Nutrients

The nutritional value of rice depends on several factors. First of all, it varies according to the rice strain, that is white rice, brown rice, red rice, or black rice, which have a different percentage of distribution in different regions of the world [54]. After that, the nutritional value of rice depends on the nutrient quality of the soil in which it is grown, if and how it is polished or processed, and if and how it is enriched and how it is prepared before consumption [55].

A 100 g serving of unenriched white rice provides an average of 360 calories, distributed between carbohydrates, proteins, fats, and fibers. Rice is also a good source of B vitamins and several dietary minerals including manganese. Raw white rice contains 66% carbohydrates, mostly starch, 11% dietary fibers, 4% beta-glucans, 7% fats, and 17% proteins. Cooked unenriched white rice is composed of 68% water, 28% carbohydrates, 13% protein, and fat in minimal quantity (less than 1%). Cooked short-grain white rice provides the same food energy and contains moderate amounts of B vitamins, iron, and manganese (10–17% of daily value, DV) per 100-g serving [21].

Starch and proteins, as main components of rice grains, accumulate in specific organelles called amyloplasts and protein bodies, respectively, in the endosperm cells and in the aleurone layer. Endosperm cells contain many amyloplasts with multiple starch grains and protein bodies with glutellin (protein body II) and prolamine (protein body I), which are storage proteins. On the other hand, the cells in the aleurone layer contain another type of protein body called grain aleurone, with non-storage proteins and small amyloplasts. The protein content of rice grains is of course lower than meat (15–25%) and cheese (20%), but is higher than dairy milk (3.3%) and yoghurt (4.3%). About 6–7% of polished rice and about 13% of rice bran is protein [56].

Amino acid score, in combination with protein digestibility, which refers to how well a given protein is digested, is the method used to determine if a protein is complete (i.e., whether it contains an adequate proportion of each of the nine essential amino acids necessary in the human diet). Together with the amino acid score, the digestibility of proteins determines the values for Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and Digestible Indispensable Amino Acid Score (DIAAS). DIAAS was proposed in March 2013 by the FAO to replace the PDCAAS. DIAAS provides a more accurate measure of the number of amino acids absorbed by the body or the contribution of the protein to the needs of amino acids and nitrogen in humans, as it estimates the digestibility of amino acids at the end of the small intestine. PDCAAS, already adopted by the FAO in 1993 as a method for determining the quality of proteins is based on an estimate of crude protein digestibility determined over the total digestive tract, and values stated using this method generally overestimate the number of amino acids absorbed [57]. Compared with casein, which has a DIAAS of 101, rice has a DIASS of 47, whereas wheat has a DIASS of 48, oat has a DIASS of 57, and corn (Maize) has a DIASS of 36 [58]. If instead we take into consideration the PDCAAS, rice bran protein has a PDCAAS of 0.90, whereas casein has a PDCASS of 1.00, and rice endosperm protein has a PDCAAS of 0.63 [59]

#### *2.6. Maize (Corn)*

Maize, also known as corn, is a large grass plant already domesticated by the native populations of Mexico about 10,000 years ago. The word corn derives from the term "mahiz", with which the indigenous Taino people of the Caribbean and Florida called the plant, later transliterated into Spanish. In the United States, Canada, Australia, and New Zealand, the term mainly refers to maize with the term "corn", derived from the shortening of the expression "Indian corn", which mainly refers to maize, which is the staple cereal of Native Americans [20].
