Influence of heat treatment of goat milk on casein micelle size, rheological and textural properties of acid gels and set type yoghurts

Effects of pasteurization on set yogurt fortified with astaxanthin-rich yolk: Evaluation of physicochemical properties, stability, and biological activity

Pasteurization usually has a large influence on yogurt and astaxanthin. This study aimed to investigate the effects of 3 pasteurization methods, including low-temperature, long-time treatment at 63°C for 30 min (LTLT-1) and 65°C for 30 min (LTLT-2), and high-temperature, short-time treatment at 75°C for 15 s (HTST), on the physicochemical properties, stability, and biological activity of set yogurt fortified with astaxanthin-rich yolk. The results showed that the LTLT-2 group had a higher astaxanthin retention, with no significant difference from the LTLT-1 group. The in vitro digestion results also confirmed that LTLT-2 had a high free radical scavenging capacity. Temperatures between 63°C and 65°C are within a safe range for preventing significant heat degradation of astaxanthin. Over the 21-d storage period, LTLT-2 significantly outperformed LTLT-1 and HTST regarding texture and particle size. This work demonstrates that the pasteurization conditions of 65°C for 30 min could be used to prepare a functional set yogurt with stable quality and antioxidant activity.

Decoration of Fe3O4-vitamin C nanoparticles on alginate-chitosan nanocomplex: Characterization, safety, bioacessibility boost and Iron Nanofortification in A2 goat milk gels

In this study, an alginate-chitosan (AL-CS) nanocomplex decorated with vitamin C coated iron oxide nanoparticles (Fe3O4-vit C NPs) was investigated as a novel nanoiron fortification agent. The Fe3O4-vit C NPs decorated on AL-CS nanocomplex underwent comprehensive characterization, including zeta potential, fourier transform infrared spectroscopy, X-ray diffraction, and UV-vis spectroscopy. The transmission electron microscopy (TEM) analysis confirmed the decoration of Fe3O4-vit C NPs on AL-CS nanocomplex. The dynamic light scattering and thermogravimetric analysis showed enhanced thermal properties of decorated nanocomplex than the undecorated control. Biocompatibility testing on HepG2 cell lines revealed improved compatibility, while intestinal Caco2 cell lines showed approximately 51 % greater bioacessibility than controls. Further, 8 mg of Fe3O4-vit C NPs decorated AL-CS nanocomplex nanofortified 80 g of A2 goat milk gels (GMGs) which provided 0.072 mg/g of nanoiron without showing significant changes in texture and color compared to the control A2 GMGs. The PCA analysis helped to identify the impact of various factors for the preparation of decorated nanocomplex.

Goat's Skim Milk Enriched with Agrocybe aegerita (V. Brig.) Vizzini Mushroom Extract: Optimization, Physico-Chemical Characterization, and Evaluation of Techno-Functional, Biological and Antimicrobial Properties

The aim of this study was to develop a novel functional ingredient-goat's skim milk enriched with Agrocybe aegerita (V. Brig.) Vizzini mushroom extract (ME/M)-using Central Composite Design (CCD). The optimized ME/M ingredient was evaluated for its physico-chemical, techno-functional, biological, and antimicrobial properties. Physico-chemical properties were analyzed using Attenuated Total Reflectance Fourier Transform Infrared (ATR-FTIR) spectroscopy, Scanning Electron Microscopy (SEM), and Dynamic Light Scattering (DLS). The ingredient exhibited a polymodal particle size distribution and contained glucans, along with a newly formed polypeptide resulting from the selective cleavage of goat milk proteins. A 0.1% ME/M solution demonstrated good emulsifying and foaming properties. Additionally, ME/M showed strong antiproliferative effects on human cancer cell lines, particularly Caco-2 (colorectal) and MCF7 (breast) cancer cells. The ingredient also promoted HaCaT cell growth without cytotoxic effects, suggesting its safety and potential wound-healing properties. Furthermore, the addition of ME/M to HaCaT cells inoculated with Staphylococcus aureus resulted in reduced IL-6 levels compared to the control (without ME/M), indicating a dose-dependent anti-inflammatory effect. The optimized ME/M ingredient also exhibited antibacterial, antifungal, anticandidal, and antibiofilm activity in one-fourth of MIC. These findings suggest that the formulated ME/M ingredient has strong potential for use in the development of functional foods offering both desirable techno-functional properties and bioactive benefits.

Impact of ultrasonic and heat treatments on the physicochemical properties and rennet-induced coagulation characteristics of milk from various species

This study investigates the effects of heat and ultrasonic treatments on the physicochemical parameters and rennet-induced coagulation properties of milk from a variety of species, including cow, goat, buffalo, and donkey. Milk samples were subjected to heat treatments at different temperatures (65 °C, 80 °C, 90 °C, 100 °C) and ultrasonic treatment at varying power levels (200 W, 400 W, 600 W, 800 W, 1000 W). The results revealed that changes in turbidity, particle size, zeta potential, secondary structure, and surface hydrophobicity were altered by both ultrasonic and heat treatments, as well as the kind of milk. Ultrasonic treatment of cow milk decreased α-helix content while increasing β-turn content. Under similar ultrasonic treatment, goat milk showed a considerable increase in β-sheet content, whereas β-turn and random coil contents decreased compared to control samples. Notably, the water-holding capacity of gels formed from all four types of milk increased significantly with the intensity of ultrasonic and heat treatments. The hardness of buffalo milk gels increased significantly after ultrasonic and thermal treatments, ranging from 63 °C for 30 min to 90 °C for 15 min, but the hardness of cow and goat milk gels increased in varying degrees compared to their control samples. Furthermore, gels from cow and goat milk had higher storage modulus (G') and loss modulus (G'') than those from buffalo and donkey milk, and changes in G' and G'' from the examined milk were altered by ultrasonic and heat treatments. These findings offer important insights into refining milk processing procedures to improve dairy product quality and usefulness.

Perspectives on the yogurt rheology

The oral processing of yogurt is a dynamic process involving a series of deformation processes. Rheological knowledge is essential to understand the structure and flow properties of yogurt in the mouth and to explore its relationship with sensory perception. Yogurt is rheologically characterized as a non-Newtonian viscoelastic material. The rheological properties of yogurt are affected by many factors, from production to consumption. Therefore, rheological measurements are widely used to predict and control the final quality and structure of yogurts. Recent studies focus on the elucidation of the effects of cultures and processes used in production, as well as the design of different formulations to improve the rheological properties of yogurts. Moreover, the science of tribology, which dominates the surface properties of interacting substances in relative motion to evaluate the structural sensation in the later stages of eating in addition to the rheological properties that give the feeling of structure in the early stages of eating, has also become the focus of recent studies. For a detailed comprehension of the rheological properties of yogurt, this review deals with the factors affecting the rheology of yogurt, analytical methods used to determine rheological properties, microstructural and rheological characterization of yogurt, and tribological evaluations.

Physicochemical, sensory, and antioxidant characteristics of stirred-type yogurt enriched with Lentinula edodes stipe powder

The Lentinula edodes stipe (LES), a by-product of L. edodes fruiting body processing, is rich in dietary fiber, protein, and polysaccharides, which can be served as the functional ingredient in dairy products. In this study, stirred yogurts fortified with 1%, 2%, and 3% LES were prepared, and the effects of LES on the changes in color, pH, titratable acidity (TA), viable lactic acid bacteria (LAB) cells, syneresis, viscosity, texture, and antioxidant activity of the flavored yogurt were monitored at the beginning and the end of storage. The LES decreased the lightness, increased the red-green color values and yellow-blue color values, decreased the pH values, and increased the contents of TA, the viable LAB cells, and the antioxidant activity of yogurt samples in a dose-dependent manner. The addition of LES showed double-edged effects on the texture of yogurt, which significantly reduced firmness and viscosity but decreased the syneresis. Compared with plain yogurt, the 2% LES-fortified yogurt exhibited similar index values of texture parameters and higher scores of the appearance, fermented odor, taste quality, and overall acceptance, suggesting that this might be the optimal dose for industrial production. After cold storage for 28 days, pH values of all yogurt samples further decreased with increasing of TA. Interestingly, syneresis of LES-fortified yogurt decreased and the viable LAB cells and antioxidant activity of 3% LES-fortified yogurt slightly decreased. Therefore, LES is beneficial to improve physicochemical, sensory, and antioxidant properties of yogurt, which has the potential to be used in functional dairy products.

Revolutionizing goat milk gels: A central composite design approach for synthesizing ascorbic acid-functionalized iron oxide nanoparticles decorated alginate-chitosan nanoparticles fortified smart gels

Goat milk gels (GMGs) are popular food due to their high water content, low-calorie density, appealing taste, texture enhancers, stability, and satiety-enhancing characteristics, making them ideal for achieving food security and zero hunger. The GMGs were optimized using the central composite design matrix of response surface methodology using goat milk powder (35-55 g), whole milk powder (10-25 g), and potato powder (10-15 g) as independent variables. In contrast, complex modulus, flow stress, and forward extrudability were chosen as dependent variables. The maximum value of complex modulus 33670.9 N, good flow stress 7863.6 N, and good extrudability 65.32 N was achieved under optimal conditions. The optimized goat milk gel was fortified with ascorbic acid-coated iron oxide nanoparticle (magnetic nature) decorated alginate-chitosan nanoparticles (AA-MNP@CANPs), making it nutritionally rich in an economically feasible way-the decorated AA-MNP@CANPs characterized for size, shape, crystallinity, surface charge, and optical characteristics. Finally, the optimized fortified smart GMGs were further characterized via Scanning electron microscopy, Rheology, Texture profile analysis, Fourier transforms infrared (FTIR), and X-Ray Diffraction (XRD). The fortified smart GMGs carry more nutritional diversity, targeted iron delivery, and the fundamental sustainability development goal of food security.

Acid and rennet gelation properties of sheep, goat, and cow milks: Effects of processing and seasonal variation

Gelation is an important functional property of milk that enables the manufacture of various dairy products. This study investigated the acid (with glucono-δ-lactone) and rennet gelation properties of differently processed sheep, goat, and cow milks using small-amplitude oscillatory rheological tests. The impacts of ruminant species, milk processing (homogenization and heat treatments), seasonality, and their interactions were studied. Acid gelation properties were improved (higher gelation pH, shorter gelation time, and higher storage modulus (G') by intense heat treatment (95°C for 5 min) to comparable extents for sheep and cow milks, both better than those for goat milk. Goat milk produced weak acid gels with low G' (<100 Pa) despite improvements induced by heat treatments. Seasonality had a marked impact on the acid gelation properties of sheep milk. The acid gels of late-season sheep milk had a lower gelation pH, no maximum in tan δ following gel formation, and 70% lower G' values than those from other seasons. We propose the potential key role of a critical acid gelation pH that induces structural rearrangements in determining the viscoelastic properties of the final gels. For rennet-induced gelation, compared with cow milk, the processing treatments of the goat and sheep milks had much smaller impacts on their gelation properties. Intense heat treatment (95°C for 5 min) prolonged the rennet gelation time of homogenized cow milk by 8.6 min (74% increase) and reduced the G' of the rennet gels by 81 Pa (85% decrease). For sheep and goat milks, the same treatment altered the rennet gelation time by only less than 3 min and the G' of the rennet gels by less than 14 Pa. This difference may have been caused by the different physicochemical properties of the milks, such as differences in their colloidal stability, proportion of serum-phase caseins, and ionic calcium concentration. The seasonal variations in the gelation properties (both acid and rennet induced) of goat milk could be explained by the minor variation in its protein and fat contents. This study provides new perspectives and understandings of milk gelation by demonstrating the interactive effects among ruminant species, processing, and seasonality.

Rheological Properties of Goat Milk Coagulation as Affected by Rennet Concentration, pH and Temperature

Various factors affect rennet coagulation and consequently cheese yield, but the subject of research has been mainly the cow milk. For the purpose of goat cheese production optimization, this paper investigated the influence of enzyme concentration (0.01–0.054 g/L), pH (6.5–6.1) and temperature (27–35 °C) on rennet coagulation of goat milk. Coagulation time (RCT), aggregation rate (AR), and gel firmness (G’60 and GF), were measured by oscillatory rheometry. The decrease in rennet concentration extended RCT. At lower rennet concentrations, a lower AR was recorded, which ranged from 0.02 Pa/s to 0.05 Pa/s. The decrease in pH from 6.5 to 6.1 caused a two times shorter RCT, and a two times faster AR. There was no effect of pH on the firmness of the rennet gel. The increase in coagulation temperature from 27 °C to 35 °C reduced the RCT of pasteurized milk from 12.6 min to 8.6 min, and caused a linear increase in the AR, but did not significantly affect the firmness of the gel. The present study revealed that the optimization of the rennet coagulation process could be directed towards pH lowering, or temperature increase, since they accelerate the process, but do not alter the examined gel firmness parameters.

Recent Insights Into Processing Approaches and Potential Health Benefits of Goat Milk and Its Products: A Review

Goat milk is considered to be a potential source of various macro- and micro-nutrients. It contains a good proportion of protein, fat, carbohydrates, and other nutritional components which help in promoting nutritional and desirable health benefits. Goat milk is considered to be superior in terms of numerous health benefits, and lower risk of allergy, when compared to the milk of other species. Several processing techniques such as pasteurization, ultrafiltration, microfiltration, and ultrasound have been employed to enhance the quality and shelf life of goat milk and its products. The diverse range of goat milk-based products such as yogurt, cheese, fermented milk, goat milk powder, and others are available in the market and are prepared by the intervention of advanced processing technologies. Goats raised in pasture-based feeding systems are shown to have a better milk nutritional composition than its counterpart. Goat milk contains potential bioactive components, which aids in the maintenance of the proper metabolism and functioning of the human body. This review gives insight into the key nutritional ingredients and bioactive constituents present in goat milk and their potential role in the development of various functional foods using different processing technologies. Goat milk could be considered as a significant option for milk consumption in infants, as compared to other milk available.

Heat-Induced Interaction of Milk Proteins: Impact on Yoghurt Structure

Heating milk for yoghurt preparation has a significant effect on the structural properties of yoghurt. Milk heated at elevated temperature causes denaturation of whey protein, aggregation, and some case gelation. It is important to understand the mechanism involved in each state of stabilization for tailoring the final product. We review the formation of these complexes and their consequence on the physical, rheological, and microstructural properties of acid milk gels. To investigate the interactions between denatured whey protein and casein, the formation of covalent and noncovalent bonds, localization of the complexes, and their impact on ultimate gelation and final yoghurt texture are reviewed. The information regarding this fundamental mechanism will be beneficial to develop uniform quality yoghurt texture and potential interest of future research.

Changes in Native Whey Protein Content, Gel Formation, and Endogenous Enzyme Activities Induced by Flow-Through Heat Treatments of Goat and Sheep Milk

The aim of the present study was to assess the effects of different flow-through heat treatments—68, 73, 78, 85, 100 °C for 16 s—applied to in-line homogenized goat and sheep milk. Alkaline phosphatase (ALP) activity in raw goat milk was 324.5 ± 47.3 μg phenol/mL, and that of lactoperoxidase (LPO) was 199.3 ± 6.7 U/L. The respective activities in raw sheep milk were 7615 ± 141 μg phenol/mL and 319 ± 38.6 U/L. LPO activity was not detected in both milk kinds treated at 85 °C for 16 s. Residual enzyme activities at 73 °C for 16 s with respect to the initial levels in raw milk were higher in goat than in sheep milk. The whey protein fraction of sheep milk was more heat sensitive compared to goat counterpart. Sheep milk rennet clotting time (RCT) was not affected by the treatments, while curd firmness decreased significantly (p < 0.05) at 100 °C for 16 s. Treatments more intense than 73 °C for 16 s increased the RCT of goat milk significantly but inconsistently and decreased curd firmness significantly, while yoghurt-type gels made from 73 °C or 78 °C for 16 s treated goat milk exhibited the highest water-holding capacity.