## 1 Introduction  
According to World Health Organization (WHO), by 2030, the world's population is expected to reach the super-aging stage, with 12.5% of the world's population aged 60 or older at present [1]. According to projections, there will be 1.5 billion people over the age of 65 in the world by 2050, an increase from 727 million in 2020 [2]. In Taiwan, approximately 24% of the population is expected to be aged 60 and above by 2030 [1]. Age-related anabolic resistance to the dietary amino-acid-induced protein synthesis in skeletal muscle results in a lack of protein for muscular growth. This may lead to sarcopenia, a condition marked by a progressive decline in muscle mass, strength, and function. Also, the aged population consumes insufficient amounts of proteins with important biological functions, which raises the possibility of a loss of muscle mass and may exacerbate sarcopenia [3,4]. As per recommendations from the European Society for Clinical Nutrition and Metabolism (ESPEN), a protein intake of 1.0-1.2 g/kg body weight per day is helpful in maintaining/increasingmuscle mass and decreasing the risk of physical disability, which is higher than the recommended dietary allowance (R.D.A.) of 0.8 g/kg/d [2; 5]. Additionally, the need for dietary proteins has increased due to changes in lifestyle and the growing human population. Past studies have also shown that older persons who consume the recommended amount of protein have reduced frailty risks and lean mass loss than those who consume less protein [6; 7; 8]. The recommended daily protein intake for the elderly, however, is a hard target to attain, increasing the risk of protein malnutrition. The insufficient consumption of protein in the older population can be attributed to multiple reasons, mainly including reduced energy requirement, physical dependence for buying and preparing food, anorexia due to aging or medical conditions, neurosensorial changes in food preference, poor dentition, and food insecurity owing to monetary and social limitations [9]. On the other hand, vegetarians may experience protein deficiency and insufficient intake of essential amino acids in the long run because of their dietary restrictions. The protein intake in the elderly population can be increased by supplementing the regularly eaten food with a high amount of protein such as noodles, which is one of the staple foods in many Asian countries [10; 11]. Noodles are usually made from wheat flour, which makes them rich in carbohydrates but deficient in proteins [12]. Some additives have been used in the noodle-making process to enhance the nutritional value of noodles. [PERSON] et al. used a mixture of refined wheat flour, soy flour, and sorghum flour to make multigrain noodles, and the noodles were found to have enhanced nutritional and antioxidant properties [12]. [PERSON] et al. mixed heat moisture treatment corn starch, high-amylase corn starch, or green banana flour with wheat flour to make a low-GI noodle, and the noodles showed good acceptability [13]. Wheat flour can be fortified with protein to increase the protein content in the noodles and meet the overall protein requirements of the elderly population. Soy protein is an ideal supplement for wheat flour owing to its excellent nutritional content, positive effects on calcium metabolism, and ability to decrease cholesterol [14; 15]. Various soy products have been reported to fortify wheat flour, viz., soy protein [14], soy milk [16], soy protein hydrolysate [17], etc. Soy protein may improve cognitive function in the elderly [18] and has been found to improve glycemic control and decrease HbA1c compared to casein [19]. Soybean protein isolate (SPI) is extracted from soybeans after the removal of the majority of fat and carbohydrates, resulting in high protein content. SPI contains a well-balanced amino acid composition, is an important protein resource and an excellent food additive.