Protein-bound D-amino acids, and to a lesser extent lysinoalanine, decrease true ileal protein digestibility in...

Area of Science:

• Food Science
• Nutritional Biochemistry
• Animal Nutrition

Background:

• Food processing, particularly heat and alkali treatment, can alter protein structure.
• This alteration may lead to the formation of D-amino acids and cross-links like lysinoalanine (LAL).
• The impact of these modifications on protein and amino acid digestibility is not fully understood.

Purpose of the Study:

• To investigate the effect of heat and alkali treatment on protein-bound D-amino acids and LAL formation.
• To determine how these modifications influence the prececal digestibility of proteins and individual amino acids.
• To elucidate the role of D-amino acids and LAL in reduced protein digestibility.

Main Methods:

• Purified casein, beta-lactoglobulin, and wheat protein meals were prepared and (15)N-labeled.
• Proteins were treated with heat (65°C) and alkali (pH 10.5-11.5) for 6 or 24 hours.
• Miniature pigs were fed test meals, and ileal chyme was collected to calculate digestibility based on (15)N and amino acid recovery.

Main Results:

• Protein treatment significantly increased D-amino acid residues and LAL formation, with L-asparagine and aspartate being particularly susceptible to racemization.
• Prececal protein digestibility decreased by 13-18% after 24 hours of treatment.
• Digestibility of individual L-amino acids decreased by 10-15%, while D-amino acids and LAL showed approximately 35% digestibility.

Conclusions:

• Heat and alkali treatment of proteins lead to increased D-amino acids and LAL formation.
• These modifications significantly reduce protein and amino acid digestibility in pigs.
• D-amino acids appear to be the primary factor responsible for decreased digestibility, likely by interfering with peptic cleavage.