Effect and mechanism of freezing on the quality and structure of soymilk gel induced by different salt ions.

BACKGROUND: The increasing attention toward frozen soy-based foods has sparked interest. Variations exist in the quality and structure of soymilk gels induced by different salt ions, leading to diverse changes post-freezing. This study compared and analyzed the effects of calcium chloride (CC), magnesium chloride (MC) and calcium sulfate (CS) on the quality characteristics and protein structure changes of soymilk gels (CC-S, MC-S and CS-S) before and after freezing, and clarified the mechanisms of freezing on soymilk gel. RESULTS: The formation rate of soymilk gel is influenced by the type of salt ions. In comparison to CS and MC, soymilk gel induced by CC exhibited the fastest formation rate, highest gel hardness, lowest moisture content, and smaller gel pores. However, freezing treatment deteriorated the quality of soymilk gel induced by different salt ions, leading to a decline in textural properties (hardness and chewiness). Among these, the textual state of CC-induced soymilk gel remained optimal, exhibiting the least apparent damage and minimal cooking loss. Freezing treatments prompt a transition of soymilk gel secondary structure from ß-turns to ß-sheets, disrupting the protein's tertiary structure. Furthermore, freezing treatments also fostered the crosslinking between soymilk gel protein, increasing the content of disulfide bonds. CONCLUSION: The quality of frozen soymilk gel is influenced by the rate of gel formation induced by salt ions. After freezing, soymilk gel with faster gelation rates exhibited a greater tendency for the transformation of protein-water interactions into protein-protein interactions. They showed a higher degree of disulfide bond formation, resulting in a more tightly knit and firm frozen gel network structure with denser and more uniformly distributed pores. © 2024 Society of Chemical Industry.

Effects of removing phytic acid on the bioaccessibility of Ca/Fe/Zn and protein digestion in soymilk.

BACKGROUND: Soymilk is a high-quality source of protein and minerals, such as calcium (Ca), iron (Fe), and zinc (Zn). However, phytic acid in soymilk restricts mineral and protein availability. We here investigated the effects of removing phytic acid on the physicochemical properties, mineral (Ca, Fe, and Zn) bioaccessibility, and protein digestibility of soymilk. RESULTS: Physicochemical property analysis revealed that the removal of phytic acid reduced protein accumulation at the gastric stage, thereby facilitating soymilk matrix digestion. The removal of phytic acid significantly increased Zn bioaccessibility by 18.19% in low-protein soymilk and Ca and Fe bioaccessibility by 31.20% and 30.03%, respectively, in high-protein soymilk. CONCLUSION: Removing phytic acid was beneficial for the hydrolysis of high-molecular-weight proteins and increased the soluble protein content in soymilk, which was conducive to protein digestion. This study offers a feasible guide for developing plant-based milk with high nutrient bioaccessibility. © 2024 Society of Chemical Industry.

An Investigation into the Performance and Mechanisms of Soymilk-Sized Handmade Xuan Paper at Different Concentrations of Soymilk.

Invaluable paper relics that embody a rich traditional culture have suffered damage, requiring urgent restoration. In this context, the utilization of soymilk as a sizing agent holds great significance and reverence. This study investigates the use of soymilk as a sizing agent for Xuan paper and evaluates its effects on various properties and the long-term behavior of the paper. The findings reveal that the application of soymilk as a sizing agent for Xuan paper imparts distinct properties, including hydrophobicity, improved mechanical properties, and unique chromaticity. These characteristics-arising from the papillae on the surface of the Xuan paper, the protein folding of the soy protein, and hydrogen-bonding interactions between the soy protein and paper fibers-play a crucial role in shaping the paper's unique attributes. From a physicochemical perspective, the aging process leads to multiple changes in paper properties. These changes include acidification, which refers to a decrease in pH, as well as a decline in mechanical strength, an increase in chromaticity, and a decrease in the degree of polymerization (DP) of the paper. The Ekenstam equation is employed to predict the lifespan of the paper, showing longer lifespans for Sheng Xuan paper and a negative correlation between soymilk concentration and lifespan in soymilk-sized paper. Our work provides valuable insights for the preservation and maintenance of paper, highlighting the potential benefits and challenges of using soymilk for surface sizing.

Viscosity of evaporated soymilk prepared in the laboratory using normal and 11S-lacking soybean seeds.

BACKGROUND: Soymilk is utilized not only as a beverage but also as an alternative to bovine milk, including products such as yoghurt and cream. Evaporated soymilk is expected to be utilized as condensed milk. Raw and heated soymilk samples prepared in our laboratory were evaporated and then subjected to viscosity measurement. The soymilk samples were made from two different varieties: Fukuyutaka, which contains 7S and 11S globulin proteins; and an 11S-lacking soybean (Nanahomare). RESULTS: Raw Fukuyutaka soymilk had a lower viscosity and could be concentrated to a solids content of over 300 g kg-1 compared to heated soymilk (around 250 g kg-1 ), but the viscosity changes of Nanahomare soymilk showed an opposite trend. Only 7S globulin was denatured during evaporation at 75 °C and likely affected the interaction between proteins and oil bodies. This tendency was remarkable in the Nanahomare soymilk. The strange viscosity change behavior of evaporated Nanahomare soymilk, number of protein particles, intrinsic fluorescence and flow behavior suggest that thermally denatured 7S globulin accelerates the interactions between oil bodies, whereas 11S globulin, which is probably in its native state, suppresses the acceleration by denatured 7S globulin. CONCLUSION: Raw soymilk containing native globulins shows a slower increase in viscosity during evaporation. However, denatured 7S globulin accelerates the increase in viscosity during evaporation through interactions between oil bodies. The effect of the denatured state of individual proteins on interactions is expected to be useful in understanding the interaction between proteins and in controlling their properties and functions. © 2022 Society of Chemical Industry.

Engineering of Leuconostoc citreum for Efficient Bioconversion of Soy Isoflavone Glycosides to Their Aglycone Forms.

Soy isoflavones are phytochemicals that possess various beneficial physiological properties such as anti-aging, anti-tumor, and antioxidant properties. Since soy isoflavones exist in glycoside forms, their bioavailability requires initial hydrolysis of the sugar moieties bound to them to be efficiently absorbed through the gut epithelium. Instead of conventional chemical hydrolysis using acids or organic solvents, alternative strategies for enhancing the bioavailability of soy isoflavones using biological methods are gaining attention. Here, we engineered Leuconostoc citreum isolated from Korean kimchi for efficient bioconversion of soy isoflavone glycosides into their aglycone forms to enhance their bioavailability. We first constructed an expression module based on the isoflavone hydrolase (IH)-encoding gene of Bifidobacterium lactis, which mediates conversion of isoflavone glycosides to aglycone forms. Using a high copy number plasmid and bicistronic expression design, the IH was successfully synthesized in L. citreum. Additionally, we determined enzymatic activity of the IH using an in vivo ß-glucosidase assay and confirmed its highly efficient bioconversion efficiency for various types of isoflavone glycosides. Finally, we successfully demonstrated that the engineered L. citreum could convert isoflavone glycosides present in fermented soymilk into aglycones.

Comparison on Protein Bioaccessibility of Soymilk Gels Induced by Glucono-δ-Lactone and Lactic Acid Bacteria.

In this study, the protein bioaccessibility of soymilk gels produced by the addition of glu-cono-δ-lactone (GDL) and fermentation with lactic acid bacteria (LAB) was examined using an in vitro gastrointestinal simulated digestion model. The in vitro protein digestibility, soluble protein content, free amino acids contents, degree of hydrolysis, electrophoretic patterns, and peptide content were measured. The results suggested that acid-induced soymilk gel generated by GDL (SG) showed considerably reduced in vitro protein digestibility of 75.33 ± 1.00% compared to the soymilk gel induced by LAB (SL) of 80.57 ± 1.53% (p < 0.05). During the gastric digestion stage, dramatically higher (p < 0.05) soluble protein contents were observed in the SG (4.79−5.05 mg/mL) than that of SL (4.31−4.35 mg/mL). However, during the later intestinal digestion phase, the results were the opposite. At the end of the gastrointestinal digestion phase, the content of small peptides was not significantly different (p > 0.05) between the SL (2.15 ± 0.03 mg/mL) and SG (2.17 ± 0.01 mg/mL), but SL showed higher content of free amino acids (20.637 g/L) than that of SG (19.851 g/L). In general, soymilk gel induced by LAB had a higher protein bioaccessibility than the soymilk gel coagulated by GDL.

Comparative nutritional and antimicrobial analysis of Himalayan black and yellow soybean and their okara.

BACKGROUND: Soybean is believed to have good nutraceutical potential which is important for human health. Yellow soybean (YS) is generally used for the production of soymilk and other products, while black soybean (BS) is less explored. During the production of soymilk, residue, called okara is generated which is reported to have a good amount of nutrient content. Studies are generally performed with YS while BS is less explored. The present work is a comparison of the nutraceutical potential of BS and YS and their okara, mainly in terms of proximate, minerals, antinutrients, and isoflavone content and bioactivity of all types of samples in terms of antioxidant and antimicrobial activity. RESULTS: Compared to raw soybean, protein content decreased significantly in both types of okara. Phytochemicals like ascorbic acid, catechin, quercetin, and gallic acid were significantly (P < 0.05) high in BS residue in comparison to respective raw soybean. Among isoflavones, daidzin and genistin were found significantly varying among all the samples, and glycitin and glycitein were not present in YS. CONCLUSION: The nutraceutical potential and antimicrobial activity were comparative for both the raw beans and their okara, while the phytochemical contents and antioxidant activity were higher in the case of BS and its okara. © 2022 Society of Chemical Industry.

Facile synthesis of single-crystalline Fe-doped copper vanadate nanoparticles for the voltammetric monitoring of lethal hazardous fungicide carbendazim.

The highly selective and sensitive electrochemical detection of highly toxic fungicide carbendazim (CBZ) by the iron (Fe)-doped copper vanadate (CuVO4; CuV) is discussed. The Fe-doped copper vanadate (Fe-CuV) is prepared by the simple co-precipitation method followed by an annealing process which produced high crystallinity. The material properties of Fe-CuV are characterized by XRD, Raman spectrometry, XPS analysis, HRTEM, and SAED pattern. The electrochemical characterization of Fe-CuV towards CBZ detection are done by CV and DPV techniques. The Fe-CuV/GCE exhibits good electroanalytical activity towards the electro-oxidation of CBZ at the potential of 0.81 V vs Ag/AgCl. The developed sensor electrode revealed a linear range of 0.01 to 83.1 µM and a limit of detection of about 5 nM. In addition, Fe-CuV/GCE reveals good storage stability (RSD = 2.63%) and reproducibility (RSD = 2.85%) for the electro-oxidation of CBZ. The electrode material was applied to the detection of CBZ in apple juice and soy milk samples, and the results were discussed. Thus, our projected Fe-CuV/GCE can be employed as electrode material in a rapid onsite sensor for the detection and determination of noxious pollutants.

Production of Functional Buttermilk and Soymilk Using Pediococcus acidilactici BD16 (alaD+).

Functional foods or drinks prepared using lactic acid bacteria (LAB) have recently gained considerable attention because they can offer additional nutritional and health benefits. The present study aimed to develop functional drinks by the fermentation of buttermilk and soymilk preparations using the Pediococcus acidilactici BD16 (alaD+) strain expressing the L-alanine dehydrogenase enzyme. LAB fermentation was carried out for 24 h and its impact on the physicochemical and quality attributes of the fermented drinks was evaluated. Levels of total antioxidants, phenolics, flavonoids, and especially L-alanine enhanced significantly after LAB fermentation. Further, GC-MS-based metabolomic fingerprinting was performed to identify the presence of bioactive metabolites such as 1,2-benzenedicarboxylic acid, 1-dodecene, 2-aminononadecane, 3-octadecene, 4-octen-3-one, acetic acid, azanonane, benzaldehyde, benzoic acid, chloroacetic acid, colchicine, heptadecanenitrile, hexadecanal, quercetin, and triacontane, which could be accountable for the improvement of organoleptic attributes and health benefits of the drinks. Meanwhile, the levels of certain undesirable metabolites such as 1-pentadecene, 2-bromopropionic acid, 8-heptadecene, formic acid, and propionic acid, which impart bitterness, rancidity, and unpleasant odor to the fermented drinks, were reduced considerably after LAB fermentation. This study is probably the first of its kind that highlights the application of P. acidilactici BD16 (alaD+) as a starter culture candidate for the production of functional buttermilk and soymilk.

Synbiotic fermented soymilk with Weissella cibaria FB069 and xylooligosaccharides prevents proliferation in human colon cancer cells.

AIM: Studies on the anticancer effects of synbiotic fermented soymilk are rare. The aim of the present study was to evaluate the effect of synbiotic fermented soymilk supplemented with xylooligosaccharides and inoculated with Weissella cibaria FB069 (FSMXW) in the proliferation of colon cancer cell and compare it with the effect of soymilk inoculated with Lactobacillus rhamnosus GG (LGG). METHODS AND RESULTS: Both FB069 and LGG were able to grow in soy-based products and rapidly reduce their pH as a result of fermentation. The addition of XOS significantly enhanced the acidification rate, viscosity and total cell concentration in fermented soymilk inoculated with W. cibaria FB069. However, the same effect was not observed following inoculation with LGG. Moreover, the synbiotic FSMXW showed higher dextran, folate, GABA and aglycone content. FSMXW inhibited the proliferation of Caco-2 and HCT116 cell lines, by reducing the transcription of MD2, TLR4, MyD88, and NF-κb. CONCLUSIONS: The synbiotic soymilk containing XOS and W. cibaria FB069 increase nutrient and functional compounds through fermentation process. SIGNIFICANCE AND IMPACT OF THE STUDY: Our finding suggests that W. cibaria and XOS can be potentially employed in developing functional foods and health-related products.

Spectroscopy of an intrinsic fluorophore in animal and plant milk for potential identification of their quality.

Riboflavin (RF), commonly known as vitamin B2, is an essential ingredient in any milk variety of animal origin. The photophysics of the molecule RF, including its interaction with biological macromolecules, are well studied. Here, we have investigated the possibility of the molecule as a potential biomarker of milk quality. We also found omnipresence of this molecule in milk of plant origin (soy milk). Spectroscopic studies on various animal and plant milks of different commercial origins confirmed the potential of RF for use in identifying the quality of the milk varieties. Our developed strategy involved identification or spectroscopic signature of RF by measuring optical density at 365 nm (quality factor 1) and fluorescence intensity around 520 nm (excitation at 365 nm; quality factor 2) on a very small amount of whole milk (10 µL). We also developed a prototype device called Mil-Q-Way to be used in the real field. The required interfacing software in the LabView platform was also developed. A 2-parameter plot (quality factor 1 on the x-axis and quality factor 2 on the y-axis) called the Mil-Q-Way plot clearly differentiates the quality of milks of different commercial origins. The low-cost device based on simple spectroscopy was shown to screen for the presence of harmful adulterants in drinkable milk.

Valorisation of By-Products from Soybean (Glycine max (L.) Merr.) Processing.

In recent years, increased awareness of the health benefits associated with consuming soy-based foods, knowledge of milk-related allergies and a move towards more sustainable food production have led to an increase in the number of available soy-based products. The biggest producers in the world, the USA, South America and China, are from the Pacific region. This enormous production is accompanied by the accumulation of related by-products, in particular, a substance that is known as okara. Okara is a paste that is rich in fibre (50%), protein (25%), fat (10%), vitamins and trace elements. Its proper use would lead to economic advantages and a reduction in the potential for polluting the environment. Its high fibre content and low production costs mean that it could also be used as a dietary supplement to prevent diabetes, obesity and hyperlipidaemia. Chemical or enzymatic treatment, fermentation, extrusion, high pressure and micronisation can all increase the soluble fibre content, and thus improve nutritional quality and processing properties. However, the product also degrades rapidly due to its high moisture content (70-80%), which makes it difficult to handle and expensive to dry by conventional means. The aim of this paper is therefore to thoroughly study the existing literature on this subject in order to develop a general protocol for okara exploitation and valorisation. A cost/benefit analysis could drive the design of eco-friendly, sustainable protocols for the preparation of high-value nutritional products.

The contribution of milks and formulae to micronutrient intake in 1-3 years old children in urban China: a simulation study.

BACKGROUND AND OBJECTIVES: A recent dietary survey in 5 big cities in China provided information on various milk options consumed by 1-3 years old children. To investigate the nutritional role of these milks (young-child formula (YCF), cow's milk, others), simulation analyses based on this survey were performed. METHODS AND STUDY DESIGN: We studied daily intakes of calcium, iron, zinc, vitamins A, B-1, B-2, C and E and compared these to the Chinese DRIs. In Scenario 1, consumption of cow's milk, kid's milk and/or soy milk was replaced with matching amounts of YCF (n=66 children). In Scenario 2, where 348 children exclusively consumed YCF, YCF was replaced with matching amounts of cow's milk. RESULTS: Scenario 1 revealed significant increases in total dietary intakes of iron, vitamins A, B-1, C and E upon substitution of the various milks with YCF. The proportions of children not meeting the Estimated Average Requirement (EAR) for these nutrients dropped from 29, 26, 61, 53 and 54 % to 12, 11, 50, 27 and 24%, respectively. In Scenario 2, the hypothetical substitution of YCF by cow's milk increased the proportions of children not meeting the EAR for these nutrients, calcium and zinc from 11, 6, 49, 15, 28, 42, and 8 to 45, 24, 78, 69, 59, 44, and 20, respectively. Execution of Scenario 2 in subgroups of 1-2- and 2-3 years old children revealed similar results. CONCLUSIONS: YCF may help to reduce the risk of insufficient intake of several key micronutrients for toddlers, independent of age.

Impact of soymilk consumption on 2,4-dinitrofluorobenzene-induced contact hypersensitivity and gut microbiota in mice.

Soymilk is rich in phytochemicals such as soy isoflavones (SIs) and soyasaponins (SSs). Dietary SIs and SSs display inhibitory effects on contact hypersensitivity (CHS), which was reported in a mouse model for allergic contact dermatitis (ACD); however, the beneficial effects of soymilk consumption on CHS remain unknown. Here, we studied the effects of drinking soymilk on CHS and gut microbiota. Soymilk consumption attenuated ear oedema and swelling, decreased the infiltration of Gr-1-positive cells into ear tissues, and reduced the production of chemokine (C-X-C motif) ligand 2 and triggering receptor expressed on myeloid cells-1 in ear tissues. The analysis of bacterial 16S ribosomal RNA gene sequences indicated that CHS caused changes in the gut microbiota structure and that consuming soymilk reduced these changes. These results suggest that soymilk consumption may be of therapeutic value for patients with ACD and may help control the balance of intestinal microbiota.

Erosive potential of soy-based beverages on dental enamel.

BACKGROUND: This study aimed to investigate the erosive potential of soy-based beverages in comparison to fruit juices of the same flavor. METHODS: Human enamel blocks were randomly divided into 9 groups (n = 8), according to the beverage category (soy or non-soy juices). The initial pH, TA and ß at the original pH value were measured in triplicate. The composition of calcium, phosphate and total protein was analyzed using the specific colorimetric method. The fluoride analysis was performed using a selective electrode. The degree of saturation (DS) and the critical pH (CpH) of each beverage with respect to hydroxyapatite (HAp) and fluorapatite (FAp) were calculated using the computational software. Enamel samples were immersed into 67.5 mL of each drink for 120 minutes. Enamel surface loss (ESL) and differences in surface roughness (ΔRaE-S) were analyzed by a 3D non-contact profilometer. RESULTS: Non-soy beverages exhibited the lowest pH values (2.93 to 3.40). The highest values of calcium concentration were founded in soy-based formulations. Juices with soy in their composition tend to have high DS when compared with non-soy based beverages (p = .0571). Soy beverages produced less ESL than non-soy beverages (p < .05). ΔRaE-S was not significantly different between the categories. The ESL and ΔRaE-S were positively correlated with initial pH and buffering capacity in soy-based beverages. On the other hand, in non-soy beverages, the ESL was negatively correlated with the TA to 7.0 and the fluoride composition whereas the ΔRaE-S was negatively correlated with the TA to 5.5. CONCLUSIONS: The erosive potential of soy beverages was lower than non-soy based beverages.

Physical, mechanical and water barrier properties of yuba films incorporated with various types of additives.

BACKGROUND: To apply yuba as an edible film, we evaluated film properties after adding various additives, including plasticizer (glycerol and sorbitol), cross-linking agent (oxidized ferulic acid), emulsifier (sodium pyrophosphate), thicker (sodium carboxymethyl cellulose) and lipid (beeswax), alone or in combination (sodium pyrophosphate and sorbitol; sodium carboxymethyl cellulose and glycerol; and beeswax and glycerol). RESULTS: The addition of beeswax and oxidized ferulic acid enhanced the water resistance of the film, showing a decreased solubility in water and swelling ratio. The results for tensile strength and elongation showed opposite trends, except for sorbitol, sodium pyrophosphate, and sodium carboxymethyl cellulose and glycerol. Tensile strength of sodium carboxymethyl cellulose (9.3 MPa) was increased compared to that of yuba without additive (3.5 MPa). Elongation was increased in glycerol (132%) compared to that in the control (8%). Water vapor permeability decreased in all samples by 0.7 to 8 times compared to that of the control. X-ray diffraction analysis found that blending additives influenced the crystalline degree and second structure of the film. Atomic force microscopy revealed that the control (37 nm) and sodium carboxymethyl cellulose and glycerol (47 nm) exhibited smooth surface and lower roughness values compared to glycerol (84 nm) and sodium carboxymethyl cellulose and glycerol (87 nm). CONCLUSION: Our results confirmed that yuba could be used as edible film with a wide range of applications depending on types of additive and purpose of use. The results of the present study revealed that sodium carboxymethyl cellulose and glycerol-added yuba film had exceptional edible film properties, including water resistance, elongation and water vapor permeability based on principal component analysis. © 2018 Society of Chemical Industry.

Application of a clean-up procedure using a ternary liquid phase system combined with pre-concentration by microextraction in the analysis of seven pesticides from soya milk.

BACKGROUND: A method has been developed based on a three-phase system, followed by dispersive liquid-liquid microextraction for the extraction of seven pesticides from soya milk prior to analysis by gas chromatography-flame ionization detection. The base of this method is the different extraction capability of the components of soya milk according to each of the phases involved. In this procedure, a homogeneous solution consisting of soya milk and a water-miscible solvent (acetonitrile) is separated into two phases in the presence of Na2 SO4 and the analytes are extracted into the produced acetonitrile droplets. The acetonitrile phase is mixed with a pre-concentration solvent to perform the next microextraction procedure for further enrichment of the analytes. RESULTS: Limits of detection and quantification were reached in the ranges of 0.11-0.35 and 0.35-1.20 µg L-1 , respectively. Enrichment factors and extraction recoveries were in the ranges of 562-933 and 56-93%, respectively. Relative standard deviations were ≤7% for intra- (n = 6) and inter-day (n = 5) precisions at two concentrations of 10 and 50 µg L-1 of each analyte. CONCLUSION: The proposed method was applied to the analysis of pesticides in soya milk samples at µg L-1 concentrations. © 2019 Society of Chemical Industry.

Cross-linked α-galactosidase aggregates: optimization, characterization and application in the hydrolysis of raffinose-type oligosaccharides in soymilk.

BACKGROUND: Cross-linked enzyme aggregates (CLEAs) of α-galactosidase, partially purified from maize (Zea mays) flour, were prepared. The impact of various parameters on enzyme activity was examined to optimize the immobilization procedure. Biochemical characterization of the free and immobilized enzyme was carried out. Stability (thermal, pH, storage and operational stability) and reusability tests were performed. The potential use of the free enzyme and the CLEAs in hydrolysis processes of raffinose-type oligosaccharides present in soymilk was investigated. RESULTS: α-galactosidase CLEAs were prepared with 47% activity recovery under optimum conditions [1:5 (v/v) enzyme solution:saturated ammonium sulfate solution ratio; 7.5 mg protein and 0.1% (v/v) glutaraldehyde, 6 h, 4 °C, 150 rpm]. α-galactosidase CLEAs exhibited increased stability in comparison to the free enzyme. The CLEAs and the free enzyme showed a maximum activity at 40°C and their optimal pH values were5.5 and 6.0, respectively. Kinetic constants (KM , Vmax and kcat ) were calculated for the free enzyme and the CLEAs in the presence of p-nitrophenyl-α-d-galactopyranoside, stachyose, melibiose and raffinose. The effect of various chemicals and sugars on enzyme activity showed that both enzyme forms were significantly inhibited by HgCl2 and galactose. The CLEAs hydrolyzed 85% of raffinose and 96% of stachyose. CONCLUSION: The α-galactosidase CLEAs, with their satisfactory enzymatic characteristics, have much potential for use in the food and feed industry. © 2019 Society of Chemical Industry.

Does lactic fermentation influence soy yogurt protein digestibility: a comparative study between soymilk and soy yogurt at different pH.

BACKGROUND: Lactic acid bacteria fermentation allows soymilk to form a yogurt-like product accompanied by protein acidic coagulation. It is not known whether the coagulation of soy protein during fermentation influences protein digestibility when ingested. In the present study, soymilk (pH 6.3) and soy yogurt (SY) at different pH (6.0, 5.7, 5.4 and 5.1) were subjected to in vitro gastrointestinal digestion (GIS) and a comparison study was conducted. RESULTS: Lactic fermentation allowed the pH of soymilk to reduce gradually to 5.1 in 330.0 min. A decline in pH resulted in the volume-weighted mean diameters D[4,3] and D[v,90] increasing from 0.81 to 97 µm and 1.82 to 273 µm, respectively. Predominant proteins lost their solubility between pH 6.0 and 5.7. Application of GIS allowed SY samples, especially SY-5.7, SY-5.4 and SY-5.1, to reveal particles with a predominant peak at approximately 10 µm and also lower soluble proteins compared to soymilk, with reduction percentages of 18%, 28% and 43%. The cleavage pattern of soy protein during GIS was scarcely affected by the sample pH. However, a lower quantity of the band at 33.9 kDa was found in SY-5.7, SY-5.4 and SY-5.1. CONCLUSION: The results of the present study demonstrate that lactic fermentation altered soy protein digestibility. With the process of protein coagulation, SY-5.7, 5.4 and 5.1 had a lower bioaccessible protein content compared to that of soymilk. © 2018 Society of Chemical Industry.

Effect of transglutaminase on rennet-induced gelation of skim milk and soymilk mixtures.

BACKGROUND: Protein gels made from cow milk and soymilk can yield products of exceptional value. Transglutaminase (TG) affect rennet-induced gelation of proteins, and improves the functionality of the final products. In this paper, TG and rennet were added to skim milk and soymilk mixtures simultaneously, and the rennet-induced coagulation was studied. Diffusing wave spectroscopy and rheology measurements were used to access the structural changes of the mixtures during renneting. Syneresis analysis and microscopy can give more information for understanding the system. RESULTS: Soymilk and TG have synergetic effects and inhibit rennet-induced gelation to a certain degree. With increasing soymilk and TG, elastic index and storage modulus decreased, gelation time was delayed, and curd yield and moisture content increased. At excess soymilk and TG, no curds can be formed. There were significant effects of soymilk and TG on curd microstructure. Soymilk inhibited the aggregation of casein micelles and contributed to more coarse and heterogeneous networks. TG limited reorganization of the proteins, leading to more homogenous networks with small pores. CONCLUSION: The use of soymilk and TG simultaneously impair rennet-induced gelation and curd syneresis, and consequently lead to a higher yield of high-moisture curd. © 2018 Society of Chemical Industry.