Soymilk and tofu properties as influenced by soybean storage conditions

Abstract

Soybeans were stored at two temperatures, 20~ and 30~ and two relative humidities, 65% and 85%. The amount of protein extracted into soymilk decreased by about 14% of the initial extractability in all cases after eight months of storage. The decline in protein extractability could not be explained by decreases in pH, nor by loss of solubility of certain protein components. Tofu made from beans that were stored at 85% relative humidity became less uniform in microstructure toward the end of the storage period. The volume of whey produced increased with bean storage time.

Effect of soybean aging on the quality of soymilk, firmness of tofu and optimum coagulant concentration

“…These results are in agreement with those observed by Thomas et al (1989), Chang (2004, 2008) and Kong et al (2008). During storage, the high temperature and relative humidity cause damage to grain tegument and activate the enzymes involved in aerobic respiration, causing the peroxidation of membrane phospholipids, resulting in loss of cellular compartmentalization (Santos, Menezes, & Villela, 2005;Trawatha, TeKrony, & Hildebrand 1995) and causing a series of chemical reactions, such as hydrolysis and oxidation of lipids, increased acidity (Kong et al, 2008;Thomas et al, 1989) and protein denaturation (Hou & Chang, 2004a;Hou & Chang, 2004b). These events could be responsible for the decrease in solid extraction and especially protein, due to its partial denaturation (Kamizake, Varéa et al, 2014).…”

“…This result disagrees with those obtained by Thomas et al (1989), Hou and Chang (1998) and Kong et al (2008). However, Murphy et al (1997) reported a decrease in tofu firmness when it was prepared from aged soybeans, and suggested that this phenomenon could be related to structural changes in protein molecules, particularly the 11S fraction, which is responsible for the firmness of the gel (Tay, Xu, & Perera, 2005).…”

“…The molecular changes explain the reduction in protein solubility and extractability. Thus, proteins of smaller molecular mass are extracted from soymilk (Thomas et al, 1989). These proteins do not form large curd with good water retention.…”

“…In tropical countries, as well as in many Brazilian regions, with mean annual temperatures close to 27°C and relative humidity at about 80%, storing of soybean for long periods of time, under ambient conditions (uncontrolled), leads to losses in the quality of grains and their products (Kamizake, Varéa, & Prudencio, 2014;Kamizake, Yamashita, & Prudencio, 2014;Kong et al, 2008). Quality deterioration of these products consists mainly in browning, reduced solids, especially proteins, decreased yield and quality of tofu texture (Hou & Chang, 1998, 2004a, 2004b, 2004cKong et al, 2008;Saio et al, 1980;Thomas et al, 1989).…”

“…The quality of these products, besides the manufacturing process, depends on the cultivar and quality of soybean grains, and the latter is related to storage conditions, namely time, temperature and relative humidity (RH) (Hou & Chang, 1998, 2004a, 2004b, 2004cKong, Chang, Liu, & Wilson, 2008;Murphy, Chen, Hauck, & Wilson, 1997;Thomas, deMan, & deMan, 1989). In tropical countries, as well as in many Brazilian regions, with mean annual temperatures close to 27°C and relative humidity at about 80%, storing of soybean for long periods of time, under ambient conditions (uncontrolled), leads to losses in the quality of grains and their products (Kamizake, Varéa, & Prudencio, 2014;Kamizake, Yamashita, & Prudencio, 2014;Kong et al, 2008).…”