Milk coagulants

A study of lipolysis induced by adjuncts from edible Aspergillus sp. solid culture products on ripened semi-hard cheese

BACKGROUND

Aspergillus sp. has been used in traditional Japanese fermented foods. Protease-containing culture products of A. oryzae have been applied as the adjunct enzyme source to enrich the flavor in ripened cheese. Although proteolysis was stimulated, the increase of free fatty acids (FFA) was recognized in some products. Since an excess amount of FFA accumulation can cause rancidity in cheese products, the assessment of lipase activity was considered to be essential for the cheese adjunct preparation.

RESULTS

Although an equal lipase activity from the adjunct materials of A. kawachii NBRC 4308, A. luchuensis RIB 2604 and A. oryzae AHU 7139 was applied to semi-hard cheese, the FFA level was significantly higher in A. oryzae cheese than in the others. Furthermore, the profiles of volatile components were different in experimental cheeses. An in vitro study with experimental curds demonstrated that the high FFA might not depend on the lipase retainability on curds. On the contrary, the pronounced activation of the lipases occurred in A. oryzae after incubation with the curds. Moreover, incubation of the insoluble lipase that had been attached to the cells with skim milk curd extracts allowed the release of lipases from the cells into the medium with remarkable activation.

CONCLUSION

A. oryzae AHU 7139 possessed a complex lipolytic system comprising extracellular and cell-binding lipases that were attributed to the increase in FFA in A. oryzae cheese. © 2022 Society of Chemical Industry.

Review: Technological and organoleptic issues pertaining to cheeses with denomination of origin manufactured in the Iberian Peninsula from ovine and caprine milks Revisión: Aspectos tecnológicos y sensoriales de quesos con denominación de origen elaborados en la Península Ibérica con leche de oveja y de cabra

A few European countries have created Appélations d'Origine Protegée (AOP) in order to support legal protection and hence promote enforcement of high-quality standards of selected food products. This paper comprehensively reviews and updates fundamental and applied aspects encompassing tech nological and organoleptic characteristics of AOP traditional cheeses manufactured in the Iberian Peninsula, from ovine and/or caprine milks. Those cheeses from Portugal and Spain can be divided into four distinctive groups, based on milk source and rennet type: ( i) Azeitão, Castelo Branco, Évora, Nisa, Serpa, Serra da Estrela and La Serena cheeses, manufactured with raw ovine milk and coagulated via plant rennet; ( ii) Terrincho, Idiazábal, Manchego, Roncal and Zamorano cheeses, elaborated with raw ovine milk and coagulated via animal rennet; ( iii) Cabra Transmontano and Majorero cheeses, manufac tured with raw caprine milk and coagulated via animal rennet; and ( iv) Amarelo da Beira Baixa, Picante da Beira Baixa and Rabaçal cheeses, manufactured with mixtures of raw ovine and caprine milks and coagulated via animal rennet. Considerable differences between Portuguese and Spanish AOP cheeses exist; the former are, in general, characterized by softer consistencies and similarities to one another in terms of manufacturing protocols (usually encompassing coagulation of plain raw milk followed by slow draining of the curd), whereas the latter are, in general, larger and firmer.

Impedimetric biosensor for the assessment of the clotting activity of rennet

Cheese production is relied upon the action of rennet (a mixture of chymosin and pepsin) onto casein micelles of milk. For the first time, the monitoring of this interaction with electrochemical impedance spectroscopy (EIS) was used to develop a faradic impedimetric biosensor for the assessment of the clotting activity of rennet, using hexacyanoferrate(II)/(III) couple as a redox probe. Gold electrodes were modified with self-assembled monolayers of different thiols (thioctic acid, dithiobis-N-succinimidyl propionate, and cysteamine), and (artificial) casein micelles were immobilized on the modified gold surfaces. The proposed method is based on the measurement of charge-transfer resistance (R(ct)) changes attributed to the degradation of the negatively charged immobilized casein micelles by rennet to neutral biostructures. This action results in the increase of the flux of the redox probe, which exists in the bulk solution, to the surface of the electrode and, consequently, in the decrease of R(ct). Experimental parameters such as the micelle loading, the reaction time, the concentration of rennet, and the working pH, were optimized. Besides EIS measurements, cyclic voltammetry, FT-IR, and atomic force microscopy (AFM) experiments were also performed before and after the interaction of the immobilized micelles with rennet. Finally, the proposed biosensors were successfully tried for various commercial samples.

Effect of recombinant chymosin on ewes' milk coagulation and Manchego cheese characteristics

Ewes' milk coagulation was significantly influenced by the type of rennet when recombinant chymosin produced by Kluyveromyces lactis was compared with two commercial calf rennets with declared chymosin contents of 55 and 70%. Recombinant chymosin and calf rennet with 70% chymosin exhibited similar thrombelastographic characteristics, and coagulated milk more rapidly than calf rennet with 55% chymosin. The type of rennet had no effect on Manchego cheese dry matter, pH or recovery of dry matter in cheese. N soluble at pH 4·6 was the only N fraction influenced by the type of rennet, with slightly higher levels for cheese made with recombinant chymosin or with calf rennet containing 70% chymosin than for that made with rennet containing 55% chymosin. No significant differences in rheological or sensory characteristics between Manchego cheese made with recombinant chymosin and that made with the calf rennets were detected.

Immunological identification of milk-clotting enzymes

The 6 most widely used milk-clotting enzymes, i.e. chymosin, bovine and porcine pepsins and proteinases from Mucor miehei, M. pusillus and Endothia parasitica, have been purified and used to prepare rabbit antisera against each of them. The antisera were adsorbed with appropriate cross-linked antigens to remove non-specific antibodies. Monospecific antisera thus obtained were used to identify enzymes eventually added to calf or bovine rennets, using the double radial immunodiffusion technique. The threshold of sensitivity was c. 1%, expressed as clotting activity. This qualitative method complements the quantitative procedure recently proposed for determining chymosin and bovine pepsin A in commercial extracts of bovine veils.

Indirect assay of milk clotting activity of Mucor miehei proteinase (Fromase) in combined rennets

Milk clotting activity of Mucor miehei proteinase (commercial name Fromase) was determined in combined rennets as the difference between the total activity of combined rennet and the residual activity after inhibition of Fromase by the purified immunoglobulin fraction of a Fromase antiserum. The proposed method is simple, rapid, and makes possible the use of any arbitrary method for assaying milk clotting activity. The application of the immunoglobulin fraction, instead of the whole antiserum, is necessary owing to the presence of nonspecific proteinase inhibitors in blood serum.

Development of texture and flavour in cheese and other fermented products

Cheesemaking is initiated by specific hydrolysis of κ-casein, followed by random aggregation of casein particles to form a network. The structure of this curd determines its subsequent behaviour and the composition and texture of the cheese. It is affected by previous homogenization or concentration of the milk. The composition of the milk and the distribution of components in it, which are affected by season, mastitic infection and cold storage, also influence its curd-forming properties, and the composition and yield of cheese. During ripening of cheese, the final texture and the development of flavour occur. Both are influenced by the type and extent of proteolysis, catalysed by coagulant, bacterial and milk enzymes. These and other enzymic and non-enzymic reactions responsible for flavour development depend on the composition and environment within the product. Some of these reactions can be accelerated by incorporating enzymes and chemical reagents into the curd, resulting in the production of an enhanced flavour. A number of compounds responsible for the flavour of cheese and yoghurt have been identified and mechanisms for their formation and retention in the product have been postulated.

Assessment of the suitability for Cheddar cheesemaking of purified and commercial chicken pepsin preparations

Commercial and pure chicken pepsin preparations were compared with rennet as cheesemaking coagulants. From the milk clotting and caseinolytic activities and enzymic stabilities, predictions were made of the relative activities of the chicken pepsins and rennet during cheese ripening. By this means mixtures of chicken and pig pepsins for cheesemaking trials were formulated. These and mixtures of chicken pepsins with rennet were approximately additive in coagulating activity provided they were used immediately. The amounts of chicken pepsins used in laboratory scale Cheddar cheesemaking trials were minimized by acidification and calcification of the milk. The nature of the coagulant did not affect the cheesemaking conditions, yields or cheese composition. Cheeses made with chicken pepsins alone showed faster proteolysis, more intense flavour, off-flavours and bitterness and were softer than those made with rennet. Cheeses made with chicken pepsin/rennet mixtures were intermediate and those made with chicken pepsin/pig pepsin mixtures were similar to those made with rennet. It was concluded that neither of the chicken pepsin preparations was suitable for Cheddar cheesemaking and that the predictive tests had led to correct assessments.

Evaluation of bovine rennets in terms of absolute concentrations of chymosin and pepsin A

A method for determining chymosin and bovine pepsin A in commercial extracts of bovine veils, based on the use of the synthetic hexapeptide (Leu-Ser-Phe(NO2)-Nle-Ala-Leu-OMe) as reference substrate, is reported. Chymosin and bovine pepsin A were separated chromatographically from extracts and assayed for clotting activity on a reconstituted skim-milk standardized with reference chymosin and bovine pepsin A, themselves standardized in relation to the hexapeptide. The effect of pH on the absorbance difference between the hexapeptide and the Leu-Ser-Phe(NO2) tripeptide resulting from its hydrolysis was studied. It was found that the ‘optimal’ pH for determining the activities of the reference enzyme solutions was 4·7.

Six chymosin and 3 bovine pepsin A preparations were assayed on the hexapeptide to define the relation between the proteolytic activity and the amount of active enzyme. At pH 4·7 and 30 °C 1 mg chymosin and 1 mg bovine pepsin A hydrolysed 100 and 2700 μm-peptide/s respectively. The clotting activity of these preparations was assayed on a reconstituted skim-milk to standardize it and thus define the relation between the clotting time and the amount of active enzyme. Chymosin had a specific clotting activity twice that of bovine pepsin A. At equal clotting activities, bovine pepsin A was 55 times more active than chymosin on the hexapeptide at pH 4·7.

Effect of vegetable and animal rennet on chemical, microbiological, rheological and sensory characteristics of La Serena cheese

The characteristics of La Serena cheese produced using animal rennet in place of the traditional vegetable rennet were evaluated. Total solids, fat and total N were higher in whey from animal rennet than in whey from vegetable rennet. Cheese produced using animal rennet had a higher moisture content and a lower pH. Proteolysis was more rapid in the cheese produced with vegetable rennet than in the cheese produced with animal rennet, but there was less lipolysis. Enterobacteriaceae and coliform counts were respectively 1·7 and 1·4 log units higher in 60 d vegetable rennet cheese than in 60 d animal rennet cheese. Softening of cheese texture was considerably more pronounced in vegetable rennet cheese, which also showed significantly higher flavour quality and intensity.

Cheddar cheesemaking with recombinant calf chymosin synthesized in Escherichia coli

The cheesemaking properties of recombinant chymosin from Escherichia coli were compared with those of standard rennet in parallel trials with three single strain starters. For each pair of cheeses the cheesemaking characteristics, recoveries of milk solids in the curds and compositions were similar. The rates and types of proteolysis and texture development during ripening between cheeses made with the two coagulants were not significantly different.

Rheology, Microstructure, and Functionality of Low-Fat Iranian White Cheese Made with Different Concentrations of Rennet

A batch of full-fat (23% target fat) and 3 batches of low-fat (6% target fat) Iranian white cheese with different rennet concentrations (1-, 2-, and 3-fold the normal usage) were produced to study the effect of fat content reduction and promoted proteolysis on the textural and functional properties of the product. Cheese samples were analyzed with respect to their rheological parameters (uniaxial compression and small amplitude oscillatory shear), meltability, microstructure, and sensory characteristics. Reduction of fat content from 23 to 6% had adverse effects on the texture, functionality, cheese-making yield, and sensory characteristics of Iranian white cheese. Fat reduction increased the instrumental hardness parameters (storage modulus, stress at fracture, and Young's modulus of elasticity), decreased the cheese meltability and yield, and made the microstructure more compact. Doubling the rennet concentration reduced values of instrumental hardness parameters, increased the meltability, and improved the sensory impression of texture. Although increasing the rennet concentration to 2-fold the normal usage resembled somewhat the low-fat cheese to its full-fat counterpart, it appeared to cause more reduction in yield. Increasing the rennet concentration 3-fold the normal usage produced a product slightly more elastic than the low-fat cheese with normal concentration of rennet. Increasing the rennet concentration to 2-fold the normal usage was useful for improving the textural, functional, and sensory properties of low-fat Iranian white cheese.

Hydrolysis of whey proteins by proteases extracted from Cynara cardunculus and immobilized onto highly activated supports

Blends of cardosins A and B, enzymes present in aqueous extracts of the flowers of the thistle (Cynara cardunculus L.), have for long been used as rennets by the cheesemaking industry in the Iberian Peninsula. These dimeric proteases are present in the stigmae and stylets of said flowers, and are thought to play a role in sexual reproduction of the plant. In the present research effort, production of cardosin derivatives (starting from a crude extract), encompassing full stabilization of their dimeric structure, has been attempted via covalent, multi-subunit immobilization onto highly activated agarose-glutaraldehyde supports. Boiling such enzyme derivatives in the presence of sodium dodecyl sulfate and beta-mercaptoethanol did not lead to leaching of enzyme, thus proving the effectiveness of the attachment procedure. Furthermore, derivatives prepared under optimal conditions presented ca. half the specific activity of the enzyme in soluble form, and were successfully employed at lab-scale trials to perform (selective) hydrolysis of alpha-lactalbumin, one of the major proteins in bovine whey.

Isolation, purification, and alteration of some functional groups of major milk proteins: a review

This review covers selected methods of isolation and purification of mainly alpha s-casein, beta-casein, kappa-casein, beta-lactoglobulin, and alpha-lactalbumin. Selected methods of alteration of some functional groups of these proteins also were reviewed. Isolation and purification of milk proteins per se are methods of modifying the individual milk proteins. Gram quantities of these proteins can now be purified in a relatively short time using ion-exchange resins. Due to the prominent use of non-food-grade reagents in the procedures for preparation of these milk proteins, individual proteins are not maximally utilized for the manufacture of food/feed and pharmaceutical products. Therefore, intensive research efforts are needed to obviate the problems associated with underutilization of milk proteins.

Action on bovine alpha s1-casein of cardosins A and B, aspartic proteinases from the flowers of the cardoon Cynara cardunculus L

The cleavage of purified bovine alpha s1-casein separately by cardosin A and cardosin B, two distinct milk-clotting aspartic proteinases (APs) present in the stigmas of the plant Cynara cardunculus L., was studied. Casein digestion peptides were separated either by SDS-PAGE or by reverse-phase HPLC, and their N-terminal amino acid sequences were subsequently determined by automated Edman degradation, thus identifying the cleavage sites. Results showed that both enzymes exert a similar but distinct action on bovine alpha s1-casein. In common they have the preference for the bond Phe23-Phe24, and the cleavage of Trp164-Tyr165 and Phe153-Tyr154. Cardosin A also cleaves the bond Tyr165-Tyr166, whereas Cardosin B cleaves an extra type of bond, Phe150-Arg151, revealing a slightly broader specificity. A model for the action of both enzymes on bovine alpha s1-casein is proposed and discussed. In comparison with the reported action of chymosin on bovine alpha s1-casein, both cardosins proved to have a broader specificity towards this particular substrate due to a higher ability to cleave bonds between residues with large hydrophobic side-chains.

Effect of manufacturing factors, composition, and proteolysis on the functional characteristics of mozzarella cheese

Shredding and melting characteristics are vital to the function of low-moisture Mozzarella cheeses that are used as ingredients for pizza and related foods. Newly manufactured Mozzarella melts to a tough, extremely elastic, and somewhat granular consistency with limited stretch that is unacceptable for pizza. However, during the first few weeks of refrigerated storage, a dramatic transformation occurs as the unmelted cheese becomes softer and the melted cheese becomes more viscous, less elastic, and highly stretchable. Thus, the cheese attains optimal functionality for pizza. Over longer periods, Mozzarella becomes excessively soft and fluid when melted and is no longer acceptable for pizza. Low-moisture Mozzarella is correctly viewed as a cheese that requires aging. The functional characteristics of low-moisture Mozzarella are due initially to the chemical composition, including fat, moisture, NaCl, and mineral contents, and the structure of the paracasein curd matrix that is established during manufacture. Changes in functional characteristics during aging are directly related to proteolysis rate and possibly proteolytic specificity. Proteolysis during aging is influenced by manufacturing factors such as starter culture, coagulant, and stretching temperature, and possibly to indigenous proteases in the cheesemilk such as plasmin.