Texture characteristics and microstructure of skim milk mozzarella cheeses made using exopolysaccharide or non-exopolysaccharide producing starter cultures

Abstract

Three batches of mozzarella cheese were prepared using skim milk (< 0.1% fat), each with exopolysaccharide (EPS)-or non-exopolysaccharide (non-EPS)-producing starter cultures consisting of S. thermophilus and L. delbrueckii ssp. bulgaricus. The cheeses were analysed for moisture, protein and fat contents and for texture characteristics such as hardness, cohesiveness, adhesiveness, springiness, chewiness and gumminess. An Instron Universal Testing Machine was used to measure the texture characteristics while the microstructure of the cheeses was examined using a scanning electron microscope. The EPS cheeses showed 1.7% higher moisture content (on total cheese weight) than non-EPS cheeses. Both types of cheeses had similar protein content (∼43%). Most of the texture measurements decreased during storage for both types of cheese; however, adhesiveness at 50% compression increased during storage. Both types of cheese showed similar hardness and springiness values during storage; the EPS cheeses showed lower values of cohesiveness and adhesiveness during storage. The microstructure of the cheeses showed large and small voids representing the location of the serum and fat phases. The starter bacteria were located in serum channels. The exopolysaccharide was in the form of filaments, which extended from the protein matrix, probably as a result of dehydration of the EPS during SEM sample preparation. The EPS was primarily produced by S. thermophilus which was found in abundance, but not L. delbrueckii ssp. bulgaricus. The EPS cheeses were more open and porous compared to the non-EPS cheeses which could have decreased the cohesiveness and adhesiveness of the product.