Defects in process cheese

Whosever takes the trouble to collect samples of processed cheese and processed cheese spreads regularly from the normal marketing sources, and submit them to a thorough organoleptic examination, would soon come, to the conclusion that with the exception of the well known top quality products, many processed cheese products found on the market are exceedingly inferior, with regard to consistency, structure,and flavour. Three well known defects in texture can be established here, “over creaming, stickiness and sandiness”. These defects, which are most certainly of a physico- chemical nature can be observed today more frequently than bacteriological defects, e.g., the dreaded “blowing” of processed cheese due to butyric acid bacilli and other clostridia. With respect to flavour, other objectionable defects include metallic, oily, cardboardy, soapy, bitter and indeed the frequent total absence of the desired characteristic flavour. The causes of these defects can be many: unsuitable raw material, additives of non- standard flavour, unsuitable seasoning, defective dosage and a faulty processing technique. In this connection, poor flavour can occur in the presence of an unsuitably high addition of whey concentrate.

During processing the, the blend thickens progressively with holding time in the cooker. The thickening, frequently referred to as ‘creaming’ or ‘creaming effect’ may be attributed to ongoing interaction of the emulsifying salts with the casein and with the consequent increases in para-casein hydration and degree of emulsification.Both factors contribute to an increase in the apparent viscosity of the molten blend.However, extending the holding time of the molten product at high temperature results in a gradual dehydration of the dispersed sodium para-caseinate, an occurrence which has the effect of imparting elasticity and firmness to the final product.Indeed, prolonged holding results in excessive protein dehydration and aggregation,and a concomitant destabilization of the emulsion, as reflected by the exudation of ‘beads’ of free oil on the surface of the product on cooling. This defect, known as ‘over-creaming’, is also accompanied by a tendency of the product to express some free water in the cooker or on subsequent cooling.

The flavour defects can be overcome by means of extremely careful control during the whole production run. This includes careful selection of raw materials, with regard to flavour and processing properties, the correct use of emulsifying salts and attention to all the features of procedure and critical examination of all finished products.

i. Spoilage of PCPs:

Processed cheese, cheese foods and cheese spreads constitute an important part of the cheese products marketed. Normally they keep satisfactorily because of the heat used in processing, acid and salt present, containers which prevent contamination of the finished products, and perhaps other factors. However, spoilage sometimes may occurs, it may involve microorganisms or chemical changes. Pasteurized processed cheese products are not sterile, as the spore forming bacteria are not destroyed by the heat used. Their growth is controlled by proper pH, salt and Eh level.

Defects in the films used to line boxes or in jar seals may permit the entrance of moulds which find the conditions suitable for growth. Such spoilage usually occurs in only occasional package. Serious spoilage commonly involves heat resistant bacteria which, because of some irregularity grow in the packaged products.Extensive gas blowing may occur in pasteurized processed cheese products. This is caused by Cl. sporogenes and related carbohydrate fermenting bacterial sps., but fortunately, they cause no safety problem. To minimize such an unpleasant occurrence as gas blowing, the basic natural cheese stock should not contain excessive numbers of anaerobic spores, the pH of the finished processed cheese should fall between 5.6 to 5.8, and NaCl content between 2.5 to 3.5(6.0-7.5% NaCl in serum).

The instances of spoilage in process cheese by Cl. Sporogenes has been reported which involved bleaching, development of softened and crumbled areas, and faecal odour, in some areas there was a small dark slit which was considered to be due to gas. The isolation of Cl. Sporogenes and Cl. perfringens from tinned processed cheese which was gassy and had a putrid odour also has been reported. The condition was observed only in cheese in which skim milk powder was added. The same types of organisms were isolated from cheese containing no milk powder, but they did not cause deterioration.

ii. Pinking of Processed Chees

Pinking is a colour defect in processed cheese. This defect is produced by overheating the cheese in the cooker. Its chemical cause is not known, but annatto colour break down during heating may cause this defect. Also in processed cheese containing young natural cheese, the pink colour may result from the Maillard type browning

iii. Browning

In case of processed cheese foods and spreads, the non-cheese dairy products have lactose which causes browning. Bigger the container slower the cooling and more is the browning. Kraft developed a new process to control this problem. The cheese from the cooker runs out and flows on cold water and then strips and pieces of cheese is made.