs) in different parts of the SI at set times postfeeding. Methods: Male 9-wk-old pigs (n = 90; mean ± SD body weight: 28 ± 2.9 kg) were fed a diet containing 14% beef for 3 d. The beef-based diet was supplemented with green KF pulp (containing actinidin), gold KF pulp supplemented with actinidin, or gold KF pulp alone (no actinidin). The KF or actinidin amounts corresponded to the intake of 2 KFs/human meal. On day 3, pigs were killed at 0.5, 1, 3, 5, and 7 h postprandially. Stomach chyme was analyzed to determine the rate of digested nitrogen entering the SI. Apparent AA digestibility at set times was determined in the proximal, medial, and distal SI. Polynomial and correlation analyses were conducted. Results: The rate of digested nitrogen entering the SI was higher (P < 0.001) with actinidin (e.g., >44% at 5 h postprandially). Actinidin also increased the apparent AA digestibility at the proximal and medial SI (P ≤ 0.05) at set times (e.g., 42% and 15% greater for arginine, respectively), but not in general for the distal SI (P > 0.05). At the proximal SI, apparent AA digestibility was correlated more strongly with the digested nitrogen entering the SI (r = 0.73, P < 0.001; n = 57) than with gastric emptying (r = 0.64, P < 0.001) or gastric protein digestion (r = 0.57, P < 0.001). Similar trends were observed for the medial SI. Conclusion: The rate of digested nitrogen entering the SI is an accurate predictor of the rate of AA digestibility and the location of AA absorption in the pig SI.