Comparison of total milk-clotting activity measurement precision using the Berridge clotting time method and a proposed optical method

Microsyringe-assisted visual volume detection based on phase separation: the case of chymosin milk-clotting activity study

The constantly diverse demand scenarios for rapid on-site analysis have put forward high requirements for developing low-cost and user-friendly visual detection methods. Therefore, developing a visual detection method with simple operation and intuitive results has important practical value in the field of analysis and detection, but it is also challenging. In this work, we propose a microsyringe-assisted visual volume detection method based on phase separation, and apply it to analyze the milk-clotting activity of chymosin. Chymosin can cause phase separation of milk with whey in the mobile phase and curd in the gel state. The network structures of casein in curd can trap water molecules, resulting in separation of whey from curd gradually. Therefore, the analysis of chymosin milk-clotting activity can be realized according to the volume of whey measured using a portable microsyringe. This method shows a good linear correlation when the concentration of chymosin ranges from 1.02 U L-1 to 1020 U L-1 and the limit of detection of this method for chymosin is calculated to be 0.03 U mL-1. This work successfully realizes the visual analysis of chymosin milk-clotting activity based on the enzyme-triggered phase separation. It also shows great promise to be applied in other phase separation-based detection systems with the advantages of high accuracy, great portability and user-friendliness.

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.

Challenging Sustainable and Innovative Technologies in Cheese Production: A Review

It is well known that cheese yield and quality are affected by animal genetics, milk quality (chemical, physical, and microbiological), production technology, and the type of rennet and dairy cultures used in production. Major differences in the same type of cheese (i.e., hard cheese) are caused by the rennet and dairy cultures, which affect the ripening process. This review aims to explore current technological advancements in animal genetics, methods for the isolation and production of rennet and dairy cultures, along with possible applications of microencapsulation in rennet and dairy culture production, as well as the challenge posed to current dairy technologies by the preservation of biodiversity. Based on the reviewed scientific literature, it can be concluded that innovative approaches and the described techniques can significantly improve cheese production.

Clotting Properties of Onopordum tauricum (Willd.) Aqueous Extract in Milk of Different Species

Plant proteases used in cheesemaking are easily available and could increase the acceptability of cheeses, otherwise hindered by ethical issues (e.g., religions, dietary habits, aversion to genetically engineered food and food ingredients). The milk clotting potential of Onopordum tauricum (Willd.) aqueous extract as an alternative to animal rennet was assessed for the first time in milk of different species (ewe, goat, cow). Among the aerial anatomical parts, i.e., receptacle, leaves, stems, and flowers, only the latter ones showed clotting properties. A response surface methodology (RSM) was used to explore the effects of three independent variables (temperature, pH, volume of coagulant) on the milk clotting activity (MCA) of the flower extract. A second-order polynomial model adequately described the experimental data and predicted a temperature value of 55 °C, a pH value of 4.9–5.7, and a volume of coagulant of 300–500 μL (added to 5 mL of milk) as optimal conditions to maximize the MCA. At a 35 °C temperature and natural milk pH of 6.7–6.8, the estimated MCA of the O. tauricum extract was 72–87, 69–86, and 75–151, in goat’s, ewe’s, and cow’s milk, respectively. In comparison, the MCA of calf rennet was 5.4–4.9, 3.3–14.7, and 4.9–16.7 times higher than that of the plant extract in goat’s, ewe’s, and cow’s milk, respectively.

An Evaluation of the Clotting Properties of Three Plant Rennets in the Milks of Different Animal Species

Cynara cardunculus, Carica papaya and Ficus carica extracts are proposed as milk coagulants herein. Their coagulation efficiency was measured in bovine, buffalo, goat and sheep milk incubated at different temperatures. The milk-clotting and proteolytic activities as well as the lactodynamographic parameters were determined considering animal rennet as a reference coagulant. The vegetable coagulant, extracted from C. cardunculus pistils, proved to be the most suitable milk-clotting enzyme for cheesemaking, since it possesses similar milk clotting properties to conventional calf rennet. F. carica latex, but seemed to be a promising alternative coagulant at higher temperatures. The strong proteolytic activity of papain caused poor milk coagulation in all milk samples. To conclude, this result also supports the original hypothesis of this study that the excessive proteolytic nature of plant coagulants can negatively affect the cheesemaking process. The optimization of using a plant rennet in a dairy application can be done by selecting the appropriate plant rennet with a consistent clotting efficiency. These innovative manufacturing processes may also lead to the optimization and production of new cheese varieties.

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.

Codon Optimization of the "Bos Taurus Chymosin" Gene for the Production of Recombinant Chymosin in Pichia pastoris

Codon optimization of the Bos taurus Chymosin gene (CYM) for its expression in Pichia pastoris was performed in this study. A synthetic CYM gene was designed in silico by replacing codons rarely used by P. pastoris with equivalent nucleotide combinations that codify for the same amino acid but that are more frequently encountered in the genome of P. pastoris. A total of 332 nucleotides were modified to optimize 289 codons. The synthetic CYM gene was cloned into the expression vector pPICZαA and transformed into P. pastoris. The transformed strains were grown in artificial media supplemented with glycerol as a carbon source to increase biomass and then cultured in a similar medium replacing glycerol with methanol as a carbon source to initiate gene induction. Raw extracts of the growth media exhibited milk-clotting activity of 146.11 SU/mL. Produced recombinant chymosin showed coagulant activity from 25 to 50 °C, and within a pH range of 5-6.9, having optimum activity at 35-40 °C, and pH 5.0. These results show that codon optimization is a viable strategy to improve CYM gene expression levels in P. pastoris for the production of recombinant chymosin.