Rheological Properties Of Milk Research Articles

Effects of Adding Pectin to Milk in Varying Amounts on the Rheological Properties of Milk

Pectin, which is used as an additive in the food, cosmetics, pharmaceutical, and health sectors due to its safety, non-toxicity, low production cost, and high availability, is used as a thickener, gelling agent, brightener, stabilizer, emulsifier, and fat and sugar replacer in low-calorie foods. It is also used in milk and dairy products as a stabilizer to prevent proteins from clumping. In this study, the rheological properties of pectin and milk mixtures with pectin/milk powder (w/w) ratios of 0.1, 0.25, 0.5, 0.75, 1 and 1.5 were examined. First, a flow curve test was applied in the range of 0,01-1000 s-1 to obtain the viscosity curves and yield stress values of the samples. Then, an amplitude sweep test was performed at a fixed frequency of 10 rad/s and in the strain range of 0.01-100% to determine the linear viscoelastic range (LVR) of the samples and the solid and liquid structure of the samples. To determine the time-dependent behavior of the samples in non-destructive deformation, frequency sweep tests were performed at constant strain (0.01%) in the LVR range obtained from the amplitude sweep test and in the range of 0.1-100 rad/s. Finally, three interval thixotropy tests (3ITT) were performed to observe the structural recovery of the samples. As a result of rheological tests, it was determined that pectin-free milk showed Newtonian properties, other samples showed shear thinning properties, and viscosity values increased as the pectin rate increased. While all samples are solid at low strains, the liquid feature becomes dominant at high strains. It has been observed that as the pectin ratio in milk increases, the strain values at the yield point, where the liquid feature becomes dominant, also increase. Except for the sample with the highest pectin content, it was observed that the dominance of the storage modulus over the loss modulus was greater at low frequencies than at high frequencies. As a result of 3ITT, it was determined that the percentage of recovery at the 600th second increased as the pectin rate increased.

Evaluation of rheological properties of plant extracts from Mediterranean flora in goat milk

The pastoral area of internal Cilento (Campania, Southern Italy) claims many valuable cheeses and according to the oral tradition, when animal rennet was not available for goat cheeses, some wild plants were used for their curdling properties. The cheese market is in continuous evolution, looking for new cheeses but also linked to the territory and tradition. On the bases of an ethnobotanical investigation, the coagulating properties of water extracts of the wild species Teucrium chamaedrys L., Galium aparine L., Galium verum L., Silybum marianum (L.) Gaertn., Chelidonium majus L., and Urtica dioica L. were evaluated on goat milk by rheological test with a Formagraph instrument at two doses (60 μl vs. 50 μl per 10 mL goat milk) at 36 °C, and at lab-scale by micro cheesemaking test at 0.5 mL/100 mL goat milk. For all plant extracts, the best Milk Rheological Properties were found at the lowest dose of extract. In the lab-scale test, all plant extracts except C. majus showed interesting clotting behaviour. The results confirmed the pastoral tradition and opened to new perspectives to produce goat cheeses with no-animal rennet using these wild species, linked to the heritage of the geographical area. Further studies will be carried out on the chemical composition, besides the antioxidant capacity and polyphenol content, to attempt explaining the MRPs.

Effect of high-pressure-jet processing on the viscosity and foaming properties of pasteurized whole milk

The processing of milk using high-pressure technologies has been shown to dissociate casein micelles, denature whey proteins, and change the appearance and rheological properties of milk. A novel high-pressure processing technology called high-pressure-jet (HPJ) processing is currently being investigated for use in the food industry. Few studies have evaluated the effects of HPJ technology on dairy foods. The present study investigated the physicochemical and foaming properties of homogenized pasteurized whole milk processed at pressures from 0 to 500 MPa using HPJ processing. The apparent particle size exhibited a monomodal distribution in whole milk samples processed up to 125 MPa and a bimodal distribution for samples processed at 250, 375, and 500 MPa. The viscosity increased from approximately 2 to 5 mPa·s when whole milk was processed using HPJ at 375 MPa, and foam expansion increased from approximately 80 to 140% after processing at >125 MPa. Foam stability was limited to pressures in the 375 to 500 MPa range. We hypothesized that the increase in apparent particle size was due to the dissociation of casein micelles into surface-active casein protein monomers, and the formation of casein-casein and casein-fat particles. Ultracentrifugation of samples into 3 milk fractions (supernatant, serum, and precipitate), and subsequent fat and protein analysis on the 3 fractions, showed that a strong interaction between casein proteins and fat triglycerides occurred, evidenced by the increase in fat content associated with the precipitate fraction with increasing pressure. This suggests that stable casein-fat aggregates are formed when whole milk is processed using HPJ at pressure >125 MPa.

Реологические показатели сгущенных молочных консервов c сахаром

Изучено влияние гидролиза лактозы на реологические характеристики сгущенных молочных консервов с сахаром. Обоснована актуальность разработки технологии низколактозных сгущенных молочных консервов. В качестве объектов исследований использовали пастеризованное молоко (обезжиренное и цельное), ферментный препарат GODO-YNL2 (Япония), свекловичный сахар. Вязкость гидролизованных сгущенных молочных консервов с сахаром определяли на ротационном вискозиметре Реотест-2. Изучено влияние массовой доли сухих веществ на эффективную вязкость молока цельного и обезжиренного сгущенного гидролизованного с сахаром. Установлены зависимости эффективной вязкости сгущенных молочных консервов с гидролизованной лактозой от скорости деформации. Определена эффективная вязкость экспериментальных образцов: молоко обезжиренное гидролизованное сгущенное с сахаром с массовой долей сухих веществ продукта 66% − 2,8 Па*с; молоко цельное гидролизованное сгущенное с сахаром с массовой долей сухих веществ продукта 62% − 3,2±0,2 Па*с; молоко цельное гидролизованное сгущенное с сахаром с массовой долей сухих веществ продукта 64% − 3,5±0,2 Па*с. Обоснованы оптимальные показатели массовой доли сухих веществ: 66% – для обезжиренного молока; 59 и 62% – для цельного молока. Рекомендовано продолжить исследования возможности совершенствования технологии гидролизованных сгущенных молочных консервов с сахаром на основе применения стабилизационных систем.

Calcium-induced skim milk gels using different calcium salts

This study investigated the effects of heating skim milk with soluble calcium salts, calcium chloride, calcium lactate, calcium gluconate and calcium lactobionate, on the physico-chemical and rheological properties of milk. Regardless of the type of salt added, the amount of casein in milk serum decreased and the amount of calcium in centrifuge sediment increased along with the serum calcium. The amount of calcium salt required for gelation and the gel firmness (G′) varied depending on the salt. The aCa2+ order in milk was calcium chloride>calcium lactate>calcium gluconate>calcium lactobionate. With the same amount of added calcium salt, the final G′ of milk gel followed the same order. The findings from this study suggest that the different association constants and formation of an intermediate calcium complex with hydroxycarboylate groups affected the calcium ion activity, which may influence the gelation properties in milk.

Effects of Size and Stability of Native Fat Globules on the Formation of Milk Gel Induced by Rennet.

Rennet-induced gelation crucially impacts cheese structure. In this study, effects of the size and stability of native fat globules on the kinetics of rennet-induced coagulation were revealed by determining the caseinomacropeptide release rate and rheological properties of milk. Moreover, the mobility and stability of fat globules during renneting was revealed using diffusing wave spectroscopy and confocal laser scanning microscopy. By use of a 2-stage gravity separation combined centrifugation scheme, native fat globules were selectively separated into small (SFG, D4,3 = 1.87 ± 0.02 μm) and large fat globules (LFG, D4,3 = 5.65 ± 0.03 μm). The protein and fat content of SFG and LFG milk were then standardized to 3.2 g/100 mL and 1.2 g/100 mL, respectively. The milk containing different sized globules were then subjected to renneting experiments in the laboratory. Reduction of globule size accelerated the aggregation of casein micelles during renneting, giving a shorter gelation time and earlier 1/l* change. The gel produced from LFG milk was broken due to coalescent fat globules and generated coarser gel strands compared to the finer strands formed with SFG milk. Structural differences were also confirmed with a higher final storage modulus of the curd made from SFG milk than that from the LFG. In conclusion, the size of fat globules affects the aggregation of casein micelles. Moreover, fat globule coalescence and creaming during renneting, also affects the structure of the rennet gel. A better understanding of the size of globules effect on milk gelation could lead to the development of cheese with specific properties.

Viability of probiotic strains Lactobacillus acidophilus NCFM® and Bifidobacterium lactis HN019 and their impact on sensory and rheological properties of milk and dark chocolates during storage for 180 days

The popularity of chocolate as food around the world combined with high level of health-related awareness of the contemporary consumer, imposed the idea of enriching composition of different kinds of chocolate with probiotic bacterial strains. In this study, two strains of probiotic bacteria, Lactobacillus acidophilus NCFM® and Bifidobacterium lactis HN019, were incorporated in milk and dark chocolate. Final products were kept at two temperatures (4 °C and 20 °C) at which viability of added strains was monitored with the aim of determining the recommended storage temperature. In order to determine the effects of probiotics an examination of their sensory and rheological properties was carried out immediately after production (0–30 days) and during storage of 90 and 180 days. Based on the obtained results it can be seen that the probiotic strain L. acidophilus NCFM® exerted higher viability compared to strain B. lactis HN019 in both kinds of chocolates, while a greater number of cells of both strains was determined at 4 °C. The increase in yield stress of chocolates with probiotics with larger granulation was observed, while the apparent and plastic viscosity did not experience major changes. Despite the occasionally noticed sandiness, sensory properties of chocolates were not significantly changed during storage.