The researchers studied different types of rice to see how much protein they contain and how the amino acid composition varies. They found that Tongil-type rice has more protein than japonica rice. The low-protein japonica rice had lower essential amino acids, but similar overall essential amino acid content. Glutamic acid was the most abundant amino acid, while leucine was the highest essential amino acid and methionine was the lowest. The protein content of rice was influenced by factors like days to maturity, certain mineral ratios, and amylose content. Rice grown in different regions also had varying protein levels, with southern areas having higher protein content. Overall, environmental factors played a significant role in determining the protein content of rice, especially in mountainous and alpine regions.