Calcium coagulation properties of hydrothermally processed soymilk

Assessment of soy genotype and processing method on trypsin inhibitors, urease and lectins content of tofu

Tofu has a high nutritional value, but it may also contain components that may have an antinutritional effect, such as trypsin inhibitors (TI), lectins and ureases. The aim of this study was to investigate the influence of the hydrothermal-cooking process of soybean in combination with commercial chymosin-pepsin rennet on the content and activity of TI, urease and lectins in tofu. High total TI content was found in tofu (5.00-16.87%). In addition, Kunitz (KTI = 3.52-4.32%) and Bowman-Birk (BBI = 5.00-12.53%) TI were registered, and BBI was detected in polymeric (1.38-2.71%) and monomeric (3.42-9.82%) forms. TI activity of tofu was very low (5.86-9.34%), corresponding to the very low activity of urease (0.51-3.07%). The percentage of lectin (2.62-4.63%) and urease (0.03-0.12%) in tofu was low. The results showed that the applied tofu production process is very effective in reducing the content and activity of TI, urease and lectin and provides the values without nutritional harmful effect.

Composition of proteins in fresh whey as waste in tofu processing

Tofu whey is a pale-yellowish liquid with specific aroma/taste which remains as the byproduct/waste after tofu squeezing and represents an environmental problem for direct disposal. Understanding the fresh tofu whey protein composition and the activity of bioactive peptides could be useful for the application of tofu whey as a functional food additive. Tofu whey was obtained during the tofu production from six soybean genotypes by hydrothermal processing in combination with chymosin-pepsin rennet. Basic 7S globulin (14.28-19.13%), γ-conglycinin (7.73-9.31%) and β-conglycinin (10.59-12.90%) were registered of the total extracted proteins. Glycinin was present with a dominant share of acidic (24.64-27.55%) versus basic polypeptides (12.18-14.61%) in the total extracted proteins. High content of total protein (22.67-28.00%), balanced content (9.76-13.33% of the total extracted proteins) and residual activity (1.95-3.76%) of trypsin inhibitors and low lectins content (5.04-5.48% of the total extracted proteins) indicate good nutritional value of the tofu whey samples. Tofu whey can be potentially useful for application as a cheap, nutritional and functional food additive and can enable sustainable production through the recycling of waste.

Effects of sprouting of soybean on the anti-nutritional, nutritional, textural and sensory quality of tofu

Soybean (Glycine max) is a superior plant food known as the miracle golden bean due to its treasure trove of inexpensive and superior protein to high-priced meat protein. Tofu is typically thought of as a salt or acid-coagulated water-based gel containing soy lipids and proteins trapped within its gel networks. Sprouted tofu is easier to digest and contains more nutrients than regular tofu. The purpose of this study was to evaluate the nutritional and sensory quality of tofu. The study was concerned with the preparation of tofu from non-germinated and germinated soybeans of 0 (T₀), 2 (T₁), 4 (T₂) and 6 (T₃) days. The length of the radicle was 0.8, 1.5, and 2 inches for T₁, T₂, and T₃, respectively. Lipoxygenase activity, phytate inhibitory activity, urease activity, trypsin inhibitory activity, protein solubility, nutritional, and sensory quality of prepared tofu were all assessed. Longer sprouting times reduced phytate, urease, trypsin, and lipoxygenase activity while increasing protein solubility. Tofu prepared from T₃ showed significantly better physicochemical properties than others. Protein, ash, and fat contents were significantly higher in T₃. The level of nutrient content for tofu samples was in the rank of T₃>T₂>T₁>T₀. The L∗, a∗ and b∗ values were followed the same ranked as nutrient content (T₃>T₂>T₁>T₀). Sensory characteristics indicated that T₃ was significantly more acceptable to the panelist. This study concludes that tofu made from 6 day sprouted soybeans with a height of 2 inches can be a good source of nutrition for consumers.

Mineral elements, lipoxygenase activity, and antioxidant capacity of okara as a byproduct in hydrothermal processing of soy milk

Minerals and antioxidative capacity of raw okara that was obtained as a byproduct from six soybean varieties during hydrothermal cooking (HTC) of soy milk were assessed. Lipoxygenase (Lox), an enzyme deteriorating the sensory characteristics of okara, was also investigated. All genotypes had very similar concentrations of Lox (4.32-5.62%). Compared to raw soybeans, the applied HTC significantly reduced Lox content in okara (0.54-0.19%) and lowered its activity to 0.004-0.007 μmol g(-1) min (-1). Correlation between the content of Lox in soybeans and that in okara (r = 0.21;p < 0.05) was not registered. This indicates that the content of this enzyme in okara depended much more on the technological process than on soybean genotype. Very strong correlation (r = 0.99; p < 0.05) between okara Lox content and its activity was found. The most abundant minerals in raw okara were potassium (1.04-1.21 g/100g), phosphorus (0.45-0.50 g/100 g), calcium (0.26-0.39 g/100 g), and iron (5.45-10.95 mg/100 g). A very high antioxidant capacity (19.06-29.36 mmol Trolox kg(-1)) contributes to the nutritional value of raw okara.

Bioactive proteins and energy value of okara as a byproduct in hydrothermal processing of soy milk

The nutritional properties of raw okara obtained as a byproduct from six soybean varieties during hydrothermal cooking (HTC) of soy milk were assessed. The composition and residual activity (rTIA) of trypsin inhibitors (TIs), contents of lectin, proteins, fats, and carbohydrates, and energy values (EV) were correlated with the respective physicochemical properties of soybean and okara. Kunitz (KTI) and Bowman-Birk (BBI) TIs both comprised okara rTIA. TIs content was higher in okara (5.19-14.40%) than in soybean (3.10-12.17%), which additionally enriched okara by cysteine. Contents of KTI (r = 1.00;p < 0.05) and BBI (r = 0.89;p < 0.05) as well as BBI monomeric (r = 0.89;p < 0.05) and polymeric forms (r = 0.95;p < 0.05) in okara and in soybean were strongly correlated. Low urease index activity indicated that okara was heated adequately to inactivate antinutritional factors. The proximate composition of raw okara, advantageous rTIA, and a very low EV (2.74-3.78 kJ/g) qualify this byproduct for potential application in food preparation as a functional ingredient in dietary products.

Composition of proteins in okara as a byproduct in hydrothermal processing of soy milk

Protein quality, based on its subunit composition, in okara obtained as a byproduct during hydrothermal cooking of soy milk was assessed. The composition of 7S and 11S protein fractions was correlated with the physicochemical properties of protein in okara produced from six soybean varieties. The basic 7S globulin (Bg7S) and 11S protein were two main proteins in okara. Investigated soybean genotypes produced okara with mainly acidic A(5) and basic B(1,2,4) polypeptides of 11S proteins. Soybean 11S content was not an indicator of okara protein recovery or extractability. Of all tested relationships, extractable soluble protein content of okara was influenced only by soybean Bg7S (r = 0.86; p < 0.05) and its light subunit contents (r = 0.93; p < 0.05). Okara protein recovery depended on Bg7S heavy subunit content in soybeans (r = 0.81; p < 0.05). The high quantity of vegetable protein in okara (around 35%) and very high protein extractability (around 85%) qualify this byproduct for potential application in food preparation as a functional ingredient.

Assessment of soy genotype and processing method on quality of soybean tofu

Protein quality in six soybean varieties, based on subunit composition of their protein, was correlated with quality of the produced tofu. Also, protein changes due to a pilot plant processing method involving high temperature/pressure and commercial rennet as coagulant were assessed. In each soybean variety, glycinin (11S) and β-conglycinin (7S) as well as 11S/7S ratio significantly changed from beans to tofu. Between varieties, the 11S/7S protein ratio in seed indicated genotypic influence on tofu yield and gel hardness (r = 0.91 and r = 0.99, respectively; p < 0.05). Also, the 11S/7S ratio correlated with soymilk pH (r = 0.89, p < 0.05), leading to a relationship between soymilk pH with protein recovery and yield of tofu (r = 0.94 and r = 0.91, respectively; p < 0.05). The soybean β'-subunit of 7S protein negatively influenced tofu hardness (r = -0.91, p < 0.05). Seed protein composition and proportion of 7S protein subunits under the applied production method had an important role in defining tofu quality.