Measurement of air cell distributions in dairy foams

A time-resolved investigation at multiple-length scales of the structure of liquid foam stabilized by albumins from pea

HYPOTHESIS

The structural details of foams made with pea albumins are affected by the pH of the initial solution and followed heat treatment.

EXPERIMENTS

An in situ, time-resolved investigation of foams prepared with pea albumins was conducted using small-angle neutron scattering (SANS) in combination with imaging and conductance measurements. Solutions were tested at pH three pH values (3, 4.5, and 8) before and after heating (90 °C for 1 and 5 min).

FINDINGS

The characteristic structures present in the foam from the nano to the meso-scale differed during drainage depending on solution pH. Foams obtained at pH 3, had the largest bubble radius and thinnest plateau border, as well as the highest extent of liquid drainage. At pH 4.5, close to the isoelectric point of the proteins, foams displayed similar bubbles' behavior to those at pH 8, but with the largest film thickness. In this case, the proteins were extensively aggregated. Heating of the solutions prior to foaming did not significantly affect the foam aging regardless of pH. The quantification of specific surface areas and film thickness over time without sample disruption shows to be a powerful approach to designing foam structures.

Formation of pores and bubbles and their impacts on the quality attributes of processed foods: A review

Pores and bubbles significantly influence the physical attributes (like texture, density, and structural integrity), organoleptic properties, and shelf life of processed foods. Hence, the quality of foods and their acceptance by the consumers could be influenced by the properties and prevalence of pores and bubbles within the food structure. Considering the importance of pores, this review aimed to comprehensively discuss the factors and mechanisms involved in the generation of pores and bubbles during the processing of different food products. Moreover, the characteristics and effects of pores on the properties of chocolates, cheeses, cereal-based foods (like cake, puffed grains, and pasta), dried, and fried products were discussed. The impacts of bubbles on the quality of foam-based products, foam creamers, and beverages were also explored. This review concludes that intrinsic factors (like food compositions, initial moisture content, and porosity) and extrinsic factors (like applied technologies, processing, and storage conditions) affect various properties of the pores and bubbles including their number, size, orientation, and distribution. These factors collectively shape the overall structure and quality of processed food products such as density, texture (hardness, cohesiveness, chewiness), and water holding capacity. The desirability or undesirability of pores and their characteristics depends on the type of products; hence, some practical hints were provided to mitigate their adverse effects or to enhance their formation in foods. For example, pores could increase the nutrient digestion and reduce the shelf life of the products by enhancing the risk of fat oxidation and microbial growth. In conclusion, this study provides a valuable resource for food scientists and industry professionals by discussing the effects of pores on food preservation, heat, and mass transfer (including oxygen, moisture, flavors, and nutrients). Understanding the dynamic changes in porosity during processing will be effective in customization of final product quality with desired attributes, ensuring tailored outcomes for specific applications.

Passion fruit by-products (Passiflora edulis f. flavicarpa) as a potential fat replacer in ice cream

In recent years, people have become interested in consuming low-fat foods as this reduces the risk of obesity and cardiovascular disease. For this reason, this study optimized the incorporation of passion fruit epicarp (PFE) as a partial fat substitute in dairy ice cream. For this purpose, a central composite rotational design 22 was performed and 5 response variables were optimized, of which 4 variables were maximized (percentage overrun, hardness, adhesiveness, and color coordinates L*, a*, b*), while the melting rate was minimized as a function of two factors (% PFE and % fat). The stability of three types of ice cream was then evaluated: experimental ice cream (3% milk fat and 0.97% PFE), commercial ice cream (4% milk fat and 2% vegetable fat) and control ice cream (3% milk fat without PFE added), according to their physicochemical and sensory properties during 57 days of storage (-22 °C, 85% relative humidity). The results showed that it was possible to reduce the milk fat by up to 25% by adding PFE (0.97%), which significantly reduced the melting rate and resulted in higher hardness (N), adhesiveness and increased yellowness compared to the commercial samples. The optical microscopy analysis also showed that PFE keeps the air bubbles immobile due to the increased viscosity in the serum phase during the 57-day storage.

Foaming and Other Functional Properties of Freeze-Dried Mare's Milk

The aim of this study was to evaluate the effect of the freeze-drying process on the preservation of mare's milk. This was achieved through the characterization of the functional properties of reconstituted freeze-dried mare's milk. The chemical composition, bulk density, foam capacity, and ability to form emulsions of the atherogenic, thrombogenic, and hypercholesterolemic fatty acid index were investigated. The freeze-drying process did not change the proportion of the milk components in the dry matter. The moisture content of the freeze-dried mare's milk was 10.3 g/kg and the bulk was below 0.1 g/mL. The foaming capacity was 111.3%; hence, the foaming capacity of the milk was very poor. The oil binding capacity was 2.19 g/g of protein. The freeze-drying process improves the binding degree and retention of oil by milk proteins, but produced foam was unstable, short-lived, and lacked the ability to retain air fractions. The atherogenic index and thrombogenic index values calculated for reconstituted milk were 1.02 and 0.53, respectively. The hypercholesterolemia fatty acid index was 25.01.

Characterization of Fruit Sorbet Matrices with Added Value from Zizyphus jujuba and Stevia rebaudiana

Sorbets are healthy ice cream alternatives and desired frozen desserts by vegetarians and vegans. This study focuses on assessing the effects of sorbet recipe alteration through the addition of different percentages of Zizyphus jujuba powder. Stevia rebaudiana was used as a sugar substituent. A control sample and five variables were developed. Peaches from the “Laskava” (native Bulgarian) variety were used as the main ingredient. The new sorbet matrices were characterized based on their moisture and ash content, overrun, melting behavior, melting rate, water holding capacity, pH, nutritional data, soluble solids content, titratable acidity, vitamin C content, total phenolic content and antioxidant activity. The microbial load and CIELAB color of the sorbet alternatives was also evaluated. A sensory evaluation revealed the most preferred variant. Panelists evaluated the appearance (n = 6), aroma (n = 5), flavor (n = 5), mouthfeel (n = 7), and aftertaste (n = 5). The soluble solids content varied from 17.50 to 33.03%, the ash content from 0.36 to 5.21%, the moisture content from 63.77 to 80.21%. The studied sorbet matrices have an overrun in the range from 8.11 to 12.32%. Results showed that a potential for the development of peach sorbet matrices with added value and a reasonable consumer acceptability exists. Further research can perfect the recipe and provide a reference for other frozen desserts.

Structure-function relationship of licorice (Glycyrrhiza glabra) root extract-xanthan/guar gum mixture in a high sugar content system

BACKGROUND

Foam-gels are one of the most important multicomponent-model systems in aerated confectionery, and an investigation of their microstructure is desirable. In this research, the structure-function relationship of xanthan gum/guar gum (XG/GG) and licorice (Glycyrrhiza glabra) root extract powder (LEP) was investigated in a high-sugar medium. Foam-gel systems were prepared at 4:10% to 8:20% ratios of LEP to biopolymer.

RESULTS

The results show that increasing the LEP content reduced both the melting point and enthalpy, probably due to higher overrun and weaker junctions. Boosting the XG/GG ratio led the enhancement of mechanical properties, whereas increasing the LEP concentration weakened all textural parameters, which could be due to the poor structure of the network in the presence of the foaming agent, increased moisture content and overrun. In the whipped mixture samples containing 10 g kg^-1 XG/GG, higher foaming capacity was observed. By increasing the level of biopolymers, smaller and more uniform air cells were formed according to a scanning electron microscopical study. At higher concentration of LEP, smaller bubbles and increased porosity were seen, which could be attributed to the availability of surfactant in the interfacial layer.

CONCLUSION

Maximum structural strength was achieved at a 4:20 ratio of LEP to XG/GG. In rheological experiments, pseudoplastic behavior was seen in all samples. Generally, this model system can be simulated for other herbal extracts containing natural surfactants such as saponins. Achieving a more detailed understanding of these structures and their interactions could help in formulating novel food products. © 2021 Society of Chemical Industry.

Shrinkage in frozen desserts

Shrinkage is a well-documented defect in frozen desserts, yet the root causes and mechanisms remain unknown. Characterized by the loss of volume during storage, shrinkage arose during the mid-twentieth century as production of frozen desserts grew to accommodate a larger market. Early research found that shrinkage was promoted by high protein, solids, and overrun, as well as postproduction factors such as fluctuations in external temperature and pressure. Rather than approaching shrinkage as a cause-and-effect defect as previous approaches have, we employ a physicochemical approach to characterize and understand shrinkage as collapse of the frozen foam caused by destabilization of the dispersed air phase. The interfacial composition and physical properties, as well as the kinetic stability of air cells within the frozen matrix ultimately affect product susceptibility to shrinkage. The mechanism of shrinkage remains unknown, as frozen desserts are highly complex, but is rooted in the physicochemical properties of the frozen foam. Functional ingredients and processing methods that optimize the formation and stabilization of the frozen foam are essential to preventing shrinkage in frozen desserts.

Effects of structural attributes on the rheological properties of ice cream and melted ice cream

Although the ice phase greatly influences the properties of ice cream, other structural components also affect its rheological behavior, particularly after melting. In this study, mix viscosity (serum phase viscosity), extent of fat destabilization (FD), and overrun were manipulated to produce different microstructures. The effects of these structural components were evaluated on the rheological properties of the ice creams and melted ice creams. In oscillatory thermorheometry, mix viscosity and then overrun, influenced G' and tanδ below -10 °C. When ice phase decreased (between -10 and -2.7 °C), mix viscosity had reduced effects, but continued to strongly affect G' and tanδ, followed by FD, and with lower effects from overrun. When the ice phase was completely melted at 0 °C, FD had most influence on G' and tanδ, followed by overrun, and with lower effects from mix viscosity. In creep/recovery test, six-element model described well creep behavior of melted ice cream at 0 °C. Viscous behavior at lower shear rate (η0 0 °C) was most influenced by mix viscosity, followed by FD, and lower overrun effects. In stress growth measurement, transient behavior, represented by σY 0 °C, of melted matrix at 0 °C was most influenced by FD, followed by mix viscosity, with lower overrun effects. In flow ramp measurement, Hysteresis Area was most affected by mix viscosity, followed by overrun, and with lower FD effects. Moreover, correlation between Hyst 0 °C and tanδ Peak suggested that structure formation affected the magnitude of tanδ Peak. These results document the importance of microstructure on properties of melted ice cream. PRACTICAL APPLICATION: The understanding of how structural components, such as mix viscosity, fat destabilization, and overrun, affect the ice cream matrix can help manufacturers to control its rheological behavior. The influence of these structural components on the G', tanδ, η_{0 0 °C} , σ_{Y 0 °C} , and Hyst _{0 °C} can be also used to understand the structural rearrangements that occur in meltdown tests and sensory analyses for future studies. Therefore, elucidation of these mechanisms on the rheological properties can directly assist in quality control and new product development in the ice cream industry.

The microstructural, melting, rheological, and sensorial properties of high-overrun frozen desserts

Air incorporated during dynamic freezing influences the development of the microstructure and the final texture of frozen desserts. Frozen desserts were manufactured with 100-175% overrun from a constant ice cream mix formulation. Microstructural elements (fat, air, and ice phases) of the frozen desserts were then investigated and related to the melting, rheological, and sensory properties of the product. Mean ice crystal and air cell size were found to decrease with increasing overrun, and the extent of fat destabilization increased. Frozen desserts manufactured with higher overrun had slower drip-through rate and better shape retention after melting at ambient conditions, demonstrating that fat destabilization and the interplay of fat, air, and serum phases affect the melting behavior. Structural elements also influenced the rheological behavior, as measured by oscillatory thermo-rheometry. Frozen desserts had similar rheological properties at temperatures below the freezing point due to the presence of ice, and the values of G' and G″ (solid-like and viscous-like character, respectively) increased with increasing overrun above the freezing point, corresponding to a more solid-like structure. Slight differences in sensory denseness and breakdown were detected, but sensory texture was not significantly different for the frozen desserts studied. This study provided insights into the role of air in ice cream and frozen desserts, and its influence on product texture.

Nondairy ice cream based on fermented yam (Dioscorea sp.)

BACKGROUND

The demand for industrialized foods that contribute to health and well-being has characterized the new generation of consumers. Yam (Dioscorea sp.) is a nutritious food; however, it is not used very much in industrial food processes. The objective of this study was to develop and to characterize a truly dairy-free low-fat ice cream prepared from unfermented and fermented with yam dough.

RESULTS

The fermentation was conducted by Leuconostoc lactic CCMA 0415 remained viable (107 CFU/g) during 90 days of storage. The fermentation process reduced the starch concentration from 26.82% to 22.35% and the protein concentration from 4.68% to 3.99% and increased the concentration of some minerals (K, S, Cu, Mn, Zn, and Fe). The total phenolic contents for fermented and unfermented ice creams were 51 and 54 mg, respectively. The radical scavenging activity were 18% and 10% with the 1,1-diphenyl-2-picrylhydrazyl method and 44% and 26% with the 2,2'-azino-bis (3 ethylbenzo-thiazoline-6-sulfonic acid) method for the unfermented and fermented samples, respectively. The fermented and unfermented ice creams were both characterized as non-Newtonian fluids exhibiting pseudoplastic behaviors.

CONCLUSIONS

These results indicated that yam is a suitable substitute for milk, thus making it an option to produce edible lactose-free ice cream with low fat.

Time-Resolved Tomographic Quantification of the Microstructural Evolution of Ice Cream

Ice cream is a complex multi-phase colloidal soft-solid and its three-dimensional microstructure plays a critical role in determining the oral sensory experience or mouthfeel. Using in-line phase contrast synchrotron X-ray tomography, we capture the rapid evolution of the ice cream microstructure during heat shock conditions in situ and operando, on a time scale of minutes. The further evolution of the ice cream microstructure during storage and abuse was captured using ex situ tomography on a time scale of days. The morphology of the ice crystals and unfrozen matrix during these thermal cycles was quantified as an indicator for the texture and oral sensory perception. Our results reveal that the coarsening is due to both Ostwald ripening and physical agglomeration, enhancing our understanding of the microstructural evolution of ice cream during both manufacturing and storage. The microstructural evolution of this complex material was quantified, providing new insights into the behavior of soft-solids and semi-solids, including many foodstuffs, and invaluable data to both inform and validate models of their processing.

Effects of Emulsifier, Overrun and Dasher Speed on Ice Cream Microstructure and Melting Properties

Ice cream is a multiphase frozen food containing ice crystals, air cells, fat globules, and partially coalesced fat globule clusters dispersed in an unfrozen serum phase (sugars, proteins, and stabilizers). This microstructure is responsible for ice cream's melting characteristics. By varying both formulation (emulsifier content and overrun) and processing conditions (dasher speed), the effects of different microstructural elements, particularly air cells and fat globule clusters, on ice cream melt-down properties were studied. Factors that caused an increase in shear stress within the freezer, namely increasing dasher speed and overrun, caused a decrease in air cell size and an increase in extent of fat destabilization. Increasing emulsifier content, especially of polysorbate 80, caused an increase in extent of fat destabilization. Both overrun and fat destabilization influenced drip-through rates. Ice creams with a combination of low overrun and low fat destabilization had the highest drip-through rates. Further, the amount of remnant foam left on the screen increased with reduced drip-through rates. These results provide a better understanding of the effects of microstructure components and their interactions on drip-through rate.

PRACTICAL APPLICATIONS

Manipulating operating and formulation parameters in ice cream manufacture influences the microstructure (air cells, ice crystals, and fat globule clusters). This work provides guidance on which parameters have most effect on air cell size and fat globule cluster formation. Further, the structural characteristics that reduce melt-down rate were determined. Ice cream manufacturers will use these results to tailor their products for the desired quality attributes.

Synchrotron X-ray tomographic quantification of microstructural evolution in ice cream – a multi-phase soft solid

Synchrotron X-ray tomography reveals the evolving internal morphology of a multi-phase soft solid, ice cream, enabling time dependent quantitation.

The potential application of rice bran wax oleogel to replace solid fat and enhance unsaturated fat content in ice cream

The development of structure in ice cream, characterized by its smooth texture and resistance to collapse during melting, depends, in part, on the presence of solid fat during the whipping and freezing steps. The objective of this study was to investigate the potential application of 10% rice bran wax (RBW) oleogel, comprised 90% high-oleic sunflower oil and 10% RBW, to replace solid fat in ice cream. A commercial blend of 80% saturated mono- and diglycerides and 20% polysorbate 80 was used as the emulsifier. Standard ice cream measurements, cryo-scanning electron microscopy (cryo-SEM), differential scanning calorimetry (DSC), and transmission electron microscopy (TEM) were used to evaluate the formation of structure in ice cream. RBW oleogel produced higher levels of overrun when compared to a liquid oil ice cream sample, creating a lighter sample with good texture and appearance. However, those results were not associated with higher meltdown resistance. Microscopy revealed larger aggregation of RBW oleogel fat droplets at the air cell interface and distortion of the shape of air cells and fat droplets. Although the RBW oleogel did not develop sufficient structure in ice cream to maintain shape during meltdown when a mono- and diglycerides and polysorbate 80 blend was used as the emulsifier, micro- and ultrastructure investigations suggested that RBW oleogel did induce formation of a fat globule network in ice cream, suggesting that further optimization could lead to an alternative to saturated fat sources for ice cream applications.

Ice Cream Structural Elements that Affect Melting Rate and Hardness

Statistical models were developed to reveal which structural elements of ice cream affect melting rate and hardness. Ice creams were frozen in a batch freezer with three types of sweetener, three levels of the emulsifier polysorbate 80, and two different draw temperatures to produce ice creams with a range of microstructures. Ice cream mixes were analyzed for viscosity, and finished ice creams were analyzed for air cell and ice crystal size, overrun, and fat destabilization. The ice phase volume of each ice cream were calculated based on the freezing point of the mix. Melting rate and hardness of each hardened ice cream was measured and correlated with the structural attributes by using analysis of variance and multiple linear regression. Fat destabilization, ice crystal size, and the consistency coefficient of the mix were found to affect the melting rate of ice cream, whereas hardness was influenced by ice phase volume, ice crystal size, overrun, fat destabilization, and the rheological properties of the mix.