Predicting cutting and clotting time of coagulating goat's milk using diffuse reflectance: effect of pH, temperature and enzyme concentration

Effect of high hydrostatic pressure processing on the rennet coagulation kinetics and physicochemical properties of sheep milk rennet-induced gels

The effects of high hydrostatic pressure on the constituents and coagulation ability and their effect on cheese production of sheep milk have not been studied in detail. The objective of this work was to evaluate the effect of high hydrostatic pressure processing on the coagulation kinetics and physicochemical properties of sheep milk and to explore how such treatment could improve the cheesemaking process. Five batches of milk were tested: 1 untreated control batch and 4 batches each subjected to a different pressure (150, 300, 450, or 600 MPa) for 5 min at 10°C. As treatment pressure increased, values of electrical conductivity and oxidation-reduction potential were found to decrease. However, no significant reduction in pH was recorded. Treatment pressures >300 MPa produced milk with lower lightness (luminosity) and a more yellow and green hue. Pressures >150 MPa resulted in micellar fragmentation, as well as significant increases in particle size, viscosity, and water-holding capacity as a consequence of the denaturing of soluble proteins. High-pressure treatments increased the solubility of colloidal calcium phosphate, leading to a considerable increase in the concentration of minerals in the serum phase. The highest concentrations of calcium and phosphorus in the rennet whey of milk were reached at 300 MPa. Curd coagulation time was reduced by 28% at pressures >300 MPa, and an increase in the curd firming rate was observed. As treatment pressure increased to 450 MPa, the firmness, elasticity, and the percentage creep recovery of gels increased, whereas values of compliance and fracture strain were reduced. Thus, we can conclude that 300 MPa is the optimum treatment pressure for milk intended for cheesemaking by enzymatic coagulation. This pressure produced milk with optimal coagulation kinetics and water-holding properties with the least loss of fat and protein to the whey.

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.

Rennet-Induced Casein Micelle Aggregation Models: A Review

Two phases are generally recognized in the enzymatic coagulation of milk: hydrolysis and aggregation, although nowadays more and more researchers consider the non-enzymatic phase to actually be a stage of gel formation made up of two sub-stages: micellar aggregation and hardening of the three-dimensional network of para-κ-casein. To evaluate this controversy, the main descriptive models have been reviewed. Most of them can only model micellar aggregation, without modeling the hardening stage. Some are not generalizable enough. However, more recent models have been proposed, applicable to a wide range of conditions, which could differentiate both substages. Manufacturing quality enzymatic cheeses in a cost-effective and consistent manner requires effective control of coagulation, which implies studying the non-enzymatic sub-stages of coagulation separately, as numerous studies require specific measurement methods for each of them. Some authors have recently reviewed the micellar aggregation models, but without differentiating it from hardening. Therefore, a review of the proposed models is necessary, as coagulation cannot be controlled without knowing its mechanisms and the stages that constitute it.

Milk-clotting and hydrolytic activities of an aspartic protease from Salpichroa origanifolia fruits on individual caseins

In recent years, many attempts have been made to find new plant proteases to make artisan cheeses. The global increase in cheese consumption, together with a lower supply and increasing cost of calf rennet, religious factors (Islam and Judaism) and food choices (vegetarianism) have led to the search for suitable rennet substitutes for milk clotting. This study describes the milk-clotting and hydrolytic activities of an aspartic protease from Salpichroa origanifolia fruits (SoAP) on individual caseins to explore its potential use as an alternative to animal rennet. The milk-clotting index obtained for SoAP was 8.4 times lower than that obtained for chymosin. SoAP showed a higher degree of hydrolysis on α-casein than on the other fractions under the proposed conditions. RP-HPLC, mass spectrometry analyses and sequencing of the hydrolysates allowed identifying five peptides from α-casein, one peptide from β-casein, and three peptides from k-casein. In silico analysis showed that the peptides identified may display a wide variety of potential biological activities. These results demonstrate the possibility of using SoAP for the manufacture of new types or artisan cheeses, with the simultaneous added value of the potential health-promoting benefits of the bioactive peptides generated during the hydrolysis.

Rapid colorimetric analysis of multiple microRNAs using encoded hydrogel microparticles

microRNAs (miRNAs) have attracted much attention as potential biomarkers for the diagnosis of various fatal diseases. With increasing interest in miRNA detection at practical sites, colorimetric bead-based assays have garnered much attention, because these allow for simple analysis with cheap and portable devices. Among them, the encoded hydrogel microparticle-based colorimetric miRNA assay is considered as one of the promising techniques, due to its strengths, such as large multiplex capacity, acceptable sensitivity, and simple analysis. However, it still imposes a limitation in terms of the assay time, particularly the colorimetric reaction time, which is too long, making the practical application of the assay difficult and undermining its detection accuracy. In this work, we present a rapid colorimetric assay based on encoded hydrogel microparticles, which exhibits a significant decrease in the colorimetric reaction time due to two factors: (1) an increase in the number of enzymes bound to hydrogel microparticles via a post-synthesis functionalization method, and (2) an elevation in the enzyme reaction temperature during colorimetric labeling. We obtained a comparable sensitivity of the colorimetric assay with three different miRNA targets, even with a shortened colorimetric reaction time. Furthermore, we validated that our colorimetric detection method is suitable for multiplex miRNA detection, owing to its low cross-reactivity.

Effect of pH adjustment on the composition and rennet-gelation properties of milk concentrates made from ultrafiltration and reverse osmosis

The objective of this work was to investigate the effect of pH adjustment (initial pH vs. pH 6.50) on the rennet-gelation properties of concentrates made by ultrafiltration (UF) and reverse osmosis (RO). Rennet-gelation kinetics were followed by dynamic rheology and κ-casein hydrolysis by reverse-phase HPLC. At initial pH, RO concentrates had better rennet-coagulation behavior than UF concentrates and skim milk, whereas adjusting the pH to 6.50 produced the opposite results. The kinetics of κ-casein hydrolysis were similar in skim milk, and both concentrates and were not affected by pH adjustment. Differences in rennet coagulation were then related to the extent of hydrolysis required to trigger casein micelle aggregation. Small pH adjustments (<0.2 pH unit) enabled the use of RO concentrate with similar rennet-gelation behavior to UF concentrate, despite major compositional differences. This study shows that pH adjustment of RO concentrates can be a simple approach to improve their coagulation properties; however, the mechanisms behind these improvements remain to be elucidated.

A method for the inline measurement of milk gel firmness using an optical sensor

At present, selection of cutting time during cheesemaking is made based on subjective methods, which has effects on product homogeneity and has prevented complete automation of cheesemaking. In this work, a new method for inline monitoring of curd firmness is presented. The method consisted of developing a model that correlates the backscatter ratio of near infrared light during milk coagulation with the rheological storage modulus. The model was developed through a factorial design with 2 factors: protein concentration (3.4 and 5.1%) and coagulation temperature (30 and 40°C). Each treatment was replicated 3 times; the model was calibrated with the first replicate and validated using the remaining 2 replicates. The coagulation process was simultaneously monitored using an optical sensor and small-amplitude oscillatory rheology. The model was calibrated and successfully validated at the different protein concentrations and coagulation temperatures studied, predicting the evolution of storage modulus during milk coagulation with coefficient of determination values >0.998 and standard error of prediction values <3.4 Pa. The results demonstrated that the proposed method allows inline monitoring of curd firming in cheesemaking and cutting the curd at a proper firmness to each type of cheese.

Three phase partitioning, a scalable method for the purification and recovery of cucumisin, a milk-clotting enzyme, from the juice of Cucumis melo var. reticulatus

Cucumisin [EC 3.4.21.25] was first purified from Cucumis melo var. reticulatus juice by three-phase partitioning (TPP). Optimum purification parameters of the TPP system were determined as 60% ammonium sulfate saturation with 1.0:1.25 ratio of crude extract: t-butanol at pH and temperature of 8.0 and 20°C, respectively. Cucumisin was purified with 4.61 purification fold and 156% activity recovery. The molecular weight of the recovered cucumisin was determined as 68.4kDa and its isoelectric point is 8.7. Optimum pH and temperature of cucumisin were pH 9.0 and 60-70°C, respectively. The protease was very stable at 20-70°C and a pH range of 2.0-12.0. Km and Vmax constants were 2.24±0.22mgmL^-1 and 1048±25μ Mmin^-1, respectively. The enzyme was stable against numerous metal ions and its activity was highly enhanced by Ca²⁺, Mg²⁺, and Mn⁺². Cucumisin activity was 2.35-folds increased in the presence of 5mM of CaCl₂. It was inactivated by Co²⁺, Cd²⁺, Zn²⁺ and Fe²⁺ and dramatically by PMSF. Cucumisin milk-clotting activity was highly stable when stored under freezing (-20°C) compared at 4°C and 25°C. Finally, TPP revealed to be a useful strategy to concentrate and purify cucumisin for its use as a milk-clotting enzyme for cheese-making.

Optical monitoring of chemical processes in turbid biogenic liquid dispersions by Photon Density Wave spectroscopy

In turbid biogenic liquid material, like blood or milk, quantitative optical analysis is often strongly hindered by multiple light scattering resulting from cells, particles, or droplets. Here, optical attenuation is caused by losses due to absorption as well as scattering of light. Fiber-based Photon Density Wave (PDW) spectroscopy is a very promising method for the precise measurement of the optical properties of such materials. They are expressed as absorption and reduced scattering coefficients (μ a and μ s', respectively) and are linked to the chemical composition and physical properties of the sample. As a process analytical technology, PDW spectroscopy can sense chemical and/or physical processes within such turbid biogenic liquids, providing new scientific insight and process understanding. Here, for the first time, several bioprocesses are analyzed by PDW spectroscopy and the resulting optical coefficients are discussed with respect to established mechanistic models of the chosen processes. As model systems, enzymatic casein coagulation in milk, temperature-induced starch hydrolysis in beer mash, and oxy- as well as deoxygenation of human donor blood were investigated by PDW spectroscopy. The findings indicate that also for very complex biomaterials (i.e., not well-defined model materials like monodisperse polymer dispersions), obtained optical coefficients allow for the assessment of a structure/process relationship and thus for a new analytical access to biogenic liquid material. This is of special relevance as PDW spectroscopy data are obtained without any dilution or calibration, as often found in conventional spectroscopic approaches.

Usefulness of a large field of view sensor for physicochemical, textural, and yield predictions under industrial goat cheese (Murcia al Vino) manufacturing conditions

The applicability of a light backscatter sensor with a large field of view was tested for on-line monitoring of coagulation and syneresis in a goat cheese (Murcia al Vino) manufactured under industrial conditions. Cheesemaking was carried out concurrently in a 12-L pilot vat and a 10,000-L industrial vat following the normal cheesemaking protocol. Cheese moisture, whey fat content, hardness, springiness, and adhesiveness were measured during syneresis. The results obtained show that cutting time is best predicted by considering the coagulation ratio at the inflection point and the percentage increase in the ratio during coagulation, with no need for the first derivative. The large field of view reflectance ratio provided good results for the prediction of moisture content, yield, hardness, springiness, and adhesiveness of the final cheese.

Innovative uses of near-infrared spectroscopy in food processing

Near-infrared spectroscopy (NIRS) has experienced widespread use as an analytical tool in the last 3 decades. Researchers today are exploring ways of applying NIRS that expand beyond compositional analyses into process control. Processes such as meat tenderness evaluation, curd cutting, and dough mixing have traditionally been controlled by highly skilled master craftsmen; new NIRS research applications are demonstrating that these complex processes can be monitored and controlled in situ to produce consistent, high quality end products with online NIRS technology. Additionally, researchers also now have the potential ability to develop new nondestructive spectroscopic techniques to probe the underlying molecular evolution of these products during processing.