Studies On Preparation Of Processed Cheese Spread And Its Textural, Rheological Properties And Flavour

Cheese is a nutritious ferment dairy product with abundant protein, fat, amino acid,vitamin, minerals, etc. In China, because of the consumption custom, people are not adaptedto the ferment odor of nature cheese, and the processing technique is also immature, so allthese things limit the development of cheese industry in China. With its specific processingtechnique, processed cheese eliminates the ferment odor of nature cheese and adapts to theChinese people's taste and it will accord with the consumption trend of Chinese foods fromfull up type to nutritional and sanitarian type. In this thesis, the processing technique ofprocessed cheese spread and the processing parameters affecting the product properties werestudied by means of textural and rheological tests, the effects of processing on the flavour ofprocessed cheese were also studied.This thesis began with the extraction of chymosin and the preparation of Cheddar cheese,and Cheddar cheeses of different mature period were used as the cheese resources ofprocessed cheese, the processing conditions of processed cheese were then studied, they werefocused on the choosing of cheese resources, the variety and use level of meting salts and thecombination of melting salts, the determination of processing temperature and time and thedetermination of adjuvant materials use level, as the imported European processed cheesespread was used as the control sample, the processing parameters were studied and optimizedby texture tests, the results indicated that the optimal process parameters of processed cheesespread processing was to add 0.5% sodium pyrophosphate and 0.5% sodium tripolyphosphate,10% butter and 70% water(mass fraction of cheese base) into the cheese mixtures of1:1(Cheddar cheese of 1 month: Cheddar cheese of 5 months), heat the mixtures in 70~75℃water bath for 7~8min and stirring, then cool it rapidly, the texture of final product wassimilar to that of the imported cheese spread from the market and its flavor was excellent. On the basis of the determined processing parameters of processed cheese spread above,several factors affecting the characters of processed cheese were studied by TA-XT2i textureanalyzer and AR-1000 rheometer, and the microstructure of the products were observed bySEM, lots of data were obtained and analyzed, the results indicated: the moisture contents inthe processed cheese system affected the structure of protein, the interactions betweenproteins and emulsifying effects of melting salts during processing, and then affected thetextural and rheological properties of processed cheese;melting salts content didn'tdramatically affect the textural properties of processed cheese, it affected the states of thewhole system and the emulsifying effects, thereby affected the structure and rheologicalproperties;under different cooking temperature and time, the texture of products had thesimilar changes, the affect of cooking time on the rheological properties of products mightresult from the "creaming reaction", and the affect of cooking temperature on the rheologicalproperties of products might result from some further changes in the energy balance thatwould influence the strength of the cheese matrix at high temperatures (>60°C);when theproportion of young cheese in the cheese resources was increased, the elastic and viscousparts and the general intensity of the product decreased. When the proportion of young cheeseis below 100%, tanδ values increased with increasing the proportion of young cheese, but thedifference is not large, when the cheese resources consisted of the young cheeses entirely,tanδ values decreased reversely;Samples under any processing conditions, G′ values werehigher than G″ values, there was no crossover point for G′ and G″ within a magnitude, η*values decreased in across several magnitudes as frequency increased, the system exhibitedrheological behavior corresponding to a weak gel.The affect of processing on the volatile flavour compounds were studied by SPMEextraction, GC-MS separation and identification, 79 volatile compounds were identified in thecheese resources, wherein 43 derived from Cheddar cheese of 1 month autumn and 44 fromCheddar cheese of 5 months autumn, 47 volatile compounds were identified from theprocessed cheese, the numbers of the same compounds appearing in cheese resources andprocessed cheese were 35, these 35 compounds accounted for 97.25% of the volatilecompounds identified in processed cheese. Through the analysis of the changes of volatilecompounds before and after processing, it was concluded that volatile flavour compoundsdidn't have outstanding effects on the wakening of nature cheese flavour intensity.