Model mixtures evidence the respective roles of whey protein particles and casein micelles during acid gelation

Structure Response of Preadsorbed Saliva Pellicle to the Interaction between Dairy and Saliva Protein

Using the surface characterization techniques of quartz crystal microbalance with dissipation, atomic force microscopy, and scanning electron microscopy, the structure of the salivary pellicle was investigated before and after it was exposed to dairy proteins, including micellar casein, skim milk, whey protein isolate (WPI), and a mixture of skim milk and WPI. We have shown that the hydration, viscoelasticity, and adsorbed proteinaceous mass of a preadsorbed salivary pellicle on a PDMS surface are greatly affected by the type of dairy protein. After interaction with whey protein, the preadsorbed saliva pellicle becomes softer. However, exposure of the saliva pellicle to micellar casein causes the pellicle to partially collapse, which results in a thinner and more rigid surface layer. This structure change correlates with the measured lubrication behavior when the saliva pellicle is exposed to dairy proteins. While previous studies suggest that whey protein is the main component in milk to interact with salivary proteins, our study indicates interactions with casein are more important. The knowledge gained here provides insights into the mechanisms by which different components of dairy foods and beverages contribute to mouthfeel and texture perception, as well as influence oral hygiene.

High-intensity ultrasound treatment on casein: Pea mixed systems: Effect on gelling properties

This study aimed to investigate the suitability of the application of high-intensity ultrasounds (HIUS) to improve the acid induced gelation of mixed protein systems formed by casein micelles (CMs) and pea. The protein suspensions were prepared in different protein ratios CMs: pea (100:0, 80:20, 50:50, 20:80, 0:100) at 8% (w/w) total protein concentration. In the suspensions, the ultrasound treatment produced an increase in solubility, surface hydrophobicity, and a decrease in the samples' viscosity, with more remarkable differences in protein blends in which pea protein was the major component. However, the replacement of 20% of CMs for pea proteins highly affected the gel elasticity. Hence, the creation of smaller and more hydrophobic building blocks before acidification due to the HIUS treatment increased the elasticity of the gels up to 10 times. Therefore, high-intensity ultrasounds are a suitable green technique to increase the gelling properties of CMs: pea systems.

Physicochemical and Rheological Properties of Stirred Yoghurt during Storage Induced from High-Intensity Thermosonicated Goat and Cow Milk

The effect of high-intensity thermosonication (HIT) pretreatment (20 kHz frequency, output power 4000 W and 25% amplitude for 5, 10 and 15 min) on the physicochemical and rheological properties of stirred yoghurt made from goat milk was studied. Various parameters of the milk were evaluated, such as the particle size, pH and soluble calcium and phosphorus, while other parameters of the stirred yoghurt were evaluated during storage (up to 18 days), such as the rheological measurements, syneresis, pH values, titratable acidity, color, and sensory properties. The microstructure had more interconnected chains than the stirred yoghurt made from homogenized milk on the first day of the storage period. Moreover, the HIT process reduced the diameter of the fat globules in the goat milk, making them smaller than those of homogenized milk. This pretreatment could be used successfully in the production of stirred yoghurt to improve major quality parameters such as delayed syneresis, increased viscosity and enhanced sensory properties during storage.

Understanding the differences in heat-induced gel properties of twelve legume proteins: A comparative study

This study aimed to investigate the rheological and textural properties of heat-induced gels from twelve legume protein isolates at pH 3.0 and 7.0, including black kidney bean (BKPI), speckled kidney bean (SKPI), panda bean (PDPI), cowpea (CPPI), mung bean (MPI), adzuki bean (API), rice bean (RPI), black soybean (BPI), soybean (SPI), chickpea (CPI), broad bean (BRPI) and pea (PPI). SDS-PAGE revealed that 7S globulin was prominent protein in BKPI, SKPI, PDPI, CPPI, MPI, API and RPI, the main protein fraction of CPI was 11S globulin, and BPI, SPI, BRPI and PPI contained both 7S and 11S globulins as major components. Based on the gel's Power Law constant (K') and hardness, twelve legume proteins were divided into three categories with high, medium and low gel strength. BKPI, SKPI and PDPI with Phaseolin being the major protein fraction showed high gel strength regardless of pH. Electrostatic interactions, hydrophobic interactions and hydrogen bonds were the most important intermolecular forces in the formation of legume protein gel networks, of which gel strength at pH 3.0 and pH 7.0 was significantly affected by electrostatic interactions and hydrogen bonds, respectively. Moreover, gel strength was also remarkably negatively influenced by the non-network proteins. SEM observation indicated that the microstructure of gels at pH 7.0 was denser and more homogeneous than that at pH 3.0, leading to better water holding capacity. These findings would be of great importance for understanding the differences in legume protein gels, and also laid the scientific support for expanding applications of legume proteins in gel-based foods.

Regulation of yak longissimus lumborum energy metabolism and tenderness by the AMPK/SIRT1 signaling pathways during postmortem storage

AMPK can activate nicotinamide phosphoribosyltransferase (NAMPT), increasing the ratio of oxidized nicotinamide adenine dinucleotide (NAD+)/reduced nicotinamide adenine dinucleotide (NADH) ratio, leading to the activation of the energy receptor SIRT1. This pathway is known as the AMPK/SIRT1 signaling pathway. SIRT1 deacetylates and activate LKB1, which is activated by phosphorylation of AMPK (Thr172) and inhibited by phosphorylase-mediated dephosphorylation of AMPK. At the same time, increased AMP/ATP and NAD+/NADH ratios lead to the activation of AMPK and SIRT1. SIRT1 and AMPK can activate each other forming a positive feedback loop, which can strengthen catabolism and weaken anabolism thus maintaining energy homeostasis of energy metabolism. At present, there has been no systematic study on AMPK-associated signaling cascades in stored yak meat and details of the AMPK/SIRT1 signaling under these conditions are not known. In this study, NAD+, NADH were added to yak longissimus thoracic muscles to study AMPK pathway regulation by AMPK/SIRT1 signaling. NAD+ significantly increased the activity of AMPK and glycolysis during postmortem maturation, increased the rate of energy metabolism, and increased the expression of AMPK protein, indicating that NAD+ increased energy metabolism in the stored muscle by promoting AMPK activity. NADH treatment inhibited both AMPK activation and glycolysis, together with increasing the pH in the muscle. The results showed that SIRT1 activation elevated the activity of AMPK, leading to its phosphorylation and the activation of glycolysis. Thus, AMPK activity was found to increase in yak meat as an adaptation to hypoxic conditions. This allows more effective regulation of energy production and improves the tenderness of the meat.

Response Surface Optimization of Solar Drying Conditions and the Effect on the Quality Attributes and Drying Characteristics of Qula Casein

The objective of this study was to investigate the potential application of a mixed-mode solar dryer to Qula dehydration in the Qinghai-Tibet Plateau of China. A three-factor five-level central composite rotatable design (CCD) of the response surface methodology (RSM) was employed to evaluate the influences of drying process variables on quality attributes in terms of lipid oxidation [peroxide (POV) and thiobarbituric acid reactive substance (TBARS)] and Maillard reaction (5-hydroxymethylfurfural, 5-HMF). The impact of drying temperature (30−50 °C), material thickness (5−15 mm), and wind velocity (0.4−1.4 m/s) on the color, POV, TBARS, and 5-HMF of Qula were studied. Optimum operating conditions were found to be a temperature of 43.0 °C, material thickness of 11.0 mm, and wind velocity of 1.0 m/s based on the minimum of POV, TBARS, and 5-HMF. In this condition, the values of POV, TBARS, and 5-HMF were 0.65 meq/kg, 0.516 mg/kg, and 4.586 mg water/L, respectively, which are significantly lower than for drying of Qula by open sun-drying (p < 0.05). Compared with open sun-drying, the drying time of Qula by solar drying was shortened by 61.5%. The results indicate that the mixed-mode solar dryer is a feasibility drying technology for Qula and could effectively improve the quality of products.

ISOLASI PROTEIN KACANG MERAH DAN KACANG HIJAU MENGGUNAKAN METODE ASAM BASA DIKOMBINASIKAN DENGAN PROSES ENZIMATIS

Red beans (Phaseolus vulgaris L.) and greens beans (Phaseolus raditus L.) proteins contain high amount of essential amino acids lysine and leucine. The study aimed to determine the optimum conditions for protein isolation process from red beans and green beans flour to produce the highest protein content. Additionally, an enzymatic hydrolysis was aimed to produce isolates or protein concentrates of red beans and green beans with good digestibility. The research method used was the Response Surface Methodology (RSM) Box-Behnken Design with Design Expert 10. The variables used in this process were extraction temperature (30-50°C), extraction pH (8.50-9.50), and time extraction (30-60 minutes). The results showed that the optimum conditions for the extraction of red beans protein were extraction pH of 8.60, temperature of 30°C, and time of 30.1 minutes, with the resulting protein content of 86.88±1.38% with and a validity value of 0.91. Meanwhile, the optimum conditions for the green beans protein extraction process were extraction pH of 8.83, extraction temperature of 30°C, extraction time of 30 minutes which yielded protein content of 88.27±1.08% and a validity value of 0.97. Enzymatic hydrolysis using of 3% (w/w) bromelain enzyme on red bean and mung bean protein concentrate powder was able to increase protein digestibility by 15.61 and 14.51%, respectively.

Effects of polymerized whey protein on goaty flavor and texture properties of fermented goat milk in comparison with β-cyclodextrin

Goaty flavor and poor consistency may impact consumer acceptance of fermented goat milk. The undesirable characteristics can mainly be attributed to the presence of short-medium chain free fatty acid (SM-FFA) especially C6-C10 fatty acids and low αs1-casein content in goat milk. This study aimed to investigate the effects of polymerized whey protein (PWP) on goaty flavor as well as the texture properties of fermented goat milk in comparison with β-cyclodextrin (β-CD). Samples were evaluated on sensory properties, SM-FFA contents, texture, and apparent viscosity. Compared with control, the fatty acids contents (C6, C8, C10) decreased significantly in fermented goat milk with 0·5% β-CD (22, 71, 54%, respectively) and with 0·7% PWP (45, 58, 71%, respectively). There was a synergistic effect of 0·3% β-CD and 0·6% PWP in decreasing the contents of SM-FFA (C6, C8, C10) sharply by 89, 90, 79%. Under the same percentage of addition, yogurts made with β-CD showed a higher (P < 0·05) apparent viscosity than those with PWP. However, the addition of PWP could increase the texture parameters of fermented goat milk (P < 0·05). Combination of PWP and β-CD presented a more desirable texture and consistency in fermented goat milk. Results indicated that polymerized whey protein can be used to reduce the goaty flavor and improve the texture of fermented goat milk.

Characterization of yogurts made with milk solids nonfat by rheological behavior and nuclear magnetic resonance spectroscopy

The effect of adding milk solids nonfat (MSNF) on the physical properties and microstructure of yogurts was investigated. The physical properties of fat free yogurt, fat free with MSNF yogurt, whole fat yogurt, and whole fat with MSNF yogurt were analyzed using shear viscosity, viscoelasticity, and texture analysis. The two yogurts with MSNF had higher consistency coefficient (K), storage modulus (G′), yield stress, and hardness. To gain insight into the multiphase system, nuclear magnetic resonance (NMR) and brightfield microscope images were acquired. The addition of MSNF significantly modified NMR relaxation time; T₁ values were reduced significantly. Brightfield microscope images showed that the size of the protein network of the two yogurts with MSNF added was greater than that of the two yogurts without MSNF added. The microstructural information supported the physical information. The results showed that the increase in MSNF contributed positively to strengthening the physical/mechanical properties of yogurt.