The effect of mixing temperature on the flavour expression of processed cream cheese

Abstract

Although manufacturing conditions affect the texture of processed cheese, the effects of manufacturing conditions on flavour expression, and the mechanisms for these effects are unknown. This study investigated the effects of mixing temperature on the flavour expression of processed cream cheese and aimed to determine whether the content of aroma compounds in the matrix, the texture, and hydrophobic interactions between aroma compounds and the matrix contribute to flavour expression. Four model cheeses with mixing temperatures of 30 °C, 60 °C, 75 °C, and 88 °C were prepared. Sensory analysis, volatile aroma compound evaluations using HS-SPME and SAFE-GC/MS, texture analysis, microstructure observation, and hydrophobicity evaluation were conducted. The result showed that the decrease of scores for perceptions of “Yoghurt aroma”, “Acidity”, and “Acetic aroma” with increasing mixing temperature was due to the generation of aroma compounds. The decrease in scores for “Overall flavour intensity” was due to the product's hardened texture.

Introduction

Natural cheese and emulsifying salts constitute the main raw materials used to make processed cheese. In addition, substances, such as pH adjusters, stabilisers, salt, and flavouring agents are added to adjust the cheese's flavour, physical properties, and storage stability. The manufacturing process involves mixing of raw materials, thermal emulsification, filling, and cooling.

Multiple studies have reported that the physicochemical properties of processed cheese depend on manufacturing aspects such as natural cheese ingredients (Acharya & Mistry, 2005; Shimp, 1985; Templeton & Sommer, 1930), emulsifying salt (Mizuno & Lucey, 2005; Templeton & Sommer, 1936; Thomas, Newell, Abad, & Turner, 1980), heating temperature (Glenn, Daubelt, Farkas, & Stefanski, 2003; Jeon, Chung, & Kwak, 2010; Lee, Steffe, Euston, Foegeding, & McKenna, 2003; Rayan, Kalab, & Ernstrom, 1980), mixing conditions (Drake, 1973), and the size of the milk fat globules generated by the homogeneous treatment process (Glenn et al., 2003; Lee et al., 2003; Rayan et al., 1980.) Several aroma compounds related to the flavour of natural cheese have been identified (Iwasawa, Suzuki–Iwashima, Iida, & Shiota, 2014; Singh, Drake, & Cadwallader, 2003; Wendin, Langton, Caous, & Hall, 2000). The aroma compounds in natural cheese affect the concentration and variation of aroma compounds in the processed cheese matrix; however, there have been few reports about the effects of manufacturing processes on the flavour expression of processed cheese.

In dairy products other than processed cheese, there are known effects of the manufacturing process on the expression of aroma components, for example, fatty acids, lactones, and methyl ketones derived from fat and lactose are generated during heating process (Iwatsuki, 1999; Iwatsuki et al., 2000; Jeon et al., 2010; Juan, Barron, Ferragut, & Trujillo, 2007; Kobayashi, 2011). The concentrations of methylketones and aldehydes reportedly increase because of the oxidation of long-chain fatty acids (Bertuzzi, McSweeney, Rea, & Kilcawley, 2018; Singh et al., 2003). However, a complete understanding of the changes in aroma compounds that takes place in processed cheese manufacturing remains unclear.

In other foods, there are known effects of physicochemical properties on flavour expression. Aroma compounds available in the headspace can be described in terms of molecular weight, molar volume, solubility, hydrophobicity, concentration of salts, pH, and temperature (Druaux & Voilley, 1997; Lubbers, Landy, & Voilley, 1998; Seuvre, Philippe, Rochard, & Voilley, 2006). Several mechanisms are involved in whether an aroma compound is present in the headspace; these include mass transfer, matrix structural hindrance, and flavour–matrix interactions (Odake, Roozen, & Burger, 2000; Seuvre, Espinosa, & Voilley, 2000). The food structure (Druaux & Voilley, 1997; Seuvre et al., 2000) and texture (Szczesniak, Brandt, & Freidman, 1963) have been reported to influence the release of aroma compounds. Also, the size of fat particles in emulsified food may influence flavour release (Seuvre et al., 2000). Arvisenet, Voilley, and Cayot (2002) reported that the interactions between food components and aroma compounds govern the release of aroma molecules from the food matrix into the headspace. The interaction between aroma compounds and proteins involves specific binding, adsorption, absorption, entrapment, and covalent binding reactions (Kinsella, 1989). According to Shiota, Isogai, Iwasawa, and Kotera (2011), the hydrophobicity of the matrix influences the release of aroma compounds. In processed cheese, the release of aroma compounds from the food matrix is also attributed to such physicochemical properties as structure, texture, size of fat globules and hydrophobicity of the cheese matrix, which changes during the heating process; however, the relationship between these changes and aroma releases remains unclear.

This study investigated the effects of the heating temperature during the manufacture of processed cream cheese, in terms of its flavour expression, i.e., the perception of aroma and taste. Another aim was to identify the factors related to flavour expression for the processed cream cheese. The following three results were hypothesised and examined for validation: (1) changes to the content of aroma compounds in the matrix, (2) changes in texture, and (3) changes in the hydrophobic interaction between aroma compounds and the cheese matrix. This study focused on 30 aroma compounds known to contribute to dairy aroma (Iwasawa, Suzuki-Iwashima, Iida, & Shiota, 2014; Singh et al., 2003). Some of these compounds, such as acetic acid, also contribute to taste.

Natural cream cheese was used as the raw material. Four model processed cheeses with mixing temperatures of 30 °C, 60 °C, 75 °C, and 88 °C were prepared. Flavour expression for each of these was evaluated by sensory analysis. As aroma components can be perceived in retronasal olfaction, the aroma components volatising to the headspace at 37 °C were measured using headspace solid-phase-microextraction (HS-SPME) with gas chromatography–mass spectroscopy (GC/MS). To determine the concentrations of aroma compounds in the matrix, the aroma components extracted without volatising treatment were measured using solvent-assisted-flavour-evaporation (SAFE) with GC/MS. These data allowed us to validate the influence of the concentration of aroma compounds in the matrix on the amount of aroma compounds released into the headspace. Note that the numbers and types of components extracted by HS-SPME and SAFE differ (Thomsen, Gourrat, Danguin, & Guichard, 2014). HS-SPME is very poor for high-molecular-weight volatiles but very good for low-molecular-weight volatiles. SAFE is not as useful for very volatile compounds. Further, it has been unclear whether the amounts of components detected by these methods exceed the odour threshold. Therefore, at the time of SAFE-GC/MS analysis, gas chromatography–olfactometry (GC/O) analysis using an olfactory detection port (ODP) was also performed. Aroma components that could be perceived were considered to at least affect the flavour expression of the processed cheese. Thus, the study considered the influence of the concentration of aroma compounds in the matrix on the amount of release of aroma compounds into headspace only for the components detected by all of these three processes: HS-SPME-GC/MS, SAFE-GC/MS, and SAFE-GC/O. Microstructure observations were conducted using scanning electron microscopy. The texture, the insoluble fraction contents, and the hydrophobicity of soluble fractions were determined. These data allowed us to validate the influence of physicochemical properties on the release of aroma compounds into the headspace.

To clarify the mechanism taking place in the manufacturing condition that yields flavour expression, research that comprehensively evaluates the texture, structure, aroma releases, and concentration of aroma in the matrix should help produce better quality processed cheese.