Proteins differ in their quality based on both amino acid content, digestibility and bioavailability. Chicken is a good source of proteins high in essential amino acids, but processing may influence the digestibility. Processing may also affect gastrointestinal oxidative stability and the formation of harmful peroxidation products, e.g. malonaldehyde (MDA).

Main conclusions

• HPP, MW, US and PEF treatment of chicken did not significantly affect protein digestibility.
• PEF treatment in combination with heat treatment caused increased peroxidation during digestion.

Purpose

Investigate whether processing (heating, HPP, MW, US, PEF) of chicken filet influence protein digestibility and formation of MDA during in vitro digestion.

Methods

Samples of chicken filet underwent different treatments and were stored frozen. The samples were thawed and minced in a food processor before being subjected to a static in vitro digestion model (Infogest).

Portions of PEF and US treated samples (raw) were also heat-treated before digestion. Samples were withdrawn from the gastric- and intestinal phases and protein breakdown products (peptides) were analyzed by Size Exclusion Chromatography (SEC).

Concentration of dissolved proteins was measured by the Dumas method, and levels of MDA equivalents were measured by the TBARS method.

Treatments

• Raw (control)
• Cooked
• Cooked + MW
• Cooked + HPP
• PEF
• PEF + heated (70°C, 20 min)
• US
• US + heated (70°C, 20 min)

What was examined:

1. Protein dissolved during digestion (DUMAS)

• Heat treatment caused reduced protein solubility during digestion
• No effects were observed of the other treatments (HPP, MW, PEF, US)

2. Protein digestibility (SEC)

• Heat treatment influenced protein digestion by causing reduced degradation of proteins to peptides. Hence, raw samples seem to be better digested that cooked.
• No effects were observed of the other treatments (HPP, MW, PEF, US) and there were no significant differences between these treatments.

3. Formation of MDA during digestion (TBARS)

• Heat treatment resulted in higher levels of MDA
• MDA levels increased during digestion for all samples
• The increase in MDA during digestion was highest when PEF treatment preceded heat treatment. A similar, but less pronounced trend was also observed for US.
• When rapeseed oil was digested together with the samples, a significant increase in MDA was observed for “raw”, but not heat treated samples.