Molecular Plant Breeding 2025, Vol.16, No.1, 93-104 http://genbreedpublisher.com/index.php/mpb 100 7.3 Quality of protein achieved The quality of protein in bred maize varieties has been significantly enhanced, particularly in terms of essential amino acids. The QPM lines, for example, have been shown to contain 1.9 times more tryptophan and double the quality index compared to non-QPM lines (Bhatnagar et al., 2004). This improvement is crucial as tryptophan and lysine are essential amino acids that are often deficient in regular maize. Moreover, the introduction of the o16 gene alongside the o2 gene has led to hybrids with enhanced levels of lysine and tryptophan. These pyramided lines (o2o2/o16o16) exhibited up to 64% and 86% increases in lysine and tryptophan, respectively, over the original hybrids (Sarika et al., 2018). This dual-gene approach has proven effective in significantly boosting the amino acid profile of maize. 8 Nutritional Impact Assessment 8.1 Comparison of nutritional values with standard maize varieties Quality Protein Maize (QPM) varieties have been developed to address the nutritional deficiencies found in standard maize varieties. Studies have shown that QPM varieties generally have a higher quality of protein due to increased levels of essential amino acids such as lysine and tryptophan. For instance, QPM lines were found to have 1.9 times more tryptophan and double the quality index compared to non-QPM lines, despite having a 7% lower overall protein content (Amegbor et al., 2022a). Additionally, QPM varieties have been shown to contain higher levels of other essential nutrients, such as carotenoids and tocopherols, which are crucial for human health (Chander et al., 2008). In comparison to standard maize varieties, QPM has demonstrated superior nutritional profiles. For example, a study comparing northern adapted cultivars of common maize with QPM found that QPM had double the amount of lysine and arginine, and higher levels of tryptophan and cysteine, resulting in a better balance of essential amino acids (Zarkadas et al., 1995). This improved amino acid profile makes QPM a more nutritious option, particularly in regions where maize is a staple food and protein malnutrition is prevalent. 8.2 Protein bioavailability and digestibility The bioavailability and digestibility of protein in QPM are critical factors that determine its nutritional efficacy. Research indicates that QPM varieties not only have higher levels of essential amino acids but also exhibit improved protein digestibility. For instance, the amino acid score of QPM, adjusted for digestibility, was found to be significantly higher than that of conventional maize varieties, indicating better protein quality (Zarkadas et al., 1995). This is particularly important for populations that rely heavily on maize as a primary protein source. Moreover, transgenic QPM varieties have been developed to further enhance protein content and quality. A study on transgenic lysine-rich maize showed that the insertion of the lysine-rich sb401 gene increased the total protein and lysine content, leading to an improved amino acid score and overall nutritive value (Tang et al., 2013). These advancements suggest that QPM can provide a more bioavailable and digestible protein source compared to standard maize varieties, thereby addressing protein malnutrition more effectively. 8.3 Implications for human health and diet quality The enhanced nutritional profile of QPM has significant implications for human health and diet quality, particularly in developing countries where maize is a staple food. The increased levels of essential amino acids in QPM can help combat protein malnutrition, which is a major health issue in these regions. For example, a meta-analysis of community-based studies found that the consumption of QPM instead of conventional maize led to a 12% increase in the rate of growth in weight and a 9% increase in the rate of growth in height in infants and young children with mild to moderate undernutrition (Gunaratna et al., 2010). Furthermore, the adoption of QPM varieties can improve overall diet quality by providing a more balanced intake of essential nutrients. The higher levels of carotenoids, tocopherols, and other micronutrients in QPM can contribute to better health outcomes, including improved immune function and reduced risk of chronic diseases (Chander et al., 2008; Prasanna et al., 2020). Therefore, the integration of QPM into the diets of populations that rely on maize as a staple food can have profound positive effects on public health and nutritional status.
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