Effects of pre-cooked cheeses of different emulsifying conditions on mechanical properties and microstructure of processed cheese
Introduction
Processed cheese is mainly prepared by mixing, heating to melting, stirring the mixture of raw cheeses, emulsifying salts, water and limited amounts of additional ingredients in a reaction container (Bennett et al., 2006). The most important part of the process is heating for a period of time with continuous stirring (emulsifying process) until a homogeneous mass is formed. The emulsifying process contributes to the qualities of processed cheese, especially the viscosity and mechanical properties. This phenomenon of the viscosity rising during continuous cooking is called the “creaming effect” and the continuous cooking is called “creaming”. Also, the cooling and storage can cause the creaming effect due to the changes in the protein network essentially (Kawasaki, 2008a, Kawasaki, 2008b). Creaming is very important in processed cheese manufacturing, because it affects the sizes of the milk fat globules and structure of the protein network, changes of which are considered to contribute to the viscosity of melted cheese or the firmness of the final product (Satou, Dousako, & Igoshi, 2010). Recently, increasing focus for processed cheese production has been placed on the functional properties that contribute to food texture, to enhance versatility in end-use applications (Giri et al., 2014, Lee et al., 2015, Shabani et al., 2016, Sharma et al., 2016, Solowiej et al., 2014).
The functional properties of processed cheese are affected by many factors including: types and characters of natural cheeses, additional ingredients, emulsifying conditions, fat content, moisture content, pH, storage, ripening and so on (Bunka et al., 2012, Guinee, 2004, Hennelly et al., 2005, Mizuno and Lucey, 2005, Guinee and O’Callaghan, 2013, Banks, 2004, Everard et al., 2007, Kiziloz et al., 2009, Ong et al., 2012, El-Bakry et al., 2010). Besides, pre-cooked cheese is often used to improve the functional properties of processed cheese during industry manufacturing. Pre-cooked cheese is essentially processed cheese. For example, after the production is completed, the processed cheese remaining in the pipeline is often used as a pre-cooked cheese in the following production. Pre-cooked cheese can affect the creaming effect, and is often used to adjust viscosity or firmness based on the purpose. It was suggested that the potency of pre-cooked cheese is mainly influenced by types of emulsifying salts, and storage period. In general, in the cases of using long-chain phosphates, more stirring strength, or longer storage period, the potency of pre-cooked cheese will become stronger (Satou et al., 2010, Kawasaki, 2008a, Kawasaki, 2008b, Lee et al., 2003, Noronha et al., 2008, Shirashoji and Jaeggi, 2006). In other words, the creaming effect will happen positively in these cases. However, it is unclear what the effects of pre-cooked cheeses of different emulsifying conditions have on the functional properties of processed cheese.
The aim of this present work was to investigate the effects of pre-cooked cheeses of different emulsifying conditions on the mechanical properties and microstructure of processed cheese, and how the pre-cooked cheeses with different protein networks affect the microstructure and mechanical properties of processed cheese. With a better understanding of this, it will be beneficial to use pre-cooked cheese to control the protein network contributing to the functional properties of processed cheese in more cases effectively, as well as help optimize the quality attributes in processed cheese.
Section snippets
Materials
Gouda cheese and Cheddar cheese were used as raw cheeses. Sodium polyphosphate, disodium phosphate, and sodium bicarbonate were obtained from Megmilk Snow Brand Company, Ltd. (Tokyo, Japan). 50% glutaraldehyde (TAAB) and 2% osmium tetraoxide (Chiyoda Pure Chemical Ind., Ltd., Japan) were used. The other chemicals were of special grade. Distilled water was used for all processed cheeses preparation.
Processed cheese preparation
A Rapid Viscosity Analyzer (RVA-4, Newport Scientific Ltd., Australia) was used to manufacture the
Viscosity profile analysis
The effects of pre-cooked cheeses of different emulsifying conditions on the viscosities of processed cheeses were shown in Fig. 1. It was shown that the viscosities of PCLS and PCHS were smooth, and there was no increase in any viscosity, which meant that a creaming effect did not occur when adding the pre-cooked cheese with the short stirring time of 10 min, However, the viscosities of PCLL and PCHL increased apparently in the latter half, which meant that the addition of the pre-cooked
Conclusions
In the current study, the addition of pre-cooked cheese with a short stirring time had no obvious impact on the protein network of processed cheese. The random network brought low viscosities and a gradual increase in the fracture stress/strain curve. The addition of pre-cooked cheeses with long stirring time caused the protein network to become fine-stranded. The fine-stranded network caused the creaming effect, and brought yielding points in the mechanical properties. The pre-cooked cheese
Acknowledgements
The first author would like to acknowledge the support of Kazunao Fusa, Yuya Yanagisawa, and Takaaki Mutoh of Megmilk Snow Brand Company, Ltd. for the materials and advice, and the laboratory members Keita Inoue and Natsumi Moriguchi for helpful discussions. Urika Watanabe performed the experiments. Wei Fu and Takashi Nakamura wrote and edited the paper.
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