Rheological and structural properties of enzyme‐induced gelation of milk proteins by ficin and Polyporus badius

Abstract

The rheological and microstructural characteristics of ewes’ milk curd obtained by coagulating with milk‐clotting enzymes, including ficin extract and Polyporus badius were evaluated. The gelation of milk was examined by small amplitude oscillatory shear measurements (SAOS). Different concentrations of ficin and P. badius extracts (1, 3, and 5%) were utilized to coagulate milk proteins. The ewes’ samples containing ficin and mushroom enzymes were heated from 25 to 45°C at a heating rate 1°C/min and kept for 30 min. Then, the curds were cooled down to 25°C with the same heating rate. The ficin extract could induce stronger gels at 45°C and 5% ficin. Similar results were also found for 5% P. badius extract and incubation at 45°C. However, P.badius gels achieved a network with more viscous characteristics and had a softer texture than ficin gels. Therefore, it may be concluded the induced gels with mushroom had higher moisture and lower protein contents, which related to the high proteolytic activity of P. badius. The microstructure survey showed that the mushroom‐induced gel had a more compact structure. By increasing enzyme concentration, both gels showed a coarser and more compact protein network. Whereas, the P. badius gels had more fusions and folds which indicate the greater proteolysis occurred during gelation and there was greater breakdown of protein. Our findings suggest the application of ficin and P. badius enzymes to develop a novel procedure to coagulate milk proteins and providing new structures in food systems.

Ficin: A protease extract with relevance in biotechnology and biocatalysis

“…In another research, ficin was compared to Polyporus badius extract in the coagulation of milk by analyzing the rheological and microstructural characteristics of ewes milk curd [117]. The gels produced by P. badius gels were more viscous and with a softer texture than the ficin gels.…”

“…The gels produced by P. badius gels were more viscous and with a softer texture than the ficin gels. That is, they have higher moisture and lower protein contents presenting a more compact structure [117]. In another example, the coagulation of ewe milk was produced using extracts from Cynara scolymus L. cv.…”

Cynara cardunculus as a potential source of milk coagulating protease: Effects on physical properties of cow's milk

“…The evolution of the complex modulus (G) with time is shown in Figure 4 , and a sigmoidal increase in G with time was observed. Shabani et al ( 2018 ) reported that G′ value was higher than that of G′′ at the outset and throughout the experiment for ficin and Polyporus badius extract, revealed the association of proteins. Bohlin et al ( 1984 ) pointed out that this is the typical behavior of the secondary phase of milk coagulation.…”

“…The absence of fat may be responsible for this observation. Shabani et al ( 2018 ) reported that the concentration of enzymes was profoundly affected the gelation of milk protein. In addition, the milk proteins need more time to aggregate at lower concentrations of mushroom enzymes.…”

“…Different types of proteases have been used for this purpose, with natural, microbial and recombinant sources being the most common (Kumar et al, 2010 ). However, the high price of rennet and limited supply diet (vegetarianism), religious factors (e.g., Judaism and Islam) and ban on recombinant calf rennet (in France, Germany and the Netherlands) have pushed researchers to search for other sources (Shabani et al, 2018 ). As an alternative, several proteases obtained from vegetal sources such as fruits (e.g., kiwi, melon and papaya), roots (e.g., ginger rhizome), latex (e.g., Papaya fruit Carica p. and Sodom apple Calotropis procera ) and flowers (e.g., C. cardunculus and Centaurea calcitrapa ) have been recommended for use as milk clotting agents (Adetunji & Salawu, 2008 ; Domsalla & Melzig, 2008 ; Fernandez‐Salguero et al, 2002 ).…”