Reducing salt level in food: Part 1. Factors affecting the manufacture of model cheese systems and their structure–texture relationships

Abstract

A model lipoproteic matrix able to mimic hard-type cheese was produced with controlled structural and textural properties. Changes in the microstructural and rheological properties of these model cheeses made from different milk concentrate powder, anhydrous milk fat, salt contents and pH values at renneting were characterised. Rheological properties were measured by texture profile analysis, fat globule and protein aggregate size distributions by laser light scattering. Microstructural properties of the model matrices were studied by confocal laser scanning and scanning electron microscopy.

Significant differences between the matrices were found for the structural, physico-chemical and rheological parameters measured. Cheeses with higher dry matter content were significantly harder and contained more insoluble proteins than cheeses with lower dry matter content. The salt concentration and the pH at renneting had significant influence on cheese hardness and adhesiveness of rheological parameters. The model lipoproteic matrix presented air bubbles and powder aggregates which could not be avoided during the manufacture of products. However, compared with classic cheese making with rennet or acid coagulation, the technology used here allows model cheeses to be produced rapidly with a good reproducibility of texture.

Introduction

Nowadays, health authorities recommend decreasing progressively salt content in food products, because an excessive sodium intake may be a cause of pathology. The main sodium source is the sodium chloride (salt) added during food processes or preparation of meals. Considered as a flavour enhancer, salt not only acts on salty perception but also on flavour perception. Indeed, the final perception results from the integration of all the sensory informations perceived during eating. Consequently, a decrease in salt content may reduce the global acceptance of a food, particularly in increasing blandness that could result in a decrease of interest and a negative economical impact. So, reduction of salt content without any decrease of acceptability is the main challenge. This aim can be reached either by an increase of released salt in mouth during food chewing, or by an enhancement of salty perception produced by perceptual interaction with another modality. This implies to control the physical and rheological parameters of the food matrix, and/or to have a good knowledge in salty related psychophysics. By examining the factors implied in electrolytes diffusion in food matrices of different structures, the integration of salty taste with aroma perception, physiological factors such as salivary and masticatory parameters and temporal flavour release, should give some means to formulate healthy low salt foods. Indeed, texture has been identified by consumers as an important characteristic in many foods (Szczesniak, 1990), which is especially true for cheese where its texture is widely recognised as one of the most important attributes in determining both its identity and quality (Creamer & Olson, 1982; Euston et al., 2002, Jack et al., 1993). Texture not only contributes to the mouth-feel of cheese, but can also influence the flavour perception. The range of cheese textures that can be manufactured is large and is to a large extent a result of variations in moisture, fat and salt contents, pH and casein degradation, all of which are controlled by the cheese-maker (Euston et al., 2002, Lucey et al., 2003). It is known that textural characteristics of cheese are affected by their structural characteristics, composition, cheese making process, proteolysis during ripening, and fat distribution (Lobato-Calleros, Vernon-Carter, & Hornelas-Uribe, 1998). Salt (NaCl) is important in cheese manufacture for its role in preservation, controlling the growth of starter and non-starter LAB, contaminant bacteria and especially pathogens in the final cheeses (Bintsis, Litopoulou-Tzanetaki, Davies, & Robinson, 2000; Macedo, Malcata, & Oliveira, 1997). Salt levels also control various enzyme activities in cheese, modifying protein conformation, hence influencing cheese texture and directly contributing to cheese flavour (Hayaloglu, Guven, & Fox, 2002; Kaya, 2002). The role of pH in cheese texture is particularly important because changes in pH are directly related to chemical changes in the protein network of the cheese curd (Pinho, Mendes, Alves, & Ferreira, 2004). Indeed, the internal structure of the casein micelle is sensitive to pH. As well as changing charge, lowering pH releases both calcium and phosphorous from the micelle (Euston et al., 2002). The influence of the salt content on the rheological properties is indirect (Pinho et al., 2004). Addition of salt (NaCl) to casein micelle solutions affects the calcium and phosphorous equilibrium (Famelart, Le Graet, & Raulot, 1999).

The general objectives of the first part of this project were to study the influence of complex lipoproteic matrix characteristics on the transfer of aqueous solutes like salts, water, lactate, flavour compounds, by focusing the problem on model cheeses. Indeed, a real cheese matrix like during brining and ripening is a rather more complex system. For a better understanding of the fundamental phenomena, it appears therefore more suitable, in a first approach, to mimic the real hard-type cheese system by using a model matrix containing protein and fat. The purpose of this paper was to develop the manufacture process, and then characterize the structural and textural properties of a range of lipoproteic model matrices with different dry matter, fat and salt contents at different pH values.