Effect of Enzymatic Protein Deamidation on Protein Solubility and Flavor Binding Properties of Soymilk

Abstract: The effect of enzymatic deamidation by protein‐glutaminase (PG) on protein solubility and flavor binding potential of soymilk was studied. Treatment of soymilk with PG for 2 h (temperature of 44 °C and enzyme:substrate ratio (E/S) of 40 U/g protein) resulted in high degree of protein deamidation (66.4% DD) and relatively low degree of protein hydrolysis (4.25% DH). Deamidated (DSM) and control soymilks (CSM) did not differ with respect to aroma, but differed in taste characteristics by sensory evaluation. Protein solubility in DSM was enhanced at weakly acidic conditions (pH 5.0), but did not differ from non‐deamidated soymilk at pH values of 3.0 and 7.0. Odor detection thresholds for the flavor compounds vanillin and maltol were approximately 5 and 3 fold lower, respectively, in DSM than in CSM. Dose‐response curves (Fechner's law plots and n exponents from Stevens's power law) further demonstrated that DSM had a lower flavor binding potential than CSM. PG deamidation has the potential to reduce flavor binding problems encountered in high protein‐containing foods and beverages. Practical Application: The findings of this study can help lead to the development of technology to produce protein‐containing foods with improved functional properties, especially protein solubility, and potentially decreased flavor fade problems associated with flavor‐protein interactions, especially with carbonyl containing flavor compounds.     

CHANGES IN SOYMILK QUALITY AS A FUNCTION OF COMPOSITION AND STORAGE

ABSTRACT

Three soymilk products formulated with different concentrations of fat, sugar and starch were evaluated for changes in their physical properties and volatiles profile over time (3 months) under different temperatures (4, 22 and 38C) of storage. Samples were tested for pH, color, viscosity and volatile flavor changes. The pH and color of the soymilks decreased significantly during the first month of storage and then remained stable over time. Color and viscosity of the soymilk products were affected by both the soymilk composition and storage treatment. The high‐fat soymilk sample (product C) had the whitest color (lower ΔE) and the lowest viscosity. Storage at 38C negatively affected the color. The viscosities of the soymilk products stored at 4C were the lowest among the treatments. The major volatiles identified in all soymilk products were hexanal, heptanal, octanal, nonanal, hexanol, 1‐octen‐3‐ol, benzaldehyde, 2‐pentyl furan and 2‐ethyl furan. The intensities of the volatile compounds in the soymilk products increased during the first weeks of storage, particularly when stored at 38C. The intensities, however, decreased gradually over time. Among the three formulated soymilk products, the sweetened sample (product B) gave the lowest flavor intensities under all three temperatures of storage. Overall, storage at 4C and addition of sugar preserve best the soymilk quality.

PRACTICAL APPLICATIONS

Soy products are well appreciated for their nutritional and potential health benefits. Soy beverage consumption is increasing among North American consumers because of improvements in soy beverage quality and processing technologies. There is, however, a demand for new value‐added soy‐based drinks with improved “functional” (health‐benefiting) properties. Soy beverage could be an excellent carrier for “functional” or “nutritive” ingredients such as minerals, vitamins and omega 3 oils; however, addition of such ingredients may affect the stability of the product and requires the development appropriate of technologies for their incorporation. Results from this project provide new knowledge on the storage stability and quality of three different soy product formulations. The information could be useful in the establishment of optimal conditions for processing of functional soy beverages, for use by the food industry.

     

Effect of Soybean Varieties and Growing Locations on the Physical and Chemical Properties of Soymilk and Tofu

ABSTRACT: Soybean varieties and growing location greatly affected the protein content and color of soymilk and the protein content and yield of tofu ( P < 0.05). Protein content of soybeans was the most important affecting factor for the qualities of soymilk and tofu. There were significant correlations between the protein contents of soybeans and soymilks ( P < 0.05). There were also significant correlation between the soybean protein and the total solid content of soymilk (P < 0.05). Tofu moisture content had significant effect on the hardness and yield of tofu (P < 0.05). The correlation between soybean protein and tofu yield was significant at P < 0.05. The protein content and yield of tofu can be predicted by analyzing soybean protein.     

Preference Mapping of Soymilk with Different U.S. Consumers

This study determined and compared drivers of liking for unflavored soymilk with different U.S. consumer groups. A highly trained panel documented appearance, mouthfeel and flavor attributes of 26 commercial soymilks. Twelve representative soymilks were then selected for evaluation by consumers from 3 age/cultural categories (n = 75 each category; Caucasian/African American females aged 18 to 30 y; Asian females aged 18 to 30 y; Caucasian/African American females aged 40 to 64 y). Consumers evaluated overall liking and liking and intensity of specific attributes. Results were evaluated by analysis of variance, followed by internal and external preference mapping. Age had no effect on overall liking, while ethnicity did (Caucasian/African American compared with Asian; P < 0.05). Caucasians/African Americans differentiated soymilks more than Asians and assigned a wider range of liking scores than Asians (2.1 to 7.2 compared with 4.0 to 6.1). Three consumer clusters were identified. Sweet taste with vanilla/vanillin and sweet aromatic flavors and higher viscosity were preferred by most consumers and differences between consumer clusters were primarily in drivers of dislike. Drivers of dislike were not identified for Cluster 1 consumers while Clusters 2 and 3 consumers (n = 84, n = 80) disliked beany, green/grassy and meaty/brothy flavors and astringency. Cluster 3 (n = 80) consumers scored all soymilks higher in liking (P < 0.05) than Cluster 2 consumers, and were willing to overlook disliked attributes with the addition of sweet taste, whereas the Cluster 2 consumers were not. These findings can be utilized to produce soymilks with attributes that are well liked by target consumers and to tailor attributes for segments of the population that have not yet been accommodated.     

Soymilk treated by ultra high-pressure homogenization: Acid coagulation properties and characteristics of a soy-yogurt product

The effects of ultra high-pressure homogenization (UHPH) on soymilk were investigated and its suitability for soy-yogurt manufacturing was compared with conventional heat treatments (UHT and autoclaved). UHPH soymilk at 40 and 50 °C inlet temperature was treated at 200 and 300 MPa. Coagulation parameters and acidification curves were determined for the fermentation process. Textural parameters, water-holding capacity and microstructure were performed on soy-yogurts obtained after cold storage during 24 h. Results indicated that conventionally heat-treated soymilks and UHPH-treated samples exhibited different behaviour to coagulation. Heat-treated soymilk had a shorter onset of gelation, and higher aggregation rate and gel network density than UHPH-treated soymilk. However, physical quality parameters, specially firmness, were much better in UHPH than in conventional heat-treated soy-yogurts.     

Alleviation effect of heat-treated and in vitro gastrointestinal digested soymilks on AAPH-induced oxidative stress in human erythrocytes: Digested soymilks alleviate oxidative stress

To investigate the potential protective effect of raw and heat-treated soymilks after gastrointestinal digestion against chemical oxidative stress induced by 2,2′-azobis(2-amidinopropane) dihydrochloride (AAPH) on human erythrocytes, soymilk was subjected to heat treatment and in vitro gastrointestinal digestion. The inhibition rate of hemolysis, generation of reactive oxygen species (ROS), concentration of malondialdehyde (MDA), reduced glutathione (GSH) and oxidized glutathione (GSSH) and the enzyme activity of total superoxide dismutase (SOD) and cellular glutathione peroxidase (GPx) were evaluated as the biomarkers of oxidative status. Hemolysis of erythrocytes induced by AAPH was significantly inhibited by pretreatment with the digested raw soymilk (DRS) and digested heat-treated soymilk (DHS). Moreover, heat treatment prior to gastrointestinal digestion improved the inhibition effect of soymilk on erythrocytes hemolysis. The soymilk treated at 95 °C showed the highest inhibition rate, followed by 121 °C and 143 °C, revealed that the increase of temperature caused the decrease of hemolysis inhibition rate of DHS. Preincubation with the digested soymilks reduced the accumulation of MDA in erythrocytes, indicating the inhibition effect of the digested soymilks on lipid peroxidation. Results revealed that DRS and DHS alleviated the hemolysis of erythrocytes and lipid peroxidation resulted from oxidative stress by suppressing the accumulation of ROS, reducing the increase of SOD activity and decrease of non-enzymatic antioxidant GSH and enzymatic antioxidant GPx activity. Compared with raw soymilk, heat treatment improved the protective effect of the digested soymilk on erythrocytes against oxidative stress via enhancing the free radicals scavenging activity instead of improving the inhibition effect on the generation of free radicals.     

Sterilization and aseptic packaging of soymilk treated by ultra high pressure homogenization

Ultra high pressure homogenization (UHPH) was applied on soymilk to produce an aseptically packaged beverage. UHPH-treated soymilk (300 MPa, 80 °C inlet temperature and 144 °C/0.7 s at the homogenization valve) was compared with samples treated by ultra high temperature (UHT) at 142 °C for 6 s. After treatment, soymilk samples were aseptically packaged in coated paperboard cartons of 200 mL Tetra Brik containers. Tetra Brik containers were stored for 6 months at room temperature and analyzed at different days. Microbiological (total mesophilic aerobic bacteria, aerobic spores, Bacillus cereus, and enterobacteria counts), physical (dispersion stability and particle size distribution), chemical (hydroperoxide index and volatile profile evolution) and sensory analyses were performed on soymilks. Both UHPH and UHT soymilks did not present microbiological growth during storage. UHPH soymilk presented high colloidal stability and relevant decrease in hydroperoxide index during storage. On the other hand, almost all of the compounds associated to off-flavors were detected in the volatile profile of soymilk. Sensory results indicated that UHPH treatment did not produce changes in soymilk which could affect the panel perception for different UHT and UHPH soymilks and for selecting their preference.Industrial relevanceSoymilk constitutes one of the food industry sectors with the highest worldwide growth and its consumption has experienced a noticeable increase in the last years. The growing consumer demand for safe products, environmentally friendly processes and high quality nutritional foods has challenged the food industry to adapt the technological processes. This tendency impacts directly on traditional technologies, like heat treatments. In this sense, UHPH technology has been applied as an alternative to those thermal treatments. This research paper presents a comparative study between soymilk treated by UHPH and by UHT to produce a product stored at room temperature for 6 months. Results showed stable levels of oxidation, high physical stability, no microbial growth and a positive trend of sensory response during the period analyzed for UHPH soymilk. Moreover, the UHPH system was designed to work at continuous flow, allowing its application in several industrial food processes.     

Effects of Processing on Curd Yield and Nutrient Composition of Rapid Hydration Hydrothermal Cooking and Traditionally Processed Soymilk and Soybean Curd

Soymilk processed by the Rapid Hydration Hydrothermal Cooking (RHHTC) method had higher thiamin and protein when compared to traditionally extracted soymilk (P<0.0001). Traditionally processed soybean curd had higher protein (P < 0.0001) and fat (P < 0.001) while carbohydrate and ash were lower (P<0.0001) when compared to RHHTC produced soybean curd. Variation in amino acid compositions occurred in soymilks and soybean curds. RHHTC-produced soybean curd had greater curd yields than traditionally produced soybean curd.     

Comparison of ultra high pressure homogenization and conventional thermal treatments on the microbiological,physical and chemical quality of soymilk

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa in combination with different inlet temperatures (55, 65 and 75 °C) on soymilk was studied. UHPH-treated soymilk was compared with the base product (untreated), with pasteurized (95 °C for 30 s) and with ultra high temperature (UHT; 142 °C for 6 s) treated soymilks. Microbiological (total aerobic meshophilic bacteria, aerobic spores, and Bacillus cereus), physical (dispersion stability and particle size distribution) and chemical (lipoxygenase activity, hydroperoxide index and trypsin inhibitor activity) parameters of special relevance in soymilk were studied. Microbiological results showed that pressure and inlet temperature combination had a significant impact on the lethal effect of UHPH treatment. While most of UHPH treatments applied produced high quality of soymilks better than that pasteurized, the combination of 300 MPa and 75 °C produced a commercially sterile soymilk. UHPH treatments caused a significant decrease in particle size resulting in a high physical stability of samples compared with conventional heat treatments. UHPH treatment produced lower values of hydroperoxide index than heat treated soymilks although trypsin inhibitor activity was lower in UHT-treated products.     

Feasibility of using dialysis for determining calcium ion concentration and pH in calcium-fortified soymilk at high temperature

Abstract: Dialysis was performed to examine some of the properties of the soluble phase of calcium (Ca) fortified soymilk at high temperatures. Dialysates were obtained while heating soymilk at temperatures of 80 and 100 °C for 1 h and 121 °C for 15 min. It was found that the pH, total Ca, and ionic Ca of dialysates obtained at high temperature were all lower than in their corresponding nonheated Ca‐fortified soymilk. Increasing temperature from 80 to 100 °C hardly affected Ca ion concentration ([Ca²⁺]) of dialysate obtained from Ca chloride‐fortified soymilk, but it increased [Ca²⁺] in dialysates of Ca gluconate‐fortified soymilk and Ca lactate‐fortified soymilk fortified with 5 to 6 mM Ca. Dialysates obtained at 100 °C had lower pH than dialysate prepared at 80 °C. Higher Ca additions to soymilk caused a significant (P≤ 0.05) reduction in pH and an increase in [Ca²⁺] of these dialysates. When soymilk was dialyzed at 121 °C, pH, total Ca, and ionic Ca were further reduced. Freezing point depression (FPD) of dialysates increased as temperature increased but were lower than corresponding soymilk samples. This approach provides a means of estimating pH and ionic Ca in soymilks at high temperatures, in order to better understand their combined role on soymilk coagulation.     

Ultra high pressure homogenization of soymilk: Microbiological,physicochemical and microstructural characteristics

The effect of ultra high pressure homogenization (UHPH) at 200 and 300 MPa on soymilk was studied. A soymilk base product (BP) and ultra high temperature (UHT) treated soymilk were compared with UHPH treated soymilk. UHPH at 200 and 300 MPa reduced initial counts, spores and enterobacteria counts. Particle size analysis evidenced the intense reduction of particle size caused by UHPH, although the formation of aggregates was detected at 300 MPa. Colour differences between UHPH and BP or UHT soymilks were found. Treated soymilk (300 MPa) showed the lowest values of L¹, a¹ and b¹ coordinates. UHPH processed samples were more stable (showed less particle settling) than BP and UHT soymilks and these differences were also observed at days 30 and 60 of storage at 4 °C. Differential scanning calorimetry analysis indicated that soymilk proteins were partially denatured by 200 MPa, whereas UHPH treatment at 300 MPa showed the same extent of denaturation as UHT soymilk. Images of transmission electron microscopy showed the distribution and general characteristics of the colloidal particles and structures of UHPH, BP and UHT which were generally in accordance with the physicochemical parameters studied.     

Physicochemical and Sensory Properties of Soymilk-incorporated Bulgur

ABSTRACT Bulgur cooked in soymilk of 6% and 9% solid content had significantly ( P < 0.05) higher bulk density compared with bulgur cooked in soymilk of 3% solid content and control bulgur cooked in water. As the soymilk solid content increased, pilav bulgur yield increased whereas fine bulgur yield decreased. The SDS-extractability of bulgur proteins increases with the increase in soymilk solid content. Water absorption capacity of fine bulgur samples was affected by soymilk incorporation, and variations in oil absorption capacity were not significant ( P > 0.05). Soymilk incorporation improved color and sensory properties of pilav and fine bulgur. The results of this study suggest that soymilk can be successfully applied to bulgur production.     

Microbiological,physicochemical and rheological properties of fermented soymilk produced with exopolysaccharide (EPS) producing lactic acid bacteria strains

Growth of Lactobacillus plantarum 70810, Lactobacillus rhamnosus 6005 and a commercial yogurt starter culture in soymilk was investigated in the present study. It was found that the fermented soymilk using L. plantarum 70810 had significantly higher viable cell counts, water holding capacity (WHC, 88.27%), apparent viscosity (1840.35 mPa s) and exopolysaccharide (EPS) amount (832.15 mg/L) than the other two starter cultures in soymilk. Direct observation of microstructure in fermented soymilk indicated that the network structures of EPS-protein could improve the texture of fermented soymilk. Considering that the beneficial effects of L. plantarum 70810 in fermented soymilk, volatile compounds in fermented soymilk were further identified. Then the growth and fermentation characteristics of L. plantarum 70810 including changes in viable cell counts, pH, titratable acidity, apparent viscosity and EPS production during storage were investigated. In comparison to original soymilk base, the concentrations of the characteristic flavor compounds for fermented soymilk using L. plantarum 70810 increased, whereas hexanal, 2-pentylfuran and 2-pentanone in relation to beany flavor of soymilk decreased. In addition, fermented soymilk using L. plantarum 70810 maintained high viable cell count (>10⁸ cfu/mL), apparent viscosity (966.43 mPa s) and amounts of EPS (635.49 mg/mL) during storage at 4 °C for 21 days.     

Chemical Characteristics of Low-Fat Soymilk Prepared by Low-Speed Centrifugal Fractionation of the Raw Soymilk

Abstract: Large oil–protein particles (2 to 60 μm) were found in raw soymilk (or water extract of soybean), which was prepared in specific conditions. The large particles could be separated by sedimentation by centrifuging raw soymilk for 5 to 30 min at a low gravitational force ranging from 96 to 2410 × g. Chemical analysis showed that 80% to 90% of the total lipids and 30% to 40% of the total proteins were located in the precipitated fraction. The supernatant fraction had a dramatically higher protein-to-lipid ratio than the whole soymilk. The ratio of 11S/7S proteins and the ratio of 11S acidic/basic subunits were significantly (P < 0.05) higher in the precipitate than that either in the whole soymilk or in the supernatant. Besides centrifuging conditions, other factors, including soymilk concentration, grinding method, soybean variety, and soybean storage, also significantly (P < 0.05) affected the centrifugal fractionation. This study showed that low-speed centrifugation facilitated the separation of oil-protein particles from raw soymilk, and can be used as an innovative method for preparing low-fat soymilk and 11S protein-enriched ingredients. The findings also increased our understanding of the association or aggregation between proteins and lipids in raw soymilk after grinding. Practical Application: Soymilk has become a popular beverage in the Western world due to its health benefits. Consumer demands for low-fat and organic foods have been increasing in the recent years. Currently, there are no alternative methods for manufacturing low-fat soymilk from whole soybeans. We found that most, if not all, of lipids in the raw soymilk were located in large particles, which could be separated by low-speed centrifugation. This centrifugal fractionation was investigated by varying processing parameters, soybean varieties, and soybean storage conditions. The approach has potential to be used for manufacturing low-fat soymilk. This study also has increased our understanding of the interactions between lipid and protein in raw soymilk.     

The properties and the related protein behaviors of oil bodies in soymilk preparation

Oil bodies (OBs), one of the major components of soymilk, are very important for the properties of soymilk and its related products. In this study, the properties and the related protein behaviors of OBs in the soymilk preparation were systematically examined. Raw soymilk OBs could keep their natural integrities after grinding, and they were bound by many soybean proteins (mainly β-conglycinin, glycinin, and Gly m Bd 30K) that could be removed by pH 11.0 washing. Heated soymilk OBs, including heat-induced coalesced OBs (>1 μm) and modified OBs (around 400 nm), were strongly bound by β-conglycinin and glycinin that even could not be removed by pH 11.0 washing. The oleosins (24 kDa, P29530 and P29531; 18 kDa, C3VHQ8) of raw soymilk OBs were hydrolyzed to 16 kDa polypeptides (on SDS–PAGE gel) when exposed to room temperature, while immediately heating, the raw soymilk could prevent the oleosin hydrolysis. Then, the isolated raw and heated soymilk OBs revealed different dispersion stabilities as a function of pH. At last, tofu curds were made from two reconstituted soymilks containing non-lipid soymilk and raw or heated soymilk OBs (pH 11.0 isolation), and one trend was found that tofu curds containing heated soymilk OBs had lower breaking stress and Young’s modulus than those containing raw soymilk OBs. It is considered that this study is meaningful for designing new strategies to improve the qualities of soymilk and its related products.     

Evaluation of enzymic potential for biotransformation of isoflavone phytoestrogen in soymilk by Bifidobacterium animalis,Lactobacillus acidophilus and Lactobacillus casei

Three strains of Lactobacillus acidophilus, two of Lactobacillus casei and one of Bifidobacterium were screened for β-glucosidase activity using ρ-nitrophenyl-β-d-glucopyranoside as a substrate and their potential for the breakdown of isoflavone glucosides to the biologically active aglycones in soymilk. Isoflavones quantification with HPLC and β-glucosidase activity were performed after 0, 12, 24, 36, and 48 h of incubation in soymilk at 37 °C. All six micro-organisms produced β-glucosidase, which hydrolysed the predominant isoflavone β-glucosides. There was a significant increase and decrease (P < 0.05) in the concentration of isoflavone aglycones and glucosides, respectively, in fermented soymilk. Based on the concentration of isoflavones during peak β-glucosidase activity, the hydrolytic potential was calculated. L. acidophilus 4461 had the highest aglycone concentration of 76.9% after 24 h of incubation, up from 8% in unfermented soymilk (at 0 h). It also had the best isoflavone hydrolytic index of 2.01, signifying its importance in altering the biological activity of soymilk.