Food Biochemistry and Food Processing

10

Chymosin in Cheese Making

V. V. Mistry

241

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

development of flavor and body over time and those

that are ready for consumption shortly after manu-

facture. Many cheese varieties are also expected to

develop certain functional characteristics either im-

mediately 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 trans-

formed compact mass, cheese, sometimes colored

yellow, sometimes white, and sometimes with vari-

ous 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 qual-

ities. 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 compo-

nents 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 conver-

sion of liquid to solid. In the case of most ripened

cheeses, this conversion occurs enzymatically at

higher pH and involves the transformation of the cal-

cium paracaseinate complex through controlled lactic

acid fermentation. Later on, the products of this reac-

tion and starter bacteria interact for the development

Reviewers of this article 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.

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing