Food Biochemistry and Food Processing (2 edition)

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Chymosin in Cheese Making

V. V. Mistry

Introduction

Chymosin

Rennet Manufacture

Chymosin Production by Genetic Technology

Rennet Production by Separation of Bovine Pepsin

Rennet Substitutes

Animal

Plant

Microbial

Chymosin Action on Milk

Milk Coagulation and Protein Hydrolysis by Chymosin

Factors Affecting Chymosin Action in Milk

Chymosin Concentration

Temperature

pH

Calcium

Milk Processing

Genetic Variants

Effect of Chymosin on Proteolysis in Cheese

Effect of Chymosin on Cheese Texture

References

INTRODUCTION

Cheeses are classified into those that are aged for the develop-

ment of flavor and body over time and those that are ready for

consumption shortly after manufacture. Many cheese varieties

are also expected to develop certain functional characteristics

either immediately after manufacture or by the end of the aging

period. It is fascinating that what starts in the cheese vat, as a

white liquid that is composed of many nutrients, emerges as

a completely transformed compact mass, cheese, sometimes

Reviewers of this chapter were Dr. Ashraf Hassan, Department of Dairy Science,

South Dakota State University, Brookings, and Dr. Lloyd Metzger, Department

of Food Science and Nutrition, University of Minnesota, St. Paul.

colored yellow, sometimes white, and sometimes with various

types of mold on the surface or within the cheese mass

(Kosikowski and Mistry 1997). Some cheeses may also exhibit

a unique textural character that turns stringy when heated, and

others may have shiny eyes. Each cheese also has unique flavor

qualities. Thus, cheese is a complex biological material whose

characteristics are specifically tailored by the cheese maker

through judicious blends of enzymes, starter bacteria, acid, and

temperature.

Milk is a homogeneous liquid in which components exist in

soluble, emulsion, or colloidal form. The manufacture of cheese

involves a phase change from liquid (milk) to solid (cheese).

This phase change occurs under carefully selected conditions

that alter the physicochemical environment of milk such that the

milk system is destabilized and is no longer homogeneous. In

many fresh cheeses, this conversion takes place with the help of

acid through isoelectric precipitation of casein and subsequent

temperature treatments and draining for the conversion of liquid

to solid. In the case of most ripened cheeses, this conversion oc-

curs enzymatically at higher pH and involves the transformation

of the calcium paracaseinate complex through controlled lactic

acid fermentation. Later on, the products of this reaction and

starter bacteria interact for the development of flavor and tex-

ture. All this is the result of the action of the enzyme chymosin

(Andren 2003).

CHYMOSIN

Chymosin, rennet, and rennin are often used interchangeably to

refer to this enzyme. The latter, rennin, should not be confused

with renin, which is an enzyme associated with kidneys and does

not clot milk. Chymosin is the biochemical name of the enzyme

that was formerly known as rennin. It belongs to the group of

aspartic acid proteinases, Enzyme classification (EC) 3.4.23, that

have a high content of dicarboxylic and hydroxyamino acids and

Food Biochemistry and Food Processing, Second Edition. Edited by Benjamin K. Simpson, Leo M.L. Nollet, Fidel Toldr ́a, Soottawat Benjakul, Gopinadhan Paliyath and Y.H. Hui.

©C2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

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