In Vitro Protein Digestibility of Selected Plant and Animal Foods by Multi-Enzyme Assay

The recent Food and Agricultural Organization / World Health Organization United Nations University expert consultations on protein quality have emphasized the need for protein digestibility measurements in humans. The standard in vivo oro-ileal protein digestibility measurements are invasive, expensive, time-consuming and burdensome on participants. The in vitro multi-enzyme based assays have been a promising tool for rapid, non-invasive and cost-effective protein digestibility measurements in foods. The digestibility estimates obtained from these methods have not been compared with true ileal digestibility measurements in humans. This study measured in vitro protein digestibility in selected commonly consumed plant and animal proteins, assessed the effect of heat-treatment on protein digestibility and compared the digestibility estimates with previously published human true ileal protein digestibility values. The in vitro protein digestibility in the raw plant proteins ranged from 35% in pigeon pea to 72% in rice. Cooking improved digestibility by 8% in potato to 26% in pigeon pea. The in vitro protein digestibility in freeze dried and spray dried milk powder were €85% which reduced to 73% after heat-treatment at 120°C for 40 minutes. The mean difference between the in vitro protein digestibility coefficients and the true ileal protein digestibility estimates was 4.3% (95% CI:-1.05, 9.74%). Although, the in vitro assays can be used as useful tools to predict ileal digestibility in humans, and to rank food proteins according to their digestibility, further studies are warranted for inter-laboratory validation of assays with appropriate evaluation on same protein sources against true ileal digestibility measured in humans.