Sonoprocessing improves phenolics profile, antioxidant capacity, structure, and product qualities of purple corn pericarp extract.

For the first time, purple corn pericarp (PCP) was converted to polyphenol-rich extract using two-pot ultrasound extraction technique. According to Plackett-Burman design (PBD), the significant extraction factors were ethanol concentration, extraction time, temperature, and ultrasonic amplitude that affected total anthocyanins (TAC), total phenolic content (TPC), and condensed tannins (CT). These parameters were further optimized using the Box-Behnken design (BBD) method for response surface methodology (RSM). The RSM showed a linear curvature for TAC and a quadratic curvature for TPC and CT with a lack of fit > 0.05. Under the optimum conditions (ethanol (50%, v/v), time (21 min), temperature (28 °C), and ultrasonic amplitude (50%)), a maximum TAC, TPC, and CT of 34.99 g cyanidin/kg, 121.26 g GAE/kg, and 260.59 of EE/kg, respectively were obtained with a desirability value 0.952. Comparing UAE to microwave extraction (MAE), it was found that although UAE had a lower extraction yield, TAC, TPC, and CT, the UAE gave a higher individual anthocyanin, flavonoid, phenolic acid profile, and antioxidant activity. The UAE took 21 min, whereas MAE took 30 min for maximum extraction. Regarding product qualities, UAE extract was superior, with a lower total color change (ΔE) and a higher chromaticity. Structural characterization using SEM showed that MAE extract had severe creases and ruptures, whereas UAE extract had less noticeable alterations and was attested by an optical profilometer. This shows that ultrasound, might be used to extract phenolics from PCP as it requires lesser time and improves phenolics, structure, and product qualities.

Updating the status quo on the extraction of bioactive compounds in agro-products using a two-pot multivariate design. A comprehensive review.

Extraction is regarded as the most crucial stage in analyzing bioactive compounds. Nonetheless, due to the intricacy of the matrix, numerous aspects must be optimized during the extraction of bioactive components. Although one variable at a time (OVAT) is mainly used, this is time-consuming and laborious. As a result, using an experimental design in the optimization process is beneficial with few experiments and low costs. This article critically reviewed two-pot multivariate techniques employed in extracting bioactive compounds in food in the last decade. First, a comparison of the parametric screening methods (factorial design, Taguchi, and Plackett-Burman design) was delved into, and its advantages and limitations in helping to select the critical extraction parameters were discussed. This was followed by a discussion of the response surface methodologies (central composite (CCD), Doehlert (DD), orthogonal array (OAD), mixture, D-optimal, and Box-Behnken designs (BBD), etc.), which are used to optimize the most critical variables in the extraction of bioactive compounds in food, providing a sequential comprehension of the linear and complex interactions and multiple responses and robustness tests. Next, the benefits, drawbacks, and possibilities of various response surface methodologies (RSM) and some of their usages were discussed, with food chemistry, analysis, and processing from the literature. Finally, extraction of food bioactive compounds using RSM was compared to artificial neural network modeling with their drawbacks discussed. We recommended that future experiments could compare these designs (BBD vs. CCD vs. DD, etc.) in the extraction of food-bioactive compounds. Besides, more research should be done comparing response surface methodologies and artificial neural networks regarding their practicality and limitations in extracting food-bioactive compounds.

Impact of formulation and saliva on acid milk gel friction behavior.

UNLABELLED: Rheological analysis is commonly used to evaluate mechanical properties in studies of food behavior. However, rheological analysis is often insufficient to describe food texture as evaluated by descriptive sensory analysis. Additionally, traditional rheometry does not account for changes in food behavior as a function of saliva incorporation into the food during mastication. The objectives of this study were to evaluate friction behavior of acid milk gels with and without the addition of saliva, and to determine relationships between frictional behaviors and mechanical and sensory behaviors. Acid milk gels were prepared with 12.5% total solids comprising nonfat dry milk, whey protein isolate, waxy maize starch, and gelatin in different ratios. The addition of starch was found to have significant impact on acid milk gel frictional behavior. Addition of saliva resulted in a change in frictional behavior over the entire sliding speed range measured. Correlations were found between rheological, tribological, and sensory behavior, suggesting that an underlying mechanism may impact both viscosity and friction behavior. Additional study is needed to further explore the links between food structure, rheology, tribology, and sensory texture. PRACTICAL APPLICATION: Application of tribology in food science allows measurement of friction behavior of foods. Matching both rheological and tribological behavior is important to creating reduced-fat or reduced-sugar products with similar mouthfeel to the original product.

Effect of disulfide interactions and hydrolysis on the thermal aggregation of ß-lactoglobulin.

The roles of sulfhydryl/disulfide interactions and acid/pepsin hydrolysis on ß-lactoglobulin (ß-lg) thermal aggregation at acidic pH 3.35 and 2 were studied using rheology, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), transmission electron microscopy (TEM), and Western blotting. Pepsin promoted additional hydrolysis compared to the acid-hydrolyzed control sample based on a 12% increase in free amino groups. Hydrolysis with pepsin also resulted in an increase in the apparent viscosity by 2 logs upon heating 8% ß-lg solutions at pH 3.35. Seemingly, hydrolysis promoted thermal aggregation of ß-lg, correlating well with viscosity increases. Large microgels were observed in heated pepsin hydrolysates using TEM, supporting the increased viscosities of these dispersions. During thermal aggregation (85 °C, 3 h) of ß-lg at pH 3.35, beyond the existence of limited disulfide interactions, acid hydrolysis and noncovalent interactions more likely play a crucial role in defining the functionality of acidified powdered modified whey ingredients.

Expanded functionality of modified whey protein dispersions after transglutaminase catalysis.

The functionality of whey dispersions, prepared with a modified whey protein concentrate (mWPC) ingredient, was significantly altered after cross-linking with microbial transglutaminase (TGase) upon pH adjustment to 8. Test TGase-mWPC solutions, pH 8, gelled faster than control mWPC dispersions, as measured in real time; whereas, the gelling temperature of pretreated TGase-mWPC samples (37 °C, 2.5 h) increased from 67.8 to 74.8 °C with a minimal change in gel strength. Prolonged prior incubation with the enzyme (37 °C, 20 h) raised the gel strength in both control mWPC and TGase-mWPC dispersions, though these values were approximately 2.7 times lower in TGase-mWPC samples. Furthermore, the gelling temperature was raised by 9 °C after extensive polymerization. The water holding capacity was not impacted by enzymatic processing while emulsions prepared with TGase-mWPC dispersions proved very stable with no evidence of phase separation during storage at room temperature for 1 mo. Moreover, the apparent viscosity of TGase-mWPC emulsions exhibited a 10-fold increase compared to nonenzyme-treated mWPC samples. The particle size was nearly 11 µm in covalently linked TGase-mWPC test fractions compared with 8 µm in nonpolymerized mWPC dispersions. Ultimately, the functional characteristics of TGase-mWPC ingredients may be designed to deliver superior performance, especially with regard to improving heat and emulsion stability.

Transglutaminase catalysis of modified whey protein dispersions.

UNLABELLED: Transglutaminase (TGase) cross-linking reactions were accomplished using a heat-modified whey protein concentrate (mWPC) substrate after pH adjustment to 8. Based on earlier reports, the degree of lactosylation with respect to beta-lactoglobulin was lower in mWPC dispersions than measured in commercial whey concentrate (cWPC) protein solutions. In this study, a higher concentration of free sulfhydryl groups was detected in soluble supernatant fractions. Both factors potentially impact the availability of reactive lysine/glutaminyl residues required for TGase reactivity. The addition of 10 mM dithiothreitol (DTT) to the substrate mix, CBZ-glutaminyl glycine and hydroxylamine, revealed a 3.6-fold increase in TGase activity, likely due in part to maintenance of the catalytic cysteine residue in a reduced state. Furthermore, inclusion of DTT to mWPC dispersions significantly raised the apparent viscosity, independently of enzyme modification, while the rate of polymerization increased 2-fold based on OPA assay measurements. Limited cross-linking slightly increased the apparent viscosity, whereas extensive coupling lowered these values compared to equivalent nonenzyme-treated mWPC samples. Carbohydrate-staining revealed formation of glyco-polymers due to covalent linkages between glucosamine and mWPC proteins after TGase processing. Again, the apparent viscosity decreased after extensive enzymatic modification. Larger particles, sized 11.28 mum, were observed in the structural matrix of TGase-mWPC-fixed samples compared to 8 mum particles in control mWPC samples as viewed in scanning electron micrographs. Ultimately, the functional characteristics of TGase-mWPC ingredients may be custom-designed to deliver alternative functional attributes by adjusting the experimental reaction conditions under which catalysis is achieved. PRACTICAL APPLICATION: Taken together, these results suggest that unique TGase-mWPC and/or TGase-mWPC-glucosamine ingredients may be designed to provide novel, value-added, polymeric/glyco-polymeric protein products that afford added benefit for the milk industry.

Calcium effects on the functionality of a modified whey protein ingredient.

The primary objective for this study addressed the effects of supplemental calcium on the functional properties of a modified whey protein ingredient (mWPC), prepared by acidification to pH 3.35, followed by extended heat treatment, gelation, and spray drying. In the presence of added calcium (mWPC-Ca2+), protein solutions showed increased thickening capacity, especially under refrigeration temperatures, compared to dispersions made with mWPC alone. A rheological assessment included the determination of (i) power law parameters, (ii) viscoelastic properties, and (iii) the effects of heating and cooling on these protein systems. The sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) banding profile suggested that various disulfide-linked molecular forms of beta-lactoglobulin, bovine serum albumin, and immunoglobulin were likely formed during manufacturing of the mWPC ingredient based on the patterns obtained when electrophoresis was performed in the absence of beta-mercaptoethanol compared to those observed with commercial WPC samples. An enhanced water-holding capacity was measured in mWPC-Ca2+ dispersions. Differential scanning calorimetry established that the addition of calcium salts caused a 2-fold increase in the amount of bound or unfreezeable water compared to mWPC controls. The physical appearance of the network structure varied significantly upon visualization with scanning electron microscopy, in which case the formation of large, rounded, spherical structures was noted in mWPC-Ca2+ samples, ascribed to an increased surface tension caused by the higher salt content. Ultimately, such attributes may afford distinct advantages for whey-based ingredients intended for application within food systems, especially under cold processing conditions.

Physicochemical variables affecting the rheology and microstructure of rennet casein gels.

The rheology and microstructure of a rennet casein system were studied in the pH range from 5.8 to 12.0 during cooling from 80 to 5 degrees C at four cooling rates: 0.5, 0.1, 0.05, and 0.025 degrees C/min. A dramatic increase in storage modulus with pH was observed during cooling at a fixed cooling rate. Continuous networks were formed for gels at pH 7.2 and above, while a discontinuous network was observed for gels below pH 6.5. The monotonic increase in storage modulus with pH could be correlated to the number of net (negative) charges and the strength of the hydrophobic interactions. At a higher pH, the protein micelles were larger due to weaker hydrophobic interactions and stronger repulsive electrostatic interactions resulting from more charges. When these protein micelles aggregated into flocs during cooling, the flocs had similar sizes at different pH values but a smaller fractal dimension at a higher pH. Consequently, for systems of the same protein and salt concentrations, more flocs were present in the gels at a higher pH, which subsequently generated more cross-links and a higher storage modulus. The pH also determined how the cooling rate affected the gel properties. At pH 5.8 and 6.5, the gels were firmest at the fastest cooling schedule, and the cooling rate did not show a trend in affecting the gel strength at the other three rates. On the other hand, a slower cooling rate generated a firmer gel at pH 7.2 and 12.0. The analysis of casein interactions suggests that the cooling rate affected the casein floc size only when repulsive interactions enabled a slow flocculation (at higher pH values) comparable with temperature change rates during cooling. For rennet casein gels of pH within the range of processed cheese products (pH 5.8 and 6.5), particle or cluster rearrangements created more uniform networks for gels cooled at slower schedules and weakened the structure.

Mechanical properties of foods used in experimental studies of primate masticatory function.

In vivo studies of jaw-muscle behavior have been integral factors in the development of our current understanding of the primate masticatory apparatus. However, even though it has been shown that food textures and mechanical properties influence jaw-muscle activity during mastication, very little effort has been made to quantify the relationship between the elicited masticatory responses of the subject and the mechanical properties of the foods that are eaten. Recent work on human mastication highlights the importance of two mechanical properties-toughness and elastic modulus (i.e., stiffness)-for food breakdown during mastication. Here we provide data on the toughness and elastic modulus of the majority of foods used in experimental studies of the nonhuman primate masticatory apparatus. Food toughness ranges from approximately 56.97 Jm(-2) (apple pulp) to 4355.45 Jm(-2) (prune pit). The elastic modulus of the experimental foods ranges from 0.07 MPa for gummy bears to 346 MPa for popcorn kernels. These data can help researchers studying primate mastication select among several potential foods with broadly similar mechanical properties. Moreover, they provide a framework for understanding how jaw-muscle activity varies with food mechanical properties in these studies.

Cooling effects on a model rennet casein gel system: part I. Rheological characterization.

The gelation of a model rennet casein system was studied during cooling at different rates. During cooling, casein network structure development was proposed to evolve over a few steps at different length scales: molecules, particles, flocs, or network. Rennet casein flocs are fractal in nature, and fractal dimension and floc size are two variables affecting the rheology and microstructure of a rennet casein gel. Casein structure formation during cooling from 80 to 5 degrees C at four different rates (0.5, 0.1, 0.05, and 0.025 degrees C/min) was monitored by dynamic rheological tests, and a stronger gel developed at a slower cooling rate. During different cooling schedules, similar fractal dimensions were observed due to a lack of difference in the colloidal interactions. Differences among rheological data were possibly caused by variability in floc size, as observed in the second part of this paper. A larger number of smaller-sized flocs enabled gelation at a higher temperature and created a stronger network at a slower cooling rate. Controlling cooling schemes thus provides an approach for manipulating casein gelation and the microstructure for a system of fixed chemical compositions.

Cooling effects on a model rennet casein gel system: part II. Permeability and microscopy.

Microscopy and permeability studies were performed to further illustrate the cooling effects on rennet casein gel structure and help interpret the rheological observations in the first part of this paper. Samples of gels cooled from 80 to 5 degrees C at four rates (0.5, 0.1, 0.05, and 0.025 degrees C/min) were studied with a confocal laser scanning microscope. A larger number of smaller flocs were generated at slower cooling rates, creating more cross-links within a network and corresponding to a stronger gel. Formation of a larger number of smaller flocs was hypothesized to result from a greater degree of doublet formation because the system spent more time within the temperature region where doublet formation is favored when cooled at slower rates. The doublets represent sites available for floc growth, similar to nucleation sites for crystal growth. Microscopy results further substantiated that the cooling effects were different from the aging effects because cooling affected floc size, and aging enabled the addition of idle flocs into the casein network. The conclusions for the cooling effects on floc size were further supported by permeability tests. A smaller permeability coefficient resulted from smaller flocs obtained with a slower cooling schedule. This study showed the importance of controlling floc numbers to modulate the strength of a gel, and cooling rates provide an approach of modulating functional properties when the chemical composition of a system is fixed.