In vitro determination of the protein quality of maize varieties cultivated in Malawi using the INFOGEST digestion method

There is an urgent need to alleviate protein deficiencies in low-income countries where cerealbased diets dominate. The objective of this study was to use the INFOGEST static digestion method and a recently established analytical workflow to determine the in vitro amino acid digestibility and protein quality of seven maize varieties grown in Malawi. Protein quality was measured using the in vitro digestible indispensable amino acid score (DIAAS). Amino acid digestibility was higher for the dehulled, low fibre, provitamin A maize flour (66%), compared to whole grain maize flours (51-61%), suggesting that the presence of fibre reduced digestibility (p < 0.05). Lysine was the limiting amino acid in all varieties, with the following DIAAS values for each variety; Provitamin A maize - 24, SC 719 - 32, Mtsikinya - 37, SC 167 - 39, Quality protein maize (QPM) - 40, Bantum - 40, SC 403 - 44. In addition to the variety of maize, protein quality was dependent on the level of processing and the agronomic practice applied with higher protein quality for the SC 403 variety in which zinc enriched fertilizer was applied. Comparing protein quality data with published in vivo data showed that DIAAS data were in closer agreement than amino acid digestibility data, which was slightly lower than published values, with mean in vitro amino acid digestibilities of 56-70% compared to a mean in vivo value of 77%. Overall, the in vitro method was able to correctly predict both the direction and magnitude of response. The INFOGEST digestion method coupled with the new analytical workflow will therefore be useful in the screening of high protein cereal crops and subsequent development of cereal-based foods with high protein quality.

Automated summary

There is an urgent need to address protein deficiencies in low-income countries with cereal-based diets. This study used the INFOGEST static digestion method and a new analytical workflow to evaluate the protein quality and amino acid digestibility of seven maize varieties grown in Malawi. The results showed that higher fiber content reduced amino acid digestibility, and lysine was the limiting amino acid. Protein quality was also influenced by processing level and agronomic practices. In vitro data were closer to in vivo data compared to amino acid digestibility data. The INFOGEST method coupled with the new workflow can be helpful in screening high protein cereal crops and developing cereal-based foods with higher protein quality.