Progress 01/01/16 to 12/31/20
Outputs
Target Audience:Scientific community and the food industry. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Four graduate students were financially supported throughout the entire project. How have the results been disseminated to communities of interest?Five papers (including two new papers in 2020) have been published in high impact factor journals. Two other papers have been submitted, one of which is under revision. Another paper has been prepared for submission. In addition, the project has resulted in seven poster presentations at the annual meetings of the Institute of Food Technologists in 2018-2020 and one oral presentation at the annual meeting of American Dairy Science Association in 2019. The project also resulted in one MS thesis, as well as a dissertation expected in 2021. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
In completion of the project, we reduced the turbidity and improved the stability of skim milk powder (SMP) dispersions and studied fundamental physicochemical properties leading to the improved functionalities in Objective 1, and the findings in Objective 1 were used to prepare nonfat dry milk (NFDM)-based model beverages with neutral and acidic pH for evaluation of physicochemical properties in Objective 2 and flavor profile and sensory properties in Objective 3 during 10-week storage at refrigerated and ambient storages. Detailed results can be found in annual progress reports and publications, and a synopsis of project findings is presented below. Our project may expand the use of casein-containing dairy ingredients in the growing functional beverages sector. In Objective 1, different strategies were studied for dispersions at pH 6.8, pH 4.5, and pH 3.0 and below that represent distinctly different properties of casein micelles. At pH 6.8, reduction of SMP dispersion turbidity was enabled with food-grade chelating agents that resulted in dissociation of casein micelles and therefore the reduced dispersion turbidity. The turbidity, dimension and morphology, and ionic composition of 5% w/v SMP dispersions added with 0-30 mM sodium tripolyphosphate, trisodium citrate, or sodium hexametaphosphate (SHMP) were studied before and heating at 90 ºC for 5 min. An intermediate chelator concentration resulted in the smallest particle dimension and the lowest turbidity of dispersions, and heating overall reduced the particle dimension but increased the turbidity of some dispersions. At the same molar concentration, SHMP was the most effective in reducing dispersion turbidity and resulted in the most stable dispersion turbidity after heating. At pH 4.5, nearby the isoelectric point of caseins, three anionic polysaccharides were studied to stabilize caseins against aggregation and precipitation. The dispersion turbidity was further reduced with a pH-cycle treatment, by first alkalizing dispersion pH from neutral to 11.30 to dissociate casein micelles, followed by acidification to pH 4.5 during which polysaccharide-casein nanocomplexes formed. Structures and mechanisms leading to the reduced dispersion turbidity and the improved dispersion stability were studied. Propylene glycol alginate stabilized caseins by forming both covalent conjugates and non-covalent nanocomplexes. Dextran sulfate chelated calcium in casein micelles and formed nanocomplexes with casein in the core and polysaccharide on the shell. The core-shell type nanocomplexes were also the case for carboxymethylcellulose (CMC), and the higher density of chelating carboxylate groups of CMC reduced the dispersion particle dimension and turbidity to a greater extent and improved the stability of dispersions at increased ionic strengths. The polysaccharide on nanocomplexes enabled the stability against aggregation at pH 4.5. At pH 3.0 and below, translucent dispersions with 5% w/v SMP were observed after direct acidification with citric acid and heating. A lower dispersion turbidity was observed at a lower pH. The clarity of dispersions was further affected by the heating temperature and duration. Gluconic acid was additionally studied as a more effective chelating agent than citric acid in dissociating casein micelles, and the dispersion acidified with gluconic acid was clearer than those acidified with citric acid and hydrochloric acid. The macroscopic dispersion appearance was supported by quantitative turbidity, particle dimension, and electron microscopy structures. Three batches of lemon-flavored beverages with 5% and 7.5% w/w NFDM acidified to pH 2.5 and neutral pH vanilla beverages with 5% or 10% w/w NFDM, 0 (control) or 0.43% w/w SHMP were produced to study physicochemical properties and shelf-sterility in Objective 2 and volatile profiles, descriptive sensory analysis, and consumer panels in Objective 3 during 10-week storage at 4 °C or room temperature (RT, 21 °C). Sterility was observed at the formulation and thermal treatment conditions used for all beverages. Before storage, physicochemical properties of model beverages showed the similar trends as those in Objective 1 when comparing to the controls. For neutral vanilla beverages, the turbidity was stable during storage at 4°C but increased when stored at RT. The increase in viscosity during storage was insignificant for the 5% NFDM beverage with SHMP, but was significant for the 10% NFDM beverage with SHMP. Additionally, the 10% NFDM beverage with SHMP became a gel during storage at RT but remained fluidic at 4°C. The heat treatment used to manufacture vanilla beverages reduced the abundance of volatiles. Beverages with SHMP had a low soapy flavor and salty taste but had no apparent differences in other sensory attributes when compared to the control without SHMP. The vanilla and milky flavor of neutral beverages decreased after 70-day refrigerated storage. For the lemon-flavored acidic beverages, the beverage with 5% NFDM had higher aroma and lemon flavor than the 7.5% one, although the same volatile compounds were observed in the two beverages, and the flavor intensity decreased after refrigerated storage. Similar to neutral vanilla beverages, physicochemical properties were more stable for acidic beverages during 70-day storage at 4°C than at RT. The acidic beverage with 7.5% NFDM was gel-like and, despite being infeasible for use as drinks, could be used to provide satiety. For both groups of beverages, the reduced turbidity of beverages was not appreciated by consumer panels, pointing to the need of prior education of consumers when developing such beverages.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2021
Citation:
Choi, I. and Q. Zhong. 2020. Gluconic acid as a chelator to improve clarity of skim milk powder dispersions at pH 3.0. Food Chemistry. 344: 128639. DOI: 10.1016/j.foodchem.2020.128639.
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2021
Citation:
Li, N., I. Choi, J. Vuia-Riser, B. Carter, M. Drake, and Q. Zhong.* 202x. Physicochemical and sensory properties of lemon-flavored acidic beverages formulated with nonfat dry milk during storage. Drafted.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Choi, I., N. Li, J. Vuia-Riser, B. Carter, M. Drake, and Q. Zhong. (2020). Neutral skim milk powder beverages with turbidity reduced by sodium hexametaphosphate: Physicochemical properties during storage. The 2020 IFT Annual Meeting & Food Expo, July 13-15, Chicago, IL (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Li, N., I. Choi, J. Vuia-Riser, B.G. Carter, M. Drake, Q. Zhong. 2020. Storage stability of acidic protein beverage formulated with skim milk powder. The 2020 IFT Annual Meeting & Food Expo, July 12-15 (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Li, N., and Q. Zhong. 2020. Effects of carboxymethylcellulose charge density on the formation of nanocomplexes with casein micelles stable at pH 4.5. The 2020 IFT Annual Meeting & Food Expo. July 12-15, Chicago, IL (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Li, N., and Q. Zhong. 2020. Casein core-polysaccharide shell nanocomplexes stable at pH 4.5 enabled by chelating and complexation properties of dextran sulfate. The 2020 IFT Annual Meeting & Food Expo. July 12-15, Chicago, IL (poster presentation).
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Choi, I. and Q. Zhong. 2020. Physicochemical properties of skim milk powder dispersions prepared with calcium-chelating sodium tripolyphosphate, trisodium citrate, and sodium hexametaphosphate. Journal of Dairy Science. 103(11): 9868-9880. DOI: 10.3168/jds.2020-18644.
- Type:
Journal Articles
Status:
Accepted
Year Published:
2021
Citation:
Li, N. and Q. Zhong. 2021. Effects of polysaccharide charge density on the structure and stability of carboxymethylcellulose-casein nanocomplexes at pH 4.5 prepared with and without a pH-cycle. Food Hydrocolloids. Accepted.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2021
Citation:
Choi, I., N. Li, J. Vuia-Riser, B. Carter, M. Drake, and Q. Zhong. 2021. Neutral pH nonfat dry milk beverages with turbidity reduced by sodium hexametaphosphate: Physicochemical and sensory properties during storage. LWT-Food Science and Technology. Under review.
|
Progress 01/01/16 to 12/10/20
Outputs
Target Audience:Scientific community and the food industry. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Four graduate students were financially supported throughout the entire project. How have the results been disseminated to communities of interest?Five papers (including two new papers in 2020) have been published in high impact factor journals. Two other papers have been submitted, one of which is under revision. Another paper has been prepared for submission. In addition, the project has resulted in seven poster presentations at the annual meetings of the Institute of Food Technologists in 2018-2020 and one oral presentation at the annual meeting of American Dairy Science Association in 2019. The project also resulted in one MS thesis, as well as a dissertation expected in 2021. What do you plan to do during the next reporting period to accomplish the goals?
Nothing Reported
Impacts
What was accomplished under these goals?
In completion of the project, we reduced the turbidity and improved the stability of skim milk powder (SMP) dispersions and studied fundamental physicochemical properties leading to the improved functionalities in Objective 1, and the findings in Objective 1 were used to prepare nonfat dry milk (NFDM)-based model beverages with neutral and acidic pH for evaluation of physicochemical properties in Objective 2 and flavor profile and sensory properties in Objective 3 during 10-week storage at refrigerated and ambient storages. Detailed results can be found in annual progress reports and publications, and a synopsis of project findings is presented below. Our project may expand the use of casein-containing dairy ingredients in the growing functional beverages sector. In Objective 1, different strategies were studied for dispersions at pH 6.8, pH 4.5, and pH 3.0 and below that represent distinctly different properties of casein micelles. At pH 6.8, reduction of SMP dispersion turbidity was enabled with food-grade chelating agents that resulted in dissociation of casein micelles and therefore the reduced dispersion turbidity. The turbidity, dimension and morphology, and ionic composition of 5% w/v SMP dispersions added with 0-30 mM sodium tripolyphosphate, trisodium citrate, or sodium hexametaphosphate (SHMP) were studied before and heating at 90 ºC for 5 min. An intermediate chelator concentration resulted in the smallest particle dimension and the lowest turbidity of dispersions, and heating overall reduced the particle dimension but increased the turbidity of some dispersions. At the same molar concentration, SHMP was the most effective in reducing dispersion turbidity and resulted in the most stable dispersion turbidity after heating. At pH 4.5, nearby the isoelectric point of caseins, three anionic polysaccharides were studied to stabilize caseins against aggregation and precipitation. The dispersion turbidity was further reduced with a pH-cycle treatment, by first alkalizing dispersion pH from neutral to 11.30 to dissociate casein micelles, followed by acidification to pH 4.5 during which polysaccharide-casein nanocomplexes formed. Structures and mechanisms leading to the reduced dispersion turbidity and the improved dispersion stability were studied. Propylene glycol alginate stabilized caseins by forming both covalent conjugates and non-covalent nanocomplexes. Dextran sulfate chelated calcium in casein micelles and formed nanocomplexes with casein in the core and polysaccharide on the shell. The core-shell type nanocomplexes were also the case for carboxymethylcellulose (CMC), and the higher density of chelating carboxylate groups of CMC reduced the dispersion particle dimension and turbidity to a greater extent and improved the stability of dispersions at increased ionic strengths. The polysaccharide on nanocomplexes enabled the stability against aggregation at pH 4.5. At pH 3.0 and below, translucent dispersions with 5% w/v SMP were observed after direct acidification with citric acid and heating. A lower dispersion turbidity was observed at a lower pH. The clarity of dispersions was further affected by the heating temperature and duration. Gluconic acid was additionally studied as a more effective chelating agent than citric acid in dissociating casein micelles, and the dispersion acidified with gluconic acid was clearer than those acidified with citric acid and hydrochloric acid. The macroscopic dispersion appearance was supported by quantitative turbidity, particle dimension, and electron microscopy structures. Three batches of lemon-flavored beverages with 5% and 7.5% w/w NFDM acidified to pH 2.5 and neutral pH vanilla beverages with 5% or 10% w/w NFDM, 0 (control) or 0.43% w/w SHMP were produced to study physicochemical properties and shelf-sterility in Objective 2 and volatile profiles, descriptive sensory analysis, and consumer panels in Objective 3 during 10-week storage at 4 °C or room temperature (RT, 21 °C). Sterility was observed at the formulation and thermal treatment conditions used for all beverages. Before storage, physicochemical properties of model beverages showed the similar trends as those in Objective 1 when comparing to the controls. For neutral vanilla beverages, the turbidity was stable during storage at 4°C but increased when stored at RT. The increase in viscosity during storage was insignificant for the 5% NFDM beverage with SHMP, but was significant for the 10% NFDM beverage with SHMP. Additionally, the 10% NFDM beverage with SHMP became a gel during storage at RT but remained fluidic at 4°C. The heat treatment used to manufacture vanilla beverages reduced the abundance of volatiles. Beverages with SHMP had a low soapy flavor and salty taste but had no apparent differences in other sensory attributes when compared to the control without SHMP. The vanilla and milky flavor of neutral beverages decreased after 70-day refrigerated storage. For the lemon-flavored acidic beverages, the beverage with 5% NFDM had higher aroma and lemon flavor than the 7.5% one, although the same volatile compounds were observed in the two beverages, and the flavor intensity decreased after refrigerated storage. Similar to neutral vanilla beverages, physicochemical properties were more stable for acidic beverages during 70-day storage at 4°C than at RT. The acidic beverage with 7.5% NFDM was gel-like and, despite being infeasible for use as drinks, could be used to provide satiety. For both groups of beverages, the reduced turbidity of beverages was not appreciated by consumer panels, pointing to the need of prior education of consumers when developing such beverages.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Choi, I. and Q. Zhong. 2020. Gluconic acid as a chelator to improve clarity of skim milk powder dispersions at pH 3.0. Food Chemistry. DOI: 10.1016/j.foodchem.2020.128639.
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Choi, I. and Q. Zhong. 2020. Physicochemical properties of skim milk powder dispersions prepared with calcium-chelating sodium tripolyphosphate, trisodium citrate, and sodium hexametaphosphate. Journal of Dairy Science. 103(11): 9868-9880. DOI: 10.3168/jds.2020-18644.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2021
Citation:
Li, N. and Q. Zhong. 2020. Effects of carboxymethylcellulose charge density on the formation of nanocomplexes with casein micelles stable at pH 4.5. Food Hydrocolloids. Under revision.
- Type:
Journal Articles
Status:
Under Review
Year Published:
2021
Citation:
Choi, I., N. Li, J. Vuia-Riser, B. Carter, M. Drake, and Q. Zhong. 202x. Neutral pH nonfat dry milk beverages with turbidity reduced by sodium hexametaphosphate: Physicochemical and sensory properties during storage. Food Research International. Under review.
- Type:
Journal Articles
Status:
Awaiting Publication
Year Published:
2021
Citation:
Li, N., I. Choi, J. Vuia-Riser, B. Carter, M. Drake, and Q. Zhong.* 202x. Physicochemical and sensory properties of lemon-flavored acidic beverages formulated with nonfat dry milk during storage. Drafted.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Choi, I., N. Li, J. Vuia-Riser, B. Carter, M. Drake, and Q. Zhong. (2020). Neutral skim milk powder beverages with turbidity reduced by sodium hexametaphosphate: Physicochemical properties during storage. The 2020 IFT Annual Meeting & Food Expo, July 13-15, Chicago, IL (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Li, N., I. Choi, J. Vuia-Riser, B.G. Carter, M. Drake, Q. Zhong. 2020. Storage stability of acidic protein beverage formulated with skim milk powder. The 2020 IFT Annual Meeting & Food Expo, July 12-15 (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Li, N., and Q. Zhong. 2020. Effects of carboxymethylcellulose charge density on the formation of nanocomplexes with casein micelles stable at pH 4.5. The 2020 IFT Annual Meeting & Food Expo. July 12-15, Chicago, IL (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2020
Citation:
Li, N., and Q. Zhong. 2020. Casein core-polysaccharide shell nanocomplexes stable at pH 4.5 enabled by chelating and complexation properties of dextran sulfate. The 2020 IFT Annual Meeting & Food Expo. July 12-15, Chicago, IL (poster presentation).
|
Progress 01/01/19 to 12/31/19
Outputs
Target Audience:Scientific communities and dairy foods industry. Changes/Problems:Near the isoelectric point of caseins, such as pH 4.5, it was proposed that stable SMP dispersions with low turbidity would be prepared by adding polysaccharides into the derivatized SMP (heating at around pH 3.0) dispersions. This method improved the stability of SMP dispersions but did not work well to reduce the turbidity. Instead, the mixture of casein and polysaccharides was treated with the pH cycle method to improve both the stability and transparency of casein dispersions around pH 4.6. Micellar casein was used instead of SMP to better study the mechanism. For beverages with neutral pH, calcium chelators were added because they were effective to reduce the turbidity of SMP beverages without major changes in physicochemical properties of the beverages after heating. Originally, beverages with 10% w/v SMP at pH 3.0, 4.0, 5.0, and 6.0 were proposed. However, this SMP content resulted in gelation at the proposed conditions. As a result, acidic beverages with 5% or 7.5% w/v SMP were prepared at pH 2.5 by heating, while neutral beverages with 5% or 10% w/v SMP were produced at pH 6.8 after adding sodium hexametaphosphate. What opportunities for training and professional development has the project provided?Two graduate students were financially supported in this reporting period by this grant and they were supported to attend the annual meeting of the Institute of Food Technologists and American Dairy Science Association. How have the results been disseminated to communities of interest?Two poster presentations were given at the Annual Meeting of the Institute of Food Technologists in New Orleans, LA. One oral presentation was given at the annual meeting of American Dairy Science Association. Three research papers have been published. What do you plan to do during the next reporting period to accomplish the goals?We have completed experiments and are working on more publications and presentations generated from this project.
Impacts
What was accomplished under these goals?
In this reporting period, we did more research in Objective 1. Carboxymethylcellulose (CMC) was used to stabilize casein micelle dispersions at pH 4.5 and the physicochemical properties of casein-CMC complexes at pH 4.5 as influenced by CMC charge density were studied. Micellar casein and CMC with the same molecular weight (250 kDa) but different charge densities (CMC0.7, CMC0.9 and CMC1.2) were hydrated at mass ratios of 5:1, 4:1, 3:1, 2:1 and 1:1. The mixtures were treated with a pH-cycle method by increasing the pH to 11.3 with 4.0 M NaOH and then decreasing the pH to 4.5 with citric acid. The "casein-CMC3:1 no pH-cycle" control sample was prepared by direct acidification to pH 4.5 after hydration. With the pH-cycle treatment, the casein-CMC3:1 dispersion had the lowest turbidity and was stable during 30-day storage at room temperature for all CMC treatments. CMC chelated calcium and caused the disassociation of casein micelles, thus lowering turbidity even for the "casein-CMC3:1 no pH-cycle" dispersions at pH 4.5. The transparency was further improved after the pH-cycle treatment due to the extensive dissociation of casein micelles over pH 11.0 and formation of smaller casein-CMC nanocomplexes during the following acidification. As CMC charge density increased, the turbidity of casein-CMC3:1 dispersions decreased (absorbance at 600 nm being 1.25, 0.91, and 0.57, respectively, for CMC0.7, CMC0.9, and CMC1.2 treatments), zeta-potential decreased (from -31.8, -35.1, to -37.2 mV), and particle dimension measured in dynamic light scattering (from 379, 392, to 188 nm) and atomic force microscopy also decreased, corresponding to the increased CMC fraction forming nanocomplexes. In addition, we have completed Objectives 2 and 3. We produced lemon-flavored acidic beverages according to the previous report about reducing SMP dispersions at pH 2.4-3.0. For these beverages, 5% and 7.5% w/v SMP were mixed with sugar, crystallized lemon, and sodium benzoate, followed by acidification to pH 2.5 with citric acid, heating at 90 °C for 1 min, hot filling in glass bottles at 85 °C, and cooling in an ice bath. Descriptive sensory analysis was conducted after 1 and 10 weeks of storage at 4 °C and consumer testing was conducted after two weeks of storage at 4 °C. Volatile analysis was conducted before and after heat treatment. In addition, samples were stored at 4 °C or room temperature (RT, 21 °C) for 10 weeks and characterized for physical, chemical, and microbiological properties every two weeks. For these acidic beverages, the heat treatment had no effect (p > 0.05) on volatile compounds. According to the sensory analysis, all beverages had a low soapy flavor intensity. Following refrigerated storage, lemon flavor decreased in the 5% SMP beverage and viscosity increased in the 10% SMP beverage. During 10-week storage, pH values were stable at ~pH 2.4 at both temperatures. Turbidity was more stable at 4 °C than at RT for both 5% (378-479 vs. 427-872 NTU) and 7.5% (2412-3136 vs. 2663-3556 NTU) SMP treatments. The hydrodynamic diameter of the 5% SMP treatment was more stable at 4 °C (145-177 nm) than at RT (153-378 nm), whereas the zeta potential was stable (near 10 mV) for all samples. The viscosity of 5% SMP beverage increased slightly from 8.4 to 10.3 mPa-s at 4 °C after 10-week storage, but significantly (p < 0.05, from 9.6 to 27.1 mPa-s) at RT, causing a gel-like sample. For the 7.5% SMP beverage, viscosity was stable for 10 weeks at a shear rate ~50 s-1 when measured at the storage temperature. More aggregated casein molecules were observed in transmission electron microscopy after 10 weeks, particularly for samples stored at RT, regardless of SMP concentration. Both formulations showed an increase in redness (a*) and blueness (b*) during storage (p < 0.05). All formulations had no detectable microorganisms during storage. We also produced neutral vanilla beverages based on reducing SMP dispersion turbidity with chelating agents. The neutral beverages were formulated with 5 or 10% w/v SMP, 0 (control) or 7 mM sodium hexametaphosphate (SHMP), sucralose, vanilla liquid extract and sodium benzoate and were adjusted to pH 6.8 with phosphoric acid. Following heating at 138 °C and 330 kPa for 3 s, beverages were cooled to 10 °C, homogenized at 20.7 mPa, and packed in polyethylene terephthalate bottles. Physicochemical and microbiological properties, volatile analysis, descriptive sensory analysis, and storage stability measurement were conducted the same as acidic lemon beverages. The heat treatment reduced (p < 0.05) relative abundance of most volatile compounds. The addition of SHMP contributed to a low but distinct soapy flavor and increased salty taste, but had no other apparent sensory effects on flavor, astringency, and viscosity. Beverages with 10% SMP had higher astringency and viscosity than beverages with 5% SMP (p < 0.05). Refrigerated storage decreased aroma intensity as well as milky and vanillin flavors (p < 0.05). During storage, the beverage pH was stable (~6.8) at 4 °C but decreased slightly at RT. SHMP beverages had lower and stable turbidity, 169 NTU for 5% and 389-525 NTU for 10% SMP treatment, at 4 °C (approximately doubled at RT), compared with the control (>4000 NTU). Samples with SHMP had smaller particles than the controls (106 vs 181 nm at RT; 112 vs 225 nm at 4 °C). The zeta-potential of all samples was stable (~-11 mV) at both temperatures. Controls at both SMP concentrations did not show significant increases in viscosity, whereas a slight (from 6.93 to 11.0 mPa-s) and drastic increase (from 6.16 to 60.8 mPa-s) were observed for 10% SMP beverages with SHMP stored at 4 °C or RT, respectively. The 10% SMP beverage with SHMP developed gel-like properties at 21 °C, with the storage modulus increasing from 0.01 to 4.08 Pa after 10 weeks, whereas the increase in storage modulus, from 0.01 to 0.10 Pa, was much smaller when stored at 4 °C. Only the 10% SMP sample with SHMP stored at 4 °C did not show significant changes in L*, a*, or b* values during storage (p = 0.05). All formulations showed sterility during storage at both temperatures.
Publications
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Li, N. and Q. Zhong. 2020. Stable casein micelle dispersions at pH 4.5 enabled by propylene glycol alginate following a pH-cycle treatment. Carbohydrate Polymer. 233: 115834.
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Choi, I. and Q. Zhong. 2020. Physicochemical properties of skim milk powder dispersions after acidification to pH 2.43.0 and heating. Food Hydrocolloids. 100: 105435.
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Choi, I. and Q. Zhong. 2019. Comparison of physicochemical properties of skim milk powder dispersions as affected by sodium tripolyphosphate, trisodium citrate, and sodium hexametaphosphate. The 2019 IFT Annual Meeting & Food Expo, June 2-5, New Orleans, LA. Paper #P01-015 (poster presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Choi, I. and Q. Zhong. 2019. Physicochemical properties of skim milk powder dispersions acidified by gluconic acid, hydrochloric acid, and citric acid. The 2019 ADSA Annual Meeting, June 23-26, Cincinnati, OH. Dairy Foods: Chemistry #384 (oral presentation).
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2019
Citation:
Li, N. and Q. Zhong. 2019. Stable casein micelle dispersions at pH 4.5 enabled by propylene glycol alginate following a pH-cycle treatment. The 2019 IFT Annual Meeting & Food Expo, June 2-5, New Orleans, LA. Paper #P01-075 (poster presentation).
- Type:
Journal Articles
Status:
Published
Year Published:
2020
Citation:
Li, N. and Q. Zhong. 2020. Casein core-polysaccharide shell nanocomplexes stable at pH 4.5 enable by chelating and complexation properties of dextran sulfate. Food Hydrocolloids. 103: 105723.
|
Progress 01/01/18 to 12/31/18
Outputs
Target Audience:Food Scientists attending the Institute of Food Technologists annual meeting. Changes/Problems:The originally proposed soluble soybean polysaccharide and high-methoxyl pectin were not able to achieve the project goal of preparing stable dispersions at an acidity around the isoelectric point of caseins (pH 4.6). After screening various polysaccharides, we identified two other polysaccharides, propylene glycol alginate and dextran sulfate, that were capable of stabilizing casein dispersions at pH 4.5. What opportunities for training and professional development has the project provided?Three graduate students were financially supported in this reporting period by this grant and they were supported to attend the annual meeting of the Institute of Food Technologists. How have the results been disseminated to communities of interest?One E-poster presentation was given at the Annual Meeting of the Institute of Food Technologists in Chicago, IL. What do you plan to do during the next reporting period to accomplish the goals?The objectives 2 and 3 of this project are underway and are expected to be completed in 2019. We also are working on publications and presentations generated from this project.
Impacts
What was accomplished under these goals?
In this reporting period, we have completed the objective 1 by studying different strategies to reduce skim milk powder (SMP) dispersions at pH 2.4-3.0, pH 4.5 (near the isoelectric point of caseins), and neutral pH. Following progresses reported in previous years, we focused on the mechanisms leading to observations at pH 2.4-3.0 and neutral pH. For transparent 5% w/v SMP dispersions after acidification to 2.4-3.0 using citric acid and heating at 90 °C for 2 min, colloidal calcium phosphate (CCP) that enables micellar structure of casein was released after acidification, causing disruption of CCP bridges and therefore the decreased hydrodynamic diameter of casein micelles. Further reduction in turbidity of acidified SMP dispersions, e.g., from 1805 NTU to 1072 NTU at pH 3, was enabled by heating, possibly due to weakened hydrophobic interactions between caseins. Additionally, the type of acidulants was observed to affect the dissolution of CCP. Gluconic acid resulted in a greater extent of calcium release from CCP (615 mg/L) than citric acid (533 mg/L) and hydrochloric acid (504 mg/L). However, the concentration of free calcium ions in the dispersion was the lowest for the gluconic acid treatment (325 mg/L) compared to citric acid (428 mg/L) and hydrochloric acid (534 mg/L) treatments, suggesting the strong chelating ability of gluconic acid. At neutral pH, addition of calcium chelators produced translucent dispersions. Sodium hexametaphosphate was more effective than trisodium citrate and sodium tripolyphosphate not only to reduce the dispersion turbidity at a concentration as low as 2 mM but to maintain the dispersion stability after heating at 90 °C for 2 min. The concentration of free calcium ions after chelator addition was not correlated to the reduced dispersion turbidity, suggesting different interactions between calcium and calcium chelators to form complexes. Dissociation of casein micelles at both acidic and neutral pH was confirmed using transmission electron microscopy and scanning transmission electron microscopy. To stabilize dispersions at pH 4.5, two polysaccharides and micellar caseins were studied. Particles were measured with dynamic light scattering (DLS) and atomic force microscopy (AFM). Interaction forces between casein and polysaccharides were studied with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Fourier-transform infrared spectroscopy, as well as impacts of SDS, urea, and NaCl on dispersion particle size distribution. The first polysaccharide was propylene glycol alginate (PGA), and micellar caseins (1% w/v) were hydrated with PGA at mass ratios of 4:1, 3:1, 2:1, 1:1, and 1:1.5 in deionized water. A pH-cycle method was used to form casein-PGA complexes by adjusting mixtures to pH 11.30 with 5.0 M NaOH, incubating for 1 h at 21°C, and then acidifying to pH 4.5 with citric acid solutions. The control sample with equal masses of casein and PGA was directly acidified to pH 4.5. With the pH-cycle treatment, the dispersion turbidity decreased as the amount of PGA increased, and the dispersions with casein-PGA mass ratios of 1:1 and 1:1.5 had the lowest turbidity of 200-260 NTU. However, only the dispersion with equal masses of casein and PGA was absent of both precipitation and gelation during 30-day storage at 21°C. In contrast, the control sample had a turbidity of over 4000 NTU and was unstable. DLS and AFM results indicated that dispersion transparency was related to both the size and mass density of particles. With the pH-cycle treatment, hydrolysis of PGA was observed in SEC-HPLC and AFM due to cleavage of ester bonds at alkaline conditions, and casein micelles were disassociated at alkaline pH and re-associated during acidification with simultaneous formation of complexes with PGA. Molecular force analyses suggested that both covalent and non-covalent (mainly electrostatic and hydrophobic) interactions contributed to complex formation and dispersion stability at pH 4.5. The second polysaccharide, dextran sulfate (DS), was used to improve the stability and transparency of 2% w/v micellar casein dispersions at pH 4.5 following the pH-cycle treatment. Casein and DS were hydrated in deionized water at mass ratios of 5:1, 4:1, 3:1, 2:1 and 1:1, and the corresponding dispersions at pH 4.5 after the pH -cycle treatment had the turbidity of 977, 729, 522, 383, and 336 NTU, respectively. In comparison, the control sample with casein-DS mass ratio of 2:1 directly acidified from neutral pH to pH 4.5 had a higher turbidity of 514 NTU. DS was confirmed for the ability to chelate calcium in micellar caseins to dissociate casein micelles to reduce dispersion turbidity, and additional dissociation of casein micelles was observed in the pH-cycle treatment to result in smaller casein-DS complex structures and therefore a lower turbidity than the control. According to the molecular force analyses, only electrostatic interaction was important for the casein-DS complex formation and dispersion stability at pH 4.5.
Publications
- Type:
Conference Papers and Presentations
Status:
Published
Year Published:
2018
Citation:
Choi, I. and Q. Zhong. 2018. Physicochemical properties of skim milk powder dispersions after heating at pH 2.4-3.0. The 2018 IFT Annual Meeting & Food Expo, July 15-18, Chicago, IL. Paper #E02.
- Type:
Theses/Dissertations
Status:
Awaiting Publication
Year Published:
2019
Citation:
Choi, I. 2019. Reducing skim milk powder dispersion turbidity by dissociation of casein micelles at acidic and neutral pH: Physicochemical properties and possible mechanisms. MS Thesis, the University of Tennessee, Knoxville.
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Progress 01/01/17 to 12/31/17
Outputs
Target Audience:Scientists attending the project directors' meeting in Las Vegas, NV. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?Two graduate students are being trained. How have the results been disseminated to communities of interest?Findings from the last year (2016) were presented in the project directors' meeting in Las Vegas, NV. What do you plan to do during the next reporting period to accomplish the goals?We will continue to study objective 1, focusing on mechanisms of casein micelle dissociation and formation of protein-polysaccharide complexes.
Impacts
What was accomplished under these goals?
Studies in this reporting period still were focused on Objective 1. Physical and chemical properties of dispersions with 5% w/v skim milk powder (SMP) were studied for visual clarity, turbidity, dynamic light scattering, normalized calcium ion concentration, fluorescence spectra, and scanning transmission electron microscopy (STEM). The first set of treatments focused on SMP dispersions acidified to pH 2.4, 2.7, and 3.0 by citric acid or glucono delta-lactone (GDL), followed by heating at 60, 70, 80, and 90 ? for 2, 5, 10, 30, and 60 min. The turbidity of SMP dispersions depended on both heating temperature and duration. For 10 min of heating at pH 2.4, the dispersion heated at 70 ? was observed to have the lowest turbidity (296±12 NTU) and smallest hydrodynamic diameter (122.3±10.9 nm). As heating time increased, turbidity and hydrodynamic diameter of SMP dispersions at pH 2.4 increased. For example, the average hydrodynamic diameter was 139.9±17.3 and 205.4±30.3 nm, respectively, after heating at 90 ? for 2 min and 60 min. However, the combination of optimal temperature (70 °C) and heating time (2 min) in reducing dispersion turbidity screened at the studied thermal treatment conditions did not produce the most translucent dispersion, indicating the weakening of intra-particle interactions in casein micelles requires certain thermal energy in order to be dissociated. GDL was more effective than citric acid to improve the transparency of SMP dispersions after heating at 90 °C for 10 min, for example, 299.3±2.1 vs. 474.3±14.2 NTU at pH 2.7, resulting from the reduced heterogeneity in particle size distribution. The second set of treatments was studied at neutral pH by adding sodium tripolyphosphate (STPP) in 5% w/v SMP dispersions. STPP was observed to be more effective than other calcium chelating salts such as sodium citrate, sodium phosphate dibasic, and potassium phosphate dibasic in reducing dispersion turbidity, e.g., 261 and 280 NTU for treatments with 0.5% w/v STPP and sodium citrate, respectively. The turbidity of SMP dispersions was 531, 258, 252, and 229 NTU after dissolving with 0.1, 0.5, 1.0, and 5.0 % w/v STPP, respectively. The addition of 0.5% w/v STPP reduced the average hydrodynamic diameter from 268.9±1.2 to 166.2±1.4 nm and but increased polydispersity index from 0.182 to 0.548. Calcium ion concentration in derivatized SMP dispersions increased after heating at pH 2.4-3.0, indicating the dissolution of colloidal calcium phosphate in casein micelles. Conversely, the addition of STPP in neutral SMP dispersions lowered the calcium ion concentration, possibly due to formation of calcium-STPP complexes. Intrinsic fluorescence emission spectra of SMP dispersions suggest that heating enhanced the exposure of tryptophan residues to the continuous polar phase. STEM results confirmed dissociation of casein micelles in both acidic and neutral SMP dispersions after heating and addition of STPP, respectively.
Publications
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Progress 01/01/16 to 12/31/16
Outputs
Target Audience:Scientists in academia and food industry. Changes/Problems:
Nothing Reported
What opportunities for training and professional development has the project provided?One MS student is being trained in this project and we are recruiting another doctoral student to work on this project. How have the results been disseminated to communities of interest?
Nothing Reported
What do you plan to do during the next reporting period to accomplish the goals?We will continue to study Objective 1.
Impacts
What was accomplished under these goals?
The project funding arrived to our institution much later than the expected starting date, which affected recruiting. One MS student was recruited to work on the project starting August 2016. The focus in the current reporting year was on Objective 1. Formation mechanism and physical and chemical properties of derivatized skim milk powder. The derivatization was first studied for dispersions hydrated with 5% w/v skim milk powder that was adjusted to pH 2.0-4.0 in 0.5 unit increments with 2.0 M citric acid and then heated at 60, 70, 80, 90, and 95 °C for 1, 2, 5, 10, and 30 min. Low turbidity dispersions were observed for treatments adjusted to pH 3.0 or lower after heating. Quantitative normalized turbidity, which was measured at 600 nm, and particle size distributions showed that pH and temperature were two important factors affecting dispersion clarity, while heating time had insignificant effect as long as it was longer than 5 min. The second set of experiments were similarly conducted for pasteurized skim milk. Solids content in skim milk diluted for different ratios was observed to have significantly affected dispersion turbidity after heating at pH 2.0-4.0, as observed for translucent dispersions at a solids content of 5% w/v but not at 7%, 9%, and 11% w/v. Additional tests showed that heating at a high temperature such as 110 and 135 °C improved the clarity of diluted skim milk. For example, a translucent dispersion was observed for skim milk diluted to a solids content of 6.45% w/v and adjusted to pH 3.0 after heating at 135 °C for 20 min. We continue to investigate derivatization conditions and characterize properties as affected by derivatization, as well as effects of polysaccharides on dispersion turbidity and stability.
Publications
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